Encl5_Geotechnical Investigation.pdf

Carlson Geotechnical 35 SE Bridgeford Blvd, Bend, Oregon 97702

Carlson Geotechnical A division of Carlson Testing, Inc.

Phone: (541) 330-9155 Fax: (541) 330-9163

Bend Office Eugene Office Salem Office Tigard Office

(541) 330-9155

(541) 345-0289

(503) 589-1252

(503) 684-3460

Report of

Geotechnical Investigation & Infiltration Testing

Redmond Air Center Smokejumpers Training Facility

1740 SE Ochoco Way

Redmond, Oregon

CGT Project Number B1908501

Prepared for

Pinnacle Architecture

Attn: Mr. Peter Baer

960 SW Disk Drive, Suite 101

Bend, Oregon 97702

April 10, 2019

Encl 5

Redmond Air Center Smokejumper Training Facility Redmond, Oregon CGT Project Number B1908501

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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 Rigid Retaining Walls

5.8 Floor Slabs

5.9 Pavements

5.10 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

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

Redmond Air Center Smokejumper Training Facility project. The site is located at 1740 SE Ochoco Way in Redmond, 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 initial email correspondence in

December 2018, review of the provided project documents, and subsequent correspondence in early

2019. Based on our review, we understand the project will include:

Demolition and removal of the existing building and appurtenant hardscaping features.

Construction of a new, one-story, slab-on-grade, 5,700 square-foot, office building. No below-grade levels (basements) are anticipated. Although no structural information has been provided, we assume loads will be typical for this type of building, with maximum column, continuous wall, and uniform slab loads on the order of 50 kips, 3 kips per lineal foot (klf), and 200 pounds per square foot

(psf), respectively. We understand the building will be classified as Risk Category II in accordance with Table 1604.5 of the current Oregon Structural Specialty Code (OSSC).

Installation of appurtenant hardscaping features and utilities to serve the new building.

Permanent grade changes at the site are anticipated to be relatively minimal, with cuts and fills generally limited to less than 3 feet in depth.

We understand stormwater runoff from new impervious areas at the site will be collected and discharged into an onsite stormwater collection facility(ies). Design of the facility(ies) will rest with others. Infiltration testing was requested as part of this assignment.

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 30-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 excavating five test pits to practical refusal depths of up to about 4½ 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 and rock encountered in the test pits in general accordance with American Society for Testing and Materials (ASTM) D2488 (Visual-Manual Procedure) and the ODOT Rock

Classification Criteria, respectively.

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.

Collect representative, disturbed samples of the soils encountered within the explorations in order to perform laboratory testing and confirm our field classifications.

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Perform laboratory testing on selected samples collected during our subsurface exploration.

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.

Provide geotechnical recommendations for site preparation and earthwork.

Provide geotechnical engineering recommendations for use in design and construction of shallow foundations, floor slabs, retaining walls, and subgrade preparation for 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 Basalt of Newberry volcano

(Qbn). The basalt of Newbery consists of flows of medium to dark gray, porphyritic, vesicular, basalt and basaltic andesite erupted from vents around Newberry volcano southeast of the site. Cooling of the basalt produced typically columnar or blocky fracture patterns with spacing commonly on the order of 1 to

3 feet. The unit includes flows of different ages with some of the oldest flows offset by faulting, while the youngest have spilled over fault scarps in the older flows. Localized voids and lava tubes are somewhat common within this unit, with several prominent lava tubes mapped southeast of Bend. The thickness of this unit varies widely, from a few tens of feet to greater than 3,000 feet, but is generally thinner with increasing distance from Newberry Volcano. Published geologic cross sections suggest that this unit is about 50 to 100 feet thick at and near the site. The mapping indicates these basalt flows are typically mantled in several feet of sandy soils that were blown in or deposited by ancestral streams and rivers and generally underlain by pyroclastic deposits (scoria, pumice, and lapilli and ash tuff) and older basalt flows.

