1. GEOTECH REPORT Final G2306020 Geotechnical Investigation.pdf

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

G2306020 Geotechnical Investigation

Report of

Geotechnical Investigation & Infiltration Testing

Clackamas Emergency Housing

16590 SE 114th Avenue

Clackamas County, Oregon

CGT Project Number G2306020

Prepared for

Mark Sirois

Clackamas County Community Development

2051 Kaen Rd # 245

Oregon City, OR 97045

December 1, 2023 http://www.carlsontesting.com/ mailto:atenold@carlsontesting.com mailto:bwilcox@carlsontesting.com

Clackamas Emergency Housing

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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 Design

3.2 Seismic Hazards

4.0 CONCLUSIONS

5.0 RECOMMENDATIONS

5.1 Site Preparation

5.2 Temporary Excavations

5.3 Wet Weather Considerations

5.4 Structural Fill

5.5 Permanent Slopes

5.6 Shallow Foundations

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

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

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

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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 and infiltration testing for the proposed Clackamas

Emergency Housing project. The site is located at 16590 SE 114th Avenue in Clackamas County, 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 Base Design +

Architecture, LLC, and project documents provided to us on September 22 and 29, 2023. The documents provided included a Schematic Design Site Plan, prepared by BDA, dated July 28, 2023. Based on our review, we understand the project will include:

Construction of four new, multi dwelling structures as well as an office and facility buildings (bathrooms, kitchen, laundry) to serve the new dwellings. The buildings will be one story, wood-framed, with a slab on grade floor. The multi dwelling structures have an approximate footprint of 960 square feet with a deck.

For the purposes of this report, we have assumed maximum column, continuous wall, and uniform floor slab loads will be on the order of 25 kips, 2 kips per lineal foot (klf), and 150 pounds per square foot

(psf), respectively.

Construction of a parking lot and trash enclosure on the western portion of the site and a pathway to access the dwellings. We anticipate the parking lot will be surfaced with asphalt concrete (AC).

Although no stormwater management plans have been provided, we understand that, if conditions allow, stormwater collected from new impervious areas of the site will be disposed of, at least in part, via onsite infiltration. Design of on-site stormwater facilities will rest with others. Two infiltration tests were requested in the northeastern and northwestern portions of the site as part of this assignment.

Although no grading plans have been provided, we anticipate permanent grade changes at the site will be minimal, with maximum cuts and fills on the order of 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.

Explore subsurface conditions at the site by observing the excavation of thirteen test pits to depths of up to about 9½ feet below ground surface (bgs). Details of the subsurface investigation are presented in

Appendix A.

Conduct infiltration testing in two of the test pits. Results of the infiltration testing 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.

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

Provide geotechnical recommendations for site preparation and earthwork.

Provide geotechnical engineering recommendations for use in design and construction of shallow foundations, 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 1,2 of the area, the site is underlain by younger terrace deposits of the

Clackamas River. The terrace deposits were produced by the periodic buildup of fluvial deposits about

10,000 years ago, which flank the current channel and floodplain of the Clackamas River. The terrace deposits typically consist of unconsolidated sand, gravel and cobbles. Based on nearby well logs, this unit extends to depths in excess of 100 feet below ground surface in the vicinity of the site.

2.2 Site Surface Conditions

During our field investigation, the approximate 3¾-acre site was bordered by commercial properties to the north, east and south, and an emergency housing pods facility to the west. Lithgow Creek was observed to cut across the southern portion of the site. The site was terraced; the upper portion (area of proposed site development) was relatively flat and then descended to the south at gradients of up to 1¾ horizontal to 1 vertical (1¾H:1V), to the southern portion which was also relatively flat. Partially buried structures (e.g.

foundations and retaining walls) were observed near the crest of the upper terrace. A relatively large soil stockpile was observed in the eastern portion of the upper terrace. Site layout and surface conditions at the time of our field investigation 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 thirteen test pits (TP-1 through TP-13) completed on November

10, 2023. While onsite we also observed and logged an additional test pit (TP-14) which had been excavated by others prior to our arrival onsite. The approximate exploration locations are shown on the Site Plan, attached as Figure 2. In summary, the test pits were excavated to depths ranging from about 3 to 9½ 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 investigation are summarized below.

