OCSD RFP B12 2026 ADDENDUM 1.pdf

Addendum 1 Special Testing and Inspection Services

B12-2026 5/21/2026

Subject: Addendum 1 to RFP B12-2026

Dear Proposers, Please be advised of Addendum 1 to Request for Proposals (RFP) B12-2026. Items below were added for further clarifications.

1. ADDED – Pre-proposal sign in sheet.

2. ADDED – Geotechnical Reports for Phase 2 schools.

3. REVISED – Page 5 of RFP - Description of Services.

4. ADDED – Attachment C Price Proposal in excel format.

PROPOSER QUESTIONS

1. Are the phase 3 schools supposed to be included/priced, or only the phase 2 schools?

Answer – Only the Phase 2 schools are included in this RFP.

2. Please confirm reimbursables can be included with the fees and do not need to be broken out separately.

Answer – Reimbursables can be included in the costs.

3. Please confirm no geotechnical/soils special inspections are required for the CTE project.

Answer – Geotechnical inspections are to be included per the project matrix.

4. There is a statement in 5.2-B-2 about Oregon Business License “if the offeror intends to provide installation services.” We are not technically an installer, they may have be related to the playground project, but do we need to include our business license or business license number here or in the appendix?

Answer – Yes, please include a copy of your business license.

5. I’ve been in touch with our insurance provider and there is not a standard form/letter that provides the insurance information requested. Can you please confirm whether providing all the required contact information and a sample COI is sufficient? Or is there a form you can provide that requests the required information I can have them fill out?

Answer – Contact information and a sample COI is sufficient.

6. Will CTE be included in this RFP? Attachment C doesn’t have CTE listed.

Answer – No, CTE does not have any special inspections needed.

7. Can you provide attachment C as an excel file?

Answer – Yes, provided in this addendum.

8. Can you provide the Geotechnical Reports for each school?

Answer – Yes, provided in this addendum.

9. Please see attached the requested Contract Exceptions. We will be including it in the RFP, but was advised in the pre bid meeting to submit as a Question as well.

Answer – Contract negotiations will be done with the awarded testing agency after the award period. These exceptions will be reviewed at that time.

Thank you for your continued interest.

4 4 1 2 S C O R B E T T A V E N U E

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Geotechnical Engineering Report Candy Lane Elementary School Improvements

5901 SE Hull Avenue

Milwaukie, Oregon

Prepared for:

Oregon City School District

PO Box 2110 (1417 12th Street)

Oregon City, Oregon 97045

November 3, 2025

Apex Project 25009145

© 2025 Apex Companies, LLC

4 4 1 2 S C O R B E T T A V E N U E , P O R T L A N D , O R 9 7 2 3 9 ▪ 5 0 3 . 2 4 8 . 1 9 3 9 M A I N ▪ 8 6 6 . 7 2 7 . 0 1 4 0 F A X ▪ A P E X C O S . C O M

Geotechnical Engineering Report

Candy Lane Elementary School Improvements

5901 SE Hull Avenue

Milwaukie, Oregon

Prepared for:

Oregon City School District

PO Box 2110 (1417 12th Street)

Oregon City, Oregon 97045

Prepared by:

Jack Powell, RG, LG

Project Geologist

Brian Ackerman, PE

Geotechnical Project Engineer

Reviewed by:

Ryan White, PE, GE

Principal Geotechnical Engineer

6/30/2026

Oregon City School District

Candy Lane Elementary School Improvements

Milwaukie, Oregon

Apex Companies, LLC i

Table of Contents

1 INTRODUCTION

General Purpose and Scope

1.2.1 Literature and Records Review

1.2.2 Subsurface Explorations

1.2.3 Field Infiltration Testing

1.2.4 Soils Testing

1.2.5 Geotechnical Engineering Analysis

1.2.6 Report Preparation

Project Understanding

2 SITE CONDITIONS

Surface Description Geologic Setting Subsurface Conditions Groundwater Infiltration Testing

3 GEOLOGIC HAZARDS

Slope Stability Expansive Soils Seismicity and Faulting

3.3.1 Historical Seismicity

3.3.2 Seismic Sources

3.3.2.1 Crustal Earthquakes and Faults

3.3.2.2 Cascadia Subduction Zone (CSZ) – Interface Earthquakes

3.3.2.3 Intraslab Earthquakes

3.3.2.4 Liquefaction and Lateral Spreading

3.3.3 Seismic Hazards

Flooding

4 CONCLUSIONS AND RECOMMENDATIONS

Geotechnical Design Considerations Shallow Foundations

4.2.1 Minimum Footing Widths and Design Bearing Pressure

4.2.2 Footing Embedment Depths

4.2.3 Footing Preparation

4.2.4 Lateral Resistance

Floor Slabs Seismic Design Considerations

4.4.1 Seismic Site Class

4.4.2 ASCE 41-17 Code-Based Seismic Design Parameters

4.4.3 2022 OSSC Code-Based Seismic Design Parameters

Temporary and Permanent Slopes Ground Moisture

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Pavement Design

5 CONSTRUCTION RECOMMENDATIONS

Site Preparation

5.1.1 Proofrolling/Subgrade Verification

5.1.2 Wet/Freezing Weather and Wet Soil Conditions

5.1.3 Dry Weather Conditions

Excavation Structural Fill

5.3.1 On-Site Soil

5.3.2 Borrow Material

5.3.3 Select Granular Fill

5.3.4 Crushed Aggregate Base

5.3.5 Utility Trench Backfill

5.3.6 Stabilization Material

6 ADDITIONAL SERVICES AND CONSTRUCTION OBSERVATIONS

7 LIMITATIONS

8 REFERENCES

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Supporting Data

TABLES

Table 1. Infiltration Test Results Table 2. USDA Hydrologic Soil Group Parameters Table 3. Faults within the Site Vicinity Table 4. ASCE 41-17 Seismic Design Parameters for BSE-2N and BSE-1N Table 5. ASCE 41-17 Seismic Design Parameters for BSE-2E Table 6. ASCE 41-17 Seismic Design Parameters for BSE-1E Table 7. 2022 OSSC Seismic Design Parameters Table 8. Minimum AC Pavement Sections