2.2 Site Surface Conditions

The site is located within the Redmond Air Center. At the time of our field investigation, the area of the proposed building was occupied by the existing Aspen Barracks building, grass lawns, and hardscaping features (sidewalks). In terms of topography, the site was relatively level to very gently descending to the west at an approximate slope gradient of 9H:1V (Horizontal:Vertical) with about 6 feet of vertical relief.

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 five test pits (TP-1 though TP-3, IT-1, and IT-2) and two infiltration tests (IT-1 and IT-2) completed on March 29, 2019. The approximate exploration locations are shown on the Site Plan, attached as Figure 2. In summary, the test pits were excavated using a Takeuchi

Sherrod, David R., et al., 2004. Geologic Map of the Bend 30- X 60-Minute Quadrangle, Central Oregon. United States

Geological Survey, Geologic Investigations Series Map I-2683.

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TB 260 Mini Excavator to practical refusal depths ranging from about 1 to 4½ feet bgs. Details regarding the subsurface investigation, logs of the explorations, and results of laboratory testing are presented in

Appendix A. Results of the infiltration tests are presented in the attached Appendix B. Subsurface conditions encountered during our investigation are summarized below.

2.3.2 Subsurface Materials

Logs of the explorations are presented in Appendix A. The following describes each of the subsurface materials encountered at the site.

Sandy Organic Soil (OL)

Sandy organic soil (topsoil) was encountered at the surface of all of the test pits. The sandy organic soil was typically loose to medium dense, brown, moist, fine- to medium-grained, and contained non-plastic fines and varying amounts of rootlets and roots up to 1½-inches in diameter. This soil extended to depths ranging from about ½ to 1 foot bgs.

Silty Sand (SM)

Native silty sand was encountered underlying the sandy organic soil in all of the test pits. The native silty sand was generally medium dense to dense, moist, tan and brown, fine- to medium-grained, subangular to subrounded, and contained varying amounts of brown, subangular to subrounded, gravel and cobbles up to 6 inches in diameter. This soil extended to depths ranging from about 1½ to 4½ feet bgs.

Basalt Bedrock (RX)

Basalt bedrock was encountered beneath the native silty sand in all of the test pits at depths ranging from about 1½ to 4½ feet bgs. The basalt bedrock was hard (R4), tan and gray, fresh, and vesicular. The referenced Takeuchi TB260 excavator encountered practical digging refusal within the upper few inches of the intact basalt bedrock.

2.3.3 Groundwater

Groundwater was not encountered within the depths explored on March 29, 2019. To determine approximate regional groundwater levels in the area, we researched well logs available on the Oregon

Water Resources Department (OWRD) website for wells located within Section 22, Township 15 South, Range 13 East, Willamette Meridian. Our review indicated that groundwater levels in the area are greater than 300 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.

Oregon Water Resources Department, 2019. Well Log Records, accessed April 2019 from OWRD web site:

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

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

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3.0 SEISMIC CONSIDERATIONS

3.1 Seismic Design

Section 1613.3.2 of the 2014 Oregon Structural Specialty Code (2014 OSSC) requires that the determination of the seismic site class be based on subsurface data in accordance with Chapter 20 of the

American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures (ASCE 7).

Based on the results of the explorations and review of geologic mapping, we have assigned the site as

Site Class C for the subsurface conditions encountered.

Earthquake ground motion parameters for the site were obtained in accordance with the 2014 OSSC using the Seismic Hazards by Location calculator on the ATC website . The site Latitude 44.260102°

North and Longitude 121.146716° 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) 0.383g

Spectral Acceleration, 1.0 second (S1) 0.195g

Coefficients

(Site Class C)

Site Coefficient, 0.2 sec. (FA) 1.200

Site Coefficient, 1.0 sec. (FV) 1.605

Adjusted MCE Spectral

Response Parameters

MCE Spectral Acceleration, 0.2 sec. (SMS ) 0.460g

MCE Spectral Acceleration, 1.0 sec. (SM1 ) 0.313g

Design Spectral Response

Accelerations

Design Spectral Acceleration, 0.2 seconds (SDS ) 0.307g

Design Spectral Acceleration, 1.0 second (SD1 ) 0.209g

Seismic Design Category D

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. Based on the lack of saturated conditions and presence of shallow bedrock, the soils encountered within our explorations are considered non-liquefiable.