Wells, R.E., Haugerud, R.A., Niem, A.R., Niem, W.A., Ma, Lina, Evarts, R.C., O’Connor, J.E., Madin, I.P., Sherrod, D.R., Beeson, M.H., Tolan, T.L., Wheeler, K.L., Hanson, W.B., and Sawlan, M.G., 2020. Geologic map of the greater Portland metropolitan area and surrounding region, Oregon and Washington: U.S. Geological Survey, Scientific Investigations Map SIM-3443. scale 1:63,360.

Ma, L., Madin, I.P., Duplantis, S., and Williams, K.J., 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 0-2012-02, scale 1:8,000.

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2.3.2 Subsurface Materials

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

2.3.2.1 Site Soils

Undocumented Poorly Graded Gravel with Sand and Cobbles Fill (GP Fill)

Undocumented poorly graded gravelly fill was encountered at the surface of TP-1 through TP-12.

Undocumented fill refers to materials placed without (available) records of subgrade conditions or evaluation of compaction. The poorly graded gravel fill was typically brown to gray, moist, subrounded to subangular, and contained varying amounts of cobbles up to 12-inches in diameter, and varying amounts of sand and silt fines. Varying amounts of debris was also observed within the fill soil, the debris consisted of glass, metal, plastic, concrete, brick and asphalt pieces up to 4 inches in diameter. The fill soil extended to depths of about

1 to 2½ feet bgs in TP-1 through TP-12.

Poorly Graded Gravel with Sand, Cobbles and Boulders (GP-GM)

Underlying the undocumented fill soils in TP-1 through TP-12 was native, poorly graded gravelly soil. This soil was typically dense, dark brown, moist, contained subangular gravel and cobbles up to 12-inches in diameter, a varying amount of boulders up to 18-inches in diameter, and a varying amount of silt and sand.

Some caving was observed in this material at depths of about 3 to 9½ feet bgs. This soil extended to the full depth explored in TP-1 through TP-12, about 3 to 9½ feet bgs.

The native soils encountered during our subsurface investigation were consistent with the lower Clackamas

River terrace deposits described in Section 2.1.

2.3.2.2 Stockpiled Soils

Exploration TP-13 and TP-14 were excavated into the existing soil stockpile that was observed on the eastern portion of the site. The log for TP-14 was based on the observations made of the sidewalls of the excavation.

Undocumented Poorly Graded Silty Gravel to Gravel with Sand Fill (GM Fill, GP Fill)

Undocumented gravelly fill was observed at the surface of TP-13 and TP-14. This soil was gray/brown to brown, moist to wet, angular to subrounded, up to 2-inches in diameter, and contained varying amounts of sand and silt. Varying amounts of debris consisting of plastic, brick, concrete and asphalt chunks up to 2 feet long. The stockpiled soil extended to a depth of about 2 feet bgs in TP-14. In TP-13, the silty gravel fill extended to the full depth explored, about 6 feet bgs.

Undocumented Silt with Sand Fill (ML Fill)

Underlying the undocumented silty gravel fill in TP-14, we observed undocumented silt with sand fill. This soil was typically gray/brown, wet, and exhibited low plasticity. This soil extended the full depth of the excavation, about 6 feet bgs.

2.3.3 Groundwater

We did not encounter groundwater within the depths explored at the site on November 10, 2023. To determine approximate regional groundwater levels in the area, we researched well logs available on the

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Oregon Water Resources Department (OWRD) website for wells located within Section 15, Township 2

South, Range 2 East, Willamette Meridian. Our review indicated that groundwater levels in the area generally ranged from about 45 to 65 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.

The depth to groundwater map for the Portland area indicates groundwater is present at depths of 30 feet bgs in the vicinity of the site. It should be noted that the levels reported by the referenced map are average values for a given location and incorporate a degree of uncertainty.

