Geotechnical Report Sept 2020.pdf

SUBMITTED TO:

AKS Architecture 1124 NW 50th Street Seattle, WA 98107

BY:

Shannon & Wilson, Inc.

3990 Collins Way, Suite 100 Lake Oswego, OR 97035

(503) 210-4750 www.shannonwilson.com

GEOTECHNICAL ENGINEERING REPORT

Umpqua NF and the BLM Colocation Site Development Design

ROSEBURG, OREGON

September 2020 Shannon & Wilson No: 101458-002

Umpqua NF and the BLM Colocation Site Development Design Geotechnical Engineering Report

101458-002 September 2020

PAGE INTENTIONALLY LEFT BLANK FOR DOUBLE-SIDED PRINTING

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CONTENTS

1 Introduction

1.1 Project Overview

1.2 Scope of Services

2 Site and Project Description

3 Geologic Setting

3.1 Regional Geology

3.2 Site Geology

3.3 Seismic Setting

3.3.1 Cascadia Subduction Zone: Megathrust Interface Source

3.3.2 Cascadia Subduction Zone: Intraslab Source

3.3.3 Shallow Crustal Source

4 Field Exploration

5 Laboratory Testing

6 Subsurface Conditions

6.1 Geotechnical Units

6.1.1 Fill

6.1.2 Fluvial Deposits

6.2 Groundwater

7 Seismic Ground Motions and Geologic Hazard Evaluation

7.1 Seismic Ground Motions

7.2 Seismic Hazards Evaluation

8 Geotechnical Design Recommendations

8.1 Foundation Alternatives

8.2 Spread Footing Design Recommendations

8.2.1 Frost Depth and Minimum Footing Embedment

8.2.2 Soil Bearing Capacity

8.2.3 Crushed Rock Leveling Course

8.2.4 Estimated Settlement

8.2.5 Lateral Sliding Resistance

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8.3 Basement Wall Design Recommendations

8.3.1 General

8.3.2 Lateral Earth Pressures

8.3.3 Subdrainage

8.3.4 Backfill Material and Compaction

8.3.5 Lateral Resistances

9 Construction Considerations

9.1 Temporary Cut and Fill Slopes

9.2 Groundwater Control

9.3 Control of Surface Water and Drainage

9.4 Structural Fill

9.5 Wet Weather Construction

9.6 Temporary Shoring

10 Limitations

11 References

Exhibits

Exhibit 2-1: Proposed USFS Office Building Location Exhibit 7-1: USGS Code-Based MCE and Seismic Design Parameters for Site Class D

Figures

Figure 1: Vicinity Map Figure 2: Site and Exploration Plan Figure 3: Lateral Earth Pressure Distribution on New Retaining Walls

Appendices

Appendix A: Topographic Survey Appendix B: Field Explorations Appendix C: Laboratory Test Results Important Information

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1 INTRODUCTION

1.1 Project Overview

This report presents our geotechnical design recommendations and construction considerations for the proposed US Forest Service (USFS) office building to be constructed at the existing Bureau of Land Management, Roseburg District Office. The site is located at 777 NW Garden Valley Boulevard in Roseburg, Oregon. A Vicinity Map of the site is presented as Figure 1. Our report includes a summary of the results of our field explorations and laboratory testing, evaluations of the site seismic hazards, and geotechnical conclusions and recommendations.

1.2 Scope of Services

Shannon & Wilson’s services were conducted in accordance with the scope of services defined in the Umpqua National Forest BLM Colocation Site Development Scope of Work (Amendment #4), dated February 19, 2019. The completed geotechnical design services for this project consisted of the following tasks:

Review available existing information and visit the site to observe existing site conditions and geologic hazards.

Explore the subsurface conditions for the proposed USFS office building.

Perform laboratory testing on selected soil samples to characterize soils and develop soil properties for engineering evaluation.

Provide foundation design recommendations to support the proposed USFS office building.

Provide geotechnical construction considerations and recommendations for earthwork including site and subgrade preparation, site grading and drainage, excavation, structural fill, fill placement, compaction, and wet weather construction.

Prepare a geotechnical report summarizing our field explorations, laboratory testing, subsurface soil and groundwater conditions, design recommendations, and construction considerations.

2 SITE AND PROJECT DESCRIPTION

The proposed site for the new USFS office building is located just west of the existing Bureau of Land Management structures as shown on the Site and Exploration Plan, Figure 2.

The site is currently vacant of structures and is landscaped with few mature trees present at

101458-002 September 2020 the site as can be seen in Exhibit 2-1. The site generally dips toward the south with a maximum elevation of about 481 feet and a minimum elevation of about 469 feet. The topography survey map provided by AKS for the site is presented in Appendix A.

Exhibit 2-1: Proposed USFS Office Building Location

Based on the information provided by AKS, we understand that concepts are still in development. The main floor footprint will be approximately 5,633 square feet and the gross space will be approximately 14,098 square feet. The new building will have a total of three levels including a daylight basement. The bottom of the basement is planned at elevation El. +465.6 feet. The exact spacing at the basement level between the existing BLM structure and the proposed building was not provided prior to the submittal of this report.

Additionally, building loading conditions were not provided prior to the submittal of this report. We understand that the proposed building will be designed in accordance with IBC 2018 and the Oregon Structural Specialty Code (2014).

