Geotechnical Report.pdf

T Y P E B - 3 F I N A L

Construct ASOG Complex Project Number ETRD169847

Geotechnical Report

Prepared for

Washington Air National Guard Camp Murray ANG Base

April 2023

CH2M HILL – HDR JV

241 Taylor Street, Suite 100

Dayton, Ohio, 45402

William Dunlap, PE

Project No. 170467 September 14, 2021 Final ea r t h+wa t e r

Project No. 170467 September 14, 2021 Final

Mark Swank, LG, LEG Associate Engineering Geologist mswank@aspectconsulting.com

Henry Haselton, PE, PMP Principal Geotechnical Engineer hhaselton@aspectconsulting.com

V:\170467 Camp Murray ASOC Facility\Deliverables\Final Report\170467_GeoRpt_Final_20210914.docx

ASPECT CONSULTING

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL i

1 Introduction

1.1 Scope of Services

1.2 Project Understanding

2 Site Description

2.1 Site Conditions

2.2 Geologic Setting

2.2.1 Geology

2.2.2 Faults and Seismicity

2.2.3 Geologic and Seismic Hazards

2.3 Subsurface Conditions

2.3.1 Subsurface Explorations

2.3.2 Soils

2.3.3 Groundwater

2.4 Site Soil Infiltration

2.4.1 Soil Grain-Size Analysis

2.4.2 Soil Infiltration Rate and Physical and Chemical Suitability

2.4.3 Infiltration Facility Setback Guidance

3 Conclusions and Recommendations

3.1 Seismic Design

3.1.1 Seismic Design Criteria

3.2 Foundation Design

3.2.1 Shallow Foundations

3.3 Floor Slabs and Modulus of Subgrade Reaction

3.4 Retaining Walls

3.5 Pavement Design

3.5.1 Design Traffic

3.5.2 Flexible Pavement Design

3.5.3 Rigid Pavements

4 Construction Considerations

4.1 General

4.2 Site Preparation

4.3 Proofrolling and Subgrade Verification

4.4 Wet Weather Conditions

4.5 Excavation

4.5.1 General

4.5.2 Trenches

4.5.3 Temporary and Permanent Slopes

ii FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

4.6 Structural Fill Material and Compaction

4.7 Ground Moisture

4.7.1 General

4.7.2 Perimeter Footing Drains

5 Project Design and Construction Monitoring

6 References

7 Limitations

Table 1. Geologic and Seismic Hazards Potentially Affecting the Site

Table 2. Coefficient of Permeability Results

Table 3. 2015 IBC Seismic Design Parameters

Table 4. NEHRP Description of Category IV-Type Buildings

Table 5. Spread Footing Foundation Design Recommendations1

Table 6. Fill Type and Compaction Requirements

1 Site Location Map

2 Site Exploration Map

A Subsurface Explorations

B Laboratory Test Results

C Report Limitations and Guidelines for Use

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 1

This report summarizes Aspect geotechnical engineering observations, conclusions, and recommendations for the Washington Air National Guard (ANG) ETRD 169847 Air Support Operations Group (ASOG) Complex (Project) at Camp Murray (Site), located approximately 6 miles south of Tacoma, Washington. We performed our geotechnical engineering evaluation in accordance with our subconsultant agreement authorized on September 18, 2018. The Site location is shown on Figure 1.

1.1 Our scope of services included a data review, Site reconnaissance, subsurface explorations, laboratory tests, and geotechnical analyses. This report includes:

Site and project descriptions

Distribution and characteristics of subsurface soils and groundwater based on three borings and ten test pits

Exploration logs and a Site plan showing approximate exploration locations

Infiltration test results and calculated rates

Groundwater conditions, flow, and drainage considerations

Seismic design criteria in accordance with the 2015 International Building Code (IBC) with Washington amendments

Suitable foundation types and associated design considerations

Site preparation recommendations and general earthwork construction recommendations

Pavement section designs

1.2 We understand the Project consists of constructing a consolidated facility housing building that will be used by the Air Support Operations Group (ASOG), Air Support Operations Center (ASOC), Air Support Operations Squadron (ASOS), and Combat Weather Flight (CWF) military units. In addition, the Project also includes an Open Storage Secret Information and Simulation Facility for the 111 ASOC and the 116 ASOS and an environmentally-controlled warehouse space for storing tactical and mobility gear.

The proposed 68,000 square feet (ft2) building will be a steel framed with masonry walls and a standing seam metal roof. Based on preliminary assumptions, the building foundation is anticipated to be reinforced concrete spread footings with floor slabs with no basement.

The area surrounding the building will be paved parking for organizational vehicles, non-organizational vehicles, and equipment with covered storage. Other appurtenant

2 FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

improvements including new utilities in the upper 15 feet below ground surface (bgs) and overhead lighting. An approximately 5- to 6-foot high, 200-foot long retaining wall will be constructed along the Project boundary on the west side of the building to support an access driveway.

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 3

2.1 The Site is situated on a terrace above the eastern shore of American Lake within Camp Murray. The area is bounded on the west and north by railroad tracks and 41st Division Road, on the east by Armor Drive, and abuts the Guard Area Complex on the south.

Infantry Drive traverses west-east about midway through the Site. The total area to be developed is approximately 9 acres.

The topography is primarily flat across the majority of the Site with minor ground surface undulation and depressions. Slopes steeply descend along the west and north sides down to 41st Division Road. The flat Site area slopes gently down to the southwest with surface elevations1 (EL) between about EL 254 and EL 263.

