TABLE OF CONTENTS

Abstract ...... 2

1 Introduction...... 2 1.1 Purpose...... 3 1.2 Background and Choosing the Study Sites...... 3 1.3 Scope...... 4

2 Instrumentation...... 5 2.1 Sondex...... 5 2.2 Subsurface Level...... 6 2.3 Surface points...... 6 2.4 Slope inclinometer...... 7

3 Construction...... 8

4 Measurements...... 9 4.1 Sondex...... 9 4.2 Subsurface Level...... 10 4.3 Surface Points...... 11 4.5 Slope Indicator ...... 12

5 Conclusions ...... 13

6 Recommendations ...... 15

FIGURES ...... 16

1 PERMAFROST STABILIZATION

FINAL REPORT

Abstract

The purpose of this study was to measure the deformation of two embankments in areas known for settlement and cracking. Two sites were chosen on Goldstream Road near Fairbanks Alaska for installation of several different types of movement measurement instrumentation, some of which were experimental. The movements were measured over a three year period. The results of the study show that both road sections had both relative vertical movement and lateral spreading. The total relative movements were on the order of ½ inch. It is hypothesized that these movements were a function of thawing permafrost and frost heaving and thaw weakening. If this is true, it is suggested that the proper use of geosynthetics would significantly improve the road performance. Conclusions are also drawn relative to the accuracy and applicability of the various instruments used.

1 Introduction

Roads in Interior Alaska are noted for distorting over time. Many of the road surfaces undulate in all directions and separate leaving longitudinal cracks, typically down the outside wheel path. Numerous attempts have been made to alleviate this problem, generally with minimal success. The problems are caused by a combination of factors including: · frost heaving, · thaw settlement, · a general migration of materials due to frost heaving and thaw weakening, · consolidation of compressible materials and, · creep of the sub-grade soils.

Although the general mechanisms are of distress are known (at least we think we know them), it is not easy to pinpoint the relative importance under many circumstances and the general shape

2 of the deformed embankment is not known under most circumstances. In order to effectively design remedial measures it would be helpful to understand the mode of failure of the roads.

1.1 Purpose

The purpose of this study was to instrument several sites to measure the shape of the road section as it distorted over time.

1.2 Background and Choosing the Study Sites

This study was considered a high priority by the AKDOT&PF Research board in 1993. In 1994 the AKDOT&PF Research Director became aware of a water level instrument developed by a small company in Oregon used by the US Forest Service to measure the vertical movements under test logging roads. This instrument coupled with horizontal Sondex casings, Slope Indicators casings and surface measurements could provided us with the needed information about movement of the roads.

During this time, the eastern half of Goldstream Rd. was being remodeled and an opportunity developed to have the contractor install the instrumentation. Bob McHattie (AKDOT&PF) and Tom Kinney (University of Alaska Fairbanks) choose two sites on June 6, 1994. One was at about station 542, which is about 1/4 mile east of Bucks Rd. The second site was at about station 770, which is about 1/4 mile west of Goldstream Creek. The sites were chosen because each contained the following key elements: · the site was fairly uniform with respect to section and performance over a distance of several hundred feet, · the site was typical of a low fill road construction in the Interior, · the road had shown signs of significant undulations and lateral spreading recently, · the site was scheduled to be reconstructed using a fairly standard approach, i.e., a small amount of excavation and reconstruction without special materials or construction techniques and,

3 · the site was in a relatively straight section of the road with adequate sight distance for safety.

The installation was supposed to be completed in August 1994 and the road paved that fall so the readings could start in the fall of 1994. Construction was behind schedule and the final grading of the embankments was not completed until the spring of 1995. This left the instruments half installed and very vulnerable to traffic, snow plows, and graders between the time of the initial in 1994 installation and the time construction was finished in 1995.

1.3 Scope

The scope of this study consisted of assisting in installing instrumentation at two sites on Goldstream Rd. just north of Fairbanks, Alaska, monitoring the sites over several years, and summarizing the findings.

4 2 Instrumentation

Instrumentation at each site consisted of: · three horizontal Sondex casings, · three horizontal level measurement instrument casings, · two vertical slope inclinometer casings and, · a series of markers installed on the surface to measure vertical and lateral movement. It was the intent to install thermocouples on the horizontal subsurface level casing but the proper wire could not be obtained in time for the proper installation.