3 GEOLOGIC SETTING

3.1 Regional Geology

The project site is located within the Oregon Coast Range physiographic province, near its southern boundary with the Klamath Mountains physiographic province. The basement rocks of both provinces are terranes composed of volcanic island chains, pieces of oceanic crust, and associated oceanic sedimentary rocks that welded onto the North American continental tectonic plate during the subduction of adjacent oceanic tectonic plates. The older Klamath terranes are from the Jurassic to early Cretaceous period (approximately 200

Facing West Facing Southeast

101458-002 September 2020 million to 100 million years old) and are thrust upon the late Paleocene to early Eocene (59-million- to 52-million-year-old) basement rocks of the southern Oregon Coast Range at the Wildlife Safari Thrust Fault, located just southeast of the project site.

The basement rocks of the southern Oregon Coast Range include the Siletz terrane, which consists of a thick sequence of pillow basalt, subaerial basalt, and interbedded volcaniclastic and sedimentary rocks known as the Siletz River Volcanics. The Siletz River Volcanics are thought to have originated as an oceanic island chain, plateau, or oceanic continental margin basin that was accreted or welded onto the North American continental tectonic plate in the early Eocene (Wells, and others 2000).

After the accretion of the Siletz terrane, a lowland basin (Tyee Basin) was formed adjacent to the uplifted portions of the terranes around the Roseburg area. Active deposition took place in the Tyee Basin from early to middle Eocene (about 52 to 37 million years ago). The Tyee Basin contains two sub-basins: the Umpqua Basin (which hosts the rocks of the Umpqua Group), and the Tyee Forearc Basin (which hosts the rocks of the Tyee Formation). Erosion of the different terranes around the region deposited material into these basins, which lithified and became the conglomerate, sandstone, and siltstone rocks that make up the Umpqua Group and Tyee Formation. Combined, these formations have a total composite thickness of approximately 20,000 feet (Wells, and others 2000).

The rocks of the Umpqua Group are composed mostly of mica-poor material from the terranes of the Klamath Mountains to the south. The Bushnell Rock Formation, included in the Umpqua Group, is composed of three separate members and represents the earliest sediment deposition in the Tyee Basin.

The Slater Creek Member of the Bushnell Rock Formation overlies the Bushnell Rock Formation Conglomerate and is composed of fossiliferous (molluscan fauna) sandstones and siltstones that were deposited in shallow water conditions. The shallow water origin of the Slater Creek Member suggests that a shoreline existed across the tectonic suture north of the Klamath Mountain Range during the early Eocene (Wells, and others 2000).

Much of the bedrock at lower elevations in the Roseburg area is covered by Holocene (11,700 years ago to present) Fluvial Deposits. These fluid-driven sediments were deposited relatively recently into the low-lying stream basins of the Umpqua River and associated tributaries, such as Davis Creek.

3.2 Site Geology

Based on mapping by Wells and others (2000), the geologic units underlying the project site include Holocene (< 11,700-year-old) Fluvial Deposits and the early Eocene (52- to 48-

101458-002 September 2020 million-year old) “Slater Creek Member” of the Bushnell Rock Formation. The Holocene Fluvial Deposits were encountered below Fill (material placed by humans) in the performed test pits. Bedrock depth could not be determined at the proposed site given the limited exploration depth associated with test pits.

3.3 Seismic Setting

Earthquakes in the Pacific Northwest occur largely as a result of the region’s close proximity to an active convergent plate boundary. At this boundary, dense oceanic crust is subducting beneath less dense continental crust. At this subduction plate boundary (known as the Cascadia Subduction Zone, or CSZ), the Explorer, Juan de Fuca, and Gorda Oceanic Plates are subducting beneath the overriding, westward-moving North American Plate. Oblique convergence of these plates not only results in east-west compressive strain, but also results in dextral (right lateral) shear, clockwise rotation, and north-south compression of accreted crustal blocks that form the leading edge of the North American Plate (Wells and others, 1998). The CSZ extends about 750 miles from northern California to southern British Columbia and lies approximately 98 miles west of the project site. Within the present understanding of the regional tectonic framework and historical seismicity, three broad seismogenic sources have been identified:

A mega-thrust source at the interface between the North American and Juan de Fuca plates in the CSZ;

A deep intraslab source in the subducted Juan de Fuca Plate, within the CSZ; and

A shallow crustal source within the North American Plate.

The following sections briefly describe the location, characteristics, and seismicity of each of the sources.

3.3.1 Cascadia Subduction Zone: Megathrust Interface Source

CSZ megathrust earthquakes originate along the interface between the subducting oceanic plates and the North American plate. Because of the significant uncertainty of the landward extent of a potential rupture surface, estimates of the closest distance between the project and potential rupture surface range from about 80 to 105 horizontal miles. Focal depths for megathrust earthquakes are commonly on the order of about 15 to 25 miles. Rupture of the interface could result in earthquakes with moment magnitudes on the order of 8.5 to over 9.0, with strong shaking that may last for several minutes. No large earthquakes have occurred in this zone during historic times (the last 170 years). However, geologic evidence suggests that coastal estuaries have experienced rapid subsidence at various times within the last 2,000 years (e.g., Atwater, 1987; Atwater and Hemphill-Haley, 1997) due to tectonic movement associated with megathrust earthquakes on the CSZ. It appears that ruptures of

101458-002 September 2020 this zone have occurred at irregular intervals that span from about 100 to more than 1,200 years, with an average recurrence interval of about 300 to 500 years (Atwater and Hemphill- Haley, 1997). Based on historical tsunami records in Japan (Satake and others, 1996) the most recent interplate event on the CSZ was a moment magnitude (Mw) 9 event on January 26, 1700.