The Site is currently undeveloped and heavily vegetated with a mixture of younger and older coniferous and deciduous trees with brushy undergrowth. The ground surface also has numerous fallen trees and a thick layer of detritus.

2.2

2.2.1 The geology map (Schuster et al., 2015) shows the near surface deposits at the Site as Steilacoom Gravel (Qgosg), a recessional glacial outwash deposit comprised of a mixture of silt, sand, gravel, cobbles, and boulders that may be as thick as 20 to 70 feet bgs.

Based on our experience with the local stratigraphy, Vashon till (Qgt) underlies the Steilacoom gravel and is typically comprised of unstratified and highly compacted clay, silt, sand, and gravel deposits with low permeability and porosity.

2.2.2 The Site area is located within the Puget Lowland physiographic province, an area of active seismicity that is subject to earthquakes on shallow crustal faults and deeper subduction zone earthquakes. The Site is located about 12 miles southwest of the Tacoma fault zone and 12 miles northeast of the Olympia structure. The east-striking, western Tacoma thrust fault forms the northwestern boundary of the Tacoma basin and the southwestern boundary of the Seattle uplift. Coastal marsh uplift north of the Tacoma fault at Lynch Cove and Burley, and coastal marsh subsidence south of the Tacoma fault at Wollochet Bay, indicate a minimum of 2 to 10 feet of north side-up slip on the western part of the Tacoma fault from about 1,000 years ago (Bucknam et al., 1992; Sherrod et al., 2002). No information is currently available for the Olympia structure. Several other shallow crustal faults in the region are capable of producing earthquakes and strong ground shaking.

The Site area also lies within the zone of strong ground shaking from earthquakes associated with the Cascadia Subduction Zone (CSZ). Subduction zone earthquakes occur due to rupture between the subducting oceanic plate and the overlying continental

1 All elevations reported in feet above North American Vertical Datum of 1988 (NAVD88).

4 FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

plate. The CSZ can produce earthquakes up to magnitude 9.3, and the recurrence interval is thought to be on the order of about 500 years. A recent study estimates the most recent, major subduction zone earthquake occurred on January 26, 1700 (Atwater et al., 2015).

Deep intra-slab earthquakes, which occur from tensional rupture of the sinking oceanic plate, are also associated with the CSZ. An example of this type of seismicity is the 2001 Nisqually earthquake. Deep intra-slab earthquakes typically are magnitude 7.5 or less and occur approximately every 10 to 30 years.

2.2.3 Geologic and seismic hazards are defined as those conditions associated with the geologic and seismic environment that could influence existing and/or proposed improvements. In general, the geologic and seismic hazards most commonly associated with the physical and chemical characteristics of near surface soil, rock, and groundwater are listed below. Hazards shown in bold are those development and may require consideration during the planning process.

Geologic Hazards

Slope stability Adverse soils Hydrogeology and groundwater Subsurface voids Hydrology and drainage Hazardous minerals and gases Volcanic hazards Land subsidence Erosion and sedimentation

Seismic Hazards

Liquefaction Lateral spreading Fault ground rupture Ground shaking Tsunamis Earthquake-induced landslides Seiches

Specific hazards identified above in bold are presented in Table 1 engineering judgment. Where noted with footnotes, the terminology is taken from a specific source (e.g., DNR webviewer).

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 5

Table 1. Geologic and Seismic Hazards Potentially Affecting the Site

Geologic and Seismic Hazard Examples Level of Concern

Adverse Soils

Artificial Fill

Expansive, Compressible Soil, or Organic-Rich Soils

Low, Site has some indications of past use.

None to Low

Hydrology and Drainage

Floodinga

Seiches or Standing Water

Not in FEMA 100-year floodplain

None to Low

Slope Stability Landslides and Existing Slope Movements

Low, exception along west property boundary

Hydrogeology and Groundwater

Shallow or artesian groundwater

Seepage

Permeability or percolation

None to Low

None to Low

Low

Seismic Hazards

Cascadia M9.0 scenarioa

Crustal Nisqually Magnitude

7.2 Scenarioa

Local Fault Rupture

Liquefactiona

MMIb 7

MMIb 7

None to Low

Very Low to Low Notes: a

DNR webviewer: https://geologyportal.dnr.wa.gov/ b

MMI = Modified Mercalli Intensity Scale: http://resilience.abag.ca.gov/shaking/mmi/

No significant geologic hazards that may require further evaluation during engineering design have been identified. The primary seismic hazard that could impact the Site is ground shaking from a Cascadia earthquake or Nisqually fault zone earthquake.

Liquefaction potential and fault rupture are not considered significant hazards at the Site due to the presence of dense gravels and distance of 12 miles to the nearest mapped fault.

2.3

2.3.1 On October 1, 2018, borings AB-1 through AB-3 were drilled to approximately 30 to 40 feet below ground surface (bgs). On October 3, 2018, test pits TP-1 through TP-10 were excavated to approximately 8 feet bgs. The locations of the explorations are shown on Figure 2.

Detailed descriptions of the subsurface conditions encountered in our explorations, as well as the depths where characteristics of the soils changed, are identified on the exploration logs presented in Appendix A. Soils were classified per the Unified Soil Classification System (USCS) in general accordance with ASTM International (ASTM) D2488, Standard Practice for Description and Identification of Soils (Visual and Manual

6 FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

Procedure; ASTM, 2018). A key to the symbols and terms used on the logs is provided on Figure A-1. The depths on the logs where conditions changed represent gradational variations between soil types; actual transitions may be more gradual. Both 2-inch- and 3-inch-diameter split spoon samplers were used to collect soil. For Standard Penetration Test (SPT), a correlation of 1.35 was used to convert the 3-inch-diameter blow counts to field blow counts.

