MPMG GeoTech Report Final 04.23.24~1.pdf

Report Cover Page

OMD 410133A001 AE Multi-Purpose

Machine Gun Range

Geotechnical Engineering Report

April 23, 2024 | Terracon Project No. 82235151

Prepared for:

Benham Design LLC

15 West 6th Street, Suite 900

Tulsa, OK 74119

700 NE 55th Avenue

Portland, OR 97203

P (503) 659-3281

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter

April 23, 2024

Benham Design LLC

15 West 6th Street, Suite 900

Tulsa, OK 74119

Attn: Dayne L. Weierbach

P: 918.599.4106

E: dayne.weierbach@benham.com

Re: Geotechnical Engineering Report

OMD 410133A001 AE Multi-Purpose Machine Gun Range

76966 Bombing Range Road

Boardman, Morrow County, OR

Terracon Project No. 82235151

Dear Mr. Weierbach:

We have completed the scope of Geotechnical Engineering services for the above referenced project in general accordance with Terracon Proposal No. P82235151 dated

January 12, 2024. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and floor slabs for the proposed project.

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

Sincerely, Terracon

Expires 6/30/2025

Ryan T. Houser, CEG

Project Geologist

Kristopher T. Hauck, P.E.

Senior Principal | Office Manager

OMD 410133A001 AE Multi-Purpose Machine Gun Range | Boardman, Morrow County, OR

Facilities | Environmental | Geotechnical | Materials i

Table of Contents

Report Summary .............................................................................................. i

Introduction

Project Description

Site Conditions

Geotechnical Characterization

Geology

Groundwater

GeoModel

Geologic Hazards

Seismic Hazards

Nearby Faults

Seismic Considerations

Site Class

Seismic Design Parameters

Liquefaction

Geotechnical Overview

Collapsible Soils

Reuse of Site Soils / Soil Sensitivity

General

Earthwork

Site Preparation

Subgrade Preparation

Existing Fill

Fill Material Types

Fill Placement and Compaction Requirements

Considerations for Reuse of Site Soils

Utility Trench Backfill

Grading and Drainage

Earthwork Construction Considerations

Construction Observation and Testing

Alternative Compaction Techniques

Deep Dynamic Compaction (DDC)

Rapid Impact Compaction

High-Energy Impact Compaction (HEIC)

Shallow Foundations

Design Parameters – Compressive Loads

Design Parameters – Overturning and Uplift Loads

Foundation Construction Considerations

Floor Slabs

Floor Slab Design Parameters

Floor Slab Construction Considerations

Facilities | Environmental | Geotechnical | Materials ii

Lateral Earth Pressures

Design Parameters

Pavements

General Pavement Comments

Pavement Design Parameters

Subgrade Support Characteristics

Special Military Vehicle Traffic

Other Pavement Design Considerations

Subgrade Swell Potential

Subsurface Drainage

Material Properties

Pavement Thickness Design Recommendation

Frost Considerations

General Comments

Figures GeoModel – Operations Control Area

GeoModel – MPMG Area

Attachments

Exploration and Testing Procedures Photography Log

Site Location and Exploration Plans

Exploration and Laboratory Results

Supporting Information

Note: Blue Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

Refer to each individual Attachment for a listing of contents.

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Facilities | Environmental | Geotechnical | Materials i

Report Summary

Topic Overview Statement

Project Description

Construction of a 10-lane automated multi-purpose machine gun range (MPMG) on approximately 90 acres of the site, including:

■ Three-story Range Control Tower

■ Bleacher Enclosure

■ General Instruction & Ammunition Breakdown Buildings

■ Operations / Storage Building

■ Covered Mess Shelter & Aerated Vault Latrine

With the exception of the tower, the buildings will be single-story and will consist of metal or CMU buildings.

Geotechnical Characterization

The surface soils underlying the site consisted of silty sand (SM) to depths of about 10 to 13 feet below the ground surface (bgs) in the Operations Control Area. These soils are interpreted to be wind-blown (loess) deposits and are susceptible to settlement.

The loess was underlain by dense to very dense older (cemented) loess and alluvium. Groundwater was not encountered.

Collapsible Soils

The loess soils encountered have a moderate to high risk of collapse instigated by wetting and/or loading. We estimate collapse strains range from about 0.5 to 5 percent at full saturation, which equates to about 1 to 6 inches of potential collapse-related settlements across the site if the loess were to remain in place and be utilized for support. We have provided varying levels of mitigation of this risk in the foundation and earthworks sections of this report.

Structural Support Earthwork

■ Remove existing loose loess soils and replace with properly compacted structural fill. The depth of over excavation is based on collapse settlement tolerances of the structures:

o For 1-inch of total static settlement (no risk of collapse settlement), the entire section (10 to 13 feet) of loose loess soils should be removed and recompacted.

o For 3-inches of total settlement (1-inch of static and up to about 2-inches of collapse risk), the upper 7 feet

(below existing grade) of loose loess soils should be removed and replaced.