FIGURES

Figure 1. Vicinity Map

Figure 2. Site Plan

Figure 3. Historical Seismicity

Figure 4. Regional Fault Map

Figure 5. Tectonic Setting of the Pacific Northwest

Figure 6. Spread Footing Bearing Capacity

APPENDICES

Appendix A: Field Explorations

Table A-1. Terminology Used to Describe Soil

Table A-2. Key to Test Pit and Boring Log Symbols

Figures A1–A5. Logs for Borings B-1 through B-5

Figures A6 and A7. Logs for CPT-1 and CPT-2

Appendix B: Laboratory Testing

Figure B1. Summary of Laboratory Data

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1 INTRODUCTION

General

This report presents results of Apex Companies, LLC (Apex) geotechnical engineering services for the proposed improvements to Candy Lane Elementary School located at 5901 SE Hull Avenue in Milwaukie, Oregon (site).

The general site location is shown on the Vicinity Map, Figure 1. The locations of Apex’s explorations in relation to existing site features are shown on the Site Plan, Figure 2.

Purpose and Scope

The purpose of Apex’s services was to develop geotechnical design and construction recommendations in support of the planned site improvements. This was accomplished by performing the following scope of services.

1.2.1 Literature and Records Review

Apex reviewed various published geologic maps of the area for information regarding geologic conditions and hazards at or near the site. Apex also reviewed previously completed reports for the project site and vicinity.

1.2.2 Subsurface Explorations

Five borings were advanced to depths ranging from approximately 4 to 9.5 feet below the existing ground surface (bgs) within the development footprint. The borings were logged and representative soil samples collected by a member of the Apex geotechnical engineering staff. The approximate boring locations are shown on the Site Plan, Figure 2. The interpreted boring logs are presented as Figures A1 through A5 in

Appendix A, Field Explorations.

Two cone penetration test (CPT) probes were advanced to depths ranging from approximately 2 to 7 feet bgs.

The CPT logs are presented as Figures A6 and A7 in Appendix A, Field Explorations.

1.2.3 Field Infiltration Testing

Two cased-hole, falling-head field infiltration tests were completed in borings B-3 and B-4 at depths of approximately 4 feet bgs. Infiltration testing was monitored by Apex geotechnical engineering staff.

1.2.4 Soils Testing

Soil samples were returned to our laboratory and classified in general accordance with the Unified Soil

Classification System (ASTM D2487) and/or the Visual-Manual Procedure (ASTM D2488). Laboratory tests included natural moisture contents and grain-size analyses. Laboratory test results are included in the exploration logs in Appendix A, Field Explorations; and in Appendix B, Laboratory Testing.

1.2.5 Geotechnical Engineering Analysis

Data collected during the subsurface exploration, literature research, and testing were used to develop site-specific geotechnical design parameters and construction recommendations.

1.2.6 Report Preparation

This Geotechnical Engineering Report summarizes the results of our explorations, testing, and analyses, including information relating to the following:

• Field exploration logs and site plan showing approximate exploration locations

• Laboratory test results

• Infiltration test results

• Groundwater levels and considerations

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• Geologic hazards discussion

• Shallow foundation recommendations:

o Minimum embedment o Allowable and ultimate bearing pressure o Estimated settlement o Sliding coefficient

• Earthwork and grading, cut, and fill recommendations:

o Structural fill materials and preparation o Utility trench excavation and backfill requirements o Slab and pavement subgrade preparation o Wet weather considerations

• Seismic design criteria in accordance with American Society of Civil Engineers (ASCE) 41-17 and 2022

Oregon Structural Specialty Code (OSSC) standards

• Slab-on-grade design recommendations

• Asphalt concrete (AC) pavement section recommendations

Project Understanding

Apex understands that improvements to Candy Lane Elementary School include a new cafeteria and kitchen building addition at the southeast corner of the existing school, new paved parking areas and drive lanes, and new play areas. The structural engineer has indicated that foundation and slab loads of building additions are as follows:

• Column dead and seismic loads of 20 kips and 14 kips, respectively

• Wall dead and seismic loads of 1.75 kips per linear foot (klf) and 0.7 klf, respectively

• Slab live load of 100 pounds per square foot (psf)

2 SITE CONDITIONS

Surface Description

The site is roughly rectangular and is bordered to the southwest by SE Portland Avenue, to the southeast by SE

Hull Avenue, and to the northeast and northwest by scattered residential parcels and SE Candy Lane. The site is currently occupied by the elementary school including buildings, recreation fields, play structures, landscaping, and asphalt pavement drive lanes and parking areas. Based on review of available Oregon Department of

Geology and Mineral Industries (DOGAMI) topographic and lidar data, the site has generally gentle to moderate slopes grading downward to the southwest toward the athletic fields and SE Portland Avenue.

Ground surface elevations range from a maximum of about 118 feet near the northern extent of the school area adjacent SE Candy Lane, to a minimum of about 98 feet at the southwestern edge of the site adjacent SE

Portland Avenue (NAVD88; DOGAMI, 2025). Outside of the site, the ground surface continues to slope gently down toward the south/southwest and gently upward to the north/northeast.

