Office: 18270 SW Boones Ferry Road, Suite 6, Durham, Oregon 97224

Mailing: P.O. Box 230997, Tigard, Oregon 97281

Carlson Geotechnical A Division of Carlson Testing, Inc.

Phone: (503) 601-8250 www.carlsontesting.com

Bend Office Eugene Office Salem Office Tigard Office

(541) 330-9155

(541) 345-0289

(503) 589-1252

(503) 684-3460

G2606718 Geotechnical Investigation

Report of

Geotechnical Investigation

Bethel School District Transportation and Food Facility

4202 West 6th Avenue

Eugene, Oregon

CGT Project Number G2606718

Prepared for

Skylar Fairchild

Bethel School District

4640 Barger Drive

Eugene, OR 97402

June 8, 2026 http://www.carlsontesting.com/

Bethel School District Transportation and Food Facility

Carlson Geotechnical Page 3 of 21

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Project Information

1.2 Scope of Services

2.0 SITE DESCRIPTION

2.1 Site Geology

2.2 Site Surface Conditions

2.3 Subsurface Conditions

3.0 SEISMIC CONSIDERATIONS

3.1 Seismic Site Class

3.2 Seismic Ground Motion Values

3.3 Seismic Hazards

4.0 CONCLUSIONS

4.1 Fill Materials and Soft Soils

4.2 Shallow Groundwater

4.3 Expansion Potential

4.4 Moisture Sensitive Soils

5.0 RECOMMENDATIONS

5.1 Site Preparation

5.2 Temporary Excavations

5.3 Wet Weather Considerations

5.4 Structural Fill

5.5 Shallow Foundations

5.6 Rigid Retaining Walls

5.7 Floor Slabs

5.8 Pavements

5.9 Additional Considerations

6.0 RECOMMENDED ADDITIONAL SERVICES

6.1 Design Review

6.2 Observation of Construction

7.0 LIMITATIONS

ATTACHMENTS

Site Location ........................................................................................................................................... Figure 1

Site Plan ................................................................................................................................................. Figure 2

Site Photographs .................................................................................................................................... Figure 3

Retaining Wall Pressure Distribution ...................................................................................................... Figure 4

Perimeter Footing Drain .......................................................................................................................... Figure 5

Subsurface Investigation and Laboratory Testing ............................................................................. Appendix A

Results of Infiltration Testing ............................................................................................................. Appendix B

Geophysical Survey ........................................................................................................................... Appendix C

Carlson Geotechnical Page 4 of 21

1.0 INTRODUCTION

Carlson Geotechnical (CGT), a division of Carlson Testing, Inc. (CTI), is pleased to submit this report summarizing the results of our geotechnical investigation for the proposed Bethel School District

Transportation and Food Facility project. The site is located at 4202 West 6th Avenue in Eugene, Oregon, as shown on the attached Site Location, Figure 1.

1.1 Project Information

CGT developed an understanding of the proposed project based on our correspondence with you and project documents provided to us on March 26, 2026. The documents provided included a Demo Site Plan and Office and Warehouse Plan prepared by Soderstrom Architects dated March 13, 2026. Based on our review, we understand the project will include:

• Demolition of two existing storage buildings located within the northwest and southwest portions of the site. Additionally, demolition of the existing residential structure within the southeast portion of the site.

• Construction of a new facility building. The building will be one story, steel-framed, with a slab on grade floor, and footprint of roughly 13,500 square feet. No below grade levels (basements) are planned for this project. For the purposes of this proposal, we have assumed maximum column, continuous wall, and uniform floor slab loads will be on the order of 100 kips, 3 kips per lineal foot (klf), and 250 pounds per square foot (psf), respectively.

• Construction of new paved drive lanes and parking areas to serve the new building. We assume new pavements will be surfaced with asphalt concrete (AC).

• We understand stormwater will be disposed of, at least in part, via onsite infiltration. As requested, two infiltration tests were performed at the site at depths of about 3½ and 5½ feet below ground surface

(bgs). Design of infiltration facilities will rest with others.

• Although no grading plans have been provided, we anticipate permanent grade changes at the relatively level site will include cuts and fills up to about 2 feet relative to existing grades.

1.2 Scope of Services

Our scope of work included the following:

• Contact the Oregon Utilities Notification Center to mark the locations of public utilities within a 20-foot radius of our explorations at the site. CGT also subcontracted a private utility locator service to mark the locations of detectable private utilities within the same radius.

• Explore subsurface conditions at the site by advancing 3 drilled borings to depths up to 30½ bgs, and 3 hand auger borings to depths up to 5 feet bgs. Details of the subsurface investigation are presented in

Appendix A.

• Conduct infiltration testing in two of the borings. Results of the infiltration tests are presented in Appendix

B.

• Classify the soils encountered in the explorations in general accordance with ASTM D2488 (Visual-

Manual Procedure).

• Provide a technical narrative describing surface and subsurface deposits, and local geology of the site, based on the results of our explorations and published geologic mapping.

• Provide recommendations for the Seismic Site Class, mapped maximum considered earthquake spectral response accelerations, and site seismic coefficients.

• Provide a qualitative evaluation of seismic hazards at the site, including earthquake-induced liquefaction, landsliding, and surface rupture due to faulting or lateral spread.

Carlson Geotechnical Page 5 of 21

• Provide geotechnical recommendations for site preparation and earthwork.

• Provide geotechnical engineering recommendations for use in design and construction of shallow foundations, retaining walls, floor slabs, and pavements.

