Attachment 6b: Geotech Report

Project 2020-016Bellevue College, Center forTransdisciplinary Learning &Innovation (TDI)

Attachment 6b: Geotech Report

Geotechnical Engineering Services

Center for Transdisciplinary Learning and Innovation Bellevue College Bellevue, Washington

for Bellevue College

July 8, 2021


Center for Transdisciplinary Learning and Innovation Bellevue College Bellevue, Washington

for Bellevue College

July 8, 2021

17425 NE Union Hill Road Suite 250 Redmond, Washington 98052 425.861.6000


Center for Transdisciplinary Learning and Innovation

Bellevue College Bellevue, Washington

File No. 4598-020-00

July 8, 2021

Prepared for:

Bellevue College Facilities Planning & Construction 3000 Landerholm Circle SE Bellevue, Washington 98007-6484

Attention: William Tribble

Prepared by:

GeoEngineers, Inc. 17425 NE Union Hill Road Suite 240 Redmond, Washington 98052 425.861.6000

Kyle M. Smith, PE Geotechnical Engineer

Robert C. Metcalfe, PE, LEG Principal

CRG:KMS:RCM:nld

cc: Laurie Kearney (one copy by email)

Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record.

July 8, 2021| Page i File No. 4598-020-00

Table of Contents EXECUTIVE SUMMARY .................................................................................................................................... ES-1

1.0 INTRODUCTION ............................................................................................................................................. 1

1.1. Project Description .................................................................................................................................... 1 1.2. Purpose and Scope ................................................................................................................................... 1

2.0 FIELD EXPLORATION AND LABORATORY TESTING .................................................................................... 1

2.1. Field Explorations ...................................................................................................................................... 1 2.2. Laboratory Testing .................................................................................................................................... 2

3.0 SITE DESCRIPTION ........................................................................................................................................ 2

3.1. Existing Reports ........................................................................................................................................ 2 3.2. Surface Conditions.................................................................................................................................... 2 3.3. Subsurface Soil Conditions ...................................................................................................................... 2 3.4. Groundwater Conditions ........................................................................................................................... 3

4.0 CONCLUSIONS AND RECOMMENDATIONS ................................................................................................. 3

4.1. Earthquake Engineering ........................................................................................................................... 3 4.1.1. 2018 IBC Seismic Design Information ......................................................................................... 3 4.1.2. Liquefaction Potential ................................................................................................................... 4 4.1.3. Ground Rupture ............................................................................................................................. 4 4.1.4. Landslides ...................................................................................................................................... 4

4.2. Foundations .............................................................................................................................................. 4 4.2.1. Foundation Design ........................................................................................................................ 4 4.2.2. Foundation Settlement ................................................................................................................. 5 4.2.3. Lateral Resistance ......................................................................................................................... 5 4.2.4. Construction Considerations ........................................................................................................ 5 4.2.5. Footing Drains ............................................................................................................................... 6

4.3. Below-Grade Walls and Retaining Walls .................................................................................................. 6 4.3.1. Design Parameters ........................................................................................................................ 6 4.3.2. Backdrainage ................................................................................................................................. 7 4.3.3. Other Considerations .................................................................................................................... 7

4.4. Slab-on-Grade Floor .................................................................................................................................. 7 4.4.1. Subgrade Preparation ................................................................................................................... 7 4.4.2. Design Parameters ........................................................................................................................ 7

4.5. Pavement Recommendations .................................................................................................................. 8 4.5.1. Subgrade Preparation ................................................................................................................... 8 4.5.2. New Hot Mix Asphalt Pavement ................................................................................................... 8 4.5.3. Portland Cement Concrete Pavement .......................................................................................... 8 4.5.4. Asphalt-Treated Base .................................................................................................................... 9

4.6. Earthwork .................................................................................................................................................. 9 4.6.1. Clearing and Site Preparation ....................................................................................................... 9 4.6.2. Subgrade Preparation ................................................................................................................. 10 4.6.3. Working Pad ................................................................................................................................. 10 4.6.4. Structural Fill................................................................................................................................ 11

