THESIS APPROVAL the Abstract and Thesis of Susan L. Bednarz for The

Home , Intrusive rock

THESIS APPROVAL

The abstract and thesis of Susan L. Bednarz for the Master of Science in

Geology were presented May 29, 2002, and accepted by the thesis committee and the department.

COMMITTEE APPROVALS: ______Michael L. Cummings, Chair

______Georg H. Grathoff

______Scott F. Burns

______Trevor D. Smith Representative of the Office of Graduate Studies

DEPARTMENTAL APPROVAL: ______Michael L. Cummings, Chair Department of Geology

ABSTRACT

An abstract of the thesis of Susan L. Bednarz for the Master of Science in

Geology presented May 29, 2002.

Title: Influence of Halloysite on the Engineering Behavior of Basaltic Saprolites

in Northwestern Oregon and Southwestern Washington.

Saprolite is commonly developed on Tertiary basalt in northwestern

Oregon and southwestern Washington. Basalt saprolites are often sensitive, in that they release water and lose shear strength when disturbed. Non-sensitive, featureless residual soil mantles sensitive basalt saprolites.

Borehole samples of extrusive basalt and intrusive basalt (diabase) saprolites from six study sites in northwestern Oregon were analyzed using X- ray diffraction and scanning electron microscopy (SEM). Clay mineral zonation, observed in borehole samples obtained on Mt. Scott in southeast Portland,

Oregon, show that 10Å halloysite is most abundant near the bedrock contact,

7Å halloysite is most abundant toward the middle to upper portions of the saprolite, and kaolinite is most abundant in the residual soil. Zonation of smectite is unclear. Interlayered halloysite/expandable clay is identified in almost all saprolite samples analyzed but not in the overlying residual soil samples.

Laboratory and field testing can be used to identify sensitive saprolites prior to construction. Sensitive saprolites have high natural water contents

(generally >50%), low dry densities (5.7 to 6.4 kN/m3), Atterberg limits and moisture/density relationships that vary with drying and remolding, and release water when compressed.

Engineers have linked soil sensitivity in saprolites to the presence of water-filled, hydrated (10Å) halloysite tubes that are crushed during construction, adversely affecting stripping, placement, and compaction.

Although 7Å halloysite is found in all sensitive saprolites analyzed within the study sites, 10Å halloysite is not ubiquitous to these soils. The water released during compression of sensitive soils is stored in boxwork voids (identified by

SEM analysis) and not inside individual halloysite tubes. The loss of sensitivity in surficial residual soil is due to the breakdown and collapse of the boxwork voids within the saprolite due to pedogenic processes.

INFLUENCE OF HALLOYSITE ON THE ENGINEERING BEHAVIOR OF

BASALTIC SAPROLITES IN NORTHWESTERN OREGON AND

SOUTHWESTERN WASHINGTON

SUSAN L. BEDNARZ

A thesis submitted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE in GEOLOGY

Portland State University 2002

ACKNOWLEDGMENTS

Many thanks to the following individuals who provided information, assistance, and advice towards the completion of this research: Michael

Cummings, Georg Grathoff, Scott Burns, and Sherry Cady, Portland State

University; Jim Maitland and Tim Pfeiffer of Foundation Engineering, Inc.; Derek

Cornforth, Charlie Hammond, and Brent Black of Cornforth Consulting; Jim

Griffith of the US Army Corps of Engineers; Reka Gabor, Portland, Oregon;

Reed Glasmann of Oregon State University; David Rogers of University of

Missouri, Rolla; Michael Williams of the Washington Department of

Transportation; Clackamas County Department of Transportation and

Development; Wayne Isphording, University of South Alabama. I would also like to thank the Clay Minerals Society for providing a grant to fund this research.

TABLE OF CONTENTS

ACKNOWLEDGMENTS ...... i

TABLE OF CONTENTS ...... ii

LIST OF FIGURES ...... vi

LIST OF TABLES ...... vii

INTRODUCTION ...... 1

BACKGROUND ...... 3

GEOLOGIC SETTING ...... 9

LOCAL ENGINEERING CASE HISTORIES ...... 17

Mud Mountain Dam ...... 17

Toutle River Sediment Retention Structure ...... 18

Trask River Dam Raise ...... 19

Hills Creek Dam ...... 21

Spirit Lake Memorial Highway ...... 22

H3 Tunnel, Oahu, Hawaii ...... 23

STUDY SITES ...... 24

Monterey Avenue Overcrossing, Southeast Portland, Oregon ...... 24

West Salem Site 1, Oregon ...... 25

West Salem Site 2, Oregon ...... 25

Carlton, Oregon...... 26

Silverton, Oregon ...... 26

South Salem, Oregon ...... 27

METHODS ...... 28

Field Sampling Methods ...... 29

Field Soil Sensitivity Testing ...... 30

X-Ray Diffraction Analysis ...... 30

X-ray Diffraction Analysis of -2μm Material ...... 31

X-ray Diffraction Analysis of Bulk Samples ...... 33

Toluidine Blue Treatment ...... 33

Magnetism ...... 34

Scanning Electron Microscopy ...... 35

Engineering Index Testing ...... 36

RESULTS ...... 37

X-Ray Diffraction Analysis Overview ...... 37

X-Ray Diffraction Sample Data Summary ...... 39

Monterey Overcrossing Borehole BH-3 ...... 39

Monterey Overcrossing Borehole BH-7 ...... 41

Monterey Overcrossing Borehole BH-10 ...... 43

Monterey Overcrossing Borehole BH-18 ...... 45

Monterey Overcrossing Borehole BH-27 ...... 46

Monterey Overcrossing Borehole BH-43 ...... 47

West Salem Site 1 Borehole BH-1 ...... 47

West Salem Site 2 Borehole BH-1 ...... 48

Carlton Boreholes BH-1 and BH-2 ...... 48

iii

Silverton Borehole BH-1 ...... 49

South Salem Borehole BH-2 ...... 49

Magnetism Observations ...... 50

Field Sensitivity Testing Results ...... 51

Testing for Amorphous Clay (Allophane and Imogolite) ...... 52

Scanning Electron Microscopy (SEM) Results ...... 52

Engineering Index Testing Results ...... 62

DISCUSSION ...... 64

Clay Mineralogy in Basaltic Saprolites and Residual Soil ...... 64

Clay Zonation ...... 64

Mixed-Layered Halloysite/Expandable Clay ...... 67

Desiccation of 10Å Halloysite ...... 70

Development of Sensitivity in Basaltic Saprolites ...... 70

Occurrence of Sensitive Saprolites in Other Volcanic Rocks ...... 74

Identification of Sensitive Volcanic Saprolites ...... 75

Field Index Testing ...... 75

Engineering Index Testing ...... 76

X-Ray Diffraction Analysis ...... 78

Mitigation of Sensitive Volcanic Saprolites ...... 78

CONCLUSIONS ...... 80

FUTURE WORK ...... 84

LITERATURE CITED ...... 85

APPENDICES

A Oregon and Washington Case Histories of construction in Sensitive Volcanic Saprolites…………………………………………………………94

B Engineering Test Procedures and Data…………………………………113

C Study Area Sample Descriptions………………………………………...119

D X-ray Diffraction Analysis…………………………………………………139

LIST OF TABLES

TABLE PAGE

1. Volcanic Saprolites in Northwestern Oregon and Southwestern Washington ...... 10

2. Overview of Laboratory Testing ...... 29

3. Significant XRD Peaks for Study Area Clay Minerals ...... 38

4. X-ray Diffraction Peak Parameters for Clay Minerals in Monterey Overcrossing Samples ...... 42

5. Monterey Overcrossing Borehole BH-10 XRD Mineralogy ...... 44

6. Magnetic Properties of Soil Samples ...... 51

7. Summary of Engineering Index Data ...... 63

vii

LIST OF FIGURES

FIGURE PAGE

1. Undisturbed sensitive volcanic breccia saprolite ...... 6

2. Disturbed sensitive volcanic breccia saprolite ...... 6

3. Basalt exposures in northwestern Oregon and southwestern Washington ...... 12

4. Ferruginous bauxite deposits in western Oregon and southwestern Washington ...... 14

5. Basaltic saprolite developed from Columbia River Basalt bedrock ...... 15

6. Residual clastic texture in Boring Lava breccia saprolite ...... 16

7. Vicinity map showing the location of study sites and engineering case history sites ...... 20

8. Example of kaolinite-poor saprolite ...... 40

9. Example of kaolinite-rich saprolite ...... 40

10. Residual texture visible in volcanic breccia saprolite sample SH-43-6 prior to SEM analysis...... 55

11. SEM microphotograph of sample SH-43-6 at 10X magnification ...... 56

12. SEM microphotograph of sample SH-43-6 at 50X magnification ...... 57

13. SEM microphotograph of sample SH-43-6 at 390X magnification (Box B) ...... 58

14. SEM microphotograph of sample SH-43-6 at 390X magnification (Box A1) ...... 59

15. SEM microphotograph of sample SH-43-6 at 2000X magnification (Box A2) ...... 60

16. SEM microphotograph of sample SH-43-6 at 2000X magnification (Box A3) ...... 61

viii

LIST OF FIGURES (continued)

FIGURE PAGE

17. Air-dried XRD trace of crystalline, well-ordered low cristobalite ...... 69

18. XRD trace showing expansion of halloysite peaks with glycolation ...... 72

INTRODUCTION

Saprolites form where bedrock has been exposed to prolonged tropical or wet temperate climates (Prudencio et al., 1990; Schwarz, 1997). Volcanic saprolites are commonly used as foundation and embankment soils throughout the world (Terzaghi, 1958; Sherard et al., 1963; Wesley, 1974; Hammond and

Vessely, 1998). Characteristics of volcanic saprolites affect their engineering properties and suitability as foundation soils. Engineers have previously identified clay mineralogy, specifically halloysite content, as a contributing factor to adverse engineering properties (Mitchell, 1989; Cornforth Consulting Inc.,

1991; Hammond and Vessely, 1998).

Volcanic saprolites are common in the Pacific Northwest due to climate conditions that have deeply weathered Tertiary-age basalt and andesite units.

Local engineering projects have experienced difficulties in sensitive volcanic saprolites, which release water and lose shear strength when disturbed. These difficulties have resulted in expensive “change of conditions” construction claims. Although hydrated halloysite (in conjunction with smectite) has been suspected as the cause of sensitivity in volcanic saprolites, no systematic study has confirmed this relationship.

This study examines clay mineral zonation with depth in selected northwestern Oregon basaltic saprolites, compares changes in clay mineralogy with soil sensitivity, develops a mechanism by which soils become sensitive, and addresses the correlation between halloysite and sensitive basalt and

1 andesite saprolites. Laboratory and filed testing methods are provided to identify sensitive soils. Mitigation techniques are developed based on case history information.

BACKGROUND

Saprolite is defined as “a residual regolith developed isovolumetrically on crystalline rocks, in which some or all of the primary minerals have been extensively transformed in situ to weathering products” (Velbel, 1990). Saprolite is much weaker than weathered rock but maintains the original volume, structure, and fabric of the parent rock (Pavich, 1996). During the formation of saprolites in igneous rocks, individual minerals are dissolved (leached) and weathering products (clay minerals and iron and aluminum oxides) are reprecipitated in crystal fractures along cleavage planes and around the perimeter of the mineral (Velbel, 1989). As weathering progresses, clay- and oxide-bounded, porous “negative pseudomorphs” of the original minerals form micro-boxwork structures in the saprolite (Velbel, 1989). These micro-boxworks can trap isolated pockets of water within the saprolite.

Mineralogical studies have identified both hydrated (10Å) and dehydrated (7Å) halloysite in volcanic saprolites (Glasmann and Simonson,

1985; Prudencio et al., 1990). 7Å halloysite (Al2Si2O5(OH)4) consists of a combined octahedral and tetrahedral sheet (1:1) structure, while 10Å halloysite

(Al2Si2O5(OH)4⋅2H2O) contains a 2.9Å layer of water between the combined 1:1 sheets (Moore and Reynolds, 1997). The nature of the relationship between 7Å and 10Å halloysite has not been determined. They may represent two separate phases of the same mineral or two separate minerals (Moore and Reynolds,

1997).

Halloysite forms as an intermediate weathering product in volcanic material (especially plagioclase) which later transforms to kaolinite with continued weathering (Romero et al., 1992; Jeong, 1999). Repeated alternating wet and dry cycles and a high water content of the soil in a warm humid climate favors the formation of halloysite in the soil and cause laterization (Wang et al.,

1998). Detecting abundant halloysite in lateritic paleosols facilitates the identification of paleoclimates (Wang et al., 1998).

Numerous halloysite morphologies have been identified including tubes

(Kirkman, 1981; Singh, 1996; Wang et al., 1998), plates (Mitchell, 1993), crumpled sheets (Wada and Mizota, 1982), spheroids (Prudencio et al., 1990), and ellipsoids (Jeong, 1999). Halloysite morphology is related to aluminum oxide (Al2O3) and iron oxide (Fe2O3) content (Bailey, 1989). Long tubes indicate high aluminum substitution in the tetrahedral sheet, while spheroids and plates indicate high iron substitution in the octahedral sheet (Bailey, 1989). Tubular halloysite, which is commonly found in basalt saprolites in Oregon (R.

Glasmann, personal communication, February 2001), may store free water internally within the tube.

Studies of halloysite in basalt saprolites have been conducted in many parts of the world, including Spain (Prudencio et al., 1990), Kenya (Terzaghi,

1958), Indonesia (Terzaghi, 1958), Philippines (Terzaghi, 1958), Australia

(Terzaghi, 1958; Eggleton et al., 1987) and Japan (Wada and Mizota, 1982).

Numerous articles and reports discuss halloysite in basalt and andesite

4 saprolites in western Oregon and southwestern Washington (Istok, 1981; Thrall,

1981; Glasmann, 1982; Gabor et al., 1987; Gabor and Cummings, 1988;

Mitchell, 1989; Hammond and Vessely, 1998). Additionally, studies have been conducted on halloysite in soils derived from other types of igneous rocks, predominantly silicic lava and ash deposits (Kirkman, 1981; Theng et al., 1982;

Wada and Mizota, 1982; Romero et al., 1992; Jeong and Kim, 1993; Wang et al., 1998; Jeong, 1999). These studies can be divided into two groups that show little or no overlap:

• The mineralogy, morphology, formation, and presence of halloysite based on laboratory studies and theoretical modeling conducted by mineralogists and soil scientists (e.g. Glasmann, 1982; Wada and Mizota, 1982). • Geotechnical investigations and case histories that discuss construction problems related to sensitive soils where halloysite has been identified. These documents discuss the engineering properties and performance of project soils (e.g. Terzaghi, 1958; Hammond and Vessely, 1998).

Sensitivity is defined as the ratio of the peak undisturbed (in situ) strength to the remolded strength as determined by unconfined compression testing (Mitchell, 1993). A soil with a ration greater than 4:1 is considered sensitive (McCarthy, 1998). Sensitive soils experience a significant loss of shear strength and release water when disturbed or remolded. Figures 1 and 2 show an undisturbed and remolded sensitive volcanic breccia. Although volcanic saprolites represent only one category of sensitive soils, they are particularly problematic in northwest Oregon and southwest Washington as a result of the abundance of deeply weathered volcanic material.

Figure 1. Undisturbed sensitive volcanic breccia saprolite. Note moist appearance prior to compression under hand pressure.

Figure 2. Disturbed sensitive volcanic breccia saprolite. Note wet appearance of Figure 1 sample following compression under hand pressure.

Geotechnical engineers label saprolites as “residual soil”; however, the term “residual soil” is used in this thesis to identify the featureless, highly weathered soil that overlies and is derived from the saprolite (Pavich, 1996).

The residual soil discussed below is located in the pedogenic A and B horizons and has lost all original rock texture and a portion of its original volume due to collapse of the saprolite structure (Pavich, 1996). Since engineers consider saprolites soil, the term saprolite and soil are used interchangeably.

