OR DOT 18(1)_Geotechnical_Report.pdf

REPORT C OVER PAGE

Geotechnical Engineering Report Revision 2

OR DOT 18(1)

OR 58: Coast Fork Willamette River to Lower Salt Creek Bridges Seismic Improvements to Bridges OR58: Milepost 2.46 to 38.25

Oakridge, Oregon May 20, 2022

Terracon Project No. 82205091 | WFL Geotechnical Report 10-21

Prepared for:

DJ&A PC

Missoula, Montana

Prepared by:

Terracon Consultants, Inc.

Portland, Oregon

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REPORT C OVER LETTER TO SIGN

May 20, 2022

DJ&A PC

3203 S Russell Street Missoula, Montana 59801

Attn: Mr. Daniel Lautzenheiser P: 406-721-4320 E: DanL@djanda.com

Re: Geotechnical Engineering Report – Revision 2 OR 58: Coast Fork Willamette River to Lower Salt Creek Bridges OR Highway 58 from Milepost 2.46 to 38.25 Oakridge, Oregon Terracon Project No. 82205091 | WFL Geotechnical Report 10-21

Dear Mr. Lautzenheiser:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with Terracon Proposal No. P82205091 dated January 21, 2021 and the Statement of Work for OR DOT 18(1), 0558: US-97 to I-5 (Contract No.

DTFH7015D00003, Task Order No. 69056721F000013), dated November 25, 2020. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations for the retrofit bridges (Coast Fork, Barnard, Salmon Creek, and Lower Salt Creek) of the proposed project. In addition, revisions to this report were completed following the addition of scour protection walls at the Barnard bridge location in January 2022.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon Consultants, Inc.

Kristopher T. Hauck, P.E. Ryan T. Houser, RG, CEG Principal | Office Manager Project Geologist (Geologic & Geologic Hazard Project Related Sections) Preliminary Reports Reviewed by: David A. Baska, Ph.D, CEG Senior Consultant, Gary A. Quinn, PE (MT) Principal Executive, Peter Palmerson, PE (WA) (DOT aspects review) | Steven A. Dickenson (External DOT design guidance review)

OR 58: Coast Fork Willamette River to Lower Salt Creek Bridges ■ Oakridge, Oregon May 20, 2022 ■ Terracon Project No. 82205091 | WFL Geotechnical Report 10-21

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REPORT TOPICS

1 INTRODUCTION

2 SITE & PROJECT DESCRIPTION

2.1 Site Conditions

2.2 Existing Foundations Summary & Scour Considerations

2.2.1 Coast Fork Willamette Bridge #05286

2.2.2 Barnard - Willamette Bridge #07894

2.2.3 Salmon Creek Bridge #02073C

2.2.4 Lower Salt Creek Bridge #01519A

2.3 Project Description

3 GEOLOGIC PUBLICATION REVIEW

3.1 Regional Geology

3.1.1 Site Geologic Publication Review

3.2 Regional Seismic Setting

3.2.1 Regional Faults

3.2.2 Site Seismic Hazards

4 FIELD EXPLORATION AND LABORATORY TESTING

4.1 Field Exploration

4.2 Geophysical Exploration

4.3 Laboratory Testing

5 SUBSURFACE CONDITIONS

5.1 Coast Fork Subsurface Conditions

5.1.1 Generalized Subsurface Profile

5.1.2 Groundwater Conditions

5.2 Barnard Subsurface Conditions

5.2.1 Generalized Subsurface Profile

5.2.2 Groundwater Conditions

5.3 Salmon Creek Subsurface Conditions

5.3.1 Generalized Subsurface Profile

5.3.2 Groundwater Conditions

5.4 Lower Salt Creek Subsurface Conditions

5.4.1 Generalized Subsurface Profile

5.4.2 Groundwater Conditions

6 SEISMIC CONSIDERATIONS

6.1 Recommended Design Ground Motions

6.1.1 Coast Fork Bridge Recommended Design Ground Motions

6.1.2 Barnard Bridge Recommended Design Ground Motions

6.1.3 Salmon Creek Recommended Design Ground Motions

6.1.4 Lower Salt Creek Recommended Design Ground Motions

6.2 Liquefaction Evaluations

6.2.1 Coast Fork to Lower Salt Creek Bridges

7 SPREAD FOOTINGS

7.1 Coast Fork Bridge Footings

7.1.1 Unfactored Soil Parameters for Existing Spread Footings

7.1.2 Unfactored Lateral Earth Pressures

7.2 Barnard Bridge Footings

7.2.1 Unfactored Soil Parameters for Existing Spread Footings

7.2.2 Unfactored Lateral Earth Pressures

7.3 Salmon Creek Bridge Footings

7.3.1 Unfactored Soil Parameters for Spread Footings

7.3.2 Unfactored Lateral Earth Pressures

7.4 Lower Salt Creek Bridge Footings

7.4.1 Unfactored Soil Parameters for Spread Footings

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7.4.2 Unfactored Lateral Earth Pressures

8 FOUNDATION CONSTRUCTION CONSIDERATIONS

8.1 Temporary Shoring

8.2 Dewatering

8.3 Excavations

9 EXISTING DEEP FOUNDATIONS

9.1 Lower Salt Creek Driven Pile Foundations

9.1.1 Axial Resistance

9.1.2 Lateral Resistance

10 MICROPILE FOUNDATIONS

10.1 Barnard Micropile Design Parameters

10.2 Salmon Creek & Coast Fork Micropile Design Parameters

10.3 Lateral Resistance

10.3.1 Coast Fork L-Pile Parameters

10.3.2 Salmon Creek L-Pile Parameters

10.3.3 Barnard L-Pile Parameters

10.4 Micropile Load Testing

11 MICROPILE CONSTRUCTION CONSIDERATIONS

12 SHEETPILE SCOUR PROTECTION WALL

12.1 Lateral Earth Pressures Design

12.2 Rock-Pins

12.3 Construction Considerations

13 EARTHWORK

13.1 Embankment Slopes

13.2 Earthwork Construction Considerations

14 GENERAL COMMENTS

15 REFERENCES

Note: Refer to each individual Attachment for a listing of contents.

