GR01-16_Glenn_Highway_West_Chickaloon_Grade.pdf

Geotechnical Report No. 01-16

Glenn Highway – West Chickaloon Grade Final Geotechnical Recommendation Report

AK DOT 135(5)

Matanuska-Susitna Borough, Alaska March 2016

Table of Contents

1 INTRODUCTION

1.1 Geotechnical Scope of Work

1.2 Previous and Other Geotechnical Work

2 HIGHWAY CORRIDOR SETTING

2.1 Topography, Climate, Vegetation, Geology, Seismicity, and Permafrost Areas 5

3 GEOTECHNICAL INVESTIGATION

3.1 Field Reconnaissance Visits

3.2 Subsurface Investigation

3.2.1 Subgrade Boring, Test Pits, and Geotechnical Test Borings

3.2.2 Geophysical Surveys

3.2.3 Drill Equipment, Hole Logging, and Test Boring Descriptions

3.3 Laboratory Testing

3.4 Test Boring Instrumentation and Equipment

4 GENERAL SITE CONDITIONS

4.1 Proposed Highway

4.2 Existing Highway

4.3 Subsurface Materials

4.4 Groundwater

5 GEOTECHNICAL ANALYSES AND RECOMMENDATIONS

5.1 Anticipated Roadway Excavation Uses

5.1.1 Waste

5.1.2 Hazardous Waste

5.1.3 Roadway Excavation

5.2 Slope Recommendations

5.2.1 Cut Slopes

5.2.5 Rockfall Ditches

5.2.6 Soil Embankment Slopes

6 LIMITATIONS

7 REFERENCES

Appendices

APPENDIX A – Figures APPENDIX B – Geotechnical Test Boring Logs Unified Soil Classification System Soil Descriptive Terminology Rock Descriptive Terms APPENDIX C – Laboratory Test Reports APPENDIX D - Rock Core Photography APPENDIX E – Geophysical Surveys

1 INTRODUCTION

The Glenn Highway project, from approximately MP 66.5 to MP 92, is about 25.5 miles long and includes Restoring, Resurfacing, and Rehabilitating (RRR) the Glenn Highway, from King’s River Bridge (MP 66.5) to Cascade (MP 92), to preserve and extend the service life of the highway and provide safety improvements. The Glenn Highway is considered a major transportation corridor, providing access to interior Alaska and the “Lower 48,” as well as providing a connection between the Anchorage/Wasilla area and Glennallen to the east (Figure 1).

This section of the highway is classified as a rural principle arterial-interstate and the posted speed limit is 55 MPH. The proposed highway typical section will have two 12-foot travel lanes with 6-foot paved shoulders for a total paved width of 36 feet, and the proposed design speed will be 60 MPH.

Alaska Department of Transportation (ADOT&PF) requested that the Western Federal Lands Highway Division (WFL) undertake the NEPA re-evaluation and complete the preliminary alignment and grade design for the King’s River (MP 66.5) to Cascade (MP

92) section of Glenn Highway. As funding has been approved within this 25.5 mile long corridor to advance projects, ADOT&PF has further requested WFL to deliver design plans, specifications, and estimate packages for contracting through a design, bid, build process, as well as provide construction support services for the Chickaloon River Bridge Replacement and the West Chickaloon Grade projects between MP 77.4 and 78.2 (Figure 2). The Chickaloon River Bridge construction began in summer 2015 and will be completed in Fall 2016. The West Chickaloon Grade was selected as the second priority in the highway corridor because the new Chickaloon River Bridge was built approximately 50 feet upstream of the existing bridge and requires a sharp curve at reduced speeds to exit and reenter the existing highway alignment. The West Chickaloon Grade project proposes to shift the highway alignment to better align with the new bridge configuration as soon as feasible following the opening of the new Chickaloon River Bridge for traffic.

1.1 Geotechnical Scope of Work

This report describes the data gathering procedures and presents the results of the geotechnical investigation, laboratory testing, instrumentation monitoring, geophysical surveys, and analyses. This information was used to provide final geotechnical highway cut and embankment design and construction recommendations within the Glenn Highway – West Chickaloon Grade project limits from approximately mainline Station 10083+60 to 10127+14 (Figures 3 through 6) as contained in this report.

The primary objectives of the geotechnical work were to characterize surface exposures and subsurface soil, rock, and groundwater conditions to support the large highway cut and embankment design and construction considerations and to determine potential uses of the roadway excavation from the cut for embankment construction. This work also provided an estimated area of impact for the proposed highway shift into the hillside.

Other geotechnical, materials, and environmental spill response related work within the project limits of the West Chickaloon Grade project are presented under separate cover, and include the seismic refraction study for the South Chickaloon Cut, the approach wall designs for the new Chickaloon River Bridge, a fuel spill response near MP 77.8 in October 2010, existing pavement evaluation and proposed pavement recommendations, and preliminary geotechnical recommendations for the Glenn Highway from approximately MP 66.5 to 84. The citations for these reports and memoranda are presented in the following section.

Final geotechnical recommendations presented in this report are solely based on site observations, subsurface investigations and instrumentation, geophysical surveys, material testing, and geotechnical analyses.

Plans, profiles, and cross-sections provided as part of the 70% plan-in-hand design review, dated December 12, 2015, were used in the preparation of this geotechnical report. This geotechnical report and those reports listed in the following section should be made available to prospective bidders.