The horizontal subsurface instruments were constructed by digging a trench in the road after the reconstructed embankment had been completed, but before the base and asphalt was installed. The trench went to the bottom of the original road embankment. The instrument casings were set at three elevations within the road prism, as the trench was back filled. The ends of the casings were supported and the other instrumentation was installed after the road construction was completed. Cross sections are shown through the embankments in Figures 1 and 2.

2.1 Sondex

A Sondex is a magnetic instrument that senses the location of a steel band around the casing it is pulled through. For the Sondex 4-inch corrugated plastic casings with steel rings placed at 3-foot intervals by the manufacturer were used. The instrument was pulled through the casing with a rope until the sensor indicated the presence of a steel ring. The location of the ring was then measured by a measuring tape attached to the instrument. The corrugated casing was placed in the soil and stretched or compressed along with the surrounding soil. By measuring the locations of the rings it is possible to measure the stretch and/or compression of the soil in the direction of the casing. The accuracy is typically in the order of a few tenths of an inch at each ring.

The locations of the rings on the Sondex casing were measured prior to installation and they were 3 feet apart (within 1/8 inch). The rope was placed through the casing prior to installation

5 in the field. Sondex casings were placed horizontally at three depths in each section as shown on the cross sections, Figures 1 and 2.

2.2 Subsurface Level

The Subsurface level was a special purpose (unnamed) device developed for the US Forrest Service to study the performance of their logging roads. The instrument is essentially a very accurate pressure transducer attached to a water hose and electrical cables. The pressure transducer is pulled through a tube. The other end of the water hose is set at a constant level above, and outside, the project area. The relative elevation is measured between the constant end of the hose and the pressure transducer. When the instrument arrived, it was checked in the laboratory and found capable of measuring differences in elevation of less than 0.1 inches over a distance of 100 feet. The recommended tube was a 1-inch inside diameter double steel reinforced hydraulic hose. A rope to pull the instrument was put through the tube prior to installation.

2.3 Surface points

PK nails were driven into the surface of the asphalt on 1 foot centers from the centerline to 15 feet each side, which is near the pavement edge. In addition, steel Ts were driven into the slope in about 5-foot intervals. The Ts were constructed of a 1 inch square steel box section three feet long with a 2 feet long 1-1/2-inch angle welded at 90 degrees and about 1 inch below the top of the box section. A hole was drilled in the center of the horizontal portion of the angle to assure constancy in reading location. The Ts were driven into the ground until the crossbar rested firmly on the ground surface. It was the intent that if the Ts ever frost jacked they could be re- tapped to their original location. A vertical reference point on a large tree was established near one end of each test section.

The horizontal locations of the PK nails were measured with a glass measuring tape. These measurements are generally reproducible to within about 0.05 inches in the width of the road. The primary impediment to accuracy is the elasticity of the tape and the need for a constant tension while reading. The horizontal distances to the Ts was measured with a the glass tape and

6 a plumb bob. These readings were reproducible to within about 0.2 inches. The vertical readings on both the PK nails and the Ts were measured with a surveyor's level. Reproducibility of these readings was about 0.02 inches.

A few PK nails were hit by snowplows and destroyed. Even more T's were hit by graders while plowing snow on the embankments just prior to spring breakup. Moved points were not relocated.

2.4 Slope inclinometer

A slope inclinometer is an instrument which measures the amount it is off-plumb at several locations as it is lowered down a special casing. The slope inclinometer is lowered down the casing and stopped at regular intervals to measure the amount out of plumb. By integrating the measurements over the measurement interval it is possible to get the shape of the casing. Movement is detected by comparing the measured shape at two different times. The measurements are generally considered to be accurate to about 1 inch horizontally in 100 feet.

Thirty-foot long slope inclinometer casings were installed vertically on each side of the road at each site. Arctic Alaska Testing Labs under contract with AKDOT&PF drilled the borings and installed the casings on July 19, 995. The casings were set in concrete sand, which was washed and vibrated into place. The AKDOT&PF Digitilt was used for all measurements. A Digitilt is a slope inclinometer made by the Slope Indicator Company.