3.0 SEISMIC CONSIDERATIONS

3.1 Seismic Design

Section 1613.2.2 of the 2022 Oregon Structural Specialty Code (2022 OSSC) requires that the determination of the seismic site class be in accordance with Chapter 20 of the American Society of Civil Engineers

Minimum Design Loads for Buildings and Other Structures (ASCE 7-16). We have assigned the site as Site

Class D (“Stiff Soil”) based on geologic mapping and subsurface conditions encountered during our investigation. Earthquake ground motion parameters for the site were obtained in accordance with the 2022

OSSC using the Seismic Hazards by Location calculator on the ATC website . The site Latitude 45.401263°

North and Longitude 122.54433° 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

Parameter Value

Mapped Acceleration Parameters Spectral Acceleration, 0.2 second (Ss) 0.833g

Spectral Acceleration, 1.0 second (S1) 0.368g

Coefficients

(Site Class D)

Site Coefficient, 0.2 second (FA) 1.167

Site Coefficient, 1.0 second (FV) 1.932

Adjusted MCE Spectral

Response Parameters

MCE Spectral Acceleration, 0.2 second (SMS ) 0.972g

MCE Spectral Acceleration, 1.0 second (SM1 ) 0.711g

Design Spectral Response Accelerations Design Spectral Acceleration, 0.2 second (SDS ) 0.648g

Design Spectral Acceleration, 1.0 second (SD1 ) 0.474g

Seismic Design Category (Risk Category II) D

Value determined from 2022 OSSC Table 1613.2.3(2).

Oregon Water Resources Department, 2023. Well Log Records, accessed November 2023, from OWRD web site:

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

Snyder, D.T., 2008, Estimated depth to ground water and configuration of the water table in the Portland, Oregon area: U.S.

Geological Survey, Scientific Investigations Report SIR-2008-5059, scale 1:60,000.

Applied Technology Council (ATC), 2023. USGS seismic design parameters determined using “Seismic Hazards by Location,” accessed November 2023, from the ATC website https://hazards.atcouncil.org/.

http://apps.wrd.state.or.us/apps/gw/well_log/ https://hazards.atcouncil.org/

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3.2 Seismic Hazards

3.2.1 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 soils 6,7,8

. The susceptibility of sands, gravels, and sand-gravel mixtures to liquefaction is typically assessed based on penetration resistance, as measured using SPTs, CPTs, or

Becker Hammer Penetration tests (BPTs).

Based on their dense relative density, lack of saturated conditions, static groundwater, etc., the coarse-grained soils encountered within our explorations are considered non-liquefiable. Based on review of geologic mapping and our previous experience in the area, we do not anticipate liquefiable conditions are present at depths below those explored as part of this assignment.

3.2.2 Slope Instability

We did not observe any obvious signs of past or on-going slope instability at the site. Review of the

Statewide Landslide Information Database for Oregon (SLIDO), available at the DOGAMI website , shows no historic or prehistoric landslides at or in the immediate vicinity of the site. HazVu shows a moderate to high hazard for landslides at the site, however, we anticipate those hazard levels were assigned based on the on-site slope gradients. Given the lack of evidence of previous landslides in the vicinity, and our observations while onsite, the risk of seismically-induced slope instability occurring at the site is considered low. Provided our recommendations for grading and stormwater management, as described below, are followed, the proposed development is not anticipated to increase this risk.

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.

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.

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

MNO-12.

Oregon Department of Geology and Mineral Industries, 2023. Statewide Landslide Information Database for Oregon (SLIDO), accessed November 2023, from DOGAMI web site: https://gis.dogami.oregon.gov/maps/slido/.

https://gis.dogami.oregon.gov/maps/slido/

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3.2.3 Surface Rupture

3.2.3.1 Faulting

Although the site is situated in a region of the country with known active faults and historic seismic activity, no known faults exist on or immediately adjacent to the site. Therefore, the risk of surface rupture at the site due to faulting is considered low.

3.2.3.2 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. Based on the non-liquefiable nature of the soils at the site, the risk of damage associated with lateral spread is negligible.

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. Satisfactory subgrade support for planned shallow foundations, floor slabs, and pavements can be achieved by the native, medium dense to dense, gravelly soils (GP, GP-GM), or structural fill that is properly placed and compacted on these materials during construction. These soils were encountered at depths of 1 to 2½ feet bgs within our explorations.