• Provide this written report summarizing the results of our geotechnical investigation and recommendations for the project.

2.0 SITE DESCRIPTION

2.1 Site Geology

Based on available geologic mapping of the area, the site is underlain by Pleistocene catastrophic flood deposits1,2,3 originating from glacial outburst floods of Lake Missoula. The flood deposits were produced by the periodic failure of glacial ice dams that impounded Lake Missoula in present day Montana between

18,000 to 15,000 years ago4. Floodwaters raged through Idaho, eastern Washington, and through the

Columbia River Gorge. Near Rainier, Oregon, the river channel was restricted, causing floodwaters to back up the Willamette Valley as far south as Eugene. Floodwaters in the Portland area were as much as 400 feet deep, leaving only the tops of the tallest hills dry. The flood deposits are typically split into three different facies: the coarse-grained facies, the fine-grained facies, and the channel facies.

Fine-grained Missoula flood deposits are mapped in the vicinity of the site, which typically consist of silt, clay, and fine-grained sand. Beds are generally poorly defined and thin (less than 3 feet thick).

2.2 Site Surface Conditions

The approximate 3-acre site is bordered by W 6th Avenue to the north, S Bertelsen Road to the east, W 7th

Avenue to the south, and existing commercial properties to the west. At the time of our field investigation, the site gently descended to the southwest, and was occupied by an existing residential home, two storage buildings (all to be removed), and a warehouse building (to remain) within its northeast portion. The remainder of the site was covered by AC pavement, gravel-surfaced driveways, short grasses, and scattered trees. Site layout and surface conditions are shown on the attached Site Plan (Figure 2) and Site

Photographs (Figure 3).

2.3 Subsurface Conditions

2.3.1 Subsurface Investigation & Laboratory Testing

Our subsurface investigation consisted of three drilled borings (B-1 through B-3) and three hand auger borings (HA-1 through HA-3) completed on May 6, 2026. The approximate exploration locations are shown on the Site Plan, attached as Figure 2. In summary, the borings were advanced to depths ranging from about

4 to 31½ feet bgs. Details regarding the subsurface investigation, logs of the explorations, and results of laboratory testing are presented in Appendix A. Subsurface conditions encountered during our site investigation are summarized below.

1 Ma, Madin, Duplantis, and Williams, 2012, Lidar-based Surficial Geologic Map and Database of the Greater Portland, Oregon, Area, Clackamas, Columbia, Marion, Multnomah, Washington, and Yamhill Counties, Oregon, and Clark County, Washington

Oregon Department of Geology and Mineral Industries Open-File Report O-12-02.

2 Madin, I.P., 2004. Geologic mapping and database for the Portland area fault studies: Final report, Clackamas, Multnomah, and

Washington Counties, Oregon: Oregon Department of Geology and Mineral Industries, Open-File Report O-04-02, scale

1:100,000.

3 Beeson, M.H., Tolan, T.L., and Madin, I.P., 1991. Geologic map of the Portland quadrangle, Multnomah and Washington counties, Oregon, and Clark County, Washington: Oregon Department of Geology and Mineral Industries, Geological Map Series 75, scale

1:24,000.

4 Allen, John Eliot, et al., 2009. Cataclysms on the Columbia, The Great Missoula Floods, Revised Second Edition: Ooligan Press, Portland State University.

Carlson Geotechnical Page 6 of 21

2.3.2 Subsurface Materials

The following describes each of the subsurface materials encountered at the site.

Undocumented Fill Soils (GP Fill, GC Fill, CH Fill, OH Fill)

Undocumented fill materials consisting of poorly graded gravel fill, clayey gravel fill, fat clay to fat clay with gravel fill, and organic fat clay with gravel fill were encountered at the surface of B-1 through B-3, and HA-1 through HA-2. Undocumented fill refers to materials placed without (available) records of subgrade conditions or evaluation of compaction. The fill soils extended to depths of about ¼ to 2½ feet bgs. Refer to

Appendix A for a detailed description of these materials.

Fat Clay to Fat Clay with Sand (CH)

Underlying the undocumented fill soils within all the borings was native fat clay to fat clay with sand. This soil was generally soft to very stiff, brown with gray and orange mottling, moist to wet, exhibited high plasticity, and contained trace to some fine-grained sand. This soil extended to the full depths explored in B-1, B-2, and

HA-1 through HA-3, about 4 to16 ½ feet bgs. The fat clay to fat clay with sand extended to a depth of about

20 feet bgs with B-3.

Poorly Graded Gravel with Sand (GP-GM)

Underlying the native clayey soil in B-3 was poorly graded gravel with sand. This soil was generally dense to hard, gray and brown with orange mottling, moist, subrounded, up to ½-inch in diameter, contained fine- to coarse-grained sand, and trace to some high plasticity clay fines. The soil extended to a depth of about 30 feet within boring B-3.

Poorly Graded Sand (SP)

Underlying the poorly graded gravel with sand in B-3 was poorly graded sand. This soil was generally medium dense, brown, moist, fine- to medium-grained, and contained trace high plasticity clay fines. The poorly graded sand extended to the full depth explored within B-3, about 31½ feet bgs.