1.2 Previous and Other Geotechnical Work

Information related to previous geotechnical related work within this section of the Glenn Highway, near the Chickaloon River Bridge, is included in the following reports and memoranda:

• Geotechnical Report No. 17-15, Geophysical Report for South Chickaloon Cut, AKDOT 135(3) Glenn Highway: Chickaloon Grade MP 77-79, Matanuska-Susitna Borough, Chickaloon, Alaska, prepared by Shannon & Wilson, Inc. through David Evans & Associates, Inc., November 2015.

• Geotechnical Report No. 10-14, Preliminary Geotechnical Recommendation Report, AK DOT 135(1) Matanuska-Susitna Borough, Alaska, prepared by WFL Geotechnical Section, December 2014.

• Geotechnical Report No. 07-14, Glenn Highway, Chickaloon River Bridge Final Foundation Report, AK DOT 135(2), Matanuska-Susitna Borough, Alaska, prepared by WFL Geotechnical Section, December 2014.

• Materials Memorandum, Initial Structural Pavement Recommendation, Glenn Highway Corridor MP 66.5 to MP 92, AK DOT 135(1), prepared by WFL Materials Section, July 9, 2014.

• Materials Report, Glenn Highway, Pavement Evaluation Report, prepared by WFL Materials Section, December 2013.

• Phase II Environmental Site Assessment / Release Investigation, Milepost 77 Glenn Highway, Chickaloon Alaska, prepared by Alaska Resources and Environmental Services, LLC for Big State Logistics, Inc., March 2011.

2 HIGHWAY CORRIDOR SETTING

2.1 Topography, Climate, Vegetation, Geology, Seismicity, and Permafrost Areas The topography, climate, vegetation, geology, seismicity, and susceptibility to permafrost are well documented for the Glenn Highway between MP 66.5 and 84 in Geotechnical Report No. 10-14 and should be referred to for such information.

3 GEOTECHNICAL INVESTIGATION

The geotechnical investigation consisted of reviewing previous geotechnical investigations and work within the West Chickaloon Grade project limits, published geologic maps, and other relevant geotechnical related documents.

In addition to the literature review, several field reconnaissance visits were conducted between 2013 and 2015 within the highway corridor. For the West Chickaloon Grade section, they included describing the extent of the different geologic materials and presence of groundwater, assessing potential material uses for the road cut material, evaluating existing roadway conditions, measuring existing slopes and noting their performance, and measuring key rock discontinuities where bedrock is outcropping. The work also included taking site photographs, interviewing ADOT&PF maintenance about highway cut rockfall/landslide events, and planning a geotechnical investigation.

To augment field observations, three test pits adjacent to the existing highway near subgrade boring SG-23 were dug, six test borings associated with the bridge foundation and approach design were advanced, and three more difficult access test borings were advanced atop the proposed South Chickaloon highway cut. The three test borings advanced atop the South Chickaloon Cut had downhole geophysical surveys conducted when rock was encountered. Additionally, a seismic refraction survey was completed to determine the thickness of the predominant soil layers over bedrock in the hillside to support development of the final highway cut recommendations contained in this report.

3.1 Field Reconnaissance Visits

During several site visits in the corridor between 2013 and 2015, the West Chickaloon Grade and specifically the South Chickaloon Cut were visited to determine the proposed line and grade for the new Chickaloon River Bridge alignment and to determine what the potential right-of-way needs would be for the large highway cut to the south of the new bridge.

Differing geologic materials were identified, described, and delineated for preliminary slope recommendations, the presence of groundwater, springs or seeps, and the anticipated roadway construction uses for the highway cut materials were documented.

For the exposed Chickaloon Formation rock unit in the existing highway cut between approximately Station 10105+75 and 10113+50, the prevalent rock discontinuities (fractures, faults, or joints in the rock mass) were measured to identify kinematically feasible rock structures (planes, wedges, and topples) to determine a preliminary slope angle and rockfall ditch section.

ADOT&PF Maintenance personnel were also interviewed about the existing highway cut that has been described by ADOT&PF as a rockfall prone slope.

3.2 Subsurface Investigation

3.2.1 Subgrade Boring, Test Pits, and Geotechnical Test Borings One subgrade test boring (SG14-23) was advanced within the West Chickaloon Grade project limits in order to collect subgrade information to characterize the existing pavement structural section and subgrade properties. The subgrade test boring was drilled during the 2014 preliminary geotechnical investigation and is presented in Geotechnical Report No. 10-14. Three test pits were also dug northeast of the bridge to better characterize the existing highway embankment material during the 2015 bridge construction. The subgrade test boring data and test pit laboratory test results were utilized to develop the pavement design recommendations presented in the WFL Materials Memorandum dated July 9, 2014. The test pits were dug at the direction of WFL construction engineers for the sole purpose of gathering embankment subgrade soil samples for testing. No test pit logs were produced as part of this subgrade characterization effort.

An additional nine geotechnical test borings were advanced in order to collect subsurface information for the purpose of characterizing soil, rock, and subsurface groundwater conditions for design and construction considerations for the Chickaloon River Bridge foundations and approach embankment structures and for final design of the South Chickaloon Cut slopes. One vibrating wire piezometer was installed in the South Chickaloon Cut test boring SC15-03vwp to monitor for potential groundwater.

Of the nine geotechnical test borings, six were drilled during the 2014 geotechnical investigation for the new bridge and are presented in Geotechnical Report No. 17-14.

The other three test borings were drilled during the 2015 geotechnical investigation and the test borings are presented in this report in Appendix B with the rock core photography in Appendix D. The test boring logs and rock core photography are presented in the order of increasing project stationing from south to north.