Facilities | Environmental | Geotechnical | Materials ii

Topic Overview Statement

General Earthwork

■ Existing native soils can be reused for structural fill

■ Native silty soils are sensitive to moisture variation

■ Significant shrinkage of recompacted native soils should be expected due to the low density of in-situ soils

■ Significant water will be necessary to increase the moisture content of reused native soils to achieve optimum moisture contents for compaction

Shallow Foundations

■ Shallow foundations bearing on new structural fill are recommended for building support

■ Allowable bearing pressure 2,500 psf for both options

■ Differential settlement = 2/3 total settlement

Pavements

With subgrade prepared as noted in Earthwork.

Rigid Design:

■ 8” PCC over 4” drainage layer over 4” separation layer over

6” native subgrade compacted to 90% of the maximum dry density

Aggregate Surfaced Access Roads and Parking Area:

■ 4” aggregate base course over 4” drainage layer over 4” separation layer over 6” native subgrade compacted to

90% of the maximum dry density.

Aggregate Surfaced Firing Lane Area:

■ 4” aggregate base course over 4” drainage layer over 4” separation layer over 6” native subgrade compacted to

90% of the maximum dry density.

Aggregate Surfaced Downrange Maintenance Trail:

■ Alternative 1: 4” aggregate base course over 4” drainage layer over 4” separation layer over 6” native subgrade compacted to 90% of the maximum dry density.

■ Alternative 2: 5” aggregate base course over 12” native subgrade compacted to 95% of the maximum dry density.

General Comments

This section contains important information about the limitations of this geotechnical engineering report.

1. If the reader is reviewing this report as a pdf, the topics above can be used to access the appropriate section of the report by simply clicking on the topic itself.

2. This summary is for convenience only. It should be used in conjunction with the entire report for design purposes.

Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our subsurface exploration and Geotechnical

Engineering services performed for the proposed Multi-Purpose Machine Gun Range to be located at 76966 Bombing Range Road in Boardman, Morrow County, OR. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Soil conditions

■ Groundwater conditions

■ Seismic site class per ASCE 7-16

■ Liquefaction and lateral spread potential

■ Site preparation and earthwork

■ Foundation design and construction

■ Floor slab design and construction

■ Lateral earth pressure

■ Pavement design and construction

■ Frost considerations

The geotechnical engineering Scope of Services for this project included the advancement of seventeen Standard Penetration Test (SPT) borings to depths of 11 to

51½ feet below existing ground surface (bgs), laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and exploration locations are shown on the Site Location and Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the exploration logs and/or as separate graphs in the Exploration and Laboratory Results section.

Project Description

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Facilities | Environmental | Geotechnical | Materials 2

Item Description

Information

Provided

Email request from Benham, which included:

■ “Request for Proposals (“RFP”) for architectural and

Engineering Services, Multi-Purpose Machine Gun (“MPMG”)

Range, A Project Located in Boardman Oregon, RFP Number

410133A001,” prepared by the Oregon Military Department.

Additional information was provided in subsequent emails.

Based on the emails, we understand the following:

■ Grading plans are not currently available.

■ Minimal grading will be performed.

Project

Description

Construction of a 10-lane automated multipurpose machine gun range (MPMG) on approximately 90 acres of the site, including:

■ Range Control Tower measuring 17 feet square and three stories in height;

■ Bleacher Enclosure measuring 22 feet by 33 feet on a concrete slab;

■ General Instruction Building measuring 20 feet by 40 feet on a concrete slab;

■ Operations / Storage Building measuring 20 feet by

40 feet on a concrete slab;

■ Covered Mess Shelter measuring 20 feet by 40 feet on a concrete slab;

■ Aerated Vault Latrine measuring 12 feet by 28 feet on a concrete slab with concrete vault; and,

■ Ammunition Breakdown Building measuring 12 feet by

20 feet on a concrete slab.

While these are the planned development, the location of each element is still in the planning phase. Except for the tower, the buildings will be single-story and will consist of metal or CMU buildings. We anticipate the buildings will be supported by shallow spread foundations or thickened-edge slabs.

Building

Construction

The site is located at the United States Navy’s Naval Weapons

Systems Training Facility (NWSTF) in Boardman, Oregon, which has been used for military activities since 1942. The proposed area of construction is vacant.

Facilities | Environmental | Geotechnical | Materials 3

Maximum Loads

(assumed)

Anticipated structural loads were not provided. In the absence of information provided by the design team, we have assumed the following loads in estimating settlement based on our experience with similar projects.

■ Columns: 20 kips

■ Walls: 4 kips per linear foot (klf)

■ Slabs: 200 pounds per square foot (psf)

Grading/Slopes

■ Proposed finished grade elevations for the proposed buildings are anticipated to be within 2 feet of existing site grades.

■ A grading plan was not provided. We understand grading in the range area will be minimal.

Below-Grade

Structures

A subsurface concrete vault will be constructed associated with the Vault Latrine.