Geologic Setting

The site is located within the Portland-Vancouver Basin, a tectonic depression within the physiographic province of the Puget-Willamette Lowland that separates the Cascade Range from the Coast Range, and extends from the Puget Sound, Washington, to Eugene, Oregon (Yeats et al., 1996). The Puget-Willamette

Lowland is situated along the Cascadia Subduction Zone (CSZ) where oceanic rocks of the Juan de Fuca Plate are subducting beneath the North American Plate, resulting in deformation and uplift of the Coast Range and volcanism in the Cascade Range. Northwest-trending faults accommodating clockwise rotation of the North

American Plate are found throughout the Puget-Willamette Lowland (Brocher et al., 2017; USGS, 2025).

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The greater Portland Basin is underlain by Columbia River Basalt Group (CRBG) flows consisting of numerous fine-grained volcanic eruptions between approximately 17 million years ago (Ma) and 6 Ma from fissures located in eastern Oregon, eastern Washington, and western Idaho (Beeson et al., 1991). These fissures released thousands of square kilometers of lava, inundating areas east of the Cascade Range and entering western Oregon through a Miocene gap in the Cascade Range (present day Columbia Gorge) before reaching the ocean. Magmatic compositions of the CRBG allow the flows to be subdivided into distinct formations that can be further divided into members-based geochemical, paleomagnetic, and lithological properties.

Numerous northwest-trending faults govern the topography within the basin. Uplift and down dropping of crustal blocks have created topographic high points by offsetting regional scale flood basalts and down dropping basement rocks, creating depressions and sediment basins that accommodate the fluvial deposition of Miocene to Pliocene age terrestrial sedimentary rocks (commonly Troutdale Formation and/or Sandy River

Mudstone) over the older CRBG basalt flows (Beeson et al., 1991; Evarts et al., 2004). Of these sedimentary deposits, the Troutdale Formation is the most widespread unit within the basin. These friable to moderately strong conglomerates, with minor interbeds of sandstone and claystone, consist of well-rounded CRBG clasts and other exotic metamorphic and plutonic clasts. Above these conglomerates, younger quaternary deposits have accumulated.

Cyclical Pleistocene age cataclysmic glacial floods deposited sediments and recarved the landscape within the

Portland Basin more than 40 times over a 3,000-year timespan (Burns and Coe, 2012). As floodwaters entered the basin from the Columbia River Gorge, they slowed, depositing suspended sediments and bed loads.

Topographic highpoints within the basin deflected floodwaters and generated areas that were scoured and eroded into older sediments and bedrock. These geomorphic features dominate the modern-day landscape and are indistinguishable within the Portland Basin lidar.

Local Geology

The majority of the site is mapped as underlain by coarse-grained Missoula flood deposits (Wells et al., 2020).

These Pleistocene sediments are described as consisting of primarily unconsolidated, sand, gravel, cobbles, and boulders deposited by cataclysmic floods originating from glacial Lake Missoula, which flowed down the

Columbia River and flooded the Willamette Valley. These coarse-grained facies are often locally capped by several feet of sandy silt.

Within the northern area of the site and likely underlying the Missoula flood deposits at depth, geologic mapping indicates the presence of Miocene aged Wanapum CRBG of the Frenchman Springs Member, specifically referred to as Basalt of Sand Hollow of Mackin (Twfh). This basalt is described as gray to black, variably vesicular flood basalt that is blocky to columnar jointed and sparsely plagioclase-phyric. Weathered surfaces are reported to feature brownish-red colored pisolitic soils with spheroidal boulders and frequent weathered rock fragments.

Subsurface Conditions

The site was explored by drilling five borings, designated B-1 through B-5, to depths of approximately 4 to 9.5 feet bgs. Drilling of deeper borings (B-1 through B-3) near structure areas was performed by Western States

Soil Conservation, Inc., of Hubbard, Oregon, using a track-mounted CME-55 drill rig and hollow-stem auger drilling techniques. Drilling of shallow borings (B-4 and B-5) in parking areas was performed by Dan J. Fischer

Excavating, Inc., of Forest Grove, Oregon, using a trailer-mounted drill rig and solid-stem auger drilling techniques. Two CPTs were also completed to depths of approximately 2 to 7 feet bgs by Oregon Geotechnical

Explorations, Inc., using a track-mounted CPT rig. Our borings were all terminated due to practical refusal on

Apex Companies, LLC 4 basalt or weathered basalt bedrock at depths of 4 to 9.5 feet bgs. Both CPTs were terminated due to refusal at depths of 2 and 7 feet bgs.

Apex has summarized the subsurface units as follows:

ASPHALT/BASE ROCK: Approximately 2 to 4 inches of asphalt concrete (AC) pavement overlying approximately 4 to 6 inches of base rock was encountered at the ground surface in borings B-2 and B-3.

TOPSOIL: Approximately 3 to 4 inches of brown topsoil with roots was encountered at the ground surface of borings B-1, B-4, and B-5. The topsoil was generally silty with roots and organics.

Lean CLAY (CL): Gray to brown lean clay with varying amounts of fine- to coarse-grained sand and fine to coarse, subangular gravel was encountered in borings B-3 and B-4 and

CPT-1, below the gravel base rock or topsoil, and extended to approximately 3 to

5 feet bgs. The lean clay was primarily medium stiff to very stiff, with low to medium plasticity, and was generally dry to moist.

Silty SAND (SM)/ Sandy

SILT (ML):

Gray to brown, dense/very stiff, silty sand/sandy silt was encountered below the topsoil in borings B-1 and B-5, extending to approximately 3.5 to 4 feet bgs. The silty sand/sandy silt generally had fine to coarse-grained sand and fine to coarse, angular to subangular gravel.