2.3.3 Groundwater

Groundwater was measured at depths of about 2½ to 8¾ feet bgs within B-2, B-3, and HA-3 advanced at the site on May 6, 2026. Groundwater was not observed within the remaining explorations advanced at the site on that day. To determine approximate regional groundwater levels in the area, we researched well logs available on the Oregon Water Resources Department (OWRD)5 website for wells located within Section 34, Township 17 South, Range 4 West, Willamette Meridian. Our review indicated that groundwater levels in the area generally ranged from about 3 to 20 feet bgs. It should be noted groundwater levels vary with local topography. In addition, the groundwater levels reported on the OWRD logs often reflect the purpose of the well, so water well logs may only report deeper, confined groundwater, while geotechnical or environmental borings will often report any groundwater encountered, including shallow, unconfined groundwater.

Therefore, the levels reported on the OWRD well logs referenced above are considered generally indicative of local water levels and may not reflect actual groundwater levels at the project site. We anticipate that groundwater levels will fluctuate due to seasonal and annual variations in precipitation, changes in site utilization, or other factors.

5 Oregon Water Resources Department, 2026. Well Log Records, accessed June 2026, from OWRD web site:

http://apps.wrd.state.or.us/apps/gw/well_log/.

http://apps.wrd.state.or.us/apps/gw/well_log/

Carlson Geotechnical Page 7 of 21

3.0 SEISMIC CONSIDERATIONS

3.1 Seismic Site Class

Chapter 20 of ASCE 7-22 requires that the determination of the seismic site class be determined based on either the measured (or estimated) average shear wave velocity within the upper 100 feet of the site (Vs100).

As indicated in Appendix C, we completed geophysical (Refraction Micro-Tremor or ReMi®) testing at the project site as means to measure shear wave velocities within that depth zone. The survey results indicated a weighted-average soil shear wave velocity within the upper 100 feet (Vs100) equal to 1,856 feet per second.

Based on Table 20.2-1 of ASCE 7-22, this results in a designation of Seismic Site Class C for the project site.

3.2 Seismic Ground Motion Values

Earthquake ground motion parameters for the site were obtained in accordance with ASCE 7-22 using the

ASCE Hazard Tool calculator on the ASCE website6. The site Latitude 44.052472° North and Longitude

123.163586° West were input as the site location. The following table shows the recommended seismic design parameters for the site.

Table 1 Seismic Ground Motion Values (ASCE 7-22)

Parameter Value

Mapped Acceleration Parameters Spectral Acceleration, 0.2 second (Ss) 0.89g

Spectral Acceleration, 1.0 second (S1) 0.40g

Adjusted MCE Spectral

Response Parameters (Site Class C)

MCE Spectral Acceleration, 0.2 second (SMS ) 1.03g

MCE Spectral Acceleration, 1.0 second (SM1 ) 0.57g

Design Spectral Response Accelerations Design Spectral Acceleration, 0.2 second (SDS ) 0.69g

Design Spectral Acceleration, 1.0 second (SD1 ) 0.38g

Seismic Design Category (Risk Category II) D

3.3 Seismic Hazards

3.3.1 Liquefaction

In general, liquefaction occurs when deposits of loose/soft, saturated, cohesionless soils, generally sands and silts, are subjected to strong earthquake shaking. If these deposits cannot drain quickly enough, pore water pressures can increase, approaching the value of the overburden pressure. The shear strength of a cohesionless soil is directly proportional to the effective stress, which is equal to the difference between the overburden pressure and the pore water pressure. When the pore water pressure increases to the value of the overburden pressure, the shear strength of the soil approaches zero, and the soil can liquefy. The liquefied soils can undergo rapid consolidation or, if unconfined, can flow as a liquid. Structures supported by the liquefied soils can experience rapid, excessive settlement, shearing, or even catastrophic failure.

For fine-grained soils, susceptibility to liquefaction is evaluated based on penetration resistance and plasticity, among other characteristics. Criteria for identifying non-liquefiable, fine-grained soils are constantly evolving. Current practice to identify non-liquefiable, fine-grained soils is based on moisture content and plasticity characteristics of the soils7,8,9. The susceptibility of sands, gravels, and sand-gravel mixtures to

6 American Society of Civil Engineers (ASCE), 2026. USGS seismic design parameters determined using “ASCE Hazard Tool,” accessed June 2026, from the ASCE website https://ascehazardtool.org/.

7 Seed, R.B. et al., 2003. Recent Advances in Soil Liquefaction Engineering: A Unified and Consistent Framework. Earthquake

Engineering Research Center Report No. EERC 2003-06.

https://ascehazardtool.org/

Carlson Geotechnical Page 8 of 21 liquefaction is typically assessed based on penetration resistance, as measured using SPTs, CPTs, or

Becker Hammer Penetration tests (BPTs).

The Oregon Department of Geology and Mineral Industries’ Oregon Statewide Geohazards Viewer

(HazVu)10 shows a high hazard for liquefaction at the site. Based on the soft to medium consistency of the fine-grained clayey soils encountered within the upper 10 feet of our borings and the presence of static water at depths of about 2½ to 8¾ feet bgs, the near surface clayey soils are considered potentially susceptible to liquefaction-induced settlement. Below about 10 feet bgs at the site, the soils consisted of high plasticity, stiff to very stiff, fat clays (CH), underlain by layers of poorly graded granular soils (SP, GP-GM) that were generally dense, and are therefore considered non-liquefiable.

If the property owner wishes to further define the risk of liquefaction at the site, a quantitative liquefaction triggering and settlement analysis could be performed. Such an analysis would require borings using powered drilling equipment, and is outside the scope of this assignment.

