Research & Technology Transfer

Alaska Department of Transportation & Public Facilities Research & Technology Transfer

Documenting Best Management Practices for Cutslopes in Ice‐rich Permafrost

Prepared by: Ted S. Vinson, Ph.D., P.E. Robert L. McHattie, P.E.

Date May 2009

Prepared for: Alaska Department of Transportation Statewide Research Office 3132 Channel Drive Juneau, AK 99801‐7898

Publication Number FHWA‐AK‐RD‐09‐01

Foreword

Ice-rich permafrost is often encountered during the construction of roads and other projects in Alaska. Ice-rich permafrost is typically silt with segregated ice or massive ground ice. During the thawing process there are trafficability and stability problems due to thawing of fine grained, ice-rich soils. Also, resource agencies are increasingly critical of by-products of the thawing process – particulate-rich effluent and terrain disfigurement.

Alaskan transportation engineers must employ one of two methods to deal with ice-rich permafrost encountered during construction. The decision may be to preserve the ice-rich soil in its frozen state. Preservation is possible given enough time and money. However, it is often much too expensive to preserve the frozen state of materials especially in areas of relatively warm permafrost. The alternate approach, which is addressed in this report, is to characterize and accommodate the thawing process using a design method that minimizes the negative effects of thawing. More specifically, it is necessary to control the thawing process so that the materials remain structurally stable and to make sure that the products of the process (e.g., particulate laden runoff) are disposed of in an environmentally acceptable manner.

A primary focus of this report is the problem of ice-rich cuts. The report also discusses disposal of ice-rich excavation materials and the formation of embankments using ice-rich fill. The techniques employed or proposed to mitigate the problems are described and several best management practices are presented in Appendix B.

This is a final research report (1st printing). The research was funded by the FHWA with the intention of supporting Alaskan Department of Transportation and Public Facilities (ADOT&PF) geotechnical and construction engineers who must routinely confront permafrost. It is also recommended reading for all engineering consultants involved in such work.

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Documenting Best Management Practices for Cutslopes in

Ice-rich Permafrost DOT &PF AKSAS #76987 HPR-4000(60)/ T2-07-04

6. AUTHOR(S) Ted S. Vinson, Ph.D., P.E. Robert L. McHattie, P.E.

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13. ABSTRACT (Maximum 200 words)

In northern Alaska ice-rich permafrost is often encountered during the construction of roads and other projects. When ice-rich permafrost is exposed during late spring through early fall the potential for thawing is great. Ice-rich permafrost, typically silts with segregated ice or massive ground ice, experiences a substantial reduction in strength owing to the exceedingly high water content and lack of drainage and consolidation during thaw. The result can be a quagmire that “bogs down” equipment or, if the exposure is a cutslope, slope failure. In addition to trafficability and stability problems, environmental oversight increasingly focuses attention on particulate-rich effluent and poor aesthetics which are common by-products of the thaw process. This study presents several construction projects in northern Alaska where problems due to thawing permafrost were a significant environmental concern. The techniques employed or proposed to mitigate the problems are described and several best management practices are presented.

15. NUMBER OF PAGES 14- KEYWORDS : 66 construction; environment; excavation; ice-rich permafrost; management; thawing 16. PRICE CODE

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SI* (MODERN METRIC) CONVERSION FACTORS APPROXIMATE CONVERSIONS TO SI UNITS Symbol When You Know Multiply By To Find Symbol LENGTH in inches 25.4 millimeters mm ft feet 0.305 meters m yd yards 0.914 meters m mi miles 1.61 kilometers km AREA in2 square inches 645.2 square millimeters mm2 ft2 square feet 0.093 square meters m2 yd2 square yard 0.836 square meters m2 ac acres 0.405 hectares ha mi2 square miles 2.59 square kilometers km2 VOLUME fl oz fluid ounces 29.57 milliliters mL gal gallons 3.785 liters L ft3 cubic feet 0.028 cubic meters m3 yd3 cubic yards 0.765 cubic meters m3 NOTE: volumes greater than 1000 L shall be shown in m3 MASS oz ounces 28.35 grams g lb pounds 0.454 kilograms kg T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t") TEMPERATURE (exact degrees) oF Fahrenheit 5 (F-32)/9 Celsius oC or (F-32)/1.8 ILLUMINATION fc foot-candles 10.76 lux lx fl foot-Lamberts 3.426 candela/m2 cd/m2 FORCE and PRESSURE or STRESS lbf poundforce 4.45 newtons N lbf/in2 poundforce per square inch 6.89 kilopascals kPa APPROXIMATE CONVERSIONS FROM SI UNITS Symbol When You Know Multiply By To Find Symbol LENGTH mm millimeters 0.039 inches in m meters 3.28 feet ft m meters 1.09 yards yd km kilometers 0.621 miles mi AREA mm2 square millimeters 0.0016 square inches in2 m2 square meters 10.764 square feet ft2 m2 square meters 1.195 square yards yd2 ha hectares 2.47 acres ac km2 square kilometers 0.386 square miles mi2 VOLUME mL milliliters 0.034 fluid ounces fl oz L liters 0.264 gallons gal m3 cubic meters 35.314 cubic feet ft3 m3 cubic meters 1.307 cubic yards yd3 MASS g grams 0.035 ounces oz kg kilograms 2.202 pounds lb Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T TEMPERATURE (exact degrees) oC Celsius 1.8C+32 Fahrenheit oF ILLUMINATION lx lux 0.0929 foot-candles fc cd/m2 candela/m2 0.2919 foot-Lamberts fl FORCE and PRESSURE or STRESS N newtons 0.225 poundforce lbf kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. (Revised March 2003)

TABLE OF CONTENTS

Page

INTRODUCTION 1

EROSION MECHANISMS 2

THERMAL EROSION OF ICE-RICH CUTSLOPES EXPOSED

DURING CONSTRUCTION 2

MITIGATION OF THERMAL EROSION OF ICE-RICH CUTSLOPES 4

DISPOSAL OF EXCAVATED PERMAFROST 9

USE OF EXCAVATED PERMAFROST TO BUILD AN EMBANKMENT 10

FIRE AND PERMAFROST 10

SUMMARY AND CONCLUSIONS 11

IMPLEMENTATION 11

APPENDIX A - REGULATORY ENVIRONMENT 12

APPENDIX B - BEST MANAGEMENT PRACTICES 15

ACKNOWLEDGEMENTS 25

REFERENCES 25

List of Figures

1. Photo. Road Cut in Ice-Rich Permafrost (from ADOT&PF file) …………………….…..27

2. Photo. Thaw Degradation of Cut Slope in Ice-Rich Permafrost (from ADOT&PF file)....27

3. Photo. Thawed Ice-Rich Permafrost Flowing Around a Bulldozer Blade. (Photo by Pewe, 1954) ...………………………………………………………….…………………..……..28

4. Photo. Dalton Highway Cut in Ice-Rich Permafrost – Before Thaw (from ADOT&PF file courtesy of S. Lamont and J. Russell) ...…………………………………………….……..31

5. Photo. Dalton Highway Cut in Ice-Rich Permafrost – After Thaw (from ADOT&PF file courtesy of S. Lamont and J. Russell) …………………….……………………………….34

6. Original 1969 Engineer’s Sketch of the Procedure to be Employed in a “Special Roadway Section” Defined as Ice Rich or Massive Ice Cutslopes (after Rooney, R & M Consultants, Inc., 2007) ...... ……………………………………………………………………………..35

7. Near Vertical Cutslopes with a Widened Ditch Section ……………………….………….37

8. Photo. Trees felled(cut) at the Top of a Near Vertical Cutslope in Permafrost. (from ADOT&PF file) …………………………………………………………………………...38

9. Photo. Natural Vegetation Restores Thermal Equilibrium of a Cut Slope after Several Years (from ADOT&PF file) ..…………………………………………………………….38

10. Photo. Site Overview of Sections I, II, and III in Foreground and Sections IV and V in Background August 22, 1973 (after APSC 1974) ..……………………………………….39

11. Photo. Four Test Sections and Control Section at Thermal Erosion Test Site, Hess Creek, Alaska (after APSC 1974) ………………..……………………………………………….40

12. Photo. Completed Application of Urea Formaldehyde on Section I, July 26, 1973 (after APSC 1974) …………………………………..…………………………………….……..41

13. Photo. Thermal Erosion Induced Flow Material at Toe of Slope on Sections I and II, August 22, 1973 (after APSC 1974) ..………………..…….……………………………..41

14. Photo. Thawed Material Soaking through Cloth Sections and Accumulation of Flow Material on Section III, August 2, 1973 (after APSC 1974) ...... ………………………...42