2.3.2 The subsurface conditions at the Site were inferred using the completed field explorations, readily available geologic data, and our experience with the local geology.

Soils encountered in the explorations were generally consistent with the mapped geologic units. Soil conditions included the following:

TOPSOIL AND

FOREST FLOOR

Up to 2 feet of soil mixed with organics that consisted of leaves, needles, roots, and plant detritus were observed in the explorations.

However, the plant roots and root balls of larger trees were observed extending up to 7 feet bgs into the underlying gravel deposits.

RECESSIONAL

GLACIAL

OUTWASH,

STEILACOOM

GRAVEL (Qgosg)

Interbedded deposits of sandy SILT (ML) with gravel, silty SAND (SM) with gravel, SAND (SP-SM) with silt and gravel, SAND (SP) with gravel, silty GRAVEL (GM) with sand, GRAVEL (GP) with sand, well-graded GRAVEL (GW), and poorly-graded GRAVEL (GP) were encountered in the explorations. Rounded cobbles up to 12-inch diameter were observed in the test pits excavations.

The test pits terminated within these deposits to the total excavated depth of approximately 8 feet bgs. Borings AB-01 through AB-03 encountered these deposits from beneath the topsoil to between 20 and 25 feet bgs.

The relative densities in the recessional glacial outwash deposits were medium dense to very dense with N-values between 29 and greater than 100 blows per foot (bpf). Blow counts may be higher than actual conditions do to gravel- and cobble-sized materials larger than the sampler opening.

VASHON TILL

(Qvt)

Vashon till consisting of interbedded sandy SILT (ML) with gravel, gravelly SILT (ML) with sand, silty SAND (SM) with gravel, and silty GRAVEL (GM) with sand were encountered in the borings beneath the unconsolidated recessional glacial outwash to the total depths drill of up to approximately 40 feet bgs.

The relative densities in the Vashon till deposits were very dense with N-values between 75 and greater than 100 bpf. Blow counts may be higher than actual conditions due to gravel- and cobble-sized materials larger than the sampler opening.

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 7

2.3.3 Groundwater was encountered during drilling in borings AB-1 and AB-2 between 30 and 35 feet bgs and was not encountered in AB-3 to its total drilled depth of 30.3 feet bgs.

Groundwater depths will fluctuate due to variations in rainfall, lake levels, irrigation, and season.

2.4 Soil infiltration rates have been estimated using the Soil Grain Size Analysis Method provided in the Washington State (Ecology) Stormwater Management Manual for Western Washington (Ecology, 2014).

2.4.1 Bulk samples were collected from test pits TP-1 and TP-3 at 3 feet and 7 feet bgs, respectively. Soil grain-size analysis was performed following ASTM D6913. This test accounts for the full range of soil particle sizes to produce a soil size distribution curve (Appendix B). The samples were generally representative of the soil encountered in the upper 20 feet of the explorations.

The estimated initial coefficient of permeability (COP) in centimeters per second (cm/sec) was calculated using the following relationship (Ecology, 2012):

log10(COP) = -1.57+1.90D10+0.015D60-0.013D90-2.08ffines

Where:

D10, D60, and D90 are the grain sizes in mm for which 10 percent, 60 percent, and 90 percent of the sample is more fine-grained.

Fines is the fraction of the soil (by weight) that passes the U.S. Standard No.

200 Sieve.

Layers near and above the water table or low permeability zones (e.g., a clay, dense glacial till, or rock layer) should be considered in design, while the layers below the groundwater table or low permeability zones will not significantly influence the rate of infiltration. The coefficient of permeability using the Soil Grain Size Analysis Methods are provided in Table 2 below.

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Table 2. Coefficient of Permeability Results

Test Pit

Sample Depth (bgs)

Sieve Coefficient of Permeability

Total Correction

Factor (CFT)1,2 Ksat design

(ft / hr)3 Soil

Classificationcm /sec ft / hr

TP-1 S2 at 3 feet 0.06 80 0.20 16

GRAVEL (GP)

with sand

TP-3 S3 at 7 feet 0.15 210 0.20 40

GRAVEL (GP)

with sand

Notes:

1) Correction factors based on a) Site variability and number of locations tested (CFv = 0.33 to 1.0) b)

Grain Size Test Method correction (CFt = 0.40), and c) Degree of influent control (CFm = 0.9).

2) CFT = CFv x CFt x CFm

3) Ksat design = Ksat initial x CFT

2.4.2

For infiltration facilities used for treatment purposes, the measured (initial) soil infiltration rate should be 9 inches per hour, or less. Design (long-term) infiltration rates up to 3.0 inches per hour can also be considered under certain conditions. The design infiltration also should be used for maximum drawdown time and routing calculations.

For treatment facilities used for flow controls, the physical and chemical soil characteristics determine if the soil is adequate for removing the target pollutants:

CEC/100 grams dry soil (USEPA Method 9081).

A minimum of 1.0 percent organic content for the treatment soil (ASTM D 2974).

Depth of soil used for infiltration treatment must be a minimum of 18 inches thick. Depth of soil below permeable pavements serving as pollution-generating hard surfaces may be reduced to one foot if the permeable pavement does not accept run-on from other surfaces.