Dr. Karl Terzaghi, who is credited with establishing the profession of geotechnical engineering, may have been the first to describe the properties and problems associated with sensitive volcanic soils. In the 1950’s, during the construction of the Sasumua Dam in Nairobi, Kenya, he observed and identified the engineering properties of sensitive volcanic saprolites used for the dam core

(Terzaghi, 1958). Additionally, geotechnical engineers have since tested sensitive volcanic saprolites during their site investigations for dams, roads, and other engineering structures (U.S. Army Crops of Engineers Portland Engineer

District, 1966; Hammond and Vessely, 1998). The engineering properties of these soils include low dry density, high natural water content, significant loss of shear strength when disturbed, and Atterberg limits values which show a reduction in the liquid limit and plasticity index between oven dried and air dried samples (Deere and Thornburn, 1955; Terzaghi, 1958; Pope and Anderson,

1960; Thrall, 1981). Terzaghi (1958) explained these anomalous and

7 contradictory engineering properties by theorizing that the halloysite clay forms spongy aggregates that clump together but break apart when compressed, thereby losing strength and releasing water.

Other mechanisms have been postulated as a cause for sensitivity in volcanic saprolites. Water stored in hydrated halloysite tubes may be released if these tubes are compressed and broken during construction (Hammond and

Vessely, 1998). Velbel (1990) postulates that cavities form in saprolites during isovolumetric weathering. These cavities are bounded by clay and iron oxides that form a rigid "boxwork" around these water-filled cavities. When these boxworks are compressed, the interstitial water is released. Lastly, blocked soil pores have been identified in weathered volcanic ash deposits that contain allophane, imogolite, and halloysite (Thrall, 1981). Water stored within and released from these pores may produce soil sensitivity. Although several theories to explain sensitivity in volcanic saprolites have been proposed, no absolute mechanism has been established to explain sensitivity in basaltic and andesitic flow rock and breccia.

GEOLOGIC SETTING

Significant portions of northwestern Oregon and southwestern

Washington are underlain by Tertiary and Quaternary mafic and intermediate volcanic rocks that are weathered to saprolites. Basaltic, andesitic, and dacitic units mapped in the study area include Boring Lavas, Sardine Formation,

Columbia River Basalt, Little Butte Volcanics, Goble Volcanics, Hatchet

Mountain Volcanics, Tillamook Volcanics, Siletz River Volcanics, and various undivided Quaternary and Tertiary units in both Oregon and Washington.

These units range in age from early Eocene to Pleistocene. Table 1 identifies the location and lithology of Quaternary and Tertiary volcanics and their combined exposure is shown in Figure 3. These units included flows, breccias, tuffs, associated volcaniclastic sediments, and scattered dikes and sills.

Volcanic deposits and intrusions have been grouped together for the purpose of this study.

Tertiary and Quaternary volcanic saprolites are common in Western

Oregon and Southwestern Washington. Although volcanic units range in age from Eocene to Pleistocene, a temperate climate with alternating wet and dry cycles that was present during the late Miocene through early Pliocene (Wilson,

1997) deeply weathered these rocks. Weathering since the late Miocene has formed ferruginous bauxites on Columbia River Basalt exposures in specific areas (Corcoran and Libbey, 1956; Livingston, 1966; Hook, 1976; Cummings and Fassio, 1990). Figure 4 shows the distribution of ferruginous bauxite within

Table 1. Volcanic Saprolites in Northwestern Oregon and Southwestern Washington

Locations of Formation Age Lithology Reference Abundant Exposures Western Cascades, Multnomah Pliocene to Basalt and basaltic andesite (Trimble, 1963; Walker and Boring Lavas and Clackamas Counties, Pleistocene flows and interflow breccia MacLeod, 1991; Madin, 1994) Oregon Basalt, andesite, and dacite (Hammond, 1980; Phillips, Various undivided Pliocene to Southern Washington Cascade flows, breccia, tuff, and 1987b; Phillips, 1987a; Walsh et volcanic units Pleistocene Range volcaniclastic sediments al., 1987) Andesite flows, tuff breccia, Western Cascade Range in (Thayer, 1939; Peck et al., Sardine Formation Upper Miocene and lapilli tuff, and tuff northern Oregon 1964) (Hampton, 1972; Beeson and Moran, 1979; Korosec, 1987; Willamette Valley north of Phillips, 1987b; Phillips, 1987a; Albany, Columbia County, Columbia River Walker and Duncan, 1989; Miocene Basalt flows Clatsop County, Oregon, Basalt Group Walker and MacLeod, 1991; southwest Washington (west of Yeats et al., 1996; Tolan and Interstate I-5) Beeson, 1999; Tolan et al., 2000) Various undivided Andesite and basaltic (Hammond, 1980; Phillips, volcanic units Upper Eocene andesite flows, and Southern Washington Cascade 1987b; Phillips, 1987a; Walsh et (including Hatchet to Miocene andesite and dacite breccia, Range al., 1987; Cummings, In Press) Mountain volcanics) and tuff Basalt and andesite flows; and andesite, dacite, and (Thayer, 1939; Peck et al., 1964; Little Butte Oligocene to rhyolite tuff, lapilli tuff, Western Cascade Range in Hammond et al., 1982; Sherrod Volcanics lower Miocene domes, and flows of northern Oregon and Smith, 1989) andesite, dacite, and rhyolite

Table 1. Volcanic Saprolites in Northwestern Oregon and Southwestern Washington (continued)

Locations of Formation Age Lithology Reference Abundant Exposures Basaltic andesite flows, flow Upper Eocene (Phillips, 1987b; Phillips, 1987a; breccia, and interbedded Columbia County, Oregon and Goble Volcanics to lower Walsh et al., 1987) (Walker and tuff, sandstone, and Cowlitz County, Washington. Oligocene MacLeod, 1991) siltstone Subaerial basalt flows, (Wells et al., 1983; Walker and Upper to middle pillow lava, and interbedded Tillamook Volcanics Northern Oregon Coast Range MacLeod, 1991; Wells et al., Eocene tuff, sandstone, and 1994) siltstone Subaerial basalt flows, (Bela, 1979; Wells et al., 1983; Siletz River Lower to Middle pillow lava, and interbedded Oregon Coast Range Walker and MacLeod, 1991; Volcanics Eocene tuff, sandstone, and Wells et al., 1994) siltstone (Schlicker and Deacon, 1967; Scattered across northwestern Eocene to Sherrod and Smith, 1989; Tertiary Intrusives Basalt/Diabase/Gabbro Oregon and southwestern Pliocene Walker and MacLeod, 1991; Washington highlands. Yeats et al., 1996)

SCALE: 1 cm = 15 km

Figure 3. Basalt exposures in northwestern Oregon and southwestern Washington (Walsh et al., 1987; Walker and MacLeod, 1991). 12

the study area. Flows of Boring Lava extruded during the Pleistocene also show significant weathering.

Within northwestern Oregon, saprolites are commonly very thick with a very narrow interface between the saprolite and fresh bedrock. Boreholes conducted at Mt. Scott in southeast Portland penetrated up to 11.3 m (37 feet) of decomposed basalt flows and interflow breccia before encountering competent bedrock. Figure 5 shows a saprolite that has developed on Grande

Ronde Basalt of the Columbia River Basalt Group in the south Salem Hills.

These saprolites have the consistency of soil, but preserve the original rock structure. Figure 6 shows a sample of Boring Lava volcanic breccia from the

Monterey Overcrossing study area in southeast Portland in which the relict rock structure is clearly visible.

Figure 4. Ferruginous bauxite deposits in western Oregon and southwestern Washington (after Livingston, 1966).

Figure 5. Basalt saprolite (red-brown) developed from Columbia River Basalt bedrock. Quarry is located on the east side of I-5, directly south of Willamette Vineyards (T.9 S., R. 3 W., SW ¼ of Section 2). Note sharp contact between saprolite (orange) and bedrock (gray).

Figure 6. Residual clastic texture visible in sample of Boring Lava breccia saprolite from Monterey Avenue Overcrossing project in southeast Portland. Pointer identifies outline of ash-sized clast surrounded by secondary orange clay. (Sample diameter is approximately 1.2 inches).

LOCAL ENGINEERING CASE HISTORIES

Numerous engineering projects in northwestern Oregon and southwestern Washington have experienced construction difficulties in areas underlain by sensitive volcanic saprolites. A sampling of these projects include the following:

• Mud Mountain Dam, Pierce County, Washington; • Toutle River Sediment Retention Structure, Cowlitz County, Washington; • Trask River Dam Raise, Tillamook County, Oregon; • Hills Creek Dam, Lane County, Oregon; and • Spirit Lake Memorial Highway, Cowlitz and Skamania Counties, Washington.

Additionally, a case history evaluating in situ soil strength in sensitive saprolites during the design of the H3 Tunnel in Hawaii is included to further characterize the engineering properties of this material. Appendix A contains a detailed description of each of the study area projects (with references). Figure

7 shows the approximate location of each of these sites, with the exception of

Mud Mountain Dam which is to the north. Appendix B.1 includes a discussion of engineering testing methods. The key aspects of each case history are summarized below.

Mud Mountain Dam

Mud Mountain Dam, constructed in 1941, is one of the earliest cases of construction problems related to excessively wet volcanic soils that were used for the dam core. Earth embankment soils were kiln-dried and covered with a gigantic, canvas tent to reduce the water content enough to reach compaction. 17

A small amount of colloidal clay was blamed for preventing soil drying or drainage (Anonymous, 1941a; Anonymous, 1941b).

Toutle River Sediment Retention Structure

Change of conditions claims were filed by the contractor shortly after construction began for the Toutle River Sediment Retention Structure (SRS).

Flow top breccia and Pleistocene-age debris flow saprolites, selected for the impervious dam core, became excessively wet and lost shear strength when disturbed. These soils appeared to be stable, silty to sandy gravels at optimum water content in outcrop but quickly broke down to a wet, sticky mass that caused heavy equipment to bog down in deep ruts. The contractor claimed that the presence of halloysite and smectite in the saprolites was responsible for the sensitivity of the embankment soils, although 10Å halloysite was not ubiquitous to problematic soils (Gabor and Cummings, 1988; Cornforth Consulting Inc.,

1991). They contended that excess water was trapped in the “soil grains” by halloysite, which released this water to the soil pores when disturbed. Gabor and Cummings (1988) observed that halloysite was not present in all sensitive soils and concluded that soil sensitivity was caused by microtextures within the saprolite becoming crushed during handling and releasing water trapped within micropores. Loss of shear strength due to rapid hydration of smectite was dismissed due to the low permeability of smectite-rich soils.

Trask River Dam Raise

Based on knowledge of construction difficulties in sensitive soils experienced at the Toutle River SRS, sensitive soils were anticipated in saprolites developed on Eocene-age basalt at the Trask River Dam site. During the geotechnical investigation for the dam raise, sensitive soils were encountered locally. Natural water contents ranged from 68 to 89 percent in foundation areas, but embankment fill materials were selected to reduce the in situ moisture content to between 30 and 43 percent and avoid sensitive soils (Cornforth Consultants

Inc., 1995). Foundation soils consisted of high plasticity (elastic) silt (MH) with a natural water content that usually exceeded the liquid limit. Atterberg limits tests conducted on air-dried samples produced lower liquid limits and plasticity indexes than samples that had never been dried, indicating that an irreversible change had occurred during drying (Hammond and Vessely, 1998).

As with the Toutle River SRS, the presence of halloysite and montmorillonite (smectite) was thought to cause problematic saprolite soils.

Halloysite was claimed to break down with handling and release water that was absorbed by smectite, thereby changing the character of the soil from apparently granular to cohesive. Significant 10Å halloysite was detected in the two borrow area samples that were tested for clay content and one of these samples contained significant smectite (Cornforth Consultants Inc., 1995).

Even though sensitive soils were anticipated and avoided where possible, construction equipment still became bogged down in wet weather.

Scale: 1 cm = 15 km

Toutle River SRS Spirit Lake Memorial Highway

Trask River Dam Monterey Overcrossing Carlton

Silverton West Salem 1 & 2

South Salem

Hills Creek Dam

Figure 7. Vicinity map showing the location of study sites ( ) and engineering case history sites (). (Mud Mountain Dam is north of map area.

Thus, stripping and placing of impervious core materials was limited to the dry summer months.

Hills Creek Dam

Hills Creek Dam, constructed in 1961 in south-central Oregon, was one of the first Oregon dams to experience construction difficulties related to sensitive soils (U.S. Army Corps of Engineers Portland Engineer District, 1959).

The impervious core of the dam was partially constructed of highly weathered alluvial gravel that contained colloidal clay. Although this in situ material appeared near optimum moisture content when excavated, it became wetter after handling and developed ruts. The soil’s sensitivity was attributed to small pockets of highly plastic colloidal clay mixing with lower plasticity fines during handling and an increase in the plasticity of halloysite-bearing soils as hydrated

(10Å) halloysite altered to highly plastic intermediate halloysite during drying

(U.S. Army Crops of Engineers Portland Engineer District, 1966). Clay analyses conducted by Ralph Grim for the U.S. Corps of Engineers (1966) showed 10Å, 7Å, and intermediate forms of halloysite and lesser smectite. The highly plastic intermediate halloysite was thought to be responsible for compaction problems. As with the Trask River Dam, Atterberg limits tests showed a progressive decrease in the plastic limit and the plasticity index with air and oven drying.

To mitigate against the effects of sensitive embankment soils, aggregate was added to improve drainage, roller weight was reduced, and lift thickness

21 was reduced to 0.2 m (8 inches) (U.S. Army Crops of Engineers Portland

Engineer District, 1966).

Spirit Lake Memorial Highway

During the construction of the Spirit Lake Memorial Highway in the

Western Cascades of Washington, the performance of embankments soils was assessed using test fills and laboratory testing. The natural water content of these soils was significantly above the optimum moisture content for standard compaction (Golder Associates, 1987b). In-place density measurements in hydrothermally altered tuff test fills showed an increase in dry density with two tractor passes, followed by either no further increase or a significant decrease in the dry density (and compaction) with additional passes. The in situ moisture content of test fills decreased with two tractor passes and then increased as the dry density decreased. Concurrently, deep rutting (0.5 m or 18 inches) occurred on the third and fourth tractor pass. Dry densities measured within these test fills were significantly less than the maximum dry densities established during laboratory Proctor compaction tests. The hydrothermally altered tuff was designated as waste due to its performance in test fills and high natural water content. Deposits of Holocene and Quaternary volcanic ash produced similar problems in test fills and were designated as waste.

The hydrothermally altered tuff was determined by the design engineers to have similar properties to saprolites, including poor compaction characteristics, high natural moisture content (commonly above the liquid limit),

22 low in situ densities (unit weight), anomalous Atterberg limits and Proctor test values, and low remolded strength. These properties were attributed to the presence of halloysite and the release of water held in the relict structure of the soil during construction, although the clay mineralogy was not analyzed (Golder

Associates, 1988b).

H3 Tunnel, Oahu, Hawaii

The in situ soil strength in sensitive saprolites is not accurately determined by laboratory strength testing methods. Dr. Glenn Boyce (personal communication, October 2000) observed that laboratory testing of remolded standard penetration test (SPT) samples of sensitive basalt saprolite for the H3

Highway Tunnel on Oahu, Hawaii, produced low strength values. Pile design for approach piers was based on these low strength values. Over design and waste occurred when piles could only be driven a few feet before refusal.

Similar anomalously low strength values were previously recorded during laboratory testing of relatively undisturbed tube samples for the Wilson Tunnel 4 km (2.5 miles) southeast of the H3 Highway Tunnels (Boyce and Abramson,

1991a). Due to the recognition that the basalt saprolite had structure, in situ testing was initiated for the design of the H3 Tunnels (Boyce and Abramson,

1991b). This testing included pressuremeter testing and plate load testing

(using a 460 mm diameter steel plate, attached to a load frame as per ASTM D-

4394-84) to determine accurate strength values for the design of the tunnel

(Boyce and Abramson, 1991a).

STUDY SITES

Although the study area included sites in both northwest Oregon and southwest Washington (Figure 7), laboratory analysis was conducted on samples collected by me (or under my supervision) during routine geotechnical investigations in northwestern Oregon. Most borings extended into bedrock.