3.3.2 Slope Instability

Due to the relatively level topography at and surrounding the site, the risk of slope instability at the site is considered negligible. The proposed grading includes relatively minimal planned changes in site grades and is not anticipated to increase this risk.

Surface Rupture

3.3.2.1 Faulting

No known faults exist on or immediately adjacent to the site11. Therefore, the risk of surface rupture at the site due to faulting is considered very low.

3.3.2.2 Lateral Spread

Surface rupture due to lateral spread can occur on sites underlain by liquefiable soils that are located on or immediately adjacent to slopes steeper than about 3 degrees (20H:1V), and/or adjacent to a free face, such as a stream bank or the shore of an open body of water. During lateral spread, the materials overlying the liquefied soils are subject to lateral movement downslope or toward the free face. Recognizing the proposed building will be located about 700 to 1000 feet away from the creeks, the risk of surface rupture due to lateral spread is anticipated to be low.

4.0 CONCLUSIONS

Based on the results of our field explorations and analyses, the site may be developed as described in

Section 1.1 of this report, provided the recommendations presented in this report are incorporated into the design and development. The primary geotechnical considerations at this site are presented in the following sections:

8 Bray, Jonathan D., Sancio, Rodolfo B., et al., 2006. Liquefaction Susceptibility of Fine-Grained Soils, Journal of Geotechnical and

Geoenvironmental Engineering, Volume 132, Issue 9, September 2006.

9 Idriss, I.M., Boulanger, R.W., 2008. Soil Liquefaction During Earthquakes, Earthquakes Engineering Research Institute Monograph

MNO-12.

10 Oregon Department of Geology and Mineral Industries, 2026. Oregon Statewide Geohazards Viewer, accessed May 2026 from

DOGAMI web site: http://www.oregongeology.org/sub/hazvu/index.htm.

11 U.S. Geological Survey, 2026. Quaternary fault and fold database for the United States, accessed June 2026, from USGS web site: https://earthquake.usgs.gov/hazards/qfaults/.

http://www.oregongeology.org/sub/hazvu/index.htm https://earthquake.usgs.gov/hazards/qfaults/

Carlson Geotechnical Page 9 of 21

4.1 Fill Materials and Soft Soils

As indicated above, we encountered about ¾ to 2½ feet of undocumented fill materials (GC Fill, CH Fill, GP

Fill, OH Fill) within the depths explored at the site on May 6, 2026. The fills were highly variable in terms of consistency/relative density, and were underlain by soft fat clay (CH). Where encountered at design subgrade elevation for building foundations, retaining walls, floor slabs, and pavements, we recommend removing the existing fill materials and soft clayey soils, and replacing them with imported granular structural fill in accordance with Section 5.4.2 of this report.

As an alternative to over-excavating the existing fill materials and soft soils, rammed aggregate piers

(sometimes referred to as “Geopiers”) could be installed through the existing fill/soft soils and down to the firmer soils generally encountered in our explorations below depths of about 10 feet bgs. The advantage to this approach is that conventional shallow foundations can generally be designed for a higher allowable soil bearing capacity (i.e. 4,000 to 5,500 psf), as compared to the over-excavation approach indicated above.

Additionally, through proper design, this method should significantly reduce the risk of liquefaction-induced settlements within the building pad area.

4.2 Shallow Groundwater

As indicated in Section 2.3.3 above, groundwater was measured at depths of about 2½ to 8¾ feet bgs within

B-2, B-3, and HA-3 advanced at the site on May 6, 2026. Dewatering of temporary excavations extending below the groundwater level is anticipated to be problematic due to the low hydraulic conductivity of the clayey soils (CH) that underlie the site. Geotechnical recommendations for dewatering of temporary excavations are presented in Section 5.2.3 of this report.

4.3 Expansion Potential

The native fat clay (CH) exhibited generally high plasticity, with a plasticity index of 37 and an expansion index of 101. Based on the plasticity characteristics and expansion index, the fat clay has a high expansive potential12. Foundations, floor slabs, and pavements founded directly on these soils may be subject to cyclic shrink-swell movements that can result in differential movements and distress. We recommend measures be taken to protect foundations, floor slabs, and pavements from the potentially damaging effects of shrink-swell movements. Specific recommendations for foundation, pavement, and floor slab subgrade preparation are presented in Sections 5.5, 5.6, and 5.7, respectively.

4.4 Moisture Sensitive Soils

The near surface fat clay (CH) is susceptible to disturbance during wet weather. Trafficability of this soil may be difficult, and significant damage to the subgrade could occur, if earthwork is undertaken without proper precautions at times when the exposed soils are more than a few percentage points above optimum moisture content. In the event that construction occurs during wet weather, we recommend that measures be implemented to protect the fine-grained subgrade in areas of repeated construction traffic. Geotechnical recommendations for wet weather construction are presented in Section 5.3 of this report.

5.0 RECOMMENDATIONS

The recommendations presented in this report are based on the information provided to us, results of our field investigation and analyses, laboratory data, and professional judgment. CGT has observed only a small

12 Day, Robert W. 2005. Table 9.1 – Typical Soil Properties versus Expansion Potential in Foundation Engineering Handbook: Design and Construction with the 2006 International Building Code. Published by McGraw-Hill Companies, Inc.

Carlson Geotechnical Page 10 of 21 portion of the pertinent subsurface conditions. The recommendations are based on the assumptions that the subsurface conditions do not deviate appreciably from those found during the field investigation. CGT should be consulted for further recommendations if the design of the proposed development changes and/or variations or undesirable geotechnical conditions are encountered during site development.