Applied Technology Council (ATC), 2019. USGS seismic design parameters determined using “Seismic Hazards by Location,” accessed April 2019, from the ATC website https://hazards.atcouncil.org/.

https://hazards.atcouncil.org/

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3.2.2 Slope Instability

Due to the relatively level topography at and in the immediate vicinity of the site, the risk of slope instability at the site is considered negligible.

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 considered to be 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 obtained from the native, medium dense to better, silty sand (SM), the basalt bedrock

(RX), or new structural fill that is properly placed and compacted on these materials during construction.

These soils were first encountered at depths of about ½ to 1 foot bgs in the test pits.

The primary geotechnical consideration for this project is the presence of near-surface, relatively fresh, hard (R4), basalt bedrock. As shown on the attached Site Plan, we encountered practical digging refusal of the excavating equipment on the basalt bedrock at depths of about 1½ to 4½ feet bgs during our field investigation. The presence of shallow bedrock should be factored when considering temporary excavations necessary to install shallow foundations and other below-grade features (e.g. utilities) at the site. We do not anticipate that excavation of the basalt bedrock using conventional excavation equipment will be feasible. Depending on finalized elevations, we anticipate hydraulic hammering of the bedrock will likely be required to facilitate its removal. Hydraulic hammering, if required, likely will result in increased cost and should be factored in planning. Geotechnical recommendations for temporary excavations are presented in Section 5.2 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 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

Carlson Geotechnical Page 9 of 20 development changes and/or variations or undesirable geotechnical conditions are encountered during site development.

5.1 Site Preparation

5.1.1 Demolition

Demolition of the existing building 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 asphaltic 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 and sandy organic topsoil (OL) should be removed from within, and for a minimum

5-foot margin around (where feasible), proposed structural fill, building pad, and pavement areas. Based on the results of our field explorations, topsoil stripping depths are anticipated to extend to depths of about ½ to 1 foot bgs. These materials may be deeper or shallower at locations away from the completed explorations. The geotechnical engineer or his representative should provide recommendations for actual stripping depths based on observations during site stripping. Stripped surface vegetation, and organic soils should be transported off-site for disposal, or stockpiled for later use in landscaped areas.

5.1.3 Grubbing

Grubbing of trees and shrubs 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 5.4.2 of this report.

5.1.4 Test Pit Backfills

The test pits conducted at the site 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 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.

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5.1.6 Subgrade Preparation – Building Pad & Areas to Receive Structural Fill

5.1.6.1 Dry Weather Construction

After site preparation as recommended above, but prior to placement of structural fill and/or aggregate base, the geotechnical engineer or their 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 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, stable subgrade, and replaced with imported granular structural fill in conformance with Section 5.4.2 of this report.

5.1.6.2 Wet Weather Construction

Preparation of subgrade soils during wet weather should be in conformance with Section 5.3 of this report. As indicated therein, increased base rock sections and a geotextile separation fabric may be required in wet conditions in order to support construction traffic and protect the subgrade.

5.1.7 Freezing Weather Considerations

For construction that occurs during extended periods of sub-freezing temperatures, the following special provisions are recommended:

Structural fill should not be placed over frozen ground.

Frozen soil should not be placed as structural fill.

Fine-grained (silty) soils should not be placed as structural fill during sub-freezing temperatures.

Identification of frozen soils at the site should be in accordance with ASTM D4083-01 “Standard Practice for Description of Frozen Soils (Visual-Manual Procedure)” or other approved method. The geotechnical engineer can aid the contractor with supplemental recommendations for earthwork that will take place during extended periods of sub-freezing weather, as required.

5.1.8 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. However, where temporary excavations extend into basalt bedrock, we anticipate hydraulic hammering will likely be required to facilitate its removal. 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

Carlson Geotechnical Page 11 of 20 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

5.2.2.1 Silty Sand (SM)

Conventional earthmoving equipment in proper working condition should be capable of making necessary excavations into the on-site sandy soils. For use in the planning and construction of temporary excavations at the site, an OSHA soil type “C” may should be used for the native, silty sand (SM). Some caving or sloughing of the sidewalls may occur in dry, cohesionless soils. In the event that caving of the sidewalls is observed, the sidewalls should be flattened or shored.

