Matanuska-Susitna Borough GEOTECHNICAL REPORT Parks Highway Connections Museum Drive Matanuska-Susitna Borough, Alaska March 2, 2010 Prepared By: John Thornley, PE Geotechnical Engineer 3335 Arctic Blvd., Ste. 100 Anchorage, AK 99503 Phone: 907.564.2120 Fax: 907.564.2122
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GEOTECHNICAL REPORT - Parks Highway MP 44-52 · and laboratory test procedures, and results of the subsurface exploration and laboratory tests. A supplemental letter titled “Geotechnical
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Matanuska-Susitna Borough
GEOTECHNICAL REPORT
Parks Highway Connections Museum Drive
Matanuska-Susitna Borough, Alaska
March 2, 2010
Prepared By: John Thornley, PE
Geotechnical Engineer
3335 Arctic Blvd., Ste. 100
Anchorage, AK 99503 Phone: 907.564.2120
Fax: 907.564.2122
TABLE OF CONTENTS 1.0 INTRODUCTION ...................................................................................... 1
2.0 SITE AND PROJECT DESCRIPTION ....................................................... 1
3.0 LOCAL CONDITIONS ............................................................................... 2
6.1 GROUNDWATER AND SURFACE WATER ...................................................... 5 6.2 SOILS ...................................................................................................... 5
6.2.1 Borings B-1 Through B-9 (Station 10+00 to 56+00) ................................. 6 6.2.2 Borings B-10 Through B-12 (Station 56+00 to 71+50) ............................. 6 6.2.3 Borings B-13 Through B-20 (Station 71+50 to 104+00) ........................... 7 6.2.4 Peat Deposits (Station 104+00 to 109+00) ................................................ 7
7.0 CLOSURE AND LIMITATIONS ................................................................. 8
LIST OF FIGURES Figure 1 Vicinity Map Figure 2-10 Plan and Profile Sheets Figure 11 Peat Depth Contour Map LIST OF APPENDICIES Appendix A Figure A1 Unified Soil Classification Figure A2 Frost Design Soil Classification Figure A3-A22 Boring Logs Figure A23-A26 Grain Size Curves
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GEOTECHNICAL REPORT PARKS HIGHWAY CONNECTIONS
MUSEUM DRIVE MATANUSKA-SUSTINA BOROUGH
ALASKA
1.0 INTRODUCTION This report presents the results of subsurface explorations and laboratory testing for the proposed Parks Highway Connections Museum Drive Project. The purpose of the field exploration and geotechnical studies was to define the soil and groundwater conditions for use in the design of the new roadway. To develop the criteria for use in design, 20 borings were advanced along the proposed alignment of the new road. Soil samples recovered from the borings were classified in the field by an experienced engineer with Hattenburg Dilley and Linnell, LLC (HDL) and returned to our laboratory for testing and verification. The project investigation was performed in general accordance with the procedures outlined in the “Alaska Geotechnical Procedures Manual” (ADOT&PF, 2007). Included in this report are a description of the project, subsurface exploration methods and laboratory test procedures, and results of the subsurface exploration and laboratory tests. A supplemental letter titled “Geotechnical Recommendations for Parks Highway Connections: Museum Drive”, March 2010, addresses the recommendations for design and construction for the project. The alignment description and subsurface conditions presented herein are based on our current understanding of the alignment and project as of the date of this document. Deviation from the alignment outlined within this report may require further evaluation of subsurface conditions. This report documents subsurface geotechnical conditions and provides analyses and interpretation of anticipated site conditions for the project. This report establishes a geotechnical baseline to be used in assessing the existence and scope of changed or differing site conditions. This report is intended for use by the project design engineering staff, construction personnel, bidders, and contractors.
2.0 SITE AND PROJECT DESCRIPTION This project covers the development of an approximately 1.9-mile section of roadway connecting the existing Museum Drive to the east and Sylvan Road to the west, within the Matanuska-Susitna Borough. The location of the project is shown on the vicinity map in Figure 1. It is planned that this new connection, running roughly parallel to the
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Parks Highway, will provide alternate routes for local access. The new road is classified as a collector connection. The purpose of this road extension project is to improve the collector connections within the local roads west of Wasilla as growth in this area continues. It has been estimated that development of connectors like this one will enhance local traffic mobility and safety. This connector will also reduce the vehicle-miles traveled and left turn movements onto the Parks Highway. The proposed road alignment will likely cross one stream at two locations located east of Vine Road. There is also a peat bog region at the eastern end of the alignment at the future connection with Museum Drive. These features are identified on the plan and profile sheets along with the boring locations on Figures 2 through 10.
