Geotechnical & Environmental Consultants 9725 SW Beaverton-Hillsdale Hwy., Suite 140 Portland, OR FAX

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1 Geotechnical & Environmental Consultants 972 SW BeavertonHillsdale Hwy., Suite 140 Portland, OR FAX TECHNICAL MEMORANDUM To: Mark Libby, PE / HDR Engineering, Inc. Date: October 4, 200 GRI Project No.: 444 From: Stan Kelsay, PE, GE; Gene Tupper, PE, GE; and Tammy Kimball, PE Re: Geotechnical Investigation West End Park Connection Union Street Railroad Bridge Salem, Oregon DRAFT INTRODUCTION At the request of HDR Engineering, Inc. (HDR), GRI has conducted a geotechnical investigation to aid in the design and construction of the elements associated with the west end park connection to the Union Street railroad bridge project. The Vicinity Map, Figure 1, shows the general location of the project in Wallace Marine Park, which is located on the west side of the Willamette River and west of downtown Salem, Oregon. The purpose of the geotechnical investigation was to evaluate subsurface conditions at the site and provide our preliminary conclusions and recommendations regarding design and construction of the various project elements. PROJECT DESCRIPTION As shown on the Site Plan, Figure 2, the proposed improvements consist of approximately 0 ft of paved shareduse path to be constructed immediately north of the existing Union Pacific Railroad trestle. The path will be constructed on embankment, which we estimate will have a maximum height of about 10 ft near the existing trestle and thin to match existing site grades where it connects to Musgrave Avenue. A retaining wall approximately 100 ft long will be constructed to retain a portion of the embankment. We understand the planning and design of the retaining wall system are currently in progress. We have estimated the height of the wall could approach 10 ft. Based on our discussions with you, we understand the new retaining wall likely will be a mechanically stabilized earthtype (MSE) construction. We understand the paths will likely be paved with Portland cement concrete (PCC) pavements; however, asphalticconcrete (AC) pavements may be considered for the path connecting the existing railroad alignment with the park. Our discussions with you indicate the bridge and trail extension to Wallace Road will be subjected to emergency fire truck traffic. SITE DESCRIPTION The ground surface in the project vicinity has a gentle slope and ranges from about elevation 144 ft at the west end near the proposed retaining wall location to about elevation 130 ft at the east end, where the path

2 terminates at Musgrave Avenue. An existing northsouthtrending waterline passes beneath the northeast corner of the proposed MSE retaining wall, as shown on Figure 2. The area of the proposed retaining wall is vegetated with trees, shrubs, and berry brambles. The remaining portion of the path alignment is vegetated with grass. We anticipate the site is underlain by alluvial deposits consisting of silt, sand, and gravel associated with the nearby Willamette River. FIELD EXPLORATIONS AND LABORATORY TESTING Subsurface materials and conditions for the project were investigated on July 27, 200, with three test pits, designated TP1 through TP3. The test pits were excavated with a Case 80 rubbertired backhoe provided and operated by Emery & Sons Construction of Stayton, Oregon. The general locations of the explorations are shown on Figure 2. The terms used to describe the soil encountered in the test pits are defined in Table 1. During excavation of test pit TP2, the exploration encountered an approximately 24in.diameter pipe, possibly ductile iron. This location approximately corresponds to the location of the water pipe shown on Figure 2 that runs northsouth under the proposed retaining; however, it is unclear whether it is the existing waterline shown on Figure 2 or some other unidentified pipe. The invert of the pipe is located about 4 ft below the ground surface. No granular trench backfill or pipe material was observed around the pipe. Laboratory testing of soil samples obtained from the test pits included: moisture content determinations (ASTM D 221), onedimensional consolidation testing (ASTM D243), and dry unit weight determination (ASTM D 2937). Approximate undrained shear strengths of relatively undisturbed soil samples in the field were determined using a Torvane shear device. The results of the moisture contents, Torvane shear tests, and dry unit weight are shown on the Test Pit Logs, Figure 3. A onedimensional consolidation test was performed on a relatively undisturbed sample of silt from test pit TP2. The test provides data on the compressibility of the underlying finegrained soils, necessary for settlement studies. The test results are summarized on Figure 4 in the form of a curve showing percent strain versus applied effective stress. The initial and final dry unit weight and moisture content of the sample are also shown on the figure. SUBSURFACE CONDITIONS Soil Sandy silt to silty sand was encountered from the ground surface to a depth of 9 to 10 ft in the three test pits. The silt is typically brown, and the sand is fine grained. The relative consistency of the sandy silt is medium stiff to stiff based on Torvane shear strength values of 0.2 to 1.0 tsf. We estimate the relative density of the silty sand is loose to medium dense. The natural moisture content of the silt ranges from about 1 to 28%. Washed sieve analyses of selected samples indicate this material contains 32 to % passing the No. 200 sieve. The washed sieve analysis is used to aid in the classification of the soils. The sandy silt and silty sand soils would classify as ML and SM according to the USCS system. Groundwater Groundwater was not encountered in the test pits at the time of excavation. The groundwater level in the site vicinity likely approximates the surface water level of the Willamette River located south and east of 2