Free-Standing

Retaining Walls No free-standing retaining walls are planned.

Pavements

Four pavement sections are proposed for this project:

■ Heavy Sections:

o Portland Cement Concrete (PCC) Turning Pads behind the Heavy Machine Gun Lanes o Aggregate Surface: Firing Line Access Roads, Parking

Area, and Firing Line Area o Loading: Heavy Military Vehicles including:

▪ Up-Armored High Mobility Multi-Purpose Wheeled

Vehicle (HMMWV / Humvee)

▪ Mine-Resistant Ambush Protected (MRAP) Wheeled

Vehicles

▪ 2½ Ton to 5Ton Military Trucks (Wheeled)

▪ Family of Medium Tactical Vehicle (FMTV)

(Wheeled)

▪ M113 Armored Personnel Carriers (Tracked)

■ Light Section:

o Aggregate Surface: Downrange Maintenance Trails o Loading: HMMWV / Humvee, Pickup Trucks and ATVs

We assume the pavement design period is 20 years.

Building Code

2022 Oregon Structural Specialty Code (2022 OSSC) and 42

U.S. Code 4154 - Standards for design, construction, and alteration of buildings; Secretary of Defense

Facilities | Environmental | Geotechnical | Materials 4

Terracon should be notified if any of the above information is inconsistent with the planned construction, especially the grading limits, as modifications to our recommendations may be necessary.

Site Conditions

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

Item Description

Parcel

Information

The project is located at 76966 Bombing Range Road in

Boardman, Morrow County, OR.

The approximate center of the 90-acre proposed area of development is located at the following coordinates:

■ Latitude: 45.7520° N

■ Longitude: 119.7192° W

(See Site Location)

Existing

Improvements

The site is currently in use as a bombing and military range. The area of the proposed buildings is occupied by a gravel-surfaced parking lot with storage containers. The range area is accessed by a gravel road. The range area is occupied by numerous earthen berms.

Current Ground

Cover Grass and scrub brush

Existing

Topography

The site generally descends gently to the north, with approximately 14 feet of total vertical relief.

We also collected photographs at the time of our field exploration program.

Representative photos are provided in our Photography Log.

Facilities | Environmental | Geotechnical | Materials 5

Geotechnical Characterization

Geology

Based on our review of the geologic map of the area and experience on the adjacent site, the site is underlain by eolian sand and ash (Qe - loess deposits) that extend to a depth in excess of 51½ feet. Loess soils within the site vicinity typically are comprised of eolian (wind deposited) silt and fine sand. The unit is present across the site and is material derived from the underlying Missoula Flood Deposits (described later) being re-worked and deposited once allowed to dry. Loess deposits are made up of a semi-stable soil structure commonly referred to as a “honeycomb” structure. This structure makes the soil susceptible to collapse under additional applied load and/or saturation. In addition to the collapse potential of this soils type, other characteristics of this soil unit are low relative density and high void ratios.

This loess unit can often be broken into two units consisting of Younger Loess (GeoModel

Layer 2), which was measured at 10 to 13 feet in thickness in the Operations area of the site, and older loess ranging from 20 to over 50 feet in thickness . The older loess is also described as consolidated with strong calcium carbonate contents (referred to as caliche cementation in this report). Consensus from the geologic community is that the calcium carbonate was leached from the upper loess layer by infiltrating surface water and precipitated out as the water evaporated 2,3 and is generally found in the loess deposits where mean annual precipitation is less than 15 inches. This older unit is referred to as Older Loess (GeoModel Layer 3) in this report. In general, these geologic descriptions are relatively consistent with the findings in the geotechnical borings. The cemented loess is generally not susceptible to collapse.

Madin, I.P and Gietgey, R.P., 2007, Preliminary geologic map of the Umatilla

Basin, Morrow and Umatilla Counties, Oregon, Oregon Department of Geology and Mineral Industries, Open-File Report O-07-15.

Washington Department of Transportation Publication WA-RD 69.1, Development of Guidelines for Cuts in Loess Soils, by Higgins, Fragaszy, and Beard (1985)

Engineering Geology in Washington (Volume II), Washington Division of Geology and Earth Resources – Bulletin 78, article titled “Engineering Geology of Loess in Southeastern Washington”, by J. D. Higgins, R. J. Fragaszy, and L. D Beard (p.

887-898)

Facilities | Environmental | Geotechnical | Materials 6

The loess is generally underlain by Pleistocene catastrophic flood deposits originating from glacial outburst floods of Lake Missoula (GeoModel Layer 4). Periodic failure of glacial ice dams that impounded Lake Missoula in present day Montana between 18,000 to 15,000 years ago produced catastrophic floods that flowed through northern Idaho, eastern Washington, and into northern Oregon and through the Columbia River Gorge.

These soils were deposited repeatedly over the time period, each depositional layer represents a single flood event. The flood deposits in the region extend to depths of up to about 116 feet, and generally consist of layers of silt, sand, and clay.