3.0 LOCAL CONDITIONS
3.1 General Geology The project area is located within the Cook Inlet-Susitna Lowland Section of the Coastal Trough physiographic province of Alaska. The Talkeetna Mountains border the province on the east and the Alaska Range lies to the north and west. To the south is Cook Inlet. Glacial features including ground moraines, drumlins, eskers, and outwash plains characterize the entire Cook Inlet-Susitna Lowlands. Kame and kettle topography, indicative of glacial outwash plains, is common and forms many of the hills and small rounded lakes that exist in the project area. Five major glacial advances of the Quaternary Period can be recognized throughout the vicinity ending approximately 12,000 years ago. Sediments are typically glacial derived sands and gravels with varying fines contents. Peat bogs have developed in many of the low-lying areas subsequent to the last glaciation. As the glaciers receded towards the mountains, the Susitna River drainage was established as well as the drainages in the project area. These drainages deposited sands and gravels in channel areas and fine grain sediment in floodplains.
3.2 Seismicity The project is located in an area of moderate seismicity. Large-scale earthquakes may cause ground ruptures along the roadway. Locations of potential rupture zones are outside the scope of this study and are extremely difficult to predict. Slopes and structures such as bridges and culverts along the road should be designed to accommodate large-scale earthquakes. Based on Alaska Earthquake Information Database there were 399 events above magnitude 4 in the region from 1898 to 2005. There were 49 events above a magnitude 5 of which 14 were magnitude 6 to 7.4. The
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2006 International Building Code places the area in Site Class D based on general soil properties encountered along the alignment.
3.3 Climatology The project area is located in a transitional climatic zone varying between continental and maritime climates. The zone is characterized by pronounced diurnal and annual temperature variations, moderate annual precipitation, and moderate surface winds. Average January temperatures in the area range between –2ºF and 19ºF, while average July temperatures range between 44ºF and 68ºF. The area experiences an average of 60 wet days per year in which 0.1 inch or more of precipitation accumulates. The Environmental Atlas of Alaska provided the information for the project area. Following are mean annual values for the area: Mean Annual Temperature 30ºF Mean Annual Precipitation 25 in. Mean Annual Snowfall 100 in.
Thawing Index 3000 degree days Freezing Index 3500 degree says
4.0 FIELD STUDY The geotechnical field study consisted of soil borings and peat probing. The intent of the field study was to determine the soil properties of the existing soils along the alignment. In all, 20 soil borings were each advanced to a depth of 16.5 feet below the existing ground surface. Locations of the 20 borings are detailed on Plan and Profile sheets located in Figures 2 through 10. The boring locations were typically spaced at 500-foot intervals along the proposed alignment. The borings for this study were advanced between August 3 and August 6, 2009. One-inch diameter slotted PVC pipe was installed in 10 select borings for monitoring groundwater levels along the alignment. The water levels in these borings were measured August 26, 2009, approximately 20 days after drilling was completed, which allowed for seasonal static water levels to become stabilized. Discovery Drilling Inc. of Anchorage, Alaska provided drilling services for this project using a CME 55 mounted on a Nodwell track vehicle. The borings were advanced with 3¼-inch inside diameter (I.D.) hollow stem auger. In each of the borings, split-spoon samples were collected at typically 2.5 feet, 5 feet, and 5-foot intervals thereafter. Sampling with the split-spoon was conducted using the Modified Penetration Test procedure. In the Modified Penetration Test, samples are recovered by driving a 3-inch O.D. split-spoon sampler into the bottom of the advancing hole with blows of a 340-lb. hammer free-falling 30 inches onto the drill rod. The number of blows required to advance the sampler the final 12 inches of an 18-inch penetration in the test is termed
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the Penetration Resistance, which was recorded for each sample depth. The values give a measure of the relative density (compactness) or consistency (stiffness) of cohesionless or cohesive soils, respectively. An experienced engineer from HDL was present continuously during drilling to locate the borings, observe drilling action, collect samples, log subsurface conditions, monitor groundwater encountered, and observe installation of groundwater monitoring equipment. The soils were classified in the field according to the Unified Soil Classification System (USCS) presented in Appendix A, Figure A1 and later verified by laboratory tests. A modified version of the U.S. Army Corps of Engineering Frost Design Soil Classification, presented in Appendix A, Figure A2, was used to estimate the frost characteristics of the soils based on the laboratory results. Detailed logs of the borings are presented on the plan and profile sheets in Figures 2 through 10 and in Appendix A, Figures A3 through A22. Peat probing was also performed during this geotechnical field study. The probing consisted of pushing a thin steel rod with T-handle into the regions along the alignment where peat deposits were apparent. The probe was pushed until the rod tip met refusal on firm underlying materials. The depth of probe penetration was measured and recorded. A peat depth contour map presented in Figure 11, was created for areas where peat deposits were measured.