As indicated in Section 2.3.2 of this report, the subsurface explorations indicate the majority of the proposed development site is underlain by undocumented poorly graded gravel fill (GP Fill) containing a varying amount of refuse and construction debris and extending to depths of up to about 2½ feet bgs. Based on the presence of debris, it is evident the existing fills were not placed and compacted in accordance with typical code requirements for structural fill. Due to the risk of excessive, total and differential settlements, we do not recommend relying on the undocumented fill for support of shallow foundations, floor slabs or pavements.

Where encountered at design subgrade elevations for those features, the undocumented fill materials should be over-excavated and replaced with structural fill in conformance with section 5.4 of this report.

Based on our explorations, isolated boulders may be encountered at design subgrade elevations for shallow foundations. Structural elements placed directly on boulders can result in uneven ground response. To minimize this potential, CGT recommends that boulders (i.e. particles in excess of 12-inches in diameter) encountered during foundation subgrade preparation be removed in their entirety and replaced with imported granular structural fill.

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 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.

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5.1 Site Preparation

5.1.1 Demolition

As shown on Photograph 3 on Figure 3, partially buried remnants of former buildings were observed along the crest of the upper terrace. Demolition of remnants of former buildings and appurtenant structures should include complete removal of all structural elements, including foundations and concrete slabs, where encountered in planned building pads, structural fill areas, and pavement areas. 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 (GM Fill, GP Fill) should be removed from within, and for a minimum 5-foot margin around, proposed building pad, structural fill, and pavement areas.

Based on the results of our field explorations, undocumented fill encountered at the site extended to depths of up to 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 Test Pit Backfills

The test pits conducted at the site by CGT were loosely backfilled during our field investigation. Where test pits are located within finalized building, structural fill, or pavement areas, the loose backfill materials should be re-excavated. The resulting excavations should be backfilled with structural fill in conformance with

Section 5.4 of this report.

5.1.5 Existing Utilities & Below-Grade Structures

All existing utilities at the site should be identified prior to excavation. Abandoned utility lines beneath the new buildings, 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 within, and for a minimum 5-foot margin around, the proposed building pad and pavement areas, should be completely removed and replaced with structural fill in conformance with Section 5.4 of this report.

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5.1.6 Subgrade Preparation – Building Pads & Pavements

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. 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 5.4.3 of this report.

5.1.7 Erosion Control

Erosion and sedimentation control measures should be employed in accordance with applicable 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

“C” should be used for the granular soils (GP) encountered within our explorations.

5.2.3 Utility Trenches

As evidenced during excavation of the test pits, caving of the native gravelly soils may be encountered in excavations extending more than a few feet below the ground surface. 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. Although not anticipated, 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 5.4.4.

5.2.4 Excavations Near Foundations

Excavations near footings should not extend within a 1 horizontal to 1 vertical (1H: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.

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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.

Due to their coarse-grained nature and the relative lack of fines, the native gravelly soils (GP, GP-GM) are not considered susceptible to disturbance during wet weather. The gravelly soils are anticipated to perform well under repeated construction traffic during wet weather conditions.

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 site

. 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

5.4.1.1 Concrete Debris

Concrete debris resulting from the demolition of existing buried structures and other features (foundations, retaining walls.) 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 5.4.3.

5.4.1.2 Poorly Graded Gravel (GP, GP-GM, GP Fill)

Re-use of the on-site, relatively clean, gravelly soils as structural fill is feasible, provided the materials are kept clean of organics, debris, and particles larger than 4 inches in diameter. Re-use of the on-site gravelly fill soils will likely require processing (removal) of large cobbles, occasional boulders, and debris. If reused as structural fill, these materials should be prepared in general accordance with Section 5.4.3.

5.4.2 Stockpiled Soils (GP Fill, GM Fill, ML Fill)

Re-use of the stockpiled soils (as shown on Figure 2) as structural fill may be very difficult based on the observed refuse and construction debris observed within the stockpiled soil. Re-use of the stockpiled soil will require blending of the soil to reach a homogeneous state, and processing (removal) of trash and construction debris as well as large cobbles. The moisture sensitivity of the silty soils observed in a portion of the stockpile (TP-14) should also be taken into account. These soils are sensitive to small changes in moisture content and are difficult, if not impossible, to adequately compact during wet weather. We anticipate the moisture content of these soils will be higher than the optimum moisture content for satisfactory

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

Carlson Geotechnical Page 13 of 19 compaction. Therefore, moisture conditioning (drying) should be expected in order to achieve adequate compaction. Where properly processed and moisture-conditioned, these materials should be placed in lifts with a maximum 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).