3.3.2 Cascadia Subduction Zone: Intraslab Source

CSZ intraslab earthquakes originate from within the subducting oceanic plates due to down-dip tensional forces and bending, caused by mineralogical and density changes in the plates at depth. These earthquakes typically occur 28 to 37 miles beneath the surface.

Ludwin and others (1991) estimate that the maximum Mw from this source zone would be about 7.5. Ground shaking, produced by intraplate earthquakes, would generally be less intense and less prolonged in the project area than ground motions generated by large subduction zone interface earthquake events. Historic seismicity from this source zone includes the 1949 Mw 6.7 Olympia earthquake, the 1965 Mw 6.7 earthquake between Tacoma and Seattle, and the 2001 Mw 6.8 Nisqually earthquake. While intraslab events have occurred frequently in the Puget Sound area, they are historically rare in Oregon.

3.3.3 Shallow Crustal Source

Shallow crustal earthquakes within the North American Plate have historically occurred in a diffuse pattern within the Pacific Northwest, typically within the upper 4 to 19 miles of the continental crust. The largest known crustal earthquake in the Pacific Northwest is the 1872 North Cascades earthquake at approximate Mw 6.5 to 7.0. Other examples include the 1993 Mw 5.6 Scotts Mill earthquake and the 1993 Mw 6.0 Klamath Falls earthquake.

Shallow crustal faults and folds throughout Oregon and Washington have been located and characterized by the United States Geological Survey (USGS). The USGS provides approximate fault locations and a detailed summary of available fault information in the USGS Quaternary Fault and Fold Database (USGS, 2017).

The database defines four categories of faults, Class A through D, based on evidence of tectonic movement known or presumed to be associated with large earthquakes during Quaternary time (within the last 2.6 million years). For Class A faults, geologic evidence demonstrates that a tectonic fault exists and that it has likely been active within the Quaternary period. For Class B faults, there is equivocal geologic evidence of Quaternary tectonic deformation, or the fault may not extend deep enough to be considered a source of significant earthquakes. Class C and D faults lack convincing geologic evidence of Quaternary tectonic deformation, or have been studied carefully enough to determine that they are not likely to generate significant earthquakes.

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According to the USGS Fault and Fold database, there are no Class A fault segments within approximately 30 miles of the project site. The nearest Class A fault segments mapped by the USGS are the South Slough thrust and reverse faults, located approximately 42.6 miles west of the site, with an average slip rate of less than 0.2 millimeters per year and the most recent deformation occurring within the last 15,000 years (Personius, 2002). The CSZ itself is approximately 98 miles west of the project site, with an average slip rate of approximately 40 millimeters (1.5 inches) per year and the most recent deformation occurring about 300 years ago (Personius and Nelson, 2006)

4 FIELD EXPLORATION

Shannon & Wilson explored the subsurface conditions at the proposed new building site by performing two (2) test pits, designated TP-1 and TP-2, and two (2) infiltration tests, designated I-1 and I-2. The field exploration activities were performed on May 13, 2019.

Approximate exploration locations are presented on the Site and Exploration Plan, Figure 2.

Details of the field exploration activities, including techniques used to advance the exploration locations, logs of material encountered, and infiltration test results, are presented in Appendix B.

5 LABORATORY TESTING

After test pits were completed, the soil samples were reviewed, and some were selected for laboratory testing to assist in the selection of representative engineering properties for the geotechnical units at the site. The testing program included moisture water contents, particle size analyses, and Atterberg limits tests. All soil laboratory testing was performed by Shannon & Wilson. Unless otherwise noted, all test procedures were performed in accordance with applicable ASTM International standards. Results of the laboratory tests and brief descriptions of the test procedures are presented in Appendix C.

6 SUBSURFACE CONDITIONS

6.1 Geotechnical Units

Shannon & Wilson grouped the materials encountered in our field explorations into two geotechnical units, as described below. Our interpretation of the subsurface conditions is based on the explorations and regional geologic information from published sources. The geotechnical units are as follows:

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Fill: Clayey Sand (SC) and Sandy Silt (ML).

Fluvial Deposits: Clayey Gravel with sand, with cobbles (GC), Poorly Graded Gravel with clay and sand, with cobbles (GP-GC).

These geotechnical units were grouped based on their engineering properties, geologic origins, and their distribution in the subsurface. The following subsections describe these units in more detail. The specific terminology used in our soil descriptions is presented in Appendix B, Figure B1. Unit contacts within the explorations may be more gradational than shown on the logs, and conditions may vary significantly between explorations. The following discussion is intended to provide the reader with a general overview of subsurface conditions.

6.1.1 Fill

Based on the two test pits and two infiltration tests performed as part of this study, the fill thickness ranged from approximately 1.5 feet to more than 5 feet. The fill material is made up of materials placed by humans. The Fill material observed in project exploration locations consists of Clayey Sand and Sandy Silt. The unit includes USCS group designations SC and ML.

Natural water content performed on a single sample resulted in a value of 17 percent.

Single sieve analysis test indicated fines content of 33 percent by dry weight. Single Atterberg limits test indicated a liquid limit of 50 percent with a plasticity index of 30.