5.0 LABORATORY TESTING Laboratory tests were performed on select samples recovered from the borings to verify field classifications and to determine the pertinent soil properties and behavior characteristics of the typical materials encountered along the alignment. Testing was conducted by HDL’s AASHTO certified soils laboratory. The laboratory testing was formulated with an emphasis on determining the materials classification, moisture content, and frost characteristics. The soils were classified in the field and later confirmed by laboratory testing. A total of 52 moisture content tests were performed on samples from the 20 borings. These tests were conducted in accordance with procedures described in ASTM D-2216. The results of the moisture content measurements are presented on the boring logs presented in Appendix A, Figures A3 through A22. Grain size classification tests for this project consisted of 20 mechanical sieve tests and eleven P200 tests. The results were used to verify material classification, estimate permeability characteristics, and determine frost susceptibility of the soils. The mechanical sieve tests were conducted according to procedures described in ASTM D-422. The P200 tests were conducted according to procedures described in ASTM D-
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1140. The results of the mechanical sieves and P200 tests are presented on the boring logs presented in Appendix A, Figures A3 through A22. The grain size curves are presented in Appendix A, Figures A23 through A26.
6.0 SUBSURFACE CONDITIONS The subsurface conditions along the alignment are depicted on the plan and profile sheets in Figures 2 through 10 and on the boring logs presented in Appendix A, Figures A3 through A22. The soils encountered were typically sands and gravels with varying amounts of fines. Peat deposits were found at the eastern portion of the alignment, adjacent to the existing Museum Drive, in the wetlands area.
6.1 Groundwater and Surface Water Groundwater was encountered in some borings near stream crossings, wetlands, and other areas that had perched water tables. The groundwater was found to be shallow enough to potentially affect the roadway embankment at two sections of the alignment Station 63+00 to Station 72+00 and Station 104+00 to Station 109+00. Groundwater was not found at shallow enough depth to potentially affect the roadway embankment along the rest of the project alignment. Slotted one-inch diameter PVC pipe was installed in 10 of the 20 borings. Groundwater levels were measured in these ten locations approximately 20 days after installation to allow for groundwater stabilization. Free water was observed in 3 of the borings during the time of drilling. Table 6.1 shows the measured groundwater depths in select borings during drilling and 20 days following drilling. Table 6.1 Measured Groundwater Levels
Boring Number Depth to Groundwater (ft)
During Drilling 20 Days After Drilling B-10 Not Observed 16.0 B-11 12 No PVC Installed B-12 11 9.6 B-20 16 11.5
Surface water was observed in two sections along the alignment. There was a small stream encountered on the east and west sides of Vine Road between Station 61+00 and Station 72+00. Also, surface water was observed the eastern end of the alignment at Museum Drive, the area where peat probing was performed.
6.2 Soils The following discussions of the geotechnical conditions for the project are organized into segments based on subsurface similarities along the alignment. Section 6.2.1
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discusses the soils encountered in Borings B-1 through B-9 between the west end of the alignment at Sylvan Road and 650 feet west of Vine Road (Station 10+00 to 56+00). Vine Road is at approximately Station 63+00. Section 6.2.2 discusses the soils encountered in Borings B-10 through B-12, east of Vine Road (Station 56+00 to 71+50). Section 6.2.3 discusses the soils encountered in Borings B-13 through B-20, 1,100 feet east of Vine Road to 600 feet east of Museum Drive (Station 71+50 to 104+00). Section 6.2.4 discusses the peat probing results obtained from the roadway alignment section between Boring B-20 and Museum Drive (Station 104+00 to 109+00). The majority of the project will consist of fill to bring the road to finished grade. A slight cut occurs from Station 76+00 to 78+00.