FIGURES

1- PROJECT VICINITY MAP

2- QUATERNARY FAULT & BRIDGE LOCATION

3- GEOLOGIC HAZARDS (A-B)

4- EXPLORATION PLANS (A-D)

5- SHEAR WAVE VELOCITY PROFILES (A-D)

6- GEOTECHNICAL FOUNDATION DATA SHEETS (6A – 6D)

ATTACHMENTS

EXPLORATION RESULTS

MICROPILE CAPACITY DESIGN CHARTS

SUPPORTING INFORMATION

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Geotechnical Engineering Report (Revision 1) OR 58: Coast Fork Willamette River to Lower Salt Creek Bridges

OR Highway 58 from Milepost 2.46 to 38.25 Oakridge, Oregon

Terracon Project No. 82205091 | WFL Geotechnical Report 10-21 May 20, 2022

1 INTRODUCTION

This report presents the results of our geotechnical investigation which included the following scope of services: geologic publication review, site reconnaissance, existing geotechnical report review, subsurface exploration and geotechnical engineering analysis and design services performed for the proposed seismic improvements to the bridges located along OR Highway 58 from Milepost 2.46 to 38.25 centered near Oakridge, Oregon. This report was prepared in substantial accordance with the Geotechnical Report requirements from Oregon Department of Transportation (ODOT) Geotechnical Design Manual (GDM), dated March 27, 2018, and AASHTO LRFD Bridge Design Specification, 9th Edition dated January 1, 2020. Our services were also completed in accordance with our proposal (P82205090), dated January 21, 2021.

The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil and rock conditions ■ Foundation design and construction

■ Groundwater conditions ■ Pavement design and construction

■ Site preparation and earthwork ■ Seismic ground motions

■ Geologic hazards ■ Seismic hazard evaluation

■ Excavation considerations

The final geotechnical report has subsequently been updated (Revision 1) to include Sheetpile wall design recommendations at the Barnard location as part of the project revisions to the scour protection.

The preliminary geotechnical engineering Scope of Services for this project included the advancement of several explorations at each of the bridge locations to depths ranging from approximately 5 to 100 feet below existing site grades. In addition, shear wave velocity measurements were obtained, and time-averaged shear-wave velocity in the upper 100-foot of the geologic profiles (vs30) were calculated for each of the bridge sites in support of seismic design requirements. These explorations were completed in December of 2019 and January of 2020.

Geotechnical Engineering Report – Revision 1

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Maps showing the site and exploration locations are shown on Figure 1 – Project Vicinity Map and Figures – 4(A-D) Exploration Plans, respectively. The results of the laboratory testing performed on soil samples obtained from the sites during the field exploration are included on the exploration logs and/or as separate graphs in the Exploration Results section.

2 SITE & PROJECT DESCRIPTION

2.1 Site Conditions

The proposed project consists of seismically retrofitting four bridges on OR58 (ODOT Highway

18) to create a lifeline between the Willamette Valley and Central Oregon that will be used for critical transportation following a major seismic event. The following bridges and site locations are included in the project:

■ Bridge 05286, Coast Fork Willamette River, Hwy 18 at Milepost (MP) 2.46

■ Bridge 07894, Willamette River, Hwy 18 (Barnard) at MP 33.24

■ Bridge 02073C, Salmon Creek, Hwy 18 at MP 35.98

■ Bridge 01519A, Lower Salt Creek, Hwy 18 at MP 38.25

The project bridge locations are shown in Figure 1 – Project Vicinity Map.

Previously, Terracon prepared a Geotechnical Scoping Report (October 2018) which included a review of previously prepared geotechnical engineering information for the project. We were provided a copy of ODOT As-Built Bridge Drawings, various bridge inspection reports, right-of-way plans, and a Final Seismic Retrofit Analysis Project Report prepared by HDR (PA B31261 WOC 01, dated August 8, 2014). The HDR report included a Geotechnical Engineering Report for each of the bridges of this project prepared by S&W in 2014.

2.2 Existing Foundations Summary & Scour Considerations

During the preliminary phases of this project, as-built plans and previous existing geotechnical information was reviewed. In addition, during the final design phases of this project, scour analyses were refined by the design team. The following sections describe a summary of our review of foundations as well as scour considerations of the existing foundations (since all of these bridges will be retrofits).

2.2.1 Coast Fork Willamette Bridge #05286

The Coast Fork Willamette River Bridge #05286 (Coast Fork Bridge) was proposed for replacement; however, retrofitting the bridge is now the selected alternative. The existing bridge contains seven spans supported by six bents and two interior piers. The west end starts the numbering of the piers and bents (Bent 1 is the westernmost bent). We understand that the bents and piers are supported on conventional spread footings based on our review and understanding

Responsive ■ Resourceful ■ Reliable 3 of the original plans from 1949 and the improvement plans from 1989 to present. Following maintenance operations in 2001, the footings at Pier 2 were enlarged and additional scour protection was placed around both piers and Bents 2 through 5.

While additional scour protection and foundation enlargements were completed in 2001, based on the refined scour analyses, the bents immediately adjacent to the existing riverbank have bottom of footing elevations near the scour depth. We understand that scour protection is being implemented at a minimum of location bents adjacent to the existing bank (Bents 4 and 5) since the bottom of footing is just below the scour depth.

