653-21-102_Roseburg Bldg 3-Seismic Retrofit Soils Report FInal.pdf

R e p o r t Co v e r P ag e

Roseburg VAMC Building 3 Seismic Retrofit

Geotechnical Engineering Report

March 10, 2023 | Terracon Project No. 82225133

Prepared for:

Blue Trident, LLC

7829 NE Esperione Lane

Bainbridge Island, Washington 98110

Prepared by:

TTL Associates, Inc./Terracon Consultants, Inc. Team

Toledo, Ohio/Portland, Oregon

700 NE 55th Avenue

Portland, OR 97203

P (503) 659-3281

Terracon.com

Facilities | Environmental | Geotechnical | Materials

R e p o r t Co v e r L et t e r

March 10, 2023

Blue Trident, LLC

7829 NE Esperione Lane

Bainbridge Island, Washington 98110

Attn: Mr. Brian Moll, P.E., P.S.

Re: Geotechnical Engineering Report

Roseburg VAMC Building 3 Seismic Retrofit

913 NW Garden Valley Boulevard

Roseburg, Oregon

Terracon Project No. 82225133

Dear Mr. Moll:

The TTL/Terracon Team has completed the scope of Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with

Terracon Proposal No. P8225133 dated August 29, 2022, and authorized on October 12, 2022, by TTL Associates, Inc., Purchase Order No. 2300101-01. 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.

Roseburg VAMC Building 3 Seismic Retrofit | Roseburg, Oregon

The TTL/Terracon Team appreciates 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 the TTL/Terracon Team.

Sincerely, Terracon Consultants, Inc. TTL Associates, Inc.

Ryan T. Houser, CEG

Project Geologist

Christopher P. Iott

TTL Project Manager

Kristopher T. Hauck, P.E.

Senior Principal | Office Manager

Facilities | Environmental | Geotechnical | Materials i

Table of Contents 1 Introduction

2 Project Description

3 Site Conditions

3.1 Previous Site Experience

4 Geotechnical Characterization

4.1 Geology

4.2 Seismic Hazards

4.3 Groundwater Conditions

4.4 GeoModel

5 Geotechnical Overview

6 Earthwork

6.1 Demolition

6.2 Site Preparation

6.3 Bedrock Excavation

6.4 Fill Material Types

6.5 Fill Placement and Compaction Requirements

6.6 Utility Trench Backfill

6.7 Grading and Drainage

6.8 Earthwork Construction Considerations

6.9 Construction Observation and Testing

7 Seismic Considerations

7.1 Seismic Site Class

7.2 Recommended Seismic Design Parameters

8 Shallow Foundations

8.1 Design Parameters – Compressive Loads

8.2 Design Parameters – Uplift Loads

8.3 Construction Adjacent to Existing Building

8.4 Footing Drains

8.5 Foundation Construction Considerations

9 Floor Slabs

9.1 Floor Slab Design Parameters

9.2 Floor Slab Construction Considerations

10 Lateral Earth Pressures

10.1 Design Parameters

10.2 Subsurface Drainage for Below-Grade Walls

11 Pavements

11.1 Pavement Section Thicknesses

11.2 Pavement Drainage

11.3 Pavement Maintenance

12 General Comments

Facilities | Environmental | Geotechnical | Materials ii

Diagrams Diagram 1: Uplift Loads

Diagram 2: Over Excavation Backfill with Lean Concrete

Diagram 3: Over Excavation Backfill with Structural Fill

Diagram 4: Retaining Wall Restraint Conditions

Diagram 5: Retaining Wall Backfill and Drain Placement

Tables

Table 1: Project Description

Table 2: Site Conditions

Table 3: GeoModel

Table 4: Imported Structural Fill Criteria

Table 5: Fill Compaction Requirements

Table 6: Measured Shear Wave Velocities

Table 7: Shallow Foundation Design Parameters

Table 8: Floor Slab Design Parameters

Table 9: Lateral Earth Pressure Design Parameters

Table 10: Minimum Asphaltic Concrete Section

Table 11: Minimum Portland Cement Concrete Section

Figures

GeoModel

Attachments

Exploration and Testing Procedures Photography Log

Site Location and Exploration Plans

Exploration and Laboratory Results

Supporting Information

Refer to each individual Attachment for a listing of contents.