Silty GRAVEL (GM)/

Clayey GRAVEL (GC):

Below the clay or sandy silt/silty sand in all borings, well-graded silty to clayey gravel was encountered. The gravel was generally brown-gray and fine to coarse, with varying amounts of fine- to coarse-grained sand. This deposit extended to the termination depth in all explorations, where drilling refusal was encountered on what was likely basalt boulders, and generally increased in relative density with increasing depth from dense to very dense. The gravels also occasionally resembled severely weathered/decomposed basalt bedrock and were often cobbly to bouldery.

Groundwater

Static groundwater was not encountered during our explorations. Based on a review of regional groundwater logs provided by the Oregon Water Resources Department (OWRD), we anticipate that the static groundwater level is present at a depth greater than 20 feet bgs. Please note that groundwater levels can fluctuate during the year depending on climate, irrigation season, extended periods of precipitation, drought, and other factors.

Infiltration Testing

Apex completed two cased-hole, falling-head infiltration tests in borings B-3 and B-4 at depths of approximately 4 feet bgs. The infiltration tests were either conducted within the 4.25-inch inside diameter, hollow-stem auger used to drill the boring or within a 3-inch diameter PVC pipe inserted into the boring. The auger/pipe was filled with water to achieve a minimum 1-foot-high column of water. After a period of saturation, the height of the water column in the auger/pipe was then measured initially and at regular, timed intervals. Results of our field infiltration testing are presented in Table 1.

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Table 1. Infiltration Test Results

Test Location Depth (feet bgs)

Field Measured

Infiltration Rate

(in/hr)

Soil Classification

USDA

Hydrologic Soil

Group

B-3 4 0 Clayey GRAVEL (GC) D

B-4 4 1.4 Clayey GRAVEL

(GC)/RX

C

The infiltration rates listed in Table 1 are not permeabilities/hydraulic conductivities, but are field-measured rates, and do not include correction factors related to long-term infiltration rates. The design engineer should determine the appropriate correction factors to account for the planned level of pre-treatment, maintenance, vegetation, siltation, etc. Field-measured infiltration rates are typically reduced by a minimum factor of 2 to 4 for use in design.

The presence of shallow bedrock throughout the site must also be considered, as this may further limit infiltration or make on-site stormwater disposal infeasible.

Soil types can vary significantly over relatively short distances. The infiltration rates noted above are representative of one discrete location and depth. Installation of infiltration systems within the layer the field rate was measured is considered critical to proper performance of the systems.

The United States Department of Agriculture (USDA) categorizes soils in four hydrologic soil groups, A through

D, and are designated mainly by particle size and hydraulic conductivity. Table 2 below shows general characteristics of each group as they are identified by the USDA.

Review of the USDA Soil Web Survey indicates the site consists of predominately of Woodburn Silt Loam and

Willamette Silt Loam (USDA, 2025). Each of these soil types have a USDA hydrologic soil classification of group

C. However, one of our site-specific infiltration tests had no measurable infiltration, indicating that group D may be a more accurate representation. In addition, the presence of shallow bedrock may further limit on-site infiltration of stormwater.

Table 2. USDA Hydrologic Soil Group Parameters

Soil Properties Hydrologic Soil Group

A B C D

Saturated Hydraulic

Conductivity (k)

(inches/hour) k>5.67 1.42<k<5.67 0.14<k<1.42 k<0.14

3 GEOLOGIC HAZARDS

Geologic and seismic hazards are defined as conditions associated with the geologic and seismic environment that could influence existing and/or proposed improvements. Geologic and seismic hazards that could affect the site’s development are identified below and should be considered during the planning process. Apex reviewed GIS layers within the Oregon HazVu Statewide Geozhazards Viewer and associated reports to assess potential geologic hazards for the study area. In general, the geologic and seismic hazards most commonly

Apex Companies, LLC 6 associated with the physical and chemical characteristics of near-surface soil, rock, and groundwater include the following:

• Slope stability • Hydrology and drainage • Volcanic hazards

• Adverse soils • Hazardous minerals • Permafrost and freeze-thaw

• Land subsidence • Erosion and sedimentation • Seismic hazards (liquefaction, lateral spreading, earthquake-induced landslides, ground shaking, fault ground rupture, tsunamis, and seiches)

• Subsurface voids • Hydrogeology and groundwater

Those shown in bold above are geologic and seismic hazards that could affect the site development and should be considered in the planning process. Ground shaking is a geologic hazard at the site related to seismicity, which is discussed further in the following sections.

Slope Stability

Slope stability is influenced by various factors including: (1) the geometry of the soil mass and subsurface materials, (2) the weight of materials overlying a potential failure surface, (3) the shear strength of soils along the failure surface, and (4) the hydrostatic pressure (groundwater levels) along the failure surface. The stability of a slope is expressed in terms of factor of safety (FS), which is defined as the ratio of resisting forces to driving forces. At equilibrium, the FS is equal to 1.0 and the driving forces are balanced by the resisting forces.

Failure occurs when the driving forces exceed the resisting forces, i.e., FS less than 1.0. An increase in the FS above 1.0, whether by increasing the resisting forces and/or decreasing the driving forces, reflects a corresponding increase in the stability of the mass. The actual FS may differ from the calculated FS due to uncertainty in soil strengths, subsurface geometry, failure surface location and orientation, groundwater levels, and other factors that are not completely known or understood.

Site slopes are relatively consistent, sloping gently to moderately down in areas toward the west/southwest, similar to the surrounding developed areas. Apex observed no obvious signs of recent instability at the site.

Expansive Soils

Clay soils with moderate to high plasticity were encountered in some of our explorations. However, provided the recommendations for dry soil conditions included in this report are followed, we do not anticipate the presence of these soils will negatively affect the new foundations.

