Loading...
HomeMy WebLinkAboutWVH GEOTECH 1West Valley Highway Improvement Project Geotechnical Report 2 June 2010 Prepared For: INCA Engineers, Inc. 400 112th Avenue NE, Suite 400 Bellevue, WA 98004 Prepared by: st 1109 1 Avenue, Suite 501 Seattle, WA 98101-2988 Distribution To: Don Proctor, PE / INCA Engineers CC: Sandy Glover, PE / INCA Engineers From: Jacobs Associates Prepared By: Don Reid Jacobs Associates Reviewed By: Carol Ravano, PE and Frank Pita, PE/LHG Jacobs Associates of Contents Table 1Introduction ................................................................................................................... - 1 - 1.1 General .................................................................................................................... - 1 - 1.2 Project Description ................................................................................................... - 1 - 1.3 Authorization ............................................................................................................ - 1 - 1.4 Purpose and Scope of Work .................................................................................... - 1 - 2Existing Site Conditions ............................................................................................... - 3 - 2.1 Surface Conditions................................................................................................... - 3 - 2.2 Geologic Setting ...................................................................................................... - 3 - 2.3 Field Exploration ...................................................................................................... - 4 - 2.3.1 Pavement Coring .................................................................................................. - 4 - 2.3.2 Cone Penetration Testing ..................................................................................... - 4 - 2.3.3 Geotechnical Test Pits .......................................................................................... - 5 - 2.4 Subsurface Conditions ............................................................................................. - 5 - 2.5 Groundwater Conditions .......................................................................................... - 6 - 2.6 Critical Erosion and Landslide Hazard Areas ........................................................... - 6 - 3Conclusions and Recommendations .......................................................................... - 8 - 3.1 Site Preparation and Grading Recommendations .................................................... - 8 - 3.1.1 Site Clearing, Demolition, and Removal ............................................................... - 8 - 3.1.2 Subgrade Preparation .......................................................................................... - 8 - 3.1.3 Compliance with City of Auburn Critical Areas Ordinance .................................... - 9 - 3.1.4 Structural Fill Materials and Compaction ............................................................ - 11 - 3.1.5 Wet Weather Earthwork ..................................................................................... - 11 - 3.1.6 Temporary and Permanent Slopes ..................................................................... - 12 - 3.1.7 Benching of Existing Embankment ..................................................................... - 12 - 3.2 Retaining Wall Design Recommendations ............................................................. - 13 - 3.2.1 Lateral Earth Pressures ...................................................................................... - 13 - 3.2.2 Settlement and Pre-Loading ............................................................................... - 13 - 3.2.3 Gabion and Modular Retaining Walls ................................................................. - 13 - 3.2.4 Retaining Wall Design ........................................................................................ - 13 - 3.2.5 Wall Drainage Considerations ............................................................................ - 14 - 3.3 Signal Pole Foundation Design Recommendations ................................................ - 14 - 3.4 Pavement Considerations ...................................................................................... - 15 - 3.4.1 Recommendations for Design of Pavement Section ........................................... - 15 - 3.4.2 Pavement Construction Options ......................................................................... - 16 - 3.5 Site Drainage and Erosion Considerations ............................................................. - 18 - West Valley Highway i Geotechnical Report 2 June 2010 3.5.1 Surface Water Control ........................................................................................ - 18 - 3.5.2 Erosion Control................................................................................................... - 18 - 3.6 Seismic Design Criteria .......................................................................................... - 18 - 3.6.1 General .............................................................................................................. - 18 - 3.6.2 Soil Liquefaction ................................................................................................. - 18 - 4Closure ........................................................................................................................ - 20 - 5References .................................................................................................................. - 21 - 6Figures ......................................................................................................................... - 22 - Figure 1 - Soil Investigation Locations Figures 2 and 3 - Typical Soil Profiles Figure 4 - Pavement Cores Figure 5 - Slide Analysis Figure 6 - Gabion Wall Design Figure 7 - Pavement Design Figure 8 - Pavement Construction Option 1 Figure 9 - Pavement Construction Option 2 Figure 10 - Pavement Construction Option 3 Figure 11 - Pavement Construction Option 4 Appendices ........................................................................................................................ - 34 - Appendix A - Photographs ................................................................................................ - 35 - Appendix B - CPT Logs .................................................................................................... - 37 - Appendix C - Signal Pole Foundation Soil Strength Table ................................................ - 47 - Appendix D - Pavement Design ........................................................................................ - 48 - Appendix E - Test Pit Logs ............................................................................................... - 49 - West Valley Highway ii Geotechnical Report 2 June 2010 1 Introduction 1.1 General This report presents the results of our field investigation and provides geotechnical conclusions and preliminary recommendations for design of the West Valley Highway Improvement Project located in Auburn, Washington. The purpose of this study was to complete subsurface explorations within the project alignment to characterize soil and groundwater conditions and develop geotechnical conclusions and recommendations for design and construction of the proposed improvements. 1.2 Project Description The purpose of our work is to provide INCA Engineers with geotechnical recommendations including traffic utility pole and retaining wall foundation design parameters, existing slope evaluation results, site grading recommendations, drainage options, and pavement section design parameters for the construction documents. We understand that the City of Auburn is working on improvements to West Valley Highway from the intersection of State Highway 18 to the intersection of West Main Street. Improvements to this section of West Valley Highway would include road reconstruction on West Valley Highway from SR18 to West Main Street, possible use of retaining walls to reduce sensitive area impacts, storm drainage facilities, and intersection and signal improvements at the intersection of West Valley Highway and West Main Street. 