The Missoula Flood deposits are underlain at depth by Miocene Columbia River Basalt.

Well logs in the area indicate the depth to basalt ranges from about 70 to 120 feet.

Groundwater

Groundwater was not encountered in our borings advanced to depths of up to 51½ feet bgs in February of 2024. Well logs available on the Oregon Water Resources Department

(OWRD)

website indicate that groundwater levels in the area of the site are greater than about 100 feet below site grades, depending on topography.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the explorations were performed.

Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the exploration logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

GeoModel

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in

Allen, John Eliot, et al., 2009. Cataclysms on the Columbia, The Great Missoula

Floods, Revised Second Edition: Ooligan Press, Portland State University.

5 Oregon Water Resources Department, 2024. Well Log Records, accessed February

2024, from OWRD web site: http://apps.wrd.state.or.us/apps/gw/well_log/.

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

Facilities | Environmental | Geotechnical | Materials 7 the Exploration and Laboratory Results and the GeoModel can be found in the

Figures attachment of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each exploration location, refer to the GeoModel.

Model

Layer Layer Name General Description

1 FILL

POORLY GRADED GRAVEL WITH SAND FILL (GP FILL):

fine to coarse grained, gray and brown, moist, loose, coarse grained sand

2 LOESS

SILTY SAND (SM): fine grained, light tan to gray to brown, moist to dry, loose to medium dense

OLDER

LOESS

POORLY GRADED SAND (SP) TO SILTY SAND (SM):

fine grained, light tan to gray to brown, moist to dry, moderate to strong cementation, dense to very dense

FLOOD

DEPOSITS

SILT (ML) to ELASTIC SILT (MH): tan, dry to moist, stiff to very stiff, weak cementation

Geologic Hazards

Seismic Hazards

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

We reviewed the Statewide Geohazards Viewer (HazVu) published by the Oregon

Department of Geology and Mineral Studies (DOGAMI) and available online . The viewer categorizes the expected earthquake shaking from light, moderate, strong, very strong, severe and violent; and the landslide susceptibility from low, moderate, high, and very high.

6 Statewide Geohazards Viewer (HazVu) published by the Oregon Department of

Geology and Mineral Studies (DOGAMI) https://gis.dogami.oregon.gov/hazvu/, accessed March 2024 https://gis.dogami.oregon.gov/hazvu/

Facilities | Environmental | Geotechnical | Materials 8

■ Earthquake Liquefaction Hazard: Very low

■ Expected Earthquake Shaking: Moderate

■ Landslide Susceptibility (due to earthquake): Low

Nearby Faults

The United States Geological Survey (USGS) maintains the Quaternary Fault and Fold

Database containing descriptions and locations of recently active faults within the United

States. The three closest faults to the project site include the Columbia Hills structures

(No.568), the Arlington-Shutler Butte fault (No.847), and the Unnamed fault north of

Service Anticline (No.569). Published information pertaining to each fault or fault zone is provided in the following table:

Fault Name Columbia Hills

Structures

Arlington-Shutler

Butte Fault

Unnamed Fault

North of Service

Anticline

USGS Fault

Number 568 847 569

USGS Fault Class A A B

Distance from

Fault 7½ mi NW 21 mi WSW 23 mi NE

Length of Fault 100 miles 33 miles 4 miles

Strike (degrees) N75°E N42°W N0°E

Sense of

Movement Thrust

Right lateral, Normal Normal

Dip Direction 2–80° S Vertical Vertical

Slip-rate

Category

Less than 0.2 mm/yr

Less than 0.2 mm/yr

Less than 0.2 mm/yr

Most recent prehistoric deformation

Undifferentiated

Quaternary (<1.6

Ma)

Middle and late

Quaternary (<750 ka)

Undifferentiated

Quaternary (<1.6

Ma)

Based on our review of the available fault information, the depth to bedrock, and the site’s proximity to the nearest known faults, it is our opinion that the risk of surface rupture due to ground faulting is low.

Facilities | Environmental | Geotechnical | Materials 9

Seismic Considerations

Site Class

The seismic design requirements for structures are based on Seismic Design Category.

Site Classification is required to determine the Seismic Design Category for a structure.

The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7-16.

Based on the SPT blow counts (N-Values) measured in the borings advanced as part of this project, we recommend using a Site Class of D.

ASCE 7-16 requires a site soil profile extending to a depth of 100 feet be used for seismic site classification. Explorations associated with the projects extended to a maximum depth of 51½ feet. Soil properties below the maximum depth of our borings were estimated based on our experience and knowledge of geologic conditions of the general area. Additional deeper explorations or geophysical testing may be performed to confirm the conditions below the current exploration depth.