The location of the subgrade boring and test pits were identified by a mapping-grade geographic positioning system (GPS) device. The nine geotechnical test borings from 2014 and 2015 were located by surveyors. The locations of all the test borings and the 2015 test pits are shown in Figures 3 through 6 in Appendix A, and are listed in the table below.

Table 1. Summary of test boring locations for West Chickaloon Grade.

Boring ID Station and Offset

(Feet) Elevation (Feet) What Document are these in?

SC15-01 10102+89, 135.9 LT 974.5 GR01-16

SC15-02 10107+17, 171.5 LT 1015.5 GR01-16

SC15-03vwp 10111+76, 126.9 LT 978.9 GR01-16

CRB14-01 10114+34, 27.9 RT 848.4 GR07-14

CRB14-02 10114+36, 12.4 LT 845.9 GR07-14

CRB14-03 10115+47, 3.8 RT 818.6 GR07-14

CRB14-04 10117+21, 3.9 LT 829.4 GR07-14

CRB14-05 10118+15, 8.9 LT 858.0 GR07-14

CRB14-06 10118+30, 28.3 RT 868.1 GR07-14

SG14-23 10120+16, 27.2 RT 882.4 GR10-14

TP15-01 10120+93, 6.0 LT 882.1 GR01-16

TP15-02 10121+87, 8.0 LT 889.1 GR01-16

TP15-03 10122+93, 8.0 LT 897.7 GR01-16

*Note that station, offsets, and elevations are based on the 100% design plans.

3.2.2 Geophysical Surveys

Two types of geophysical surveys were conducted to better characterize the discontinuities in the bedrock formation and to better understand the distribution of subsurface materials in the South Chickaloon Cut from approximately 10106+00 to 10112+00. The geophysical survey information was used in conjunction with the three 2015 geotechnical test borings (SC15-01, SC15-02, and SC15-03vwp) placed along the top of the South Chickaloon Cut to prepare the earthwork design for the proposed highway cut.

• Downhole Televiewer Survey Downhole televiewer surveys were completed in late-April 2015 by Colog, Inc. through a contract with HazTech Drilling, Inc. in the bedrock portion of test boring SC15-02 and SC15-03vwp. Both, optical and acoustic televiewers were used to conduct the surveys.

The intent of these downhole geophysical surveys is to provide orientations and condition surveys of the rock discontinuities in the rock. The optical televiewer is used when the borehole wall is clear enough to be videoed and rock discontinuities can be measured and assessed visually. The acoustic televiewer is used when the borehole walls cannot be seen through muddy water so they are captured by acoustic reflections from the borehole wall. The optical and acoustic televiewer surveys collect video of the borehole wall survey and capture the depth of the rock discontinuity and the compass direction, orientation, and condition of those discontinuities in each borehole. This discontinuity information is used in combination with rock outcrop orientations (when available) to analyze the kinematic feasibility of rock slope failures and provide design criteria for the rock portion of the proposed highway cut. Colog, Inc. submitted the downhole televiewer survey report for the South Chickaloon Cut on May 8, 2015, and it is provided in Appendix E.

• Seismic Refraction Survey A seismic refraction survey was utilized in conjunction with the 2015 geotechnical test borings to determine the thickness of the soil layers overlying rock in the proposed South Chickaloon Cut. Two seismic refraction survey lines were run parallel to centerline along the top edge of the cut approximately 150 feet from proposed centerline and further back on the hill top approximately 300 feet from the proposed centerline. Additional seismic refraction lines were run normal to the parallel lines at about 50 foot intervals to estimate the depth of soil overlying rock in the proposed highway cut. The geophysical survey work was completed by Shannon & Wilson through a contract with David Evans & Associates. They completed the field work in September 2015 and the geophysical survey report was submitted in November 2015. This report is listed in the previous and other geotechnical work section above, and should be made available to prospective bidders.

When using seismic refraction geophysical surveys, the accuracy for the depths from the ground surface to the interpreted subsurface boundaries are generally accepted to be within 10% of the actual depths. However, due to the presence of some unique ambiguities discovered during this geophysical survey, the accuracy of the interpreted model may be closer to 15% of the depth of the survey.

3.2.3 Drill Equipment, Hole Logging, and Test Boring Descriptions The 2014 geotechnical test borings were completed by the ADOT&PF Statewide drill crews. The subgrade test boring (SG14-23) was advanced with a truck-mounted CME 75 drill rig with a 9.5 inch solid flight auger with a 15 inch bit. The other 2014 test borings for the new Chickaloon River Bridge were advanced with a track-mounted CME 850 equipped with an auto-hammer for standard penetration tests (SPT’s) using air rotary methods with a down-hole hammer and 4-inch casing. When rock was encountered, NQ-sized coring tools were used to retrieve samples.

The 2015 geotechnical test borings were completed by HazTech Drilling, Inc of Meridian, Idaho with a CS1000 componentized drill rig that was incrementally placed by helicopter at the three test boring locations on top of the South Chickaloon Cut. The CS1000 is equipped with a cat head (manual) Standard Penetration Test (SPT) hammer.

SPT’s were completed at 2.5-foot and 5-foot intervals when in soil. The SPT consists of using a 140 pound-hammer with a 30 inch drop to drive a two inch OD split-barrel sampler between 18 and 24 inches below the bottom of the borehole and recording the number of blows for each six inch increment of penetration. The bottom two blow counts for an 18 inch sampler and the middle two blow counts for the 24 inch sampler are added together to determine the blows per foot (bpf), which is known as the field N-value.

