OR DOT CRGNSA 100(6)_Geotechnical Report for Bridges.pdf

Foundation Report

David Evans and Associates, Inc.

Western Federal Lands Highway Division

Historic Columbia River Highway Trail Viento to Mitchell Point Perham Creek and Mitchell Creek Bridges Hood River County, Oregon Task Order No. 69056718F000012

WFLHD GR 10-20

Prepared by

Oregon & Washington

October 29, 2020

TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 PROJECT DESCRIPTION

3.0 GEOLOGIC SETTING

4.0 SUBSURFACE CONDITIONS

4.1 General

4.2 Mitchell Creek

4.3 Perham Creek

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 Site Preparation

5.2 Site Grading

5.3 Structural Fill

5.4 Bridge Foundation Support

5.5 Retaining Walls

5.6 Seismic Considerations

6.0 DESIGN REVIEW AND CONSTRUCTION SERVICES

7.0 LIMITATIONS

List of Figures Figure 1 Vicinity Map Figure 2 Site Map – Mitchell Creek Figure 3 Site Map – Perham Creek Figure 4 Surcharge-Induced Lateral Earth Pressure

Appendices Appendix A Field Explorations and Laboratory Testing Appendix B Federal Highway Administration Laboratory Results Appendix C Perham and Mitchell Creek Geophysical Exploration Report

1.0 INTRODUCTION

At the request of David Evans and Associates, Inc. (DEA), GRI is providing geotechnical services to the Western Federal Lands Highway Division (WFLHD) for two new bridges along Segment E of the Historic Columbia River Highway Trail (HCRHT) in Hood River County, Oregon. The Vicinity Map, Figure 1, shows the general location of the site.

The purpose and scope of this supplemental geotechnical work is described in the WFLHD document titled “Statement of Work, Contract No. DTFH7015D00002, Task Order No. 69056718F000012, OR DOT CRGNSA 100(4), Historic Columbia River Highway State Trail, Mitchell Point (Segments E, G, and H), October 19, 2017.”

Elevations noted in this report reference the DEA project datum.

2.0 PROJECT DESCRIPTION

The Historic Columbia River Highway was constructed in the Columbia River Gorge around 1915 and connected Portland to Hood River, Oregon. Construction of US 30 in the 1950s and I-84 in the 1960s removed many sections of the highway and left upland sections disconnected. Since passage of the 1986 Columbia River Gorge National Scenic Area Act, the Oregon Department of Transportation (ODOT) has worked to connect the abandoned sections of the highway as a pedestrian and cyclist trail.

Segment E of the HCRHT is located between Viento Campground and Mitchell Point on the south side of I- 84 in Hood River County, Oregon. Segment E includes two new bridge structures: one at Perham Creek and one at Mitchell Creek. Project details are shown on the Site Plans, Figures 2 and 3.

The proposed Mitchell Creek Bridge will be constructed over Mitchell Creek at about elevation 140 ft. The proposed Perham Creek Bridge will be constructed over Perham Creek at about elevation 105 ft.

3.0 GEOLOGIC SETTING

The project is located in the Columbia River Gorge portion of the Cascades Range physiographic province of Oregon. The Columbia River Gorge is in an area of uplifted basalt flows of the Columbia River Basalt Group (CRBG). The CRBG is a series of Miocene (about 17 to 6 million years old) basalt flows that erupted from fissures and vents in northeastern Oregon, eastern Washington, and western Idaho and eventually reached the Pacific Ocean through the water gap in the Cascade Mountains created by the Columbia River.

The Columbia River eroded through the basalt flows as the rock was tectonically uplifted. A series of catastrophic floods during the late-Pleistocene age eroded the valley walls and left behind steep basalt cliffs.

The local topography south of the Columbia River is characterized by steep mountain slopes that predominantly descend to the north. Alluvial and debris-flow deposition and colluvial deposition of basalt talus are common along the HCRHT alignment.

The Mitchell Creek Bridge is located on a Quaternary alluvial fan that exits the Mitchell Creek drainage (McClaughry et al., 2012). The alluvial fan is composed of granular alluvial and debris-flow deposits. A thin prism of granular fill soils is present under the existing highway. The Mitchell Creek fault is mapped approximately 200 ft northwest of the site (McClaughry et al., 2012).

The Perham Creek Bridge is located near the mouth of the Perham Creek drainage, where it discharges into the Columbia River. The area is underlain by fill, alluvial, debris flow, and colluvial talus deposits derived from the upland rock cliffs composed of the Grande Ronde Member of the Columbia River Basalt. The Historic Columbia River Highway near the proposed bridge site is covered with rock and soil that suggest rapidly moving landslides or debris-flow processes are active at the site.

4.0 SUBSURFACE CONDITIONS

4.1 General

Subsurface materials and conditions for the proposed new bridges at Perham and Mitchell creeks were investigated on August 22, October 12 and 15, and November 7, 2018. At the Mitchell Creek site, one boring (MC-B1) was advanced to a depth of 8.3 ft using a portable rotary drill with solid-stem augers, and creek-bank exposures (BE-1 through BE-3) were evaluated to detail subsurface materials (Site Plan – Mitchell Creek, Figure 2). It should be noted due to access limitations, larger equipment was restricted from use at the Mitchell Creek site. At the Perham Creek site, one boring (PC-B1) was advanced to approximately 71.6 ft below ground surface using roto-sonic drilling techniques, and one boring (HA-1) was advanced to a depth of approximately 2 ft using a hand auger (Site Plan – Perham Creek, Figure 3). The field exploration program completed for this project is described in Appendix A. Logs of the explorations are provided on Figures 1A through 5A. The terms and symbols used to describe the soils encountered in the explorations are defined in Table 1A and on the attached legend. Laboratory testing of the samples collected was performed by Federal Highway Administration (FHWA), and the results are attached in Appendix B at the end of this report.

Two resistivity surveys were taken at each proposed bridge (four total) to supplement the borings and test pits in limited-access areas. These results can be found in the Perham and Mitchell Creek Geophysical Exploration Report in Appendix C.