2.2.2 Barnard - Willamette Bridge #07894

The Willamette River Bridge #07894 (Barnard Bridge) is proposed for retrofit. The existing bridge contains eight spans supported by six bents and two piers. The west end starts the number of the bents (Bent 1 is the westernmost). Based on our understanding of the original plans from 1954 and summarized in the geotechnical report, we understand that the piers are supported on conventional spread footings placed atop varying ground conditions. Bents 3 through 6 were placed on a 4- to 6-foot thick slab concrete. Bents 4 through 6 are bearing on Mudstone and the remaining piers on Gravel Alluvium.

Since the construction of the bridge, the main channel of the river has moved from between Bents 4 and 5 to between 3 and 4. In addition, significant additional scour protection was placed near Bent 3 due to scour risks. We understand that scour protection is being implemented at Bents 2 through 4 due to the footing elevation being just below the scour depth. It’s important to note that Bents 4 through 6 are supported on bedrock materials. Since the time from the original version of this report (August 2021), the owner and design team have elected to revise the scour protection plans for this bridge location to include a Sheetpile retaining wall around Bent 3. This revised report now includes geotechnical design recommendations coordinated during the structural design.

2.2.3 Salmon Creek Bridge #02073C

The Salmon Creek River Bridge #002073C is proposed for retrofit. The existing bridge contains three spans supported by four bents. The south end starts the number of the bents (Bent 1 is the southernmost bent and referred to as the East Approach). Based on our understanding of the modification As-Built plans from 1988, we understand that the bents are supported on conventional spread footings bearing on dense Gravel Alluvium. It should be noted that some previous bridge foundations remain in place (buried) adjacent to the existing bridge foundations.

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We understand that the foundations for this bridge are well below the potential scour depths and that additional scour protection is not planned.

2.2.4 Lower Salt Creek Bridge #01519A

The Lower Salt Creek Bridge #01519A is proposed for retrofit. The existing bridge contains three spans supported by four bents. The east end starts the number of the bents (Bent 1 is the easternmost bent). Based on our understanding of the original plans from 1965 and summarized in the geotechnical report, we understand that Bents 1 and 4 are supported on driven H-piles and Bents 2 and 3 are supported on spread footings. Both the driven piles and the spread footings are bearing in and on Gravel Alluvium, respectively.

We understand that the foundations for this bridge are well below the potential scour depths and that additional scour protection is not planned.

2.3 Project Description

Our understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired including several internal conference with the design team. This plan was prepared in substantial accordance with the Oregon Department of Transportation (ODOT) Geotechnical Design Manual (GDM) and AASHTO LRFD Bridge Design Specification Requirements and incorporated review comments from Western Federal Lands Highway Division (WFLHD) and ODOT into the final approved plan.

The following description of site and project conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Information Provided

DJ&A provided the requested Statement of Work (November 25, 2020). We were also provided with Shannon & Wilson, Inc. (S&W) Geotechnical Reports for each bridge, and Oregon Department of Transportation (ODOT) Plan and Elevation, Bent Alternative documents for each bridge prepared by HDR as well as the available scour reports for Upper Salt Creek, Coast Fork Willamette, and Barnard Willamette bridge locations.

Alignment Information

The project bridges are located at OR Highway 58 (also referred to as ODOT Highway

18) from Milepost 2.46 to 38.25 near Oakridge, Oregon. It is important to note that the Upper Salt Creek Bridge has been separated out from the retrofit bridge packages.

The retrofit bridge locations are:

■ Bridge 05286, Coast Fork Willamette River, Hwy 18 at Milepost (MP) 2.46

■ Bridge 07894, Willamette River, Hwy 18 (Barnard) at MP 33.24

■ Bridge 02073C, Salmon Creek, Hwy 18 at MP 35.98

■ Bridge 01519A, (Lower) Salt Creek, Hwy 18 at MP 38.25

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Item Description

Project Description

The project consists of seismically retrofitting four bridges on OR58 (ODOT Highway

18) to create a lifeline between the Willamette Valley and Central Oregon that will be used for critical transportation following a major seismic event.

Proposed Structures

While the particular bridge replacements and retrofits are identified, the following information summarizes the expected new or modified structures:

■ If Bridge 05286 (Coast Fork) was previously planned to be replaced. However, during this phase of the project, it was determined that the bridge is to be retrofitted. We expect existing foundations to be modified per the original TS&L documents with bent and pier column strengthening. In addition, micropile underpinning will be utilized for additional seismic loads on at least two bents near the riverbanks.

■ Bridge 07894 (Barnard) will be retrofitted. Current plans indicate retrofitting of footings where required, as well as additional stiffening along abutments and spans. We understand that retrofit includes widening of footings at Bents 2 through 7, pier wall strengthening on interior bents, pier diaphragm and strut strength improvements at Bents 1 and 7 and strengthening of steel floor-beam connections. Micropiles will also be used for footing improvements. Design scour protection at Bent 3 includes a Sheetpile wall.

■ Bridge 0207C3 (Salmon Creek) is expected to have retrofitted foundations and stiffening elements incorporated into portions of the spans. The improvements to this bridge include installing micropiles adjacent to footings at Bents 1 and 4, installation of connection brackets at all bents, and installing Fiber Reinforced Panels (FRP) at Bents 1 and 4.

■ Bridge 01519A (Lower Salt) is expected to have retrofitted abutments with stiffeners and possibly include stiffening elements incorporated in the spans. In general, this retrofit includes tying frames together and strengthening the superstructure connections. No foundation improvements (below the existing ground surface) are necessary for this alternative.

All bridge improvements currently follow the existing alignments (replacements and retrofits). Therefore, no new retaining walls and/or embankment construction is expected as part of the new or retrofitted structures.

3 GEOLOGIC PUBLICATION REVIEW

During the Preliminary Phase of the geotechnical study, we reviewed geologic and geotechnical information from published resources, as well as in-house and third party provided information.