Study sites for this thesis were selected based on the presence of basalt saprolites and the availability of samples. These sites include the following:

Monterey Avenue Overcrossing, Southeast Portland, Oregon

Over 50 borings were drilled for this project, which is located in southeast

Portland on the western slopes of Mount Scott, a Pleistocene-age volcano composed of Boring Lavas (Schlicker and Finlayson, 1979). Lava flows from

Mount Scott yield a 1.26±0.39 Ma age based on K-Ar age dating (Conrey et al.,

1996). All but one boring was logged in the field by me. Borings were conducted along both sides of I-205 between SE Sunnyside Road and SE

Johnson Creek Road. Figure C.4.1, Appendix C.4 shows the location of the study area in T. 1 S., R. 2 E., Section 33, SW ¼. Deeply weathered Boring

Lava including interbedded basalt flows and breccias are commonly mantled by

Quaternary-age fine-grained Missoula flood deposits (Willamette Silt). In most borings conducted at the site, featureless residual soil overlies the basalt saprolite that ranges up to 18.9 m (62 feet) thick. Gravel to boulder corestones developed from the Boring Lavas are common in the residual soil. Within the saprolite, alternating layers of flow rock and interflow volcanic breccia were

24 identified based on their relic textures. Saprolites are thickest in areas predominantly underlain by breccia due to higher initial permeability.

West Salem Site 1, Oregon

Six borings were drilled near the intersection of Doaks Ferry Road and

Orchard Heights Road in West Salem, Oregon, to provide geotechnical design data for a new building. The site is located in T. 7 S., R. 3 W., Section 17, SE ¼ of the SW 1/4 and is shown in Figure C.4.2, Appendix C.4. The site is located on the gently rolling Eola Hills, which are locally underlain by deeply weathered middle Miocene Grande Ronde Basalt of the Columbia River Basalt Group

(Crenna and Yeats, 1994; Yeats et al., 1996). The depth to fresh basalt varies from 2.4 to greater than 12.2 m (8 feet to 40 feet) across the site. The deep borings encountered flow rock saprolite mantled by residual soil. No interflow breccia zones were observed within the borehole samples. Saprolite excavated in test pits resembled highly weathered rock, but low Standard Penetration

Testing (SPT) N-values of 7 to 19 blows per foot indicated medium stiff to very stiff clayey silt soil.

West Salem Site 2, Oregon

One boring was drilled to a depth of 10.6 m (35 feet) for the design of a water reservoir in West Salem, Oregon. The site is located approximately 1.21 km (0.75 miles) northwest of the West Salem building site described above and is shown on Figure C.4.2, Appendix C.4. The site is underlain by deeply weathered middle Miocene Grande Ronde Basalt (Crenna and Yeats, 1994;

Yeats et al., 1996). The boring encountered 1.5 m (5 feet) of featureless residual soil and 7.2 m (23.5 feet) of saprolite above the basalt bedrock

Carlton, Oregon

Two borings were drilled for the design of a water reservoir on a hillside directly west of Carlton, Oregon. The site is located in T. 3 S., R. 4 W., Section

19, SE 1/4 and is shown in Figure C.4.3, Appendix C.4. The hillside is underlain by a deeply weathered Tertiary diabase intrusion, which cuts Eocene submarine volcanic and sedimentary rocks (Schlicker and Deacon, 1967). The borings encountered 2.7 m (9 feet) of residual soil over 6.2 m (20.5 feet) of saprolite with core stones. Fresh diabase bedrock was encountered at a depth of 9.0 m

(29.5 feet) below the ground surface.

Silverton, Oregon

One boring was drilled for the design of a water reservoir on a hillside on the east side of Silverton, Oregon. The site is located in T. 6 S., R.1 W.,

Section 35, SE ¼ of the NE ¼ and is shown in Figure C.4.4, Appendix C.4. The hillside is underlain by deeply weathered flows of the middle Miocene

Frenchman Springs Member of the Wanapum Basalt of the Columbia River

Basalt Group (Tolan and Beeson, 1999). The boring encountered 2.1 m (7 feet) of residual soil and at least 13.1 m (43 feet) of saprolite. The depth to bedrock was not defined during drilling.

South Salem, Oregon

Four borings were drilled for the design of a road in the gently rolling

Salem Hills of south Salem, Oregon. The site is located along SW Robins Lane in T. 8 S., R 3 W., Section 23, NW 1/4 and is shown in Figure C.4.5, Appendix

C.4. The site is underlain by deeply weathered, middle Miocene Grande Ronde

Basalt flows (Walker and Duncan, 1989). Borehole BH-2, which was sampled for this study, penetrated 6.4 m (21 feet) of decomposed basalt without encountering bedrock.

METHODS

Soil samples were collected from geotechnical borings drilled in SE

Portland (Monterey Overcrossing), West Salem (Sites 1 and 2), Silverton, and

Carlton, Oregon. Two different approaches to analysis were used on samples from these sites. At Monterey Avenue Overcrossing and West Salem Site 1, samples from three different borings were analyzed with XRD to observe changes in clay mineralogy with depth, soil texture, and sensitivity. At West

Salem Site 2, Silverton, and Carlton, two samples from each site were analyzed using XRD to compare variations in clay mineralogy. At South Salem, one sample of sensitive soil was analyzed using XRD for clay content. All sites were tested for magnetic minerals. One sample (Monterey Overcrossing SH-43-6) was examined to evaluate the microscopic soil texture using a scanning electron microscope (SEM). Secondary orange clay observed at Monterey

Overcrossing was evaluated for mineralogy and the presence of amorphous clays (allophane and imogolite) using Toluidine Blue and XRD. Table 2 identifies the type of laboratory testing conducted for samples from each site.

Due to the sample size collected, soil sensitivity is defined in this thesis based on the amount of water released when a soil sample is compressed under strong finger pressure. Extremely sensitive samples release abundant water, moderately sensitive samples release less water, and samples with minor sensitivity release only enough water to be barely visible without

28 magnification. Samples with no sensitivity did not release water when compressed.

Table 2. Overview of Laboratory Testing Borehole Number of Type of Test and/or Study Site Number Samples Tested Preparation1 BH-3 1 Bulk2, E3 A, G, H, D, E, T4 BH-7 9 (One bulk sample= A, G, H) A, E Monterey Avenue BH-10 7 (One bulk sample=A, G, H) Overcrossing (One sample=A, G, H, D) BH-18 3 A, G, H, D, E BH-27 1 A BH-43 1 A, SEM5 West Salem, A, G, H, E BH-1 9 Oregon Site 1 (One sample=A, G, H, D) West Salem, BH-1 2 A, G, H, E Oregon Site 2 BH-1 1 A, G, H, E Carlton, Oregon BH-2 1 A, G, H, D, E Silverton, Oregon BH-1 2 A, G, H, D, E South Salem, BH-2 2 A, G, H, E Oregon

1 Tests performed on one or more samples. XRD treatments include the following: A=air dried, G=ethylene glycol, H=heat, D=DMSO. 2 Bulk analyses consisted of air-dried random powder mounts of a representative portion of the entire sample. All other XRD samples consist of clay sized (-2μ) material. 3 E = Engineering index tests 4 T=Toluidine Blue 5 SEM = scanning electron microscope

Field Sampling Methods

During drilling, disturbed 381 mm (1.5 inch) diameter samples were obtained at 0.76 to 1.52 m (2.5 to 5 ft) intervals in conjunction with Standard

Penetration Testing (SPT). Several relatively undisturbed, 700 mm (2.75-inch) diameter samples were also obtained in the Monterey Overcrossing borings.

Although bentonite drilling mud was used during drilling, care was taken to

29 remove the mud, if present, from the samples prior to storage. Samples were stored in airtight plastic bags and were kept moist or wet prior to analysis, except where noted.

Field Soil Sensitivity Testing

Each soil sample was field tested for sensitivity either during drilling or within a week following drilling. Samples were stored in sealed plastic bags to maintain the natural moisture content of the soil. An indication of sensitivity was determined based on the soil’s ability to release water when compressed under strong finger pressure. Non-sensitive soils did not appear to change in moisture content or “wetness” under compression, while sensitive soils became visibly wet, released water, and left a film on the skin surface (Figures 1 and 2).

X-Ray Diffraction Analysis

X-ray diffraction (XRD) analyses were conducted on soil samples to evaluate the variation in clay mineralogy between sensitive and non-sensitive soils. Clay zonation with depth was studied within two borings at the Monterey

Avenue site and one boring within the West Salem site. Two or three samples were selected at the other four sites to evaluate variations in clay mineralogy between sensitive (saprolite) and non-sensitive (residual soil) samples. Clay zonation analyses were conducted on both less than 2 micrometer (-2μm) material and the entire sample (bulk analysis). Sample treatments used during

XRD analysis of -2μm material included ethylene glycol, heating to 250° for two hours, dimethyl sulfoxide (DMSO), and toluidine blue dye. Sample treatments

30 were required to more accurately identify the various clay minerals present in the soils. Table 2 includes a summary of XRD analyses at each site. Table D-1

(Appendix D) provides a detailed listing of XRD analyses and sample treatments applied to each sample. XRD traces for each sample are included in

Appendix D.3 through D.14.

X-ray Diffraction Analysis of -2μm Material

The soil samples were soaked in a solution of deionized water for between five minutes and 24 hours (as necessary to suspend the sample) and rinsed through a #230 sieve. The resultant minus #230 suspension initially flocculated in many of the samples and had to be dispersed by adding 10 to 30 grains of sodium hexametaphosphate. After settling 45 minutes, the -2μm fraction in the upper 1 cm of fluid was siphoned off, vacuumed through a

Millipore® filter, and applied as a transfer to a glass slide. This preparation limited analysis to clay-sized particles and enhanced preferred orientation of individual clay crystallites. Samples were then analyzed between 3° and 35° 2θ using Copper K-α X-radiation and a 20 mm incident beam mask. An acceleration of 40 kV and a current of 30 milliamps were used to generate X- radiation. All air-dried samples were analyzed once without treatment. The following treatments were used on selected samples and are discussed below.

Air Dried Preparation

Samples were prepared as discussed above and were analyzed immediately after application to the glass slide to minimize dehydration. Sample 31 slides were visibly moist when placed in the sample holder of the X-ray diffractometer.

Ethylene Glycol Treatment

Sample slides were placed in a covered glass jar containing ethylene glycol for seven days prior to XRD analysis to allow time for absorption and intercalation (Moore and Reynolds, 1997). Ethylene glycol treatment facilitates the identification of smectite by inducing a shift in the 001 reflection from 15Å to

17Å. Peaks between 14.5 Å and 15 Å that shift to 17 Å with glycolation are identified as smectite.

Heat Treatment

Sample slides were heated in a 250° C oven for two hours and then cooled in a desiccator prior to XRD analysis. Heat treatment causes the collapse of hydrated clays such as smectite and 10Å halloysite (Moore and

Reynolds, 1997).

DMSO Treatment

Sample slides were lightly sprayed with DMSO and placed in a sealed container for 2 days prior to XRD analysis. Treatment with DMSO causes halloysite peaks between 7.4 Å and 10.0 Å (001 reflections) and 3.6 Å (002 reflection) to shift to 11.3Å and 3.7Å, respectively (Jackson and Abdel-Kader,

1978; Gabor, 1981). Kaolinite peaks are not affected by DMSO treatment

(Gabor, 1981).

Kaolinite and 7Å halloysite are difficult to identify and separate based solely on peak position. Within this paper, 7Å halloysite and kaolinite are distinguished by the location of the 001 peak (7.15Å vs. 7.2 to 7.4Å) and based on the magnitude of 7Å peak shift measured after DMSO treatment and intercalation. Although intercalation of DMSO into the kaolinite structure has been reported (Franco and Ruiz Cruz, 2002), analyses conducted for this investigation suggest that kaolinite shows only minimal intercalation in basalt saprolites over a time period of 48 hours. Jackson and Abdel-Kader (1978) suggest the degree of kaolinite intercalation with DMSO is significantly reduced with a decrease in crystal size and iron content.

X-ray Diffraction Analysis of Bulk Samples

Bulk XRD analyses of the entire sample were conducted on two samples

(one non-sensitive and one sensitive) from Monterey Avenue Borehole BH-7 and BH-10. Bulk samples were air dried and ground with a morter and pestal to <#230 mesh and back-loaded into an aluminum sample holder to minimize orientation. Samples were scanned from 3 to 65° 2θ at a speed of 1°/min during bulk analysis of a randomly oriented powdered sample.

Toluidine Blue Treatment

The toluidine blue spot test was developed by Wada and Kakuto (1985) to identify amorphous clays such as allophane and imogolite in soils. The

+ authors contend that toluidine blue, (CH3)2N C6H3NSC6H2(CH3)NH2, changes color from blue to purplish red (metachromasis) in the presence of negatively

33 charged colloids found in soils derived from granite, andesite, and sedimentary rocks. During their testing, volcanic soils containing allophane and imogolite remain blue when tested and do not show metachromasis.

Both a sensitive and a non-sensitive soil were tested. Additionally, one sample of orange clay from the Monterey Avenue Overcrossing site was tested for allophane and imogolite. The presence of amorphous clay was suspected in this secondary clay as it appears to have been deposited by groundwater in the voids between clasts in interflow breccias. The clay is very plastic and is susceptible to severe cracking during desiccation.

Using the procedure outlined in Wada and Kakuto (1985), 0.4 g of a

0.02% solution of Toluidine blue was mixed with 0.04 g of the three soil samples and one clay sample. A control sample of decayed wood replaced by abundant allophane remained blue when tested with the above solution (G. H. Grathoff, personal communication, March 2001).

Magnetism

During sample preparation for XRD analysis, the remaining >#230 mesh material from 14 samples was tested for magnetism. Testing was conducted by adding the coarser soil fraction to a beaker full of water and then stirring the soil-water mixture with a pencil magnet. The relative abundance of magnetic grains adhering to the magnet was observed to identify soils with magnetic minerals and evaluate the presence of magnetic material with soil texture type.

Magnetic mineralogy was investigated by conducting a bulk random powder

XRD analysis of a Monterey Avenue Overcrossing sample (Sample SS-10-10).

Scanning Electron Microscopy

Scanning electron microscopy (SEM) was conducted on a relatively undistrubed sample of a sensitive decomposed volcanic breccia (SH-43-6) obtained from Monterey Avenue Overcrossing Borehole BH-43. The analysis was conducted to determine the microscopic fabric of the rock and look for boxwork structures.

In preparation for SEM analysis, the sample was broken into small clods and air dried until apparently completely desiccated. Each desiccated clod was broken in half to expose a fresh surface and several were selected that typified the decomposed breccia clasts. Samples were mounted using a five-minute epoxy and the sides of the samples were painted with colloidal graphite to facilitate electrical grounding as per Portland State University SEM laboratory procedure. The mounted samples were placed in a vacuum and sputter-coated with gold-palladium. The sample was analyzed using a JEOL Model JSM-35C scanning electron microscope operated at 15kV accelerating voltage with a working distance of 39 mm.

A series of SEM photographs of the sample were taken at magnifications of 10X, 50X, 390X, and 2000X. Scale bars are shown on the lower right corner of each photograph (Figures 11 through 16). A photograph of the sample prior to desiccation is included to show megascopic saprolite structure.

Engineering Index Testing

Index tests, including natural water content, Atterberg limits, bulk density, and grain size analyses, were conducted on borehole samples for foundation design at each of the study areas. A description of each of the index tests is included in Appendix B.1. Index tests conducted during the geotechnical investigation for a project are extremely useful in identifying problematic sensitive soils before construction begins. Engineering index test data for the borehole samples analyzed in this research are provided in Table B.2.1.

Engineering index properties for samples analyzed in this investigation are summarized in Appendix B.2. Table E.2 includes engineering index testing data for Monterey Avenue Overcrossing samples that are similar to those analyzed in this research.

RESULTS

X-Ray Diffraction Analysis Overview

Clay minerals identified by XRD analysis include 7Å and 10Å halloysite, kaolinite, smectite, and potentially mixed-layered 7Å halloysite/expandable and

10Å halloysite/expandable. The expandable clay may be smectite or a similar mineral. Non-clay minerals identified in both random bulk analyses and oriented -2μm material analyses included goethite, quartz, low cristobalite, feldspar, maghemite, chlorite, and mica. Although gibbsite commonly is present in bauxites, none was clearly identified in the bulk or -2μm samples. X-ray diffraction traces for all samples are included in Appendix D.3 to D.14. A summary table (Table D.1.1) showing samples analyzed and sample treatments is included in Appendix D.1. Diagnostic peaks for clay minerals with and without sample treatment are listed in Table 3.