2.4.3 Setback requirements for infiltration facilities are generally required by local regulations, uniform building code requirements, or other state regulations. Guidance for infiltration facility setback criteria include (Ecology 2014):

Should be set back at least 100 feet from drinking water wells, septic tanks or drainfields, and springs used for public drinking water supplies. Infiltration facilities upgradient of drinking water supplies and within 1, 5, and 10-year time of travel zones must comply with Health Dept. requirements (Washington State Wellhead Protection Program Guidance Document, DOH, 6/2010).

Additional setbacks must be considered if roadway deicers or herbicides are likely to be present in the influent to the infiltration system.

From building foundations: .

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 9

From a Native Growth Protection Easement (NGPE):

From the top of slopes >15%:

Evaluate on-site and off-site structural stability due to extended subgrade saturation and/or head loading of the permeable layer, including the potential impacts to downgradient properties, especially on hills with known side-hill seeps.

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Based on our evaluation that included data review, subsurface explorations, soil laboratory testing, and engineering analyses, the proposed Project is geotechnically-feasible provided the recommendations contained in this report are incorporated into its design and construction. Our key findings and conclusions include:

The subsurface conditions at the Site consist of topsoil and roots overlying unconsolidated recessional glacial outwash to approximately 20 to 25 feet bgs.

The unconsolidated recessional glacial outwash deposits are generally suitable for reuse.

Shallow spread footings will be an appropriate foundation type for the planned building.

Groundwater is not anticipated within the anticipated excavation depths.

Vegetation will be part of the Site clearing and preparation that will include removal and repair of large root balls and replacement with suitable backfill materials.

Stormwater infiltration is feasible but for treatment will require attenuating the rates and potentially a soil amendment layer to meet CEC and organic content requirements.

Although final grading plans had not been completed at the time of this report, we anticipate cuts and fills will generally be less than 2 feet over most of the Site. From a geotechnical perspective, earthwork excavation using conventional equipment will be feasible during construction.

3.1

3.1.1 Inertial seismic forces are expected to affect the Site and structures. Appropriate design of structures in accordance with the current version of the IBC will mitigate seismic hazards.

2 percent probability of exceedance (PE) in 50 years (2,475-year return period; IBC, 2015). The U.S. Geological Survey (USGS) has completed probabilistic ground motion studies and maps for Washington (USGS, 2014).

Current IBC design methodologies express the effects of site-specific subsurface be correlated to the average standard penetration resistance (SPT) in the upper 100 feet of the soil profile. Based on the results of our subsurface exploration program and using the 2015 IBC criteria, we recommend the Site be characterized by a Seismic Site Class C.

The code-based seismic design criteria, in accordance with the 2015 IBC, are summarized in Table 3.

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 11

Table 3. 2015 IBC Seismic Design Parameters Parameter1 Recommended Value

Site Class C Very Dense Soil and Soft Rock

Short Period Spectral Acceleration, Ss (g)2 1.291

1-Second Period Spectral Acceleration, S1 (g) 0.510

Peak Ground Acceleration, PGA (g) 0.500

Site Coefficient (Fa) 1.0

Site Coefficient (Fv) 1.3

Site Coefficient (FPGA) 0.500

Design Short Period Spectral Acceleration, SDS (g) 0.861

Design 1-Second Period Spectral Acceleration, SD1 (g) 0.442

Notes:

1) Based on the latitude and longitude of the Site: 47.120°N, 122.567°W

2) g = acceleration due to gravity

The National Earthquake Hazards Reduction Program (NEHRP) Recommended Seismic Provisions recognizes that, independent of the quality of their design and construction, include:

The intensity of ground shaking and other earthquake effects the structure is likely to experience.

, including consideration of the number of people who would ructure for its intended purpose after an earthquake.

We understand the building will be assigned an Occupancy Category Type IV.

Table 4. NEHRP Description of Category IV-Type Buildings

Category Representative Buildings Acceptable Risk IV Buildings and structures that:

Are essential to post-earthquake response (e.g., hospitals, police stations, fire stations, and emergency communications centers) or

House very large quantities of hazardous materials.

Very low risk of earthquake induced collapse.

Low risk that the building or structure will be damaged sufficiently to impair use in post-earthquake response and recovery efforts. Very low risk of release of hazardous materials.

12 FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

3.2

3.2.1 Based on our observations of the subsurface conditions at the Site, shallow foundations on spread footings may be used for building supports if placed on the recessional glacial outwash deposits. Spread footings should be established in firm, undisturbed recessional glacial outwash deposits or compacted structural fill overlying these deposits at a minimum depth of 1.5 feet below the lowest adjacent finished grade. The parameters provided below assume any deleterious materials and root systems are completely removed and replaced with structural fill, where appropriate, in accordance with the Construction Considerations in Section 4. The exposed subgrade surface of all the footings should be evaluated by a qualified geotechnical engineer or engineering geologist.

Table 5. Spread Footing Foundation Design Recommendations1

Design Item Design Information

Structures ASOG Complex Building

Bearing Material Recessional glacial outwash deposits, Steilacoom Gravel

(Qgosg), and compacted structural fill

Allowable Bearing Pressure1 4,000 psf2

Minimum Embedment Depth3 18 inches

Minimum Footing Width 24 inches

Total Estimated Settlement Differential Settlement

Less than 1 inch Less than 0.5-inch between adjacent footings

Notes:

1) Designs are based on the subsurface conditions encountered in the explorations and assumes the recommendations in the Construction Considerations Section will be adhered to.