Public sources included geology maps, soil survey maps, topographic maps, seismic information including active and inactive faults, as-built plans for the bridges and other structures, and previous project studies that included subsurface information. We performed this review prior to field exploration planning and incorporated the collected information in preparation of the Subsurface Investigation and Subsurface Exploration Plan, dated November 13, 2019.

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3.1 Regional Geology

The project locations lie within the Willamette Valley and the immediately adjacent Cascade Mountains to the east. The Willamette Valley is a broad alluvial plain, but before it became the broad plain it is today, it was a low-lying area between Coast Range mountains to the west and the Cascade Range mountains to the east. As the shifting continental shelf collided with the oceanic plate and oceanic islands to form the Coast Range (over millions of years), the broad low-lying area continued to fill in with alluvial sediment from the nearby Cascade Range, as well as distant sources glacial flood outbursts.

The Cascade Mountains were generally formed from repeated volcanic activity also initiated by the shifting continental plate and the subducting oceanic plate. At the locations of the bridges, especially the eastern milepost bridges, the narrow low-lying areas between the mountains and near the rivers and streams contain various thicknesses of relatively high-energy (i.e. sands to cobbles) alluvial sediments.

3.1.1 Site Geologic Publication Review

Site Location West Approach Mapping East Approach Mapping Underlying/Deeper Units

Bridge 05286, Coast Fork Willamette

River1, 2

Recent alluvium consisting of silt, sand, and gravel

Recent alluvium consisting of silt, sand, and gravel

Pleistocene age sand and gravel and sand and gravel terrace deposits that predate Missoula Floods

Bridge 07894, Willamette

River (Barnard) 1, 3

Recent alluvium consisting of silt, sand, and gravel

Recent alluvium consisting of silt, sand, and gravel

Little Butte Volcanics – broadly mapped as volcanic rocks of widely varying composition (ash-flow tuff, tuffaceous sandstone/siltstone, lava flows, etc)

Bridge 02073C, Salmon

Creek1, 4, 5

Quaternary glacial outwash deposits consisting of alluvium, post-glacial colluvium, and terrace deposits

Recent alluvium consisting of silt, sand, and gravel

Little Butte Volcanics – broadly mapped as volcanic rocks of widely varying composition (ash-flow tuff, tuffaceous sandstone/siltstone, lava flows, etc)

Bridge 01519A, (Lower) Salt Creek1, 4

Quaternary glacial outwash deposits consisting of alluvium, post-glacial colluvium, and terrace deposits

Quaternary glacial outwash deposits consisting of alluvium, post-glacial colluvium, and terrace deposits

Little Butte Volcanics – broadly mapped as volcanic rocks of widely varying composition (ash-flow tuff, tuffaceous sandstone/siltstone, lava flows, etc)

1. OGDC-6, Oregon Geologic Data Compilation, release 6, compiled by Rachel L. Smith and Warren P. Roe.

2. (2001) Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon: USGS

Professional Paper 1620

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Site Location West Approach Mapping East Approach Mapping Underlying/Deeper Units

3. Peck, D.L., Griggs, A.B., Schlicker, H.G., Wells, F.G., and Dole, H.M., 1964, Reconnaissance geologic map and sections of the Western Cascade Range, Oregon North of Latitude 43N: Reston, Va., U.S. Geological Survey Professional Paper 449, scale 1:250,000

4. Sherrod, D.R., 1991, Geologic map of a part of the Cascade Range between latitudes 43-44, Central Oregon:

Reston, Va., U.S. Geological Survey Miscellaneous Investigations Map I-1891, scale 1:125,000.

5. Brown, D.E., McLean, G.D., Woller, N.M., and Black, G.L., 1980, Reconnaissance geologic map of the Willamette Pass Area, Oregon, in geology and geothermal resource potential of the Willamette Pass Area, Oregon: Portland, Oregon, Oregon Dept. of Geology and Mineral Industries.

3.2 Regional Seismic Setting

As described above, the Cascade Mountains were generally formed from repeated volcanic activity initiated by the shifting continental plate and the subducting oceanic plate. Due to the proximity of the project to the interface of two tectonic plates and their movement, there are three sources of earthquakes:

■ Subduction Zone Interface: These earthquakes are located near the interface of the two plates located along the western coastline and are located about 25 miles beneath the surface. Previous studies have found evidence of the most recent subduction zone event occurring about 300 years ago which may have been a Magnitude 9 event. This likely was a full-length rupture of the Cascadia Subduction Zone (CSZ) and is the main source of the Lower Level – Operational Design Criteria referenced in the ODOT GDM.

■ Deep Intraplate: These earthquakes occur within the subducting oceanic plate (therefore deeper than Subduction Zone Interface) and are a result of the bending and molding of the subsiding plate. These sources are generally located deeper than the CSZ events with most recent events over the last 100 years ranging from Magnitude 6.5 to 7.1. These events appear more frequent along the northern section of the CSZ (Puget Sound area of Washington) than in Western Oregon.

■ Shallow Crustal: These earthquakes occur in the upper crust of the continental shelf due to the compression and rotation of the plate. The related faults are mostly located within the Coast and Cascade Ranges and have ranged in Magnitude from 5.6 to 7 over the last 150 years.

The previous geotechnical reports prepared by S&W in 2014 for these projects evaluated both a Lower Level and Upper Level ground motion hazard evaluation per the ODOT Bridge Design and Drafting Manual and are summarized in the provided reports. However, the requirements of the sources to be incorporated in the Lower Level and Upper Level have changed since their publication.