Based on analyses conducted on study area samples, DMSO appeared to intercalate within the 7Å and the 10Å halloysite structures and caused the

001 peak for both types of halloysite to expand to 11.2Å. Kaolinite, however, did not appear to expand with DMSO. Figure 8 shows the almost complete shift of the broad 7.5Å peak between 7.2Å and 9Å and the 10Å peak to 11.2Å. This saprolite sample was located at a depth of 25 to 26.5 feet. Figure 9 shows a partial expansion of the 7Å peak to 11.2Å (halloysite), with the remaining 001 peak showing a d-spacing of 7.14Å (kaolinite). This residual soil sample was

Table 3. Significant XRD Peaks for Study Area Clay Minerals

Location of Diagnostic Peak With Treatment1 Clay Mineral Air Dried Ethylene Glycol 250° Heat DMSO

7Å Halloysite 7.2Å – 7.4Å2 7.2Å – 7.4Å2 7.2Å – 7.4Å2 11.2Å3

10Å Halloysite 10Å2 10Å2 7.2Å2 11.2Å3

Kaolinite 7.15Å2 7.15Å2 7.15Å2 7.15Å3,4

Smectite 14Å – 15Å2 17Å2 9.4Å2 18Å – 19Å4

Interlayered 10Å 10Å4 10.3Å - 11Å4 7.2Å4 11.2Å4 halloysite/expandable

Interlayered 7Å 7.3Å – 9Å4 10.3Å - 11Å4 7.2Å4 11.2Å4 halloysite/expandable 1 Sample treatments described in Methods section 2 Peak locations identified in Chen (1977) 3 Peak locations identified in Gabor (1981) 4 Peak locations identified in this paper

shallow (10 to 11.5 feet deep) and showed more weathering as indicated by a lack of relic rock texture. A higher percentage of kaolinite is expected in this sample (Delvaux et al., 1990; Romero et al., 1992) and the resultant significant

7.14Å peak supports the conclusion that DMSO does not intercalate with kaolinite in basalt saprolite soils over a period of 48 hours at room temperature.

Kaolinite-rich samples were characterized by intense and symmetrical d001 peaks that were located between 7.2 and 7.3Å. Heat treatment had no effect on the location and intensity of the 7Å kaolinite peak. 7Å halloysite-rich samples were characterized by broad, asymmetrical peaks that gradually decreased toward the lower diffraction angles. Maximum peak height for 7Å halloysite was generally located between 7.3 and 8.0Å, with the 001 peak d-

38 spacing increasing with depth. Heat treatment caused the collapse of the 7.3 to

8.0Å halloysite peak to between 7.22 to 7.3Å.

X-Ray Diffraction Sample Data Summary

The following interpretations summarize the XRD analyses conducted on borehole samples at each of the study sites. All Monterey Overcrossing borings penetrated Boring Lavas saprolites. Geologic units penetrated at other study areas are identified below and are listed in Table 1.

Monterey Overcrossing Borehole BH-3

Orange, secondary clay collected from infilled primary void spaces in a breccia sample was analyzed from sample SS-3-9 to identify clay mineralogy and degree of crystallinity. Due to the highly plastic, “slimy” nature of this clay the presence of allophane, imogolite, or significant smectite was suspected.

Additionally, poorly-crystalline minerals that produce broad, poorly-defined XRD peaks were anticipated. A random orientation bulk sample that was analyzed from 3° to 65° 2θ contained well-crystalline 7Å halloysite, with only a trace amount of 10Å halloysite and hematite (using the 2.69Å peak). The random orientation of the sample appeared to intensify the 020 peak above the 001 peak. The 001 7Å halloysite peak in oriented samples generally showed the highest intensity in all samples analyzed for this research. The XRD trace for this sample is located in Appendix D.3.

Monterey Overcrossing Borehole BH-7

A detailed study of clay zonation with depth was conducted using nine samples collected in Borehole BH-7 between depths of 2.1 m (7 ft) and 13.7 m

(45 ft). Each sample was analyzed using XRD with the following treatments: air-dried, ethylene glycol, heat, and DMSO. The XRD traces are included in

Appendix D.4.

Borehole BH-7 penetrated 4.3 m (14 ft) of silt and clayey silt residual soil, over volcanic breccia saprolite (silt) to a depth of 6.1 m (20 ft). Flow rock saprolite (silty sand to sandy silt) was encountered to 9.6 m (31.5 ft) followed by breccia (sandy silt with clay) to 13.7 m (45 feet). Fresh basalt was encountered below 13.4 m. The borehole log for Borehole BH-7 is included in Appendix C.3.

Peak parameters were calculated for clay minerals in each of the samples analyzed. Appendix D.2 includes a discussion of peak parameter calculation from XRD traces. Tables D.2.1 through D.2.4 (Appendix D.2) list the peak parameters for 7Å halloysite, 10Å halloysite, kaolinite, and smectite. A summary of the net area of the diagnostic peak for each of the clay minerals is shown in Table 4 below. Net area is proportional to the abundance of a clay mineral in the soil (Moore and Reynolds, 1997).

Table 4. X-ray Diffraction Peak Parameters for Clay Minerals in Monterey Overcrossing Samples

1 Corrected Net Area of Diagnostic Peak (°counts/sec) Original Sample Depth (m) 7Å 10Å Rock Soil Texture Sensitivity Kaolinite Smectite Halloysite Halloysite Morphology Residual SS-7-2 2.1 – 2.6 60 0 315 810 Unknown None soil Residual SS-7-3 3.0 – 3.5 522 229 424 230 Unknown None soil SS-7-4 4.6 – 5.0 520 41 186 101 Flow rock Saprolite Minor SS-7-6 6.7 – 7.2 131 113 33 19 Flow rock Saprolite Moderate

SS-7-7 7.6 – 8.1 785 42 78 66 Flow rock Saprolite Moderate SS-7-8 9.1 – 9.6 469 248 76 123 Flow rock Saprolite Moderate Interflow SS-7-9 10.7 – 11.1 463 205 22 57 Saprolite Moderate breccia Interflow SS-7-11 12.8 – 13.3 344 417 18 40 Saprolite Moderate breccia Weathered SS-7-12 13.7 122 1965 18 25 Flow rock None rock

SS-18-6 4.6 – 5.0 958 0 145 41 Flow rock Saprolite None Interflow SS-18-8 7.6 – 8.1 1193 103 45 127 Saprolite Moderate breccia SS-18-9 9.1 – 9.6 553 316 59 30 Flow rock Saprolite None

1 Discussed in Appendix D.2.

The following trends in clay mineralogy were identified based on XRD analysis:

• 10Å halloysite generally increases with depth and this increase is not related to original basalt morphology. • 7Å halloysite increases with depth, and then decreases below 7.6 m (25 ft). • The 001 peak for 7Å halloysite generally becomes broader, less distinct, and more asymmetrical toward the lower diffraction angles with depth. • Kaolinite decreases with depth and is significantly more abundant in residual soil. • Smectite decreases with depth. • Trace amounts of illite and or quartz occur in residual soil samples (SS- 7-2 and SS-7-3) and are scattered within the saprolite samples (SS-7-4 and SS-7-11).

Both 7Å and 10Å halloysite in Borehole BH-7 samples expanded to

11.3Å with glycolation indicating the presence of interlayered halloysite/expandable clay. Heat treatment caused all halloysite to collapse to

7.2 to 7.2Å. Both the intensity of the peak and the degree of ordering/crystallinity of the 7Å peak increased with heat treatment.

Monterey Overcrossing Borehole BH-10

Seven air-dried samples were analyzed from Borehole BH-10 to corroborate trends in clay mineral zonation identified in Borehole BH-7. Sample

SS-7-10 was evaluated for kaolinite using DMSO. A bulk, randomly oriented sample of SS-10-10 was analyzed for total mineralogy, and an oriented sample of –2μm material was prepared for each of the sample treatments listed in Table

D.1.1. Table 5 summarizes the clay mineralogy for each random and oriented

43 sample based predominantly on air-dried analyses and comparison with analyses conducted on other Monterey Overcrossing samples.

Table 5. Monterey Overcrossing Borehole BH-10 XRD Mineralogy

Depth 7Å 10Å Other Sample Kaolinite1 Smectite (m) Halloysite1 Halloysite Minerals Not SS-10-4 4.9 – 5.3 Some2 Trace2 Some Abundant2 detectable Trace SS-10-5 6.1 – 6.6 Some Trace Some Trace goethite Trace SS-10-7 8.2 – 8.7 Abundant Some Trace Trace goethite Trace SS-10-8 9.1 – 9.6 Abundant Trace Trace Some goethite Not SS-10-9 10.7 – 11.1 Abundant Trace Trace Trace detectable Abundant maghemite, SS-10-10 12.2 – 12.6 Trace Abundant3 None Trace some hematite Trace SS-10-11 13.7 Some Trace None Some feldspar

1 The amount of 7Å halloysite vs. kaolinite is only confirmed using DMSO in Sample SS-10-7. All intermediate halloysite between 7Å and 9Å is identified as 7Å halloysite. 2 Abundance of clay mineral based on XRD peak area. 3 10Å halloysite peak in Sample SS-10-10 is located at 10.88Å

Borehole BH-10 penetrated 4.6 m (15 ft) of Willamette Silt over volcanic breccia saprolite (stiff silt with some clay) to a depth of 12.2 m (40 ft). Flow rock saprolite was encountered to 12.8 m (42 ft) followed by fresh basalt flow rock.

The borehole log for Borehole BH-10 is included in Appendix C.3. Unlike

Borehole BH-7, BH-10 may only penetrate two feet of residual soil (not sampled and not recorded in the borehole log). Thus, all samples show sensitivity, ranging from minor (SS-10-4) to extreme (SS-10-10).

Borehole BH-10 confirms many of the trends identified in Borehole BH-7.

These trends include:

• 10Å halloysite generally increases with depth and this increase is not related to original rock morphology. Sample SS-10-11 shows only trace 10Å halloysite, but this sample consists of the weathering rind on jointed basalt bedrock and did not contain abundant clay-size material. • 7Å halloysite increases with depth and then decreases below 10.7 m (35 ft) with the exception of Sample SS-10-11. • The 001 peak for 7Å halloysite generally becomes broader, less distinct, and more asymmetrical toward the lower diffraction angles with depth. • Only trace kaolinite is found in Sample SS-10-7 at 8.2 to 8.7 m (27 to 28.5 feet). • Smectite decreases with depth but is more abundant at the bottom of the boring within the weathering rind of the jointed basalt bedrock.

Similar to Borehole BH-7, the nature of the 7Å halloysite 001 peak changes with depth, becoming broader toward the lower diffraction angles, less intense, and less distinct. This broadening indicates a decrease in the degree of crystallinity and an increase in the amount of halloysite intermediate between

7Å and 9Å.

Monterey Overcrossing Borehole BH-18

Samples from Borehole BH-18 were selected to evaluate clay mineralogy variation between sensitive and non-sensitive saprolites within a single borehole. Three sequential samples collected at depths ranging from 4.6 to 9.6 m (15 to 31.5 ft) were analyzed. The upper and lower samples are non- sensitive decomposed flow rock, while the center sample at 7.6 m (25 ft) consists of moderately sensitive decomposed volcanic breccia. The peak parameters calculated for Borehole BH-18 samples (SS-18-6, SS-18-8, and SS-

18-9) are listed in Table 4.

Based on XRD analyses, clay mineralogy does not appear to vary significantly between sensitive and non-sensitive saprolites. Trends in clay variation observed in Borehole BH-7 that are replicated in these three samples include:

• Kaolinite content decreases with depth. • 10Å halloysite increases with depth. • 7Å halloysite is most abundant in the middle sample and becomes less abundant and poorly crystalline in the deepest sample.

Smectite is more common in the central, sensitive sample. Both

Boreholes BH-7 and BH-18 do not show any clear association between sensitivity and smectite content.

Interlayering of an expandable clay with both 7Å and 10Å halloysite is present in all three samples. Both the 10Å peak and the broad, asymmetrical peak between 7Å and 9Å shift to 10.6 to 10.7Å with glycolation (Figure 18).

Monterey Overcrossing Borehole BH-27

Similar to sample SS-3-9 discussed above, the orange, secondary clay from saprolite sample SS-27-7 was evaluated using XRD for mineralogy and degree of crystallinity. The air-dried, oriented sample of less than 2 micrometer sized (-2μm) material contained predominantly 7Å halloysite, with lesser amounts of smectite and 10Å halloysite, and a trace amount of hematite, illite, and quartz. Each mineral, with the exception of hematite, showed distinct peaks indicating an ordered, crystalline structure. The XRD trace for this sample is located in Appendix D.7. 46

Monterey Overcrossing Borehole BH-43

Sample SH-43-6 was photographed using SEM to evaluate the microtexture of this extremely sensitive volcanic breccia saprolite. An air-dried, oriented sample of –2μm material was analyzed by XRD to determine the clay mineralogy present in the photomicrographs of the sample. The majority of the sample consisted of 10Å halloysite, with lesser amounts of poorly crystalline 7Å halloysite, and only a trace amount of smectite. The XRD trace for this sample is located in Appendix D.7.

West Salem Site 1 Borehole BH-1

Clay zonation in Borehole BH-1 was analyzed in ten samples using XRD and the following samples treatments: air-dried, ethylene glycol, and heat.

Sample SS-1-4 was analyzed after treatment with DMSO to determine the amount of kaolinite in the saprolite. The XRD traces for these samples are included in Appendix D.9.

Borehole BH-1 penetrated 1.4 m (4.5 ft) of clay residual soil over flow rock saprolite consisting of silt with some (15 to 30%) clay and trace to some sand to the bottom of the boring 12.6 m (41.5 ft). The entire borehole appeared to remain within a single Grande Ronde Basalt flow.

7Å halloysite, kaolinite, and minor smectite was detected in all samples.

No 10Å halloysite was observed within the borehole. The -2μm fraction of the soil was not as well crystalline as the Monterey Overcrossing samples. Peaks were generally low and poorly defined. Similar to the Monterey Overcrossing 47 samples, the 7Å halloysite peak shifted to between 10.9Å and 11.1Å with glycolation indicating the presence of interlayered expandable clay.

In addition to clay minerals, significant low cristobalite and trace goethite were detected in XRD traces. The well-crystalline low cristobalite was most abundant between 4.6 m to 7.6 m (15 to 25 feet) and was characterized by sharp, distinct peaks.

West Salem Site 2 Borehole BH-1

Two samples were analyzed from Borehole BH-1 at West Salem Site 2 to evaluate the variation in clay mineralogy between non-sensitive residual soil

(SS-1-1) and sensitive saprolite (SS-1-6). 7Å halloysite/kaolinite, smectite, and trace low cristobalite, goethite, and 10Å halloysite were observed in both samples. The residual soil sample showed well-crystalline 7Å halloysite/kaolinite and some smectite. The sharpness, symmetry, and d- spacing of the residual soil 7Å peak indicates that significant kaolinite is present.

The sensitive saprolite sample contained abundant smectite and some 7Å halloysite/kaolinite. Portions of the broad 7Å peak shift to 10.7Å with glycolation indicating interlayering with expandable clay. XRD traces for Borehole BH-1 are included in Appendix D.10.

Carlton Boreholes BH-1 and BH-2

Unlike the sample areas above, the Carlton sample area is underlain by a diabase intrusion. Although clay mineralogy is very similar to that observed in the Monterey Overcrossing samples, smectite is more abundant and only trace

10Å halloysite is present. Smectite is present in all three samples analyzed, but is most abundant in sensitive saprolite Sample SS-2-6 at 4.6 to 5.0 m (15 to

16.5 ft). Abundant kaolinite and trace quartz and mica were observed in the residual soil sample (SS-2-2). Only sensitive saprolite Sample SS-1-8 showed evidence of interlayered 7Å halloysite/expandable clay. XRD traces for

Boreholes BH-1 and BH-2 are included in Appendix D.11 and D.12, respectively.

Silverton Borehole BH-1

Borehole BH-1 penetrated Columbia River Basalt Group flow rock saprolite but a different unit (Frenchman Springs Member of the Wanapum

Basalt) than was encountered at West Salem Sites 1 and 2 and South Salem.