Seismicity and Faulting

3.3.1 Historical Seismicity

Regional historical seismicity information was acquired from the Advanced National Seismic System (ANSS)

Comprehensive Catalog, hosted by the Northern California Earthquake Data Center (NCEDC), and is presented on Figure 3. These data include earthquakes with magnitudes exceeding M 2.5, within a 150-km radius of the city of Portland, Oregon, and recorded between 1963 and 2017 (NCEDC, 2017). Magnitudes within the ANSS dataset are recorded as local magnitude, surface-wave magnitude, body-wave magnitude, moment magnitude, and magnitude of completeness.

3.3.2 Seismic Sources

Several types of seismic sources exist in the Pacific Northwest, which are outlined below. Volcanic sources beneath the Cascade Range are not considered further in this study. Cascade Range earthquakes rarely exceed about M 5.0 in size and are believed to be far enough removed to not pose a threat to the site (NCEDC, 2017).

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3.3.2.1 Crustal Earthquakes and Faults

Review of the USGS Quaternary Fault Database indicates the site is located within close proximity (less than

15.5 miles or 25 km) to numerous Quaternary faults (Figure 4; USGS, 2025). Due to their proximity, the crustal faults are significant seismic sources for severe ground motion and shaking within the area, and we note that the Oatfield fault is mapped within less than 1 kilometer northeast of the site.

Table 3. Faults within the Site Vicinity

Fault Zone Name Fault ID Approximate Distance to Site

(Surface Projection in km)

Oatfield fault 875 <1

Portland Hills fault 877 2

Bolton fault 874 3

Damascus-Tickle Creek fault zone 879 5

Canby-Molalla fault 716 9

Grant Butte fault 878 9

East Bank fault 879 15

Beaverton fault zone 715 20

3.3.2.2 Cascadia Subduction Zone (CSZ) – Interface Earthquakes

The CSZ represents the boundary between the subducting Juan de Fuca tectonic plate and the overriding

North American tectonic plate (Figure 5). Recurrence intervals for subduction zone earthquakes are based on studies of the geologic record, with studies estimating a recurrence interval between 500 to 530 years for a full rupture event, and on the order of 300 years for smaller events exceeding Mw 8.0+ (Goldfinger et al., 2012).

Geologic evidence and written records from Japan suggest the most recent earthquake occurred in January

1700. The 1700 earthquake probably ruptured much of the approximate 620-mile (1,000 km) length of the CSZ and was estimated at moment magnitudes of MW 9.0. The horizontal distance from the edge of the CSZ megathrust is located approximately 139 miles (223 km) from Portland, Oregon. The current US Geological

Survey risk-based maximum credible earthquake for CSZ megathrust is MW 9.0±0.2 (USGS, 2008).

3.3.2.3 Intraslab Earthquakes

Intraslab earthquakes occur within the subducting slab. They are problematic in the sense that they do not have a surface expression or rupture the ground surface and their seismicity generates deformation along many faults within the slab (Kirby et al., 2002). The CSZ has generated significant intraslab destructive earthquakes including the 2001 MW 6.8 Nisqually earthquake in the Puget lowland. The estimated depth to the subducting Juan de Fuca plate under Portland is approximately 28 miles (40 km) (Blair et al., 2011) and should therefore be considered a seismic source.

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3.3.2.4 Liquefaction and Lateral Spreading

Liquefaction is defined as a decrease in the shear resistance of loose, saturated, cohesionless soil (e.g., sand) or low plasticity silt soils, due to the buildup of excess pore pressures generated during an earthquake. This could result in a temporary transformation of the soil deposit into a viscous fluid. Liquefaction can result in ground settlement, foundation bearing capacity failure, and lateral spreading of ground.

Based on a review of Oregon HazVu, the site is shown as having a low liquefaction hazard. Based on the subsurface conditions encountered in our explorations, our current opinion is that the risk of structurally damaging liquefaction settlement and lateral spreading at the site is low to absent.

3.3.3 Seismic Hazards

Other site-specific seismic hazards considered include earthquake-induced landslides, fault rupture, seiche and tsunami inundation, and earthquake shaking. Based on the gentle surface topography and geology at the site, the risk from landslides and earthquake-induced landslides is generally low. Due to the location of the site, the risks of seiche and tsunami inundation are absent. Though faults are mapped within less than one kilometer of the site, no faults are mapped as crossing the site; subsequently, the risk of fault rupture at the site is low

(Madin et al., 2013). Very strong to severe earthquake ground shaking will occur during a code-based seismic event on the CSZ and from local faults. Shaking duration during a CSZ event is expected to last for 5 to 7 minutes along the coast, decreasing inland to around 2 minutes closer to Portland and Seattle (Oregon

Emergency Management, 2025; Hickey, 2017). Based on our current project understanding, our opinion is that effects of earthquake ground motions can be accounted for by using code-based design procedures and the code-based design response spectrum.

Flooding

Flooding occurs when local creeks, streams, rivers, and bays are not able to transfer water away from a local area faster than the rate of accumulating water. This can occur on a local or regional scale and is highly variable based upon the configuration of individual watersheds. In the context of the Willamette River, distant upland precipitation or rapid snowmelt can have significant impact far downstream where the weather may be different. Regardless, destruction of land, infrastructure, and personal property can occur when banks, levees, and flood plains are inundated with stormwater or rapid snowmelt.

Review of available FEMA National Flood Hazard maps indicate the site is located outside of the 100- and 500-year mapped flood zone.

4 CONCLUSIONS AND RECOMMENDATIONS

Geotechnical Design Considerations

The subsurface conditions at the site generally consist of very stiff/dense or better silts, sands, and gravels underlain by relatively shallow weathered bedrock and bedrock. Based on our observations and analyses, conventional foundation support on shallow spread footings is feasible for the proposed building addition.