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3.2.1 Regional Faults

Our review of nearby faults according to the USGS Quaternary Fault and Fold Database was completed in order to locate Class A and Class B faults relative to the project site. Based on our review, Class A faults are located greater than 20 miles from each of the site locations, with the nearest site being Upper Salt Creek Bridge. There is one Class B fault that parallels Oregon Highway 58 from Oakridge to Upper Salt Creek; however, it is considered inactive. The following table presents the Class A active faults within about 25 miles of the bridge locations.

Fault Name Time Since Deformation Slip Rate

Distance from Site and

Direction1

Nearest Bridge Location for

Distance Referenced La Pine Graben Fault

Zone <130,000 years ago

<0.2 mm per year 25 miles east Upper Salt Creek

Unnamed faults north of Diamond Lake

<130,000 years ago

<0.2 mm per year 24 miles south Upper Salt Creek

1. Distance is measured from the ground surface at the bridge location to the closest trace of the mapped fault.

The nearest mapped potentially active faults are over 20 miles from each of the bridge site locations. Therefore, modifications to the design ground motions for near-fault effects are not required. See Figure 2 – Quaternary Fault & Bridge Locations for referenced faults noted above and the 6-mile radius from the bridge locations.

3.2.2 Site Seismic Hazards

Seismic hazards resulting from earthquake motions can include slope instability, liquefaction, and surface rupture due to faulting or lateral spreading. Liquefaction is the phenomenon wherein soil strength is dramatically reduced when subjected to vibration or shaking.

We reviewed the Statewide Geohazards Viewer (https://gis.dogami.oregon.gov/hazvu/) published by the Oregon Department of Geology and Mineral Studies (DOGAMI) and available online (HazVu). The Geohazard viewer is a regional hazard screening tool and is not intended to be a site-specific assessment. We performed site-specific hazard evaluations at each bridge location summarized later in this report. The viewer categorizes the expected earthquake shaking from light, moderate, strong, very strong, severe and violent; and the landslide susceptibility from low, moderate, high, and very high. Each site is presented in the Figure 3(A and B) – Geologic Hazards and shows the relevant liquefaction hazard risks for the bridge locations.

Description Hazard Range Liquefaction Hazard Low to Moderate (all locations, except Lower Salt Creek is no hazard) Earthquake Shaking Very Strong (all locations)

Landslide Susceptibility None to Low1

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Description Hazard Range

1. Generally, embankment slopes around the bridge structures range from none to low and are relatively limited in extent.

4 FIELD EXPLORATION AND LABORATORY TESTING

Terracon completed field explorations for each of the four bridge locations in November and December of 2019 and laboratory testing in January and February of 2020. Terracon prepared and submitted a Site Investigation and Subsurface Exploration Plan, dated November 13, 2019.

The following sections discuss the subsurface explorations.

4.1 Field Exploration

Unless otherwise noted, Terracon personnel provided the exploration layout. Coordinates were obtained with a handheld GPS unit and approximate elevations were obtained by interpolation from the existing survey data available from the As-Builts and current surveys. The exploration locations are presented in Figures 4(A-D) – Exploration Plans.

We advanced soil borings with trailer-, truck-, and track-mounted drill rigs using continuous flight augers (solid stem and/or hollow stem, as necessary, depending on soil conditions), mud-rotary wash methods, air-rotary casing advancer methods, and sonic coring methods. At least four samples were obtained in the upper 10 feet of each boring and at intervals not exceeding 5 feet thereafter. Soil sampling was generally completed using split-barrel sampling procedures. The samples are placed in appropriate containers, taken to our soil laboratory for testing, and classified by a geotechnical engineer. In addition, we observe and record groundwater levels during drilling and sampling.

In the split barrel sampling procedure, a standard 2-inch outer diameter split barrel sampling spoon is driven into the ground by a 140-pound automatic hammer falling a distance of 30 inches.

The automatic hammers used on this project were recently calibrated for this project and averaged 94 percent energy transmission. The number of blows required to advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the Standard Penetration Test (SPT) resistance value. The SPT resistance values, also referred to as N-values, are indicated on the boring logs at the test depths. In many locations, due to the granular and gravelly nature of the soils, we used Ring Samplers and/or Modified California Samplers to obtain more representative samples. Where larger than 2-inch split spoons were used, N-values have been correlated using an average of two methods described by LaCroix and Horn (1973) and Burmister (1948). These values are presented on the logs as shown as N* (blows/ft).

All explorations were supervised and logged by a field engineer or field geologist to record field test data, classify soils/rock, and to collect the samples from the explorations. Our exploration

Responsive ■ Resourceful ■ Reliable 10 team prepared field boring logs as part of standard drilling operations including sampling depths, penetration distances, and other relevant sampling information. Field logs include visual classifications of materials encountered during drilling, and our interpretation of subsurface conditions between samples. Final boring logs, presented in the Explorations Results section of the report, prepared from field logs, represent the geotechnical engineer's interpretation, and include modifications based on observations and laboratory tests.

The following table presents a summary of the explorations completed for this scope of services.

Boring Number Depth (ft) Bridge Location

Latitude (deg North)

Longitude (deg East)

CF-1 101.3 Coast Fork near river bank 43.9805 -122.9662 CF-2 50.2 Coast Fork near river bank 43.9808 -122.9668 CF-3 4.52 Coast Fork roadway boring 43.9815 -122.9681 CF-3a 5.82 Coast Fork roadway boring 43.9815 -122.9681 CF-4 11.5 Coast Fork roadway boring 43.9802 -122.9652 B-1 602 Barnard abutment location 43.7467 -122.5119 B-2 11.5 Barnard roadway boring 43.7475 -122.5083

SC-1 50.9 Salmon Creek abutment 43.7407 -122.4594 SC-2 101.5 Salmon Creek abutment 43.7401 -122.4592 SC-3 42 Salmon Creek roadway 43.7409 -122.4599 SC-3a 42 Salmon Creek roadway 43.7408 -122.4599 SC-4 42 Salmon Creek roadway 43.7394 -122.4585 LSC-1 11.5 Lower Salt Creek roadway 43.7303 -122.4203 LSC-2 8.52 Lower Salt Creek roadway 43.7300 -122.4187

1. This table presents a summary of locations of borings completed for this scope of services. Refer to Figures 4(A-D) for location as well as locations of previous explorations completed by others.