Three-inch diameter Shelby samples were also pushed in wet organic soils to collect undisturbed soils samples for specialized laboratory testing. When rock was encountered, wet-rotary methods were used to drill HQ- and NQ-sized core.

The three test pits dug northeast of the new Chickaloon Bridge construction were excavated by a contractor provided track-hoe and construction inspectors collected subsurface samples for laboratory testing. No test pit logs were produced as part of this subsurface investigation.

All test borings in 2014 were logged in the field by an ADOT&PF Geologist from the Central Region in Anchorage, Alaska. The 2015 test borings were logged in the field by a geotechnical engineer from Allwest Testing & Engineering.

Undisturbed Shelby tube samples were driven to the ADOT&PF laboratory in Anchorage for evaluation. They were not tested after evaluation. Disturbed samples were collected and shipped to WFL in Vancouver, Washington, where the samples and draft test boring logs were reviewed by the WFL Engineering Geologist and Geotechnical Engineer assigned to the project. Following review, selected samples of soil and rock were submitted to the WFL Materials Laboratory for testing. The final test boring logs were modified as necessary to reflect additional information from laboratory testing, instrumentation monitoring, and/or refinements to geologic interpretation of subsurface conditions.

The Unified Soil Classification System (USCS) was used to characterize the soil units encountered during the drilling operations. The USCS, as outlined in ASTM 2487 and ASTM 2488, is utilized in the test boring logs and is based on the distribution and behavior of the fine-grained and coarse-grained soil constituents. Soil descriptive terms and the USCS chart are defined and provided at the beginning of Appendix B.

When advancing test borings through bedrock or boulders, continuous rock core was recovered, when possible. Recovered rock core samples were described by the Field Drill Inspector, placed into core boxes, photographed, and transported to the WFL Materials Laboratory for further evaluation. Rock core photography is presented in Appendix D.

A modified International Society of Rock Mechanics (ISRM) set of rock descriptions were utilized to describe the rock unit materials during the drilling operations. Using the ISRM, rock classification consists of two basic assessments; one based on the intact properties of the rock, and the other based on the in-situ properties of the rock mass.

Rock descriptive terms are defined and provided prior to the boring logs at the beginning of Appendix B.

3.3 Laboratory Testing

Laboratory test results were completed for selected soil and rock samples for the 2014 and 2015 test borings. Laboratory testing consisted of soil testing and rock testing to characterize the subsurface materials and to characterize engineering properties of soil and rock that may be encountered during construction. The laboratory test results for the individual 2014 test boring samples are contained in Geotechnical Report 07-14 and 10-

14. Laboratory test results for the three 2015 test pits northeast of Chickaloon River Bridge and the three 2015 geotechnical test borings in the South Chickaloon Cut are presented in Appendix C.

All laboratory testing for the 2015 test pits and geotechnical test borings were conducted at the WFL Materials Laboratory in accordance with appropriate American Association of State Highway and Transportation Officials (AASHTO) and American Society of Testing and Materials (ASTM) test methods. Table 2 lists the test description and methods used for samples selected from the 2015 test pits northeast of the Chickaloon River Bridge and the geotechnical test borings atop the South Chickaloon Cut.

Table 2. South Chickaloon Cut geotechnical test boring laboratory tests.

Laboratory Test Description Testing Method(s) Sieve Analysis AASHTO T 11/T 27

Hydrometer Analysis AASHTO T 88 Plasticity Index (Atterberg Limits) T 89/T 90

Specific Gravity T 100 Uniaxial Compressive Strength T 22

Point load strength (ASTM D 5731) and slake durability index (ASTM D 4644) test results with point load correlations are presented in Geotechnical Report No. 07-14 for some of the sedimentary rock units that make up the Chickaloon Formation and a portion of the South Chickaloon Cut.

3.4 Test Boring Instrumentation and Equipment

Test boring SC15-03vwp is offset to the left of the proposed centerline about 126.9 feet at approximately Station 10111+76. A vibrating wire piezometer was installed in this test boring to monitor for potential groundwater from 40.9 feet below the ground surface and above. Groundwater monitoring information is presented in the Site Conditions section of this report.

Vibrating wire piezometers are used to monitor groundwater levels using pore-water pressure below the ground surface. They are ideal in a cold region since they are attached to a communication cable and grouted into the excavated annulus of the borehole that is protected by a monitoring well monument at the ground surface, alleviating the threat of freezing over the winter in an open-standpipe. Once the grout has cured an automated datalogger is wired to the vibrating wire piezometer cable to take automated, periodic measurements. The datalogger is housed in the locked well monument and can be accessed and connected on-site with a laptop computer to download the groundwater data.

4 GENERAL SITE CONDITIONS

The West Chickaloon Grade project is approximately 0.8 miles long, beginning near MP

77.4 and ending at MP 78.2. This project straddles the new Chickaloon Bridge Replacement that is currently being constructed, and it provides an improved, safer intersection with Chickaloon Road on the southwest side of Chickaloon Bridge (Figures 3 through 6 in Appendix A).