6.1.2 Fluvial Deposits

Fluvial Deposits were encountered underlying the Fill material and extended to a depth of at least 12 feet, which represents the termination depth of the test pits. The thickness of the Fluvial Deposits ranged from 10 feet to 10.5 feet in TP-1 and TP-2, respectively. This unit consists of Clayey Gravel, with sand and cobbles, and poorly graded Gravel with clay, sand, and cobbles. This unit includes USCS group designations GC and GP-GC.

Natural water content performed on a single sample in this unit resulted in a value of 10 percent. Single sieve analysis test indicated fines content of 13 percent by dry weight.

6.2 Groundwater

Groundwater was not encountered within the depth of our explorations and no instrumentation or observation wells were installed. It should be noted that groundwater level at the proposed site may vary with changes in precipitation, time of year, or other factors not observed during our subsurface exploration program. Generally, groundwater

101458-002 September 2020 highs occur at the end of the wet season, in late spring or early summer, and groundwater lows occur towards the end of the dry season, in early to mid-fall.

7 SEISMIC GROUND MOTIONS AND GEOLOGIC

HAZARD EVALUATION

Our seismic hazard evaluations for the proposed building site were performed in general accordance with the criteria in the 2014 Oregon Structural Specialty Code (OSSC) and the 2018 International Building Code (IBC). According to the building codes, the earthquake event for the seismic hazard evaluation is the Maximum Credible Earthquake (MCE) having a 2 percent probability of exceedance in a 50-year period, or a 2,475-year return period.

7.1 Seismic Ground Motions

For new structures, the 2018 IBC refers to the American Society for Civil Engineer’s (ASCE’s) Minimum Design Loads and Associated Criteria for Buildings and Other Structures, 2016 Edition (ASCE 7-16) for determination of Site Class. In accordance with the site classification criteria in ASCE 7-16, we recommend using Site Class D. This classification is assigned for this site because the soil properties, beyond a depth of 12 feet, are not known in sufficient detail to determine the site class. Seismic design parameters based on the recommended Site Class D are presented in Exhibit 7-1

Exhibit 7-1: USGS Code-Based MCE and Seismic Design Parameters for Site Class D

Seismic Parameters Value Site Class D

MCEG Peak Ground Acceleration (PGA) 0.4g

MCE Bedrock Spectral Acceleration, 0.2 second period (SS) 0.823g

MCE Bedrock Spectral Acceleration, 1.0 second period (S1) 0.468g

Short-Period Site Amplification Factor. 0.2 second period, Fa 1.171

Long-Period Site Amplification Factor. 1.0 second period, Fv 1.832

Soil MCE Spectral Acceleration, 0.2 second period, Site Class D (SMS) 0.964g

Soil MCE Spectral Acceleration, 1.0 second period, Site Class D (SM1) 0.857

Soil Peak Ground Acceleration (PGAM) 0.48g

Soil Design Spectral Acceleration, 0.2 second period, Site Class D (SDS) 0.642g

Soil Design Spectral Acceleration, 1.0 second period, Site Class D (SD1) 0.572g

Note:

PGA stands for Peak Ground Acceleration, which corresponds to spectral acceleration at zero second.

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7.2 Seismic Hazards Evaluation

Seismic hazards considered in the evaluation include ground shaking, liquefaction and associated effects (e.g., flow failure, lateral spreading, and settlement), slope instability, fault rupture, tsunami, and seiche. The primary hazard at this site is ground shaking. In our opinion, the potential for fault rupture is low given the large distance between the proposed project site and the nearest potentially active fault. At the site, the risk of seismically induced liquefaction, liquefaction-related effects, slope instability, tsunami, and seiche are low. The seismic hazard evaluation presented herein was based on available information from the Department of Geology and Mineral Industries (DOGAMI).

8 GEOTECHNICAL DESIGN RECOMMENDATIONS

For purposes of our analysis, recommendations and conclusions, it was necessary for us to assume that the results of the geotechnical explorations and laboratory testing are representative of conditions throughout the project site. However, as stated in Section 6.1, subsurface conditions should be expected to vary. We may need to revise our recommendations during construction if different conditions than those reported in our logs are encountered.

The following subsections provide our recommendations for foundation type, foundation design, and basement wall design, including frost depth and minimum footing embedment, soil bearing capacity, crushed rock leveling course, estimated settlement, lateral sliding resistance, and lateral earth pressures.

8.1 Foundation Alternatives

Based on the information provided to us by AKS concerning the proposed new building and the subsurface conditions encountered during our field exploration program, we believe that shallow foundations consisting of spread footings are appropriate at this site to support the proposed building.

8.2 Spread Footing Design Recommendations

8.2.1 Frost Depth and Minimum Footing Embedment

According to the 2017 Oregon Residential Specialty Code (ORSC), it is recommended to consider a frost depth penetration for design of 12 inches. Therefore, we recommend embedding the spread footings at or below the seasonal frost penetration depth of 12 inches.

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Loose, soft, wet, or otherwise unsuitable soils encountered at the proposed foundation depth should be over-excavated and replaced with structural fill.

8.2.2 Soil Bearing Capacity

Based on soil conditions encountered during our field exploration program, we recommend that an allowable net bearing pressure of 3,000 psf be used to proportion footings founded on dense Clayey Gravel (Fluvial Deposits), which includes a factor of safety (FS) of 3.0 against shear failure of the foundation soils. The allowable bearing pressure can be increased by one-third for seismic conditions.

Minimum strip footing dimensions should be equal or greater than 24 inches in width.

Isolated column footing dimensions should be equal or greater than 4 feet by 4 feet.