5.1 Site Preparation

5.1.1 Demolition

Demolition of existing buildings and appurtenant structures should include complete removal of all structural elements, including foundations and concrete slabs. Abandoned buried utilities should similarly be removed or grouted full. Concrete or asphalt concrete debris resulting from demolition activities may be re-used as structural fill, provided it is processed in accordance with the recommendations presented in Section 5.4.1 of this report. Alternatively, demolition debris should be hauled off site for disposal.

5.1.2 Stripping

Existing vegetation, topsoil, rooted soils, and undocumented fill soils should be removed from within, and for a minimum 5-foot margin around, proposed building pad and pavement areas. Based on the results of our field explorations, topsoil stripping depths are anticipated to be less than ½-foot bgs. Based on the results of our field explorations, undocumented fill encountered at the site extended to depths of about 2½-feet bgs.

These materials may be deeper or shallower at locations away from the completed explorations. The geotechnical engineer’s representative should provide recommendations for actual stripping depths based on observations during site stripping. Stripped surface vegetation and rooted soils should be transported off-site for disposal, or stockpiled for later use in landscaped areas. Stripped, inorganic fill materials should be transported off-site for disposal, or may be stockpiled for later use as structural fill as described in

Section 5.4.1 of this report.

5.1.3 Grubbing

Grubbing of trees should include the removal of the root mass and roots greater than ½ inch in diameter.

Grubbed materials should be transported off-site for disposal. Root masses from larger trees may extend greater than 3 feet bgs. Where root masses are removed, the resulting excavation should be properly backfilled with structural fill in conformance with Section 5.4 of this report.

5.1.4 Existing Utilities & Below-Grade Structures

All existing utilities at the site should be identified prior to excavation. Abandoned utility lines beneath the new building, pavements, and hardscaping features should be completely removed or grouted full. Soft, loose, or otherwise unsuitable soils encountered in utility trench excavations should be removed and replaced with structural fill in conformance with Section 5.4 this report. Buried structures (i.e. footings, foundation walls, retaining walls, slabs-on-grade, tanks, etc.), if encountered during site development, should be completely removed and replaced with structural fill in conformance with Section 5.4 of this report.

5.1.5 Subgrade Preparation – Building Pad, Pavements, Structural Fill Areas

After site preparation as recommended above, but prior to placement of structural fill and/or aggregate base, the geotechnical engineer’s representative should observe the exposed subgrade soils in order to identify areas of excessive yielding through either proof rolling or probing. Proof rolling of subgrade soils is typically conducted during dry weather using a fully-loaded, 10- to 12-cubic-yard, tandem-axle, tire-mounted, dump truck or equivalent weighted water truck. Areas of limited access or that appear too soft or wet to support proof rolling equipment should be evaluated by probing. During wet weather, subgrade preparation should be

Carlson Geotechnical Page 11 of 21 performed in general accordance with the recommendations presented in Section 5.3 of this report. If areas of soft soil or excessive yielding are identified, the affected material should be over-excavated to firm, unyielding subgrade, and replaced with imported granular structural fill in conformance with Section 5.4.2 of this report.

The fat clay (CH) soils should be kept moist, near optimum moisture content, and not allowed to dry out. If allowed to dry below optimum moisture content, to a point where surface cracking appears in the subgrade, the affected material should be over-excavated and replaced with imported granular structural fill.

5.1.6 Erosion Control

Erosion and sedimentation control measures should be employed in accordance with applicable City, County, and State regulations.

5.2 Temporary Excavations

5.2.1 Overview

Conventional earthmoving equipment in proper working condition should be capable of making necessary excavations for the anticipated site cuts as described earlier in this report. All excavations should be in accordance with applicable OSHA and state regulations. It is the contractor's responsibility to select the excavation methods, to monitor site excavations for safety, and to provide any shoring required to protect personnel and adjacent improvements. A “competent person,” as defined by OR-OSHA, should be on-site during construction in accordance with regulations presented by OR-OSHA. CGT’s current role on the project does not include review or oversight of excavation safety.

5.2.2 OSHA Soil Type

For use in the planning and construction of temporary excavations up to 10 feet in depth, an OSHA soil type

“B” should be used for the fine-grained alluvial soils (CH) encountered in the borings.

5.2.3 Dewatering

As indicated in Section 2.3.3, groundwater was measured at depths of about 2½ to 8¾ feet bgs within B-2, B-3, and HA-3 advanced at the site on May 6, 2026. Pumping from sumps may be effective in removing groundwater within shallow or localized excavations at the site. Pumping from multiple well points will likely be required for larger excavations and those extending below the groundwater level. The sumps or wells should be installed to remove water to a depth of at least 2 feet below the lowest elevation of the excavation, and should be installed and put into operation prior to commencing excavation. With regards to temporary dewatering, the contractor or their representative should determine the appropriate size, number, and location of sump pumps or wells. The project civil engineer should evaluate requirements for disposal of the resultant discharge.

5.2.4 Utility Trenches

Temporary trench cuts should stand near vertical to depths of approximately 4 feet in the native, fat clay

(CH) encountered near the surface of the site. If groundwater seepage undermines the stability of the trench, or if sidewall caving is observed during excavation, the sidewalls should be flattened or shored. Depending on the time of year trench excavations occur, trench dewatering may be required in order to maintain dry working conditions. Pumping from sumps located within the trench will likely be effective in removing water resulting from seepage. If groundwater is encountered, we recommend placing trench stabilization material at the base of the excavations. Trench stabilization material should be in conformance with Section 5.4.3.