5.2.2.2 Basalt Bedrock (RX)

The basalt bedrock encountered in the test pits was relatively fresh and hard (R4). An OSHA soil type

“stable rock” may be used for the basalt bedrock during planning and construction of temporary excavations at the site extending into this material. We anticipate that excavation of the bedrock using conventional excavation equipment will not be feasible. Hydraulic hammering will likely be required to facilitate excavation of the bedrock. Blasting of the basalt bedrock is not recommended due to the site’s proximity to offsite development. If the contractor proposes blasting, the geotechnical engineer should be engaged early in the design process to review pre-construction surveys, design, and monitoring plans.

5.2.3 Utility Trenches

Temporary trench cuts should stand near vertical to depths of approximately 4 feet bgs in the native, silty sand (SM) and basalt bedrock (RX) encountered at the site. If caving of the sidewalls 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 present at the base of utility excavations, we recommend placing trench stabilization material at the base of the excavations. Trench stabilization material should be in conformance with Section 5.4.3 of this report.

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.

5.3 Wet Weather Considerations

Notwithstanding the generally arid conditions of the Redmond area, soil conditions should be evaluated in the field by the geotechnical engineer or his representative at the initial stage of site preparation to determine whether the recommendations within this section should be incorporated into construction.

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5.3.1 Overview

Due to its fines content, the near-surface silty sand (SM) is moisture sensitive and susceptible to disturbance during wet weather. Trafficability of this soil 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. 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 or their 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, stable subgrade, and replaced with imported granular structural fill in conformance with Section 5.4.2 of this report.

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, 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

10 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 excavation 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 granular material should be placed in one lift over the prepared, undisturbed subgrade, and compacted using non-vibratory equipment until well keyed.

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 or their representative should be contacted to evaluate compaction of structural fill as the material is

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

Carlson Geotechnical Page 13 of 20 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

5.4.1.1 Asphalt & Concrete Debris

Asphalt and concrete debris resulting from the demolition of existing foundations, slabs, and 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 and/or asphalt 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 of this report.

5.4.1.2 Silty Sand (SM)

Re-use of this soil as structural fill may be difficult because this soil is sensitive to small changes in moisture content and is difficult, if not impossible, to adequately compact during wet weather. We anticipate the moisture content of this soil will be higher than the optimum moisture content for satisfactory compaction. Therefore, moisture conditioning (drying) should be expected in order to achieve adequate compaction. If used as structural fill, this soil should be free of organic matter, debris, and particles larger than 4 inches. When used as structural fill, this soil should be placed in lifts with a maximum loose thickness of about 12 inches at moisture contents within –1 and +3 percent of optimum, and compacted to not less than 90 percent of the material’s maximum dry density, as determined in general accordance with ASTM D1557 (Modified Proctor).

5.4.1.3 Basalt Bedrock (RX)

Re-use of excavated basalt bedrock as structural fill is feasible, provided it can be processed (crushed, or blended with imported granular material) to achieve a fill that is fairly well graded between coarse and fine. If re-used as structural fill, the processed material should be prepared in conformance with that recommended for imported granular structural fill in Section 5.4.2 of this report.

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 10 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 15 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 90 percent of the material’s maximum dry density, as determined in general accordance with ASTM D1557 (Modified

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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 10 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 (up to 24 inches thick), and compacted until well-keyed.

5.4.4 Floor Slab 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 10 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.

5.4.5 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 12 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

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.

5.4.6 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, State of Oregon, Standard Specifications for Highway Construction.

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 or fill slopes constructed at the site, if any, should be graded at 2H:1V or flatter.

Constructed slopes should be overbuilt by a few feet depending on their size and gradient so that they can be properly compacted prior to being cut to final grade. 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.