3 the site. Shallow perched groundwater may approach the ground surface during periods of prolonged, intense precipitation. CONCLUSIONS AND RECOMMENDATIONS General The subsurface explorations indicate the project area is underlain by relatively firm, sandy silt to silty sand to a depth of at least 10 ft, the maximum depth explored. Groundwater was not encountered in the explorations at the time of excavation; however, we anticipate it may approach the ground surface during heavy or prolonged precipitation. In our opinion, the site is suitable for the proposed development from a geotechnical engineering standpoint. The following sections of this technical memorandum present our conclusions and recommendations concerning earthwork and design and construction of the MSE walls. Structural Fill We anticipate the embankment for the path will have a maximum height of about 10 ft. In our opinion, onsite or imported, organicfree soils approved by the geotechnical engineer may be used to construct structural fills of the embankment. Suitable structural fill material for use in the MSE wall is discussed in the section below. However, finegrained soils are sensitive to moisture content and should be placed only during the dry summer months. During the wet winter and spring months, fills should be constructed using imported, relatively clean, granular materials. Approved organicfree, finegrained soils used to construct structural fills should be placed in 9in.thick lifts (loose) and compacted using pneumatic or segmentedpad rollers to a density not less than 9% of the maximum dry density as determined by ASTM D 98. Fill placed in landscaped areas should be compacted to a minimum of 90% ASTM D 98. In our opinion, the moisture content of finegrained soils at the time of compaction should be controlled to within about 3% of optimum. Some aeration and drying of finegrained soils may be required to meet the above recommendations for compaction. Imported granular materials used to construct structural fills during wet weather should consist of material with a maximum size of up to in. and not more than about % passing the No. 200 sieve (washed analysis). The first lift of granular fill material placed over the silt subgrade should be in the range of 12 to 18 in. thick (loose). Subsequent lifts should be placed 12 in. thick (loose). All lifts should be compacted with a mediumweight (48in.diameter drum), smooth, steelwheeled, vibratory roller until well keyed. Generally, a minimum of four passes with the roller is required to achieve compaction. We recommend that permanent and temporary fill slopes should be made no steeper than 2H:1V and 1H:1V, respectively. Our experience indicates that silt and sand soils exposed in fill slopes are susceptible to erosion. To minimize erosion, surface drainage should be directed away from the slopes and the slopes protected from erosion by vigorous plant growth or armored with fragmental rock up to in. in size. To enhance plant growth and retard erosion, it may be necessary to install mulch or a revegetation mat/fabric. MSE Retaining Wall As previously discussed, we understand a portion of the path embankment will be supported with an MSE wall. The approximate location of the MSE wall is shown on Figure 2. Drainage of the MSE backfill is a 3