1.3 Authorization Our work was performed in general accordance with our proposal that was submitted to Sandy Glover, PE, on 3 November 2009. Notice to Proceed for this investigation was received on 4 February 2010 from INCA Engineers. This report has been prepared for the exclusive use of INCA Engineers and its authorized agents for specific application to this project in accordance with generally accepted geotechnical/civil engineering practices. 1.4 Purpose and Scope of Work The purpose of this investigation is to evaluate the subsurface conditions and pavement sections along the project alignment and to provide geotechnical recommendations for the proposed new signal pole foundations, retaining walls, drainage facilities, and roadway widening. Our scope of work consists of the following tasks: Preliminary site visits to evaluate the site conditions, evaluate access, plan the field investigation, and locate potential boring and monitoring well locations; Review readily available existing documents for the project area; Coordination of utility location at boring and coring locations; Preparation of City of Auburn Right-of-Way Use Permit and traffic control plans; Coordination of the field investigation, supervision of drilling, coring, and cone penetration testing (CPT) subcontract work. Logging the soil test pits and pavement cores, and observing the cone penetration tests; Preparing a summary geotechnical report, including: 1.Descriptions of the site and test locations; 2.Summary test pit logs; West Valley Highway - 1 - Geotechnical Report 2 June 2010 3.Descriptions of the surface and subsurface conditions along the project alignment; 4.Recommendations for the signal pole foundation design; 5.Recommendations for retaining wall structures; 6.Recommendations of the pavement section design; 7.Site grading recommendations; 8.Groundwater monitoring results; 9.Estimations of infiltration rates for existing road prism; 10.Evaluation of unstable slopes and implications for design. West Valley Highway - 2 - Geotechnical Report 2 June 2010 2 Existing Site Conditions This section provides a discussion of the general surface and subsurface conditions observed along the project corridor at the time of our investigation. Interpretations of the site conditions are based on the results of our review of available information including results from previous geotechnical investigations at the site, site reconnaissance, and information collected during our subsurface exploration. 2.1 Surface Conditions The project alignment is the section of West Valley Highway between the intersection of State Highway 18 and the intersection of West Main Street. It is a busy two lane road with traffic signals at the intersection of West Valley Highway and West Main Street. The project alignment is flat, with a steep bank sloping upwards on the west side of the road. This slope appears to have been cut many years ago, possibly in the 1930s when the road was first paved. Mature scrub and vegetation covers most of the face of the cut surfaces. There is surficial sloughing along the slope. An older slide is evident at the south end of the alignment, in the location of the state highway sign. There is an unlined drainage ditch, which drains to catch basins, at the base of the slope. On the east side of the alignment, the embankment slopes downward to the east and is approximately 8 ft high. There is a drainage ditch at the base of the embankment adjacent to a man-made berm. The berm appears to have been used as a narrow access; it is now discontinuous and covered with turf. Further to the east is the Goedecke property, an area that was previously farmland and contains wetlands, uplands, wetland mitigation tracts, and the Goedecke Site for Mill Creek. This section of West Valley Highway appears originally to have been paved with brick overlying Portland Cement Concrete (PCC). Over the years, it has been widened and overlain with Asphalt Treated Based (ATB) and Asphaltic Concrete (AC). 2.2 Geologic Setting The project site is located in the Puget Sound Basin, a region bounded by the Cascade Range on the east and the Olympic Mountains on the west. Topography and landforms in the region were formed primarily by repeated advance and retreat of glaciers over the past 1.2 million years. During glacial periods, the southwestern margin of the Cordilleran ice sheet flowed southeastward from British Columbia into the Puget Sound Basin of Western Washington on at least five occasions. The most recent episode of glaciation was the Vashon Period of the Fraser Glaciation. Sediments from this glacial episode are widely exposed at the surface in the Puget Lowland. Deposits associated with this geologic process include very dense glacial till (Vashon till), advance outwash deposits (sand and gravel), and pro-glacial lacustrine (fine sand, silt and clay) sediments. All these deposits were over-ridden by ice and are therefore dense in their character. As the Vashon glacier receded, large quantities of melt water were discharged from it. The melt water sorted the material in its path and left very gravelly and sandy sediments from 4 feet to 100 feet in thickness. These deposits are called Vashon Recessional Outwash and their consistency, because they have never been over-ridden by ice, are less dense and, in some cases, loose and soft. Following the end of the glacial period, alluvium from rivers and slope erosion down the hillsides accumulated in the valleys. West Valley Highway - 3 - Geotechnical Report 2 June 2010 The soil units on the project site originate from several different geologic events described above. For example: The western hillside is composed of Pre-Olympia deposits, material that was deposited by streams between glacial ice events. This material was over-ridden by the glaciers so it is very dense. The permeability is controlled by localized iron-oxide cemented layers, interbedded and intermixed fine and coarse grained layers. (Derek B. Booth, Kathy A. Troost & Aaron P. Wisher, March 2007) The near horizontal valley floor materials are a result of stream deposition into a valley left by the melting ice. These post glacial processes primarily consisted of modern stream and river alluvium deposited over the recessional outwash from the glacier melt waters. Since no ice has compressed these units, their current consistency is soft and loose. There is fill material under the roadway and in the embankment, which appears to be the same material as the hillside on the west side of West Valley Highway. During construction of the road, the slope was probably cut, and the material from this cut was placed on top of the valley sediments to form the subgrade for the road. 2.3 Field Exploration The site reconnaissance was performed by Jacobs Associates (JA) staff to evaluate site access and set the preliminary CPT and test pit locations. JA coordinated the utility locate requests and traffic control plans. Follow-up site visits were performed on 3 February and 11 March 2010 by Don Reid to check for any utility conflicts at the proposed CPT and test pit locations. A City of Auburn Right-of-Way (ROW) Use permit was obtained by JA prior to beginning the subsurface explorations. Subsurface field investigations were performed on 16 and 17 March 2010 by Don Reid and Steve Guarente of JA. The field investigation consisted of coring four (4) 4-inch diameter holes in the roadway pavement section, advancing ten (10) Cone Penetration Tests (CPTs), and excavating seven (7) exploratory test pits. An additional site reconnaissance was performed on 31 March 2010 by Don Reid to assess the slope on the west side of the roadway. 2.3.1 Pavement Coring Pavement coring was performed on 17 March 2010 by Seattle Concrete Coring under subcontract to JA. The coring was performed to verify in-situ pavement thickness, and to provide access to the underlying soil layers for sampling and testing. Coring along the project alignment was performed using an electric diamond core drilling machine with a 4-inch diameter core barrel. Each pavement core sample was retrieved, washed, measured, and documented. Photos of the cores are shown in Appendix A. At completion of CPT testing, core holes were backfilled with quick-setting cement grout and sealed with asphalt on the surface. 