4.1 Proposed Highway

The beginning of the project approaches the South Chickaloon Cut on a roughly 10-foot high embankment section from approximately Station 10083+60 to 10100+50, and diverges northward from the existing highway near Station 10087+00 to align with the new Chickaloon River Bridge. From approximately 10100+50 to 10113+50 the proposed highway alignment shifts northward about 80 feet into the approximately 1300-foot long South Chickaloon Cut with proposed cuts ranging from 120 to 150 feet high (Figure 7 and 8). At about Station 10114+00 the highway intersects with Chickaloon Road before crossing the new Chickaloon River Bridge between about Station 10114+50 and 10118+50 (Figure 9). From the northeast end of the bridge, the proposed alignment begins to shift southward to rejoin the existing Glenn Highway alignment by 10127+14 by shaving-off the top of the existing embankment to the right of proposed centerline and placing minor embankments to the left of centerline (Figure 10). At approximately mainline Station 10114+00, at the mainline intersection with Chickaloon Road, Chickaloon Road will be raised approximately 12 feet to match the new bridge and highway elevation. The reconstruction of Chickaloon Road will take approximately 800 feet of embankment section to match the existing roadway to the northwest (Figure 11).

Generally, the proposed new Glenn Highway alignment and the associated Chickaloon Road intersection work is constructing embankments on fairly well drained gravels and sands and excavating the large highway cut through the hill southwest of the highway intersection with Chickaloon Road to align with new Chickaloon River Bridge.

4.2 Existing Highway

The existing highway is comprised of two 11-foot lanes with 1-foot paved shoulders for a total paved roadway width of 24 feet. The current asphalt surface is generally in moderate to good condition and does not display signs of frost-heave or thaw weakening.

Additional roadway information and recommendations are contained in the 2014 WFL Materials Memorandum and their 2013 Pavement Evaluation Report listed in Section 1.2.

The ditches along the base of the South Chickaloon Cut from approximately Station 10100+50 to 10113+50 are generally no wider than 4 to 8 feet and are flat and filled-in with rockfall debris (Figure 7 and 8). ADOT&PF Maintenance personnel describe this section as having frequent rockfall during the spring and fall months, primarily associated with freeze-thaw cycling and strong precipitation and wind events. They also indicated that large round rocks, up to about 4 feet in dimension have fallen from the oversteepened and unvegetated portion of the cut and enter the travel lanes, resulting in oil pan and tire damages to vehicles. Most of the rockfall was described as entering the westbound lane.

In the South Chickaloon Cut, near Station 10106+50, completely weathered, weak sedimentary rock units of the Chickaloon Formation were observed in the northeastern, lower portion of the existing cut. More prominent and resistant layers of intrusive rock were measured tilting to the north between 39 and 60 degrees along the bedding of the sedimentary rocks. However, tensile fractures within the sedimentary and intrusive rock layers were oriented to the east and southeast between 37 and 45 degrees, daylighting out of the existing and proposed cut. In general, the sedimentary rocks were in a moderately to highly weathered condition and were very weak to weak rock in the limited exposures in the cut (Figure 8).

In the southwestern half of the cut, no bedrock was observed on the surface. Normally consolidated and overconsolidated glacial fluvial deposits are exposed and produce a majority of the rockfall where the cut is locally oversteepened between 45 and 60 degrees (Figure 7). However, from approximately Station 10100+50 to 10104+50 the existing cut slopes are vegetated and apparently stable and are oriented between 35 and 39 degrees (1V:1.5H to 1V:1.25H). At the brow of the existing cut there is a fine, sandy silt that appears to evenly cap the hill.

4.3 Subsurface Materials

The subgrade test boring (SG14-23) and the three construction test pits (TP15-01, TP15- 02, and TP15-03) northeast of the Chickaloon River Bridge are predominately composed of Silty Gravel with Sand, Poorly Graded Gravels with Sand (GP), Poorly graded gravel with silt and sand (GP-GM), and Poorly graded sand with silt and gravel (SP-SM) that is brown in color and is moist to wet with subrounded to subangular gravels. All of these samples are non-plastic. The laboratory test results for the three test pit soil samples indicate there is between 4.2% and 5.5% fines in the samples collected. No groundwater was observed in the test borings.

The subsurface materials encountered and the groundwater observations in the six 2014 Chickaloon River Bridge geotechnical test borings are described in Geotechnical Report No. 07-14. The six test borings described under separate cover for the new Chickaloon River Bridge are named CRB14-01, CRB14-02, CRB14-03, CRB14-04, CRB14-05, and

CRB14-06.

A total of three test borings (SC15-01, SC15-02, and SC15-03vwp) were advanced in 2015 to characterize the subsurface materials and groundwater conditions in the South Chickaloon Cut. In addition to the widely spaced geotechnical test borings, a seismic refraction study was completed atop the existing cut to better understand the lateral extent of the geologic materials present within the proposed highway cut. In general, three engineering geologic units were observed in the test borings and four seismic layers were observed in the seismic refraction survey. They are illustrated in a fence diagram in Figure 12 and are described as follows (from youngest to oldest):

Wind-Blown (Loessal) Deposit: Sandy Silt (ML) with organics, very soft to soft, medium to dark brown and gray, moist, non-plastic, fine-grained sand, homogenous.

Seismic velocities are below 1000 feet per second (fps). All three test borings encountered this soil unit. Estimated unit thickness ranges from 5.5 to 14.5 feet at the test boring locations.