Facilities | Environmental | Geotechnical | Materials i

Report Summary Topic & Report

Section

Overview Statement

Project

Description

Seismic retrofit for the existing masonry 3-story building. A new elevator will be added to the interior or immediately adjacent to the outside wall of the building.

Geotechnical

Characterization

■ Residual soils over basalt bedrock. Basalt is present at the approximate foundation elevation of the existing structure.

■ Groundwater not observed during our current exploration;

however previous explorations at the site encountered groundwater perched on top of the bedrock.

Earthwork

Shallow basalt bedrock is weathered and can likely be excavated with conventional earth moving equipment. Intact bedrock will likely require pneumatic hammers for excavation. The residual soils overlying the bedrock are generally silty in nature and will be available for reuse as structural fill in dry weather only.

Shallow

Foundations

Shallow foundations bearing on a minimum leveling course of

2 inches are recommended for support of new foundations. The following values are applicable for new and existing foundations:

■ Allowable bearing pressure = 5,000 psf

■ Expected settlements: < 1-inch total, < 1/2-inch differential

Shallow

Foundations &

Lateral Earth

Pressures

Cantilevered walls can be designed using the resistance values in

Section 8 Shallow Foundations. Earth pressures acting are provided in Section 10 Lateral Earth Pressures.

Pavements

No traffic loadings were provided for new pavements associated with the proposed seismic retrofit. We recommend new pavements be founded on undisturbed, native soils capable of passing a proof roll, bedrock, or new structural fill and have the following minimum design thicknesses:

■ 4 inches AC over 8 inches granular base; or

■ 5 inches PCC over 4 inches granular base

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

1 Introduction

This report presents the results of the TTL/Terracon Team subsurface exploration and

Geotechnical Engineering services performed for the proposed seismic retrofit for Building

3 in the existing U.S. Department of Veterans Affairs Medical Center (VAMC) Campus located at 913 NW Garden Valley Boulevard in Roseburg, Oregon. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil and rock conditions

■ Groundwater conditions

■ Seismic site classification per ASCE 7-16

■ Site specific seismic hazards investigation in accordance with OSSC Chapter

1803.6.1

■ Site Specific Seismic Spectral Analyses (ASCE 41-17)

■ Site preparation and earthwork

■ Demolition considerations

■ Dewatering considerations

■ Foundation design and construction

■ Floor slab design and construction

■ Minimum pavement sections

■ Lateral earth pressure

■ Frost considerations

The geotechnical engineering Scope of Services for this project included the advancement of three (3) borings to depths of 7 to 27 feet below existing ground surface (bgs), completion of two lines of ReMi (Refraction Microtremer) to develop a one-hundred-foot depth soil profile, laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and boring 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 boring logs and/or as separate graphs in the Exploration Results section.

2 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

Table 1: Project Description

Item Description

Information

Provided

Information was provided in an August 24, 2022, email from TTL

Associates that included a map showing the location of Building 3, as well as some structural drawings for the existing structure. Based on our subsequent telephone conversations, the TTL/Terracon Team understands the project is classified as Risk Category II.

Project

Description

The project will address seismic deficiencies in Building 3 by renovating the interior spaces and correcting all facility condition deficiencies to create a building that meets modern seismic design criteria. In addition, we understand a new elevator will be constructed. The elevator may be constructed within the footprint of the existing structure or immediately adjacent to one of the exterior walls.

Proposed

Structure

The existing structure (Building 3) consists of a masonry exterior with concrete foundations and building columns/walls. The building will be seismically retrofitted. We anticipate additional foundations will be constructed as part of the retrofit to support additional shear walls.

Risk Category

(provided) Risk Category II (Ancillary facility)

ASCE 41-17

Earthquake

Hazard Levels

(provided)

BSA-1N, BSE-2N, BSE-1E and BSE-2E.