Carlson Geotechnical Page 12 of 21

5.2.5 Excavations Near Foundations

Excavations near footings should not extend within a 1½ horizontal to 1 vertical (1½H:1V) plane projected out and down from the outside, bottom edge of the footings. In the event excavation needs to extend below the referenced plane, temporary shoring of the excavation and/or underpinning of the subject footing may be required. The geotechnical engineer should be consulted to review proposed excavation plans for this design case to provide specific recommendations.

5.3 Wet Weather Considerations

For planning purposes, the wet season should be considered to extend from late September to late June. It is our experience that dry weather working conditions should prevail between early July and mid-September.

Notwithstanding the above, soil conditions should be evaluated in the field by the geotechnical engineer’s representative at the initial stage of site preparation to determine whether the recommendations within this section should be incorporated into construction.

5.3.1 Overview

Due to their fines content, the on-site clayey soils (CH) are susceptible to disturbance during wet weather.

Trafficability of these soils may be difficult, and significant damage to subgrade soils could occur, if earthwork is undertaken without proper precautions at times when the exposed soils are more than a few percentage points above optimum moisture content. For wet weather construction, site preparation activities may need to be accomplished using track-mounted equipment, loading removed material onto trucks supported on granular haul roads, or other methods to limit soil disturbance. The geotechnical engineer’s representative should evaluate the subgrade during excavation by probing rather than proof rolling. Soils that have been disturbed during site preparation activities, or soft or loose areas identified during probing, should be over-excavated to firm, unyielding subgrade, and replaced with imported granular structural fill in conformance with Section 5.4.2.

5.3.2 Geotextile Separation Fabric

We recommend a geotextile separation fabric be placed to serve as a barrier between the prepared subgrade and granular fill/base rock in areas of repeated or heavy construction traffic. The geotextile fabric should meet the requirements presented in the current Oregon Department of Transportation (ODOT)

Standard Specification for Construction (ODOT SSC), Section 02320.

5.3.3 Granular Working Surfaces (Haul Roads & Staging Areas)

Haul roads subjected to repeated heavy, tire-mounted, construction traffic (e.g. dump trucks, concrete trucks, etc.) will require a minimum of 18 inches of imported granular material. For light staging areas, 12 inches of imported granular material is typically sufficient. Additional granular material or geo-grid reinforcement may be recommended based on site conditions and/or loading at the time of construction. The imported granular material should be in conformance with Section 5.4.2 and have less than 5 percent material passing the U.S.

Standard No. 200 Sieve. The prepared subgrade should be covered with geotextile fabric (Section 5.3.2) prior to placement of the imported granular material. The imported granular material should be placed in a single lift (up to 24 inches deep) and compacted using a smooth-drum, non-vibratory roller until well-keyed.

5.3.4 Footing Subgrade Protection

A minimum of 3 inches of imported granular material is recommended to protect fine-grained, footing subgrades from foot traffic during inclement weather. The imported granular material should be in conformance with Section 5.4.2. The maximum particle size should be limited to 1 inch. The imported

Carlson Geotechnical Page 13 of 21 granular material should be placed in one lift over the prepared, undisturbed subgrade, and compacted using non-vibratory equipment until well keyed.

Surface water should not be allowed to collect in footing excavations. The excavations should be draped and/or provided with sumps to preclude water accumulation during inclement weather.

5.4 Structural Fill

The geotechnical engineer should be provided the opportunity to review all materials considered for use as structural fill (prior to placement). Samples of the proposed fill materials should be submitted to the geotechnical engineer a minimum of 5 business days prior their use on site13. The geotechnical engineer’s representative should be contacted to evaluate compaction of structural fill as the material is being placed.

Evaluation of compaction may take the form of in-place density tests and/or proof roll tests with suitable equipment. Structural fill should be evaluated at intervals not exceeding every 2 vertical feet as the fill is being placed.

5.4.1 On-Site Soils – General Use

Recognizing the relatively limited grading (fill placement) associated with this project and their moisture sensitivity, we do not recommend re-using the onsite clayey soils as structural fill. We recommend using imported granular material for structural fill.

5.4.1.1 Asphalt Concrete Debris

Debris resulting from the demolition of existing pavements can be re-used as structural fill if processed/crushed into material that is fairly well graded between coarse and fine. The processed/crushed concrete should contain no organic matter, debris, or particles larger than 4 inches in diameter. Moisture conditioning (wetting) should be expected in order to achieve adequate compaction. When used as structural fill, this material should be placed and compacted in general accordance with Section 5.4.2.

5.4.1.2 Concrete Debris

Concrete debris resulting from the demolition of existing rigid pavements and other features (foundations, floor slabs, sidewalks, driveways, etc.) can be re-used as structural fill if processed/crushed into material that is fairly well-graded between coarse and fine. The processed/crushed concrete should contain no organic matter, debris, or particles larger than 4 inches in diameter. Moisture conditioning (wetting) should be expected in order to achieve adequate compaction. When used as structural fill, this material should be placed and compacted in general accordance with Section 5.4.2.

If the on-site materials cannot be properly moisture-conditioned and/or processed, we recommend using imported granular material for structural fill.