2.3.2 Cone Penetration Testing In-Situ Engineering, under subcontract to JA, performed ten (10) electric cone CPTs along the project alignment on 17 March 2010. CPTs were performed to determine soil characteristics including soil classification, soil strength, and stratigraphy. This information was analyzed and incorporated in the formulation of our project design recommendations. The CPT soundings were performed using electric cone penetrometers and piezo-cone penetrometers. The penetrometers were advanced into the ground using a hydraulic ram mounted in a truck having a weight of approximately 20 tons. The cone and piezo-cone penetrometers have a diameter of approximately 1.4 West Valley Highway - 4 - Geotechnical Report 2 June 2010 inches. Cone tip resistance (Q) and sleeve friction (F) were recorded on the penetrometer during all CPT cs soundings. The pore water pressure during penetration was measured behind the tip (P) in piezo-cone w soundings. Data was recorded at approximately 2 cm intervals using an on-board computer to provide a near continuous profile of the soil conditions encountered during penetration. The friction ratio (Fs/Qc) was computed for each test interval. Continuous profile plots of equivalent Standard Penetration Test N- values, and color coded soil behavior type, are generated and presented on the CPT logs. A summary of the approximate CPT locations and test depths are presented in Figure 1, Section 5; CPT results are presented in Appendix B. During cone penetration testing, refusal was established as tip resistance pressures over 300 tons per square foot (TSF). Tests performed in the roadway alignment (CPTs 3, 5, 8 and 9) met refusal at relatively shallow depths. Refusal depths increased with distance from the hill side. 2.3.3 Geotechnical Test Pits To supplement the information obtained from the CPTs, subsurface conditions along the project alignment were explored by excavating seven (7) test pits to expose and record the soil conditions below the ground surface. Samples were collected from all the test pits. The approximate locations of the exploratory borings are indicated on Figure 1. 2.4 Subsurface Conditions Based on the results of the field exploration program and our review of available geologic information, the project alignment is interpreted to be existing roadway pavement underlain by roadway fill. The fill is underlain by alluvial deposits, consisting of SILT and CLAY, poorly graded fine SAND, and silty SAND. These deposits are underlain by glacial soils. Illustrations of profiles typical for the alignment are presented in Figures 2 and 3. Each material type is discussed below. Pavement Three of the four cores of the existing road surface revealed a pavement cross-section 20 inches thick, as illustrated in Figure 4. The majority of the pavement appears to consist of a 7.5 inch thick top layer of asphaltic concrete (AC), underlain by 3 inches of asphalt treated base (ATB), underlain by 4 inches (2 courses) of brick, underlain by 1.5 inches of sand and gravel (brick leveling course), and 4 inches of Portland cement concrete (PCC). There was one core consisting of 11 inches of AC, with no brick or PCC below. We assume that this core was through pavement which had been added to widen the original PCC/brick/AC roadway (see Photos, Appendix A) Figure 4 also contains pavement section thickness information from a previous geotechnical investigation, performed by King County in 1972 (P.I.12084B); these are marked H-1 and H-2 and were taken at the south end of the project site. Road Fill On the west side of the road, the fill layer underlying the pavement is up to 3 feet thick (depth roughly 5 feet); on the east side of the road, there was fill below the roadbed to a depth of up to 16 feet. The fill consisted of medium dense to very dense, medium to coarse silty SAND or dense, fine silty, sandy GRAVEL. The moisture content of the fill was generally dry (see Photos, Appendix A). Valley Infill Alluvium This unit is variable in consistency and was encountered beneath the fill on the east side of the road and in the valley floor east of the road. The upper 3 to 4 feet of the alluvium consisted of medium dense, fine to coarse silty SAND and fine to coarse silty, sandy GRAVEL. Beneath this was a 1 foot layer of soft, silty CLAY and clayey SILT underlain by a 2 West Valley Highway - 5 - Geotechnical Report 2 June 2010 foot layer of medium dense, highly permeable, clean fine SAND. From approximately 7 to 16 feet deep there were interbedded layers of soft, silty CLAY, clayey SILT, and silty SAND. Glacial Soils The hillside on the west side of the road is composed of Pre-Olympia deposits, a very dense, fine to coarse sandy, fine to coarse GRAVEL, trace silt. This unit formed the original slope which was cut into for road construction and which underlies this area, as illustrated on Figures 2 and 3. The CPT probe cannot penetrate this layer because of the density of the soil. Hence, the CPT indicates valley alluvium are above the dense layer. 2.5 Groundwater Conditions Groundwater was observed during test pit excavations at a depth of 6 ft below ground surface, or approximate elevation 62 feet, in both test pit T-01 and test pit T-03. In both cases, the test pit wall caved in from approximately 5 feet below ground surface, as shown in Photos, Appendix A. The soil at this depth was highly permeable, and the pits filled quickly and caved-in after excavation. It should be noted that the groundwater conditions reported on the summary logs are for the specific locations and dates indicated, therefore may not necessarily be indicative of other locations and/or times. Furthermore, it is anticipated that groundwater conditions will vary depending on local subsurface conditions, the weather, and other factors. Groundwater levels in the project alignment zone are expected to fluctuate seasonally, with maximum groundwater levels generally occurring during the winter and spring months. We estimate the infiltration rate in the road embankment fill to be in the order of 10E-5 cm/sec or 0.2 gallons/day/ft². This value is typical of soils of this type. 2.6 Critical Erosion and Landslide Hazard Areas The slope on the west side of West Valley Highway is classified as a geologic hazard area on the City of Auburn critical areas maps; the entire slope is in a critical erosion hazard area and a portion of the slope is in a potential landslide hazard area. On 31 March 2010, Don Reid of JA visited the site to evaluate and classify the slope in accordance w ACC Section 16.10.080. The measurement data were used to calculate the range of slopes that make up the hillside on the west side of the road. The height of the cut slope varies from 0 to 20 feet along the alignment and has a slope of between 45 ° and 72° (100% and 300%). The slope of the hillside above the cut is between 30% and 50% (estimated from Google Earth and on-site inspection). A section where the cut is the highest is illustrated in Photos, Appendix A. As stated in Section 16.10.080-G.1, the U.S. Department of Agriculture classifies slopes as having a greater. Based on these criteria, this slope does hazard. Auburn City Code 16.10.080-G.2 classifies landslide hazards as follows: Landslide hazard areas are classified as Class I, Class II, Class III, or Class IV as follows: a. Class I/Low Hazard-Areas with slopes of 15 percent or less. b. Class II/Moderate Hazard-Areas with slopes of between 15 percent and 40 percent and that are underlain by soils that consist largely of sand, gravel, or glacial till. c. Class III/High Hazard-Areas with slopes between 15 percent and 40 percent that are underlain by soils consisting largely of silt and clay. West Valley Highway - 6 - Geotechnical Report 2 June 2010 d. Class IV/Very High Hazard-Areas with slopes steeper than 15 percent with mappable zones of emergent water (e.g., springs or ground water seepage), areas of known (mappable) landslide deposits regardless of slope, and all areas with slopes 40 percent or greater After evaluating the slope on the west side of the alignment, we estimate that 90% of the alignment is in a Class IV/Very High Hazard Area. Based on these analyses, all activities in this area must be in compliance with the Critical Areas Ordinance, addressed below. West Valley Highway - 7 - Geotechnical Report 2 June 2010 3 Conclusions and Recommendations Based on conditions observed in the explorations and results of our engineering evaluation; construction for the proposed City of Auburn West Valley Highway Improvement Project is considered to be feasible using conventional means and methods. Geotechnical conclusions and recommendations are presented in the following sections for the earthwork including road subgrade preparation, retaining wall and signal pole foundation design, and recommendations for a new pavement section. It is our opinion that there are no geotechnical constraints that would preclude project construction as planned, provided that our recommendations are incorporated into the design. Our design recommendations and conclusions were developed based on our current understanding of the project. If the nature of the proposed construction is changed, JA should be notified so we can confirm or re-evaluate our recommendations. 