Finished Floor

Elevation Existing floor elevations will remain.

Maximum Loads

(assumed)

■ Columns: 200 kips

■ Walls: 4 kips per linear foot (klf)

■ Slabs: 150 pounds per square foot (psf)

Grading/Slopes No grading is anticipated to be performed as part of this seismic retrofit

Below-Grade

Structures

Renovations to the existing structure and basement retaining walls will likely require below grade structure improvements.

Free-Standing

Retaining Walls

Retaining walls are not expected to be constructed as part of site development to achieve final grades.

Facilities | Environmental | Geotechnical | Materials 3

Item Description

Pavements

We understand new pavements will be associated with the seismic retrofit and elevator addition. No traffic loadings were provided prior to preparation of this report. We assume new pavements will be limited to a new access roadway to the elevator addition area and localized areas of reconstruction where existing pavements are impacted by the proposed project.

Estimated Start of

Construction

The TTL/Terracon Team 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.

3 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.

Table 2: Site Conditions

Item Description

Parcel

Information

The project consists of Building 3 at the southern end of the VAMC

Campus located at 913 NW Garden Valley Boulevard in Roseburg, Oregon.

Building 3 is located at the following approximate coordinates:

■ Latitude: 43.2227° N

■ Longitude: 123.3662° W

See Site Location

Existing

Improvements

Building 3 consists of a three-story brick building. The lower level is partially embedded into the ground surface.

Existing Plans

Existing plans for the structure indicate that the top of footings of interior columns at an elevation of about 447 ft, which is about 8 ft below the existing exterior grade.

Current Ground

Cover

Building 3 is surrounded by grass lawn areas and landscaped planters.

Existing

Topography

The site is nearly level, with less than 3 feet of total vertical relief within the immediate project area.

We also collected photographs at the time of our field exploration program. Representative photos are provided in our Photography Log.

Facilities | Environmental | Geotechnical | Materials 4

3.1 Previous Site Experience

Terracon previously completed a geotechnical report for seismic upgrades to numerous buildings at the VAMC campus, the results of which were presented in our draft report entitled “Geotechnical Engineering Report, VA Medical Center Upgrades, 913 NW Garden

Valley Blvd, Roseburg, Oregon,” Terracon Project No. 82185070, dated May 24, 2019.

Building 3 was not included part of our previous work at the site.

4 Geotechnical Characterization

4.1 Geology

Based on our review of the Geologic mapping the site is underlain by a thin layer of

Quaternary Fluvial deposits consisting of unconsolidated or poorly consolidated river deposits consisting of moderately sorted, sub-angular to well-rounded boulders, gravel, sand, and silt. The fluvial deposits were not encountered during the current exploration but were encountered during our 2019 exploration of the northern portion of the VAMC campus. Mapping indicates the fluvial deposits are underlain by early Eocene and late

Paleocene Siletz River Volcanics, which comprises the majority of the basement rock of the Oregon Coast Range. The volcanics consist primarily of pillow lava, submarine breccia, and interbedded submarine sedimentary deposits. In the Roseburg area, these volcanics are exposed in tightly folded uplifts and are comprised of pillow basalt, pillow breccia, basaltic sandstone, and mudflow breccia. Our explorations encountered the basalt, presented below as GeoModel Layer 4. In-place weathering of the basalt produced a silty gravel residual soil presented below as GeoModel Layer 3.

4.2 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.

1 Wells, R.E., Jayko, A.S., Niem, A.R., Wiley, B.T., Baldwin, E., Molenaar, K.M., Wheeler, K.L., DuRoss, C.B., Givler, R.W., Bukry, D., Elder, W., McKeel, D., and Marincovich, L., 2000, Geologic map and database of the Roseburg 30' X 60' quadrangle, Douglas and

Coos Counties, Oregon, U.S. Geological Survey, Open-File Report OFR-2000-376, 1:100,000.

Facilities | Environmental | Geotechnical | Materials 5

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.