7 3 Construction

The sites at stations 770 and 542 were constructed on August 18 and 19 1994, respectively. The construction techniques were virtually identical for each site. A trench about 5 feet wide was excavated through the fill. The bottom was leveled by hand with the aid of a laser level. In general, the road fill consisted of dredge tailings, which is a very random mixture of materials from 6-inch rock to silt. Generally it has a course broken rock appearance with a nearly full matrix on smaller particles. The bottom of the trench was just below the bottom of the fill, which was in black fibrous peat at both sections.

The Sondex casings and the hydraulic hose were set in the trench about 6 inches apart and held in place with hand placed fill material. Next, a layer of fill was placed several inches over and around the casings by hand. Large particles were avoided in this bedding material, however, particles in excess of 1-1/2 inch were common. Once this was completed, the trench was filled to the next instrument string location. The fill was placed with a front end loader and compacted by hand operated vibratory compactors in about 12-inch lifts. The fill stopped with the embankment fill because this was as far as construction of the road had progresses at that point in the construction project.

The lower casings would exit the fill below the surrounding ground hence the casings were curved gently to the surface out past the tow of the embankment. The casings and wires were coiled up where they exited the ground and were protected with plastic and timber markers to protect them from future construction.

The rest of the installation was completed in the spring of 1995, after final fill placement, grading and paving had been completed. A wooden platform was constructed on each end to support the casings and wires and to provide a firm location for measurements. The ends of the casings and wires were encased in a wooden box with a latch on it for protection. The PK nails, Ts and Slope Indicator casings were also installed in the spring of 1995.

8 4 Measurements

Measurements were taken as described below between the early summer of 1995 and the fall of 1997. The readings result in two types of conclusions. The first relates to the viability of different types of instrumentation and the other relates to the performance of the embankment.

4.1 Sondex

An attempt was made to read the Sondex casings in the early summer of 1995 when the other instrumentation was installed. However, none of the ropes could be moved. After considerable effort is was discovered that the upper Sondex casings had collapsed and the lower ones were full of water and frozen. An attempt was made to thaw them using a 12 volt electric heater but it was not successful.

Attempts were made to read the Sondex casings on several occasions throughout the following years. It was found that the upper and lower casings at each site were crushed or otherwise blocked during installation. The middle casing at each site was open but wasn't free of frost until mid summer. The bottom casing was frozen throughout the reading period.

The best set of measurements from each section is shown on Figure 3. The horizontal axis is the distance of the point from the centerline of the road and the vertical axis shows the total amount the casing has stretched or compressed from the centerline. From the best set of data, it appears that the measured displacement could be at least an inch from the actual. From both sets of data it appears that the north side of the embankment is compressing slightly and the south side is stretching. The data from Station 542 considers a little less than one year of movement and the data from Station 770 considers a little less than two years. There does indeed appear to be more movement at Station 770 than at Station 542. Although these trends make sense we are not convinced that the data is accurate enough for our purpose.

9 4.2 Subsurface Level

It was impossible to pull the level instrument through any of the hoses more than a few feet. Upon further checking, it was found that the instrument had never been pulled more than 30 feet in any previous installation and that was through a hose, which was stretched tight during installation. In the laboratory we found that the tension needed to pull the instrument through the hose increased dramatically with distance and any curvature in the hose made it much more difficult.

Several different schemes were tried, including pushing and pulling with several different materials and filling the hose with a lubricant first, but all were unsuccessful. Next, an attempt was made to weight the instrument and drag it through the open Sondex casings in such a way that it would be on the low point of the casing at all times. During this time, the instrument ceased to work and was sent back to the manufacturer. The manufacturer indicated that the instrument had moisture in the electronics. In addition they indicated there was no way to dry it out and it would have to be replaced. In addition, if it were replaced there was no way to make the new one moisture resistant. Replacement would have been very costly and time consuming. The instrument was never retrieved from the manufacturer.