However, one sample taken at 2.5 feet bgs in boring B-3, near the building addition, encountered medium stiff clay soils. The subsequent sample in this boring was very dense. To avoid designing based on unique and localized “worst-case” subsurface conditions, we have based our geotechnical recommendations on the subsurface conditions encountered across the majority of the site. This approach requires overexcavation of any medium stiff or softer clay soils, if encountered. Overexcavations should expose underlying dense/very stiff soils and be backfilled with structural fill prepared in accordance with section 5.3 of this report.

Our borings encountered shallow refusal on dense layers at depths as shallow as 2 feet bgs. Excavation without heavy duty equipment may be challenging.

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Shallow Foundations

Shallow spread footings bearing on very stiff/dense or better native silts, sands, and gravels may be used to support foundation loads associated with the proposed building additions, provided the recommendations in this report are followed. Footings should not be supported on undocumented fill or on medium stiff clay soils.

4.2.1 Minimum Footing Widths and Design Bearing Pressure

Allowable and ultimate bearing resistances considering 18 inches of embedment are presented in Figure 6 as a function of footing width. Allowable bearing resistances considered an allowable stress design (ASD) FS equal to 3. These are net bearing pressures that can be used to evaluate existing footings or design new footings.

The weight of the footing and overlying backfill can be disregarded in calculating footing sizes. The recommended bearing pressures apply to the total of dead plus long-term live loads. Allowable bearing pressures may be increased by one-third for seismic and wind loads for new footings, and one-half for seismic loading of existing footings.

Any new continuous wall and isolated spread footings should be at least 18 and 24 inches wide, respectively.

New footings will settle in response to column and wall loads. Based on our evaluation of the subsurface conditions and our analysis, we estimate post-construction settlement will be less than 1 inch for the column and perimeter foundation loads. Differential settlement will be on the order of one-half of the total settlement between new footings.

4.2.2 Footing Embedment Depths

Apex recommends that all footings be founded a minimum of 18 inches below the lowest, adjacent grade. The footings should be founded below an imaginary line projecting upward at a 1H:1V (horizontal to vertical) slope from the base of any adjacent, parallel utility trenches or deeper excavations.

4.2.3 Footing Preparation

Excavations for new footings should be carefully prepared to a neat and undisturbed state and compacted until stiff. A representative from Apex should confirm suitable bearing conditions and evaluate all exposed footing subgrades. Observations should also confirm that loose or soft materials have been removed from new footing excavations and concrete slab-on-grade areas. Localized deepening of footing excavations may be required to penetrate loose, wet, or deleterious materials.

Apex recommends a 4-inch-thick layer of compacted, crushed rock be placed over the footing subgrades to help protect them from disturbance.

4.2.4 Lateral Resistance

Lateral loads can be resisted by passive earth pressure on the sides of footings and grade beams, and by friction at the base of the footings. A passive earth pressure calculated using an equivalent fluid weight (EFW) of 250 pounds per cubic foot (pcf) may be used for footings confined by native soils and new structural fills.

The allowable passive pressure has been reduced by a factor of two to account for the large amount of deformation required to mobilize full passive resistance. Adjacent floor slabs, pavements, or the upper 12-inch depth of adjacent unpaved areas should not be considered when calculating passive resistance. For footings supported on native soils or new structural fills, use a coefficient of friction equal to 0.35 when calculating resistance to sliding. These values do not include an FS.

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Floor Slabs

Satisfactory subgrade support for building floor slabs can be obtained from the very stiff/dense native silt, sand, and gravel subgrade prepared in accordance with our recommendations presented in the Site

Preparation, Wet/Freezing Weather and Wet Soil Conditions, and Select Granular Fill sections of this report. A minimum 6-inch-thick layer of imported granular material should be placed and compacted over the prepared subgrade. Thicker aggregate sections may be necessary where undocumented fill is present, soft/loose soils are present at subgrade elevation, and/or during wet conditions. Imported granular material should be composed of crushed rock or crushed gravel that is relatively well graded between coarse and fine, contains no deleterious materials, has a maximum particle size of 1 inch, and has less than 5% by dry weight passing the US

Standard No. 200 Sieve.

Floor slabs supported on a subgrade and base course prepared in accordance with the preceding recommendations may be designed using a modulus of subgrade reaction (k) of 150 pounds per cubic inch

(pci).

Seismic Design Considerations

4.4.1 Seismic Site Class

Based on the soil conditions encountered in our subsurface explorations, Site Class C is appropriate for use in design.

4.4.2 ASCE 41-17 Code-Based Seismic Design Parameters

Apex understands the seismic evaluation for the existing structure will be completed in accordance with ASCE

41-17 (Seismic Evaluation and Retrofits of Existing Buildings), which also references ASCE 7-16 (Minimum

Design Loads for Buildings and Other Structures). ASCE 41-17 provides recommendations for evaluating seismic hazards based on four hazard levels: BSE-1N, BSE-2N, BSE-1E, and BSE-2E. These hazard levels represent the Basic Performance Objective Equivalent to New Building Standards (BPON) and Basic

Performance Objective Equivalent to Existing Buildings (BPOE).

The seismic design criteria, in accordance with ASCE 41-17, are summarized in Tables 4 through 6.