15. Photo. Mass Flow Pulling Excelsior Downslope on Repaired Section III, August 22, 1973 (after APSC 1974) ..……………………………………………………………………….42

16. Sand and Gravel layer with Insulation at an Ice-Rich Cut Along the Dempster Highway, NWT (after Claridge and Mirza, 1981 ..…………………………………………………..43

iii

17. Photo. Kotzebue Runway Improvement - April through August 2006 (from ADOT&PF file courtesy of S. Lamont) ………………..………………………………………………48

18. Photo. Containment Structure for Excavated Permafrost on the North Slope of Alaska from ADOT&PF file courtesy of G. Griffin) …………..………………………………….……49

19. Photo. During wintertime excavation of ice-rich materials in western Alaska, nearby snow may be the only material available that can be piled up to provide retainment for excavated permafrost. (from ADOT&PF file courtesy of S. Lamont) …………..…….……………52

20. Photo. A Forest Fire in a Permafrost Environment (courtesy of A. Scott) ……….………54

List of Tables

1. Soil Erosion Code (after Claridge and Mirza(6)) ………………………………………….3

1 INTRODUCTION

Thawing of ice-rich permafrost has produced a number of problems on Alaska transportation projects including substantially reduced equipment mobility, uncontrolled erosion and runoff, and slope failures. The consequences of thawed ice-rich permafrost are environmental distress, project delays, change orders, and claims. Well-defined procedures are lacking to dispose of excavated ice-rich permafrost and manage a site with exposed ice-rich permafrost. In the context of this report, the definition of “ice-rich” permafrost is permafrost with a water content sufficiently high to cause “problems” upon thawing. Given this context, and the recent advancement of environmental regulations, monitoring, and enforcement, the definitions of “ice- rich” and “problem” can be expected to change with time.

Unfortunately, a number of construction problems related to thawed ice-rich permafrost, documented more than one-half century ago, still occur. In many instances the mitigation strategies employed to reduce the consequences of thawing permafrost only met with partial success or were completely unsuccessful.

At present, the construction engineer charged with the successful completion of a project in a permafrost environment has few, if any, resources available to identify a suitable mitigation strategy, particularly in an era of increasingly stringent and challenging environmental regulations. Environmental pressures continue the trend of making long accepted Alaska Department of Transportation and Public Facilities (ADOT&PF) methods for dealing with ice- rich permafrost either undesirable or unacceptable.

ADOT&PF is required to develop and implement a Storm Water Pollution Prevention Plan (SWPPP) under the Construction General Permit (CGP) for construction sites. A SWPPP is a document that describes the nature and extent of a construction activity and the measures that are used to ensure that sediment and other pollutants are not carried into the storm water discharges from the construction site. To control these pollutants, the contractor can use a variety of measures, referred to as Best Management Practices (BMPs). The BMPs form the basis of the SWPPP, and the contractor must select a BMP based on the conditions at the construction site. For a SWPPP to be effective the contractor must properly design, construct, and maintain the BMPs during the life of the project.

The purpose of this Summary Report is to compile and synthesize all available information related to BMPs to mitigate problems related to thawed ice-rich permafrost exposed by construction operations. Additional information is provided on [1] disposal of excavated ice-rich permafrost (e.g., stockpiles), [2] the use of ice-rich permafrost as an embankment material, and [3] the effect of fire on a permafrost environment. A brief description of the SWPPP regulatory environment is provided in Appendix A.

EROSION MECHANISMS

The rate of erosion is affected by a number of variables. The most significant are: soil type, vegetation, climate (e.g., intensity and duration of precipitation) and drainage basin characteristics (e.g., length and steepness of slopes, drainage density, relief, size of watershed). Transportation corridor construction activities which cause surface disturbance such as clearing vegetation, excavation of ditches, side and through-cuts, diversion and concentration of flow generally cause the rate of erosion to accelerate.

Accelerated erosion may result from hydraulic and thermal processes, acting separately or in concert. Rainfall and flowing water are the two principal agents of hydraulic erosion. The susceptibility of a disturbed site to hydraulic erosion depends primarily on soil properties, slope, and corresponding flow velocity. Silts and fine sands are most susceptible whereas gravels are least susceptible to hydraulic erosion. Clay soils are less susceptible than silts and fine sands owing to their structure and cohesion. Thermal erosion is caused by alterations in drainage patterns, removal of surface vegetation cover, or excavations in permafrost. Thermal erosion is generally associated with rapid thawing of ice-rich, fine-grained permafrost. The thermal regime is extremely sensitive to ponding of water and channelization of runoff.

Severe accelerated erosion is always observed when drainage is uncontrolled through an area of ground disturbance. When the ground cover is removed or disturbed subsidence and entrapment of water often occurs. If water begins to flow erosion gullies form. Cross drainage flows across a transportation corridor; longitudinal drainage is parallel to the corridor. Ponding should be prevented by providing cross drainage at appropriate locations, often more frequent than would otherwise be necessary for directing identified drainage courses across the corridor. If longitudinal ditches are necessary protective liners should be considered. Ditch checks are used to reduce flow velocity and to control the sediment load. Ditch checks are often used to control erosion in longitudinal ditches at the toes of cuts in fine-grained soils. Ditches should not be constructed in fine-grained permafrost.

Claridge and Mirza(6) presented a soil erosion classification system for northern climates (Table 1). They expressed the potential for a soil to erode in terms of a Soil Erosion Code (SEC). The SEC is based on the soil gradation (coarse, fine or mixed), whether the soil is frozen or unfrozen, and the ice-content of the frozen soil (as a percentage by volume). The soil descriptions in Table 1 are adopted from the Unified Soil Classification system.

THERMAL EROSION OF ICE-RICH PERMAFROST EXPOSED DURING CONSTRUCTION

In northern Alaska exposure of ice-rich permafrost during construction of roads and other projects is an all too common occurrence (Figure 1). Ice-rich permafrost exposed during late spring through early fall has a very high potential to thaw. Permafrost excavated in winter will

cause severe problems if it is not properly disposed of prior to spring thaw. When thawed, ice- rich permafrost, typically silts with segregated ice or massive ground ice, experiences a Table 1 Soil Erosion Code (after Claridge and Mirza(6))

SEC SOIL GENERAL EROSION DESCRIPTION CHARACTERISTICS POTENTIAL FG or Clean sand and gravel with little or no Free draining,, medium to high density, Very low to nil UG fines (<7% silt and clay content) occurs in frozen and unfrozen states , massive ice inclusions are uncommon. FS or Silty sand & gravel, silt, sand & gravel, Found in frozen & unfrozen soils. Massive ice Low to medium depending US or cobbles & boulders, Fine-grained inclusions may be encountered especially in on thermal conditions, material <50%. colluvial deposits. topography & hydrology. FM or Sandy or gravelly silt or clay. Fine- Either frozen or unfrozen. High ice content or Moderate to high. UM grained material >50%. massive ice segregation common. FL or Silt-organic &inorganic silt, and clayey Occurs in frozen & unfrozen state. High ice High UL silt. content common in unfrozen silt.

FC or Clay or silty clay. Varies in moisture content, in-place density Moderate to high. UC and color. FP Peat and organic matter. High moisture, low density. Low to medium depending on silt content. FB or Bedrock, unweathered. Non erodible. UB SEC = soil erosion code; F denotes frozen soil and rock; U denotes unfrozen material.

substantial reduction in strength owing to the exceedingly high water content and lack of drainage and consolidation during the thawing process. The result can be a quagmire in which construction equipment is “bogged down” or, if the exposure is on a cutslope, a slope failure will result (Figure 2). Aside from trafficability and stability problems, serious environmental issues arise when thawed particulate laden fluids (sometimes dense slurries) must be controlled. R & M Consultants, Inc. (16) summarized the possible consequences of thermal erosion as follows: • Settlement-induced depressions resulting in water ponding • Surficial movement or sliding of thawed materials also involving the interception of drainage structures • Redeposition of slope material that may result in the covering or destruction of previously installed erosion control treatments • Headward erosion and severe gully and fissure development, particularly in areas of cross drainage • Stream pollution by excessive sediment transport.

Thawing of ice-rich soils has posed problems since the first construction projects in permafrost environments. During the summer of 1954 the Alaska Road Commission exposed ice-rich permafrost (lake silts) two miles north of Paxson (Figure 3). Upon thawing, the material actually started to flow. Problems associated with thawing of ice-rich permafrost occurred on a number of North American road projects over the next half-century and have been reported for a number of international projects as well. Slumping of thawed material was noted on several cutslopes in ice-rich permafrost along the Qinghai-Tibet railroad. Chinese researchers report a close correlation relating thaw damage to the orientation of the cutslope (which has been noted by a number of other professionals). Specifically, failures on south facing slopes were usually more

common and dramatic than failures on north facing slopes. The south facing slope has a warmer mean annual ground temperature below the sliding mass due to more intense solar heating when compared to the north facing slope.