■ Earthquake Liquefaction Hazard: N/A (unlikely)

■ Expected Earthquake Shaking: Strong

■ Landslide Susceptibility (due to earthquake): Low

Additional discussion of seismic hazards is presented in Seismic Considerations in the

Supporting Information section of this report.

4.3 Groundwater Conditions

We observed our explorations while drilling and after completion for the presence and level of groundwater. Groundwater was not encountered in our explorations advanced in November

2022 to depths of up to 27 feet bgs. We encountered perched groundwater during our 2019 exploration at the site on the northern portion of the VAMC site at depths of about 2½ to

10 feet bgs.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings 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 boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

4.4 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

2 Statewide Geohazards Viewer (HazVu) published by the Oregon Department of Geology and Mineral Studies (DOGAMI) https://gis.dogami.oregon.gov/hazvu/, accessed

December 2022 https://gis.dogami.oregon.gov/hazvu/

Facilities | Environmental | Geotechnical | Materials 6 the Exploration 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 boring location, refer to the GeoModel.

Table 3: GeoModel

Model

Layer Layer Name General Description

1 FILL

3 inches of ASPHALT CONCRETE over POORLY GRADED

GRAVEL FILL (GP); fine grained, angular, gray, medium dense

2 TOPSOIL

TOPSOIL (OH); medium plasticity, dark brown, moist, medium stiff

RESIDUAL

SOIL

SILTY GRAVEL WITH SAND (GM); fine to coarse grained, subangular, dark brown to gray, moist, loose to very dense

4 BEDROCK

BASALT; gray to orangish brown, extremely fractured, very close fracture spacing, moderately weathered

5 Geotechnical Overview

Based on the subsurface conditions encountered at the site and the planned development, the site is feasible for development from a geotechnical perspective. Strong bedrock was encountered within 7 feet bgs providing competent bearing conditions for conventional foundation support of existing and new foundations associated with the seismic retrofit. Based on our understanding of previous development and the elevations of the encountered bedrock, it appears the existing structure foundations are supported on the bedrock encountered.

The near surface soils (above the bedrock) are moisture sensitive and/or loose. Therefore, exterior construction subgrades could become unstable with typical earthwork and construction traffic, especially after precipitation events. Section 8 Shallow Foundations addresses support of new foundations directly bearing on the bedrock or engineered fill.

While groundwater was not encountered during our 2022 exploration, since the basement floor level is on, or very close to, the bedrock surface, perched groundwater may be encountered during excavation. This potentially increases if construction takes place during the wet winter months. A sump-pump is located near the northwest corner of the existing building based on the provided as-built drawings. We recommend the condition of the sump pump be determined, and that new foundations avoid this area if possible.

Facilities | Environmental | Geotechnical | Materials 7

Contractors should be prepared for bedrock excavations with rock excavation equipment in order to extend excavations into the bedrock.

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

New pavements may be founded on native residual soil (GeoModel Layer 3) or basalt bedrock (GeoModel Layer 4). Minimum pavement design sections are provided in section

11 Pavements.

Section 12 General Comments provides an understanding of the report limitations.

6 Earthwork

Earthwork is anticipated to include minor demolition of slabs to provide access for new foundations, excavations for foundations and new pavements, and limited engineered fill placement and/or backfill around possible exterior elevator foundations. 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.

6.1 Demolition

Existing slabs, reinforcement, and utilities should be removed from the footprint of new foundations including the elevator pit.

6.2 Site Preparation

Prior to placing new foundations, existing fill and deleterious materials should be removed.

If the elevator is installed outside of the building footprint, existing vegetation, root mat, and topsoil should be removed. Organic-rich fat clay soils (topsoil) were encountered near the surface from 12 to 18 inches in places and should be expected to be included in the stripping depths.

Since new foundations will be located on the interior of the existing structure and limited excavations on the exterior of the structure, subgrades should be evaluated by observation and hand probing by geotechnical personnel.

Prior to construction of new pavements, existing fill, vegetation, and topsoil should be removed. Prepared pavement subgrades should be proof rolled prior to placement of base

Facilities | Environmental | Geotechnical | Materials 8 rock with an adequately loaded vehicle such as a fully-loaded tandem-axle dump truck.