5.4.2 Imported Granular Structural Fill – General Use

Imported granular structural fill should consist of angular pit or quarry run rock, crushed rock, or crushed gravel that is fairly well graded between coarse and fine particle sizes. The granular fill should contain no organic matter, debris, or particles larger than 4 inches, and have less than 5 percent material passing the

U.S. Standard No. 200 Sieve. For fine-grading purposes, the maximum particle size should be limited to

1½inches. The percentage of fines can be increased to 12 percent of the material passing the U.S. Standard

No. 200 Sieve if placed during dry weather, and provided the fill material is moisture-conditioned, as necessary, for proper compaction. Imported granular fill material should be placed in lifts with a maximum

13 Laboratory testing for moisture density relationship (Proctor) is required. Tests for gradation may be required.

Carlson Geotechnical Page 14 of 21 thickness of about 12 inches, and compacted to not less than 95 percent of the material’s maximum dry density, as determined in general accordance with ASTM D1557 (Modified Proctor). Proper moisture conditioning and the use of vibratory equipment will facilitate compaction of these materials.

Granular fill materials with high percentages of particle sizes in excess of 1½ inches are considered non-moisture-density testable materials. As an alternative to conventional density testing, compaction of these materials should be evaluated by proof roll test observation (deflection tests), where accepted by the geotechnical engineer.

5.4.3 Trench Base Stabilization Material

If groundwater is present at the base of utility excavations, trench base stabilization material should be placed. Trench base stabilization material should consist of a minimum of 1 foot of well-graded granular material with a maximum particle size of 4 inches and less than 5 percent material passing the U.S. Standard

No. 4 Sieve. The material should be free of organic matter and other deleterious material, placed in one lift, and compacted until well-keyed.

5.4.4 Trench Backfill Material

Trench backfill for the utility pipe base and pipe zone should consist of granular material as recommended by the utility pipe manufacturer. Trench backfill above the pipe zone should consist of well-graded granular material containing no organic matter or debris, have a maximum particle size of ¾ inch, and have less than

8 percent material passing the U.S. Standard No. 200 Sieve. As a guideline, trench backfill should be placed in maximum 12-inch-thick lifts. The earthwork contractor may elect to use alternative lift thicknesses based on their experience with specific equipment and fill material conditions during construction in order to achieve the required compaction. The following table presents recommended relative compaction percentages for utility trench backfill.

Table 2 Utility Trench Backfill Compaction Recommendations

Backfill Zone Recommended Minimum Relative Compaction

Structural Areas1,2 Landscaping Areas

Pipe Base and Within Pipe Zone 90% ASTM D1557 or pipe manufacturer’s recommendation

88% ASTM D1557 or pipe manufacturer’s recommendation

Above Pipe Zone 92% ASTM D1557 90% ASTM D1557

Within 3 Feet of Design Subgrade 95% ASTM D1557 90% ASTM D1557

1 Includes proposed building, pavement areas, structural fill areas, exterior hardscaping, etc.

2 Or as specified by the local jurisdiction where located in the public right of way.

5.4.5 Controlled Low-Strength Material (CLSM)

CLSM is a self-compacting, cementitious material that is typically considered when backfilling localized areas. CLSM is sometimes referred to as “controlled density fill” or CDF. Due to its flowable characteristics, CLSM typically can be placed in restricted-access excavations where placing and compacting fill is difficult. If chosen for use at this site, we recommend the CLSM be in conformance with Section 00442 of the most recent, ODOT SSC. The geotechnical engineer’s representative should observe placement of the CLSM and obtain samples for compression testing in accordance with ASTM D4832. As a guideline, for each day’s placement, two compressive strength specimens from the same CLSM sample should be tested. The results of the two individual compressive strength tests should be averaged to obtain the reported 28-day

Carlson Geotechnical Page 15 of 21 compressive strength. If CLSM is considered for use on this site, please contact the geotechnical engineer for site-specific and application-specific recommendations.

5.5 Shallow Foundations

5.5.1 Subgrade Preparation

Satisfactory subgrade support for shallow foundations can be obtained from a minimum of 12 inches of imported granular structural fill (“granular pad”) that is properly placed and compacted on the native, medium stiff to better, clayey soils (CH) during construction. Once over-excavations are made, the clayey subgrade soils should not be exposed to periods of wetting or drying, but should be backfilled as soon as possible. The geotechnical engineer’s representative should be contacted to observe subgrade conditions prior to placement of forms, reinforcement steel, or granular backfill. If soft, loose, or otherwise unsuitable soils are encountered, they should be over-excavated as recommended by the geotechnical representative at the time of construction. The resulting over-excavation should be brought back to grade with imported granular structural fill in conformance with Section 5.4.2.

5.5.2 Minimum Footing Width & Embedment

Minimum footing widths should be in conformance with the current OSSC. As a guideline, CGT recommends individual spread footings have a minimum width of 24 inches. We recommend continuous wall footings have a minimum width of 18 inches. All footings should be founded at least 18 inches below the lowest, permanent adjacent grade to develop lateral capacity and for frost protection.

5.5.3 Bearing Pressure & Settlement

Footings founded as recommended above should be proportioned for a maximum allowable soil bearing pressure of 2,000 pounds per square foot (psf). This bearing pressure is a net bearing pressure, applies to the total of dead and long-term live loads, and may be increased by one-third when considering seismic or wind loads. For foundations founded as recommended above, total settlement of foundations is anticipated to be less than 1 inch. Differential settlements between adjacent columns and/or bearing walls should not exceed ½ inch. If an increased allowable soil bearing pressure is desired, the geotechnical engineer should be consulted. Please note that these recommendations are based on the assumption that undocumented fill materials and soft clayey soils will be removed from within the proposed building pad area.