Glacial Fluvial Deposit: This unit has a large range of USCS classifications as would be expected in a fluvial deposit. Generally the material ranges from a Poorly Graded Gravel with silt/clay and sand (GP-GM)(GP-GC), Clayey Gravel with sand (GC), and a Silty Gravel with sand (GM) to a Silty Sand with gravel (SM), Poorly Graded Sand with silt

(SP-SM) and Silty, and a Clayey Sand with gravel (SC-SM). It is medium dense to very dense, brown to gray to black to tan to cream in color and is moist. Most of the samples contain coarse grained sand and angular to round gravels. Cobbles and boulders up to approximately 3.5 feet were encountered in the test borings and up to about 4 feet were observed in the existing highway cut. This soil unit contains normally consolidated soils and overconsolidated soils. The presence of oversteepened glacial fluvial soils in portions of the existing highway cut and the results of the seismic refraction study indicate there are differing densities of glacial fluvial deposit materials within this unit, but the generally dense to very dense nature of the deposit makes this distinction undiscernible in the test borings. Seismic velocities in the normally consolidated portion of this deposit are between 1500 to 3500 fps and range in the seismic refraction model from 10 to 90 feet thick. The overconsolidated portion of this deposit has seismic velocities ranging from 4600 to 8500 fps, and is between 10 and 50 feet thick within the cut. All three test borings encountered this soil unit. Estimated unit thickness ranges from 52.5 in test boring SC15-03vwp to greater than 180 feet in test boring SC15-01.

The overconsolidated deposits, when present, lie below the normally consolidated glacial fluvial deposits and are the result of glacial ice overrunning the fluvial deposit in front of the glacier and compacts it as the ice thickens when the glacier moves down-valley.

When the glacier retreats up-valley during a warming period, as is the case today, the overconsolidated deposit is left behind and new glacial fluvial materials are deposited on top of the older, overconsolidated materials as the glacier retreats.

Chickaloon Formation: This unit consists of alternating layers of siltstone, sandstone, coal, and intrusive rock layers that have varying degrees of calcite veins. This bedrock formation was encountered in test boring SC15-02 and SC15-03vwp and seismic velocities range from 7500 to 10000 fps. In test boring SC15-02, bedrock was observed from 119 to 180 feet bgs and in test boring SC15-03vwp the bedrock was observed from 67 to 145 feet bgs. The subunits within the Chickaloon Formation are described as follows:

Siltstone, dark gray, fine-grained, fresh to slightly weathered, very weak to medium strong rock (R1 to R3). Discontinuities are extremely close to moderately spaced and are in fair to good condition. Rock Quality Designation (RQD) is between 11% and 100%, and Fracture Frequency (FF) ranges from 1 to 3.75. Uniaxial Compressive Strength (UCS) tests ranges from 1350 to 14030 pounds per square inch (psi), indicating that pockets of the siltstone are strong rock (R4). Estimated sedimentary bed thickness ranges from 12 to 23 feet. Siltstone was encountered alternating with coal seams and beds and sandstone layers throughout test boring SC15-02 and SC15-03vwp. The lower UCS test values appear to correlate with the presence of coal seams, and the higher values appear to be correlated with the abundance of calcite veins present in the rock core.

Sandstone, gray, medium to coarse grained, fresh, medium strong to strong rock (R3 to R4). Discontinuities are closely to moderately spaced and are in good to excellent condition. RQD is between 65% and 70%, and FF ranges from 1.4 to 2.

UCS tests range from 6650 to 16010 psi, indicating that pockets of the sandstone are very strong rock (R5). Cross-bedded sandstone is often observed with siltstone layers in the test borings. Estimated sedimentary bed thickness ranges from 1 to 23 feet. The lower UCS values appear to correlate with the presence of siltstone layers and the higher values appear to be correlated with pure sandstone layers.

Coal, dark gray to black, very fine-grained, fresh, very weak to weak rock (R1 to R2). Discontinuities are extremely close to very closely spaced and are in poor to good condition. Estimated sedimentary bed thickness is between 2.8 and

3.0 feet in the test borings. This rock unit is of primary concern when kinematic analysis and rock slope stability were assessed.

Intrusive Rock, olive, fresh, medium strong rock (R3). Discontinuities are closely spaced and are in good condition with appreciable calcite veins. Estimated unit thickness is at least 2.2 feet thick, and was only encountered in test boring SC15- 03vwp. The intrusive rock was emplaced after the sedimentary rocks formed, follows the bedding structure, and is largely responsible for the low grade contact metamorphism in the Chickaloon Formation.

4.4 Groundwater

Groundwater was only measured in test boring SC15-02 at approximately 120 feet bgs, and it is not clear that this measurement was groundwater. It is likely this groundwater measurement is drilling fluids remaining in the test boring since it is a foot below the geologic contact between the glacial fluvial deposits and bedrock. The other subgrade boring, test pits, and South Chickaloon Cut borings did not encounter groundwater during excavation or drilling operations. Additionally, mottled soils within the glacial fluvial deposits indicate that groundwater may periodically perch on discontinuous, impermeable fine-grained layers, but no seeps or springs have been reported or observed in the existing South Chickaloon Cut, or during the progression of constructing the new Chickaloon River Bridge. Therefore, groundwater within the project limits appears to be closely correlated to the river elevations and likely perches upon bedrock.

Test boring SC15-03vwp had a vibrating wire piezometer installed to a depth of 40.9 feet bgs and bedrock was encountered at 67 feet bgs. Figure 13 presents the results of the groundwater monitoring and precipitation for test boring SC15-03vwp. Between May 4th and December 14th, 2015, no groundwater was detected above 40.9 feet bgs. The blue line in Figure 13 shows that no groundwater was measured above the location of the vibrating wire piezometer.

5 GEOTECHNICAL ANALYSES AND RECOMMENDATIONS

5.1 Anticipated Roadway Excavation Uses

Proposed grading operations within the West Chickaloon Grade project limits will require construction of cuts and fills. Excavations will be in windblown sandy silts with organics, glacial fluvial soils, and the Chickaloon Formation materials. Material will also be generated during clearing, grubbing, and site preparation in advance of roadway excavation and embankment construction.