2) Pounds per square foot

3) The recommended allowable bearing pressure applies to the total of dead plus long-term-live loads.

Allowable bearing pressures may be increased by one-

For use in design, an ultimate coefficient of friction of 0.45 may be assumed along the interface between the base of a cast-in-place concrete footing and the subgrade soils. An ultimate passive earth pressure of 450 pounds per cubic foot (pcf) may be assumed for structural fill replacement or gravel soils adjacent to below-grade elements. The upper 1 foot of passive resistance should be neglected in design. The recommended coefficient of friction and passive pressure values are ultimate values that do not include a safety factor. We recommend applying a factor of safety of at least 1.5 in design for determining allowable values for coefficient of friction and passive pressure.

3.3 Concrete slabs-on-grade should be designed in accordance with the American Concrete

360R-10 Guide to Design of Slabs-on-Ground (ACI, 2010).

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For slabs that are designed as beam-on-elastic foundation, a modulus of vertical subgrade reaction of 150 pounds per cubic inch (pci) may be utilized. Satisfactory support for building floor slabs can be obtained from the subgrades prepared in accordance with our recommendations presented in the Site Preparation and/or Wet-Weather/Wet-Soil Conditions sections of this report. A minimum 6-inch-thick layer of imported granular material should be placed and compacted over the prepared subgrade. Imported granular material should be composed of crushed rock or crushed gravel that is relatively well-graded between coarse and fine, contains no deleterious materials, has a maximum particle size of 1 inch, and has less than 5 percent by dry weight passing the US Standard No. 200 Sieve.

3.4 Current plans show an approximately 200-foot-long, 5- to 6-foot-tall retaining wall on the west side of the Project. Yielding walls, such as cantilever retaining walls, should be designed using a lateral earth pressure based on an equivalent fluid having a unit weight of 35 pcf. Nonyielding walls, such as basement walls, should be designed using a lateral earth pressure based on an equivalent fluid having a unit weight of 55 pcf. These earth pressure values assume level backfill conditions exist behind the wall, and that a subsurface drain combined with a free draining wall backfill material is utilized to prevent the build-up of unbalanced hydrostatic forces. Refer to the Drainage Considerations section below for subsurface drain recommendations.

The lateral seismic soil pressure for design of the retaining walls was derived using the Mononobe Okabe method. Taking into account the possible backfill soil properties, ground shaking representing the calculated PGA, and assuming a relatively flat backslope behind the retaining wall, the average lateral seismic soil pressure is equivalent to 12H (where H is the height of the wall). The seismic increment is represented by a uniform rectangular pressure along the height of the wall.

Overcompaction of the backfill behind walls should be avoided. In this regard, we recommend compacting the backfill to about 90 percent of the MDD (ASTM D1557).

Heavy compactors and large pieces of construction equipment should not operate within 5 feet of any embedded wall to avoid the buildup of excessive lateral pressures.

Compaction close to the walls should be accomplished using hand-operated vibratory plate compactors.

Lateral forces that may be induced on the wall due to other surcharge loads should be considered by the structural engineer.

3.5 We understand that construction of the new facility will require new pavement sections in both hot mix asphalt (HMA) and rigid pavement (PCC). Our pavement recommendations were developed using the Unified Facilities Criteria (UFC) Pavement Design for Roads and Parking Areas Manual (Department of Defense, 2016). Pavement-Transportation Computer Assisted Structural Engineering (PCASE software, v. 2.09.05 Desktop) publicly available through the USACE website (USACE) is mandatory for the design of roads and parking areas trafficked by special military vehicles and for all vehicle types

14 FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

outside of the United States and its territories and possessions. The UFC 3-201-01 describes special military vehicles as cranes, aircraft tow tractors, forklifts, container handling vehicles, tracked vehicles, heavy military cargo trucks (greater than 10,000 pounds (4535 kg) (e.g., Heavy Expanded Mobility Tactical Truck (HEMTT), Heavy Equipment Transport Systems (HETS), Palletized Load Systems (i.e. M1074, M1075), Mine-Resistant Ambush Protected (MRAP), and Stryker vehicles. We are assuming none

. Therefore, we have developed the pavement recommendations using the Washington State Department of Transportation (WSDOT) Pavement Policy Manual (WSDOT, 2018) based upon American Association of State Highway and Transportation Officials (AASHTO) design methods. The new pavements were designed based on a 20-year design life.

Materials for pavements designed in accordance with the UFC should conform to requirements in Unified Facility Guide Specifications (UFGS). Per the UFC, to the greatest practical extent, local materials that meet requirements of WSDOT and are in accordance to UFC requirements, should be used.

3.5.1 A traffic volume has not provided to calculate an equivalent single axle load (ESAL), which is a standard traffic load used in pavement design. Depending on the size of a vehicle, the load may correspond to more than one ESAL per vehicle. In addition, to the traffic volume growth rate, WSDOT incorporates a traffic volume growth rate and an ESAL growth rate in an attempt to account for the increases in applied load transmitted through the tires over the pavement life. We are assuming lightly loaded traffic primarily consisting of passenger vehicles will be using the parking areas throughout the design pavement life and heavier vehicles will remain within the project roadways. Using traffic and ESAL growth rates of 0 percent and a 20-year design life, the estimated number of design ESALs are 80,000 and 720,000 for the parking areas and roadways, respectively.