A recent example (from 2005 to 2007) of thaw related problems is provided by the Dalton Highway, just north of Milepost 35. Figure 4 shows a cut that extended about 300 m (1,000 ft) in total length. During exploratory drilling, the cut volume was judged to be bedrock and weathered bedrock. The cut was designed to have a stepped backslope and also incorporated an interceptor ditch for collecting water along the top of the slope (to prevent erosion of the slope face). The cut design was appropriate for the expected fairly competent weathered bedrock. However, much of the bedrock cut material was not only highly weathered but also ice-rich. This resulted in challenges to stabilize both cut slopes and stockpiles of excavated material. The excavated material was stockpiled (see Figure 4b) without a containment berm. Fortunately, the stockpile of excavated material didn't “run” as it thawed. However, there were cutslope failures and maintenance issues that required attention as shown in Figure 5. The photos emphasize three major types of damage and the associated environmental problem created during thawing: (1) damage above the cutslope, (2) damage on the cutslope, and (3) ditch damage. The damage creates and/or exacerbates the problem of high-particulate runoff. With much (and long term) attention to ditch maintenance, such problems have “healed’ themselves in the past when thawing progressed to a depth at which additional slumping and soil loss finally ceased. However, this may take an unacceptably long time.

MITIGATION OF THERMAL EROSION OF ICE-RICH CUTSLOPES

Documented concern for the instability of cutslopes in ice-rich permafrost and massive ground ice was presented in the 1969 design guidelines for the 123 km (56 mile) Livengood to Yukon River initial segment of the Trans Alaska Pipeline System (TAPS) haul road(19), generally referred to as the Dalton Highway. The original engineer’s sketch of the recommended mitigation procedure is shown in Figure 6. Basically, the mitigation procedure allows thermal erosion to occur. The thermal equilibrium of the cutslope is slowly reestablished when the vegetal mat removed during construction is naturally restored.

An alternate mitigation strategy is to develop a thermal barrier between the permafrost and the warm ambient air temperatures. In nature, the vegetation overlying the permafrost creates a thermal barrier through a combination of low conductivity and evaporative heat transport. Artificial thermal barriers include (17): • Radiation protection in the form of a high reflectivity surface treatment • Conduction protection in the form of a low conductivity surface treatment • Promotion of heat exchange at the surface through a system that provides shading and high evaporation characteristics Rooney notes that convective heat transfer that can be induced by the surface characteristics of a thermal erosion treatment is probably of secondary importance.

Anecdotal and published sources of information suggest that several techniques have previously been employed, with varying degrees of success, to mitigate problems related to thawing ice-rich permafrost. The two primary techniques are as follows:

1. Near vertical cutslopes with a widened ditch section to accommodate sloughing. Berg and Smith(4) based on observations along the TAPS haul road presented the procedure shown in Figure 7a. At the time of construction trees are cleared (by hand to minimize environmental damage) for a distance equal to 1½ HCUT (Figure 8). The cut is nearly vertical (1/4H to 1V). The road grade is undercut approximately 1.5 m (5 ft) before placement of the gravel embankment. Wide ditches that will accommodate slumpage while facilitating drainage flow and “cleanout” are constructed at the toe of the slope. Granular linings and check or diversion structures are installed in the ditch. During the first summer the slope degrades rapidly. Hydraulic seeding is applied late in the thaw season (for best results). The lateral ditch is cleaned as necessary. The rate of degradation of the backslope decreases over a number of years. After 5 or 6 years the slope usually becomes relatively stable, having stabilized at a grade significantly less than the original cut, and covered with surface vegetation that restores thermal equilibrium (Figure 9). Vegetative reseeding should not be initiated until slope stabilization is confirmed by field observation.

A recent modification to the Rooney/Berg and Smith approach has been presented by McHattie(13), as shown in Figure 7b. McHattie’s recommendation incorporates a separation dike to insure complete containment of thawed material and a chimney drain in the retention dyke to facilitate drainage of the water in the contained thawed material.

The Berg and Smith recommendation was based on the performance of near vertical cuts in ice- rich silt made on the 90 km (56 mi) Livengood to Yukon River segment of the Dalton Highway(20). The cuts were made following observations by the project consultants of similar ice-rich fine-grained soil cutslopes along the Alaska Highway(19). The design consultants recommended that near vertical cuts with extra wide ditch sections to accommodate cutslope sloughing and erosion be used. Alyeska Pipeline Service Company (APSC) monitored the performance of these segments and the natural restabilization and revegetation of these slopes was deemed satisfactory. However, it was anticipated that the performance of cutslopes could be improved with the addition of surface treatments that would retard thermal erosion.

2. Moderate cutslopes (generally 1.5 to 1 to 3 to 1) with a surface treatment. The first documented study to evaluate surface treatments on cutslope stability was at a test site along the Dalton Highway, approximately 5 km (3 mi) south of Hess Creek and 40 km (25 mi) north of Livengood(2,3). The ice-rich, fine-grained soil in this area insured that an exposed or disturbed cut slope at the test site would be especially susceptible to thermal erosion. Four test sections were originally proposed by Rooney(17) as follows: • Section I – Urea formaldehyde foam – this material is degradable and forms an insulative blanket to reduce thermal conductivity • Section II – Shredded organics (with a high specific surface area) – an evaporative heat barrier • Section III – Fiberglass and paint spray - radiation protection in the form of a high reflectivity surface treatment

• Section IV - Urea formaldehyde foam and gravel blanket – to study the effects of drainage beneath a thermal protection system.

The surface treatments as they were actually constructed between July 18 and August 3, 1973, are shown in Figures 10 and 11 and included: • Section I - Urea formaldehyde foam (10 cm, 4 in.) covering an AMXCO excelsior blanket. • Section II - Two layers of AMXCO excelsior blanket, each 5 cm (2 in.) thick.. • Section III (E & W) - Burlap (E) sprayed with titanium dioxide (TiO2 )and “Dynel” nylon fabric (W) sprayed with TiO2. (Two layers of AMXCO excelsior blanket were placed over this section owing to problems which developed during construction). • Section IV - Urea formaldehyde foam (5 cm, 2 in.) over “Dynel” nylon fabric over a sand layer (15 cm, 6 in.) • Section V - Control section – untreated bare slope

Slope No. 1, containing Sections I, II, and III, was covered by a layer of moss, grass, and brush. The depth of thaw was between 0.4 and 0.8 m (1.5 and 2.5 ft). Layers of massive ice, 0.4 to 0.9 m (1.5 to 3.0 ft) thick, and high ice content soil were encountered in the slope. Slope No. 2, containing Sections IV and V, was also covered by a layer of moss, grass, and brush. The depth of thaw was between 0.6 to 0.9 m (2.0 and 3.0 ft). Scattered ice layers were present in the silty soil comprising the slope. Section I and IV, with the urea formaldehyde foam, were installed July 24 and 25. In both Sections I and IV the urea formaldehyde foam was applied as a thermal insulator. However, in Section IV, the inclusion of the sand layer provided an additional means of protection against thermal erosion. The two “halves” of Section III were installed to examine the effectiveness of a highly reflective surface. The AMEX used on Section II was intended to provide an evaporative heat barrier.

Construction of the test sections was initiated in mid-July and the surface was continuously worked. Progressive thawing of the frozen excavated slopes occurred, resulting in limited equipment production, increased difficulty in working each slope and an excessive amount of hand work.