For discussion, we describe the subsurface conditions for each of the project areas shown in Table 1 below individually.

Table 1: PROJECT AREAS

Area Exploration ID General Subsurface Conditions Mitchell Creek MC-B1, BE-1 through BE-3 Fill, alluvial fan deposits

Perham Creek PC-B1, HA-1 Fill, alluvial fan deposits, talus deposits

In the discussion of each area, the materials disclosed by the explorations have been grouped into categories based on their physical characteristics and engineering properties.

4.2 Mitchell Creek

Boring MC-B1 and bank exposures BE-1, BE-2, and BE-3 were evaluated for subsurface materials and conditions in the area of the proposed bridge across Mitchell Creek. The following units were encountered at this location:

PAVEMENT

FILL

ALLUVIAL FAN DEPOSITS

A detailed description of these units and a discussion of the groundwater conditions at the site are presented below.

PAVEMENT. Asphaltic-concrete (AC) pavement was encountered at the ground surface in boring MC-B1 and bank exposure BE-1. The AC is about 3 to 7 in. thick and is underlain by approximately 5 to 6 in. of crushed-rock base course.

FILL. Beneath the pavement in boring MC-B1, possible dark brown silt fill with variable amounts of clay, fine- to coarse-grained sand, and angular gravel was encountered to a depth of 7.5 ft. Based on SPT N-values ranging from 10 to 41 blows/ft of sampler penetration, we estimate the relative consistency of the fill is stiff to hard. The natural moisture content of the fill material in MC-B1 ranges from 14 to 18%. The fill material in boring MC-B1 contains cobbles and boulders. Wood debris and possible concrete fragments are present in the fill material in MC-B1 below 4 ft.

Gravel and cobble fill was encountered under the AC pavement in bank exposure BE-1 to a depth of 6 ft.

The gravel and cobbles are subrounded to subangular and contain some brown, fine-to coarse-grained sand and trace silt, with roots and organics scattered throughout.

ALLUVIAL FAN DEPOSITS. Exposed at bank exposure BE-2 was red-brown, sandy silt, with trace clay and subrounded to angular gravel and cobbles and organic material and roots scattered throughout. Hard basalt rock boulders up to about 8 ft in diameter were observed at the site. It should be anticipated these boulders are also present within the alluvial fan deposits. The sand ranged from fine to coarse grained. A very similar material was observed at bank exposure BE-3, although the color appears brown to gray-brown. A layer of leaves and organic material approximately 6 in. thick covered both bank exposures at the ground surface. It should be noted boring MC-B1 encountered refusal at a depth of approximately 8.3 ft in fresh to slightly weathered, medium-hard to hard (R3 to R4) basalt rock (possible boulder). Based on review of the electrical resistivity logs, we anticipate the alluvial fan deposits underly the fill and possible fill at depths of 5 to 20 ft below existing grade.

4.2.1 Groundwater. Groundwater was not encountered within the explorations. Regional groundwater is present near the elevation of the Bonneville Pool, at about elevation 90 ft. However, we anticipate groundwater will likely mirror the creek elevation at the proposed bridge-end bents. During periods of extended wet weather, we anticipate groundwater may become perched within the upper units.

4.3 Perham Creek

Borings PC-B1 and HA-1 were advanced to the north and south (respectively) of Perham Creek to evaluate subsurface materials and conditions in the area of the proposed bridge. The following units were encountered at this location:

FILL

ALLUVIAL FAN DEPOSITS

TALUS DEPOSITS

The following paragraphs provide a detailed description of these units and a discussion of the groundwater conditions at the site.

FILL. Gravel fill was encountered in explorations PC-B1 and HA-1 to a maximum depth of 9 ft, and possible gravel fill extends down to a depth of 23 ft in boring PC-B1. The fill material contains variable amounts of silt, fine- to coarse-grained sand, gravels, and cobbles. The relative density of the gravel fill and possible fill is medium dense to dense based on SPT blow counts and visual observation. The natural moisture content of the gravel fill and possible fill ranges from approximately 6 to 16%. In boring PC-B1, asphalt fragments were observed at 3.5 ft below ground surface and there was a 3-in.-thick, heavily rooted zone at the ground surface. A 3-in. layer of leaves and organic debris was observed at the surface of boring HA-1 and refusal was encountered on a cobble or boulder at 2 ft. While not encountered within the explorations, it should be anticipated boulders may be present within the granular fills.

ALLUVIAL FAN DEPOSITS. Alluvial fan deposits were encountered underlying the fill in boring PC-B1. The fan deposits consist of red-brown to gray-brown, sandy, silty gravel. An approximately 0.5-ft-thick, light-brown, clayey sand layer, with trace gravel, was encountered at a depth of 34 ft. The sand ranged from fine to coarse grained. Based on drilling observations, the relative density of the sandy, silty gravel is medium dense. The natural moisture content of the alluvial fan deposits is approximately 20%. While not encountered within the explorations, it should be anticipated cobbles and boulders may be present within the granular soils

TALUS DEPOSITS. Underlying the alluvial fan deposits is gray to red-brown, sandy, angular gravel talus deposits containing variable amounts of silt and cobbles. The sand ranged from fine to coarse grained. Based on SPT N-values of 50 blows for less than 6 in. of sampler penetration (defined as practical refusal), the relative density of the talus is very dense. While not encountered in our explorations, it should be anticipated boulders may be present within the talus deposit.

4.3.1 Groundwater. Groundwater was not encountered within the explorations. Regional groundwater is present near the elevation of the Bonneville Pool, at about elevation 90 ft. However, we anticipate groundwater will likely mirror the creek elevation at the proposed bridge-end bents. During periods of extended wet weather, we anticipate groundwater may become perched within the upper units.

5.0 CONCLUSIONS AND RECOMMENDATIONS

The explorations indicate the Perham Creek area is underlain by granular fill soils, granular alluvial fan/debris flow deposits, and colluvium/talus deposits. The Mitchell Creek area is underlain by granular fill soils and granular alluvial fan/debris flow deposits from areas upland in the Mitchell Creek drainage. As a result of the cobbles and boulders encountered within the explorations, it should be anticipated excavation at both the Mitchell Creek and Perham Creek project sites may be difficult.