8.2.3 Crushed Rock Leveling Course

Given the presence of cobble and boulders in the Fluvial Deposits unit, we recommend a crushed rock leveling course be placed beneath the spread footings or mat foundation. This layer should be a minimum of 12-inches thick. Material and compaction recommendations are discussed and presented is Section 9.4, Structural Fill.

Under slab on grade, the leveling course should be 6 inches and it should be compacted to per Section 9.4 of our report. We will include this recommendation when we update our report to final.

8.2.4 Estimated Settlement

The allowable bearing pressure recommended in Section 8.2.2 is based on, and limited by, a maximum allowable settlement of 1 inch. For these soils, the settlement is expected to occur as the loads are applied. We estimate that differential settlement will be less than 1/2-inch.

8.2.5 Lateral Sliding Resistance

The soil resistance available to withstand lateral foundation loads is a function of the frictional resistance, which can develop on the base of the foundation. The allowable frictional resistance may be computed using a coefficient of friction of 0.35. Note that only the dead load should be considered in calculating the lateral sliding resistance.

Soil resistance in the form of soil passive resistance should not be considered in the top 12 inches of soil. As such, the lateral sliding resistance should only be computed from the frictional resistance component developing at the base of the foundation, given the recommended foundation embedment of 12 inches (Section 8.2.1).

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8.3 Basement Wall Design Recommendations

8.3.1 General

We understand that the proposed building will have a daylight basement. The basement wall will be required to withstand the lateral earth pressures acting on it under static and seismic conditions. We recommend the basement walls to be supported on foundations consisting of a continuous spread footing system. The spread footing design recommendations are provided in Section 8.2.

We recommend that the basement walls be designed as non-yielding walls based upon the restriction at the top of the walls (the first-floor concrete slab). For design purposes, we have assumed that subdrainage systems will be installed to prevent hydrostatic pressure from developing behind all basement walls. Also, we have assumed that the backfill behind the basement walls is flat.

This section will provide our basement wall design recommendations for lateral earth pressures, subdrainage, backfill material and compaction, and lateral resistance.

8.3.2 Lateral Earth Pressures

In general, the lateral earth pressures on the basement walls depend on the type of wall (i.e., yielding or non-yielding), the type and method of placement of backfill against the wall, the magnitude of surcharge weight on the ground surface adjacent to the wall, the slope of the backfill, and the design criteria. We recommend that at-rest (non-yielding wall) earth pressures be considered for the basement walls. We recommend that cantilever retaining walls and gravity retaining walls utilized around the site but not at the building structure be considered yielding walls.

Based on the structural design information and the above assumptions, the lateral earth pressures on the walls were developed according to AASHTO LRFD (AASHTO, 2017). The static lateral earth pressure acting on walls consists of two components: static earth pressure and static surcharge pressure. The seismic lateral earth pressure on walls consists of three components: static earth pressure, static surcharge pressure, and seismic earth pressure.

The distributions of these lateral pressures are shown in Figure 3, Lateral Earth Pressure Distribution on New Basement Walls.

8.3.3 Subdrainage

Suitable drainage for walls can be provided by granular backfill material and a wall base subdrain system consisting of a 6-inch-diameter perforated or slotted drain pipe. The perforated or slotted drain pipe should be wrapped in an envelope of filter material at least

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12 inches thick and confined by a separation geotextile. The filter material consists of 3/8-inch minus and is specified in Section 02610.10(a) of the OSSC . The subdrain should be above the typical groundwater level, convey any collected seepage to the end of the wall, and daylight at low spots below the wall elevation.

8.3.4 Backfill Material and Compaction

The wall backfill material should be in accordance with standard ODOT Granular Wall Backfill (Section 00510.12 of the OSSC), which consists of 1-inch minus material. Heavy compaction equipment should not be allowed closer than 3 feet to the basement walls to prevent high lateral earth pressures and/or wall yielding and/or damage. Required compaction of wall backfill within 3 feet of the walls shall be obtained using hand-operated compaction equipment, such as a vibrating plate compactor.

8.3.5 Lateral Resistances

Based on our evaluation, the static and seismic lateral resistance of the basement walls can be provided by the frictional resistance, which can develop on the base of the foundation system. The allowable frictional resistance may be computed using a coefficient of friction of 0.35. Note that only the dead load should be considered in calculating the lateral sliding resistance.

9 CONSTRUCTION CONSIDERATIONS

9.1 Temporary Cut and Fill Slopes

Temporary cut slopes are typically the responsibility of the contractor and should comply with applicable local, state, and federal safety regulations, including the current OSHA Excavation and Trench Safety Standards. For general guidance, we suggest that temporary construction slopes be made at 1.5 Horizontal to 1 Vertical (1.5H:1V) or flatter. In areas of loose fills, very soft soil, or groundwater seepage, flatter slopes are likely to be required.

9.2 Groundwater Control

Groundwater was not encountered in the two performed test pits, which only extended to a depth of 12 feet. As such, we do not anticipate groundwater to be encountered within the explored depth if excavation and construction activities are performed during the dry season. If excavations will extend below the explored depth and/or will take place during the wet season, the contractor should design/plan for mitigation measures against groundwater and perched water during construction.

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9.3 Control of Surface Water and Drainage

Proper grading should be maintained to direct surface drainage away from open excavations, exposed soils, and completed foundations. Any water collected, as well as any excavated soil, should be treated and disposed of in a manner meeting local, state, and federal environmental regulations and requirements.