Two samples were analyzed for variation in clay content with soil type and sensitivity. The non-sensitive residual soil sample (SS-1-2) showed abundant kaolinite, with some 7Å halloysite and trace amounts of smectite, cristobalite, quartz, and goethite. The sensitive saprolite sample (SS-1-4) showed 7Å halloysite and trace amounts of smectite and goethite. Portions of the broad, asymmetrical 7Å peak in the saprolite sample expanded to 11Å after glycolation which indicated the presence of interlayered halloysite/expandable clay. XRD traces for Borehole BH-1 are included in Appendix D.13.

South Salem Borehole BH-2

Borehole BH-2 penetrated Grande Ronde Basalt saprolite. One moderately sensitive saprolite sample (SS-2-6) was analyzed to evaluate clay

49 mineralogy. The sample contained 7Å halloysite/kaolinite with trace amounts of smectite and goethite. Similar to West Salem Sites 1 and 2 saprolite samples,

Sample SS-2-6 did not contain 10Å halloysite and the peaks were broad and poorly-defined. Portions of the broad, asymmetrical 7Å peak in the saprolite sample expanded to 10.8Å after glycolation, indicating the presence of interlayered halloysite/expandable clay. XRD traces for Borehole BH-2 are included in Appendix D.14.

Magnetism Observations

Thirteen samples from a variety of sites were tested for magnetism using a hand-held pencil magnet placed in a soil-water suspension. Abundant magnetic material was retained on the magnet in strongly magnetic samples.

Testing of weakly magnetic samples produced only minor magnetic material.

The results of this testing are shown in Table 6. Except for one example, saprolite samples contained magnetic material and residual soil samples were not magnetic.

To evaluate the magnetic mineralogy of a bulk sample, Monterey

Overcrossing Sample SS-10-10 was analyzed using random powder XRD analysis between 3° and 65° 2θ (Appendix D.5). This analysis showed the presence of reddish-brown maghemite, the ferromagnetic form of Fe2O3 that forms in soils and is isostructural with magnetite (Schwertmann and Taylor,

1989). Maghemite was identified using the 2.52 and 2.96Å peaks.

Table 6. Magnetic Properties of Soil Samples

Site Sample Depth (m) Soil Texture Magnetism SS-7-9 10.7 – 11.1 Saprolite Strong SS-10-10 12.2 – 12.6 Saprolite Strong

Monterey Avenue SS-18-6 4.6 – 5.0 Saprolite Strong Overcrossing SS-18-8 7.6 – 8.1 Saprolite Strong SS-18-9 9.1 – 9.6 Saprolite Strong SH-43-6 6.6 – 7.2 Saprolite Strong

West Salem Site 1 SS-1-4 3.0 – 3.5 Saprolite Weak SS-1-1 8.0 – 1.2 Residual soil None West Salem Site 2 SS-1-6 4.6 – 5.0 Saprolite Weak SS-1-8 7.6 – 8.1 Saprolite Strong Carlton SS-2-2 1.4 – 1.8 Residual soil None SS-2-6 4.6 – 5.0 Saprolite Strong Silverton SS-1-2 1.5 – 2.0 Residual soil Strong

South Salem SS-2-6 4.6 – 5.0 Saprolite None

Soils containing exclusively silt and clay-sized material were generally not magnetic. Saprolite samples that contained abundant >#230 mesh grains were generally more magnetic. Magnetism is attributed to the presence of secondary maghemite based on XRD analysis of Monterey Overcrossing

Sample SS-10-10.

Field Sensitivity Testing Results

Field sensitivity testing on all the study site samples identified the following trends:

• Soil sensitivity generally increases with depth. • Saprolite soils are generally sensitive. 51

• Residual soils are not sensitive. • Volcanic breccia saprolites are more sensitive than flow rock or intrusive rock saprolites.

Although soil sensitivity appears generally to increase with depth, one sample of flow rock saprolite (Monterey SS-18-8) did not appear sensitive, even though it was beneath a sensitive volcanic breccia. Table C.1.1 (Appendix C.1) identifies the field sensitivity of each sample.

Testing for Amorphous Clay (Allophane and Imogolite)

Samples of a non-sensitive residual soil, sensitive saprolite, and a secondary orange clay were tested for allophane and imogolite using the toluidine blue spot test (Wada and Kakuto, 1985). These samples included

Monterey Overcrossing samples SS-7-2, SS-7-9, and SS-7-4 (orange clay portion). The soil – solution mixture created for each sample turned purple, indicating that neither allophane nor imogolite were present.

Scanning Electron Microscopy (SEM) Results

A series of SEM photos were taken of Monterey Overcrossing Sample

SH-43-6 using resolutions of 10X, 50X, 390X, and 2000X to identify the nature of primary and secondary porosity within a volcanic breccia saprolite. Figure 10 shows a slightly enlarged (1.7X) photograph of the sample prior to analysis.

Secondary orange and white clay has precipitated in relict rock joints and inter- clast voids. A white clay has replaced the plagioclase phenocrysts.

Sample SH-43-6 was obtained at a depth of 6.6 to 6.7 m (21.5 to 22 ft), directly above the weathered rock interface. Basalt bedrock was sampled (rock

52 core) below a depth of 7.0 m (23.5 feet). Sample SH-43-6 is best described as a soft, dark brown mottled orange, damp to moist low plasticity silt with trace

(<15%) fine sand. The consistency of the sample is based on a SPT N-value of

3 blows per foot obtained at 6.1 to 6.6 m (20 to 21.5 feet). Although the sample can be crushed under moderate finger pressure, it is only in the early stage of saprolite formation and still retains much of the original rock texture and greater than 50 percent original minerals (R. Glasmann, personal communication,

February 2001). Even though the sample is not completely weathered, it is sensitive and freely releases water when compressed under finger pressure.

XRD analysis of the -2μm fraction identified significant amounts of 10Å halloysite in this sample, with lesser amounts poorly crystalline 7Å halloysite, and only trace amounts of smectite.

At 10X magnification (Figure 11), primary porosity consists of large (0.5 to 4 mm) voids within and surrounding the breccia clast. The voids appear to be partially or completely infilled with a secondary mineral. In addition to the primary porosity, secondary micro-voids are visible on a portion of a volcanic breccia clast that has been outlined (Box A).

At 50X sample magnification (Figure 12), Box A1 shows enlarged micro- voids or boxworks as defined by Velbel (1990) that are visible in the breccia clast (Box A, Figure 11). A smooth, secondary, white, clay-like mineral is visible in the upper right hand corner (Box B).

At 390X sample magnification (Figure 13), the secondary mineral in Box

B appears extremely smooth with conchoidal fractures cutting surfaces. This material shows desiccation cracking. At 390X sample magnification (Figure

14), the portion of the breccia clast within Box A1 clearly shows a boxwork structure of angular dissolution voids bounded by clay septa. Boxes A2 and A3 enclose the two different textural morphologies present within Box A1 (Figure

12).

At 2000X sample magnification (Figure 15), the boxwork morphology within Box A2 (Figure 14) consists of 10 to 40μm voids. These voids form isolated, pockets within the in situ soil structure. At the same magnification, apparent iron oxides are visible as rounded clusters in Box A3 shown in Figure

16 (R. Glasmann, personal communication, November 2001)

Figure 10. Residual texture visible in volcanic breccia saprolite sample SH-43-6 from Monterey Avenue Overcrossing. Sample is approximately 70 mm (2.75 inches) in diameter (thumb tack for scale). Note orange clay infilling a relict rock joint and white clay replacing relict plagioclase phenocrysts.

Figure 11. SEM photomicrograph of Sample SH-43-6 at 10X magnification. Note the primary porosity in decomposed volcanic breccia. 56

Figure 12. SEM photomicrograph of Box A from Sample SH-43-6 at 50X magnification. Box A1 encloses portion of decomposed basaltic breccia clast. Box B encloses secondary white clay-like precipitate in a primary void or vesicle. 57

Figure 13. SEM photomicrograph of Box B from Sample SH-43-6 at 390X magnification showing close-up of white secondary clay-like precipitate filling a void or vesicle in a decomposed basaltic breccia clast. 58

Figure 14. SEM photomicrograph of Box A1 from sample SH-43-6 at 390X magnification showing boxwork structure in decomposed basaltic breccia clast. Box A2 shows dissolution voids bounded by clay septa. Box A3 contains apparent iron oxide material. 59

Figure 15. SEM photomicrograph of Box A2 from Sample SH-43-6 at 2000X magnification showing close-up view of boxwork structure. Note the extremely thin clay septa dividing the dissolution void near the center of the picture (Banding on photograph caused by charging artifacts.) 60

Figure 16. SEM photomicrograph of Box A3 from Sample SH-43-6 at 2000X magnification showing close-up of apparent iron oxides. 61

Engineering Index Testing Results

Index testing of study area samples included natural water content and

Atterberg limits. Laboratory testing results are shown in Table B.2.1, Appendix

B.2. Natural water content tests were conducted on all but two of the samples.

Atterberg limits tests were conducted on West Salem Site 2, Sample SS-1-6

(saprolite) and Silverton, Sample SS-1-2 (residual soil). In addition to index testing of samples analyzed for this project, index testing on similar samples from Monterey Avenue Overcrossing are shown in Table B.3.1, Appendix B.3.

These tests included natural water content, Atterberg limits, percent <#200 mesh, and wet and dry unit weight. Table 7 includes a summary of the average engineering index testing data for both sensitive and non-sensitive samples

(and similar samples) tested at each study site.

Engineering index test results show that volcanic saprolites generally consist of high plasticity silts (MH) while residual soil generally consisted of high plasticity clay (CH). The moisture content of the saprolite soils is extremely high

(59% average) and their dry unit weight is very low (5.6 to 6.4 kN/m3 or 36 to 41 lb/ft3 for volcanic breccia saprolite). Residual soil samples are characterized by a lower water content (generally between 20% to 30%) and higher unit weight

(13.8 kN/m3 or 88 lb/ft3).

The moisture content of study area samples generally increase with depth and then decrease just before the rock interface. The most sensitive soils generally show the highest natural water content and there is a dramatic 62 difference in water content between residual and saprolite soils. Three samples obtained from Monterey Avenue Overcrossing boreholes show moisture contents near or above their liquid limits indicating that these soils will lose all shear strength when disturbed.

Table 7. Summary of Engineering Index Testing Data

Average Wet/Dry Natural Atterberg Percent Unit Weight Site Sensitivity Water Limits <#200 in kN/m3 Content (LL/PI/USCS)1 mesh (lb/ft3) (%)

Not 2 19/14 3 41 57/26/MH N/A sensitive (120/88) Monterey Avenue Overcrossing 16/6.0 Sensitive 63 86/32/MH 65 (101/39) Not 39 N/A N/A N/A sensitive West Salem Site 1 Sensitive 57 N/A N/A N/A Not 17 N/A N/A N/A sensitive West Salem Site 2 Sensitive 55 51/6/MH N/A N/A Not 39 N/A N/A N/A sensitive Carlton Sensitive 42 N/A N/A N/A Not 37 57/36/CH N/A N/A sensitive Silverton Sensitive 56 N/A N/A N/A

South Salem Sensitive 63 N/A N/A N/A

1 LL = Liquid limit, PI = Plastic index, USCS = Unified Soil Classification System symbol 2 Residual soil classification at Monterey Avenue Overcrossing included a CH, CL, and MH. An average value is not representative of these soils. 3 Not determined

DISCUSSION

Clay Mineralogy in Basaltic Saprolites and Residual Soil

Laboratory research conducted for this paper investigates the characteristics of individual clay minerals or mixtures and clay mineral zonation in basalt saprolites and residual soil. The following discussions compare this research with research conducted by others.

Clay Zonation

Zonation in clay mineralogy was observed in detail in Boreholes BH-7 and BH-10 at Monterey Overcrossing in southeast Portland and in Borehole

BH-1 at West Salem Site 1. Selected borehole samples from the other study sites were used to evaluate and confirm trends in clay mineralogy zonation observed in the Monterey Overcrossing borings. Based on the XRD analyses, vertical clay zonation did not appear to be significantly affected by original rock texture (i.e. flow verses interflow zones). 7Å halloysite is present in all zones and appears interlayered with expandable clay only within the saprolite. 10Å halloysite is rarely observed in the residual soil and is also commonly interlayered with expandable clay in the saprolite. Basaltic saprolites analyzed within the study area showed the following vertical zonation of the 1:1 clay minerals:

10Å halloysite (deep saprolite)→ 7Å halloysite (intermediate saprolite) → kaolinite (shallow residual soil)

Smectite is most abundant near the rock interface; no clear zonation within the borehole samples was observed. Previous research has shown the highest smectite concentration in the lower portions of the saprolite or closest to the rock interface (Glasmann and Simonson, 1985; Eggleton et al., 1987;

Watanabe et al., 1992; Righi et al., 1999), no clear trend in smectite zonation is observed in the study site samples. Abundant smectite is observed in the residual soil (Monterey Sample SS-7-2, Appendix D.4) and also near the rock interface (Carlton Sample SS-1-8, Appendix D.11). High smectite concentrations in the residual soil may be partially attributed to contamination from overlying soils or be due to clay enrichment in the B soil horizon. Even though the formation of smectite usually requires low leaching rates and poorly drained soils, the formation of smectite and halloysite in well-drained soils may be controlled by the microenvironment developed in isolated, fluid-filled microboxworks. Glasmann and Simmson (1985) postulated that it might be possible for reducing conditions to exist in these water-filed voids even in an aerated soil.

Zonation in the clay mineral crystallinity was also observed within study site samples. The 7Å halloysite 001 peak appeared sharp and distinct in shallow samples, but became broad and poorly defined with depth. The 001 peak became asymmetrical toward the low diffraction angles with depth. These peak characteristics may indicate decrease in crystallinity with depth, the

65 presence of intermediate halloysite varieties, interlayering with expandable clay, or all three.

Allophane and imogolite, which have been associated with sensitive saprolites (Thrall, 1981), are composed of a solid solution between silica, alumina, and water (Wada, 1989). Both minerals are x-ray amorphous and are commonly associated with halloysite (Wada, 1989). They are most common in saprolites formed in volcanic ash but have been found in soils derived from basalts in warm, tropical environments (Moore and Reynolds, 1997). Allophane forms hollow spherules (35 to 50Å in diameter), while imogolite forms tubes (18 to 20Å in diameter) (Moore and Reynolds, 1997). Both minerals form gels that are thought to contain water in their structure and block water-filled pores

(Thrall, 1981). Since no allophane or imogolite were detected in any of the samples tested, soil sensitivity observed in saprolites at the study area sites cannot be attributed to these minerals.

In addition to systematic variations in clay mineralogy and crystallinity, zonation in the abundance of well crystalline low cristobalite or opal C (SiO2) is present in the -2μm size soil material is present at the West Salem Site 1. This mineral is formed during the laterization process as dissolved SiO2 is carried downward by groundwater and precipitated as metastable layered cristobalite

(Jones and Segnit, 1972). Laterization is a de-silication process in which silica, alkalies, and alkaline earths are leached from the soil (Corcoran and Libbey,

1956). Due to the low energy environment, the stable SiO2 polymorph, quartz,

66 is unable to form (Jones and Segnit, 1972). Tridymite also precipitates in low energy environments, but the sharpness and location of the low cristobalite peaks in the West Salem Site 1 samples indicate limited tridymite.

Low cristobalite, although rare in soils, is characterized by sharp, symmetric XRD peaks and is usually associated with pyroclastic rocks (Drees et al., 1989). At West Salem Site 1, low cristobalite is most abundant between 4.6 m and 8.1 m (15.0 and 26.5 feet), based on peak height. Physical and chemical conditions at this depth interval appear to favor the precipitation of well-ordered cristobalite and may be related to current or ancient fluctuations in groundwater levels. Figure 17 shows crystalline, well-ordered low cristobalite in the air-dried

XRD trace for Sample SS-1-7 at 7.6 to 8.1 m (25 to 26.5 feet) at West Salem

Site 1.

Mixed-Layered Halloysite/Expandable Clay

Mixed-layered halloysite/expandable clay was identified in study site samples of sensitive saprolite. Previous research indicates that pure halloysite doesn’t expand with glycolation (Glasmann and Simonson, 1985; Delvaux et al.,

1990; Moore and Reynolds, 1997). However, in interlayered halloysite/smectite clays, Delvaux and others (1990; 1992) observe a shift in the 10Å halloysite peak to 10.5Å, with a broadening towards the low diffraction angles, after exposure to ethylene glycol.