The following sections of this report provide our geotechnical conclusions and recommendations concerning earthwork and design and construction of bridges.

5.1 Site Preparation

The project site is mantled with a layer of duff/organics with an average thickness of about 8 in. The duff soils are generally fine grained and contain a large percentage of organic matter. Prior to construction, the organic-rich duff soil should be stripped from the proposed bridge alignment. It should be anticipated deeper stripping and grubbing will be necessary where trees and shrubs are located within the proposed bridge alignment. The stripped materials are not suitable for use as compacted structural fill.

Following stripping or excavation to subgrade level, the resulting subgrade within the area of the improvements should be evaluated by qualified geotechnical engineering staff, and soft soils or areas of unsuitable material should be overexcavated and replaced with select borrow (as per FHWA FP-14, Section 704.07). See the Structural Fill section of this report below for additional details. As previously discussed, based on review of the electrical resistivity, we anticipate fill may extend up to depths of 20 ft at the Mitchell Creek Site. It should be anticipated some overexcavation may be necessary due to the presence of fill.

5.2 Site Grading

Final grading across the project should provide for positive drainage of surface water away from exposed slopes to minimize erosion. Prior to placing pavement base-course aggregate, subgrade should be sloped to a minimum 0.5% slope to aid in drainage. Temporary excavation slopes should be made no steeper than about 1H:1V (Horizontal to Vertical), and permanent cut and fill slopes constructed with native materials should be no steeper than 2H:1V. It should be anticipated cobbles and boulders will be encountered within excavations and cut slopes. Where boulders are encountered on an exposed finished slope face, an experienced geotechnical professional should be contacted to evaluate boulder stability and the necessity of removal. In general, structural fills should extend a minimum horizontal distance of 1 ft beyond the limits of the improvements, such as the edge of new pavements.

Our experience indicates the near-surface sandy silt soils are sensitive to moisture content. When these soils are in excess of 4 to 5% of their optimum moisture content, they typically become weak and unstable when disturbed and remolded by wheeled construction traffic. Based upon our experience with similar soils, we anticipate the optimal moisture content would be between 8 and 15%. We anticipate the near-surface soils within the limits of the bridge abutment will likely be above optimum at the time of construction. For this reason, we recommend a 12-in.-thick, granular work pad be constructed on the bridge abutment to limit disturbance of the underlying subgrade. We recommend the granular work pad consist of select borrow per FHWA FP-14, Section 704.07.

5.3 Structural Fill

5.3.1 Embankment Fill. We anticipate the heights of fills will vary across the site and may be as thick as 10 ft but will typically be less than 5 ft at the bridge bents. In general, on-site or imported, organic-free soils in accordance with FHWA FP-14, Section 204.10, and approved by the geotechnical engineer may be used to construct structural fills. The on-site sand soils typically contain boulders and cobbles. Oversized boulders should be removed or crushed in accordance with Section 204.10.

Construction of embankment fills should be completed in conformance with FHWA FP-14, Section 204.

Approved organic-free soils used to construct structural fills should be placed in 12-in.-thick lifts (loose) and compacted using a segmented-pad roller to a density not less than 95% of the maximum dry density determined by American Association of State Highway and Transportation Officials standard method T99 (AASHTO T99). The moisture content of soils at the time of compaction should be controlled to within 2% of optimum. Some aeration and drying of the on-site silty sand soils may be required to meet the recommended compaction criteria. Fill placed in landscaped areas should be compacted to about 90% of the maximum dry density determined by AASHTO T99.

5.3.2 Select Borrow. Imported or on-site granular material used to construct work pads should be in conformance with FHWA FP-14, Section 704.07, and consist of granular material, such as sand, sandy gravel, or fragmental rock with a maximum size up to about 3 in. and not more than 5% passing the No. 200 sieve (washed analysis). Select borrow should be placed in lifts up to about 12 in. thick (loose). All lifts should be compacted to at least 95% of the maximum density determined by AASHTO T99. If the lifts are compacted with hand-operated equipment, the lifts will likely need to be reduced to 6 to 9 in. thick (loose).

5.3.3 Base Course Aggregate. Base-course aggregates for construction of the Mitchell Creek Bridge abutment pavement base course should meet the requirements of FHWA FP-14, Table 703-2, Type C material and consist of crushed aggregate having a maximum size up to about 1 in. with not more than 5% passing the No. 200 sieve (washed analysis). Pavement base course should follow the guidelines in FHWA FP-14, Section 301. Pavement base course should be placed in lifts of up to 6 in. (loose) and compacted to a minimum 95% of the maximum density determined by AASHTO T180.

5.3.4 Fill Settlement. We anticipate fills will be required for construction of the proposed new Mitchell Creek Bridge abutment. We understand final project grading plans are still in preparation; however, we anticipate maximum fill heights of approximately 5 ft from the existing grade. In general, soils encountered are granular, with trace clay or silt to clayey or silty contents. Due to access limitations, physical explorations around Mitchell Creek were limited to a single solid-stem-auger boring near the east side of the proposed bridge abutment and several shallow test pits within the exposed banks of Mitchell Creek. We anticipate settlement due to the placement of embankment fills will be less than about 1 in. The majority of this settlement will likely occur during construction as the embankment fill is placed.

5.4 Bridge Foundation Support

5.4.1 General. The maximum combined dead and live service loads on each of the bridge abutments is unknown at this time; however, we anticipate maximum loads of approximately 200 kips per bent. We anticipate the bridges will be supported by micropiles for constructability reasons. Depending on the actual locations of the bridge abutments, scour may need to be considered for design of the micropiles and embankment fills. Scour depths of Mitchell Creek and Perham Creek were evaluated by the project structural engineer, DEA, and are included in the project plans. Recommendations for micropile foundations are included below. The following parameters were utilized for our design of the proposed bridge foundations.