3.1 Site Preparation and Grading Recommendations 3.1.1 Site Clearing, Demolition, and Removal The amount of pavement and embankment demolition that will be necessary is dependent on the final design, which is not known at this time. We understand that the decision to leave the existing roadbed in place or remove it has not been made. This topic is discussed in Section 3.4.2. Site clearing and demolition must be performed in compliance with City of Auburn Code 15.74. We recommend that any removed organic material not be reused directly as structural fill. Any asphalt and concrete rubble may be reused as structural fill if it can be adequately processed and meet WSDOT specifications for the intended use. In some cases, the existing utilities on site must be relocated. The underlying site soils do contain gravels and cobbles, and may contain boulders. The contractor should be prepared to handle gravels, cobbles or boulders if encountered during excavation and construction. 3.1.2 Subgrade Preparation Roadway subgrade preparation for areas of new pavement is expected to consist of stripping and clearing of all vegetation and deleterious materials, possibly removal of existing pavement, and excavation of loose and soft subgrade material. Following clearing, stripping, and any required excavation to remove unsuitable material, and before placement of any structural fill, the upper 12 inches of exposed soil should be scarified and moisture-conditioned. Over-excavation of unsuitable subgrade material should be in accordance with Section 2-03.3(14) E of the 2010 WSDOT Standard Specifications. The prepared subgrade should be proof-rolled with a loaded dump truck, large self-propelled vibrating roller, or equivalent piece of equipment in the presence of a qualified geotechnical or civil engineer to check for the presence of soft, loose, and/or disturbed areas. If any soft, loose, and/or disturbed areas are revealed during proof rolling, these areas should either be moisture conditioned and re-compacted to the required density, or removed and replaced with Select Borrow meeting the requirements in Section 9-03.14(2) of the 2010 WSDOT Standard Specifications, and compacted to the required density. The new roadway embankment materials will be placed on highly stratified soil, many layers of which are compressible. We anticipate that the new embankment will settle between 3 and 6 inches in a non- uniform fashion due to the compressibility of varying underlying soils. We recommend two possible options to improve the subgrade and minimize the effect of settlement: Install vertical stone columns in the subgrade to strengthen the soil before construction of the new road embankment. Constructing stone columns will provide a stable foundation for the West Valley Highway - 8 - Geotechnical Report 2 June 2010 embankment such that settlement will not be an issue. A typical stone column improvement program would be 2-foot diameter stone columns, 30 feet deep on 9 foot centers. The columns would cover the entire area under the new embankment. The stone column construction will take approximately one week and requires site preparation similar to that needed for embankment placement. Construct a new road embankment using geogrid reinforcement and then preload the embankment to accelerate the settlement process so that the majority of the vertical movement will occur prior to the pavement placement. We recommend pre-loading the embankment with 6 feet of fill (~750 PSF) for a period of 1 to 1.5 months prior to pavement. Interlocking blocks may be required to confine the preload soil next to the existing roadway. Either of these recommendations will result in a stable embankment. The preloading option is typically less expensive; however this may be offset by the time delay involved and double handling of the preload soil. The decision of which option to use will be left up to the owner. 3.1.3 Compliance with City of Auburn Critical Areas Ordinance As stated in Section 2.6 above, the slope on the west side of West Valley Highway has Class IV/Very High landslide hazard based on the ACC 16.10. Therefore, in order to build the proposed road layout in this area, all site activities must be in compliance with the City of Auburn Critical Areas Ordinance. The west edge of the proposed new roadway will be directly above the west edge of the existing roadway, i.e., there will be no expansion of the roadway to the west, the direction of the critical slope. Buffers and best management practices (BMPs) for working in the vicinity of the slope are discussed below. Hazard Identification and Evaluation The slope on the west of the West Valley Highway is prone to both erosion and landslides due to its geologic composition and the steepness of the slope. The slope is mostly covered with native and non- native vegetation, which is the best prevention for surficial erosion. This vegetation should not be removed. Careful planting of native vegetation would aid in erosion control of this hillside. Landslides tend to occur because groundwater or surface water infiltrates the soil and causes failure planes. Adding weight to the top of slopes and undermining the toe of slopes are other contributing factors to landslides. Since there are residences above the slope, it is necessary to notify them about landslide prevention practices, i.e., diverting surface water away from the slope and not adding additional weight to the top of the slope. As stated below, the construction activities associated with the West Valley Highway project will not alter the topography of the slope. Buffers Based on ACC Section 16.10.090-A, buffer areas must be established for all development in or adjacent to critical areas, in order to protect life, property and resources from risks associated with development on unstable or critical lands. Buffers typically consist of an undisturbed area of native vegetation retained to achieve the purpose of the buffer. In order to comply with the ordinance, the buffer shall be protected during construction by placement of a temporary barricade, notice of the presence of the critical area, and implementation of appropriate erosion and sedimentation controls. In the case of these geologic hazard areas, buffers will be measured from the top, toe, and along the sides of the slope. In the case of the slope along West Valley Highway, we recommend that the buffer along the top edge of the slope extend 50 feet west (above) the slope. Along the sides and the toe of the slope, we recommend that this buffer extend 15 feet. The buffer along the toe of the slope has already been encroached upon by West Valley Highway - 9 - Geotechnical Report 2 June 2010 the existing roadway, catch basins, and storm drain pipes.. However, it is the intent of the project to not further encroach into the critical area or its buffer. We will discuss methods to adequately protect the slope and the proposed development. Best Management Practices (BMPs) In order to permit development within the critical slope buffer, it is necessary to meet the provisions of ACC16.10.100, 16.10.110, 16.10.120, and 16.10.130, which address the alteration or development of critical areas; the mitigation standards, criteria and plan requirements; the performance standards for mitigation planning; and the monitoring program and contingency plan, respectively. In general, the development will not increase the instability or create a hazard to the site or adjacent properties, or result in a significant increase in sedimentation or erosion. As stated in ACC 16.10.100-E-2c, after reviewing the final construction documents, if the Critical Areas the risk of damage from the proposal, both on-site and off-site, are minimal subject to the conditions set forth in the report, that the proposal will not increase the risk of occurrence of the potential geologic