The proof rolling should be performed under the observation of the Geotechnical Engineer or representative. Areas excessively deflecting under the proof roll should be delineated and subsequently addressed by the Geotechnical Engineer. Such areas should be removed and recompacted. Excessively wet or dry material should either be removed or moisture conditioned and recompacted.

6.3 Bedrock Excavation

Bedrock materials were encountered as shallow as about 7 feet bgs. The RQD values of the recovered rock cores within boring B-1 ranged from about 0 to 26 percent, which is indicative of rock quality varying from very poor to poor. Our previous explorations at the site encountered rock with RQD values up to 97% (excellent). In our opinion, poor quality and/or closely jointed fair quality rock could be excavated using normal rock construction equipment that is equipped with rock teeth, rippers, and/or breakers. The contractor should be prepared to utilize hydraulic or pneumatic breakers, or blasting, to assist in bedrock removal where higher quality rock is encountered. We anticipate blasting is not feasible during construction of this seismic retrofit due to the potential for damage to the existing structure. It should be noted that rock excavation and ripping is dependent on operator skill and experience. Rippability of rock is also dependent on rock conditions that will be encountered during construction and details of methods used to rip. These methods include, but are not limited to, cross-ripping techniques, number of shanks, tooth angle, and tooth penetration. Work area space constrictions can have an impact on the ability to rip bedrock.

Over-breakage of bedrock in foundation and utility excavations should be anticipated and will result in additional quantities of concrete or backfill material. Disturbed or blasted material below design grades must be removed and replaced with compacted fill.

6.4 Fill Material Types

Fill required to reach finished grades is anticipated to be very limited in area; therefore we recommend using imported granular backfill or lean concrete where fill is needed.

Imported Fill Materials: Imported 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.

Facilities | Environmental | Geotechnical | Materials 9

Table 4: Imported Structural Fill Criteria

Soil Type 1 Specifications Acceptable Parameters

(for Structural Fill)

Common Fill

Oregon Standard Specifications for

Construction (OSSC) Section

00300.13 Selected General Backfill

All locations across the site. Dry weather only acceptable

Select Fill OSSC Section 00330.14 Selected

Granular Backfill 2

All locations across the site.

Wet and Dry weather acceptable.

Crushed

Aggregate Base

(CAB)

OSSC Section 02630.10 Dense

Graded Aggregate (2”-0 to ¾”-0) 2

All locations across the site.

Wet and Dry weather acceptable.

Trench Backfill OSSC Section 00405.14 for Trench

Backfill with additional stipulations 4

Acceptable materials include

Common and Select Fill listed above.

Subgrade

Stabilization

OSSC 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

OSSC Section 00405.13, Pipe

Zone Material

Thickness above and below pipe recommended by utility engineer

1. Controlled, compacted fill should consist of approved materials that are free (less than 3% by weight) of organic matter and debris (i.e. wood sticks 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 12% 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.

6.5 Fill Placement and Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Facilities | Environmental | Geotechnical | Materials 10

Table 5: Fill Compaction Requirements

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 1,2,3

95% of max. above and below foundations and within 1 foot of finished pavement subgrade

92% of max. when more than 1 foot below finished pavement subgrade

Water Content

Range

Low plasticity cohesive: -2% to +3% of optimum

High plasticity cohesive: 0 to +4% of optimum

Granular: -2% to +2% of optimum

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

Proctor test (ASTM D1557).

2. High plasticity cohesive fill should not be compacted to more than 100% of standard Proctor maximum dry density.

3. 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.

6.6 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 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

Facilities | Environmental | Geotechnical | Materials 11 other lightweight compactors. Where trenches are placed beneath slabs or footings, the backfill should satisfy the gradation and expansion index requirements of engineered 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.

6.7 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 program should be established to effectively seal and maintain joints and prevent surface water infiltration.