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

5.4.3 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

1½ inches. 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 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.

5.4.4 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.

5.4.5 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.

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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

85% ASTM D1557 or pipe manufacturer’s recommendation

Above Pipe Zone 92% ASTM D1557 88% ASTM D1557

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

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

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

5.4.6 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 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 Permanent Slopes

Permanent cut slopes constructed at the site should be graded at 2H:1V or flatter. The surface of all slopes should be protected from erosion by seeding, sodding, or other acceptable means. Adjacent on-site and off-site structures should be located at least 5 feet from the top of slopes. Although not anticipated for this project, in the event fill slopes are to be constructed on portions of the site exhibiting gradients steeper than

5H:1V, the geotechnical engineer should be consulted to review the proposed construction and provide specific recommendations for preparation of sloping surfaces.

5.6 Shallow Foundations

5.6.1 Subgrade Preparation

Satisfactory subgrade support for shallow foundations can be obtained from a minimum 4 inches of imported granular structural fill (granular pads) placed on the native, medium dense to dense, gravelly soils (GP, GP-

GM), or new structural fill that is properly placed and compacted on these materials during construction. The granular pads are recommended to assist with fine-grading and help achieve a more uniform surface for foundation concrete.

The geotechnical engineer’s representative should be contacted to observe subgrade conditions prior to placement of the granular pads. 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. Boulders encountered within foundation excavations should similarly be removed. The resulting over-excavation(s) should be brought back to grade with imported granular structural fill in conformance with Section 5.4.3. The

Carlson Geotechnical Page 15 of 19 maximum particle size of over-excavation backfill should be limited to 1½ inches. All granular pads for footings should be constructed a minimum of 6 inches wider on each side of the footing for every vertical foot of over-excavation.

5.6.2 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. For one- to two-story, light framed structures, we recommend continuous wall footings have a minimum width of 12 inches and 15 inches respectively. All footings should be founded at least 18 inches below the lowest, permanent adjacent grade to develop lateral capacity and for frost protection.

5.6.3 Horizontal Setback from Descending Slopes

Foundations constructed within or near descending slopes should be setback a minimum of 8 feet from the slope surface. This distance should be measured between the face of the slope and the bottom, outside edge of the respective foundation. Organic topsoil and loose surface soils (if present) should not be included when determining this distance. The geotechnical engineer or his representative should be contacted to observe foundation subgrade conditions and confirm this recommended minimum setback is achieved.

5.6.4 Bearing Pressure & Settlement

Footings founded as recommended above should be proportioned for a maximum allowable soil bearing pressure of 2,500 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.

5.6.5 Lateral Capacity

A maximum passive (equivalent fluid) earth pressure of 300 pounds per cubic foot (pcf) is recommended for design of footings cast neat into excavations in suitable native soil or confined by 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 12-inch-depth of adjacent, unpaved areas should not be considered when calculating passive resistance.

An ultimate coefficient of friction equal to 0.45 may be used when calculating resistance to sliding for footings founded as recommended above.

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5.7 Floor Slabs

5.7.1 Subgrade Preparation

Satisfactory subgrade support for slabs constructed on grade, supporting up to 150 psf area loading, can be obtained from the native, medium dense to better, poorly graded gravel (GP, GP-GM), or new structural fill that is properly placed and compacted on these materials during construction. The geotechnical engineer’s representative should observe floor slab subgrade soils to evaluate 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. The resulting over-excavation should be brought back to grade with imported granular structural fill as described in Section 5.4.3.

5.7.2 Crushed Rock Base

Concrete floor slabs should be supported on a minimum 6-inch-thick layer of crushed rock (base rock).