Interlayered halloysite/expandable clay was observed in at least one saprolite sample from each of the six study sites. In Monterey Avenue Overcrossing

Sample SS-18-8, the low diffraction angle portion of the broad(7.3Å - 9Å) peak shifts to 10.5Å (Figure 18). The 10Å halloysite 001 peak in this sample also shifts to 10.5Å after glycolation. This shift of the lower diffraction angle portion of a broad 7Å halloysite peak (7.4Å

Research conducted for this thesis does not identify if the interlayered clay is smectite, and thus it is only identified as expandable clay. Interlayering may only include a small amount of expandable clay (10%) with R0 ordering

(Reichweite) (Moore and Reynolds, 1997). Additionally, interlayered 10Å halloysite may separate into smectite and 7Å halloysite with glycolation-based peak shifts observed in Monterey Overcrossing Sample SS-10-10 (Appendix

D.5). Interlayering does not appear to be present in residual soils containing abundant kaolinite, indicating that the interlayered halloysite/expandable clay is destroyed and converted to 7Å halloysite and kaolinite (Monterey Overcrossing

Sample SS-7-2, Appendix D.4).

Figure 17. Air-dried XRD trace of crystalline, well-ordered low cristobalite in West Salem Site 1 sample SS-1-7 (25 to 26.5 feet deep).

Desiccation of 10Å Halloysite

Previous research has indicated that 10Å halloysite converts to 7Å halloysite if desiccated (Churchman et al., 1972; Gillott, 1987) and that dehydration of 10Å halloysite is irreversible (Bailey, 1989). Costanzo and Giese

(1985) suggest that 10Å halloysite is unstable under ambient conditions (room temperature and less than 90% relative humidity) and rapidly dehydrates if not immersed in water. Although subjected to desiccation at room temperature, conversion of 10Å halloysite to 7Å halloysite does not appear to have occurred in Monterey Overcrossing samples at any depth. XRD analysis of an air-dried and pulverized sample (Monterey Overcrossing sample SS-10-10) showed a distinct 001 halloysite peak at 10Å. Similarly, Monterey Overcrossing Sample

SS-7-12 was completely desiccated during storage, but still contains abundant

10Å halloysite (Appendix D.4). However, based on the higher d-spacing of the

10Å halloysite peak (10.88Å) in sample SS-10-10 and the shift with glycolation from 10.04Å to 10.43Å, this sample contains interlayered 10Å halloysite/expandable clay. This clay mixture may be more resistant to desiccation than pure 10Å halloysite. The data obtained from XRD analyses of study site samples indicate that the conversion from 10Å halloysite to 7Å halloysite in saprolites is complex and not exclusively related to soil desiccation.

Development of Sensitivity in Basaltic Saprolites

Previous engineering hypotheses have attributed sensitivity in volcanic saprolites to the presence of hydrated (10Å) halloysite (Mitchell, 1989) or the

70 combined presence of halloysite and smectite (Cornforth Consulting Inc., 1991).

This hypothesis contends that water-filled 10Å halloysite tubes crush when compacted releasing the water into the soil and causing moist soil to become wet and lose shear strength (Mitchell, 1989). Additionally, water released by the halloysite is absorbed by smectite, further lowering the shear strength of the soil

(Cornforth Consulting Inc., 1991). However, even if both 7Å and 10Å halloysite form tubes (Singh and Gilkes, 1992), the energy required to rupture these small tubes would be excessive. Furthermore, the amount of stored water within the interior of the tubes would be inadequate to produce the effects observed in sensitive soils. The average outside diameter of a halloysite tube is 0.07μm, the inner diameter is 0.03μm, and tubes may be several microns in length (Grim,

1962). The volume of an individual tube is 1.4 X 10-3 μm. Conversely, a 10μm boxwork void can store 1000μm3 of water, or 710,000 times the amount of water stored in a halloysite tube. Cummings (In Press) summarizes the source of water in sensitive saprolites in the following manner:

“The crystallization of halloysite, smectite, and other clay minerals and development of bonding between particles at the same time primary minerals are dissolving and the porosity is evolving provides an opportunity for water to be trapped in the saprolite and bedded sediments. Mechanical working progressively disrupts the bonds and releases pore water.” Based on XRD clay data and SEM photographs included in this paper, sensitivity is not a function of the formation of any specific clay mineral or clay mineral association, but the development of clay-bounded boxwork voids that trap and isolate water in the saprolite structure. Sensitive saprolites form in

Figure 18. Expansion of 10Å halloysite peak, half of the 7Å halloysite peak, and the broad peak between 7Å and 10Å to 10.5Å with glycolation. This expansion indicates that the halloysite has interlayered with an expandable clay. (Sample Monterey SS-18-8, the blue trace is air-dried, the green trace is glycolated, and the red trace is heated). 72

flow rocks, interflow breccias, tuffs, and well crystalline intrusive rock (diabase) and are not related to the formation of clay minerals in weathered volcanic glass.

Both 7Å and 10Å halloysite are stable in environments that form saprolite boxworks. XRD data obtained from Monterey Avenue Overcrossing samples in

Borehole BH-18 indicate that clay mineralogy doesn’t vary significantly within a saprolite between sensitive and non-sensitive soils, and 10Å halloysite is not ubiquitous to sensitive soils. This observation supports the conclusion that soil microstructure, and not clay mineralogy, is the controlling factor in the development of sensitive soils.

Sensitivity in volcanic soils is found only in saprolites and is not observed in residual soils where physical movement, desiccation, and pedogenic processes have destroyed the original soil texture. Saprolites form isovolumetrically, while the formation of residual soil is not isovolumetric and involves the collapse the saprolite (boxwork) structure (Pavich, 1996). Causes for in situ mineralogic and morphologic changes that destroy sensitivity include the following:

• Soil creep on slopes. • Pedogenic processes within the A and B soil horizons. • Pedoturbation (soil mixing) by roots and burrowing animals. • Shrinking and swelling of expandable clays (smectite) in the vadose zone with seasonal wetting and desiccation.

Each of the above processes works incrementally to break down the saprolite boxwork structure, destroying the clay bounded voids and releasing trapped water. Once the boxwork texture is destroyed, it cannot be recreated.

Occurrence of Sensitive Saprolites in Other Volcanic Rocks

Sensitive basalt saprolites are found in the study sites and at The Trask

River Dam Raise project site. Laboratory testing of Trask River Dam Raise project soils identified properties similar to those found in study site samples.

Halloysite was encountered in all samples tested for this project, but the clay mineralogy varied in each sample.

Sensitive saprolites do not form exclusively on basalt. Case history information (Appendix A) identifies sensitive saprolites forming on flows and tuffs composed of andesite (Toutle River SRS and Spirit Lake Memorial

Highway) and dacite (Toutle River SRS and Hills Creek Dam). Clay mineralogy studies conducted for the Toutle River SRS identified variable clay mineralogy including 7Å and 10Å halloysite, smectite, kaolinite, vermiculite, and expandable mixed layer clay (Cummings, In Press). These clays were detected in sensitive flow rock, breccia (debris flow), and volcaniclastic saprolites. Only a minor amount of halloysite is present in portions of one sensitive unit (Hatchet

Mountain volcanics) (Cummings, In Press). X-ray diffraction analyses conducted for the construction of Hills Creek Dam identified similar variation in clay mineralogy in sensitive weathered terrace gravel, although halloysite was present in each sample tested (U.S. Army Crops of Engineers Portland

Engineer District, 1966). Although the clay mineralogy was not consistent in sensitive saprolites tested for these projects, similar construction difficulties were experienced at each site.

Based on study site and case history data, sensitive soils should be suspected within any volcanic saprolite. The presence of sensitive saprolites does not appear to be related to original igneous rock type or texture or any specific clay mineral, but the isovolumetric leaching of silica and other elements to form microscopic water-filled boxwork voids bounded by aluminum and iron- based secondary minerals. Basically, the conditions that lead to boxwork formation in volcanic saprolites are similar to those that favor the formation of halloysite.

Identification of Sensitive Volcanic Saprolites

Based on engineering case history information and techniques developed for this research, field, index, and laboratory tests can be conducted to identify sensitive volcanic saprolites prior to construction.

Field Index Testing

Field index testing during the geotechnical investigation can alert the designers to the presence of sensitive volcanic saprolites in the project area and can identify the need for additional laboratory testing. Sensitive volcanic saprolites can commonly be identified by crushing a clod of soil with strong finger pressure (Figures 1 and 2) and observing if the soil becomes wet. If the

75 soil shows no discernable increase in moisture content after crushing, it is most likely not sensitive.

Sensitive volcanic saprolites also feel cold to the touch. During test pit excavations, stick your hand into the pile of soil in a backhoe bucket. If the soil feels abnormally cold, then it is sensitive (with a high water content) and should not be used for embankment material without further testing. This technique was used successfully by Brent Black of Cornforth Consulting (personal communication, April 2000) during the geotechnical exploration for the Trask

River Dam raise.

Prior to construction, build test embankment fills to assess potential compaction difficulties. Make numerous passes with the type and size (weight) of earth moving equipment to be used during construction.

Engineering Index Testing

Once field sensitivity testing has indicated the presence of sensitive soils, additional index testing can be conducted to determine the engineering properties of these soils and estimate their performance during construction.

The following index tests should be conducted on soils identified for foundation and embankment materials:

Natural Water Content

Sensitive soils have high natural moisture contents and are usually greater than 50% water, by weight. These soils may appear only moist in exposures. 76

Unit Weight (Dry Density)

Due to the abundant void space in sensitive saprolites, they have low dry densities. Samples of volcanic breccia saprolite form Monterey Avenue

Overcrossing have low dry unit weights of 5.7 to 6.4 kN/m3 (36 to 41 lbs/ft3). A non-sensitive residual soil at the same site had a unit weight of 13.8 kN/m3 (88 lbs/ft3).

Atterberg Limits Test

Atterberg limits tests are extremely helpful in identifying sensitive volcanic saprolites. Sensitive soils are generally high plasticity silts (MH) and often have natural moisture contents equal to or greater than the liquid limit of the soil. Atterberg limits change between moist, air-dried, and oven dried samples. Both the liquid limit and the plastic index decrease with increased drying.

Proctor (Moisture-Density) Tests

Conduct Proctor tests on all materials to be used for embankment fills to identify sensitive soils. Since the maximum dry density and optimum moisture content become higher and drier, respectively, with working, pulverize soils prior to Proctor testing to obtain accurate maximum dry density and optimum water content of soils under actual construction conditions (Cornforth Consulting Inc.,

1991). Conduct Proctor density tests on samples obtained from test fills to more accurately identify compaction parameters prior to construction (Cornforth

Consulting Inc., 1991). Additionally, Harvard miniature compaction testing may

77 provide more accurate compaction parameters than can be obtained with

Proctor testing (T. Smith, personal communication, May 2002)

X-Ray Diffraction Analysis

If index test results for project area soils are similar to values typical for sensitive soils, XRD analysis can be helpful identifying the presence of halloysite and smectite. Even though halloysite crystals may not store significant water, both 7Å and 10Å halloysite (along with smectite) are commonly associated with sensitive saprolites based on XRD analyses conducted for this research and other engineering projects. Additionally, the presence of intermediate halloysite, which may increase the plasticity of the soil

(U.S. Army Crops of Engineers Portland Engineer District, 1966), should be evaluated. This intermediate halloysite shows either intermediate degrees of hydration (U.S. Army Crops of Engineers Portland Engineer District, 1966) or interlayered 7Å and 10Å halloysite.

Mitigation of Sensitive Volcanic Saprolites

If sensitive volcanic saprolites have been identified by field and laboratory testing, and these soils must be worked during construction, mitigate against adverse effects by manipulating the soil as little as possible. Use light compaction equipment, limiting scraper size to 20 tons (D. H. Cornforth, personal communication, April 2000). Less manipulation and lighter compaction will limit the crushing of water-filled saprolite boxworks and reduce the amount of soil drying required.

During fill placement, don’t try to dry back the soil too much with disking or spreading. Increased manipulation will cause the soil to release more water and become wetter. Place soil only during dry weather and grade embankments to facilitate drainage. Limit lift thickness to enhance the soil’s ability to dry.

CONCLUSIONS

Halloysite is an abundant clay mineral in sensitive basaltic and andesitic saprolites in northwestern Oregon and southwestern Washington. These soils release water and lose shear strength when compressed. 7Å halloysite was detected in all sensitive soils analyzed. 10Å halloysite was abundant in only a few of the sensitive samples analyzed, and was absent or present in trace amounts in most samples. Both 7Å and 10Å halloysite appear to be stable in the soil environment that forms sensitive saprolites and 10Å halloysite was stable after desiccation at room temperature.

The significant amount of water released during compression of sensitive soils is stored in boxwork voids, and not inside individual halloysite tubes or spheres as has been previously suggested. These voids form by selective crystal dissolution and precipitation along crystal perimeters and cleavage planes. Both the small size and the amount of energy required breaking individual halloysite crystals make them unlikely sources of stored water. Clay- bounded boxwork voids, identified during SEM analysis, seem the most viable source of adequate water to cause soil sensitivity. Thus, soil microstructure, hot halloysite, is critical in the formation of sensitive soils.

Soils lacking relict texture (residual soils) are not sensitive. The loss of sensitivity in surficial residual soils is due to a breakdown and collapse of the boxwork voids within the saprolite. This collapse is caused by near surface soil

80 creep, shrinking and swelling of expandable clays (smectite) with seasonal wetting and desiccation, and pedoturbation by roots and burrowing animals.

Clay mineral zonation was observed in borehole samples obtained on

Mt. Scott in southeast Portland (Monterey Overcrossing). 10Å halloysite was most abundant toward the base of the saprolite (near the bedrock contact). 7Å halloysite was most abundant toward the middle to upper portions of the saprolite, and kaolinite was most abundant in the overlying, featureless residual soil. Clay zonation was not significantly influenced by original rock type (flow rock vs. breccia) in the basalts. Although smectite was more abundant near the rock interface, no clear zonation was identified for smectite in these samples.

Selected samples from five other sites in northwestern Oregon confirmed this zonation. Testing for allophane and imogolite confirmed the lack of amorphous clay in these samples.

Interlayered halloysite/expandable clay which expands with glycolation was identified in almost all saprolite samples analyzed, but not in the residual soil samples. The disappearance of clay interlayering may be related to collapse of the saprolite structure and/or the chemical conditions (including hydration) present near the surface in the residual soil.

In addition to clay zonation, one site in the Eola Hills of West Salem

(West Salem Site 1) showed variation in the abundance of low cristobalite with depth caused by silica dissolution and reprecipitation lower in the soil profile.

Maximum concentrations of well-crystalline low cristobalite occurred between

4.6 m and 8.1 m (15.0 and 26.5 ft).

Construction problems related to sensitive volcanic saprolites have been documented in northwestern Oregon and southwestern Washington since the

1940’s and include Mud Mountain Dam, Hills Creek Dam, the Toutle River

Sediment Retention Structure, the Trask River Dam raise, and the Spirit Lake

Highway. Difficulties experienced during the construction of these structures include excessive rutting during stripping and placing of embankment materials, soils that are wet of optimum, and difficulty in achieving compaction.

Laboratory and field testing are invaluable tools in identifying sensitive saprolites during the geotechnical investigation phase of design. These tests include natural water content, dry unit weight, Atterberg limits, X-ray diffraction, and field sensitivity measurements. Sensitive saprolites are generally high plasticity silts (MH) that have anomalously high natural water contents (>50%), low dry unit weight (5.7 to 6.4 kN/m3), Atterberg limits that decrease with drying, generally contain halloysite but little or no kaolinite, and possess the ability to release water and become wet when compressed under strong finger pressure.

Proctor density test maximum densities and optimum water contents vary with the amount of soil working. Residual soils, however, are generally high plasticity clays (CH), have lower natural water contents (20 to 40%), and have higher dry unit weights (14 kN/m3)

Methods to mitigate the impact of sensitive saprolites include manipulating the soils as little as possible with light weight equipment, placing thin embankment lifts to allow the soil to dry, and grading fills to enhance drainage.