3.5.2 Layer thicknesses and total pavement structure over subgrade soils for HMA pavements are based on four criteria:

Depth to provide a minimum level of serviceability for the design period recognizing that periodic surface renewals may be needed, Depth to prevent excessive rutting, Depth to prevent premature fatigue cracking of the HMA layers, and

Depth to provide adequate frost depth protection.

The following pavement recommendations and assumptions are based on our observations, testing, and experience:

20-year design life

Resilient modulus of 10,000 psi and 28,000 psi assumed for the Site soils and aggregate base, respectively, Initial and terminal serviceability index of 4.5 and 3.0, respectively

Reliability and standard deviation of 85 percent and 0.50, respectively

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 15

Structural layer coefficients of 0.42 and 0.13 for the asphalt and crushed surfacing base course (CSBC), respectively

Based on these parameters and the variable vehicle types accessing the parking lot areas and roadways, we recommend the minimum flexible pavement requirements be:

3 inches of HMA over 6 inches of CSBC in parking areas; and, 6 inches of HMA over 6 inches of CSBC in roadways

Heavy construction traffic on new pavements or partial pavement sections (such as base course over the prepared subgrade) will likely exceed the design loads and could potentially damage or shorten the life of the pavements. Therefore, we recommend the contractor take appropriate precautions to protect the subgrade, base course, and pavement during construction.

Pavement subgrades should be prepared in accordance with the Site Preparation section of this report. The asphalt binder should be performance graded according to WSDOT SS 9- 02.1(4) - Performance Graded Asphalt Binder. The AC should consist of ½ -inch, dense, hot-mix asphalt (HMA). The minimum and maximum paving lift thicknesses should be 1.5 and 3.0 inches, respectively. The AC should conform to WSDOT SS 5- 04.3(7)A - Mix Design, WSDOT SS 9-03.8(2) - HMA Test Requirements, and WSDOT ss 9-03.8(6) - HMA Proportions of Materials. The AC should be compacted to 91 percent of the maximum theoretical density (Rice value) of the mix, as determined in accordance with ASTM D 2041, following tile guidelines set in WSDOT ss 5-04.3(10) - Compaction.

3.5.3 Based on the past performance of PCC under a variety of traffic conditions (various ESAL levels), WSDOT policy advises to use slab thicknesses of 0.67 feet or greater.

Based on the assumed traffic loading, the recommended rigid pavement section is 8 inches PCC (undoweled) over 6 inches CSBC.

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4.1 All work should be performed in conformance with the appropriate Unified Facilities Guide Specifications (UFGS, 2018) Division and Section. Earthwork show be completed in conformance with UFGS, Division 31 Earthwork.

Earthwork is typically most economical when performed under dry weather conditions.

Appropriate erosion control measures should be implemented prior to beginning earthwork activities in accordance with the local regulations. In our opinion, excavation can generally be accomplished using standard excavation equipment. While not directly observed in our subsurface explorations, the presence of potential obstructions, such as small boulders, buried logs, or other debris, in the fill or other deposits should be anticipated.

4.2 Site preparation within the proposed construction footprint should include removal of fill and soils containing roots, organics, debris, and any other deleterious materials. The contractor must use care during Site preparation and excavation operations, so that any bearing surfaces are not disturbed. If disturbance does occur, the disturbed material should be removed to expose undisturbed material or be compacted in place to acceptable criteria as determined by the geotechnical engineer.

All footing excavations should be trimmed neat and the bottom of the excavation should be carefully prepared. All loose or softened soil should be removed from the footing excavation or compacted in place prior to placing reinforcing steel bars. We recommend that footing excavations be observed by the geotechnical engineer prior to placing steel and concrete to verify the recommendations in this report have been followed.

The subgrade under the pavement section areas should be prepared by scarifying, moisture conditioning, and recompacting a minimum of 12 inches below the bottom of the base course. Materials generated during earthwork should be transported off-site or

4.3 Following Site preparation, and prior to placing an aggregate base for the pavement sections, the exposed subgrade should be evaluated either by proofrolling or a similar method of subgrade verification. The subgrade should be proofrolled with a fully loaded dump truck or similar heavy, rubber-tire construction equipment to identify unsuitable areas. If evaluation of the subgrades occurs during wet conditions, or if proofrolling the subgrades will result in disturbance, they should be evaluated by Aspect using a steel foundation probe. We recommend that a qualified geotechnical engineer be retained to observe the proofrolling and perform the subgrade verifications. Unsuitable areas identified during the field evaluation should be compacted to a firm condition or be excavated and replaced with structural fill.

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 17

4.4 If earthwork is to be performed or fill is to be placed in wet weather or under wet conditions, when soil moisture content is above optimum and difficult to control, the following recommendations apply:

Earthwork should be performed in small areas to minimize exposure.

Structural fill placed during wet weather should consist of approved materials meeting the criteria details below.

Excavation or the removal of unsuitable soils should be followed promptly by the placement and compaction of the specified structural fill.

The size, type, and access of construction equipment used may have to be limited to prevent soil disturbance.

The ground surface within the construction area should be graded to promote runoff of surface water away from the slopes and to prevent water ponding.

The ground surface within the construction area should be properly covered and under no circumstances should be left uncompacted and/or exposed to moisture.

Soils that become too wet for compaction should be removed and replaced with specified compacted structural fill.

Excavation and placement and compaction of fill should be observed by the geotechnical engineer to verify that all unsuitable materials are removed prior to placement, compaction requirements are met, and site drainage is appropriate.

Erosion and sedimentation control should be implemented in accordance with best management practices (BMPs).