Test section performance was monitored by APSC during the summers of 1973 and 1974. The cutslopes were generally at 1.5 to 1. All test sections were sprayed with the same grass seed mixture after construction. Sections I to IV were designed to retard slope thaw by reducing conductive heat transfer at the slope surface. Section I (Figure 12) was left exposed to take advantage of the high reflectivity of the urea foam. During the second summer large thaw induced depressions developed under the insulation and large downslope movements of the thawed soil occurred. The slope movements destroyed 70% of the insulation. Thaw depths averaged 0.7 m (2.3 ft) in 1974. Section II was designed to reduce heat transfer by an evaporative or wicking action (promoted by the American Excelsior Company (AMXCO) “Curlex” blanket). It experienced failure during the first summer (Figure 13), especially near the toe, with much of the failed material flowing into the ditch. By the end of the second summer 50% of the slope was covered with the excelsior blanket, a vertical scarp had formed at the top of the slope, and the overall appearance was similar to Section I. Thaw depths averaged 0.8 m (2.6 ft) in 1974. Section III was originally burlap (E) or nylon (W) painted with high reflectivity

7 titanium dioxide paint to promote high reflectivity. The covering for the test section reportedly became soaked and distorted with mudflows during construction. Two layers of excelsior blanket were placed over this material. Section III failed repeatedly in 1973 (Figures 14 and 15). Mass movements in this test section were greater than the other four sections during 1973. Thaw depths in 1974 were 0.9 m (3 ft) at the toe and greater than 1.5 m (5 ft) at the top of the slope. The Section IV insulation layer was treated with straw mulch and seed to stimulate vegetation growth. The sand filter layer was intended to intercept meltwater and reduce excess porewater during periods of rapid thawing. Very little evidence of soil movement, sloughing, or meltwater release was observed in this section thru 1974. Thaw depths were 0.6 to 0.9 m (2 to 3 ft) in 1974. Test section V (control) experienced considerable caving and sloughing in 1973. The material was not transported far from the slope, as was the case for Sections I and II. By the end of the summer (1973) a vertical scarp developed at the top of the slope. No caving, sloughing, or erosion was observed in 1974 and sparse vegetation appeared on the slope surface. Thaw depths were 0.9 to 1.2 m (3 to 4 ft) in 1974.

In 1983, ten years after the test sections were constructed, ADOT&PF consultants Mageau and Rooney(12) visited the test sections to evaluate longer term performance and general slope conditions. They noted that all the slopes were stable. However, significant slope deterioration caused by large volume reduction and downslope movement occurred on the majority of the test sections. Revegetation was well established on slopes which had experienced significant slope displacement and consequent flattening of the slope. Revegetation on steeper, less deformed slopes was not well established or non-existent. More specific conclusions from their study are: • The primary effect of surface treatments with high insulative properties is to reduce the depth of thaw penetration, thermal erosion, and subsequent instability on a short term basis (one or two thaw seasons). The effect of insulation on seasonal thaw penetration decreases with time as the insulating properties of the surface treatment deteriorate. The surface treatment deteriorates as the slope surface deforms either by settlement or mass transport. • Surface treatments that rely solely on high reflectivity to reduce heat transfer are ineffective in retarding thaw penetration. • All slopes experienced sloughing, mass transport and settlement for at least several thaw seasons after construction; all slopes were stable after ten years. Settlement represented the greatest component of volume change; the remaining portion was attributed to downslope movement of thawed soil. • Revegetation appears to be most successful on ice-rich slopes which have experienced considerable displacement and flattening. The presence of surface treatments inhibits vegetative growth.

McRoberts et al.(14) considered several methods to insulate 55 cutslopes along the Norman Wells pipeline alignment including gravel, wood chips, and styrofoam®. Wood chips were selected owing to their local availability and ease in handling in cold weather. At some locations the thickness of the wood chips was 1.5 m (5 ft) (11).

The major disadvantage of wood chips is heat generated by microbial activity(8,15). All of the monitored wood chip layers indicated self-heating during the first few summers; six slopes exhibited heating throughout the winter months, generally related to “hot spot” areas where the

wood chip thickness exceeded 1.4 m (5 ft) and where a large proportion of aspen/spruce wood chips were present.

Kestler et al.(9) evaluated a number of techniques to rapidly stabilize thawing soils to provide enhanced (military) vehicle mobility. While the results of their study may not relate directly to the objectives of this study, it is important to review them in the event they are proposed as a mitigation technique in the future. Specifically, Kestler et al. considered chunkwood, tire chips, tree slash, tire mats, wood mats, hand-assembled wood pallets, PVC fascine, and several types of geosynthetics, some of which were development or newly developed products. Of these techniques chunkwood may have applicability as a slope treatment in the context of the current study. Chunkwood is produced by shredding whole trees to produce wood chucks approximately 3.8 cm (1.5 in.) thick and from 1 to 20 cm (0.5 to 8 in.) in diameter. The chunkwood was mixed with sand in a ratio of 3 parts chunkwood to 1 part sand by volume. The density of the chunkwood/sand mixture was approximately 800 kg/m3 (50 pcf). Chunkwood has a long history of successful application for the USFS. Chunkwood roads have been in place for ten years with no required improvements(1).

Claridge and Mirza(6) provided a summary of their experience with erosion control along the TAPS haulroad. They reached a number of conclusions related to the current study, as follows: • Near-vertical slopes (1/4 to 1.0) can be successful in all ice-rich fine-grained permafrost when the cut height is ≤ 2 m (7 ft). Near-vertical slopes (1/4 to 1.0) may be successful in ice-rich silt and colluvium permafrost when the cut height is ≤ 6 m (20 ft). • Steep or near-vertical slopes (1/4 to 1.0) in predominately clay permafrost with segregated ice are generally not successful when the cut height is > 1.5 m (5 ft). Cuts in clayey soils require insulation, sand and gravel buttressing, riprap protection or a combination of these methods. • Conventional cuts have generally been successful when ice content is < 15% (by volume) in sand, gravel and other soils. • Revegetation is required for all cuts, except the near-vertical slopes (1/4 to 1.0) which require periodic surveillance and maintenance. • Cut slopes in ice-rich fine-grained soils should not be made without providing suitable insulation protection. With near-vertical cutslopes (1/4 to 1.0) the insulation protection develops slowly without applied treatments. As the cutslope recedes, the sloughed material at the toe provides stability and the vegetative mat above the cutface slumps over the exposed thawing permafrost. Conventional sloped cuts may recede a considerable distance owing to lack of vegetation. Thermal protection may be provided with coarse sand and/or gravel layer, a layer of manufactured insulation (optional), and a vegetation mat (Figure 16).

Four additional techniques have been reported but are not well documented, as follows: 1. Cut the slope very flat (3 to 1 or flatter) with no surface treatment. The presumption is that slow thawing of the lower angled slopes would result primarily in soil settlement with little or no lateral movement. Fine-grained very high ice content materials which experience rapid thawing may flow even if cut at a very low slope (flatter than 6 to 1). Examples of thawed materials observed to flow along a very slight cutslope angle occurred adjacent to the Glenn Highway about 20 miles west of Glennallen. It is worth noting that these and other materials

found within the Copper River Basin may exhibit unusual/unexpected stability behavior due to their unique marine origin and geologic history. 2. Cover the cutslope with a vegetation mat (closed netting) to provide minor insulation plus shading. 3. Reduce the slope inclination to 1.5 or 2 to 1, place topsoil on the slope; seed at 2 to 3 times the “normal” application rate (best suited to non-ice-rich permafrost). 4. Cut the ice-rich permafrost slope about 1.5 to 1 and place a gravel buttress (i.e., berm or blanket) adjacent to the slope face (buttress height = cutslope height). The horizontal width of the buttress is approximately 2.4 m (8 ft) to facilitate construction, and the buttress sideslope is approximately 1.5 to 1. The inclination must be less than the angle of repose of the gravel. Claridge and Mirza(6) discuss the successful application of a buttress of crushed rock on a section of the Dempster Highway (NWT). The buttress does not need to be thick enough to eliminate thaw entirely. It functions by reducing the rate of thaw and facilitates drainage and thaw consolidation. It protects the slope from both thermal and hydraulic erosion. With proper attention to gradation characteristics it may also enhance air convective heat transfer in the buttress.

A successful example of large scale erosion stabilization of permafrost is provided by the runway improvement project at the Kotzebue airport. The top of a hill that extended into aircraft glidepaths was excavated to improve the approach to the runway as shown in Figure 17. Synthetic matting was placed on a large area of exposed permafrost in spring 2006 to retard thaw and erosion and promote stabilizing plant growth. Vegetation was established by late summer 2006.

Kinney(10) recently presented the concept of an erosion control soil (ECS) and demonstrated the concept with two projects in the Seattle, Washington area. An ECS is a soil manufactured of natural materials with the correct combination of physical, chemical, and biological properties to provide a sustainable system in the required environment. It produces an erosion resistant, free draining vegetation mat in a very efficient manner. The concept of an ECS has not been used in a permafrost environment

DISPOSAL OF EXCAVATED PERMAFROST

Disposal of excavated material is one of the most common problems associated with exposing ice-rich permafrost. It is not acceptable to simply dispose of excavated permafrost at a convenient location without regard to the environmental consequences of failure or runoff from the eventually thawed material. One solution to the disposal of excavated permafrost is to construct retention berms and place the permafrost inside the berms. When the ice-rich permafrost eventually thaws it is restricted to the area inside the berms. The retention berms shown in Figures 18 and 19 allowed the thaw water to escape. Future retainment schemes may be complicated if excess water generated during thawing needs treatment prior to release from the containment area.