Based on conversations with the WFL Design Team, it is understood that soil and rock excavated within the roadway excavation will be used for embankment construction.

Based on this assumption, and the current understanding of materials in the proposed South Chickaloon Cut, excavated materials have been divided into the following categories:

1) Waste

2) Roadway Excavation

5.1.1 Waste

Waste is defined as materials that, based on the geotechnical investigation, laboratory testing, and experience, cannot be placed as embankment fill in a manner that results in adequate compaction, strength, and settlement characteristics using reasonable and accepted construction practices.

The wind-blown (loessal) deposits that blanket the top of the South Chickaloon Cut and coal layers in the bedrock formation should be wasted because they contain varying levels of organics and are very weak to weak in strength and do not meet the unclassified borrow requirements outlined in the Standard Specifications Section 704.06. Roadway excavation materials that are appreciably above optimum moisture content and soils containing organic material and wood debris, such as those generated during clearing and grubbing operations for the project should also be wasted.

Waste materials should be transported offsite to a suitable disposal site or stockpiled locally for later use in landscaping and/or non-structural fill applications.

5.1.2 Hazardous Waste

Embankment construction is shown in the general area of the 2010 petroleum spill area, between approximately Station 10106+50 and 10110+00 on the existing Glenn Highway.

It is recommended that no excavation in the east bound lane and shoulder, and pull out be allowed in this general area because disturbance of soils identified in the 2010 spill release area will need to be field screened for petroleum, oil, and lubricant contamination in accordance with ADEC regulations. Handling or disposal of these soils will need ADEC approval and require specialized disposal regulations. The specifics surrounding the Phase II Environmental Site Assessment / Release Investigation is available under separate cover, and is listed in Section 1.2.

5.1.3 Roadway Excavation

The roadway excavation materials typically consist of granular, relatively free-draining soil and rock materials. Based on lab test results from soil and rock samples attained during the geotechnical investigation within the proposed South Chickaloon Cut, from approximately Station 10100+50 to 10113+50, there are abundant glacial fluvial gravels and non-coal bearing Chickaloon Formation bedrock materials that can be used to construct the proposed embankment sections within the West Chickaloon Grade project limits. However, the glacial fluvial deposits may require processing to meet unclassified borrow specifications outlined in Standard Specification Section 704.06.

Localized springs, seeps, and moist to wet interbeds composed of silt, clay, silty sand, and clayey sand could be encountered during excavation of the South Chickaloon cut.

This material may be above optimum moisture content and may require aeration before embanking. Where possible, such materials should be segregated during grading and either wasted or aerated prior to placement in embankments.

5.2 Slope Recommendations

Site observations, reviewing the Glenn Highway corridor where similar geologic materials have been excavated and exposed, evaluating the subgrade, test pit, and the geotechnical test boring and laboratory test data within the West Chickaloon Grade project limits were utilized to develop final cut slope and ditch configurations and general embankment slope recommendations.

5.2.1 Cut Slopes

In general, minor roadway excavation is planned outside the South Chickaloon Cut in soils. For those instances where minor cuts are required in soils as the alignment and slopes are adjusted for driver’s line of sight, a 1V:2H or flatter should be utilized. Slope rounding following the WFL standard detail should be completed at the crest of all soil cut slopes.

• South Chickaloon Cut The proposed South Chickaloon Cut will require excavation in soil and rock materials (Figure 12). This large cut was assessed through visual observation and reviewing cuts in the Chickaloon Formation within the immediate Glenn Highway corridor, interviewing ADOT&PF Maintenance personnel about past slope performance, and conducting a thorough geotechnical investigation that included advancing three test borings atop the existing highway cut, conducting downhole geophysical surveys in the bedrock portion of test boring SC15-02 and SC15-03vwp, and completing a seismic refraction survey to characterize and determine the lateral extent of the subsurface soil and rock units.

Rock Analyses Unconfined compressive strength tests in the Chickaloon Formation indicate that the intact rockmass strength when coal is not present ranges from 2830 to 16010 psi. Based on this testing in the siltstone and sandstone members and the weathering state and qualitative strength of the intrusive rock layer encountered in the Chickaloon Formation, it appears that the stability of the bedrock portion of the South Chickaloon Cut will largely be governed by failure along discontinuities within the rockmass. However, of primary concern in the Chickaloon Formation is the differential weathering characteristics between some of the rock unit layers (siltstone and coals) and the very weak to weak strength of the thin coal beds and their orientation to the proposed South Chickaloon Cut alignment. Steep cuts in the sedimentary and intrusive layers identified in the South Chickaloon Cut will likely result in differential weathering of the weaker layers, resulting in loss of support and slope instability for the stronger layers above.

Stability of the rock portion of the cut was assessed by measuring exposed rock outcrop discontinuities and combining those with rock discontinuity information measured in the downhole geophysical surveys. This yielded a statistically significant number of orientations for kinematic, rock slope stability analysis for the bedrock portion of the proposed South Chickaloon Cut alignment. The kinematic analysis for the bedrock utilized Dips Version 6.012 software produced by RocScience.

For the kinematic analysis, a total of 129 discontinuity orientations were utilized to statistically contour and develop three design planes and three intersections from those design planes that form rock wedges. The collected data was used in the kinematic analysis to evaluate the feasibility of the rock slope discontinuities forming unstable planar, wedge, and/or topple structures as they daylight in the proposed South Chickaloon Cut face. Table 3 lists the design planes and intersections used for the kinematic feasibility analysis below:

Table 3. Potential design planes and intersections used for kinematic feasibility analysis.