6.2.1 Borings B-1 Through B-9 (Station 10+00 to 56+00) The soils encountered in Borings B-1 through B-9 (Figures 2 through 5 and A3 through A11), between Sylvan Drive and Vine Road, are relatively similar in soil composition. There is a vegetative mat consisting of organics with tree roots in the upper 0.5 to 1.5 feet of the borings. The soils typically consist of poorly graded and well graded sandy gravel. These soils contain fine grained soils (passing the #200 sieve) ranging between 2.5 to 6.7 percent and are considered slightly to non-frost susceptible, or F1 to NFS (Figure A2). The moisture contents range from 1.9 to 6.7 percent. The relative density of these coarse grained soils is generally medium dense to very dense. Rock fragments at the tip of the split-spoon sampler indicate that cobbles greater than 3 inches were encountered. Two of the borings, B-4 and B-8, encountered sandy silt below the vegetative mat. In Boring B-4 the silt layer was found to be approximately 4.5 feet in thickness, to a depth of 6 feet below the vegetative mat. Boring B-8 encountered a 2-foot layer of sandy silt terminating at a depth of approximately 2.5 feet below existing ground. These fine-grained soils are soft and should be considered highly frost susceptible, or F4 frost classification. The sandy silt in Boring B-4 had over 83 percent passing the #200 sieve and had an in-situ moisture content of 34 percent. These localized sandy silt deposits, where encountered, will cause pavement distress by frost heaving. Groundwater was not encountered in any of these borings advanced during the drilling process or when monitoring well water levels were measured after drilling.
6.2.2 Borings B-10 Through B-12 (Station 56+00 to 71+50) This section of the alignment includes the three borings directly east of Vine Road. Borings B-10 through B-12 (Figures 6, 7, and A12 through A14) have been grouped because of their topographic, groundwater, and surface water setting, identified on Figures 6 and 7. There is a small stream that flows across and adjacent to the proposed alignment. Groundwater was encountered in Borings B-11 and B-12 during drilling. As seen in Table 6.1, groundwater levels were found to be 9.6 feet below existing ground and deeper. The measured groundwater levels may vary seasonally.
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The soils encountered in each of the borings were covered by a vegetative mat at the surface. Sandy silt was encountered in Borings B-10 and B-12 to approximately 3 feet below ground and should be considered highly frost susceptible. Below the sandy silt, gravelly sand and sandy gravel was encountered. Boring B-11 soils consisted of gravelly sand to sandy gravel and did not encounter sandy silt to the depths of the boring. The coarse-grained soils encountered are considered to be non-frost susceptible or NFS, due to the fines contents of less than 6 percent. These soils were found to have relative densities ranging between dense to very dense.
6.2.3 Borings B-13 Through B-20 (Station 71+50 to 104+00) Along the alignment, after Boring B-12, there is a significant rise in the ground surface topography, east of the small stream. Boring B-13 was advanced at the top edge of that slope. The soils encountered from Boring B-13 through B-20 (Figures 7 through 10 and A15 through A22) were found to be similar. These borings encountered a 6-inch thick vegetative mat of organics and tree roots. The soils consisted primarily of silty, gravelly sand to silty, sandy gravel with fines contents ranging from 12.5 to 32.2 percent. These soils are considered to be moderately frost susceptible and are classified as F2 and F3 soils. Rock fragments at the tip of the split-spoon sampler indicate that cobbles greater than 3 inches were encountered within the soil matrix. Moisture contents of these soils range from 4.0 to 8.4 percent. The relative densities of these soils range from medium dense to very dense. A layer of sandy silt was encountered just below the vegetative mat in Borings B-16, B-17, and B-20 with thicknesses of 4.5 feet, 2 feet, and 2 feet, respectively. These fine grained soils ranged from loose near the surface to very hard with depth. The sandy silt, as discussed previously, is considered highly frost susceptible, or classified as an F4 soil. Groundwater was encountered in Boring B-20. A 1-inch slotted PVC pipe was installed in this boring and ground water levels were measured to be approximately 11.5 feet below the ground surface.
6.2.4 Peat Deposits (Station 104+00 to 109+00) Between Boring B-20 and Museum Drive, surface water and a significant peat deposit were observed. Peat probing was performed in order to develop a contour map of the approximate peat thickness and is presented in Figure 11. Peat thickness in this area ranges from less than 10 inches to greater than 90 inches within the proposed roadway alignment right-of-way. There is an open body of water located to the south of this alignment. No other peat deposits were observed along the Museum Drive Extension Project alignment.