Seismic Design Parameters

The following seismic design parameters may be used for design of the proposed structures:

Description Value

2022 Oregon Structural Specialty Code (2022 OSSC) Site Class D 1,2

Site Latitude 45.7520° N

Site Longitude 119.7192° W

Ss Mapped Spectral Acceleration for Short (0.2 second) Period3 0.409g

S1 Mapped Spectral Acceleration for 1 Second Period3 0.160g

Fa Site Coefficient, 0.2 second 1.473

Fv Site Coefficient, 1.0 second 2.280

SMS 0.603g

SM1 0.365g

SDS 0.402g

SD1 0.243g

Facilities | Environmental | Geotechnical | Materials 10

Description Value

1. Seismic site classification in general accordance with the 2022 OSSC, which refers to ASCE 7-22.

2. See above for site class discussion.

3. These values were obtained using online seismic design maps and tools available on the Applied Technology Council (ATC) website referenced in

Section 1613.2.1 of the 2022 OSSC.

Liquefaction

Liquefaction is the phenomenon where saturated soils develop high porewater pressures during seismic shaking and lose their strength characteristics. This phenomenon generally occurs in areas of high seismicity, where groundwater is shallow and loose granular soils or relatively low- to non-plastic fine-grained soils are present.

Groundwater is present at a depth of approximately 100 feet bgs according to on-site well logs within Missoula Flood Deposits near the contact with the underlying bedrock gravel and sands. These materials are not considered to be susceptible to liquefaction.

Geotechnical Overview

The site appears suitable for the proposed construction based upon geotechnical conditions encountered in the explorations, provided that the recommendations provided in this report are implemented in the design and construction phases of this project.

Collapsible Soils

The primary geotechnical consideration for this site is that the upper 10 to 13 feet of loess (GeoModel Layer 2) soils are loose and susceptible to collapse. Structures founded directly on these soils could experience total and differential settlements exceeding 1 inch. These soils were deposited by wind and the soil particles are generally considered to be oriented in a “honeycomb” like structure, which can make them susceptible to high volumetric strains due to collapse of the soil structure. The collapse of the “honeycomb” structure is typically instigated by wetting and/or loading. Based on laboratory consolidation and collapse testing for this project and others in the similar widespread deposit, this soil is susceptible to collapse upon loading and wetting generally ranging from 0.5 to about 5 percent strain at full saturation. Laboratory testing from samples collected from nearby sites indicates collapse potential of about 1.2 to 4.5 percent. We estimate that this hazard equates to about 1 to 6 inches of potential collapse-related settlements across the site if the loess were to remain in place and be utilized for support.

Facilities | Environmental | Geotechnical | Materials 11

Proposed structures to be supported by shallow foundations will likely require some level of soil improvement to reduce total and differential settlements to acceptable levels.

Based on a foundation embedment depth of 2 feet for frost protection, we offer the following alternatives for subgrade improvement beneath new structures:

■ Complete Removal and Recompaction: Where total settlements need to be limited to less than 1-inch and mitigation of all collapse related settlements, loose loess soils (GeoModel Layer 2) should be over excavated to expose dense to very dense Older Loess (GeoModel Layer 3). The surface of the underlying soils should be scarified, wetted and compacted prior to placement of new structural fill. The existing fill and native soils encountered at the site are suitable for reuse as structural fill. Traditional removal and recompaction could be combined with the use of Rapid Impact Compaction or High Energy Impact Compaction techniques to densify some of the materials in-place without the need for complete over excavation. These methods are described in the Alternative Compaction

Techniques section below.

■ Partial Removal and Recompaction: Where structures can tolerate total settlements of 3 inches, a partial over excavation could be implemented where the site soils are removed to a depth of 5 feet below the bottom of footing elevation (7 feet below site grades) and recompacted as described above. As an alternative to remove and replace, the Alternative Compaction Techniques could also be used to improve the minimum 5-foot thick zone below footings. This option does not reduce potential collapse related settlements as much as the first option, since some of the loose loess soils would remain in place.

Reuse of Site Soils / Soil Sensitivity

The soils at the site are generally suitable for reuse as structural fill . Due to the low density of the loess (GeoModel Layer 2) and the expected compacted density, we expect significant shrinkage during earthwork reuse of the site soils that should be accounted for in the grading planning. Reused loess materials may lose 10 to 25 percent of their volume during recompaction.

The near surface loess (silty sand) could become unstable with typical earthwork and construction traffic, especially after precipitation events. The effective drainage should be completed early in the construction sequence and maintained after construction to avoid potential issues. If possible, the grading should be performed during the warmer and drier times of the year. If grading is performed during the winter months, an increased risk for possible undercutting and replacement of unstable subgrade will persist. Additional site preparation recommendations, including subgrade improvement and fill placement, are provided in the Earthwork section.

Facilities | Environmental | Geotechnical | Materials 12

General

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration and Laboratory Results), engineering analyses, and our current understanding of the proposed project. The

General Comments section provides an understanding of the report limitations.

Earthwork

Earthwork is anticipated to include clearing and grubbing, excavations, and structural fill placement. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations, floor slabs, and pavements.

Site Preparation

Prior to placing fill, existing vegetation, topsoil, and root mats should be removed.

Complete stripping of the topsoil should be performed in the proposed building and parking/roadway areas.