4 significant consideration for the design and performance of the wall. When finegrained backfill is used, such as the onsite silty soils, we recommend providing a drainage blanket at the back of the MSE wall reinforcement zone and at the bottom of the wall, in addition to the drainage blanket constructed between the backfill and the face of the wall. In addition, the MSE wall design should include positive drainage measures to prevent ponding of surface water behind the top of the wall. Assuming a horizontal backfill and fully drained conditions, we recommend using an equivalent fluid unit weight of 3 pcf for active earth pressure conditions which assumes yielding of the wall can be tolerated. This equivalent fluid unit weight is based on an assumed total unit weight of 120 pcf and effective angle of internal friction, φ, of about 32 for structural backfill. Additional load behind the wall due to uniformly distributed surcharge pressures at the ground surface may be estimated using an active coefficient of lateral earth pressure, Ka, of The resulting lateral pressure distribution behind the wall due to a uniformly distributed surcharge will be rectangular. Resistance to lateral loads can be provided by friction acting at the base of the wall. We anticipate the MSE wall foundation material will consist of medium dense/stiff, silty sand to sandy silt. The recommended ultimate value for the coefficient of friction, µ, at the base of the wall is 0., assuming the foundation material beneath the MSE retained backfill has an effective friction angle, φ, of 32 o and effective cohesion, c, of 0 tsf. We recommend applying a factor of safety of at least 1. to the ultimate value of the coefficient of friction to determine the allowable value for evaluation of sliding. However, a lower coefficient of friction between the reinforcing elements and the underlying soil may represent the critical case and should be determined by the MSE wall designer. For areas where the ground line in front of the MSE wall will be nearly horizontal and the toe of the wall will be provided with a minimum of 1 ft of embedment, the ultimate bearing capacity may be estimated in accordance with the following equation as a uniform distribution. Qult (psf) = 1,100B, where B is the width of reinforcing layers in feet In accordance with AASHTO guidelines, a factor of safety of 2. should be applied to this ultimate value to determine the allowable bearing capacity. Based on both stability and settlement considerations, we recommend a minimum reinforcement length for the MSE wall of no less than 0.8 times the height of retained backfill plus the equivalent height of uniformly applied surcharge pressure at the top of the backfill. Based on soil properties of an assumed total unit weight of 120 pcf and effective angle of internal friction, φ, of about 32 for structural backfill and the wall described above, we estimate the wall has a factor of safety against sliding and overturning greater than 2.. Based on the results of the consolidation testing, we anticipate the underlying deposit of silty sand to sandy silt is not highly compressible. Therefore, for a maximum MSE wall height of 10 ft and length of 100 ft, we estimate a total settlement of less than 1 in., with the majority of this settlement occurring as the wall is constructed. Lesser settlements would be expected for either a wider zone of reinforcement or a shorter wall. To assist HDR evaluate the effect of the settlement on the existing water line, we estimate the 4

5 settlement will be greatest at the face of the wall and will decrease to a negligible amount at an approximate horizontal distance of about twice the wall height from the face of the wall. If other types of retaining walls are used for this project, we would be pleased to provide the geotechnical information needed to assist with the design of these structures. Pavement Section We understand the new paths for the trail will consist of Portland cement concrete (PCC). The bridge and trail to Wallace Road, which follows the alignment of the existing railroad tracks, will be subjected to emergency use by a fire truck. Although we did not complete any explorations along this portion of the alignment, our observations at the site and our experience with railroads indicate the tracks are likely underlain by 1 to 2 ft, or more, of coarse ballast rock. If some damage of the trail can be tolerated, we recommend paving the trail with a in. thickness of PCC to support the emergency fire truck traffic. If damage to the trail cannot be tolerated, we recommend paving the trail with an 8in.thickness of PCC. The PCC pavement should be underlain by a 4in.thick cushion of crushed rock, assuming the existing railroad alignment is underlain by relatively clean, crushed ballast rock. If the existing railroad alignment is underlain by silty material or granular material containing more than about % passing the No. 200 sieve, the PCC pavement should be underlain by 10 in. of crushed rock base course. All crushed rock base course should be as outlined in the City of Salem Street Design Standards for bikeway construction. We understand the path connecting the existing railroad alignment with the park will consist of Portland cement concrete (PCC) or possibly asphaltic concrete (AC), and this portion of the path will be subjected to pedestrian, bicycle, and some maintenance vehicle traffic. For the anticipated traffic, we recommend paving the path with 4 in. of PCC underlain by 4 in. of crushed rock base course. It may be prudent to increase the thickness of PCC to in. if the path will be heavily used by maintenance vehicles. If the path will be paved with AC, we recommend the pavement for the path consist of a 2in. thickness of asphaltic concrete (AC) over a in. thickness of crushed rock base. This section should be considered minimal thickness, and it should be assumed that some maintenance will be required over the life of the pavement (1 to 20 years). If the path will be used heavily by maintenance vehicles, we recommend a minimum section of 2. in. of AC underlain by 9 in. of crushed rock base course, as outlined in the City of Salem Street Design Standards for bikeway construction. The pavement sections provided above are based on the assumption that the pavement subgrade consists of firm, undisturbed onsite silt/sand soils or structural fill. In addition, the pavement sections assume that construction will be accomplished during the dry season. If wetweather pavement construction is considered, it will likely become necessary to increase the thickness of crushed rock base course to support construction equipment. Where practical, pavement area subgrades should be proof rolled with a loaded dump truck or other heavy, rubbertired equipment prior to and after the placement of the base course. Soft areas identified by proof rolling should be overexcavated and backfilled with structural fill. DESIGN REVIEW AND CONSTRUCTION SERVICES We welcome the opportunity to review and discuss construction plans and specifications for this project as they are being developed. In addition, GRI should be retained to review all geotechnicalrelated portions