There are two important conclusions to be drawn from these experiences. The first is to check any experimental instrumentation careful in the exact environment it is to be used in before trying to use it. This instrument had been used to measure the vertical deformation within logging roads which is a very similar situation. It had not been used in a damp environment or in an installation over 30 feet long. The second lesson is to fully recognize the problems associated with pulling anything through a small diameter tube. It is very difficult and the degree of difficulty increases rapidly with curvature and length. Attempts to push the instrument with a thin rod were equally unsuccessful.

10 4.3 Surface Points

The surface points were measured several times each year. Typical data is shown on Figures 4 though 11. The first four figures show data for Station 542 and the second four show data for Station 770. Within each set of four, the first two figures show relative vertical movement from the centerline and the second two show lateral spreading from the centerline. The first of each pair of figures shows the data to 50 feet on each side of centerline and the second shows data on the pavement, i.e., 15 feet on each side of centerline.

Several things became obvious regarding the measurements. · Trees are not very good Arctic benchmarks. The absolute measurements based on the benchmarks are not meaningful hence all vertical data was reduced to relative information from road centerline. · Both the vertical and horizontal measurements from the Ts have significant scatter (Figures 4,6,8, and 10). Unfortunately, it is not obvious whether the scatter is due to inaccuracies in measurements, movement of the Ts, or movement of the ground surface.

Station 542 - Figure 5 indicates that the edges of the pavement surface settled in the order of ½ in. relative to the centerline in two years. Figure 4 indicates the embankment on the south side of the road is probably settling relative to the centerline but the road is probably settling relative to the embankment on the north side.

Figure 7 indicates lateral spreading of the pavement surface on the order of 1.5 inches on each side of the centerline during the same two-year period. Figure 6 indicates that the portion of the embankment just outside the road is stretching relative the centerline but that the toe of the embankment is probably being compressed.

Station 770 - Figure 9 indicates the south half of the road has settled about 1/2 inch relative to the centerline while the centerline has settled about ¼ in. relative to the north half of the road. Figure 8 indicates that the entire embankment is tipping to the south at roughly the same angle as

11 the road surface. There is a possibility that the north drainage ditch is settling relative to the centerline.

Figure 11 indicates that the south half of the road stretched about 1-1/2 in. while the north half did not stretch over the same period. Figure 10 is not definitive regarding the stretch of the embankment. It would appear that there is more movement of the Ts than there is of the embankment.

4.5 Slope Indicator

The slope indicators were read several times per year. For various reasons, some of the readings were more accurate than others. One problem was that the casings were broken off several times during the study leaving the instrument reference point at different levels. Since readings were made every foot and the casings were not vertical, a difference of 6 to 9 inches in elevation makes a significant difference in the results. The most consistent readings have been shown on Figures 12 through 15. The slope indicator readings show consistently less than 1/2 inch of lateral movement of the road edges

In addition, the slope indicators show a considerable amount of disturbance at a depth of about 15 to 20 feet. This is about the depth of the permafrost, which could indicate either that the permafrost is thawing and causing the slope inclinometer casing to buckle or that the permafrost is creeping. In the author's opinion, the first explanation is the more plausible one because of the fairly random shape of the disturbance.

12 5 Conclusions

Two different types of conclusions can be drawn from this study. The first deals with the topic of the study, e.g., the movement of the embankment. The second deals with the instrumentation used in the study.

Regarding embankment movement The purpose of the study was to measure the deforming shape of the road as it settled and spread apart. The lateral spreading from of the road surface is shown below as it was estimated from the three kinds of lateral spreading data. The slope inclinometer consistently shows less movement than the surface nails and the Sondex is not consistent with the other methods of measurement in either magnitude or direction. It is the authors opinion that the surface nails yield the most accurate results. It is reasonable that there was an inch or so of lateral spreading in the first year or two. This is in good agreement with previous research conducted for DOT/PF on a similar topic several years ago.

Slope Indicator Surface Nails Sondex Location Stretch Figure Stretch Figure Stretch Figure Sta. 542 North 0.4 12 1.4 6 -2 3 Sta. 542 South 0.4 13 1.4 6 1 3 Sta. 770 North 0.6 14 0.4 11 -1 3 Sta. 770 South 0.3 15 1.7 11 3 3 Table 1 - Lateral spreading of the road surface between 1995 and 1997.