5.7.2.1 Conventional Base Rock

Floor slab base rock should consist of well-graded granular material (crushed rock) containing no organic matter or debris, have a maximum particle size of ¾ inch, and have less than 5 percent material passing the

U.S. Standard No. 200 Sieve. Floor slab base rock should be placed in one lift 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). We recommend “choking” the surface of the base rock with sand just prior to concrete placement. Choking means the voids between the largest aggregate particles are filled with sand, but does not provide a layer of sand above the base rock. Choking the base rock surface reduces the lateral restraint on the bottom of the concrete during curing. Choking the base rock also reduces punctures in vapor retarding membranes due to foot traffic where such membranes are used.

5.7.2.2 Gas Permeable Base Rock

Floor slab base rock in areas where radon gas mitigation is desired should consist of open-graded crushed rock containing no organic matter or debris, with all material passing through a 2-inch sieve and retained on the ¼-inch sieve, in accordance with Section 1812.2.1, Bullet 1, of the 2022 OSSC.

CGT recommends that a minimum 10-mil polyethylene sheeting or equivalent material with equal or greater tensile strength, resistance to puncture, resistance to deterioration, and resistance to water-vapor transmission be placed on top of the gas-permeable base rock to act as a soil-gas-retarder. Placement and installation of this sheeting should be in conformance with that indicated in Section 1812.2.2 of the

2022 OSSC.

The geotechnical engineer or their representative should be contacted to observe gas-permeable base rock conditions prior to placement of the soil-gas-retarder.

5.7.3 Design Considerations

For floor slabs constructed as recommended, an effective modulus of subgrade reaction of 400 pounds per cubic inch (pci) is recommended for the design of the floor slab. A higher effective modulus of subgrade reaction can be obtained by increasing the base rock thickness. Please contact the geotechnical engineer for additional recommendations if a higher modulus is desired. Floor slabs constructed as recommended will likely settle less than ½ inch. For general floor slab construction, slabs should be jointed around columns and walls to permit slabs and foundations to settle differentially.

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5.7.4 Subgrade Moisture Considerations

Liquid moisture and moisture vapor should be expected at the subgrade surface. The recommended crushed rock base is anticipated to provide protection against liquid moisture. Where moisture vapor emission through the slab must be minimized, e.g. impervious floor coverings, storage of moisture sensitive materials directly on the slab surface, etc., a vapor retarding membrane or vapor barrier below the slab should be considered. Factors such as cost, special considerations for construction, floor coverings, and end use suggest that the decision regarding a vapor retarding membrane or vapor barrier be made by the architect and owner.

If a vapor retarder or vapor barrier is placed below the slab, its location should be based on current American

Concrete Institute (ACI) guidelines, ACI 302 Guide for Concrete Floor and Slab Construction. In some cases, this indicates placement of concrete directly on the vapor retarder or barrier. Please note that the placement of concrete directly on impervious membranes increases the risk of plastic shrinkage cracking and slab curling in the concrete. Construction practices to reduce or eliminate such risk, as described in ACI 302, should be employed during concrete placement.

5.8 Pavements

5.8.1 Subgrade Preparation

Pavement subgrade preparation should be performed in general accordance with the recommendations presented in Section 5.1.6 above. Subgrade surfaces should be crowned (or sloped) for proper drainage in accordance with specifications provided by the project civil engineer.

5.8.2 Pavement Design Sections

Recommendations for pavement design sections were not included as part of this assignment, but could be provided, upon request, for an additional fee.

5.9 Additional Considerations

5.9.1 Drainage

Subsurface drains should be connected to the nearest storm drain, on-site infiltration system (to be designed by others) or other suitable discharge point. Paved surfaces and grading near or adjacent to the buildings should be sloped to drain away from the buildings. Surface water from paved surfaces and open spaces should be collected and routed to a suitable discharge point. Surface water should not be directed into foundation drains, if incorporated, or onto site slopes.

5.9.2 Expansive Potential

The near surface native soils consist of gravelly soils with minimal fines. These soils are not considered to be susceptible to appreciable movements from changes in moisture content. Accordingly, no special considerations are required to mitigate expansive potential of the near surface soils at the site.

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6.0 RECOMMENDED ADDITIONAL SERVICES

6.1 Design Review

Geotechnical design review is of paramount…