FOUNDATION DESIGN PARAMETERS

Effective Friction Angle Effective Cohesion (psf) Moist Unit Weight (pcf) 34 0 120

5.4.2 Micropiles. Micropiles are typically small-diameter (typically 5 to 9 in.), drilled-and-grouted, steel-cased piles having a minimum wall thickness of 0.375 in. The proposed wall thickness should be evaluated by the structural engineer based on the design structural capacity. Micropiles are typically constructed by drilling a cased hole to the desired depth into a bearing layer, placing a reinforcing bar to the bottom of the hole, and pumping grout to form a bond zone as the casing is partially withdrawn. The steel casing typically extends from the pile cap to the top or slightly below the bond zone to provide load transfer into the bond zone and structural rigidity at the top of the pile. Bond-zone lengths typically depend on the type of soils and the contractor’s construction methods. It should be noted explorations encountered practical refusal at depths less than the anticipated micropile bond zone. The assumptions presented in this report should be verified on site at the time of installation.

For the subsurface conditions at the site, we recommend the bond zone begin a minimum of 10 ft below the existing grade or below the estimated depth of scour, whichever is deeper. Additionally, the bond zone for production micropiles should have a minimum length of 10 ft within the underlying gravelly soils. We estimate micropiles at least 6 in. in diameter installed a minimum of 20 ft below existing grade at the site can develop strength-limit-state nominal bond stresses of 4 to 6 ksf and service-limit-state nominal bond stresses of 2 to 3 ksf. The bond strengths are highly dependent on the micropile contractor’s means and methods and may result in higher or lower values than those noted above. Depending on the contractor’s selected method, micropiles may need to be lengthened to achieve the required design capacity with appropriate resistance factors. Additionally, bond lengths should be limited to about 40 ft in total length. To provide adequate spacing between individual piles to avoid group reductions in axial capacity, all piles should be installed with a minimum center-to-center spacing of at least 3 pile diameters or 30 in., whichever is greater.

We anticipate the settlement of micropiles installed in accordance with these recommendations will be limited to the elastic shortening of the pile. Where micropiles are installed within the scour zone, we recommend the structural engineer evaluate buckling of the micropile assuming an unsupported micropile above the estimated scour depth.

In accordance with the AASHTO Load and Resistance Factor Design Bridge Design Specifications (LRFD BDS), resistance factors must be applied to the nominal bearing resistance, nominal uplift resistance, and nominal lateral resistance for micropiles. The recommended resistance factors for micropile design are summarized in the following table. These resistance factors assume a minimum of one verification test will be completed per site.

RESISTANCE FACTORS FOR MICROPILE DESIGN

Micropile Resistance Factors

Strength Limit State

Service Limit State

Bearing Resistance 0.60 1.00

Uplift Resistance 0.60 1.00

Lateral Resistance 1.00 1.00

The actual design of micropiles is typically developed by a specialty contractor based on the performance criteria provided by the owner’s geotechnical and structural engineers. Prior to installation of production micropiles, sacrificial verification-test piles should be installed near the production-pile locations. The verification load test should be performed to confirm the design soil-grout adhesion capacities of the micropiles and the optimum length of the bond zone. Verification tests should be limited to a maximum bond length of approximately 5 ft. The verification-test pile should be tested to a minimum of 100% of the strength limit state nominal bond stress or 200% of the service-limit bond stress, whichever is greater. We also recommend proof testing about 10% of the production piles to 150% of the service limit load. The verification and proof tests for the compression loads should be performed in tension to facilitate the testing.

A successful verification or proof test will typically sustain the test load for at least 10 minutes with less than

0.04 in. of creep movement. In addition, the measured deflection at the service load needs to be less than the maximum allowable deflection specified by the structural engineer.

For conditions of lateral loading, we anticipate the micropiles will be evaluated using the computer software LPILE developed by Ensoft, Inc., of Austin, Texas.

Recommended input parameters for the various soil units for the LPILE analysis are tabulated below for static and seismic conditions.

MITCHELL CREEK SOIL PROPERTIES FOR LPILE ANALYSIS

Soil Unit

Depth, ft

LPILE

Soil Type

Condition

Soil Properties K, pci γ’, pcf φ’ c, psi ε50

Fill 0 to 20 Sand (API) Static & Seismic 90 57.6 34° N/A N/A

Alluvial Fan Deposits 20 + Sand (API) Static & Seismic 100 62.6 35° N/A N/A

PERHAM CREEK SOIL PROPERTIES FOR L-PILE ANALYSIS

Soil Unit

Depth, ft

LPILE

Condition

Soil Properties K, pci γ’, pcf φ’ c, psi ε50

Fill 0 to 23 Sand (API) Static & Seismic 90 57.6 34° N/A N/A

Alluvial Fan Deposits 23 to 35 Sand (API) Static & Seismic 90 57.6 34° N/A N/A

Talus Deposits 35 + Sand (API) Static & Seismic 125 62.4 38° N/A N/A

It should be noted that LPILE provides isolated, single-micropile capacities. Depending on the direction of the loading and layout of the shafts, group effects may need to be considered. Group effects can be modeled in LPILE by applying an appropriate p-modifier in non-liquefiable soils. The p-modifier is a function of the center-to-center spacing and tabulated below.

P-MODIFIERS FOR GROUP EFFECTS

Center-to-Center Pile Spacing

P-Modifiers for Rows 1, 2, and 3+

3D 0.80, 0.40, 0.30

5D 1.00, 0.85, 0.70

Additional resistance to lateral loads can be provided by passive soil resistance against the shaft cap. We recommend this resistance be evaluated on the basis of equivalent fluids having unit weights of 500 pcf and 250 pcf for the strength and service limit states, respectively. These values assume the micropile-cap excavations will cast neat against firm, undisturbed soil or the micropile-cap excavation will be backfilled with select borrow. To observe compliance with the intent of our recommendations, the design concepts, and the plans and specifications, we are of the opinion all construction operations dealing with micropiles should be observed by a GRI representative on a full-time basis.