USE OF EXCAVATED PERMAFROST TO BUILD AN EMBANKMENT

A problem in western Alaska, also related to permafrost degradation, is the use of excavated permafrost to construct a road or airfield embankment. This unusual practice is necessary owing to the scarcity of suitable embankment fill at some locations. Permafrost is excavated in the winter and placed in the location of the required embankment (similar to the embankment shown in Figure 19). Over a period of several years the permafrost fill progressively thaws and becomes increasingly stable and viable as a runway embankment. If the thawed material is restrained from lateral spreading and flow, it eventually settles, drains and can be shaped and compacted to form the final load supporting embankment. Snow berms can be placed adjacent to the embankment sideslopes to retain the thawing permafrost. Thawed soil, initially retained by the snow berm, drains and forms its own soil berm that continues to contain the spread of additional thawed material after the snow disappears.

If compaction of frozen soil is attempted it must be done with heavy rollers to break down the frozen chunks(7). Frozen soil compaction will result in an open void structure and springtime snow meltwater infiltration will occur. An embankment placed with material from a permafrost pit source will likely take years to consolidate and stabilize. GeoEngineers reports that in Western Alaska, with frozen silt as the only available material, ADOT&PF personnel were unanimous in preferring thawed borrow pit sources; frozen pits are often preferred by contractors. Use of thawed material insures that volume changes associated with ice melting in frozen material will occur prior to placement of the material in the embankment.

FIRE AND PERMAFROST

Fires are known to cause deep thawing of permafrost in interior Alaska (21). The influence of fire on permafrost depends on type of vegetation, moisture, and the rate of burning. If a fire moves rapidly through an area, or the surface peat and moss layer is moist, the permafrost may not be significantly disturbed. If the surface vegetation is very dry, it may be almost totally consumed by the fire, robbing the permafrost of its insulative and evapotransporative cover. Also, some trees such as black spruce burn with high intensity. In the discontinuous zone, masses of thin permafrost below a large fire of this type may disappear. Figure 20 illustrates the effect of fire in a permafrost environment.

Bolstad(5) states: “Severe erosion has resulted in the past from bulldozer-constructed firelines in permafrost terrain. In an attempt to reduce erosion and gullying, several waterbarring techniques and seeding treatments were tested on permafrost and nonpermafrost catlines. Standard water bars and berm dikes constructed at 9 to 15 m (30 to 50 ft) intervals on sloping terrain were effective in reducing erosion. Vegetative check dams on permafrost soils were ineffective. Seed growth was more successful on permafrost than on nonpermafrost soils. Fertilized lines resulted in better seed success than unfertilized lines."

SUMMARY AND CONCLUSIONS

Engineers in Alaska should carefully examine past practices to alleviate problems related to: • exposed and thawing ice-rich permafrost • disposal of excavated ice-rich permafrost • the use of permafrost to construct an embankment.

Increasing resource agency oversight requires evaluating all methods previously employed to address these problems, a number of which are reported herein, with respect to their environmental acceptability in addition to their engineering/constructability attributes. Best construction management practices will develop after a balance between reasonably attainable environmental goals and economical/practical engineering solutions is achieved.

IMPLEMENTATION

Appendix B contains implementation recommendations resulting from this research. Recommendations are presented in a format similar to existing ADOT&PF SWPPP Guide BMPs. Permafrost engineering experience to date dictates that only conceptual design recommendations are presented at this time. The authors were faced with the reality that no detailed design standards or limiting parameters have been established for any design measures identified during this study. None of the design features have been systematically tested in field trials through a full range of soil types and thermal conditions.

The near vertical cut with wide ditch design (previously discussed), generally termed the ablation method, has been used for several decades in Alaska. The ablation method appears to have the greatest application history of all the measures presented herein and would appear to be closest to a tested and proven technology. The ablation method recently became a target of environmental-based litigation because of the possibility that it could contribute silty meltwater to roadside ditch flow. An updated environmentally acceptable version of the design is included in Appendix B.

APPENDIX A - REGULATORY ENVIRONMENT

The Alaska Department of Transportation and Public Facilities (DOT&PF) prepared a Guide (2005) which explains the requirements of the National Pollutant Discharge Elimination System (NPDES) Storm Water Construction General Permit (CGP) for construction sites. The guide focuses on the development and implementation of a Storm Water Pollution Prevention Plan (SWPPP) required for coverage under the CGP.

A SWPPP is a document that describes the nature and extent of a construction activity and the measures that are used to ensure that sediment and other pollutants are not carried into the storm water discharges from the construction site. To control these pollutants, the contractor can use a variety of measures, referred to as Best Management Practices (BMPs). The BMPs form the basis of the SWPPP, and the contractor must select a BMP based on the conditions at the construction site. For a SWPPP to be effective, the contractor must properly design, construct, and maintain the BMPs during the life of the project.

The Guide presents 17 commonly used BMPs, along with application, design, construction, inspection, maintenance, and removal guidelines. Additional BMPs are given on the DOT&PF environmental Web site:

http://www.dot.state.ak.us/stwddes/dcsenviron/index.shtml

The BMPs must be carefully analyzed before they are recommended for use in a permafrost environment. The Guide makes no reference to permafrost, frozen, freezing, thawing, or thermal. An excellent compilation of BMPs for temperate climates has been prepared by CALTRANS, specifically: “CALTRANS Construction Site Best Management Practices (BMPs) Manual”, March 2003.

To insure the wording in this report and the 2005 Guide are not contradictory the wording in this section, in general, is taken directly from the 2005 Guide. Any reference to “you” or to “the contractor” in the 2005 Guide refers to the contractor or contractor’s designee. The term “operator” or “site operator” refers to the person or persons in charge of the day-to-day activities at a construction site.

Summary of Applicable Water Quality Laws and Regulations. Federal and state governments have passed numerous laws to minimize environmental harm from storm water discharge at construction sites. Some of these laws and subsequent regulations require the implementation of erosion and sediment control measures, while others mandate that construction activities maintain water quality. The two most important water quality related laws and regulations are the Federal Clean Water Act and the State of Alaska Water Quality Standards, as defined in the Alaska Administrative Code (18 AAC 70).

The 1972 amendments to the Federal Water Pollution Control Act (known as the Clean Water Act or CWA) form the primary law controlling construction site discharges and setting water quality standards. The CWA, implemented by the Environmental Protection Agency (EPA),

required site operators to comply with a General Permit or an individual NPDES permit. In 1990, the EPA published regulations classifying construction projects that disturb more than 5 acres as industrial dischargers. From 1990 until 1998, a contractor had to either obtain an individual NPDES permit or comply with the stipulations of a General Permit. In 1992, the EPA issued a Construction General Permit for Alaska, Permit Number AK-R-10. This permit required the site operator to prepare a SWPPP detailing the operator’s erosion and sediment control plan, permanent storm water management plan, and excavated material control plan, then file a Notice of Intent with EPA before the start of any earth-disturbing activities. In 1998, EPA reissued the General Storm Water Permit for Construction Activities. In 2003, EPA modified the Storm Water General Permit to include both large and small construction activities (i.e. all construction projects disturbing 1 acre or more of ground). For complete regulatory information on the Storm Water General Permit for Large and Small Construction Activities, visit the following Web site:

http://cfpub1.epa.gov/npdes/stormwater/const.cfm?program_id=6

The primary requirement of the EPA Storm Water General Permit for Large and Small Construction Activities is the development and implementation of a Storm Water Pollution Prevention Plan (SWPPP). The SWPPP is a written storm water management plan to preserve water quality by minimizing or eliminating the pollutants in the storm water discharges from construction activities. EPA requires the preparation of a SWPPP before the start of any construction activities that disturb 1 acre or more of land. For all projects disturbing 1 acre or more, the contractor must minimize potentially harmful water quality impacts by using BMPs to control erosion and sedimentation.

The Alaska Department of Environmental Conservation (DEC) sets water quality standards for Alaska waters and regulates discharges into these waters. All discharges of storm water from construction projects disturbing 5 acres or more that are authorized under the EPA Storm Water General Permit for Large and Small Construction Activities must be reviewed by DEC, and require a plan review fee.