5.5.4 Lateral Capacity

A maximum passive (equivalent fluid) earth pressure of 150 pounds per cubic foot (pcf) is recommended for design of footings cast neat into excavations in suitable native soil or confined by imported granular structural fill that is properly placed and compacted during construction. The recommended earth pressure was computed using a factor of safety of 1½, which is appropriate due to the amount of movement required to develop full passive resistance. In order to develop the above capacity, the following should be understood:

1. Concrete must be poured neat in excavations or the foundations must be backfilled with imported granular structural fill,

2. The adjacent grade must be level,

3. The static ground water level must remain below the base of the footings throughout the year.

4. Adjacent floor slabs, pavements, or the upper 24-inch-depth of adjacent, unpaved areas should not be considered when calculating passive resistance.

Carlson Geotechnical Page 16 of 21

An ultimate coefficient of friction equal to 0.45 may be used when calculating resistance to sliding for footings founded on a minimum of 12 inches of imported granular structural fill (crushed rock) that is properly placed and compacted during construction.

5.5.5 Subsurface Drainage

Recognizing the fine-grained alluvial soils encountered at this site, we recommend placing foundation drains at the exterior, base elevations of perimeter continuous wall footings. Foundation drains should consist of a minimum 4-inch diameter, perforated, PVC drainpipe wrapped with a non-woven geotextile filter fabric. The drains should be backfilled with a minimum of 2 cubic feet of open graded drain rock per lineal foot of pipe.

The drain rock should also be encased in a geotextile fabric in order to provide separation from the surrounding fine-grained soils. Foundation drains should be positively sloped and should outlet to a suitable discharge point. The geotechnical engineer’s representative should observe the drains prior to backfilling.

Roof drains should not be tied into foundation drains.

5.6 Rigid Retaining Walls

5.6.1 Footings

Retaining wall footings should be designed and constructed in conformance with the recommendations presented in Section 5.5, as applicable.

5.6.2 Wall Drains

We recommend placing retaining wall drains at the base elevation of the heel of retaining wall footings.

Retaining wall drains should consist of a minimum 4-inch-diameter, perforated, HDPE (High Density

Polyethylene) drainpipe wrapped with a non-woven geotextile filter fabric. The drains should be backfilled with a minimum of 2 cubic feet of open graded drain rock per lineal foot of pipe. The drain rock should be encased in a geotextile fabric in order to provide separation from the surrounding soils. Retaining wall drains should be positively sloped and should outlet to a suitable discharge point. The geotechnical engineer’s representative should be contacted to observe the drains prior to backfilling. Roof or area drains should not be tied into retaining wall drains.

5.6.3 Wall Backfill

Retaining walls should be backfilled with imported granular structural fill in conformance with Section 5.4.2 and contain less than 5 percent passing the U.S. Standard No. 200 Sieve. The backfill should be compacted to a minimum of 90 percent of the material’s maximum dry density as determined in general accordance with

ASTM D1557 (Modified Proctor). When placing fill behind walls, care must be taken to minimize undue lateral loads on the walls. Heavy compaction equipment should be kept at least “H” feet from the back of the walls, where “H” is the height of the wall. Light mechanical or hand tamping equipment should be used for compaction of backfill materials within “H” feet of the back of the walls.

5.6.4 Design Parameters & Limitations

For rigid retaining walls founded, backfilled, and drained as recommended above, the following table presents parameters recommended for design.

Carlson Geotechnical Page 17 of 21

Table 6 Design Parameters for Rigid Retaining Walls

Retaining Wall Condition

Modeled

Backfill

Condition

Static Equivalent

Fluid Pressure (SA)1

Seismic

Equivalent Fluid

Pressure (SAE) 1,2

Surcharge from

Uniform Load, q, Acting on Backfill

Behind Retaining Wall

Not Restrained from Rotation Level (i=0) 29 pcf 40 pcf 0.22*q

Restrained from Rotation Level (i=0) 52 pcf 56 pcf 0.38*q

1 Refer to the attached Figure 4 for a graphical representation of static and seismic loading conditions. Seismic resultant force acts at 0.6H above the base of the wall.

2 Seismic (dynamic) lateral loads were computed using the Mononobe-Okabe Equation as presented in the 1997 Federal

Highway Administration (FHWA) design manual. Static and seismic equivalent fluid pressures are not additive.

The above design recommendations are based on the assumptions that:

• The walls consist of concrete cantilevered retaining walls ( = 0 and = 24 degrees, see Figure 4).

• The walls are 10 feet or less in height.

• The backfill is drained and consists of imported granular structural fill ( = 38 degrees).

• The grade behind the wall is level, or sloping down and away from the wall, for a distance of 10 feet or more from the wall.

• The grade in front of the walls is level or ascending for a distance of at least 5 feet from the wall.

Re-evaluation of our recommendations will be required if the retaining wall design criteria for the project vary from these assumptions.

5.7 Floor Slabs

5.7.1 Subgrade Preparation

Satisfactory subgrade support for floor slabs constructed on grade can be obtained from a minimum of 12 inches of imported granular structural fill (subbase) that is properly placed and compacted on the native, medium stiff to better, fat clay (CH) during construction. The geotechnical engineer’s representative should be contacted to evaluate floor slab subgrade surface consistencies. If soft, loose, or otherwise unsuitable soils are encountered, they should be over-excavated as recommended by the CGT geotechnical representative at the time of construction.