FUTURE WORK

Since microstructure is the controlling mechanism in the formation of sensitive volcanic saprolites, additional SEM analysis should be conducted to investigate the following:

• Determine the microstructure of residual soils to confirm that boxwork voids have been destroyed or filled. • Evaluate the microstructure of more silicic volcanic saprolites including andesites through rhyolites to see if sensitivity is related to boxwork structures in these rocks. • Compare the microstructure of sensitive ash deposits that contain allophane and imogolite to see if boxworks are present or if water is stored within these clay minerals. Additional investigation is necessary to evaluate the relationship between

7Å and 10Å halloysite in a soil environment. The mechanism that causes 10Å halloysite to lose its water layer and convert to 7Å halloysite is undetermined.

Furthermore, the role (if any) of interlayered expandable clay in this process should be investigated.

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APPENDIX A OREGON AND WASHINGTON CASE HISTORIES OF CONSTRUCTION IN SENSITIVE VOLCANIC SAPROLITES

Appendix A.1 Mud Mountain Dam, Pierce County, Washington

One of the earliest records of construction problems in the Pacific

Northwest related to excessively wet volcanic soils was observed in 1941 at the

Mud Mountain Dam, located in Pierce County 76 km (47 miles) southeast of

Seattle, Washington. The design of the earth and rock-fill embankment had to be modified to include more rock when embankment soils could not be dried back to optimum moisture content for compaction (Anonymous, 1941c). The presence of a small amount of colloidal clay was blamed for preventing the soil from adequately drying or draining (Anonymous, 1941c). To allow for construction during wet weather, a huge canvas tent was suspended over the earth-fill core to prevent rainwater infiltration (Anonymous, 1941b). Additionally, construction of the impervious core was completed using oil-burning kilns to reduce the moisture content of embankment soils by 2.5% to 5% (Anonymous,

1941a).

Appendix A.2 Toutle River Sediment Retention Structure, Cowlitz County, Washington

The Toutle River Sediment Retention Structure (SRS) was constructed by the US Corps of Engineers (COE) to impound volcaniclastic debris deposited during the 1980 eruption of Mount St. Helens. The Toutle River valley, which is located in the Cascade Range of southwest Washington, was partially infilled with debris flows and lahars during the 1980 eruption of Mount St. Helens. The location of the SRS was selected to prevent upstream eruptive material from washing downstream during flooding and impacting shipping on the Columbia

River.

Shortly after dam construction began, Granite Construction claimed a change of conditions and initiated litigation (Cornforth Consulting Inc., 1991;

Cummings, In Press). Problematic soil and rock was encountered in several geologic units, including Tertiary-age decomposed andesitic and basaltic flow rock and flow top breccia (Hatchet Mountain volcanics), Pleistocene-age debris flow material (saprolitic diamicton), layered clay-rich deposits (“the slimes”), and pre-eruption river alluvium. Although these materials appeared stable in situ, once disturbed they became excessively wet and slippery, extremely difficult to compact, and unstable in the dam core and waste piles.

Heavy equipment used to place and compact impervious core material routinely created deep ruts and bogged-down. The decomposed flow-top breccia of the Hachet Mountian volcanics and the debris flow material were selected for the impervious core (Cornforth Consulting Inc., 1991). According to 96

Granite, “The Impervious Material was very deceiving. When viewed in a cut slope, it appeared to be gravelly in nature, fairly dry and stiff, very stable and almost at optimum water content. As it was disturbed by construction equipment, the water inside the structure of the clay and relic rock clasts was freed, and material that had appeared to have good bearing capacity was reduced to a wet, sticky mass that scrapers could not operate efficiently upon…The more manipulation by construction equipment, the more excess water and instability was realized” (Cornforth Consulting Inc., 1991). The layered clay-rich deposits and pre-eruption river alluvium, designated as waste material, were difficult to strip due to rutting and flowed when placed in spoils piles (M. L. Cummings, personal communication, April 2000).

Granite Construction claimed that the presence of halloysite and smectite in volcaniclastic soils created water sensitive soils that were responsible for the construction problems at the SRS. They claimed that halloysite held water “in the soil grain” and resisted drying. During stripping and placing of borrow materials, the halloysite “grains” broke apart, releasing water into the soil pores.

This additional water has to be removed before adequate compaction can be attained. The optimum moisture content of the in situ borrow soil was ±4% lower than the optimum moisture content of the fill soils. Extensive disking, used by Granite to aerate and dry the fill soils, exacerbated the problem by increasing the maximum dry density of the soil, decreasing its optimum moisture content, and further lowering its shear strength.

To support Granite’s claim, clay mineral analyses were conducted on sensitive soils. Gabor and Cummings (1988) identified smectite and 7Å halloysite (with minor kaolinite and vermiculite) in the Hachet Mountain volcanics flow top breccia. Total clay content ranged between 31% and 100%.

The debris flow material contained 37% to 64% clay minerals including predominantly 7Å halloysite, with generally lesser amounts of 10Å halloysite, smectite, and vermiculite. Kaolinite was detected near the upper contact of the debris flow saprolite at the approximate location of a paleosurface (Cummings,

In Press). Layered clay-rich deposits contained 18% to 43% clay minerals, including 7Å halloysite, 10Å halloysite, chlorite, smectite, vermiculite, kaolinite, and mixed-layer clays. Significant 10Å halloysite was found in three out of the seven samples. The matrix of pre-eruption alluvial deposits contained 18% to

46% total clay minerals, predominantly 7Å halloysite, chlorite, smectite, vermiculite, and lesser kaolinite (one sample) and mixed-layer clays. 10Å halloysite is present in two of the six samples. Gabor and Cummings (1988) and Cummings (In Press) concluded that soil sensitivity was caused when microtextures in saprolites were crushed during handling and water trapped within micropore spaces was released. Cummings (In Press) observes that volcaniclastic deposits have become bonded by precipitated clay minerals and silica as weathering progresses within local deposits from the 1980 eruption.

Due to this bonding, micropores form isovolumetrically in the saprolite during

98 leaching (Cummings, In Press). 10Å halloysite was not ubiquitous to the problem soils.

Swelling in smectite-rich soils was dismissed by Warkentin (1988) as a cause of the rutting problems experienced during SRS construction. He discounted rapid swelling and loss of shear strength in these soils due to their low hydraulic conductivity and contended that a 0.9 m (3-foot) thick layer of soil would require months to reach an expanded condition. He did acknowledge that decomposed volcanic rock can be crushed by heavy equipment,

“…releasing clay minerals, amorphous minerals, halloysite, or smectite, and the water associated with them” and creating a “…smeary clay with excess water.”

Gabor and Cummings (1988), however, hypothesized that water freed from crushed micropores was absorbed by adjacent smectite crystallites. Based on the ubiquitous presence of water within the saprolitic soil structure, low hydraulic conductivity would not inhibit swelling of smectite minerals.

In addition to swelling from pore-derived water, slaking within smectite- rich flow rock and flow breccia caused by repeated wetting and drying transformed apparently hard rock into soil when exposed to the air. Such degradation occurred along haul roads constructed out of hard blocks of flow breccia (D. H. Cornforth, personal communication, April 2000).

Appendix A.3 Trask River Dam Raise, Tillamook County, Oregon

The Trask River Dam impounds Barney Reservoir in the Coast Range of northwestern Oregon (Figure 3). The dam site is located on a deeply weathered uplifted erosional surface that forms the core of the northern Oregon

Coast Range. The dam area is underlain by Eocene-age Siletz River Volcanics composed of submarine basalt flows, pillow lavas, flow breccias, and siltstone and shale interbeds (Wells et al., 1983; Wells et al., 1994). Bedrock is mantled by an average of 50 feet of saprolite soil (Hammond and Vessely, 1998).

In 1995, construction for the enlargement of the dam was initiated and anticipated sensitive soils were encountered in selected areas (C. M.

Hammond, personal communication, May 2000). Cornforth Consultants, Inc.

(1993) identified these soils as sandy silts and silty sands with lesser clay-sized material. The natural water content of the soils encountered during the geotechnical investigation for the dam raise averaged 60%, but ranged up to

100%. Cornforth Consultants, Inc. (1995) found that natural water contents in the foundation area of the expanded dam averaged 68%, but ranged up to 89%.

In situ water contents for the existing embankment fill ranged between 30% and

43%. Atterberg limits testing on foundation soils identified high plasticity silts with relatively high liquid limits (46% to 80%) and low plastic indexes (<27%).

The natural moisture content of the majority of the foundation soils exceeded their liquid limits.

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Borrow areas were selected to attempt to avoid sensitive saprolites.

Atterberg limits testing on borrow soils identified high plasticity silts with relatively high liquid limits (50% to 75 %) and low plastic indexes (<20%). In the borrow areas, the liquid limit did not exceed the natural water content of the soil.

Atterberg limits varied for moist and air-dried samples. Even after rehydrating prior to testing, the air-dried samples showed lower liquid limits and plastic indexes than samples that had never been dried, indicating an irreversible change had occurred during drying.

Compaction testing (standard Proctor—ASTM D698) was conducted on test fills composed of borrow soils (Cornforth Consultants Inc., 1995). Maximum dry densities ranged from 11.3 to 13.2 kN/m3 (72 to 84 lb/ft3), with optimum moisture contents of 32% to 42%. Although these values showed a slight seasonal variation between July and October, in every case the optimum moisture content ranged from 6% to 15% less than the natural moisture content.

The problematic soils had relict rock texture (saprolite) and were “…very sensitive to handling and moisture due to the presence of halloysite and montmorillonite clay minerals” (Hammond and Vessely, 1998). “Upon handling, halloysites frequently break down and release water trapped in the soil grain.

Smectites, and to a lesser degree vermiculites, readily accept free water and may expand and soften when additional free water is available.” (Cornforth

Consultants Inc., 1995). This absorption of water by expandable clay minerals

101 supposedly changes the texture of the soil from granular to cohesive (Cornforth

Consultants Inc., 1995).

Clay analyses conducted on two borrow area samples with natural moisture contents greater than 45% identified 66% hydrated (10Å) halloysite

(with an additional 34% possible 7Å halloysite) in one sample, and 42% hydrated halloysite (with 53% smectite) in the second. These samples were collected at depths of 1.5 to 2.0 m (5 to 6.5 feet). The four other borrow samples tested had natural moisture contents 24% to 44% and contained chloritized vermiculite, 7Å halloysite, and possibly mixed layered kaolinite and halloysite.

Since the geotechnical engineering for the Trask River Dam raise was conducted after the SRS change of conditions claim, sensitive soils were anticipated and avoided, where possible. However, anticipation of adverse soil conditions did not eliminate all construction problems. Construction equipment still became bogged-down in wet weather limiting stripping and placing of impervious core materials to the dry summer months (Hammond and Vessely,

1998). Lighter equipment was used to compact the fill in the dam core. The weight of the scrappers was limited to 178 kN (20 tons), instead of 445 kN (50 tons) (D. H. Cornforth, personal communication, April 2000).

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Appendix A.4 Hills Creek Dam, Lane County, Oregon

Hills Creek Dam was one of the first Oregon dams to experience construction difficulties related to sensitive volcanic saprolites. The dam, which was completed in 1961 by the Army Corps of Engineers, impounds the Middle

Fork of the Willamette River. It is located approximately 8 km (5 miles) southeast of Oakridge in the Western Cascades of central western Oregon.

The dam site is underlain by massive lapilli tuff and hydrothermally altered, highly fractured dacite of the Oligocene to lower Miocene-age Little Butte

Volcanics (U.S. Army Corps of Engineers Portland Engineer District, 1954;

Peck et al., 1964). The lapilli tuff bedrock has been deeply weathered and fractured and joints are either open or partially infilled with secondary colloidal clay (U.S. Army Corps of Engineers Portland Engineer District, 1954). Within the river channel, the bedrock is overlain by “older” (Pliocene or Pleistocene) valley fill consisting of highly weathered, gravel in a cemented matrix of silt and clay (decomposed volcanic ash) (U.S. Army Corps of Engineers Portland

Engineer District, 1954). Colloidal clay coats sand and gravel clasts and fills voids in the older valley fill. The upper 10 to 15 feet of the older valley fill had been reworked by the river. More recent alluvium flood plain deposits of silty sand, fresh valley boulder gravel mantle the older valley fill.

The impervious core of the dam was constructed of both reworked and in situ older valley fill gravel deposits, but only the in situ gravel was difficult to

103 place and compact (U.S. Army Corps of Engineers Portland Engineer District,

1959). Although the valley fill gravel appeared near the optimum moisture content when excavated from the borrow area, it appear wetter after spreading.

Core fill consisting of the sensitive in situ gravel rutted, became more plastic, and caused 50-ton rollers to become stuck. The sensitive fill could not be compacted properly even when spread and allowed to dry for 24 hours. The

COE attributed soil sensitivity to small pockets of highly plastic colloidal clay mixing with lower plasticity fines during remolding and an increase in the plasticity of halloysite-bearing soils as hydrated halloysite is altered to highly plastic intermediate halloysite during drying.

An Atterberg limits test run on a sample from the impervious core material showed a progressive reduction in the plastic limit and plasticity index with air drying followed by oven drying. This trend is similar to that observed within sensitive soils at the Trask River Dam.

Soft colloidal clay that filled voids and coats gravel and sand grains in the in situ older alluvium is blamed for these construction problems even though grain size analyses identified the older gravel deposits as well graded with 2% to 4% silt and clay size material (U.S. Army Crops of Engineers Portland

Engineer District, 1966). Clay analyses conducted by Dr. Ralph Grim on the silt and clay sized matrix material identified predominantly of 10Å, 7Å, and intermediate forms of halloysite, with lesser smectite (U.S. Army Crops of

Engineers Portland Engineer District, 1966). Dr. Grim advanced the following

104 hypothesis regarding the unusual properties of soils that contain partially hydrated halloysite:

“…2H2O [dehydrated] or 4H2O [hydrated] form [of halloysite] has very low plasticity. Its

[Atterberg] limits are very low and sometimes it appears to be substantially nonplastic.

In an intermediate state of hydration with a moisture content between the 2 and 4 H2O form the mineral has very different properties – it may be and usually is quite plastic and very difficult to compact. When the molecular layer is complete (4H2O) or when it is absent (2 H2O), the silicate layers are held together rigidly. When the water layer is partially present, the silicate layers are easily split apart and very different properties develop” (U.S. Army Crops of Engineers Portland Engineer District, 1966).

To improve compaction within the sensitive older valley fill, each lift was covered by a 0.76 m (2.5 foot) lift of “random” rock (U.S. Army Crops of

Engineers Portland Engineer District, 1966). This more permeable aggregate created a layered fill that allowed the excessively wet sensitive alluvium to drain.

Additionally, the weight of the roller was reduced to 178 kN (20 tons) which produced only 12 inch ruts. A D-9 tractor was required to pull the lighter roller across the fill. Eventually, Dr. Arthur Casagrande recommended minimizing rutting by reducing the lift thickness to 0.2 m (8 inches), compacting each lift with two passes of the tractor treads after spreading, and sloping the core of the dam to promote drainage (U.S. Army Crops of Engineers Portland Engineer

District, 1966). Following implementation of these modifications, construction of the dam core was completed.

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Appendix A.5 Spirit Lake Memorial Highway, Cowlitz and Skamania Counties, Washington

Spirit Lake Memorial Highway (SR 504) is located in Cowlitz and

Skamania Counties in southwest Washington. Damage caused by debris torrents along the Toutle River during the 1980 eruption of Mount St. Helens required 32 km (20 miles) of the existing SR 504 to be rebuilt and an additional

40 km (25 miles) of road was built to reach the Coldwater Lake observation area near the mountain (Golder Associates, 1988a). Construction of the new road was completed in six segments.

The project area is located in the Washington Western Cascades and is underlain by Tertiary-age volcanic rocks consisting of andesite and basalt flows, agglomerates, and tuffs (including lahar deposits). These volcanic rocks have subsequently been intruded and hydrothermally altered by andesite, basalt, and gabbro dikes and sills. Bedrock is mantled by Pleistocene and Holocene ash deposits, glacial drift, colluvium, and alluvium (Golder Associates, 1988a).

Performance of the construction materials, including embankment soil, was assessed during the geotechnical investigation for Segment 3 of the new road (Golder Associates, 1987b). The field test procedure consisted of placing a 1.0 to 1.5 foot layer of soil in a loose condition and then measuring the density change after successive passes of a D8 or D7G track-type tractor. Prior to field testing, laboratory testing was conducted on embankment soils to determine

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Atterberg limits, dry density, natural moisture content and standard Proctor values for maximum dry density and optimum moisture content.