2. These borings were precluded from achieving the planned depth due to auger and/or casing penetration refusal.

4.2 Geophysical Exploration

Terracon performed testing using a system consisting of a seismograph and 24 geophones to perform a site-specific seismic class survey and to measure shear wave velocities of the subsurface soil/rock profiles. One linear array of 24 geophones, spaced about 13 feet apart for a total line length of 300 feet, was placed in accessible areas. We performed one array for each side of the river for each of the bridge approaches.

The data collected was processed using a wavefield-transformation data-processing technique and an interactive Rayleigh-wave dispersion-modeling tool. The ReMi surface wave technique derives a shear wave profile and an average shear-wave velocity along the array for a corresponding depth of about 100 feet. The results are presented in the Figures 5(A-D) – Shear

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Wave Velocity Profiles. Shear wave velocities were used to derive the ground motions for the Lower Level seismic event and to calculate shear modulus for the structural engineer’s use in bridge modeling.

Bridge Location Test Location Time-Averaged Shear Wave

Velocity of 100-foot Profile v30 ft/sec (m/sec)

Coast Fork West Approach 1,902 (579.7) East Approach 2,103 (640.8)

Barnard West Approach 2,083 (634.9) East Approach 1,846 (562.5)

Salmon Creek West Approach 1,965 (598.8) East Approach 1,724 (525.5)

Lower Salt Creek West Approach 2,372 (723.1) East Approach 1,585 (483.0)

4.3 Laboratory Testing

The project engineer reviewed field data and assigned various laboratory tests to better understand the engineering properties of various soil/rock strata. Laboratory test plans were prepared for each bridge site and submitted for WFLHD and ODOT review and approval prior to commencing the laboratory testing. Procedural standards noted below are for reference to methodology in general. In some cases, local practices and professional judgement require method variations. Standards noted below include reference to other related standards. Such references are not necessarily applicable to describe the specific test performed.

■ ASTM D2216 Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass

■ ASTM D4318 Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils

■ ASTM D6913 Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis

■ ASTM D1883 Standard Test Method for California Bearing Ratio (CBR) of Laboratory- Compacted Soils

The laboratory testing program included examination of soil/rock samples by an engineer. Based on the material’s texture and plasticity, the soil samples were described and classified in accordance with the Unified Soil Classification System.

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5 SUBSURFACE CONDITIONS

We have developed a general characterization of the subsurface conditions based upon our review of the published geologic information, previous geotechnical explorations and reports, current subsurface exploration, laboratory data, geologic setting and our understanding of the project. These characterizations form the basis of our geotechnical analyses and evaluation of site preparation and foundation options. Conditions encountered at each exploration point are indicated on the individual logs. The logs can be found in the Exploration Results section.

Geotechnical Data Sheets for each of the bridges can be found in Figures 6A to 6D – Geotechnical Data Sheets.

Groundwater levels presented in the subsurface conditions are based on our observations in the field; it should be understood fluctuations can occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structures may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

5.1 Coast Fork Subsurface Conditions

Previous explorations were completed in 2000 by ODOT. ODOT completed three borings to the north of the existing bridge. One boring was completed on the east side of the river (near Bents 4 and 5) and two borings along the west side of the river (one near Bent 2 and the other near Bent 3 and Pier 1). Terracon completed four supplemental explorations as part of this scope of services, two deeper borings (50 to 100 ft bgs) on each side of the river and two shallow pavement borings.

5.1.1 Generalized Subsurface Profile

The following table provides our geotechnical understanding of subsurface conditions. The strata described are in relative order as encountered from the ground surface to the termination depths of the borings. However, in some locations the alluvium layers can be interlayered between and within the lower units described.

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Model Layer

Layer Name

Thickness (ft)

Depths to Bottom of Layer (ft)

General Description Consistency / Density

01 Fill 2 ½ to 7 ½ feet

2 ½ to 7 ½ feet where encountered

Sandy Gravel with some silt, orange-brown to green-gray, fine to coarse, subangular to angular

Dense

Fine-

Grained Alluvium

4 to 6 ½ feet

4 to 6 ½ feet where encountered

Silt with sand to Sandy Silt and Silty Sand, non-plastic to low plasticity, brown Loose

03 Sand Alluvium

3 feet in CF-2; 1- to

2-foot layers in the lower strata

4 to 6 feet at surface layers and 22 to 25 feet within lower layers

Sand to Sand with silt, orange-brown to gray, fine to medium grained

Medium dense

04 Gravel Alluvium 1

6 ½ to 12 feet 20 to 24 feet

Sandy Gravel with variable amounts of silt, brown and gray, fine to coarse, rounded

Medium dense to dense

05 Gravel Alluvium 2

80 feet where penetrated Not Determined

Gravel, gray, brown, yellow, red, orange, green, fine to coarse, rounded, often with clay coating

Dense to very dense

The conditions noted in the table were consistent with those anticipated based on the geologic publication review.

5.1.2 Groundwater Conditions

Water levels were not summarized or presented on the boring logs provided by ODOT in the geotechnical report. The groundwater level was assumed to be hydraulically connected to the river level and was assumed to be at an elevation of 490 feet for their analyses (approximate high-water elevation from the As-Built plans). The boreholes completed for this scope were observed while drilling and after completion for the presence and level of groundwater. Groundwater levels observed during our explorations were consistent with the estimated elevation near the river elevation at the time of drilling and estimated at about 482 ft.