4.5

4.5.1 The near-surface soils at the Site can be excavated with conventional earthwork equipment. Sloughing and caving should be anticipated in loose, noncohesive materials.

A qualified geotechnical engineer should be retained to review the grading and utility plans when they become available for comparison with encountered field conditions;

additional work may be required to better define the impact on the Project.

4.5.2 All excavations should be made in accordance with applicable Occupational Safety and Health Administration (OSHA) and State regulations. The contractor is solely responsible for adherence to the OSHA requirements. Trench cuts should stand relatively vertical to a depth of approximately 4 feet bgs, provided no groundwater seepage is present in the trench walls. Open excavation techniques may be used in the clay, silt, silty sand, and sandy silt, provided the excavation is configured in accordance with the OSHA requirements, groundwater seepage is not present, and with the understanding that some sloughing may occur. The trenches should be flattened if sloughing occurs or seepage is present. If shallow groundwater is observed during construction, use of a trench shield or other approved temporary shoring is recommended for cuts that extend below

18 FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

groundwater seepage, or if vertical walls are desired for cuts deeper than 4 feet bgs. If dewatering is used, we recommend that the type and design of the dewatering system be the responsibility of the contractor, who is in the best position to choose systems that fit the overall plan of operation.

4.5.3 Maintenance of safe working conditions, including temporary excavation stability, is the sole responsibility of the contractor. All temporary cuts in excess of 4 feet in height that are not protected by trench boxes, or otherwise shored, should be sloped in accordance with OSHA requirements.

With time and the presence of seepage and/or precipitation, the stability of temporary unsupported cut slopes can be significantly reduced. We recommend planning the construction schedule to have excavation occur during the summer months and to minimize the amount of time that the temporary slopes will be unsupported during construction. The contractor should monitor the stability of the temporary cut slopes and adjust the construction schedule and slope inclination accordingly. Vibrations created by traffic and construction equipment may cause caving and raveling of the face of the temporary slopes. At no time should soil stockpiles, equipment, and other loads be placed immediately adjacent to an excavation.

In general, shallow surface soils, such as topsoil and unconsolidated soils that will be subject to excavation and sloping on the Site classify OSHA Soil Classification Type C.

These soils are expected to fail at steep angles. Temporary excavation side slopes (cut slopes) are anticipated to stand as steep as 1.5H:1V within the topsoil and unconsolidated soils. The cut slope inclinations estimated above are for planning purposes only and are applicable to excavations without inflowing perched groundwater or runoff.

Permanent slopes for the project should have a maximum inclination of 2H:1V. Access roads and pavements should be located at least 5 feet from the top of temporary slopes.

Surface water runoff should be collected and directed away from slopes to prevent water from running down the face.

4.6 Structural fill, including base rock, should be placed over subgrades that have been prepared in conformance with the Site Preparation and Wet-Weather/Wet-Soil Conditions sections of this report. Source material may be derived from on-site sources, or imported. The on-site soils will likely contain over-sized materials but may be suitable for reuse on the Project, provided the soil meets the material requirements described below and can be sufficiently screened. Soil derived from saturated excavations should be anticipated to be less suitable for use as fill due to elevated moisture contents.

Execution of the work must be performed in compliance with UFGS Division 31 23

00.00 20, Part 3 Execution.

General fill specifics are provided in Table 6.

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Table 6. Fill Type and Compaction Requirements

Fill Type UFGS Specification Details

Lift Thickness1 and Compaction

Requirements2

On-Site Soil UFGS Division 31 23 00.00 20; Part

2, 2.1.7 Backfill and Fill Material 8 to 12 inches

Dependent on Application

Imported Granular Materials

UFGS Division 31 23 00.00 20; Part 2, 2.1.7 Backfill and Fill Material4

9 inches 95 percent

Crushed Aggregate Base

UFGS Division 32 11 23.00 20; Part 2, 2.1.1 Coarse Aggregate

WSDOT SS 9-03.9(3) Crushed Surfacing Top Course or Base

Course 9 inches

100 percent

Retaining Walls UFGS Division 31 23 00.00 20; Part

2, 2.4.1 Porous Fill 90 percent

Foundation Base Aggregate

UFGS Division 31 23 00.00 20; Part 2, 2.1.8 Select Material4

9 inches 95 percent

Utility Backfill UFGS Division 31 23 00.00 20; Part

2, 2.3 Utility Bedding Material Refer to Part 3 of UFGS Division 31 23 00.00 20

Notes:

1. Maximum uncompacted thickness.

2. MDD, as determined by ASTM D1557, except for Utility Bedding Material, as determined by

ASTM D698.

3. Fraction passing the U.S. Standard No. 4 Sieve, less than 5 percent by dry weight should pass the U.S. Standard No. 200 Sieve.

4.7

4.7.1 The perimeter ground surface and hardscaping should be sloped to drain away from all structures and away from adjacent slopes. Gutters should be tight-lined to a suitable discharge and maintained as free-flowing. Any crawl spaces should be adequately ventilated and sloped to drain to a suitable, exterior discharge.

4.7.2 Due to the potential for perched groundwater, we recommend perimeter foundation drains be installed around all proposed structures. The foundation subdrainage system should include a minimum 4-inch-diameter perforated pipe in a drain rock envelope. A nonwoven geotextile filter fabric, such as Mirafi 140N or equivalent, should be used to completely wrap the drain rock envelope, separating it from the native soil and footing backfill materials. The invert of the perimeter drain lines should be placed approximately at the bottom of footing elevation. Also, the subdrainage system should be sealed at the ground surface. The perforated subdrainage pipe should be laid to drain by gravity into a

20 FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

non-perforated, solid pipe and finally connected to the Site drainage stem at a suitable location. Water from downspouts and surface water should be independently collected and routed to a storm sewer or other outlet. This water must not be allowed to enter the bearing soils.