5.6 Shallow Foundations

5.6.1 Subgrade Preparation

Satisfactory subgrade support for shallow foundations can be obtained from the native, medium dense to better, silty sand (SM), the native basalt bedrock (RX), or new structural fill that is properly placed and compacted on these materials during construction. These materials first encountered at depths of about

½- to 1 foot bgs within our explorations in the vicinity of the building pad. The geotechnical engineer or their representative should be contacted to observe subgrade conditions prior to placement of forms, reinforcement steel, or granular backfill (if required). 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. The maximum particle size of over-excavation

Carlson Geotechnical Page 16 of 20 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, we recommend individual spread footings have a minimum width of 24 inches. We recommend continuous wall footings have a minimum width of 15 inches. All footings should be founded at least 18 inches below the lowest, permanent adjacent grade to develop lateral capacity and for frost protection.

5.6.3 Bearing Pressure & Settlement

Footings founded as recommended above should be proportioned for a maximum allowable soil bearing pressure of 3,000 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.

5.6.4 Lateral Capacity

A maximum passive (equivalent fluid) earth pressure of 200 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 0.35 may be used when calculating resistance to sliding for footings founded on the native soils described above. An ultimate coefficient of friction equal to 0.45 may be used when calculating resistance to sliding for footings founded on a minimum of 6 inches of imported granular structural fill (crushed rock) that is properly placed and compacted during construction.

5.7 Rigid Retaining Walls

5.7.1 Footings

Retaining wall footings should be designed and constructed in conformance with the recommendations presented in Section 5.6, as applicable.

Carlson Geotechnical Page 17 of 20

5.7.2 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 or their representative should be contacted to observe the drains prior to backfilling. Roof or area drains should not be tied into retaining wall drains.

5.7.3 Wall Backfill

Retaining walls should be backfilled with imported granular structural fill in conformance with

Section 5.4.2 and contain less than 10 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.

5.7.4 Design Parameters & Limitations

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

Table 3 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 34 pcf 0.22*q

Restrained from Rotation Level (i = 0) 52 pcf 52 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 8 feet or less in height.

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

No line load or point load surcharges are imposed behind the walls.

Carlson Geotechnical Page 18 of 20

The grade behind the wall is level, or sloping down and away from the wall, for a distance of 8 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.

5.8 Floor Slabs

5.8.1 Subgrade Preparation

Satisfactory subgrade support for slabs constructed on grade, supporting up to 200 psf area loading, can be obtained from the native, medium dense to better, silty sand (SM), the native, basalt bedrock (RX), or new structural fill that is properly placed and compacted on these materials during construction. The geotechnical engineer or their 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 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 5.4.2 of this report.

5.8.2 Crushed Rock Base

Concrete floor slabs should be supported on a minimum 6-inch-thick layer of crushed rock (base rock) in conformance with Section 5.4.4 of this report.

5.8.3 Design Considerations

For floor slabs constructed with a 6-inch base rock layer as recommended, an effective modulus of subgrade reaction of 250 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.

5.8.4 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

Carlson Geotechnical Page 19 of 20 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.

5.9 Pavements

Subgrade preparation for pavements at the site should be in conformance with Section 5.1.6 of this report. Pavement subgrade surfaces should be crowned (or sloped) for proper drainage in accordance with specifications provided by the project civil engineer. Pavement section design was not part of this current assignment. CGT would be pleased to provide recommendations for design section(s) for new pavements at the site, upon request, for an additional fee.

5.10 Additional Considerations

5.10.1 Drainage

Subsurface drains, if any, 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 building should be sloped to drain away from the building. 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 or retaining wall drains.

5.10.2 Expansive Potential

The near surface native soils consist of non-plastic, silty sand (SM) and basalt bedrock (RX), and are not considered 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.

6.0 RECOMMENDED ADDITIONAL SERVICES

6.1 Design Review

Geotechnical design review is of paramount importance. CGT recommends the geotechnical design review take place prior to releasing bid documents to contractors.

6.2 Observation of Construction

Satisfactory earthwork, foundation, floor slab, and pavement performance depends to a large degree on the quality of construction.