5.2 Barnard Subsurface Conditions

The previous geotechnical report prepared in 2014 included four borings within and immediately adjacent to the alignment. One boring was completed on the west side of the river (near Bent 1 within the alignment) and three borings along the east side of the river (one near Bent 4, one near Bent 5 and the other near Bent 8). Terracon completed two supplemental explorations as part of this scope of services, one deeper boring along the western approach and one shallow boring on the east side of the approach.

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5.2.1 Generalized Subsurface Profile

The following table provides our geotechnical understanding of subsurface conditions. The strata described are in relative order as encountered from the ground surface to the termination depths of the borings.

Model Layer

Layer Name

Thickness (ft)

Depths to Bottom of Layer (ft)

General Description Consistency / Density

01 Fill 2 to 18 feet in western borings

2 to 18 feet where encountered

Sandy Gravel with some silt, contains cobbles, possible boulders, concrete debris, trace wood debris

Medium dense to very dense

02 Sand Alluvium

2- to 5-foot layers on top of and within the

Gravel Alluvium

Various 5 to 23 ft as layers on top of and within the Gravel Alluvium

Sand to Silty Sand, brown to dark gray, medium grained to medium to coarse grained for

Sand

Loose to medium dense

03 Gravel Alluvium

10 ½ to 33 ½ feet

12 ½ to 48 feet, East approach to West approach, respectively

Gravel with variable amounts of sand and silt, with cobbles and boulders, brown and dark gray, fine to coarse, subangular to rounded

Dense to very dense

04 Little Butte Volcanics

17 feet where penetrated Undetermined

Tuffaceous Mudstone, fresh to slightly weathered, blue-gray, widely spaced jointing, trace mineral infilling, locally with layers of weathered very stiff clay

Soft to hard

5.2.2 Groundwater Conditions

The previous borings were performed using mud-rotary methods which introduces water into the borehole. This method makes it difficult to ascertain a water level reading while drilling. However, the groundwater level was assumed to be hydraulically connected to the river level and was assumed to be at an elevation of 1,080 feet, the estimated high-water elevation from the As-Built plans. Groundwater in boring B-1 was observed about 22 feet below the ground surface, an approximate elevation of 1,069 feet.

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5.3 Salmon Creek Subsurface Conditions

Two boring logs are displayed on the As-Built drawings from 1988 and appear to have been completed and prepared by ODOT. One boring was completed on the south side of the river and one boring along the north side of the river. Terracon complete four supplemental borings at this bridge location to further the understanding of the subsurface conditions, two deeper borings (50 to 100 ft bgs) on each side of the river and two shallow pavement borings.

5.3.1 Generalized Subsurface Profile

The following table provides our geotechnical understanding of subsurface conditions. The strata described are in relative order as encountered from the ground surface to the termination depths of the borings.

Model Layer

Layer Name

Thickness (ft)

Depths to Bottom of Layer (ft)

General Description Consistency / Density

01 Fill 7 ½ to 10 feet

7 ½ to 10 feet where penetrated

Sandy Gravel with cobbles, occasional boulders, brown to gray

Loose to Dense

02 Gravel Alluvium

53 feet where penetrated 63 feet

Sandy Gravel with cobbles, occasional boulders, brown to gray

Dense to very dense

03 Sand Alluvium >37 feet Not Determined

Silty Sand to Sand with gravel, brown to black, red-brown, medium to fine

Dense to very dense

5.3.2 Groundwater Conditions

No groundwater observations or measurements were presented in the information provided for review. However, given the granular nature of the subsurface conditions, we would expect the groundwater level to be hydraulically connected to the water level in the river. Groundwater levels in borings SC-1 and SC-2 were observed about 14 to 13 feet below the ground surface, respectively, at approximate elevations of 1,151 to 1,152 feet. According to the As-Built plans, estimated high water level is about 1,167.5 feet (converted to NAVD88).

5.4 Lower Salt Creek Subsurface Conditions

The geotechnical report prepared in 2014 by S&W included completion of two borings within and immediately adjacent to the alignment. One boring was completed on the west side of the river

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(between Bent 1 and 2 adjacent to the alignment) and one boring along the east side of the river (near Bent 4 within the alignment). Terracon completed two shallow borings for the pavement approaches at this location.

5.4.1 Generalized Subsurface Profile

The following table provides our geotechnical understanding of subsurface conditions. The strata described are in relative order as encountered from the ground surface to the termination depths of the borings. However, in some locations the Sand Alluvium layers can be interlayered between and within the lower units described.

Model Layer

Layer Name

Thickness (ft)

Depths to Bottom of Layer (ft)

General Description Consistency / Density

01 Fill 11 to 14 ½ feet 11 to 14 ½ feet

Sandy Gravel with silt to Gravel with sand, gray and brown, fine to coarse grained, angular to subrounded, some cobbles and few boulders

Dense to very dense

02 Colluvium Below the fill to depths of 14 ½ to

17 feet

14 ½ to 17 feet (where encountered)

Silty Sand, dark brown, low to medium plasticity fines, fine to medium grained

Medium dense

03 Sand Alluvium

11 feet thickness

11-foot layer to a depth of 44 feet

(where encountered)

Silty Sand, brown, stratified, fine to medium sand with non-plastic fines

Medium dense

04 Gravel Alluvium 1

22 to 26 feet 33 to 43 feet

Sandy Gravel with variable amounts of silt, few cobbles and occasional boulders, brown and dark gray, fine to coarse, subangular to subrounded

Medium dense to very dense

05 Gravel Alluvium 2

Boring terminated in this stratum

Undetermined – borings terminated in this unit

Sandy Gravel to Sandy Clayey Gravel, tan-brown to gray, fine to coarse, subangular to subrounded

Very dense

5.4.2 Groundwater Conditions

The previous borings were performed using mud-rotary methods, which introduces water into the borehole. This method makes it difficult to ascertain a water level reading while drilling. However, Responsive ■ Resourceful ■ Reliable 17 the groundwater level was assumed to be hydraulically connected to the river level and was assumed to be at an elevation of 1,309 feet for previous analyses by S&W.