Discontinuity ID Dip Direction of Discontinuity (Compass Azimuth Bearing)

Dip of Discontinuity (Degrees)

Plane A 107 30 Plane B 012 18 Plane C 209 36

Rock Wedge Intersection of Plane A and C

322 67

Rock Wedge Intersection of Plane A and B

225 74

Rock Wedge Intersection of Plane B and C

113 86

*A magnetic declination of 170 East was used for this site.

The kinematic analysis was used to determine the recommended cut slope angle for the bedrock portion of the cut. The design planes and intersections are represented in the dip vector plotted stereonet provided in Figure 14 as the maroon planes. The shaded contouring shows the density of discontinuities measured with similar dip and dip directions. The design planes were selected from the heavy contour locations. The thick blue line with arrows represents the trace of the proposed South Chickaloon Cut alignment from 036 to 053 degrees. The arrows show the side that the cut will daylight the potential rock structures.

Based on engineering geology experience and judgment and considering the absence of large-scale failures documented in the existing Glenn Highway cut, a conservative 350 friction angle was used for the shear strength along the rock discontinuities in the cut.

Planar, wedge, and toppling failures are kinematically feasible for the bedrock portion of the South Chickaloon Cut. However, the controlling stability mode based on the kinematic analysis is planar failure within the variable hot zone contoured near Design Plane A (Figure 14). To limit the potential feasibility of this planar failure in a high cut and limit the additional risk associated with the presence of thin, laterally persistent coal seams and layers that will daylight in the cut, it is recommended that the bedrock section of the South Chickaloon Cut be cut no steeper than 1V:1H. This will also limit the potential for rock degradation undermining stronger sedimentary and intrusive rock layers in the new cut.

Production blasting techniques will likely be required for excavating the Chickaloon Formation when encountered. Blasting must be allowed for in the contract following the requirements outlined in Section 205 so the contractor is prepared to excavate using blasting methods, if required.

Soil Analyses In addition to the kinematic analysis completed for the discontinuities in the bedrock unit, a slope stability model was developed for analysis of the proposed highway cut stability utilizing Slide Version 6.016 software from RocScience. The stability model includes a two layer system with no groundwater and the three layer system shown in Figure 15 in Appendix A. The three layer system includes groundwater perched on the geologic contact between the bedrock and overlying glacial fluvial deposits and the wind-blown (loessal) deposits. Shear strength correlations with index tests and relative densities were utilized to assign strength parameters to each of the subsurface units.

The stability analysis for the South Chickaloon Cut indicates that the fluvial glacial deposits should be cut no steeper than 1V:1.5H and the wind-blown sandy silt deposits should be cut no steeper than 1V:2H. In both stability cases analyzed, the new cut slopes at the orientations shown in Figure 15 will meet the design standard factor of safety of 1.25.

Due to the erosive nature of the wind-blown sandy silt deposit and the glacial fluvial deposits that will be exposed in the proposed cut, it is recommended that measures be taken to control erosion on the newly formed cut slope. Such measures should include both short-term and long-term strategies for erosion management, like using erosion control matting with designed revegetation for the non-cohesive, glacial fluvial deposits.

In addition, we recommend that the tops of cut slopes be graded so that surface drainage is not conveyed directly onto the cut face. This may not be needed much in this cut because the natural ground slopes away from the cut face for a majority of the cut.

Compound Cut A “compound cut” or “broken cut” slope generally consists of a steeper slope recommendation in the underlying rock and a flatter slope recommendation in the overlying soils (Figure 15). Utilizing the test borings and the seismic refraction surveys for the cut, a subsurface model was developed and provided to the WFL Design Team to estimate the proposed “hinge points” where the bedrock cut slope angle would transition to the glacial fluvial deposit soils and transition again at the wind-blown (loessal) deposits in the proposed cut. However, based on the depth of the seismic refraction survey and the presence of the overconsolidated glacial fluvial deposits overlying bedrock, it is recommended that the final rock location and “hinge points” be determined in the field during construction, which will require adjustments to slope limits during construction of the compound cuts. To accommodate this level of uncertainty in the lateral extent and depth of the subsurface geologic contact between the bedrock and the glacial fluvial deposits, the following information should be presented in a special contract requirement that replaces Section 204.06(a) Rock cuts:

Variable thicknesses of soil (overburden) will be encountered throughout the project length. The Contractor is advised that the South Chickaloon Cut is steep with difficult access and may require the use of specialized excavation and construction methodologies to establish the top of the cut for compound cut slopes (soil over rock).

The top of the rock portion of the compound cut will be verified by the Contractor during pioneer access or initial excavation. All costs associated with this work are subsidiary to Roadway Excavation.

Construct the final soil cut prior to commencing drilling for rock blasting or other rock excavation methods unless authorized by the CO. When rock blasting is used, perform work according to Section 205.

Scale all rock slopes as the excavation process progresses and slopes are still accessible to the equipment. All costs associated with scaling work are subsidiary to Roadway Excavation.

Excavate rock cuts to 6 inches below subgrade within the roadbed limits. Backfill to subgrade with topping or other suitable material. Compact the material according to Subsection 204.11.

To summarize the cut slope recommendations for the South Chickaloon Cut, and as illustrated in Figure 15, when in rock, slopes should be cut at 1V:1H.