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4.6.5. Permanent Cut and Fill Slopes ................................................................................................... 14 4.6.6. Utility Trenches ............................................................................................................................ 14 4.6.7. Sedimentation and Erosion Control ........................................................................................... 14

4.7. Excavations ............................................................................................................................................. 14 4.7.1. Temporary Cut Slopes ................................................................................................................. 15

4.8. Infiltration Considerations ...................................................................................................................... 16 4.9. Drainage Considerations ........................................................................................................................ 16 4.10. Recommended Additional Geotechnical Services ................................................................................ 16

5.0 LIMITATIONS ............................................................................................................................................... 17

6.0 REFERENCES .............................................................................................................................................. 17

LIST OF FIGURES

Figure 1. Vicinity Map Figure 2. Site Plan Figure 3. Wall Drainage and Backfill Figure 4. Compaction Criteria for Trench Backfill

APPENDICES

Appendix A. Field Explorations Figure A-1 – Key to Exploration Logs Figures A-2 through A-7 – Log of Borings Figures A-8 through A-10 – Log of Test Pits

Appendix B. Laboratory Testing Figures B-1 and B-2 – Sieve Analysis Results

Appendix C. Boring Logs from Previous Studies Appendix D. Report Limitations and Guidelines for Use

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EXECUTIVE SUMMARY

This report contains the results of our geotechnical engineering services for use in the design of the proposed Center for Transdisciplinary Learning and Innovation (TDI). This summary is presented for introductory purposes only and the complete recommendations presented in this report must be used for project design. The project consists of constructing a two-story building located immediately north of the existing parking garage and east of Kelsey Creek Road on the Bellevue College campus. The building will be cut slightly into the hillslope with below-grade walls needed on the east side of the lower level. The lower level of the building will be at Elevation 393 feet and will daylight to the west.

Subsurface Conditions

The subsurface conditions at the site were evaluated by drilling six borings and excavating three test pits in the vicinity of the building footprint, as shown on Figure 2. The near-surface soils consist of loose to medium dense fill and/or weathered glacial till overlying dense to very dense relatively unweathered glacial till. Borings B-2 through B-6 encountered very dense weathered glacial till about 2.5 to 3.5 feet below the ground surface (bgs). Boring B-1, the northern most boring, encountered 5 feet of fill and/or medium dense weathered till, which were underlain by very dense glacial till. The deeper relatively unweathered glacial till generally consists of dense to very dense silty sand with gravel. Groundwater seepage was not observed in the explorations.

Seismic Design

The site is classified as Site Class C, in accordance with the 2018 International Building Code (IBC).

Structural Fill

Imported gravel borrow should be used as structural fill under all building elements, especially in wet weather conditions.

Reuse of On-site Materials

The native glacial till is expected to be suitable for use as structural fill during the summer months and may be used as fill in the wet weather months in areas needing only 90 percent compaction (ASTM D 1557) by utilizing good construction practices. We do not recommend using the native glacial till during wet weather when 95 percent compaction is required. If wall backfill is planned during the wet weather months, then we also recommend using imported gravel borrow.

Temporary Cut Slopes

We anticipate that the entire building footprint may be excavated using temporary open cut slopes inclined at 1H:1V (horizontal to vertical) for cuts made in the dense to very dense till soils. Cuts made in the surficial medium dense till and in fill soils should be no steeper than 1½H:1V, unless approved by the geotechnical engineer.

Foundation Design

The building can be supported on conventional spread footings bearing on undisturbed dense to very dense glacial till or on structural fill placed over these soils. Footings bearing on very dense till may be designed

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using an allowable soil bearing value of 8,000 pounds per square foot (psf). Footings bearing on suitable undisturbed medium dense to dense weathered glacial till or on structural fill placed over undisturbed medium dense glacial till may be designed using an allowable soil bearing value of 3,000 psf. All loose or otherwise unsuitable soils should be removed from below building foundations. The allowable bearing value may be increased by one-third for short duration loads such as wind or seismic events.