Other federal and state laws and regulations applicable to storm water discharges from construction activities are as follows: The Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) Section 1057 of this act requires the U.S. Department of Transportation to develop erosion control guidelines for the construction of all federally funded highway projects. To satisfy the provisions of Section 1057, the Federal Highway Administration (FHWA) has adopted the American Association of State Highway and Transportation Officials’ (AASHTO) “Highway Drainage Guidelines,” which address erosion and sediment control. Every state highway agency must comply with these AASHTO guidelines for projects that use federal highway funds. The Coastal Zone Act Reauthorization Amendments of 1990 This act requires that every state participating in the federal Coastal Management Program use erosion and sediment control management measures. Alaska’s Coastal Management Program (ACMP) requires that estuaries, wetlands, tide flats, lagoons, rivers, streams, and lakes be managed to protect natural vegetation, water quality, important fish and wildlife habitat, and natural water flow. The ACMP states in part that contractors for projects within the coastal zone must use “all feasible and prudent steps

14 to maximize conformance” with this requirement. State and federal resource agencies that issue permits often require erosion control measures to ensure that a project will be consistent with the ACMP. Section 404 Permit of the Clean Water Act. The U.S. Army Corps of Engineers (USACE) administers this requirement. A permit is required for dredging, grubbing, excavating, or filling in rivers, streams, lakes, ponds, tidelands, and wetlands. The 404 permit usually requires erosion and sediment controls to ensure minimal harm to jurisdictional areas. Alaska Statute 41.14.870, Anadromous Fish Act. The Alaska Department of Natural Resources (ADNR) regulates construction activities that will affect freshwater anadromous fish habitat. Any activity that will pollute or change the natural flow or bed of a stream important for the spawning, rearing, or migration of anadromous fish must be approved by ADNR to ensure that the construction plans and specifications will protect fish and game. Often, the ADNR permit requires an erosion and sediment control plan.

APPENDIX B - BEST MANAGEMENT PRACTICES

Tentative recommendations are presented herein as indicated in the Implementation section of this report:

• The BMPs presented are in the development stage.

• Experience to date requires that BMPs in this report are presented as conceptual design recommendations. No detailed design standards have been established for the BMPs. The highway/construction engineer must work closely with regional geotechnical personnel to address project specific thermal, stability, and drainage issues. The design must consider the properties of materials that will be available at the project site.

• Design concepts presented in this report have not been systematically tested in field trials through a full range of soil types and thermal conditions.

• The BMPs presented in this report must remain serviceable long after project construction is completed. Design features intended to minimize damage or pollution due to permafrost degradation must remain functional with little or no maintenance as a permanent part of the project and/or until thermal equilibrium is reestablished and the feature is no longer required.

1. Controlled Ablation

Objectives and Applications The preferred method of controlling thermal erosion is to select design measures which minimize or eliminate thawing of ice-rich permafrost or massive ground ice. Should a cut section be required through these materials and it is determined that the mitigation method presented herein (and others presented elsewhere) would not be adequate to prevent an adverse impact to the environment or to the integrity of the transportation corridor, an adjustment to the alignment should be considered. Minimal cuts in ice rich areas should be eliminated with design grade changes.

Common Failures Generally Due to Faulty Installation or Failures Consult with Regional Geotechnical Engineer.

Other Considerations Use of the separation berm in this design requires consideration of an overflow drainage feature in an extreme rain event or heavy snow runoff. Standpipes and/or slot bypass drains may be added if appropriate.

Relationship to other ESC Measures Consult with Regional Geotechnical Engineer. The gravel buttress features (see BMP 2) serves a purpose functionally similar to the Controlled Ablation BMP. It can be used in place of the Controlled Ablation BMP for cut heights up to 3 m (10ft). It is a recommended alternative with the cutslope height exceeds 3 m (10ft). Insulated thermal blankets (see BMP 3) may be used on cut slopes in fine-grained permafrost soils that will not self-stabilize. This method may also be used on cuts through fine-grained permafrost soils where slope height and gravel availability make gravel buttresses impractical.

Alternative Sediment Control Measures Consult with Regional Geotechnical Engineer.

Design Consult with Regional Geotechnical Engineer.

Materials As required by specific design details and location.

Installation (refer to Figures) • Initial control of thermal erosion will consist of cutting the slope at a ratio of 1/4 to 1 (nearly vertical) • Provide a wide ditch at the base of the cut to allow removal of material, if necessary, and allow deposition of some overlying material during the stabilization process. A separation/retention berm, with or without internal drainage, depending on the availability of a free draining material for the berm, may be required to insure control and containment of particulate laden runoff and thaw weakened material with a sufficiently high water content that it may flow. The minimum width of the ditch without a separation berm is 2.4 m (8 ft). The minimum width of the ditch with a separation berm is 4.2 m (14 ft) including the width of the separation berm. The minimum height of the separation berm is 0.8 m (2.5 ft) with 1½ to 1 sideslopes. Use of steeper berm sideslopes to a maximum of 1 to 1 may be possible. The berm may or may not have a flat crown.

16 • Hand clear the area beyond the slope stake limit to allow controlled ablation of the slope, typically a distance equal to 1½ times the height of the slope. Any tree over 10 cm (4 in.) diameter and vegetation taller than 1.5 m (5 ft) shall be removed. The clearing activities must be conducted in a manner to insure the organic mat is not damaged. • All slash and timber will be removed from the cleared area to minimize tearing the organic mat. Stumps should be cut as close to the soil surface as possible (i.e., less than 0.3m (1 ft)). The application of a stranded wire fastened to the stumps may be considered to provide additional tensile strength to the organic mat and reduce tearing of the mat. All tree cutting should be accomplished with hand tools; heavy equipment should not be used outside the limits of the excavated area. • The organic mat will drape over the face of the slope as the cut degrades which will shade and insulate the face. The mat will be reinforced with biodegradable netting if necessary to prevent tearing of the mat. No netting of any kind will be used in fish bearing streams. • Vegetation seeding should be attempted only on relatively stable potions of the slope at selected times. • Diversion levees may be designed above ablating slopes on a site specific basis. • See design illustration for construction sequence. The separation berm with internal drainage features and additional site drainage measures may require consultation with the Regional Geotechnical Engineer.

Inspection Consult with Regional Geotechnical Engineer.

Maintenance Design so that maintenance is minimal or, preferably, none is required. Maintenance to eliminate localized ponding must be performed. The thawed material retained by the berm should not be removed as it serves to buttress the thawing slope.

Removal Not to be removed.

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2. Gravel Buttress

The gravel buttress feature serves a purpose functionally similar to the Controlled Ablation BMP. It can be used in place of the Controlled Ablation BMP for cut heights up to 3 m (10 ft). It is a recommended alternative when the cutslope height exceeds 3 m (10 ft).

Common Failures Generally Due to Faulty Installation or Failures Consult with Regional Geotechnical Engineer.

Other Considerations Consult with Regional Geotechnical Engineer.

Relationship to other ESC Measures Consult with Regional Geotechnical Engineer.

Alternative Sediment Control Measures Consult with Regional Geotechnical Engineer.

Design Consult with Regional Geotechnical Engineer.

Materials As required by specific design details and location. Free draining materials must be used in constructing this design feature.

Installation (refer to Figure) A gravel or rockfill buttress may be used to control thawing of cut slopes in fine-grained permafrost that will not self-stabilize. The buttress may be placed with minimum compaction if the angle of repose of the material is greater than inclination of the finished slope. For a finished slope inclination of 1½ to 1 the angle of repose must be greater than 35 degrees.

The cut slope will generally be no steeper than ½ to 1 and consistent with the global slope stability and thermal requirements to achieve the cut. A geotextile, typically needle punched and stretched tight, may be placed on top of the cut slope to facilitate placement of the buttress. The top of the buttress should generally be a minimum of 2.7 m (8 ft) wide to facilitate construction. The gradation characteristics of the buttress may be specified to insure that convective heat transfer will occur in the buttress.

Specific site conditions (especially topography) and equipment availability will dictate the extent to which standard construction techniques and design features must be modified to accommodate placement of the buttress. Construction of a free draining buttress may require temporary 19 equipment access to expedite material placement. For example, if the blanket is constructed using scrapers, temporary ramps must be provided both up-station and down-station from the blanket to allow ingress and egress of construction during placement of the blanket fill. Additional cutting of the natural slope may be required to provide for the additional width of the blanket.

Inspection Consult with Regional Geotechnical Engineer.

Maintenance Design so that maintenance is minimal or, preferably, none is required.

Removal Not to be removed.

3. Insulated Thermal Blanket

Common Failures Generally Due to Faulty Installation or Failures Consult with Regional Geotechnical Engineer.

Other Considerations Consult with Regional Geotechnical Engineer.

Relationship to other ESC Measures Consult with Regional Geotechnical Engineer.

Alternative Sediment Control Measures Consult with Regional Geotechnical Engineer.