From reviewing the vertical surface movement measurements based on the nails and Ts it became obvious that benchmarks, e.g. large trees, move throughout the year. In order for these data to be meaningful all the data had to be normalized to some point. Since there was a lot of variability and perhaps movement on the Ts, the most logical point was the nail on the centerline of the road. These measurements as shown on Figures 4 and 8 do show the differential movement felt by cars on the road but do not show total movement which would be helpful in

13 terms of determining the absolute vertical movement which may lead to the mechanics causing movement.

Based on the data shown which assumes the centerline does not move, it appears that the south side of the road at each section is going down on the order of 1/4 inch per year. The north side appears to be going down a similar amount on section 542 but up at station 770. It is also possible that the entire road is settling but the measurements from the Ts are not accurate enough to draw this conclusion with such small total movement.

Regarding instrumentation Several things were learned about instrumentation which should be remembered in future projects. · It is necessary to install an arctic benchmark for meaningful results. · It is difficult to measure to Ts driven into the ground. Although the method seems reasonable the results are questionable. · The PK nails appear to work well. · The underground level tried in this study did not work in this environment due to problems with pulling the instrument through tight quarters and moisture in the electronics. · Sondex measurements are not accurate enough unless several inches of stretching or compression are achieved. In addition, care must be exercised in installing the Sondex casings and ice in the casing is a serious problem.

14 6 Recommendations

This study would have been best done using a combination of vertical and horizontal slope inclinometers and vertical Sondex casings in conjunction with surface measurements. If horizontal casings are to be used they should be heat-traced and there should be some practical way developed of removing moisture.

In the author's opinion, both of these road sites are failing because of thawing permafrost and a steady migration of soils to the south cause by cyclic freezing and thawing. This is probably a very common combination of factors. Geosynthetics could be used effectively to limit the lateral spreading which would also reduce the vertical deformation and dramatically increase the useful life of the pavement system. The author has not seen a practical way to solve the thawing permafrost problem. The two most reasonable scenarios involve construction with open graded materials to get the air convection and the use of snow sheds. Planting trees along the south border and using aggressive snow removal in the critical areas could also be used to benefit the road performance.

15 FIGURES

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Figure 1 - Goldstream Rd Sta. 542 - Cross Section

110 North North Inclinometer South Inclinometer South 105 2 ft below surface

100 4 ft below surface

7.7 ft below surface 95

Clayey, silty, sandy GRAVEL Black Fiberous Peat 90 with cobbles to 8" (weathered schist tailings)

85

Elevation - ft 80

75

70

Ground Surface Slope indicator Top instrument casings 65 Middle instrument casings Bottom instrument casings Bottom of embankment

60 -60 -45 -30 -15 0 15 30 45 60 Distance from CL of road - ft. Figure 2 - Goldstream Rd Sta. 770 - Cross Section

110

105 North Inclinometer South Inclinometer

North South 100

3 ft below surface 95 7 ft below surface

90 11.5 ft below surface

85 Clayey, silty, sandy GRAVEL with cobbles to 8" (weathered schist tailings) Black Fiberous Peat

Elevation - ft 80

75

70

Ground Surface Slope indicator Top instrument casings 65 Middle instrument casings Bottom instrument casings Bottom of embankment Top of permafrost 60 -60 -45 -30 -15 0 15 30 45 60 Distance from CL of road - ft. Figure 3 - Goldstream Rd. - Sondex Data 10

Sta 770 - 5/16/97

Sec 542 - 6/14/96 R2 = 0.8677 Poly. (Sta 770 - 5/16/97) 5 Poly. (Sec 542 - 6/14/96)

0

R2 = 0.7204

-5 Stretch of casing from CL - in.