9.4 Structural Fill

Structural fill material should consist of imported and well-graded 3/4-inch minus crushed rock, with amount of material passing the No. 200 sieve not exceeding 5.0 percent by weight. Structural fill should be placed in 6-inch to 8-inch thick loose lifts and uniformly compacted to 95 percent of the maximum density as determined by ASTM D1557. The foundation concrete should be cast directly onto structural fill, if applicable.

9.5 Wet Weather Construction

Excavation and construction operations may expose the on-site soils to inclement weather conditions. The stability of exposed soils may rapidly deteriorate due to a change in moisture content (i.e. wetting or drying) or the action of heavy or repeated construction traffic. Accordingly, if subsurface construction occurs during periods of rain, foundation excavations should be adequately protected from the elements and from the action of repetitive or heavy construction loadings.

9.6 Temporary Shoring

Based on our communication with AKS and the design team, we understand that current plans are to install a shoring system between the existing BLM building and the site of the new building due to the limited spacing and the presence of utilities (i.e., gas, water, and irrigation lines).

Traditionally the temporary shoring system design is the contractor’s responsibility. Given the presence of gravel and cobbles in the Fluvial Deposits unit, we believe traditional sheet pile is not feasible at this site. Alternatively, a cantilever soldier pile wall system can be considered as a feasible shoring solution for this site. Further, the contractor should retain a licensed geotechnical and structural engineer to design the temporary shoring wall based upon the site-specific conditions considering protection of existing buildings and underground utilities.

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10 LIMITATIONS

The analyses, conclusions, and recommendations contained in this report are based on site conditions as they presently exist, and further assume that the explorations are representative of the subsurface conditions throughout the site; that is, the subsurface conditions everywhere are not significantly different from those disclosed by the explorations. If subsurface conditions different from those encountered in the explorations are encountered or appear to be present during construction, Shannon & Wilson should be advised at once so that these conditions can be reviewed, and the recommendations reconsidered, where necessary. If there is a substantial lapse of time between the submission of this report and the start of construction at the site, or if conditions have changed because of natural forces or construction operations at or adjacent to the site, it is recommended that Shannon & Wilson review this report to determine the applicability of the conclusions and recommendations.

Within the limitations of scope, schedule, and budget, the analyses, conclusions, and recommendations presented in this report were prepared in accordance with generally accepted professional geotechnical engineering principles and practice in this area at the time this report was prepared. Shannon & Wilson makes no other warranty, either express or implied. These conclusions and recommendations were based on Shannon & Wilson’s understanding of the project as described in this report and the site conditions as observed at the time of our explorations.

Unanticipated soil conditions are commonly encountered and cannot be fully determined by merely taking soil samples from widely spaced test borings. Such unexpected conditions frequently require that additional expenditures be made to attain a properly constructed project. Therefore, some contingency fund is recommended to accommodate such potential extra costs.

This report was prepared for the exclusive use of the AKS for the building structure at the existing BLM facility in Roseburg, Oregon. This report contains interpretations, conclusions, and recommendations for the planned new building, it should be provided to the Contractors for their information or reference only and not as a basis of Contractor bidding, and evaluation of differing conditions during construction. Also, since this report contains interpretations and conclusions, it should not be construed as a warranty of subsurface conditions.

The scope of Shannon & Wilson’s present work did not include environmental assessments or evaluations regarding the presence or absence of wetlands, or hazardous or toxic substances in the soil, surface water, groundwater, or air, on or below or around this site, or

101458-002 September 2020 for the evaluation or disposal of contaminated soils or groundwater should any be encountered.

Shannon & Wilson has prepared “Important Information About Your Geotechnical/Environmental Report” to assist you and others in understanding the use and limitations of our reports and is attached at the end of this report.

11 REFERENCES

Atwater, B.F., 1987, Evidence for great Holocene earthquakes along the outer coast of Washington State: Science, v. 236, p. 942-944.

Atwater, B.F., and Hemphill-Haley, E., 1997, Recurrence intervals for great earthquakes of the past 3500 years at Northeastern Willapa Bay, Washington: U.S. Geological Survey Professional Paper 1576.

Department of Geology and Mineral Industries (DOGAMI) website, https://www.oregongeology.org/gis, accessed 06/22/2019

Ludwin, R.S., Weaver, C.S., and Crosson, R.S., 1991, Seismicity of Washington and Oregon in Slemmons, D.B., E.R. Engdahl, M.D. Zoback, and D.D. Blackwell (eds.), Neotectonics of North America, p. 77-98.

Oregon Standard Specifications for Construction, current edition 2018 (OSSC, edition 2018).

Oregon Residential Specialty Code, current edition 2017 (ORSC, Edition 2017).

Personius, S.F., compiler, 2002, Fault number 890, South Slough thrust and reverse faults, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults, accessed 06/24/2019.

Personius, S.F., and Nelson, A.R., compilers, 2006, Fault number 781, Cascadia subduction zone, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/hazards/qfaults, accessed 06/24/2019.

Satake, K., Shimazaki, K., Tsuji, Y., and Ueda, K., 1996, Time and size of a giant earthquake in Cascadia inferred from Japanese tsunami records of January 1700, Nature, 379,

p. 246-249.

USGS, 2017, Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/hazards/qfaults, accessed 05/02/2017.