6.8 Earthwork Construction Considerations

Shallow excavations for the proposed structures are anticipated to be accomplished with conventional construction equipment where soils were encountered. Refer to Section 6.3

Bedrock Excavation section for a discussion around bedrock excavation. 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

Facilities | Environmental | Geotechnical | Materials 12 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.

The groundwater table could affect overexcavation efforts, especially for overexcavation and replacement of lower strength soils. A temporary dewatering system consisting of sumps with pumps may be necessary to achieve the recommended depth of overexcavation depending on groundwater conditions at the time of 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 TTL or Terracon are 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.

6.9 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 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

Facilities | Environmental | Geotechnical | Materials 13 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.

7 Seismic Considerations

7.1 Seismic Site Class

The seismic design requirements for buildings and other 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 and the 2022 Oregon Structural Specialty Code. Shear wave velocities were measured at the site using ReMi geophysical survey. The profile results are presented in the Exploration and Laboratory Results section of this report, and are summarized in the following table:

Table 6: Measured Shear Wave Velocities

ReMi Array Time-Averaged Shear Wave Velocity

(Vs100)

East-West 3,796 ft/sec

North-South 3,600 ft/sec

Based on the shear wave velocities measured at the site and the soil/bedrock properties observed at the site and as described on the exploration logs and results, our professional opinion is for that a Seismic Site Classification of B be considered for the project.

7.2 Recommended Seismic Design Parameters

Seismic design parameters were determined in accordance with ASCE 41-17 using four levels of ground motion hazard (BSE-1E, BSE-1N, BSE-2E and BSE-2N). The results of our analyses and resultant design parameters are presented in the Site-Specific Ground Motion

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Study in the Supporting Information section of this report. The final selection of which level of seismic design parameters to use in design of the proposed retrofit and addition rests with the VA and design team.

8 Shallow Foundations

If the site has been prepared in accordance with the requirements noted in Section 6

Earthwork, the following design parameters are applicable for shallow foundations. In addition, since we estimate that the existing foundations are supported on the bedrock, these parameters would be applicable to the existing foundations. We recommend a minimum 2-inch layer of granular Select Fill be placed over the exposed bedrock to act as a bond break and leveling course beneath new foundations.

8.1 Design Parameters – Compressive Loads

Table 7: Shallow Foundation Design Parameters

Item Description

Maximum Net Allowable Bearing

Pressure 1, 2

5,000 psf – foundations bearing on granular structural fill extending to bedrock. This value may also be used for existing foundations bearing on bedrock.

Required Bearing Stratum 3 Bedrock (GeoModel Layer 4) or granular structural fill extending to GeoModel Layer 4

Bond Break / Levelling Course Minimum 2-inch-thick layer of Select Fill

Minimum Foundation Dimensions

■ Columns: 30 inches

■ Continuous: 18 inches

Ultimate Passive Resistance4

(equivalent fluid pressures) 400 pcf (granular backfill)

Sliding Resistance 5 Ultimate coefficient of friction 0.4 (granular material)

Minimum Embedment below

Finished Grade 6

Exterior footings in unheated areas: 18 inches

Exterior footings in heated areas: 18 inches

Interior footings in heated areas: 12 inches

Estimated Total Settlement from

Structural Loads 2 Less than about 1 inch

Estimated Differential Settlement 2, 7 About ½ of total settlement

1. The maximum 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.

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Item Description

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

Additional geotechnical consultation will be necessary if higher loads are anticipated. These values can be increased 33% for short-term wind and seismic loading condition cases.

3. Unsuitable or soft soils should be overexcavated and replaced per the recommendations presented in Section 6 Earthwork.

4. Use of passive earth pressures require the sides of the excavation for the spread footing foundation to be nearly vertical and the concrete placed neat against these vertical faces or that the footing forms be removed and compacted structural fill be placed against the vertical footing face. Assumes no hydrostatic pressure.

5. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Frictional resistance for granular materials is dependent on the bearing pressure which may vary due to load combinations. For fine-grained materials, lateral resistance using cohesion should not exceed ½ the dead load. We recommend a minimum factor of safety of 1.5 for design.