Design Consult with Regional Geotechnical Engineer.

Materials As required by specific design details and location.

Installation (refer to Figure)

Insulated thermal blankets may be used on cut slopes in fine-grained permafrost soils that will not self-stabilize. This method may also be used on cuts through fine-grained permafrost soils where slope height and gravel availability make gravel buttresses impractical. The select material beneath the insulation should be a sand and/or gravel or similar non-frost susceptible material. The minimum thickness of this layer (measured perpendicular to the slope face) is 0.9 m (3 ft). The sand and/or gravel layer may be placed with minimum compaction if the angle of repose of the material is greater than inclination of the finished slope. For a finished slope inclination of 1½ to 1 the angle of repose should be greater than 35 degrees. The minimum thickness of the topsoil layer (measured perpendicular to the slope face) is 0.6 m (2 ft). A degradable synthetic or natural erosion control netting may be required. Plantings should be made on the slope. A salvaged peat and moss layer may be placed on the slope as additional insulation and to hasten revegetation.

Inspection Consult with Regional Geotechnical Engineer.

Maintenance Design so that maintenance is minimal or, preferably, none is required.

Removal Not to be removed.

SYNTHETIC ORNATURAL EROSION CONTROl.. NETTING

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4. Retention Berm

Objectives and Applications Disposal of excavated material is one of the most common problems associated with exposing ice-rich permafrost. It is not acceptable to simply stockpile excavated permafrost at a convenient location without regard to the environmental consequences of failure or runoff from the eventually thawed material. One solution to the disposal of excavated permafrost is to construct retention berms and place the permafrost inside the berms. When the ice-rich permafrost eventually thaws it is restricted to the area inside the berms. The retention berms shown herein allow the thaw water to escape.

Common Failures Generally Due to Faulty Installation or Failures Consult with Regional Geotechnical Engineer.

Other Considerations Consult with Regional Geotechnical Engineer.

Relationship to other ESC Measures Consult with Regional Geotechnical Engineer.

Alternative Sediment Control Measures Consult with Regional Geotechnical Engineer.

Design Consult with Regional Geotechnical Engineer

Materials As required by specific design details and location.

Installation Two types of retention berms are illustrated. Ideally the retention berm will be constructed with gravel or a similar free draining material. If a free draining material is not available the internal drainage features will be required. An overflow drainage feature may be required to accommodate an extreme rain event or heavy snow runoff. Standpipes and/or slot bypass drains may be added if appropriate. The retention berm should be approximately 1/3 the height of the excavated permafrost stockpile. The berm may or may not have a flat crown.

Inspection Consult with Regional Geotechnical Engineer. The thaw water should be sampled prior to release to determine if treatment may be required.

Maintenance Design so that maintenance is minimal or, preferably, none is required.

Removal Not to be removed.

RtTDIfIOil _

RtTDIfIW BEIIII WITH IlIIElIYAL DRAIN'''''

ACKNOWLEDGMENTS

Sam Lamont, John Ryer, Guan Griffin, Jesse Reinikainen, Jeff Currey, and Jeff Russell, ADOT&PF, Northern Region-Construction Section, provided a substantial number of the photographs and valuable insights into the history of the projects and issues described herein. Audry Scott provided the post-fire photographs. Jim Rooney provided information and photographs on the early mitigation techniques employed on the Livengood to Yukon River initial segment of the TAPS haul road. Kris Benson reviewed the report and provided many valuable comments and suggestions. Appendix B was reviewed by Lon Krol, Dwight Stuller, Ron Hollingsworth, and Jeff Russell. Clint Adler, Chief of Research, ADOT&PF, provided the funding for the study through his Office and Jim Sweeney managed the contract. The contribution of these individuals is gratefully acknowledged.

REFERENCES

1. Arola, R., Hodek, R.J., Bowman, J.K., and Schulze, G.B. (1991). “Forest roads built from chunkwood: production, characterization, and utilization.” North Central Experiment Station, USDA Forest Service, General Technical Report NC-145, St. Paul, MN. 2. Alyeska Pipeline Service Company (APSC). (1974). “Report on thermal erosion test sites, Hess Creek, Alaska (Phase I - July-August, 1973).” Report Number TE-005. 3. Alyeska Pipeline Service Company (APSC). (1975). “Hess Creek thermal erosion site - 1974 Evaluation.” Report Number TE-006. 4. Berg, R, and Smith, N. (1976). “Observations along the pipeline haul road between Livengood and the Yukon River.” US Army CRREL Special Report 76-11. Oct. 1976. 5. Bolstad, R. (1971). “Catline rehabilitation and restoration.” In: Slaughter C.W.; Barney, R.J.; Hansen, G.M., eds. Fire in the northern environment––a symposium: Proceedings of a symposium; 1971 April 13-24; Fairbanks, AK. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station: pp.107-116. 6. Claridge, F.B. and Mirza, A.M. (1981). “Erosion control along transportation routes in northern climates.” Arctic. Vol. 34, No. (June 1981), pp. 147-157. 7. GeoEngineers, Inc. (2004). “Airport design and construction considerations for improving life-cycle costs in the Yukon-Kuskokwim Delta, Alaska.”, AKSAS Project 56405, PSA P32044, prepared for ADOT&PF, Aug. 2004. 8. Hanna, A. J. and McRoberts, E. C. (1988) “Permafrost slope design for a buried oil pipeline.” Proceedings, Fifth International Conference on Permafrost, Trondheim, Norway, pp. 1247-1252. 9. Kestler, M. A., Shoop, S. A., Henry, K. S., Stark, J. A., and Affleck, R. T. (1999). “Rapid stabilization of thawing soils for enhanced vehicle mobility – a field demonstration project.” US Army CRREL Report 99-3. Feb. 1999. 10. Kinney, T. personal communication, Oct.. 2008.

25 11. Macinnes, K. L., Burgess, M. M., Harry, D. G., and Baker, T. H. W. (1989) “Environmental studies no. 64, permafrost and terrain research and monitoring: Norman Wells Pipeline, volume 1 – environmental and engineering considerations; volume 2 – research and monitoring results: 1983-1988.” Northern Affairs Program. Indian and Northern Affairs Canada. Dec. 1989. 12. Mageau, D.W. and Rooney, J.W. (1984). “Thermal erosion of cut slopes in ice-rich soil.” FHWA-AK-RD-85-02 Final Report. Alaska Department of Transportation and Public Facilities. 13. McHattie, R. M., personal communication, Nov. 2007. 14. McRoberts, E.C., Nixon, J.F., Hanna, A.J., and Pick, A.R. (1985). “Geothermal considerations for wood chips used as permafrost slope insulation.” Proceedings, International Symposium on Ground Freezing, Sapporo, Japan, Aug. 1985, Vol. 1, pp. 305-312. 15. Pick, A. R. (1987) “Use of wood chips for permafrost slope stabilization.” Proceedings, Canadian Society of Civil Engineering Centennial Conference, Montreal, Canada, pp. 345-365. 16. R & M Consultants, Inc. (1973) “Case studies of hydraulic and thermal erosion.” Report Number HD-003, November. 17. Rooney, J.W. (1973) “A Study of thermal erosion control techniques.” Proposal submitted to Alyeska Pipeline Service Company 18. Rooney, J.W. and Condo, A.C. (1984) “Hess Creek thermal erosion test site: frozen cut slope surface treatments.” Proceedings, Third International Specialty Conference on Cold Regions Engineering, ASCE, Edmonton, Alberta. 19. Rooney, J. W., R & M Consultants, Inc., Anchorage, AK, personal communication, Nov. 2007. 20. Smith, N. and Berg, R. (1973) “Encountering massive ground ice during road construction in Central Alaska.” Proceedings, Second International Conference on Permafrost, Yakutsk, USSR, pp. 730-736. 21. Swanson, D.K. (1996), “Susceptibility of permafrost soils to deep thaw after forest fires in interior Alaska, U.S.A., and some ecologic implications.” Arctic and Alpine Research, Vol. 28, No. 2 pp. 217-227.

Figure 1 Photo. Road Cut in Ice-Rich Permafrost (from ADOT&PF file)

Figure 2 Photo. Thaw Degradation of Cut Slope in Ice-Rich Permafrost (from ADOT&PF file)

Figure 3 Photo. Thawed Ice-Rich Permafrost Flowing Around a Bulldozer Blade. Ice-Rich Permafrost (Lake Silts) were Exposed During the Construction of the Richardson Highway (Photo by Pewe, 1954)

(4.a) Newly constructed cutslope in ice-rich permafrost. Note interceptor ditch at top of slope and stepped cut face.