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Wells, R.E., Jayko, A.S., Niem, A.R., Black, G., Wiley, T., Baldwin, E., Molenaar, K.M., Wheeler, K.L., DuRoss, C.B., and Gilver, R.W., 2000, Geologic Map and Database of the Roseburg 30 x 60’ Quadrangle, Douglas and Coos Counties, Oregon: U.S.

Geological Survey Open-File Report 00-376, scale 1:100,000.

Wells, R.E., Weaver, C.S., and Blakeley, R.J., 1998, Fore-arc migration in Cascadia and its neotectonic significance: Geology, v. 26, p. 759-762.

SITE

LOCATION

Copyright:© 2013 National Geographic Society, i-cubed

Umpqua NF and the BLM Colocation Site Development Design Roseburg, Oregon

FIG. 1

VICINITY MAP

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Scale in Miles

Site Location

Idaho

Washington

NevadaCalifornia

ED

ED

I-2

I-1

TP-2

TP-1

Umpqua NF and the BLM Colocation Site Development Design Roseburg, Oregon

SITE AND EXPLORATION PLAN

FIG. 2

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Scale in Feet

LEGEND

ED Designation and Approximate Location of Test Pit

&( Designation and Approximate Location of Infiltration Test

NOTES

1. Aerial imagery obtained through Google Maps Satellite.

TP-1

I-1

LATERAL EARTH PRESSURE

DISTRIBUTION ON NEW

RETAINING WALLS

FIG. 3SHANNON & WILSON, INC.

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SOIL BACKFILL

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H

Drained granular backfill material

34H

YIELDING WALL SOIL COMPONENT

RESULTANT FORCE (P )

P = (34H x H2 ) lbs/ft wall

3 H

R

R

YIELDING WALL SURCHARGE COMPONENT

0.26q

RESULTANT FORCE (P )

P = 0.26qH lbs/ft wall

2 H

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TOTAL LATERAL EQUIVALENT FLUID PRESSURES

SURCHARGE, q

SURCHARGE

COMPONENT

NOTES

1. Units are pounds per square foot (psf).

2. Backfill unit weight of 130 pcf.

3. Backfill friction angle is 36 deg.

4. Wall backfill is assumed to be drained granular backfill material.

5. Seismic pressures provided for peak ground acceleration associated with having a 2 percent probability of exceedance in a 50-year period, or a 2,475-year return period.

YIELDING WALL SEISMIC BACKFILL COMPONENT

RESULTANT FORCE (P )

Pr =(20H x H2 ) lbs/ft wall20H

R

SEISMIC BACKFILL

COMPONENT

55H

NON-YIELDING WALL SOIL COMPONENT

RESULTANT FORCE (P )

P = (55H x H2 ) lbs/ft wall

3 H

R

R

NON-YIELDING WALL SURCHARGE COMPONENT

0.41q

RESULTANT FORCE (P )

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2 H

R

R

NON-YIELDING WALL SEISMIC BACKFILL COMPONENT

RESULTANT FORCE (P )

Pr = (50H x H2 ) lbs/ft wall

R

50H

Umpqua NF and the BLM Colocation Site Development Design Roseburg, Oregon

3 H 2

3 H

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Appendix A

Topographic Survey

CONTENTS

Topographic Survey of BLM Roseburg Campus (provided by AKS)

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Appen dix B: Field Ex plorat ions

Appendix B

Field Explorations

CONTENTS

B.1 General ..................................................................................................................................... B-1

B.2 Test Pits .................................................................................................................................... B-1

B.2.1 Drilling ........................................................................................................................ B-1

B.2.2 Disturbed Sampling .................................................................................................. B-1

B.2.3 Pit Abandonment ...................................................................................................... B-1

B.2.4 Material Descriptions ............................................................................................... B-1

B.2.5 Logs of Test Pits ......................................................................................................... B-2

B.3 Infiltration Testing ................................................................................................................. B-2

Exhibits

Exhibit B-1: Infiltration Test Results .............................................................................................. B-2

Figures

Figure B1: Soil Description and Log Key Figure B2: Log of Test Pit TP-1 Figure B3: Log of Test Pit TP-2

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B.1 GENERAL

Shannon & Wilson, Inc. (Shannon & Wilson) explored the subsurface conditions at the proposed new building site by performing a total of two (2) test pits, designated TP-1 and TP-2, and two (2) infiltration tests, designated I-1 and I-2. The field exploration program was performed on May 13, 2019. Approximate exploration locations are presented on the Site and Exploration Plan, Figure 2. This appendix describes the techniques used to advance and sample the test pits and perform the infiltration tests and presents logs of the materials encountered during the field exploration program.

B.2 TEST PITS

B.2.1 Drilling

Test pits TP-1 and TP-2 were each advanced to a depth of about 12 feet below existing ground surface (bgs) at the time of our field exploration plan, which corresponded to the maximum reach of the excavator. The test pits were performed by Brent Ridley Construction, out of Grand Pass, Oregon, using a Caterpillar (CAT) 308E2 CR excavator equipment.

A Shannon & Wilson geotechnical engineer was present during the exploration activities to locate the pits, log the material encountered in the pits, collect disturbed soil samples for laboratory testing, and conduct infiltration testing.

B.2.2 Disturbed Sampling

Disturbed samples were collected in the test pits, typically at 2.5- to 7.5-foot depth intervals, from the material excavated and piled up by the excavator. All disturbed samples were visually identified and described in the field, sealed to retain moisture, and returned to the Shannon & Wilson laboratory for additional observation and testing.