5.5 Retaining Walls

5.5.1 General. Final plans indicate the Perham Creek Bridge will be constructed with reinforced concrete wingwalls with a maximum height of about 11 ft, and the Mitchell Creek Bridge will be constructed with gabion-faced, mechanically stabilized earth (gabion/MSE) wingwalls with a maximum height of about 16 ft.

Reinforced concrete walls should be constructed in accordance with Section 258 of FP-14 and Gabion/MSE walls should be constructed in accordance with Sections 253 and 255 of FP-14. GRI should be contacted if other types of retaining walls are to be considered for this project.

Retaining wall recommendations presented below are based on the subsurface conditions disclosed by the explorations and the results of our analyses.

5.5.2 Lateral Earth Pressures. Design lateral earth pressures for retaining walls depend on the type of construction, i.e., the ability of the wall to yield. Possible conditions are 1) a wall laterally supported at its base and top, such as a conventional basement wall, and therefore unable to yield to the active state and 2) a retaining wall, such as an MSE wall, that yields to the active state by tilting, or deflecting, about its base. A conventional basement wall and cantilever retaining wall are examples of non-yielding and yielding walls, respectively. The ground motions associated with a code-based earthquake will result in additional lateral earth pressures on retaining walls due to inertial loads from the retained soil.

Recommended equivalent fluid unit weights to compute lateral earth pressures for cantilever retaining wall design are provided below for static and seismic conditions based on horizontal backfill behind the wall.

EQUIVALENT FLUID UNIT WEIGHT

Condition Equivalent Fluid Unit

Weight, pcf Static 37

Seismic (1,000-Year) 46

These earth pressures assume the walls are fully drained, i.e., hydrostatic pressure cannot build up on the back of the wall. The seismic earth pressure is based on the 1,000-year hazard level and was determined using methods proposed by Agusti and Sitar (2013). Additional lateral loading due to surcharge loads in the backfill area can be estimated using the guidelines provided on Figure 4.

The lateral earth pressure criteria presented above are appropriate if the retaining walls are fully drained. We recommend installation of a permanent drainage system behind all the retaining walls. The drainage system can either consist of drainage blanket of rock or continuous drainage panels placed against the back of the wall or behind the reinforced soil zone. The drainage blanket of rock should have a minimum width of 1 ft and should meet the specifications for granular rock backdrain in Subsection 703.17 of the FP-14. The drainage blanket or drainage panels should extend to the base of the wall where water should be collected in a perforated pipe that is sloped to drain. The perforated drainpipe should discharge onto the downslope away from the wall or to a suitable outlet such as an approved storm drain. In addition, the wall design should include positive drainage measures to prevent ponding of surface water behind the top of the wall.

It should be understood that MSE walls must undergo some lateral deformation to mobilize the active earth pressures and shear strength of the reinforcement. Based on our experience, it is anticipated that the lateral deformation will be less than about 1 in. for a 15-ft-high MSE wall.

5.5.3 Foundation Design Parameters. The Perham Creek Bridge wingwalls will be supported on the abutment foundations, and the Mitchell Creek Bridge MSE wingwalls will be founded in granular fill soils or granular alluvial fan/debris flow deposits. Recommended design parameters for the MSE wall are included in the following table.

FOUNDATION DESIGN PARAMETERS

Effective Friction Angle: 34° Effective Cohesion: 0 psf

Unit Weight: 134 pcf

In accordance with Table 11.5.7-1 of the AASHTO LRFD manual, resistance factors must be applied to the nominal bearing resistance and nominal sliding resistance for MSE wall design. The recommended resistance factors are provided below.

RESISTANCE FACTORS FOR PERMANENT MSE WALLS

Strength Limit State

Service Limit State

Bearing Resistance: 0.65 1.0 Sliding Resistance: 1.0 1.0

The MSE wall should be established in firm, undisturbed, native soils relatively free of organic material.

Recommended nominal bearing resistance values for the Strength and Service limit states are provided below.

NOMINAL BEARING RESISTANCE

Strength Limit State: 10 ksf Service Limit State: 4.5 ksf

We estimate the total settlement of the MSE wall designed in accordance with the recommendations presented above will be less than 1 in. Our experience indicates the majority of these settlements will occur as the wall is constructed. In this regard, we recommend waiting a minimum of two weeks to pave the trail following construction and backfill of the retaining wall to reduce the amount of post-construction settlement.

In accordance with the Section 11.10.2.2 of the AASHTO LRFD manual, recommended minimum embedment depths for the MSE wall are included in the following table and are based on the slope of the ground surface in front of the wall.

MINIMUM EMBEDMENT DEPTHS

Horizontal: 1 ft

Slope up to 3H:1V: 2 ft

Slope up to 2H:1V: 3 ft

To provide more uniform support, the base of the MSE wall should be founded on a minimum-12-in.

thickness of imported granular material that conforms to Subsection 704.01 of FP-14. In areas where frost-susceptible soils are encountered, we recommend the toe of the wall be provided a minimum of 2 ft of embedment, which corresponds to the anticipated frost depth at the Mitchell Creek Bridge.

Lateral loads (seismic, soil, etc.) can be resisted partially or completely by frictional forces developed between the base of the wall and the underlying soil. The total frictional resistance between the base of the wall and the soil is the normal force times the coefficient of friction between the soil and the base of the wall. We recommend an ultimate value of 0.40 for the coefficient of friction for an MSE wall constructed on structural fill. The normal force is the sum of the vertical forces (dead load plus real live load).

5.5.4 Gabion/MSE Walls. Gabion/MSE walls are internally stabilized by layers of corrosion-protected steel or geogrid reinforcement. For preliminary design purposes, the reinforcing lengths for gabion/MSE walls are commonly on the order of 70% of the exposed wall height. The gabion baskets should be filled with material conforming to the requirements of Subsection 705.01 of FP-14. Imported granular material conforming to Subsection 704.08 of FP-14 should be used in the reinforced zone for gabion/MSE walls.