Table 4. ASCE 41-17 Seismic Design Parameters for BSE-2N and BSE-1N

Parameter Short Period 1 Second

Maximum Direction Spectral Acceleration SS = 0.86 g S1 = 0.38 g

Site Class C

Site Coefficients Fa = 1.2 Fv = 1.5

BSE-2N: Adjusted Spectral Acceleration SXS = 1.03 g SX1 = 0.57 g

BSE-1N: Adjusted Spectral Acceleration SXS = 0.68 g SX1 = 0.38 g g= Acceleration due to gravity

Table 5. ASCE 41-17 Seismic Design Parameters for BSE-2E

1,000-year Maximum Direction Spectral Acceleration SS, 5/50 = 0.60 g S1, 5/50 = 0.27 g

Site Class C

Site Coefficients Fa = 1.26 Fv = 1.5

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BSE-2E: Adjusted Spectral Acceleration SXS = 0.76 g SX1 = 0.4 g

Table 6. ASCE 41-17 Seismic Design Parameters for BSE-1E

250-year Maximum Direction Spectral Acceleration SS, 20/50 = 0.23 g S1 ,20/50 = 0.09 g

Site Class C

Site Coefficients Fa = 1.3 Fv = 1.5

BSE-1E: Adjusted Spectral Acceleration SXS = 0.3 g SX1 = 0.13 g

4.4.3 2022 OSSC Code-Based Seismic Design Parameters

The current seismic design criteria for this project are based on the 2022 Oregon Structural Specialty Code

(OSSC). The seismic design criteria, in accordance with the 2022 OSSC, are summarized in Table 7.

Table 7. 2022 OSSC Seismic Design Parameters

Maximum Credible Earthquake Spectral Acceleration Ss = 0.86 g S1 = 0.38 g

Site Class C

Site Coefficient Fa = 1.2 Fv = 1.5

Adjusted Spectral Acceleration SMS = 1.03 g SM1 = 0.57 g

Design Spectral Response Acceleration Parameters SDS = 0.68 g SD1 = 0.38 g

MCEG Peak Ground Surface Acceleration PGA = 0.38

Site Amplification Factor at PGA FPGA = 1.2

Site-Modified Peak Ground Acceleration PGAM = 0.46g

Temporary and Permanent Slopes

All temporary cut slopes should be excavated with a smooth-bucket excavator, with the slope surface repaired if disturbed. In addition, upslope surface runoff should be rerouted to not run down the face of the slopes.

Equipment should not be allowed to induce vibration or infiltrate water above the slopes, and no surcharges are allowed within 25 feet of the slope crest.

Permanent cut and fill slopes up to 10 feet high can be inclined at 2H:1V in very stiff/dense or better silts, sands, or gravels, or compacted structural fill. If slow seepage is present, use of a rock blanket or a suitably revegetated, reinforced erosion control blanket may be required. Apex should be consulted if seepage is present; additional erosion control measures, such as additional drainage elements, and/or flatter slopes, may also be required. Exposed soils that are soft or loose may also require these measures. Fill slopes should be over-built and cut back into compacted structural fill at the design inclination using a smooth-bucket excavator. Erosion control is critical to maintaining slopes.

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Ground Moisture

The perimeter ground surface and hard-scape should be sloped to drain away from all structures and away from adjacent slopes. Gutters should be tight-lined to a suitable discharge and maintained as free-flowing. All crawl spaces (if present) should be adequately ventilated and sloped to drain to a suitable, exterior discharge.

Pavement Design

The provided pavement recommendations were developed using the American Association of State Highway and Transportation Officials (AASHTO) design methods and references the associated Oregon Department of

Transportation (ODOT) specifications for construction. Our evaluation considered a maximum of 10 school buses per day for a 20-year design life.

The minimum recommended pavement section thicknesses are provided in Table 8. Depending on weather conditions at the time of construction, a thicker aggregate base course section could be required to support construction traffic during preparation and placement of the pavement section.

Table 8. Minimum AC Pavement Sections

Traffic Loading AC (inches) Base Course (inches) Subgrade

Pull-in Car Parking Only 3 9 Stiff subgrade as verified by

Apex personnel* Drive Lanes and Access

Roads 4 9

* Subgrade must pass proofroll

The asphalt cement binder should be selected following ODOT SS 00744.11 – Asphalt Cement and Additives.

The AC should consist of ½-inch hot mix asphalt concrete (HMAC) with a maximum lift thickness of 3 inches.

The AC should conform to ODOT SS 00744.13 and 00744.14 and be compacted to 91% of the maximum theoretical density (Rice value) of the mix, as determined in accordance with ASTM D2041.

Heavy construction traffic on new pavements or partial pavement sections (such as base course over the prepared subgrade) will likely exceed the design loads and could potentially damage or shorten the pavement life; therefore, we recommend construction traffic not be allowed on new pavements, or that the contractor take appropriate precautions to protect the subgrade and pavement during construction.

If construction traffic is to be allowed on newly constructed road sections, an allowance for this additional traffic will need to be made in the design pavement section.

5 CONSTRUCTION RECOMMENDATIONS

Site Preparation

Construction of the proposed site improvements may involve clearing and grubbing of the existing vegetation or demolition of possible existing structures. In vegetated areas, site stripping should include removing topsoil, roots, and other deleterious materials to a minimum depth of 6 inches bgs. Demolition should include removing existing pavement, utilities, etc., throughout the proposed improvements area. Underground utility lines or other abandoned structural elements should also be removed. The voids resulting from removal of foundations or loose soil in utility lines should be backfilled with compacted structural fill. The base of these excavations should be excavated to stiff native subgrade before filling, with sides sloped at a minimum of

1H:1V to allow for uniform compaction. Materials generated during demolition should be transported off site or stockpiled in areas designated by the owner’s representative.

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5.1.1 Proofrolling/Subgrade Verification

Following site preparation and prior to placing aggregate base over shallow foundation, floor slab, and pavement subgrades, the exposed subgrade should be evaluated either by proofrolling or another method of subgrade verification. The subgrade should be proofrolled with a fully loaded dump truck or similar heavy, rubber-tire construction equipment to identify unsuitable areas. If evaluation of the subgrades occurs during wet conditions, or if proofrolling the subgrades will result in disturbance, they should be evaluated by Apex using a steel foundation probe. We recommend that Apex be retained to observe the proofrolling and perform the subgrade verifications. Unsuitable areas identified during the field evaluation should be compacted to a stiff condition or be excavated and replaced with structural fill.