hazard, and that measures to eliminate or reduce risks have been incorporated into its recommendations;. To meet these criteria, construction activities must not change the nature of the geologic hazard. We therefore recommend the following: The profile of the west side of the roadway and the slope should remain the same. The roadway will not be widened in the direction of the critical slope and buffer zone. The project should include an adequate drainage system to intercept and convey runoff at the toe of the slope to prevent prolonged saturation of the buffer area that could increase erosion and slope instability potential. According to the City of Auburn, portions of the existing drainage system along the toe of the slope have failed and require replacement. Additional cross drains should be installed as needed to intercept and convey hillside and roadway runoff. Portions of the existing drainage system can be used and tied into the proposed drainage system. The existing storm water ditch will not be excavated any deeper or wider. In much of the existing drainage ditch, there is a layer of organic material and sloughed soil on top of the native soil at the base of the ditch (see Figures 2 and 4). This material above the native soil can be removed to improve the cross sectional area of the ditch without changing the stability of the adjacent hillside. There will be no change in the amount of impervious surface coverage in the buffer zone. There will be changes to the types of impervious surfacing in this area. Do not remove existing vegetation from the face of the slope. Careful planting of native vegetation would aid in erosion control of this hillside. Identify and remove any water flowing from sources above the site. Notify residents above the slope about landslide prevention practices, i.e., diverting surface water away from the slope and not adding additional weight to the top of the slope. Construction activities will not touch the existing slope in any way. The slope buffer shall be protected during construction by placement of a temporary barricade, notice of the presence of the critical area, and implementation of appropriate temporary erosion and sedimentation controls (TESCs). Specific recommendations for TESCs, etc. will be provided when the design is more complete. West Valley Highway - 10 - Geotechnical Report 2 June 2010 3.1.4 Structural Fill Materials and Compaction For imported soil to be used as general structural fill, we recommend using a clean, well-graded sand and gravel such as Gravel Borrow, specified in Section 9-03.14(1) of the 2010 WSDOT Standard Specifications. On site soils may be used for structural fill if they meet the WSDOT criteria for Gravel Borrow. We expect that all of the existing road bed fill will meet the WSDOT criteria. The fill in the top 2-3 foot layer in the Goedecke Site may be suitable for re-use, however many pockets of organic materials, roots and wood debris will be encountered which is unsuitable. If the design for the east shoulder includes porous pavement, we recommend that the top five feet of underlying fill be Permeable Ballast as specified in WSDOT Specifications Section 9-03.9 (2). This material has less than 2% fines, and is therefore more permeable than Gravel Borrow. In general, the structural fill and the drainage material should be placed in eight-inch horizontal lifts and compacted to a minimum of 95 percent of its maximum dry density, as determined by test method ASTM D-1557 (Modified Proctor). The procedure to achieve the specified minimum relative compaction depends on the size and type of compacting equipment, the number of passes, thickness of the layer being compacted, and certain soil properties. Before fill control can begin, the compaction characteristics of the fill material must be determined from representative samples of the structural and drainage fill. A study of compaction characteristics should include determination of optimum and natural moisture contents of these soils at the time of placement. We recommend that a qualified geotechnical or civil engineer be on site to observe the appropriate lift thickness and adequacy of the subgrade preparation. A sufficient number of in-place density tests should be performed as the fill is being placed to determine if the required compaction is being achieved. If earthwork is performed during extended periods of wet weather or in wet conditions, the structural fill should conform to the recommendations provided in the Wet Weather Earthwork section below. 3.1.5 Wet Weather Earthwork Earthwork-related construction will be influenced by weather conditions. The existing subsurface soil at the site contains significant amounts of fine-grained sands and silts, which will make the existing subsurface soil sensitive to moisture. Traversing the exposed subsurface soils in wet weather with construction equipment will also lead to subgrade degradation. Furthermore, these soils may be difficult to compact if their moisture content significantly exceeds the optimum. Site grading activities using moisture-sensitive soil should normally occur during the relatively warmer and drier period between mid- summer to early fall. For wet weather construction we recommend the following: Earthwork should be performed in small areas to minimize exposure to wet weather. Excavation or the removal of unsuitable soil should be followed promptly by placement and compaction of wet weather structural fill. The size and type of construction equipment used may have to be limited to prevent soil disturbance. Under some circumstances, it may be necessary to excavate soil with a backhoe to minimize subgrade disturbance caused by equipment traffic. Material used as structural fill should consist of clean, granular soil with less than 5 percent passing the U.S. Standard No. 200 sieve, based on wet sieving the fraction passing the ¼-inch sieve. The fine-grained portion of the structural fill soil should be non-plastic. The Shoulder Ballast material specified for the drainage layer meets these criteria. The ground surface within the construction area should be graded to promote runoff of surface water and to prevent ponding of water. The ground surface within the construction area should be sealed by a smooth drum vibratory roller, or the equivalent, and under no circumstances should soil be left un-compacted and exposed to moisture. West Valley Highway - 11 - Geotechnical Report 2 June 2010 Excavation and placement of structural fill material should be under the full time observation of a representative of a qualified geotechnical or civil engineer, to determine that the work is being accomplished according to the project specifications and the recommendations contained herein. Bales of straw and/or geotextile silt fences should be strategically located to control erosion and the movement of soil. 3.1.6 Temporary and Permanent Slopes In order to accommodate the possible construction of the new retaining walls, temporary excavations into existing slopes along the roadway may be required. Based on the soil conditions observed in our explorations and projected typical shallow foundation depths, we anticipate that the temporary excavations for retaining walls will generally encounter existing roadway fill consisting of medium dense, medium to coarse silty Sand or medium dense, silty, fine to coarse sandy Gravel. Temporary excavations into roadway fill should be sloped no steeper than 1½H:1V unless field verified by a qualified Engineer. Temporary excavation slopes should be protected by covering with plastic sheeting or other approved means to prevent erosion. Temporary excavation slopes should be the sole responsibility of the contractor. All local, state, and federal safety codes should be followed. The contractor should implement measures to prevent surface water runoff from entering excavations. All temporary excavation slopes should be monitored by the contractor during construction for any evidence of instability. If instability is detected, the contractor should flatten the temporary excavation slopes or install temporary shoring. If groundwater or groundwater seepage is present, flatter excavation slopes should be expected. In areas where sufficient right of way width is available, the permanent embankment should be sloped no steeper than 2H:1V. We analyzed the stability of the new embankment using Slide Slope Stability software (see Figure 5). Input into Slide consisted of the following: Existing foundation soil parameters as shown on Figures 2 and 4; Structural fill as specified in Section 3.1.4 above; A 2H:1V sloped face; A 750 lb/ft² surcharge on top of slope; and Assumed saturated soils under slope. The results indicate a static factor of safety for global failure of 1.2 with the surcharge in place and a factor of safety 1.4 with the surcharge removed. With geogrid installed, the factor of safety for global failure is over 2.0 for both surcharge and unloaded conditions. To prevent erosion, permanent slopes should be hydro-seeded as soon as practical or covered with either mulch or erosion control netting/blankets, and bonded fiber matrix. 