5.6 Seismic Considerations

5.6.1 Seismic Forces and Site Class. We understand the proposed new Mitchell Creek and Perham Creek bridges are to be designed to withstand seismic loading in accordance with the AASHTO LRFD BDS as modified by the AASHTO Project Development and Design Manual (PDDM). Based on the AASHTO LRFD BDS, bridges must be designed for a “low probability of collapse, but may suffer significant damage and disruption to service” in response to a 1,000-year return-interval earthquake (7% probability of exceedance in 75 years).

The AASHTO LRFD BDS uses the 2002 U.S. Geological Survey (USGS) seismic-hazard maps to evaluate earthquake-induced peak bedrock acceleration (PBA). For seismic analysis, the AASHTO LRFD BDS methodology develops the design-level spectra using two parameters at spectral periods of 0.2 and 1.0 sec (SS and S1). The bedrock spectral response parameters were obtained from the USGS Uniform Hazard Response Spectra Curves. The 0.2- and 1.0-sec parameters identified for the sites are noted in the tables below. Site coefficients Fa and Fv are then used with a site-class designation to adjust the bedrock spectral accelerations to ground-surface spectral accelerations. Based on review of the soil profile at the bridge abutments, we recommend designing the bridges for Site Class D. The recommended seismic parameters are summarized below.

MITCHELL CREEK RECOMMENDED SEISMIC PARAMETERS (45.7013°N, 121.6238°W)

Return Interval PBA, g SS, g S1, g Fa Fv 500-year 0.14 0.29 0.13 1.56 2.29

1,000-year 0.20 0.41 0.19 1.47 2.04

PERHAM CREEK RECOMMENDED SEISMIC PARAMETERS (45.6992°N, 121.6373°W)

Return Interval PBA, g SS, g S1, g Fa Fv 500-year 0.14 0.30 0.13 1.56 2.29

1,000-year 0.20 0.41 0.19 1.47 2.04

5.6.2 Other Seismic Considerations. In terms of potential seismic-related hazards in the area, we anticipate the risk of liquefaction, lateral spreading, settlement, or ground subsidence for the site is low.

Based on review of the USGS Quaternary Fault and Fold database, two unnamed faults of the “Faults near the Dalles” (Fault Number 580) are located within a kilometer of the two bridge sites. However, it should be noted that the estimated slip rates of these faults are less than 0.2 mm/year, and they are considered active within the last 1.6 Ma based on the 1995 Geomatrix report (Geomatrix, 1995). Additionally, the USGS does not consider the Faults near the Dalles as seismogenically active within its Probabilistic Seismic Hazard Maps. Considering the location and activity of known and mapped faults in the area, we anticipate the

This document has been submitted electronically.

Expires 12-2021 potential for fault rupture or displacement at the site is low, unless occurring on a previously unknown or unmapped fault. The risk of tsunami and seiche at the site is absent.

6.0 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 geotechnical-related portions of the plans and specifications to evaluate whether they are in conformance with the recommendations provided in this report. To observe compliance with the intent of our recommendations, the design concepts, and the plans and specifications, we are of the opinion all construction operations dealing with earthwork and foundations should be observed by a GRI representative. Our construction-phase 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 different from those described in this report.

7.0 LIMITATIONS

This report has been prepared to aid in the evaluation and design of planned improvements for the HCRHT, including a proposed new bridge over Mitchell Creek and a proposed new bridge over Perham Creek. The scope is limited to the specific project and location described herein. Our description of the project elements represents our understanding of the significant aspects of the project relevant to the existing geologic/geotechnical conditions at the site. In the event any changes in the conceptual design of proposed improvements are planned, we should be given the opportunity to review the changes and modify or reaffirm the conclusions and recommendations of this report in writing.

The analyses and recommendations discussed in this report are based on the data obtained from our review of applicable background information, site reconnaissance, subsurface explorations at the indicated locations, and other sources of information discussed in this report. In the performance of subsurface investigations, specific information is obtained at specific locations at specific times. However, it is acknowledged variations in soil and rock conditions may exist between exploration locations. The variations in soil and rock conditions in the geologic units encountered at the site are considerably high. This report does not reflect any variations that may exist. The nature and extent of variations may not become evident until construction. If, during construction, subsurface conditions differ from those described in this report, we should be advised at once, so we can observe these conditions and reconsider our recommendations where necessary.

Submitted for GRI, George A. Freitag, CEG Jason D. Bock, PE Principal Associate

References

Federal Highway Administration (FHWA), 2014, Standard specifications for construction of roads and bridges on federal highway projects – FP-14.

Geomatrix Consultants, Inc., 1995, Seismic design mapping, State of Oregon, Technical report to Oregon Department of Transportation, Salem, Oregon, under Contract 11688, January 1995, unpaginated, 5 pls., scale 1:1,250,000.

McClaughry, J. D., Wiley, T. J., Conrey, R. M., Jones, C. B., and Lite, K. E., 2012, Digital geological map of the Hood River Valley, Hood River and Wasco Counties, Oregon, Oregon Department of Geology and Mineral Industries, Open File Report O- 12-03.

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Tunnel No. 4

Tunnel No. 1

Tunnel No. 3

Hill

Mitchell Point

Ru Poi

MITCHELL CREEK

PERHAM CREEK

R IG

VICINITY MAP

OCT. 2020 JOB NO. 6075 FIG. 1

0 1/2 1 MILE

North

USGS TOPOGRAPHIC MAP

MOUNT DEFIANCE, OREG. (2017)

DAVID EVANS AND ASSOCIATES, INC.