(4.b) View across permafrost disposal pile at new cutslope face in ice-rich permafrost. The volume of material exceeded the boundary limits of the permitted area.

(4.c) Ice-rich permafrost cutslope just starting to thaw. The ice-rich permafrost overlies bedrock; water is collecting at the interface.

(4.d) Ice-rich permafrost cutslope just starting to thaw. An ice lens is visible in the center of the photograph.

(4.e) Closeup of ice lens shown in frame 4 d. The ice lens has a very high ice content with the volume of the ice substantially greater than the volume of the soil.

Figure 4 Photo. Dalton Highway Cut in Ice-Rich Permafrost – Before Thaw (from ADOT&PF file courtesy of S. Lamont and J. Russell).

(5.a) Pockets of thaw failure along cut face – a gravel drainage blanket (left side of photo) was installed to slow thawing, retard slumping of thawed material and provide drainage during the thawing process

(5.b) Advanced thaw condition along ice-rich permafrost cutslope shows ditch filling with saturated silt

(5.c) Advanced thaw degradation of cutslope shows block failures and runoff of highly fluid silt into ditch

(5.d) Advanced thaw degradation of cutslope in coarser grained permafrost.

(5.e) Advanced cutslope thaw with silty runoff flowing in ditch and general slumping of coarser material

Figure 5 Photo. Dalton Highway Cut in Ice-Rich Permafrost – After Thaw (from ADOT&PF file courtesy of S. Lamont and J. Russell). Each photograph shows damage that occurred as thawing progressed. The photos emphasize three major types of damage and the associated environmental problem created by thawing: (1) damage above the cutslope, (2) damage on the cutslope, and (3) ditch damage. The damage creates and/or exacerbates the problem of high- particulate runoff. With much (and long term) attention to ditch maintenance, such problems have “healed’ themselves in the past when thawing progressed to a depth at which additional slumping and soil loss finally ceased. However, this may take an unacceptably long time. Methods must be devised to minimize, or hopefully eliminate, the types of damage shown in the photographs. Photograph 5.a (left side) shows an example of a gravel drainage blanket used to slow thawing, retard slumping of thawed material and provide drainage during the thawing process.

Figure 6 Original 1969 Engineer’s Sketch of the Procedure to be Employed in a “Special Roadway Section” Defined as Ice Rich or Massive Ice Cutslopes (after Rooney, R & M Consultants, Inc., 2007)

!.1.~ ____ 1.5H mln.------J

Tree Stumps

Mineral Soil

Ice-rich Soil and Lenses T

Granular Embankment

a. Initial frozen cut profile.

\ "' \ \ Sparse- Grass Stond " \ on Stable Slope \ /

b. End of first thaw season. Slope is mostly unstable and very unsightly; ditch will require cleaning if massive ice is present.

Grosses, Ftreweed Birch and WI !tow Trees

c. End of fifth or sixth thaw season. Slope stabilizes with reduced thaw and vegetation established. Free water from minimal thawing is used by plants whose root systems develop new organic material.

(7.a) Idealized Development of Stability in Ice Rich Cut (after Berg and Smith, 1976)

II/ITIAL 1:\JI" AIlD 'IRE~ RD«lVAL

------

!lID nr nfiH OR SIXIH lHo\W Su.soY

SI:FARATION BEAll SEPARATION BEAll WITH IIITI!RIIAL DRUIIo\m

(7.b) Modification to Rooney Approach (after McHattie, 2008)

Figure 7 Near Vertical Cutslopes with a Widened Ditch Section

Figure 8 Photo. Trees felled (cut) at the Top of a Near Vertical Cutslope in Permafrost. (from ADOT&PF file)

Figure 9 Photo. Natural Vegetation Restores Thermal Equilibrium of a Cut Slope after Several Years (from ADOT&PF file)

Figure 10 Photo. Site Overview of Sections I, II, and III in Foreground and Sections IV and V in Background August 22, 1973 (after APSC 1974).

II i. III Urea formal bc:elsior i'-It. Excelsior Blan~et dehydeFoam BI

IV V ..... Ur-ea Fo:rmiillidehyde Foam 0 Control ~ InsuJati,on I Dyne! Fabric: 1- 2f, over Sand Riter e:: ~

Figure 11 Photo. Four Test Sections and Control Section at Thermal Erosion Test Site, Hess Creek, Alaska (after APSC 1974).

Figure 12 Photo. Completed Application of Urea Formaldehyde on Section I, July 26, 1973 (after APSC 1974).

Figure 13 Photo. Thermal Erosion Induced Flow Material at Toe of Slope on Sections I and II, August 22, 1973 (after APSC 1974).

Figure 14 Photo. Thawed Material Soaking through Cloth Sections and Accumulation of Flow Material on Section III, August 2, 1973 (after APSC 1974).

Figure 15 Photo. Mass Flow Pulling Excelsior Downslope on Repaired Section III, August 22, 1973 (after APSC 1974).

Figure 16 Figure. Sand and Gravel layer with Insulation at an Ice-Rich Cut (after Claridge and Mirza(6)). The system protects the slope from thermal and hydraulic erosion. The sand and gravel layer reduces the rate of thaw and facilitates drainage and thaw consolidation.

(17.a) Kotzebue runway in September 2005; the hill in the center of the photograph extends into the glidepath of aircraft. Severely eroded areas are clearly visible.

(17.b) April 2006 - The top of a hill that extended into the aircraft glidepath was excavated to improve the approach to the runway. Synthetic matting (center brown areas) was placed on exposed permafrost to retard thaw and erosion and promote stabilizing plant growth. An excavated permafrost disposal containment area is shown in the upper right corner of the photograph (ref. Figure 19a).

(17.c) April 2006 - The synthetic mat is rolled on the exposed cut surface.

(17.d) April 2006 –The mat rolls are overlapped approximately 30 cm (1 ft)

(17.e) April 2006 –The mats are secured with pins driven into the underlying permafrost.

(17.f) April 2006 – Pins used to secure mats; pins were bent in “hard” permafrost.

(17.g) April 2006 –Mat placement nearing completion; the runway is visible in the background.

(17.h) August 2006 – Vegetation in the matted area appears to be well established.

(17.i) August 2006 – Bare spots are visible but overall the revegetation of the area appears to be successful.

(17.j) August 2006 – A drainage ravine is lined to prevent further erosion.

Figure 17 Photo. Kotzebue Runway Improvement - April through August 2006 (from ADOT&PF file courtesy of S. Lamont).

(18.a) Overview of containment berm for thawing permafrost.

(18.b) Closeup of excavated frozen gravel.

Figure 18 Photo. Containment Structure for Excavated Permafrost on the North Slope of Alaska (from ADOT&PF file courtesy of G. Griffin)

(19.a) Snow berm surrounding right side of ice-rich permafrost disposal pile (ref. upper right of photograph (17.b)). Pickup trucks at the bottom and a track hoe at the top of the embankment provide scale.

(19.b) April 2006 - Close-up view of newly placed snow berm and excavated ice-rich permafrost behind snow berm

(19.c) April 2006 - Close-up view of snow berm and “blocky” character of excavated permafrost. The snow berm at this location is approximately 2 m (7 ft) in height. The “snow” berm is composed of snow plus miscellaneous vegetation, soil and rock detritus unavoidably included as the snow is collected.

(19.d) Berm at the beginning of spring thaw. Vegetation collects in the berm when the snow is “pushed up”. The organic debris remains as the snow melts.

(19.e) May 2006 - Organic material contained in snow berm that remains after spring thaw.

(19.f) August 2006 - Vegetation growth on disposal pile.

Figure 19. Photo. During wintertime excavation of ice-rich materials in western Alaska, nearby snow may be the only material available that can be piled up to provide retainment for excavated permafrost. Photographs 19.a, b, and c show the newly constructed snow berm. Photographs 19.d and e show the berm after it progressed through spring and summer thawing. The vegetative matter in the berm is exposed and remains as the snow thaws. During thaw, the increasingly exposed vegetation and other non- snow materials helps shade and insulate the underlying remaining frozen berm. The retained permafrost stayed in place as it thawed suggesting the berm may not have been necessary (from ADOT&PF file courtesy of S. Lamont).

(20.a) Forest fire in a permafrost environment. Degrading permafrost is clearly visible

(20.b) Severe erosion has resulted in the past from bulldozer-constructed firelines, termed “catlines” in permafrost terrain (right center in photograph).

(20.c) The proximity of the forest fire to the road may result in serious thaw sediment deposition in the drainage ditches and flow into adjacent drainages and streams.

Figure 20 Photo. Forest Fire in a Permafrost Environment (courtesy of A. Scott).