3.1.7 Benching of Existing Embankment When constructing the permanent embankment, the existing embankment must be benched to ensure a competent bond between the new and existing soil masses. Cuts 3 to 4 feet horizontally and vertically are made as the fill is installed. The actual heights of the cuts will be determined in the field by a qualified Engineer. The benching continues up the slope to within 5 feet horizontally and vertically of the buried utilities under the shoulder of the embankment. Benching must not be performed until a 5 foot buffer has been clearly marked by the Contractor after verifying the location of the utilities. The installation of Road Mesh or geogrid which spans between the new and existing embankments will mitigate any effects of not benching the upper portion of them embankment. (See Section 3.4.2 below) West Valley Highway - 12 - Geotechnical Report 2 June 2010 3.2 Retaining Wall Design Recommendations We anticipate that retaining walls will be needed to support the new roadway embankment along portions of the alignment where there is not sufficient width within the project right of way to use a 2H:1V permanent embankment slope. The width of the embankment construction right of way is dependent upon criteria such as property lines and wetland buffers zones, which have not been determined yet. The following sections provide recommendations for retaining walls. 3.2.1 Lateral Earth Pressures Design of any retaining walls should include appropriate lateral earth pressures caused by any adjacent surcharge loads. For uniform surcharge pressures due to vehicular loading, fill, or pavement placed behind the wall, a uniformly distributed horizontal load of the coefficient of active earth pressure, K a =0.26, times the surcharge pressure should be added for yielding walls. Where large surcharge loads such as heavy trucks, a crane, or other construction equipment are anticipated in close proximity to the retaining walls, the walls should be designed to accommodate the additional lateral pressures resulting from the surcharge load. Applicable vertical surcharge loads should include loads from fill or pavement above the top of the wall and surcharge due to vehicular traffic. We used a vertical surcharge load of 100 PSF to account for additional loads from fill or pavement behind the top of the wall and a vertical surcharge of 250 PSF to account for vehicular loading. 3.2.2 Settlement and Pre-Loading We anticipate that the new embankment will settle between 3 and 6 inches in a non- uniform fashion due to the compressibility of varying underlying soils. We have provided recommendations to mitigate the effects of settlement on the roadway in Section 3.1.2. 3.2.3 Gabion and Modular Retaining Walls The retaining wall will be installed before complete ground settlement has occurred and will settle and deform during and after construction. Therefore we recommend using a retaining wall system that has some flexibility to accommodate this movement. A gabion wall such as one by Hilfiker (http://www.hilfiker.com/gabface/index.html) or Maccaferri (http://www.maccaferri- northamerica.com/retaining_walls.aspx) is the most suitable design because of its flexibility. Rigid retaining structures such as Gravity Stone or Crib Lock are not recommended, because these types will show the deformation caused by settlement. In order to accommodate planting of vegetation on the face of the wall, we recommend that topsoil be placed in the outer one-foot of the gabion basket. 3.2.4 Retaining Wall Design Based on a surveyed contour map of the site provided by INCA Engineers, we estimate that the tallest retaining structure required on the alignment to be approximately 10 feet. Therefore we performed an analysis, using Maccaferri software, of a gabion wall retaining structure 10 feet tall, as shown in Figure 6. To model normal use conditions, we used a vertical load of 100 PSF to account for additional loads from fill or pavement behind the top of the wall and a vertical load of 250 PSF to account for vehicular loading. To model conditions during pre-loading, we used a vertical surcharge of 780 PSF on the backfill. Based on the analysis, we recommend a retaining structure as shown in Figure 6. The wall has three vertical layers of gabion baskets and is four baskets deep on the bottom, two deep in the middle, and one deep on the top layer. After a layer of baskets is installed with backfill compacted behind it, geogrid is West Valley Highway - 13 - Geotechnical Report 2 June 2010 placed on top of the soil, spanning between the gabion basket and the benched surface of the existing embankment. Care must be taken to ensure the backfill is fully compacted, as described above, and flush with the gabion and bench surfaces to avoid pinching of the geogrid when compacting subsequent lifts. 3.2.5 Wall Drainage Considerations The preceding lateral earth pressure recommendations assume that sufficient drainage is provided behind the retaining walls to prevent build-up of hydrostatic pressure. The clean, coarse rock backfill in the gabion baskets is permeable enough to provide sufficient drainage without the addition of a drainage system behind the wall. Shoulder ballast is placed as backfill with a fabric filter separating the fill and the gabion wall, as shown in Figure 6. If any other type of wall is used, we should be notified so we can provide recommendations for drainage behind the wall. 3.3 Signal Pole Foundation Design Recommendations We understand that new signal pole foundations will be placed at the corners of West Valley Highway and West Main Street. The signal pole foundations will be designed in accordance with the WSDOT design methodology. Based on the results of our field exploration and engineering analyses, it is our opinion that the proposed new traffic signals can be supported on drilled shaft foundations. The drilled shafts should be embedded sufficiently to resist lateral forces and resulting overturning moments. Our calculations of allowable lateral bearing pressures for the foundation design was based on the data from CPTs and Table 17.2 of WSDOT Geotechnical Design Manual M 46-03 (Appendix C). From the raw CPT data, we calculated average weighted values of SPT at depths of 5 ft, 10 ft and 15 ft. Bearing pressures were matched to the SPT values in Table 17.2. The results, summarized in Table 1 below, show that the lowest allowable lateral bearing pressure we recommend using is 2900 psf. Given this expected bearing pressure, WSDOT Standard Plan J-28.30.01 Steel Light Standard Foundation Type A is appropriate. The plan can be found at http://www.wsdot.wa.gov/Design/Standards/Plans.htm#SectionJ. It should be noted that the top two feet of soil at the northwest corner (CPT-01) is very dense, well graded gravel. The CPT data show soft soils at this depth because the material was too dense to penetrate with the probe. Therefore, the first two feet were drilled with an auger and the hole was filled with loose soil before the CPT started. Hence, the SPT values for this region are actually exceptionally high, not very low as presented in the data. Table 1-Recommended Allowable Lateral Bearing Pressures Depth Weighted Allowable Lateral Signal CPT of SPT Average Bearing Pressure Location Location Count SPT (Table 17.2) (feet) psf psi NW Corner CPT-01 5 18 3100 446400 10 27 4200 604800 15 28 4200 604800 SE Corner CPT-02 5 17 2900 417600 10 22 3780 544320 15 17 2900 417600 West Valley Highway - 14 - Geotechnical Report 2 June 2010 With respect to City of Auburn Code 16.10.100- E- 3, Seismic Hazard Areas, it is our opinion that liquefaction issues are not relevant to the signal pole design, since the foundations are going to be well above the water table and the soils are very dense. Construction methods for traffic signal foundations typically involve drilling a vertical shaft with a single-flight auger drill rig, placing a reinforcing steel cage into the drilled hole, and filling the hole with concrete. Depending on ground conditions, the hole may be cased or uncased and the concrete placed by free-fall or with a tremie pipe. For small diameter holes (3 to 4 feet in diameter) advanced above the ground water table, the soil should have sufficient stand time to allow construction of the foundations without casing. Large cobbles and boulders are typically encountered in glacial deposits and large pieces of debris may be present within the fill deposits. The single-flight auger should be large enough to handle these large soil particles and/or debris. A qualified geotechnical engineer should observe drilled shaft excavation and concrete placement. This will allow the opportunity to confirm conditions indicated by our explorations and/or provide corrective recommendations adapted to conditions observed during construction. 