Five test fills were constructed in Segment 3. Two of these test fills were used to evaluate the workability of the hydrothermally altered tuff (Golder

Associates, 1987b). Both test fills were composed of soils with significant fines

(48% and 50% <#200 mesh) that consisted of low plasticity silts (ML) with very low plastic indexes (5% and 9%). In both cases, the natural moisture content of the soil was significantly (6% and 11%) above the optimum moisture content for standard compaction. Maximum dry densities and optimum moisture contents established during standard Proctor compaction tests (ASTM D698) averaged

16 kN/m3 (99 lb/ft3) and 22%, respectively.

In-place density measurements on the hydrothermally altered tuff test fills showed an increase in dry density with two tractor passes, followed by either no further increase or a significant decrease in the dry density with additional passes (Figure A.5.1) (Golder Associates, 1987b). Dry densities measured within these test fills were significantly less than the maximum dry densities as established by standard Proctor moisture/density testing (ASTM D698). The in situ moisture content of the test fills decreased with two tractor passes and then increased as the dry density decreased (Golder Associates, 1987b).

Concurrently, pumping and deep rutting occurred on the third tractor pass in one test fill and on the fourth in the other. Ruts ranged from 0.2 to 0.5 m (8 to

18 inches) deep (Figure A.5.2). Based on the results of these test fills and the

107 above optimum natural water content and high silt content of this material, the altered tuff was identified as unworkable (Golder Associates, 1987b).

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FIGURE IS INCLUDED IN GEOLOGY DEPARTMENT AND LIBRARY THESIS COPY

Figure A.5.1. Effect of compaction on density on hydrothermally altered tuff test fill (Golder Associates, 1987b).

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FIGURE IS INCLUDED IN GEOLOGY DEPARTMENT AND LIBRARY THESIS COPY

Figure A.5.2. Rutting in a sensitive hydrothermally altered tuff test fill during construction of the Spirit Lake Memorial Highway (Golder Associates, 1987b).

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Portions of Segments 1, 2, 4, 5, and 6 are also underlain by hydrothermally altered and weathered andesite and tuff (“Completely Altered

Rock”) (Golder Associates, 1987a; Golder Associates, 1988c; Golder

Associates, 1988d; Golder Associates, 1988a; Golder Associates, 1988b).

These units contain 30% corestones in a decomposed matrix of sand, gravel, and low plasticity silt and clay (ML and CL). In each of these segments, the optimum water contents in the altered andesite and tuff were significantly lower than the natural water contents indicating that the soils would require extensive drying prior to compaction. Thus, Golder classified “Completely Altered Rock” in all six segments as waste material. Golder Associates (1988b) describe andesite and tuff saprolites in the following manner:

“The Completely Altered Rocks appeared to exhibit some properties typical of residual soils. Properties generally attributed to residual soils include poor compaction characteristics, high natural moisture contents often above the liquid limit, Atterberg Limit and compaction results sensitive to the method of drying, low in situ unit weights, local zones of low in situ strengths, and low remolded strengths. This behavior is generally attributed to the types of clay minerals present, often including halloysite, and the retained structure of the parent bedrock. The completely altered rocks encountered in Segment 4 exhibited many of these properties, including low in situ unit weights and high in situ moisture contents, often exceeding the liquid limit and well above the optimum Proctor compaction moisture contents…The Completely Altered Rock

111 has a low in situ unit weight and a high water content attributed, at least in part, to the relict structure of the formation. Once excavated, place, and recompacted the structure will be destroyed and the resulting fill will be at a water content in excess of optimum.”

Portions of Segment 1 of the Spirit Lake Memorial Highway are underlain by Holocene and Quaternary volcanic ash (Golder Associates, 1988a). The thickness of ash deposits range from 0.6 to 7.0 m (2 to 23 feet) thick and

Atterberg Limits testing identified both ash deposits as low plasticity silts (ML).

The dry unit weights of the Holocene and Quaternary volcanic ash are approximately 9.4 to 14.1 kN/m3 (60 and 90 lb/ft3), respectively. The anomalously low dry unit weight of the Holocene volcanic ash indicates a high amount of porosity undoubtedly related to the mode of deposition. Natural water contents for Holocene and Quaternary volcanic ash average 45% and

40%, respectively, but range from 22% to 83%. Natural moisture contents were significantly higher (14%) than optimum moisture contents obtained for standard

Proctor compaction tests (ASTM D 698). The in situ strength of both ash deposits is higher than that indicated by Standard Penetration Testing during drilling. Effective angles of internal friction (φ) ranged from 32 to 35 degrees with an effective cohesion of 4.8 to 14.3 kN/m2 (100 to 300 lb/ft2). Construction difficulties were anticipated by Golder Associates in both ash deposits due to their high natural water content, high silt content, and apparent cementation and these materials were designated as waste. 112

APPENDIX B ENGINERING TEST PROCEDURES AND DATA

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Appendix B.1 Discussion of Engineering Test Procedures

Natural Moisture Content (ASTM D2216)

The natural or in situ soil moisture content is the ratio of the weight of water in a given volume of soil to the weight of the solid particles within that same volume and is reported as a percentage. The test requires placing a soil sample in a 71°C degree oven for a period of 24 hours before calculating the dry weight. Using this method, water trapped within soil voids is evaporated.

Atterberg Limits (ASTM D4318)

Atterberg limits discussed in this report include the plastic limit, liquid limit, and plastic index and classify the amount of plasticity in cohesive soils.

These tests are conducted on material finer than #40 mesh including fine sand, silt, and clay. Although the methods for determining the plastic and liquid limits are somewhat arbitrary, these limits are widely used by engineers to classify soils and predict their engineering properties. The plastic limit is defined as the moisture content at which a thread of soil just begins to crack and crumble when rolled to a diameter of 3 mm (1/8 inch). The liquid limit is defined as the moisture content at which a 2 mm wide groove in a soil sample closes for a distance of 13 mm (½ inch) when dropped 25 times in a standard brass cup.

The cup on the liquid limit device falls 10 mm each time at a rate of 2 drops per second. The plasticity index is the difference in moisture content between the liquid limit and the plastic limit. Accurate Atterberg limits are recorded on soil

114 samples that have never been desiccated. Air-drying or oven drying sensitive soils changes their Atterberg limits.

Inorganic soils are classified into four categories based their plasticity as identified by their liquid limit and plastic index. These categories include low plasticity silt (ML), low plasticity or “lean” clay (CL), high plasticity or “elastic” silt

(MH), and high plasticity or “fat” clay (CH). Soils that are finer than #40 mesh, but cannot be rolled into a 1/8 inch thread at any moisture content are identified as nonplastic (NP).

Unit Weight

The unit weight or density of a soil sample is the ratio of the weight of the soil to the total volume of the soil and is commonly reported in lb/ft3, kN/m3, or g/cm3. Natural (moist), saturated, and dry unit weight are commonly calculated.

Dry density is used for moisture/density (Proctor) tests (see below).

Void Ratio

The void ratio of a soil sample is the ratio of the volume of the voids contained in the soil to the volume of the soil solids, expressed as a decimal.

The void ratio is determined by consolidation testing.

Maximum Dry Density (ASTM D 698)

The maximum dry density of a soil is defined as the highest density (or greatest compaction) that the soil can attained under a specific compactive effort. Greater compaction can be obtained if larger (heavier) earthmoving

115 equipment is used. The maximum dry density is determined by conducting a standard or modified Proctor or moisture-density test to measure the compacted soil’s density at a variety of water contents. The water content of the soil is critical to attaining maximum dry density. As water is added to the soil, it facilitates compaction by allowing individual soil particles to move over one another more easily. As even more water is added to the soil, the voids between the particles begin to fill with water, further increasing the density of the soil. However, when most of the voids become full, the water begins to push the soil particles apart, lowering the soil dry density. The optimum water content of the soil occurs when the majority of the soil voids are filled with water and the maximum dry density is reached.

Percent –200 Mesh

To determine the percentage of silt and clay-sized material in a sample, the sample is washed through a 200-mesh sieve and the remaining +200-mesh material is oven dried at 110° and weighed. The natural water content of the soil is measured to calculate the initial dry weight of the soil. The difference between the initial and washed sample weight is the weight of the –200 mesh material in the sample. The percent –200 mesh is the ratio of the weight of the

–200 mesh material over the initial dry weight, expressed as a percent.

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Appendix B.2 Engineering Index Test Data for Samples Analyzed Using X-Ray Diffraction

Table B.2.1 Engineering Test Results for X-ray Samples1

Atterberg Natural Water Site Borehole Sample Limits Content (%) (LL/PI/USCS)2 Monterey Avenue BH-3 SS-3-9 40 SS-7-2 32 SS-7-3 43 SS-7-4 58 SS-7-6 55 Monterey Avenue BH-7 SS-7-7 52 SS-7-8 34 SS-7-9 68 SS-7-11 75 SS-7-12 333 SS-10-4 31 SS-10-5 66 SS-10-7 74 Monterey Avenue BH-10 SS-10-8 83 SS-10-9 72 SS-10-10 69 SS-10-11 253 SS-18-6 60 Monterey Avenue BH-18 SS-18-8 74 SS-18-9 52 Monterey Avenue BH-27 SS-27-7 58 SS-1-1 26 SS-1-2 40 SS-1-3 51 West Salem Site 1 BH-1 SS-1-4 56 SS-1-5 61 SS-1-6 55 SS-1-1 17 West Salem Site 2 BH-1 SS-1-6 55 51/6/MH BH-1 SS-1-8 50 Carlton SS-2-2 39 BH-2 SS-2-6 33 SS-1-2 37 57/36/CH Silverton BH-1 SS-1-4 56 South Salem BH-2 SS-2-6 63

1 Soil sensitivity for each sample is identified in Table C.1.1 (Appendix C.1) 2 LL = Liquid limit, PI = Plastic index, USCS = Unified Soil Classification System symbol 3 Samples contain abundant rock material

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Appendix B.3 Engineering Index Test Data for Monterey Avenue Similar Samples

Table B.3.1 Engineering Test Results for Similar Monterey Avenue Samples

Wet/Dry Natural Atterberg Unit Percent Borehole/ Depth Soil Water Sample Soil Texture Sensitivity Limits Weight in –200 Test Pit (m) Description Content (LL/PI/USCS)1 kN/m3 mesh (%) (lb/ft3) 16/6.4 BH-17 SH-17-2 3.0 - 3.7 Silt with sand Moderate 59 90/45/MH 75 (101/41) BH-28 SS-28-4 5.8 - 6.2 Silt with sand Extremely 69 68/27/MH --- 68 Decomposed TP-4 S-4-3 2.9 - 3.0 Clayey silt breccia Moderate 61 97/5/MH --- 73

Sandy clay 16/5.7 BH-40 SH-40-3 3.8 - 4.4 Moderate 65 87/50/CH 45 with silt (101/36) Decomposed BH-46 SS-46-5 7.6 - 8.1 Sandy silt None 58 56/16/MH ------basalt TP-9 S-9-1 1.5 - 1.7 Clay 22 70/38/CH ------Residual soil None 19/14 BH-44 SH-44-4 5.3 - 5.9 Clay with silt 32 45/25/CL --- (120/88)

1 LL = Liquid limit, PI = Plastic index, USCS = Unified Soil Classification System symbol

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APPENDIX C STUDY AREA SAMPLE DESCRIPTIONS AND STUDY SITE LOCATIONS

119

Appendix C.1 Geologic Properties of Study Area Samples

Table C.1.1. Geologic and Engineering Properties of Study Area Samples

Soil/Rock Study Depth Original Borehole Sample Soil/Rock Description1 Sensitivity Texture Site (m) Lithology 2 Description Basalt Secondary Monterey BH-3 SS-3-9 9.4 – 9.9 Medium dense silty sand Moderate interflow orange clay in Avenue breccia void space SS-7-2 2.1 – 2.6 Stiff clayey silt None Unknown Residual soil SS-7-3 3.0 – 3.5 Stiff clayey silt None SS-7-4 4.6 – 5.0 Stiff silt Minor SS-7-6 6.7 – 7.2 Very stiff sand silt Basalt flow SS-7-7 7.6 – 8.1 Medium dense silty sand Moderate rock Monterey SS-7-8 9.1 – 9.6 Dense silty sand Saprolite BH-7 Avenue SS-7-9 10.7 – 11.1 Stiff sandy silt with some clay Basalt Moderate interflow SS-7-11 12.8 – 13.3 Loose silty sand breccia Highly Basalt flow SS-7-12 13.7 Extremely weak to very weak basalt N/A weathered rock flow rock SS-10-4 4.9 – 5.3 Hard clayey silt with trace sand Minor SS-10-5 6.1 – 6.6 Stiff silt Moderate SS-10-7 8.2 – 8.7 Stiff silt Moderate Basalt flow Saprolite SS-10-8 9.1 – 9.6 Stiff silt with trace clay Moderate rock Monterey BH-10 SS-10-9 10.7 – 11.1 Medium stiff silt Extreme Avenue SS-10-10 12.2 – 12.6 Medium stiff sandy silt Extreme Highly Basalt flow SS-10-11 13.7 Weak to very weak basalt N/A weathered rock flow rock

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Soil/Rock Study Depth Original Borehole Sample Soil/Rock Description1 Sensitivity Texture Site (m) Lithology 2 Description Basalt flow SS-18-6 4.6 – 5.0 Loose silty sand None rock Basalt Monterey BH-18 SS-18-8 7.6 – 8.1 Stiff silt with some sand Moderate interflow Saprolite Avenue breccia Basalt flow SS-18-9 9.1 – 9.6 Medium dense sand with some silt None rock Secondary Monterey Basalt flow BH-27 SS-27-7 10.7 – 11.1 Medium dense silty sand Moderate orange clay in Avenue rock void space Basalt Monterey BH-43 SH-43-6 6.6 – 7.2 Soft silt with some silt and sand Extreme interflow Saprolite Avenue breccia Hard clay with some silt and trace SS-1-1 0.8 – 1.2 None Residual soil sand SS-1-2 1.5 – 2.0 Very stiff silt with some clay None SS-1-3 2.3 – 2.7 Medium stiff silt with some clay None SS-1-4 3.0 – 3.5 Medium stiff silt with some clay Minor Medium stiff silt with some clay and SS-1-5 4.6 – 5.0 Moderate West trace fine sand Basalt flow Salem, BH-1 Medium stiff silt with some clay and rock Site 1 SS-1-6 6.1 – 6.6 trace fine sand and gravel-sized Moderate Saprolite angular clasts SS-1-7 7.6 – 8.1 Stiff silt with trace clay and sand Moderate SS-1-8 9.1 – 9.6 Stiff silt with some sand Moderate SS-1-9 10.7 – 11.1 Stiff sandy silt Moderate Medium stiff silt with trace sand and SS-1-10 12.2 – 12.6 Moderate clay West SS-1-1 0.8 – 1.2 Hard clayey silt None Residual soil Basalt flow Salem BH-1 Hard sandy silt with some clay and SS-1-6 4.6 – 5.0 Moderate rock Saprolite Site 2 trace gravel-sized angular clasts 121

Soil/Rock Study Depth Original Borehole Sample Soil/Rock Description1 Sensitivity Texture Site (m) Lithology Description2 Stiff silt with sand and gravel-sized BH-1 SS-1-8 7.6 – 8.1 Moderate Saprolite angular clasts Basaltic dike Carlton SS-2-2 1.4 – 1.8 Very stiff clayey silt None Residual soil or sill BH-2 Stiff sandy silt with trace angular SS-2-6 4.6 – 5.0 Extremely Saprolite gravel-sized angular clasts Stiff clay with trace fine to coarse SS-1-2 1.5 – 2.0 None Basalt flow Residual soil Silverton BH-1 sand rock SS-1-4 3.0 – 3.5 Stiff sandy silt Moderate Saprolite South Basalt flow BH-2 SS-2-6 4.6 – 5.0 Medium stiff clayey silt Moderate Saprolite Salem rock

1Key to soil and rock descriptions in Appendix C.2 2Residual soil shows no original rock texture and has been subjected to more sever weathering, desiccation, soil creep, and bioturbation. Saprolite, while classified as a soil, shows relict rock texture including phenocrysts, joints, and breccia clast boundaries.

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REMAINING APPENDICES ARE INCLUDED IN THE GEOLOGY DEPARTMENT AND LIBRARY THESIS COPIES

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