6. Embedment necessary to minimize the effects of frost and/or seasonal water content variations. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

7. Differential settlements are noted for equivalent-loaded foundations and bearing elevation as measured over a span of 50 feet.

8.2 Design Parameters – Uplift Loads

Uplift resistance of spread footings can be developed from the effective weight of the footing and the overlying soils. As illustrated on the subsequent figure, the effective weight of the soil prism defined by diagonal planes extending up from the top of the perimeter of the foundation to the ground surface at an angle, , of 20 degrees from the vertical can be included in uplift resistance. The maximum allowable uplift capacity should be taken as a sum of the effective weight of soil plus the dead weight of the foundation, divided by an appropriate factor of safety. A maximum total unit weight of 120 pcf should be used for the backfill. This unit weight should be reduced to 40 pcf for portions of the backfill or natural soils below the groundwater elevation.

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Diagram 1: Uplift Loads

8.3 Construction Adjacent to Existing Building

Differential settlement between the new isolated foundations and the existing building is expected to approach the magnitude of the total settlement of new footings. Expansion joints should be provided between the existing building and the proposed addition to accommodate differential movements between the two structures. Underground piping between the two structures should be designed with flexible couplings and utility knockouts in foundation walls should be oversized so minor deflections in alignment do not result in breakage or distress. Care should be taken during excavation adjacent to existing foundations to avoid disturbing existing foundation bearing soils.

New isolated footings should bear at or near the bearing elevation of immediately adjacent existing foundations. Depending upon their locations and current loads on the existing footings, footings for the new addition could cause settlement of adjacent walls. To reduce this concern and risk, clear distances at least equal to the new footing widths should be maintained between the addition’s isolated footings and footings supporting the existing building. This clear distance is not required where new foundations are to be structurally tied (doweled) perpendicular to the existing foundations.

We understand existing foundations may support additional load from the walls of the new additions. It is possible additional loads on the existing foundations could cause other

Facilities | Environmental | Geotechnical | Materials 17 building settlements to occur. The structural capacity of existing foundations should be evaluated by a licensed structural engineer, where increases in loading are planned.

8.4 Footing Drains

A perforated rigid plastic drain line installed at the base of footings along the perimeter of the structures. The invert of a drain line around a building area or exterior retaining wall should be placed near foundation bearing level. The drain line should be sloped to provide positive gravity drainage to daylight or to a sump pit and pump. The drain line should be surrounded by clean, free-draining granular material meeting the specifications for Select

Fill as defined in Section 6.4 Fill Material Types. The free-draining aggregate should be encapsulated in a filter fabric. The granular fill should extend to within 2 feet of final grade, where it should be capped with compacted native material to reduce infiltration of surface water into the drain system.

8.5 Foundation Construction Considerations

As noted in Section 6 Earthwork, the footing excavations should be evaluated under the observation of the Geotechnical Engineer. The base of all foundation excavations should be free of water and loose soil/rock, prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing soil/rock disturbance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the footing excavations should be removed/reconditioned before foundation concrete is placed.

If unsuitable bearing materials are observed at the base of the planned footing excavation, the excavation should be extended deeper to suitable materials, and the footings could bear directly on these materials at the lower level or on lean concrete backfill placed in the excavations. The lean concrete replacement zone is illustrated on the sketch below.

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Diagram 2: Over Excavation Backfill with Lean Concrete

Overexcavation for structural fill placement below footings should be conducted as shown below. The overexcavation should be backfilled up to the footing base elevation, with granular Select Fill placed, as recommended in Section 6 Earthwork.

Diagram 3: Over Excavation Backfill with Structural Fill

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9 Floor Slabs

Design parameters for floor slabs assume the requirements in Section 6 Earthwork have been followed. Specific attention should be given to positive drainage away from the structure and positive drainage of the aggregate base beneath the floor slab.

9.1 Floor Slab Design Parameters

Table 8: Floor Slab Design Parameters

Item Description

Floor Slab

Support1

Minimum 6 inches of free-draining (less than 5% passing the U.S.