5.1.2 Wet/Freezing Weather and Wet Soil Conditions

Due to the presence of fine-grained silt and sands in the near-surface materials at the site, construction equipment may have difficulty operating on the near-surface soils when the moisture content of the surface soil is more than a few percentage points above the optimum moisture required for compaction. Soils disturbed during site preparation activities, or unsuitable areas identified during proofrolling or probing, should be removed and replaced with compacted structural fill.

Site earthwork and subgrade preparation should not be completed during freezing conditions, except for mass excavation to the subgrade design elevations.

Protection of the subgrade is the responsibility of the contractor. Construction of granular haul roads to the project site entrance may help reduce further damage to the pavement and disturbance of site soils. The actual thickness of haul roads and staging areas should be based on the contractors’ approach to site development, and the amount and type of construction traffic. The imported granular material should be placed in one lift over the prepared undisturbed subgrade and compacted using a smooth-drum, non-vibratory roller. A geotextile fabric should be used to separate the subgrade from the imported granular material in areas of repeated construction traffic. The geotextile should meet the specifications of ODOT SS Section 02320.10 and

SS 02320.20, Table 02320-4 for soil separation. The geotextile should be installed in conformance with ODOT

SS Section 00350 – Geosynthetic Installation.

5.1.3 Dry Weather Conditions

Clay soils should be covered within 4 hours of exposure by a minimum of 4 inches of crushed rock or plastic sheeting during the dry season. Exposure of these materials should be coordinated with the geotechnical engineer so that the subgrade suitability can be evaluated prior to being covered.

Excavation

Depending on the depth of site excavation, additional equipment may be required to advance excavations through the harder rock. For the purposes of this report, rock excavation would apply to subsurface materials that require systematic drilling and blasting or the use of a pneumatic rock hammer that cannot be excavated with a CAT 235 excavator, or equivalent, equipped with rock teeth. The project schedule and budget should include a contingency for rock excavation and increased backfill volumes. Apex should be retained to review the grading and utility plans when they are available for comparison with encountered field conditions.

Additional work may be required to better define the impact on the project.

All excavations should be made in accordance with applicable Occupational Safety and Health Administration

(OSHA) and state regulations. The contractor is solely responsible for adherence to the OSHA requirements.

Trench cuts should stand relatively vertical to a depth of approximately 4 feet bgs, provided no groundwater

Apex Companies, LLC 14 seepage is present in the trench walls. Open excavation techniques may be used provided the excavation is configured in accordance with the OSHA requirements, groundwater seepage is not present, and with the understanding that some sloughing may occur. Trenches/excavations should be flattened if sloughing occurs or seepage is present. Use of a trench shield or other approved temporary shoring is recommended if vertical walls are desired for cuts deeper than 4 feet bgs. If dewatering is used, we recommend that the type and design of the dewatering system be the responsibility of the contractor, who is in the best position to choose systems that fit the overall plan of operation.

Structural Fill

The extent of site grading is currently unknown; however, Apex estimates that cuts and fills will be on the order of up to 5 feet to raise the grades within the proposed site. Structural fill should be placed over subgrade that has been prepared in conformance with the Site Preparation and Wet/Freezing Weather and Wet Soil

Conditions sections of this report. Structural fill material should consist of relatively well-graded soil, or an approved rock product that is free of organic material and debris, and contains particles not greater than 4 inches nominal dimension.

The suitability of soil for use as compacted structural fill will depend on the gradation and moisture content of the soil when it is placed. As the amount of fines (material finer than the US Standard No. 200 Sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and compaction becomes more difficult to achieve. Soils containing more than about 5% fines cannot consistently be compacted to a dense, non-yielding condition when the water content is significantly greater (or significantly less) than optimum.

5.3.1 On-Site Soil

Near surface soils encountered in our explorations consist primarily of silt and clay soils, which may be difficult to use as structural fill, except during extended periods of dry weather. Even with construction during the dry summer grading season, it could take several days of frequent aeration to dry soils to near the optimum moisture content for compaction. If used, the material should be placed in lifts with a maximum uncompacted thickness of approximately 8 inches and compacted to at least 92% of the maximum dry density, as determined by ASTM D1557 (modified proctor).

5.3.2 Borrow Material

Borrow material for general structural fill construction should meet the requirements set forth in ODOT SS

00330.12 – Borrow Material. When used as structural fill, borrow material should be placed in lifts with a maximum uncompacted thickness of approximately 8 inches and compacted to not less than 92% of the maximum dry density, as determined by ASTM D1557.

5.3.3 Select Granular Fill

Selected granular backfill used during periods of wet weather for structural fill construction should meet the specifications provided in ODOT SS 00330.14 – Selected Granular Backfill. The imported granular material should be uniformly moisture conditioned to within about 2% of the optimum moisture content and compacted in relatively thin lifts using suitable mechanical compaction equipment. Selected granular backfill should be placed in lifts with a maximum uncompacted thickness of 8 to 12 inches and be compacted to not less than 95% of the maximum dry density, as determined by ASTM D1557.

5.3.4 Crushed Aggregate Base

Crushed aggregate base course below floor slabs, spread footings, and asphalt concrete pavements should be clean crushed rock or crushed gravel that contains no deleterious materials and meets the specifications provided in ODOT SS 02630.10 – Dense-Graded Aggregate, and has less than 5% by dry weight passing the US

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Standard No. 200 Sieve. The crushed aggregate base course should be placed in lifts with a maximum uncompacted thickness of 8 to 12 inches and be compacted to at least 95% of the maximum dry…