South North

-10 -40 -30 -20 -10 0 10 20 30 40 Distance from C - ft.L Figure 4 - Goldstream Rd. Sta 542 - Vertical Movement of Surface

2.00

South North 1.50

1.00

0.50

0.00

-0.50 6/24/96

8/29/96 -1.00 5/16/97 Relative movement from 5/25/95 - in

6/17/97 -1.50 8/29/97

-2.00 -50 -40 -30 -20 -10 0 10 20 30 40 50 Distance from CL - ft. Figure 5 - Goldstream Rd. Sta 542 - Vertical Movement of Paved Surface 1.0 South North 0.8

0.6

0.4

0.2

0.0

-0.2 6/24/96 8/29/96 -0.4 Movement from 5/25/95 - in 5/16/97

6/17/97 -0.6 8/29/97 -0.8

-1.0 -15 -10 -5 0 5 10 15 Distance from CL - ft. Figure 6 - Goldstream Rd. Sta. 542 - Lateral Spreading of Surface

3.0 South North 2.5

2.0

1.5

1.0

0.5

0.0

11/22/95 -0.5 Spreading from 5/25/95 - in. 6/24/96 8/29/96 -1.0 5/16/97 6/17/97 -1.5 8/29/97

-2.0 -50 -40 -30 -20 -10 0 10 20 30 40 50 Distance from CL - ft. Figure 7 - Goldstream Rd. Sta. 542 - Lateral Spreading of Paved Surface 2.0

South North 11/22/95 6/24/96 1.5 8/29/96 5/16/97 6/17/97 1.0 8/29/97

0.5

0.0 Spreading from 5/25/95 - in.

-0.5

-1.0 -15 -10 -5 0 5 10 15 Distance from CL - ft. Figure 8 - Goldstream Rd. Sta. 770 - Vertical Movement of Surface Distance from CL - ft -50 -40 -30 -20 -10 0 10 20 30 40 50 -1.0

South North

-0.5

0.0

0.5 6/24/96

8/29/96

1.0 5/16/97

Movement from11/14/95 - in 6/17/97

8/29/97 1.5

2.0 Figure 9 - Goldstream Rd. Sta. 770 - Vertical Movement of Paved Surface

Distance from CL - ft -15 -10 -5 0 5 10 15 -0.5 South North -0.4

-0.3

-0.2

-0.1

0.0

0.1 6/24/96

0.2 8/29/96 Movement from11/14/95 - in 5/16/97 0.3 6/17/97

0.4 8/29/97

0.5 Figure 10 - Goldstream Rd. Sta 770 - Lateral Spreading of Surface

10

South 11/22/95 North 8 6/24/96

6 8/29/96 5/16/97 4 6/17/97

8/29/97 2

0

-2

-4 Spreading from 5/25/95 - in

-6

-8

-10 -50 -40 -30 -20 -10 0 10 20 30 40 50 Distance from CL - ft. Figure 11 - Goldstream Rd. Sta 770 - Spreading of Paved Surface

2.0 South North 11/22/95

1.5 6/24/96

8/29/96

5/16/97 1.0 6/17/97

8/29/97

0.5

0.0 Spreading from 5/25/95 - in

-0.5

-1.0 -15 -10 -5 0 5 10 15 Distance from CL - ft. Figure 12 - Goldstream Rd. Sta. 542 North Slope Indicator Deflection from initial readings on 10/18/95 - in -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0

North/East South/West

9/7/96 - Downslope

9/7/96 - Along CL 5 8/28/97 - Downslope

8/28/97 - Along CL

10

15 Depth - ft.

20

25

30 Figure 13 - Goldstream Rd. Sta 542 South Slope Indicator

Deflection from initial readings on 10/18/95 - in. -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0

North/East South/West

9/7/96 - Downslope

9/7/96 - Along CL 5 8/28/97 - Downslope

8/28/97 - Along CL

10

15 Depth - ft.

20

25

30 Figure 14 - Goldstream Rd. Sta 770 North Slope Indicator

Displacement relative to initial reading on 8/10/95 - in. -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0

South/West North/East

10/18/95 - Downslope

10/18/95 - Along CL

5 9/7/96 - Downslope 9/7/96 - Along CL

8/29/97 - Downslope

8/29/97 - Along CL

10

15 Depth - ft.

20

25

30 Figure 15 - Goldstream Rd. Sta 770 South Slope Indicator Deflection relative to initial readings on 8/29/95 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0

North/East South/West

10/18/95 - Downslope

10/18/95 - Along CL

5 9/17/96 - Downslope 9/17/96 - Along CL

8/28/97 - Downslope

8/28/97 - Along CL

10

15 Depth ft.

20

25

30