3.4 Pavement Considerations We performed analyses for the design of flexible and rigid pavement sections along the project site. The design sections were developed using the City of Auburns Standards for Pavement Design and the Association of State Highway and Transportation Officials design procedure (AASHTO 1993). 3.4.1 Recommendations for Design of Pavement Section The existing pavement in most of the roadway consists of a section 20 inches thick, consisting of PCC, brick, ATB, and ACPnly ACP. Given the age of the roadway and the traffic volume, we presume that the underlying soils will not settle further in these areas. The challenge for this project will be to construct a new embankment which will have minimal settlement after pavement placement and to reduce differential movement between the existing and new embankments. Based on discussions with INCA Engineers, we are assuming that the existing pavement section will not be removed entirely, but will be left in place as part of the base course. The pavement design incorporates this assumption. This provides a base course which exceeds the design thickness and stiffness requirements. The soils below the existing pavement, the subgrade, are at least average condition or better, as defined in WSDOT Pavement Policy. Our geotechnical investigation revealed that the existing subgrade is composed of medium dense to very dense, medium to coarse silty Sand or dense, fine silty, sandy Gravel. Pockets of softer materials may exist, though the small amount of rutting and fatigue cracking in the existing pavement suggests they are not significant. The longitudinal and transverse cracking in the existing pavement appear to be reflection cracks from the edges of previous layers of asphalt overlays. The pavement design is based on the following traffic data, provided to us by INCA Engineers: Average Daily Traffic (ADT) = 5,000 Growth factor = 3.5 percent per year Growth period = 20 years West Valley Highway - 15 - Geotechnical Report 2 June 2010 For the purposes of our design, an equivalent single axle load (ESAL) of 5,000,000 was used for each of the traffic directions. A summary of ESAL calculations is presented in Appendix D. Our design consists of two separate pavement systems: flexible and rigid. A flexible pavement system has a bituminous surface, and a rigid system has a surface of Portland cement concrete (PCC). Both systems were designed using WSDOT standards. Based on the analyses, we recommend the following: For the Flexible Pavement Section, a minimum of 4 inches of hot mix asphalt (HMA, overlaying 4 inches of HMAB base course, overlaying 6inches of densely compacted, crushed surfacing base course (CSBC) (see Figure 7). For the rigid pavement system, we recommend using a minimum of 10 inches of PCC overlaying 6 inches of hot mix asphalt base course (HMAB) (see Figure 7). The assumptions for the flexible pavement and rigid pavement systems are shown in Appendix D. 3.4.2 Pavement Construction Options Flexible Pavement We suggest 3 options for the installation of HMA road surface: Option 1: Use existing road bed as base course with final road surface grade elevation higher The entire depth of the existing road surface is left in place, and the east edge of asphalt is saw-cut to expose a clean edge for mating to the new embankment. The new embankment base course (consisting of 4 inches of hot mix asphalt base course (HMAB) on top of 6 inches of CSBC) is leveled flush with the existing pavement surface. The joint between the new embankment and the existing road base course is spanned by a geotextile fabric or mesh, which provides tensile strength for resistance against cracking. Road Mesh, made by Maccaferri, and Petromat, made by Industrial Fabrics Inc. are two such materials. Two 2-inch lifts of of HMA wearing course is installed on top of the geotextile or mesh, as shown in Figure 8. Option 2: Mill top 4 inches of existing road bed as base course to maintain existing road surface elevation The top 4 inches of the road surface is milled and the spoils removed. The new embankment base course (consisting of 4 inches of HMAB on top of 6 inches of CSBC) is finished flush with the new milled pavement surface. The joint between the new embankment and the existing road base course is spanned by a geotextile, as described in Option 1, prior to installation of the designed 4 inches of HMA wearing course (two 2-inch lifts). The road surface elevation will remain the same as before construction (see Figure 9). Option 3: Remove existing pavement to the top of the brick layer Mill the top 9 to 10 inches of the existing pavement, exposing the red brick. Proof roll the fill on either side of the brick (the brick layer does not span the entire road section) according to the procedures in 3.1.2 above. After installation of the new embankment fill, install a geogrid spanning from the existing road bank to the new embankment. Install 6 inches of CSBC, 4 inches feet of HMAB base course and 4 ½ inches of HMA wearing course. The new road surface elevation will be 0.2 inches higher than the original surface (see Figure 10). West Valley Highway - 16 - Geotechnical Report 2 June 2010 Rigid Pavement Option 4: Remove existing pavement to the top of the concrete layer Remove the top 16 inches of existing pavement, exposing the concrete layer. Proof roll the fill on either side of the brick (the concrete layer does not span the entire road section) according to the procedures in 3.1.2 above. After installation of the fill of new embankment, install a Petromat (or equivalent) spanning from the existing road bank to the new embankment at the depth of 16 inches. Install 6 inches of HMAB and 10 inches of Portland cement concrete as wearing course. The PCC pavement should have non-dowelled joints every 12 feet (see Figure 11). The pavement designs offer a range of costs and benefits, which are outlined in Table 2. The more expensive designs (Options 3 and 4) will provide the highest performance. We estimate that Option 3 will provide the most resistance to longitudinal cracking. All four options are feasible without altering the toe of the critical area slope. Table 2- Pavement Options PAVEMENT CONSTRUCTION OPTIONS OPTION BENEFITS DRAWBACKS a. The least expensive option. a. Limited strength against cracking along seam between existing and new base course if the new base settles after preloading. b. The option with the lowest environmental b. Requires feathering of the pavement to the 1 impact. existing pavement on the north and south ends of the alignment. c. Avoids interaction with the critical high c. Some uncertainty about consistency of base slope west of the road. course strength. a. A limited amount of material to mill and a. Limited strength against cracking along seam remove from site. between existing and new base course if the new base settles after preloading. 