6 of the plans and specifications to evaluate whether they are in conformance with the recommendations provided in this memorandum. Additionally, to observe compliance with the intent of our recommendations, design concepts, and the plans and specifications, we are of the opinion that all construction operations dealing with earthwork and wall construction should be observed by a GRI representative. Our constructionphase services will allow for timely design changes if site conditions are encountered that are different from those described in our report. If we do not have the opportunity to confirm our interpretations, assumptions, and analyses during construction, GRI cannot be responsible for the application of our recommendations to subsurface conditions that are different from those described in this memorandum. LIMITATIONS This technical memorandum summarizes the results of subsurface explorations and laboratory testing completed for this project and provides our conclusions and recommendations regarding the design and construction of the proposed improvements. The scope of this report is limited to the specific project and location described herein, and our description of the project represents our current understanding of the significant aspects of the proposed improvements. These preliminary recommendations are subject to revision and/or confirmation after the project requirements are better defined. Because the design of the project is still being developed, we anticipate that some changes in the design or location of the project elements as outlined in this report, may be made. Consequently, we should be given the opportunity to review any changes and to modify or reaffirm the conclusions and recommendations of this memorandum in writing. The conclusions and recommendations submitted in this memorandum are based on the data obtained from the test pits made at the locations indicated on Figure 2 and from other sources of information as discussed in this report. In the performance of subsurface investigations, specific information is obtained at specific locations at specific times. However, it is acknowledged that variations in soil conditions may exist between exploration locations, and this memorandum does not necessarily reflect these variations. The nature and extent of variation may not become evident until construction. If, during construction, subsurface conditions different from those encountered in the explorations are observed or encountered, we should be advised at once so that we can observe and review these conditions and reconsider our recommendations where necessary. Submitted for GRI, H. Stanley Kelsay, PE, GE Gene M. Tupper, PE, GE Tamara G. Kimball, PE Principal Project Engineer Project Engineer 444 TECHNICAL MEMO (REV 1040)

7 Table 1 GUIDELINES FOR CLASSIFICATION OF SOIL Description of Relative Density for Granular Soil Standard Penetration Resistance Relative Density (Nvalues) blows per foot very loose 0 4 loose 4 10 medium dense dense 30 0 very dense over 0 Description of Consistency for FineGrained (Cohesive) Soils Standard Penetration Torvane Resistance (Nvalues) Undrained Shear Consistency blows per foot Strength, tsf very soft 2 less than 0.12 soft medium stiff stiff very stiff hard over 30 over 2.0 Sandy silt materials which exhibit general properties of granular soils are given relative density description. GrainSize Classification Modifier for Subclassification Boulders Percentage of 12 3 in. Other Material Adjective In Total Sample Cobbles 3 12 in. clean 0 2 Gravel trace /4 3 /4 in. (fine) 3 /4 3 in. (coarse) some Sand sandy, silty, 30 0 No. 200 No. 40 sieve (fine) clayey, etc. No. 40 No. 10 sieve (medium) No. 10 No. 4 sieve (coarse) Silt/Clay pass No. 200 sieve

8 DELORME 3D TOPOQUADS, OREGON WEST SALEM WEST, OREG. (1cd) 1999 North MILES G R I HDR ENGINEERING, INC. UNION STREET RAILROAD BRIDGE VICINITY MAP AUG. 200 JOB NO. 444 FIG. 1

1 2 3 4 7 8 F SHEET PREPARED BY: TP3 HDR Engineering, Inc. E TP2 D C TP1 EXISTING WATER STA. 1+00 MATCHLINE, SEE SHT 104 NO.