HISTORIC COLUMBIA RIVER HIGHWAY TRAIL, SEGMENT E

G R I

SITE PLAN – MITCHELL CREEK

OCT. 2020 JOB NO. 6075 FIG. 2

0 160 FT

North

BORING COMPLETED BY GRI

(OCTOBER 15, 2018)

BANK EXPOSURE OBSERVED BY GRI

(OCTOBER 12, 2018)

SITE PLAN FROM FILE BY USDOT FHWA (NOVEMBER 7, 2018)

HCRH STATE TRAIL (SEGMENTS E-G-H)

MC-B1

BE-1 BE-2

BE-3

G R I

SITE PLAN – PERHAM CREEK

OCT. 2020 JOB NO. 6075 FIG. 3

0 160 FT

North

BORING COMPLETED BY GRI

(AUGUST 22, 2018)

HAND-AUGERED BORING COMPLETED BY GRI

(NOVEMBER 7, 2018)

SITE PLAN FROM FILE BY USDOT FHWA (NOVEMBER 7, 2018)

HCRH STATE TRAIL (SEGMENTS E-G-H)

HA-1

PC-B1

APPENDIX A

Field Explorations and Laboratory Testing

A-1

FIELD EXPLORATIONS AND LABORATORY TESTING

FIELD EXPLORATIONS

Subsurface materials and conditions for the proposed new bridges at Perham and Mitchell creeks were investigated on August 22, October 12 and 15, and November 7, 2018. At the Mitchell Creek site, one boring (MC-B1) was advanced to a depth of 8.3 ft using a portable rotary drill with solid-stem augers, and creek-bank exposures (BE-1 through BE-3) were evaluated to detail subsurface materials (Site Plan – Mitchell Creek, Figure 2). It should be noted due to access limitations, larger equipment was restricted from use at the Mitchell Creek site. At the Perham Creek site, one boring (PC-B1) was advanced to approximately 71.6 ft below the ground surface using roto-sonic drilling techniques, and one boring (HA-1) was advanced to a depth of approximately 2 ft using a hand auger (Site Plan – Perham Creek, Figure 3). The Mitchell Creek boring was completed using a Big Beaver Portable Drill owned and operated by PLI Systems, Inc. The Perham Creek boring was completed using a Roto Sonic TST 150T owned and operated by Yellow Jacket Drilling.

Logs of the explorations are provided on Figures 1A through 5A. Each log presents a descriptive summary of the various types of materials encountered in the boring and notes the depths where the materials and/or characteristics of the materials change. To the right of the descriptive summary, the numbers and types of samples taken during the drilling operation are indicated. Farther to the right, natural moisture contents are presented. The terms and symbols used to describe the materials encountered in the borings are defined in Tables 1A and on the attached legend.

LABORATORY TESTING

General The samples obtained from the borings were examined by the Federal Highway Administration (FHWA) in its laboratory, where the natural moisture content and fines contents of representative samples were determined. A summary of the FHWA laboratory results is provided in Appendix B.

Table 1A: GUIDELINES FOR CLASSIFICATION OF SOIL

Description of Relative Density for Granular Soil

Standard Penetration Resistance Relative Density (N-values), blows per ft

Very Loose 0 - 4 Loose 4 - 10

Medium Dense 10 - 30 Dense 30 - 50

Very Dense over 50

Description of Consistency for Fine-Grained (Cohesive) Soils

Standard Penetration Torvane or Resistance (N-values), Undrained Shear

Consistency blows per ft Strength, tsf Very Soft 0 - 2 less than 0.125

Soft 2 - 4 0.125 - 0.25 Medium Stiff 4 - 8 0.25 - 0.50

Stiff 8 - 15 0.50 - 1.0 Very Stiff 15 - 30 1.0 - 2.0

Hard over 30 over 2.0

Grain-Size Classification Modifier for Subclassification Boulders:

>12 in.

Cobbles:

3 - 12 in.

Gravel:

1/4 - 3/4 in. (fine) 3/4 - 3 in. (coarse) Sand:

No. 200 - No. 40 sieve (fine) No. 40 - No. 10 sieve (medium) No. 10 - No. 4 sieve (coarse) Silt/Clay:

pass No. 200 sieve

Primary Constituent SAND or GRAVEL

Primary Constituent SILT or CLAY

Adjective Percentage of Other Material (by weight) trace: 5 - 15 (sand, gravel) 5 - 15 (sand, gravel) some: 15 - 30 (sand, gravel) 15 - 30 (sand, gravel) sandy, gravelly: 30 - 50 (sand, gravel) 30 - 50 (sand, gravel) trace: <5 (silt, clay) Relationship of clay and silt determined by plasticity index test some: 5 - 12 (silt, clay) silty, clayey: 12 - 50 (silt, clay)

MC-B1 S-2 4.0 -- 14 -- -- -- -- SILT

S-3 6.0 -- 18 -- -- -- -- SILT

PC-B1 S-2 5.0 93.0 6 -- -- -- -- FILL

S-3 10.0 88.0 9 -- -- -- -- GRAVEL

S-5 20.0 78.0 16 -- -- -- -- GRAVEL

S-6 30.0 68.0 20 -- -- -- -- Sandy GRAVEL

HA-1 S-1 0.5 -- 11 -- -- -- -- FILL

S-2 1.5 -- 8 -- -- -- -- FILL

SUMMARY OF LABORATORY RESULTS

Elevation, ftDepth, ftSampleLocation

Table 2A

Sample Information Dry Unit

Weight, pcf Liquid

Limit, % Plasticity Index, %

Moisture Content, %

Fines Content, %

Atterberg Limits

All testing performed by Western Federal Lands Highway Division Materials Testing Laboratory

Groundwater level after drilling and date measured

Groundwater level during drilling and date measured

Flush-mount monument set in concrete

Symbol

Concrete, well casing shown where applicable

Symbol Description

Symbol

FIELD MEASUREMENTS

Sandy GRAVEL; clean to some silt and clay

GRAVEL; clean to some silt, clay, and sand

Silty SAND; up to some clay and gravel

CLAY; up to some silt, sand, and gravel

Gravelly CLAY; up to some silt and sand

Sandy CLAY; up to some silt and gravel

Silty CLAY; up to some sand and gravel

Vibrating-wire pressure transducer

BEDROCK SYMBOLS

Symbol

FILL

Typical Description

BASALT

MUDSTONE

Rock quality designation (RQD, %)

3.0-in. O.D. split-spoon sampler with recovery

(ASTM D3550)