Although no evidence of fill (other than the gravel parking area) or underground facilities (such as septic tanks, cesspools, basements, and utilities) was observed during the exploration and site reconnaissance, such features could be encountered during construction. If unexpected fills or underground facilities are encountered, such features should be removed, and the excavation thoroughly cleaned prior to backfill placement and/or construction.

Subgrade Preparation

Depending on the settlement tolerances of the proposed structures, existing loose loess soils beneath proposed buildings should be removed to a depth of * feet (partial removal) to 10 to 13 feet (complete removal) beneath proposed finished floor elevations.

The exposed over excavated subgrade should be, once properly cleared and benched where necessary, scarified to a minimum depth of 10 inches, moisture conditioned as necessary, and compacted per the compaction requirements in this report. Upon completion of compaction, the prepared subgrades should be proofrolled with an adequately loaded vehicle such as a fully-loaded tandem-axle dump truck. The proofrolling should be performed under the observation of the Geotechnical Engineer of

Record (Terracon). Areas excessively deflecting under the proofroll should be delineated

Facilities | Environmental | Geotechnical | Materials 13 and subsequently addressed by the Geotechnical Engineer. Such areas should be removed and replaced with moisture conditioned recompacted materials. Excessively wet or dry material should either be removed or moisture conditioned and recompacted.

Compacted structural fill soils should then be placed to the proposed design grade and the moisture content and compaction of subgrade soils should be maintained until foundation or pavement construction.

Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively workable;

however, the workability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unworkable conditions develop, workability may be improved by scarifying and drying.

Existing Fill

As noted in Geotechnical Characterization, a thin layer of previously placed gravel fill was placed in the existing parking area at the site. We have no records to indicate the degree of control, and consequently, the fill is considered unreliable for support of shallow foundations. The existing fill is suitable for reuse as structural fill at the site.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 10 feet of structures or pavements.

General fill is material used to achieve grade outside of these areas.

Reuse of On-Site Soil: Excavated on-site soil may be selectively reused as structural fill, provided it meets the requirements detailed below.

Fill Materials: Structural fill materials should meet the following material property requirements. Regardless of its source, compacted fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade.

Fill Type 1 Specifications

Acceptable Location for Placement

(for Structural Fill)

Common Fill

Oregon Department of Transportation

Standard Specifications for Construction

(ODOT SSC) Section 00330.13 Selected

General Backfill

(Maximum PI = 10% and LL = 40%)

All locations across the site. Dry weather only acceptable

Facilities | Environmental | Geotechnical | Materials 14

Fill Type 1 Specifications

Acceptable Location for Placement

(for Structural Fill)

Select Fill ODOT SSC Section 00330.14 Selected

Granular Backfill 2

All locations across the site.

Wet and dry weather acceptable.

Crushed

Aggregate Base

Course (CABC)

ODOT SSC Section 02630.10 Dense

Graded Aggregate

(2”-0 to ¾”-0) 2

All locations across the site.

Wet and dry weather acceptable.

Base Course

Drainage Layer

ODOT SSC Section 02630.11 Open-

Graded Aggregate

Pavement areas where drainage layer recommended.

Trench Backfill ODOT SSC Section 00405.14 for Trench

Backfill with additional stipulations 4

Acceptable materials include Common and

Select Fill listed above.

Subgrade

Stabilization

ODOT SSC Section 00330.14 for

Selected Granular Backfill above groundwater seepage and OSSC Section

00330.16 for Stone Embankment

Material with additional stipulations 4

12-inch compacted lift in wet or soft subgrades encountered in subgrade and other utility excavations.

Bedding &

Haunching

ODOT SSC Section 00405.13, Pipe Zone

Material

Thickness above and below pipe recommended by

Electrical Engineer

1. Controlled, compacted fill should consist of approved materials that are free

(free = less than 3% by weight) of organic matter and debris (i.e. wood or roots greater than ½ inch in diameter). A sample of each material type should be submitted to the geotechnical engineer for evaluation.

2. Material should have a maximum aggregate size of 2 inches, and a minimum laboratory CBR of 20% for granular soils, and no more than 8% passing the No. 200 sieve by weight determined by ASTM D6913. Fines should have a Plasticity Index (PI) of less than 20% per ASTM D4318. Reclaimed glass will not be accepted.

3. The contractor shall select the appropriate material for use based on the current and forecasted weather conditions at the time of construction.

4. Maximum aggregate size shall be limited to 2½ inches.

Fill Placement and Compaction Requirements

Structural should meet the following compaction requirements.

Facilities | Environmental | Geotechnical | Materials 15

Item Structural Fill

Maximum Lift

Thickness

8 inches or less in loose thickness when heavy, self-propelled compaction equipment is used

4 to 6 inches in loose thickness when hand-guided equipment

(i.e. jumping jack or plate compactor) is used

Minimum

Compaction

Requirements 1,2

95% of max. above and below foundations and within 2 feet of finished pavement subgrade

92% of max. when more than 2 feet below finished pavement subgrade

Water Content

Range

-2% to +2% of optimum

1. Maximum density and optimum water content as determined by the modified

Proctor test (ASTM D1557).

2. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least

70% relative density (ASTM D4253 and D4254). Materials not amenable to density testing should be placed and compacted to a stable condition observed by the Geotechnical Engineer or representative.

Considerations for Reuse of Site Soils

The in-situ moisture contents of the native soils (in particular the loess) are significantly below optimum moisture contents. In general, the loess soil’s in-situ moisture contents ranged from 4 to 14 percent. Optimum moisture (the moisture content at which the greatest density of the soil can be obtained from compaction) for the native loess soils is approximately 11 percent. Therefore, significant amounts of water may be needed for compaction of the site soils to the required dry density.

In addition, we estimate that the compacted dry density of the materials should be on the order of about 110 pcf (95 percent of the modified proctor maximum density of

115.8 pcf) and the in-situ dry density ranges from about 82 to 99 pcf. Therefore, it should be noted that reused fill volume could experience shrinkage factors on the order of 0.75 to 0.9 when removed and replaced. This should be considered when estimating earthwork volumes.

Utility Trench Backfill

Any soft or unsuitable materials encountered at the bottom of utility trench excavations should be removed and replaced with structural fill or bedding material in accordance with public works specifications for the utility be supported. This recommendation is particularly applicable to utility work requiring grade control and/or in areas where

Facilities | Environmental | Geotechnical | Materials 16 subsequent grade raising could cause settlement in the subgrade supporting the utility.

Trench excavation should not be conducted below a downward 1:1 projection from existing foundations without engineering review of shoring requirements and geotechnical observation during construction.

On-site materials are considered suitable for backfill of utility and pipe trenches from

1 foot above the top of the pipe to the final ground surface, provided the material is free of organic matter and deleterious substances.

Trench backfill should be mechanically placed and compacted as discussed earlier in this report. Compaction of initial lifts should be accomplished with hand-operated tampers or other lightweight compactors. Where trenches are placed beneath slabs or footings, the backfill should satisfy the gradation and expansion index requirements of structural fill discussed in this report. Flooding or jetting for placement and compaction of backfill is not recommended.

For low permeability subgrades, utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath the building should be effectively sealed to restrict water intrusion and flow through the trenches, which could migrate below the building. The trench should provide an effective trench plug that extends at least 5 feet from the face of the building exterior. The plug material should consist of cementitious flowable fill or low permeability clay. The trench plug material should be placed to surround the utility line. If used, the clay trench plug material should be placed and compacted to comply with the water content and compaction recommendations for structural fill stated previously in this report.

Grading and Drainage

All grades must provide effective drainage away from the building during and after construction and should be maintained throughout the life of the structure. Water retained next to the building can result in soil movements greater than those discussed in this report. Greater movements can result in unacceptable differential floor slab and/or foundation movements, cracked slabs and walls, and roof leaks. The roof should have gutters/drains with downspouts that discharge onto splash blocks at a distance of at least 10 feet from the building.

Exposed ground should be sloped and maintained at a minimum 5% away from the building for at least 10 feet beyond the perimeter of the building. Locally, flatter grades may be necessary to transition ADA access requirements for flatwork. After building construction and landscaping have been completed, final grades should be verified to document effective drainage has been achieved. Grades around the structure should also be periodically inspected and adjusted, as necessary, as part of the structure’s maintenance program. Where paving or flatwork abuts the structure, a maintenance

Facilities | Environmental | Geotechnical | Materials 17 program should be established to effectively seal and maintain joints and prevent surface water infiltration.

Earthwork Construction Considerations

Shallow excavations for the proposed structure are anticipated to be accomplished with conventional construction equipment. Deeper excavations for utilities could encounter strongly cemented soils with difficult excavation conditions. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of grade-supported improvements such as floor slabs and pavements.

Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed.

If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part

1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety or the contractor's activities; such responsibility shall neither be implied nor inferred.

Excavations or other activities resulting in ground disturbance have the potential to affect adjoining properties and structures. Our scope of services does not include review of available final grading information or consider potential temporary grading performed by the contractor for potential effects such as ground movement beyond the project limits. A preconstruction/ precondition survey should be conducted to document nearby property/infrastructure prior to any site development activity. Excavation or ground disturbance activities adjacent or near property lines should be monitored or instrumented for potential ground movements that could negatively affect adjoining property and/or structures.

Construction Observation and Testing

The earthwork efforts should be observed by the Geotechnical Engineer (or others under their direction). Observation should include documentation of adequate removal of surficial materials (vegetation, topsoil, and pavements), evaluation and remediation of

Facilities | Environmental | Geotechnical | Materials 18 existing fill materials, as well as proof rolling and mitigation of unsuitable areas delineated by the proof roll.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as recommended by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,500 square feet of compacted fill in the building areas and 5,000 square feet in pavement areas. Where not specified by local ordinance, one density and water content test should be performed for every 100 linear feet of compacted utility trench backfill and a minimum of one test performed for every 12 vertical inches of compacted backfill.