6 SEISMIC CONSIDERATIONS

The ODOT GDM and AASHTO design manuals specify two earthquake ground motion hazard performance levels for evaluation of bridges. The first level (Lower Level) prescribed by ODOT GDM to be considered is the “operational level” and is considered to be developed from a full rupture of the Cascadia Subduction Zone (CSZE). This is defined as an approximate 500-year return interval, and the design values are determined by a tool developed by Portland State University (accessible at http://csz.cee.pdx.edu/ and downloaded January 22, 2020). The required input for use of this tool is the average shear wave velocity of the upper 100-foot soil profile.

The second event (Upper Level) is defined as having a 1,000-year return period and is considered a “Life-Safety” performance criteria. These design parameters are developed by US Geological Survey (USGS) and are published in Hazard Maps for the Pacific Northwest Region for use according to the AASHTO LRFD design methodology. However, the ODOT GDM provides a tool based on the USGS maps, but provides Fpga, Fa, and Fv for use in ODOT projects The design motions are developed from all potential earthquake sources and are determined by modifying the soft rock spectral accelerations based on the soil Site Class as provided in the ODOT GDM.

The following design tables presents the ODOT GDM ARS Design tool values as the recommended design values. These values can be obtained at the following web address:

https://www.oregon.gov/odot/Bridge/Docs_Seismic/ODOT_ARS_V2014.16.xlsx, downloaded December 12, 2019. The recommended design parameters are provided in the following sections.

6.1 Recommended Design Ground Motions

The seismic design requirements for structures are based on Seismic Design Category. Site Classification is required to determine the Seismic Design Category for a structure. The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of shear wave velocity. We used the average shear wave velocity calculated from the geophysical testing recently completed at the site. This calculated value is presented in each of the following design tables for each site.

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6.1.1 Coast Fork Bridge Recommended Design Ground Motions

Description

Lower Level (M9 Cascadia

Subduction Zone)3 Upper Level

(1,000-year Return Period) 3

Site Classification 1 C

Soil Profile Shear Wave Velocity (v30) 2 610 m/sec

Site Latitude (North) 43.9806o

Site Longitude (East) -122.9663o

Peak Ground Acceleration (PGA) - 0.205

Short Period Acceleration, SS - 0.43

1-Second Period Acceleration, S1 - 0.196

PGA Site Factor, FPGA - 1.2

Short-Period Site Factor, Fa - 1.3

Long-Period Site Factor, Fv - 1.5

Peak Design Acceleration Coefficient, As 0.153 0.246

Short-Period Design Acceleration, SDS 0.293 0.559

Long-Period Design Acceleration, SD1 0.171 0.294

Period of Spectrum Response Corner, To 0.12 0.11

Period of Spectrum Response Corner, Ts 0.58 0.53

1. Seismic site classification in general accordance with the 2014 AASHTO and 2019 ODOT GDM. Site Class calculations based on 100-foot soil profiles using the time-averaged shear wave velocities at site.

2. These values were calculated by shear wave velocity measurements collected from ReMi Testing at each of the bridge locations. Testing completed on both sides of the crossing and averaged for the CSZE input.

3. These values were obtained using online seismic design maps and tools provided by the 2014 USGS Seismic

Hazard Data and PSU’s Cascadia Subduction Zone database. Per the report Impact of Cascadia Subduction Zone Earthquake on the Evaluation Criteria of Bridges, Technical Report SR770, these values differ from the 2014 AASHTO guidelines. All of these values are greater than 2014 AASHTO.

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CSZE Lower Level Design Response Spectrum

Period T(sec) Spectral Acceleration (g)

0 0.153

0.05 0.173

0.1 0.258

0.15 0.292

0.2 0.293

0.25 0.289

0.3 0.286

0.4 0.272

0.5 0.247

0.6 0.221

0.7 0.207

0.8 0.196

1 0.171

1.5 0.126

2 0.098

2.5 0.08

3 0.066

Values presented above are directly from the PSU Cascadia Subduction Zone Event tool for the site location and shear wave velocity reported above.

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6.1.2 Barnard Bridge Recommended Design Ground Motions

Description

Lower Level (M9 Cascadia

Subduction Zone) 3

Upper Level (1,000-year Return

Period) 3

Site Classification 1 C

Soil Profile Shear Wave Velocity (v30) 2 599 m/sec

Site Latitude (North) 43.7469o

Site Longitude (East) -122.5110o

Peak Ground Acceleration (PGA) - 0.165

Short Period Acceleration, SS - 0.346

1-Second Period Acceleration, S1 - 0.153

PGA Site Factor, FPGA - 1.235

Short-Period Site Factor, Fa - 1.3

Long-Period Site Factor, Fv - 1.5

Peak Design Acceleration Coefficient, As 3 0.116 0.204

Short-Period Design Acceleration, SDS 3 0.233 0.45

Long-Period Design Acceleration, SD1 3 0.142 0.229

Period of Spectrum Response Corner, To 3 0.12 0.1

Period of Spectrum Response Corner, Ts 3 0.61 0.51

1. Seismic site classification in general accordance with the 2014 AASHTO and 2019 ODOT GDM. Site Class calculations based on 100-foot soil profiles using the measured shear wave velocities at site.

2. These values were calculated by shear wave velocity measurements collected from ReMi Testing at each of the bridge locations.