No. 200 sieve) CAB compacted to at least 95% of ASTM D 1557 2, 3

Estimated Modulus of Subgrade

Reaction 2

■ 150 pounds per square inch per inch (psi/in) for point loads supported on compacted subgrades or structural fill

■ 275 psi/in for point loads supported on a 2-inch layer of granular fill placed on bedrock

1. Floor slabs should be structurally independent of building footings or walls to reduce the possibility of floor slab cracking caused by differential movements between the slab and foundation.

2. Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade condition, the requirements noted in Section 6 Earthwork, and the floor slab support as noted in this table. It is provided for point loads.

For large area loads the modulus of subgrade reaction would be lower.

3. Free-draining granular material should have less than 5% fines (material passing the No. 200 sieve). Other design considerations such as cold temperatures and condensation development could warrant more extensive design provisions.

The use of a vapor retarder should be considered beneath concrete slabs on grade covered with wood, tile, carpet, or other moisture sensitive or impervious coverings, when the project includes humidity-controlled areas, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

Saw-cut contraction joints should be placed in the slab to help control the location and extent of cracking. For additional recommendations, refer to the ACI Design Manual. Joints or cracks should be sealed with a waterproof, non-extruding compressible compound specifically recommended for heavy duty concrete pavement and wet environments.

Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other construction objectives, our experience indicates differential movement between the

Facilities | Environmental | Geotechnical | Materials 20 walls and slabs will likely be observed in adjacent slab expansion joints or floor slab cracks beyond the length of the structural dowels. The Structural Engineer should account for potential differential settlement through use of sufficient control joints, appropriate reinforcing or other means.

9.2 Floor Slab Construction Considerations

Finished subgrade, within and for at least 10 feet beyond the floor slab, should be protected from traffic, rutting, or other disturbance and maintained in a relatively moist condition until floor slabs are constructed. If the subgrade should become damaged or desiccated prior to construction of floor slabs, the affected material should be removed, and structural fill should be added to replace the resulting excavation. Final conditioning of the finished subgrade should be performed immediately prior to placement of the floor slab support course.

The Geotechnical Engineer should observe the condition of the floor slab subgrades immediately prior to placement of the floor slab support course, reinforcing steel, and concrete. Attention should be paid to high traffic areas that were rutted and disturbed earlier, and to areas where backfilled trenches are located.

10 Lateral Earth Pressures

10.1 Design Parameters

Structures with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to values indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction, and/or compaction and the strength of the materials being restrained. Two wall restraint conditions are shown in the diagram below. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement. The “at-rest” condition assumes no wall movement and is commonly used for basement walls, loading dock walls, or other walls restrained at the top. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls (unless stated).

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Diagram 4: Retaining Wall Restraint Conditions

Table 9: Lateral Earth Pressure Design Parameters

Earth

Pressure

Condition 1

Coefficient for

Backfill Type 2

Surcharge

Pressure 3 p1 (psf)

Equivalent Fluid Pressures

(psf) 2,4

Unsaturated 5 Submerged 5

Active (Ka) Granular - 0.31 (0.31)S (40)H (80)H

At-Rest (Ko) Granular - 0.47 (0.47)S (55)H (90)H

1. For active earth pressure, wall must rotate about base, with top lateral movements

0.002 H to 0.004 H, where H is wall height. For passive earth pressure, wall must move horizontally to mobilize resistance. Fat clay or other expansive soils should not be used as backfill behind the wall.

2. Uniform, horizontal backfill, compacted to at least 92% of the ASTM D 1557 maximum dry density, rendering a maximum unit weight of 120 pcf.

3. Uniform surcharge, where S is surcharge pressure.

4. Loading from heavy compaction equipment is not included.

5. To achieve “Unsaturated” conditions, follow guidelines in Section 10.2

Subsurface Drainage for Below-Grade Walls. “Submerged” conditions are recommended when drainage behind walls is not incorporated into the design.

Backfill placed against structures should consist of granular soils or low plasticity cohesive soils.