B.2.3 Pit Abandonment

After soil sampling was completed, the test pits were backfilled with the excavated material and tamped in place with the excavator bucket without any placement or compaction control.

B.2.4 Material Descriptions

In the field, soil samples were classified visually in general accordance with ASTM D2488 Standard Practice for Description and Identification of Soils (Visual-Manual Procedure).

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Consistency, color, relative moisture, degree of plasticity, peculiar odors and other distinguishing characteristics of the samples were noted. Once returned to the laboratory, soil samples were re-observed, various standard classification tests were performed, and field classifications were modified, as necessary, in accordance with the Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), ASTM D2487. However, ASTM D2487 was not followed in full, because it requires that a suite of tests be performed to classify a single sample. In most cases, we did not have enough of any one sample to perform all the tests required to fully classify it in accordance with ASTM D2487. The specific terminology used in the soil classifications is defined on the Soil Description and Log Key, Figure B1.

B.2.5 Logs of Test Pits

Summary logs of test pits TP-1 and TP-2, performed as part of this study, are presented in Figures B2 and B3, respectively. The left-hand portion of the log provides our description, classification, and geotechnical unit designation of the soils encountered in the pit. The middle portion of the log shows a graphic log, sample locations and designations, and drilling information. The right-hand portion of the log presents photos of the pit. Material descriptions and interfaces on the logs are interpretive, and actual changes may be gradual.

B.3 INFILTRATION TESTING

Shannon & Wilson performed two (2) infiltration tests, designated IT-1 and IT-2, at a depth of 5 feet bgs, using the Encased Falling Head Test method. The locations and depth of the infiltration tests were selected by the design team and provided to us by AKS. At the infiltration test locations, a hole was excavated with the CAT 308E2 CR excavator to a depth of 5 feet bgs. Then, a 6-inch diameter PVC pipe was inserted into the hole and pushed approximately 6 inches into the bottom to create a seal. One foot of water was then added to the bottom of the pipe to presoak the soil. Once the presoak was completed, water was again added to the pipe to return the level to 1 foot above the test surface. The drawdown was measured at approximately 3- to 15-minute intervals. The results of the infiltration tests are tabulated in Exhibit B-1.

Exhibit B-1: Infiltration Test Results

Infiltration Test Infiltration Material Infiltration Rate (in/hr)2 Infiltration Testing Depth (ft)1

IT-1

IT-2

Sandy Silt

Clayey Gravel with sand and Cobbles

7.3

4.2

NOTES:

1 Depth below existing grade at the time of our field activities.

2 Tabulated infiltration rates are unfactored.

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Appendix C: Laboratory Test Results

Appendix C

Laboratory Test Results

CONTENTS

C.1 General ..................................................................................................................................... C-1

C.1.1 Moisture (Natural Water) Content ......................................................................... C-1

C.1.2 Atterberg Limits ........................................................................................................ C-1

C.1.3 Particle-Size Analyses ............................................................................................... C-2

Figures

Figure C1: Atterberg Limits Results Figure C2: Grain Size Distribution Results

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C.1 GENERAL

Representative soil samples obtained during the field exploration activities were described and identified in the field by Shannon & Wilson. Physical characteristics of the collected samples were noted, and field descriptions and identifications were modified, as necessary, in accordance with the terminology presented in Appendix B, Figure B1. During the review, representative soil samples were selected for further testing. The material descriptions and identifications were refined/revised, as necessary, based on the results of the laboratory tests. The soil testing program included natural moisture content, Atterberg limit, and particle size analyses. The natural moisture content, Atterberg limits, and particle size analyses tests were performed by Shannon & Wilson in general accordance with applicable ASTM International (ASTM) standards.

C.1.1 Moisture (Natural Water) Content

Natural moisture content determinations were performed in accordance with ASTM D2216, on selected soil samples. The natural moisture content is a measure of the amount of moisture in the soil at the time of exploration. It is defined as the ratio of the weight of water to the dry weight of the soil, expressed as a percentage. The results of moisture content determinations are presented in the boring logs in Appendix B.

C.1.2 Atterberg Limits

Atterberg limits were determined for one selected sample in accordance with ASTM D4318.

This analysis yields index parameters of the soil that are useful in soil identification, as well as in a number of analyses, including liquefaction analysis. An Atterberg limits test determines a soil’s liquid limit (LL) and plastic limit (PL). These are the maximum and minimum moisture contents at which the soil exhibits plastic behavior. A soil’s plasticity index (PI) can be determined by subtracting PL from LL. The LL, PL, and PI of the tested sample are presented on Figure C1, Atterberg Limits Results. The results are also shown graphically on the Logs of Borings in Appendix B. For the purposes of soil description, Shannon & Wilson uses the term nonplastic to refer to soils with a PI less than 4, low plasticity for soils with a PI range of 4 to 10, medium plasticity for soils with a PI range of 10 to 20, and high plasticity for soils with a PI greater than 20.

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C.1.3 Particle-Size Analyses

Particle-size analyses were conducted in accordance with ASTM D1140. For select samples, a wet sieve analysis was performed to determine the percentage (by weight) of each sample passing the No. 200 (0.075 mm) sieve. Results of the particle-size analyses are presented in Figure C2, Grain Size Distribution Results. The percentage of each sample passing the No.

200 sieve is also shown graphically on the Logs of Borings in Appendix B.

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Important Information

Important Information About Your Geotechnical Report

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CONSULTING…