2 b. Retains existing roadway grade. b. Some uncertainty about consistency of base course strength. a. High strength against cracking along seam a. Relatively high excavation costs between existing and new base course if the new base settles after preloading. b. High degree of certainty of base course 3 strength. c. Excavation spoils may be usable as fill material a. The most durable option. a. The most expensive option b. The locations of cracks can be controlled 4 The pavement subgrade should be compacted to 95% of the maximum dry density, based on Modified Proctor (ASTM D 1557). A sufficient number of in-place density tests during grading work should be performed to confirm that the required relative compaction is being achieved. Base course materials used should meet the gradation requirements in Section 9-03.9(3) of the 2010 WSDOT Standard West Valley Highway - 17 - Geotechnical Report 2 June 2010 Specifications, and be placed in accordance with Section 4-04 of the 2010 WSDOT Standard Specifications. We recommend that a qualified geotechnical or civil engineer be on site to observe pavement subgrade preparation. The new pavement will abut existing pavement on the north and south ends, in locations to be determined in the final design. Care must be taken to design a suitable joint between the two different pavement systems. 3.5 Site Drainage and Erosion Considerations 3.5.1 Surface Water Control During site visits, we observed a constant seepage of subsurface water at three locations along the slope on the west side of the alignment: at Sta. 7+50, 8+00 and 8+30, as shown in Figure 1. Seepage from the slope at 8+00 ft is shown in Photos, Appendix A. Since the only house located close to the crest of the slope above the alignment is situated above the observed seepage, we recommend that the storm water drainage practices of this house be investigated to see if they are contributing to the seepage on the slope. The toe of the slope on the west side of the highway should not be changed during construction since it is a critical slope (Hazard Ordinance addressed in section 2.7.3 of this report); the existing drainage system appears to function adequately. Therefore, we recommend using the existing drainage ditch, storm water catch basins, and conduits for permanent groundwater and storm water runoff interception. In much of the existing drainage ditch, there is a layer of organic material and sloughed soil on top of the native soil at the base of the ditch (see Figures 2 and 4). This material above the native soil can be removed to improve the cross sectional area of the ditch without changing the stability of the adjacent hillside. 3.5.2 Erosion Control During construction at the site, implementing the recommendations presented in the section on wet weather earthwork can minimize erosion. The erosion control devices should be in place and remain in place throughout site preparation and construction. We recommend that erosion control measures implemented at the site conform to Washington State Department of Ecology 3.6 Seismic Design Criteria 3.6.1 General Design ground acceleration for the project was determined using results from the USGS website, based on the National Seismic Hazards Mapping Project completed by USGS in 2008. The peak ground acceleration (PGA) at the project site is approximately 0.57g, based on horizontal bedrock accelerations associated with a 2 percent probability of exceedance in a 50-year period. 3.6.2 Soil Liquefaction Liquefaction occurs when loose, saturated, cohesionless, poorly-graded sands temporarily lose shear strength as a result of increased pore pressures induced by vibration or earthquake shaking. Primary factors controlling the development of liquefaction include intensity and duration of strong ground motion, characteristics of subsurface soil including soil type, relative density, gradation, and age of deposits, in-situ stress conditions and the depth to groundwater. Potential effects of soil liquefaction include temporary loss of bearing capacity and lateral soil resistance, and excessive settlements upon dissipation of the excess pore pressures. West Valley Highway - 18 - Geotechnical Report 2 June 2010 The results of our subsurface investigation indicate that the soils underlying the site primarily consist of dense, well-graded silty sands and gravels with layers of cohesive silty and clayey soils, and poorly- graded sand. Given these soil types, it is our opinion that the risk of soil liquefaction at the site during the design earthquake is low. West Valley Highway - 19 - Geotechnical Report 2 June 2010 4 Closure This report has been prepared exclusively for the use of INCA Engineers and their sub-consultants and contractors for specific application to the West Valley Highway Improvements Project. The observations presented in this report are based on the subsurface explorations and observations completed for this investigation, review of previous geotechnical work in the project area, and conversations regarding the project, and are not intended, nor should they be construed to represent, a warranty, but are forwarded to assist in the planning and design process. Considerable judgment has been applied in interpreting and presenting the results. Subsurface conditions can vary substantially with depth, distance, or due to unanticipated geologic conditions, and the integrity of the geotechnical design elements depends on proper site preparation and construction procedures. As the design develops, we recommend that we be retained to review final design plans and specifications so we can revise or augment our recommendations as required. During the construction phase of the project, we recommend that we be retained to review contractor submittals and make geotechnical engineering decisions, which may be required in the event that localized variations in the subsurface conditions become apparent during construction. We appreciate this opportunity to be of service to you. Should you have any questions, or request additional information, please do not hesitate to contact us. Sincerely, JACOBS ASSOCIATES _______________________ _______________________ _______________________ Don Reid Carol Ravano, PE Frank Pita, PE/LHG Project Engineer Associate Principal West Valley Highway - 20 - Geotechnical Report 2 June 2010 5 References AASHTOO. AASHTOO Guide for Design of Pavement Structures. 1993. ASTM. ASTM D-2488, Standard Recommended Practice for Description of Soils (Visual-Manual Procedure). 2006. City of Auburn Code 2010. GeoMAPNW. Geologic Map of King County. Derek B. Booth, Kathy A. Troost & Aaron P. Wisher, March 2007 WSDOT. WSDOT Geotechnical Design Manual. 2010. WSDOT. WSDOT Standard Specifications for Road, Bridge, and Municipal Construction. 2010. WSDOT. WSDOT Pavement Policy. 2008. USGS National Seismic Hazard Mapping Project. http://www.geohazards.cr.usgs.gov. West Valley Highway - 21 - Geotechnical Report 2 June 2010 6 Figures West Valley Highway - 22 - Geotechnical Report 2 June 2010 Appendices West Valley Highway - 34 - Geotechnical Report 2 June 2010 Appendix A - Photographs Photo 1-Pavement Core Recovered at CPT-03 Photo 2-Pavement Core Recovered at CPT-09 Photo 3-Test Pit T-05 Road Fill Photo 4-Hard Native Soil on Cut Photo 5-Test Pit T-07 Hard Native Soil of Hillside Photo 6-Test Pit T-01 Groundwater and sloughing sides West Valley Highway - 35 - Geotechnical Report 2 June 2010 Photo 7- Slope of Cut and Hill Side (note small existing cantilever wall which protects the base of the drains) Photo 8- Seepage at Sta. 8+00 West Valley Highway - 36 - Geotechnical Report 2 June 2010 Appendix B - CPT Logs West Valley Highway - 37 - Geotechnical Report 2 June 2010 West Valley Highway - 38 - Geotechnical Report 2 June 2010 West Valley Highway - 39 - Geotechnical Report 2 June 2010 West Valley Highway - 40 - Geotechnical Report 2 June 2010 West Valley Highway - 41 - Geotechnical Report 2 June 2010 West Valley Highway - 42 - Geotechnical Report 2 June 2010 West Valley Highway - 43 - Geotechnical Report 2 June 2010 West Valley Highway - 44 - Geotechnical Report 2 June 2010 West Valley Highway - 45 - Geotechnical Report 2 June 2010 West Valley Highway - 46 - Geotechnical Report 2 June 2010 Appendix C - Signal Pole Foundation Soil Strength Table (WSDOT Geotechnical Design Manual M 46-03, December 2006, Chapter 17) West Valley Highway - 47 - Geotechnical Report 2 June 2010 Appendix D - Pavement Design ESAL Calculations: ÚØÉß Ê»¸·½´» Ý´¿­­ ìôëôêôé èôçôïð ïïôïîôïí Þ«­»­ ÛÍßÔ­ñ ª»¸·½´» ðòì ï ïòéë îòë îëî çî ïð îí ߪ¹ò Ü¿·´§ ݱ«²¬ ïððòè çîòî ïèòï ëéòì ßÜÔ íêèðè ííêëè êêïê îðçëë ÛÍßÔ­ñ§»¿® Ü»­·¹² Ô·º» л®½»²¬ ëõ ¿¨´» ̱¬¿´ Ç»¿®´§ Ù®±©¬¸ Ü»­·¹² Ô·º» Ü«®¿¬·±² ¬®«½µ­ ¿²¼ ¾«­»­ ÛÍßÔ­ כּ ÛÍßÔ­ ø§»¿®­÷ ïû +,41.íòëû 2Ë--2Ë01, îð West Valley Highway - 48 - Geotechnical Report 2 June 2010 Appendix E - Test Pit Logs West Valley Highway - 49 - Geotechnical Report 2 June 2010