In areas of foundation excavations, the bearing subgrade should be evaluated by the

Geotechnical Engineer. If unanticipated conditions are observed, the Geotechnical

Engineer should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

Alternative Compaction Techniques

As an alternative to complete over excavation and recompaction, some of the loose loess soils could be densified in-place using one of the following techniques. Regardless of method selected, the improvements should be performed at least 10 feet beyond the lateral extents of the building pad.

Deep Dynamic Compaction (DDC)

Deep Dynamic Compaction (DDC) is a ground improvement technique where a heavy weight dropped from a height to densify soils. Generally, a 5 to 20-ton tamper weight is repeatedly dropped from heights up to 100 feet above the ground surface in a grid pattern throughout the building pad. Grid spacing depends on the size and weight of the tamper used. This technique can improve soils up to 30 feet below the impact surface, depending on the weight of the tamper and the height from which it is dropped. This technique is well suited for densifying loose surficial soils that are prone to collapse and could be completed from the surface to improve the full depth of collapsible soils without having to complete a full depth removal and replacement.

Facilities | Environmental | Geotechnical | Materials 19

Rapid Impact Compaction

Similar to DDC, Rapid Impact Compaction (RIC) is a ground improvement technique that densifies shallow, loose granular soils using a hydraulic hammer which repeatedly strikes an impact plate. The energy impact is generally less than DDC, but can be applied in shorter timeframes between impacts. The energy is transferred to the underlying loose granular soils and rearranges the particles into a denser configuration. The impact locations are typically located on a grid pattern, the spacing of which is determined by the subsurface conditions and foundation loading and geometry. This method has limited improvement depth capabilities that range in thickness of about 5 to 7 feet.

High-Energy Impact Compaction (HEIC)

High Energy Impact Compaction (HEIC) could be implemented to densify loose loess site soils and reduce the risk of excessive settlements for lightly loaded building foundations and floor slabs. The HEIC equipment typically consists of a 12 to 18-ton, 3 and/or 5-sided impact compactor. The impact compactor is towed across the site, the repeated rotation of the compactor applies high-energy surface impacts in a predetermined and controlled application offering 100 percent site coverage. Additional geotechnical exploration should be performed after completion of the HEIC to determine the effectiveness of the ground improvement and provide final design recommendations for the proposed building foundations.

Depth of compaction is a function of actual equipment used and site soil conditions.

Available publications 7,8,9 indicate the depth of improved soils varies from about 4 to

8 feet.

Bouazza, A., and Availe, D., 2006, Verification of the effects of rolling dynamic compaction using a continuous surface wave system, Australian Geomechanics, Vol. 41, No. 2, pp. 101-108.

Scott, B., Jaksa, M., and Mitchell, P., 2021, Depth of influence of rolling dynamic compaction, Proceedings of the Institution of Civil Engineers – Ground Improvement 174(2): pp 85-94.

Bradley, Jaksa, and Kuo, 2023, Ground response of rolling dynamic compaction— a finite element modelling approach, Computers and Geotechnics, Volume 157, 2023, 105275, ISSN 0266-352X

Facilities | Environmental | Geotechnical | Materials 20

Shallow Foundations

If the site has been prepared in accordance with the requirements noted in the

Earthwork section, the following design parameters are applicable for shallow foundations or thickened portions of thickened-edge slabs.

Design Parameters – Compressive Loads

Item Description

Over Excavation Option

Complete removal and recompaction (or Full-depth Improvement) of

GeoModel Layer 2

Partial removal and recompaction (or Partial depth Improvement) of

GeoModel Layer 2

Net Allowable Bearing

Pressure 1, 2

2,500 psf 2,500 psf

Required Bearing Stratum New structural fill / Improved soils

Foundation Dimensions

■ Columns:

o Minimum: 2½ feet o Maximum: 6 feet

■ Continuous:

o Minimum: 18 inches

Ultimate Passive

Resistance

(equivalent fluid pressures)

300 pcf (reused native soil backfill)

Sliding Resistance

Ultimate coefficient of friction 0.45 (recompacted native soils)

Minimum Embedment below

Finished Grade

24 inches

Estimated Total Static

Settlement from Structural

Loads

Less than about 1 inch Less than about 1 inch

Additional Collapse Risk

Settlement Negligible About 2 inches

Estimated Differential

Settlement 2, 7

About 2/3 of total settlement

Facilities | Environmental | Geotechnical | Materials 21

1. The net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. Values assume that exterior grades are no steeper than 20% within 10 feet of structure. These values can be increased by 1/3 for short-term wind and seismic loading condition cases.

2. Values provided are for maximum loads noted in Project Description.

Additional geotechnical consultation will be necessary if higher loads are anticipated.

3. Unsuitable or soft soils should be overexcavated and replaced…