9 F SHEET PREPARED BY: TP3 HDR Engineering, Inc. E TP2 D C TP1 EXISTING WATER STA MATCHLINE, SEE SHT 104 NO. 0 VERIFY SHEET SIZE BAR IS ONE INCH ON ORIGINAL DRAWING 1" IF NOT ONE INCH, SHEET SIZE HAS BEEN MODIFIED CITY OF SALEM UNION STREET RAILROAD BRIDGE REVISIONS DESCRIPTION DATE B A STA. 9+0 MATCHLINE SEE SHT ALTERNATIVE 1 WEST PARK CONNECTION TEST PIT MADE BY GRI (JULY 27, 200) SITE PLAN FROM FILE BY HDR ENGINEERING, INC., DATED NOVEMBER 7, LEGEND CONTOURS EXISTING POWER EXISTING FENCE EXISTING ROW PROPOSED ROW PROPOSED EOP PROPOSED CENTERLINE G R I GRADING LIMITS North HDR ENGINEERING, INC. UNION STREET RAILROAD BRIDGE SITE PLAN NOTE: TALL OBJECTS MAY APPEAR TO BE OFFSET HORIZONTALLY DUE TO ANGLE OF AERIAL PHOTOGRAPH. PROJECT NO: FILE NAME: DATUM: SURVEY: HORIZ SCALE: VERT SCALE: DESIGN: DRAWN: CHECKED: APPROVED: FT SHEET TITLE DWG 1" = 20' S. HALE P. WAGGONER M. LIBBY 103 AUG. 200 JOB NO. 444 FIG. 2 8 SHEET 7 OF 19

10 TP1 Elev. 143 ft (±) Medium stiff to stiff, brown, sandy SILT to silty SAND; 8in.thick heavily rooted zone at the ground surface c = 0.80 tsf S1 w = 19% c = 0.70 tsf TP2 Elev. 143 ft (±) Medium stiff to stiff, brown, sandy SILT to silty SAND; scattered fine organics to a depth of ft, 8in.thick heavily rooted zone at the ground surface S1 w = 1% c = 0.20 tsf Depth, ft 4 S2 w = 28% c = 0.30 tsf Depth, ft 4 encountered approximately 24in. diameter iron pipe at a depth of about 4 ft S2 w = 22% c = 1.0 tsf γ d = 92 pcf 7 8 Bottom of test pit 10 ft (7/27/0) Groundwater not encountered S3 w = 19% c = 0.2 tsf minor red and black mottling between 8 and 9 ft S4 w = 2% c = 0.2 tsf 7 8 Bottom of test pit 9. ft (7/27/0) Groundwater not encountered S3 w = 2% c = 0.40 tsf S4 w = 18% c = 0.40 tsf TP3 Elev. 140 ft (±) Medium stiff, brown, sandy SILT to silty SAND; 3in.thick heavily rooted zone at the ground surface c = 0.30 tsf S1 w = 24% Depth, ft S2 w = 20% c = 0.4 tsf S3 w = 17% 9 S4 Bottom of test pit 9 ft (7/27/0) w = 17% Groundwater not encountered LEGEND = GRAB SAMPLE = 3IN.OD SHELBY TUBE SAMPLE w = NATURAL MOISTURE CONTENT c = TORVANE SHEAR STRENGTH γ d = DRY UNIT WEIGHT GROUND SURFACE ELEVATIONS FROM SITE PLAN, FIGURE 2. G R I HDR ENGINEERING, INC. UNION STREET RAILROAD BRIDGE TEST PIT LOGS AUG. 200 JOB NO. 444 FIG. 3

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