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 21

At the time of this report, plans and specifications have not been completed. If development of the Projects results in changes to the scope of work, we should be contacted to determine if our recommendations should be revised. Aspect is available to provide input to geotechnical aspects of the project plans and specifications, upon request.

This report is issued with the understanding that the information and recommendations contained herein will be brought to the attention of the appropriate design team personnel and incorporated into the project plans and specifications, and that the necessary steps will be taken to verify that the contractor and subcontractors carry out such cannot be responsible for the safety of personnel other than our own on the Site; the safety of others is the responsibility of the contractor. The contractor should notify the property owner if they consider any of the recommended actions presented herein unsafe.

We are available to provide geotechnical engineering and monitoring services during construction. The integrity of the foundations depends on proper site preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent.

22 FINAL PROJECT NO. 170467 SEPTEMBER 14, 2021

ASTM International (ASTM), 2018, 2018 Annual Book of ASTM Standards, West Conshohocken, Pennsylvania.

Atwater, B.F., S. Musumi-Rokkaku, K. Satake, Y. Tsuji, K. Ueda, and D.K. Yamaguci, 2015, The orphan tsunami of 1700 Japanese clues to a parent earthquake in North America, US Geological Survey, Professional Paper 1707.

Bucknam, R.C., Hemphill-Haley, E., and Leopold, E.B., 1992, Abrupt uplift within the past 1700 years at southern Puget Sound, Washington: Science, v. 258, p. 1611- 1614.

Department of Defense, 2016, Unified Facilities Criteria (UFC): Pavement Design for Roads and Parking Areas, UFC 3-250-01, dated November 14, 2016.

Schuster, E.J., Cabibbo, A.A., Schilter, J.F., Hubert, I.J., 2015, Geologic Map of the Tacoma 1:100,000-scale Quadrangle, Washington, November 2015, Washington Division of Geology and Earth Resources, Map Series 2015-03, scale 1:100,000.

Sherrod, B.L., Brocher, T.M., and Bucknam, R.C., 2002, Asynchronous land-level change along the Tacoma fault in A.D. 800-1200: Seismological Research Letters, v. 73, p. 240.

UFGS Working Group (UFGS), 2018, Unified Facilities Guide Specifications, online:

https://www.wbdg.org/ffc/dod/unified-facilities-guide-specifications-ufgs.

United States Army Corps of Engineers (USACE), Engineer Research and Development Center (ERDC), https://transportation.wes.army.mil/pcase/software.aspx

Washington State Department of Ecology (Ecology), 2012, Stormwater Management Manual for Western Washington.

Washington State Department of Transportation (WSDOT), 2018, Pavement Policy Manual, Multimodal Development and Delivery Pavement Office, September 2018.

Washington State Department of Transportation (WSDOT), 2016, Standard Specifications for Road, Bridge and Municipal Construction, Document M 41-10.

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL 23

Work for this project was performed for HDR, Inc. (Client) for specific application to the proposed project as described herein, and this report was prepared in accordance with generally accepted professional practices for the nature and conditions of work completed in the same or similar localities, at the time the work was performed. This report may be used only by the Client and for the purposes stated, within a reasonable time from its issuance. This report does not represent a legal opinion. No other warranty, expressed or implied, is made.

All reports prepared by Aspect Consulting for the Client apply only to the services described in the Agreement(s) with the Client. Any use or reuse by any party other than the Client is at the sole risk of that party, and without liability to Aspect Consulting.

dispute regarding the content of electronic documents furnished to others.

Recommendations presented herein are based on data that we acquired, our geotechnical engineering calculations, and judgment in accordance with our mutually agreed-upon scope of work. Variations may exist between soil and groundwater conditions reported, and those actually underlying the Site. The nature and extent of such soil variations may change over time and will not be evident before construction begins. If any soil conditions are encountered at the Site that are different from those described in this report, we should be notified immediately to review the applicability of our recommendations.

It is the Client's responsibility to see that all parties to this project, including the designer, contractor, subcontractors, etc., are made aware of this report in its entirety. The use of information contained in this report for bidding purposes should be done at the contractor's option and risk.

Our scope of our work does not include services related to construction safety precautions. Our recommendations are not intended to direct the contractors' methods, techniques, sequences or procedures. Our scope of our work also excludes the assessment of environmental characteristics, particularly those involving potentially hazardous substances in soil or groundwater.

Please refer to Appendix C for additional information governing the use of this report.

American Lake

Site Location Map Geotechnical Engineering Report

Washington Air National Guard ETRD 169847 ASOG Complex Camp Murray, Washington

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Federal Way

Fife

Gig Harbor

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Tacoma

Vashon y

Basemap Layer Credits || Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), swisstopo, © OpenStreetMap contributors, and the GIS User Community Copyright:© 2014 Esri

SITE LOCATION

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FIGURE NO.

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Site Exploration Map Geotechnical Engineering Report

Washington Air National Guard ETRD 169847 ASOG Complex Camp Murray, Washington

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Basemap Layer Credits || Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community

Source:

PROJECT NO. 170467 SEPTEMBER 14, 2021 FINAL A-1

A. Field Exploration Program

The exploration locations are shown on…