Grab Sample

Rock core sample interval

SOIL SYMBOLS

Geoprobe sample interval

INSTALLATION SYMBOLS

Grout, inclinometer casing shown where applicable

Bentonite seal, well casing shown where applicable

Grout, vibrating-wire transducer cable shown where applicable

LANDSCAPE MATERIALS

PEAT

Silty GRAVEL; up to some clay and sand

Clayey GRAVEL; up to some silt and sand

Clayey SAND; up to some silt and gravel

SILT; up to some clay, sand, and gravel

Gravelly SILT; up to some clay and sand

Sandy SILT; up to some clay and gravel

Clayey SILT; up to some sand and gravel

Gravelly SAND; clean to some silt and clay

SAND; clean to some silt, clay, and gravel

1-in.-diameter solid PVC

Symbol

BORING AND TEST PIT LOG LEGEND

Typical Description

Shelby tube sampler with recovery

(ASTM D1587)

SAMPLER SYMBOLS

Symbol

2.0-in. O.D. split-spoon sampler and Standard Penetration Test with recovery (ASTM D1586)

Sampler Description

Sonic core sample interval

Filter pack, machine-slotted well casing shown where applicable

1-in.-diameter hand-slotted PVC

Typical Description

SILTSTONE

SANDSTONE

SURFACE MATERIAL SYMBOLS

Symbol Typical Description

Portland cement concrete PAVEMENT

Crushed rock BASE COURSE

Asphalt concrete PAVEMENT

Rock core recovery (%)

B O

R

IN

G A

N D

T E

S T

P

IT

L O

G L

E G

E N

D G

R I D

A T

A T

E M

P

LA

T E

.G D

T

/2

/1

Asphalt concrete PAVEMENT (7 in.) over crushed rock BASE COURSE (5 in.)

SILT, trace to some clay, some fine- to coarse-grained sand and angular gravel, dark brown, stiff, contains cobbles and boulders (Possible Fill)

---very stiff, contains wood debris and possible concrete fragments below 4 ft

---hard below 6 ft

Sandy GRAVEL, trace silt, brown to light gray, very dense, fine- to coarse-grained sand, contains cobbles and boulders (Alluvial Fan Deposits) (10/15/2018)

Refusal on rock at 8.3 ft Groundwater not encountered

All lab testing performed by Western Federal Lands Highway Division Materials Testing Laboratory

30 in.

FIG. 1A

TORVANE SHEAR STRENGTH, TSF

UNDRAINED SHEAR STRENGTH, TSF

D

EP

TH

, F

T

Energy Ratio:

SA

M

PL

E

N O

Big Beaver Portable Drill

Surface Elevation:

Hammer Type:

1.0

Weight:

Not Available IN

ST

AL

LA

TI

O

N

0.5

Logged By:

Drilling Method:

10/15/18

IN

ST

AL

LA

TI

O

N

BORING MC-B14 in.

PLASTIC LIMIT, %

LIQUID LIMIT, %

FINES CONTENT, %

BLOWS PER FOOT

MOISTURE CONTENT, %

Solid-Stem Auger

Drilled by:

140 lb Drop:

Not AvailableSee Legend for Explanation of Symbols

SA

M

PL

E

TY

PE

BL

O

W C

O U

N T

Date Started:

Note:

N. Utevsky PLI Systems, Inc.

D

EP

TH

, F

T

Equipment:

G R

AP

H

IC

L

O G

Manual

Hole Diameter:

CLASSIFICATION OF MATERIAL

COMMENTS AND

ADDITIONAL TESTS

GPS Coordinates: 45.7007° N -121.6261° W (WGS84)

G R

I B O

R

IN

G L

O G

G

P S

N O

E

LE

V

6'

P P

G R

I D A

T A

T E

M P

LA

T

E .G

D T

/1

5/

S-1

S-2

S-3

S-4

S-5

50/2"

50/1"

1.0

7.5

8.3

OCT. 2020 JOB NO. 6075

0 100

41-50/2"

50/1"

Asphalt concrete PAVEMENT (3 in.) over crushed rock BASE COURSE (6 in.)

GRAVEL and COBBLES, some fine- to coarse-grained sand, trace silt, brown, subrounded to subangular, contains scattered organics and roots (Fill)

(10/12/2018)

No excavation performed.

Materials described on this log are an exposed face in washed-out trail crossing

Not Available

Date Started:

Excavated by: Equipment:

Note:

TORVANE SHEAR STRENGTH, TSF

0.50

G. MartinLogged By:

1.0

10/12/18

GRI

See Legend for Explanation of Symbols

BE-1 Surface Elevation:

GPS Coordinates: 45.7002° N -121.6264° W (WGS84)

TEST PITS

PLASTIC LIMIT, %

LIQUID LIMIT, %

FINES CONTENT, %

MOISTURE CONTENT, %

SA

M

PL

E

N O

G R

AP

H

IC

L

O G

D

EP

TH

, F

T

COMMENTS AND

ADDITIONAL TESTS

SA

M

PL

E

TY

PECLASSIFICATION OF MATERIAL

D

EP

TH

, F

T

FIG. 2A

G R

I T P

L O

G

G P

S

P P

N

O E

LE

V

G R

I D A

T A

T E

M P

LA

T

E .G

D T

/1

/1

Sandy SILT, trace to some subrounded to angular gravel and cobbles, trace clay, red-brown, fine- to coarse-grained sand, contains scattered organics and roots, 6-in.-thick layer of leaves and organic debris at ground surface (Alluvial Fan Deposits)

(10/12/2018)

No excavation performed.

Materials described on this log are an exposed face in washed-out trail crossing

Not Available

Date Started:

Excavated by: Equipment:

Note:

TORVANE SHEAR STRENGTH, TSF

0.50

G. MartinLogged By:

1.0

10/12/18

GRI

See Legend for Explanation of Symbols

BE-2 Surface Elevation:

GPS Coordinates: 45.7006° N -121.6255° W (WGS84)

0.8

6.0

OCT. 2020 JOB NO. 6075

5.05

0 100

0 100

Sandy SILT, trace to some subrounded to subangular gravel and cobbles, trace clay, brown to gray-brown, fine-to coarse-grained sand, contains scattered organics and roots,…