Lateral foundation loads may be resisted by passive resistance on the sides of the footings and by friction on the base of the footings. For footings supported and surrounded by either dense native soils or compacted structural fill, a coefficient of friction of 0.35 and a passive resistance of 350 pounds per cubic foot (pcf) may be used.

Footing drains should be incorporated in the design of the building.

Floor Slabs

A subgrade modulus of 150 pounds per cubic inch (pci) may be used for design of the slabs-on-grade at the site. Concrete slabs-on-grade should be supported on a 6-inch-thick capillary break layer overlain by a vapor retarder.

Below-grade walls

Below-grade walls should be provided with a free draining drainage layer and footing drainpipes. For below-grade walls constructed either neat against the dense native soils, or backfilled with compacted structural fill, we recommend the following equivalent fluid weights:

■ Allowable passive – 350 pcf

■ Active – 35 pcf

■ At rest – 55 pcf

Infiltration Considerations

Based on our review of the City of Bellevue’s criteria for infiltration infeasibility in the January 2017 Surface Water Engineering Standards, the boring logs, and the results of our geotechnical laboratory tests, we conclude that infiltration is not feasible at this site. We do not recommend that infiltration of storm water be planned due to the presence of dense to very dense, silty native glacial till located immediately below the ground surface across the site. The very dense glacial till is known to be over 75 feet thick in this area of the campus.

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1.0 INTRODUCTION

This report presents the results of our geotechnical engineering services for the Center of Transdisciplinary

Learning and Innovation (TDI) at Bellevue College in Bellevue, Washington. The location of the site and

general configuration(s) of the proposed building is shown on Figures 1 and 2, respectively.

1.1. Project Description

The TDI will be located immediately north of the existing parking garage and east of Kelsey Creek Road.

The building will have two stories and a partial day-light lower level, which will be cut into the slope to the

east. The lower level of the building will be at Elevation 393 feet and will daylight to the west. Two building

configurations were presented in the predesign report, dated November 2020, and the approximate

building footprints are shown on Figure 2. Underground utilities, hardscape and landscaping is also planned

around the building.

1.2. Purpose and Scope

The purpose of our services is to evaluate soil and groundwater conditions as a basis for developing design

criteria for the geotechnical aspects of the Center of Transdisciplinary Learning and Innovation. Field

explorations and laboratory testing were performed to identify and evaluate subsurface conditions at the

site to develop engineering recommendations for use in design of the project.

Our services were performed in general accordance with our proposal dated June 15, 2021. Authorization

to proceed with our services was provided by the Department of Enterprise Services Division of Engineering

and Architectural Services on June 16, 2021.

2.0 FIELD EXPLORATION AND LABORATORY TESTING

2.1. Field Explorations

Subsurface conditions were evaluated through a field exploration program that consisted of drilling and

sampling six borings and three test pits. The explorations were completed within the vicinity of the planned

building footprints using track-mounted drilling equipment subcontracted to GeoEngineers and a backhoe

provided by Bellevue College. The approximate locations of the borings and test pits are shown on Figure 2.

The borings, designated B-1 through B-6, were advanced to depths of about 17½ to 31½ feet below ground

surface (bgs). The test pits, designated TP-1 through TP-3, were excavated to depths of about 2½ to

3½ feet. Locations of explorations were determined in the field by tape measuring to existing site features

such as the existing landscaping and a concrete wall and fence just north of the existing parking garage.

Elevations at the exploration locations were estimated from the site survey provided by Bellevue College,

which was completed by APS Survey and Mapping. The respective ground surface elevations are shown on

the boring logs in Appendix A. Appendix A includes logs of the borings and test pits (Figures A-2 through

A-10) and details of the subsurface explorations performed.

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2.2. Laboratory Testing

Soil samples obtained from the explorations were transported to our laboratory and evaluated to confirm or modify field classifications, as well as to evaluate engineering properties of the soil. Representative samples were selected for laboratory testing consisting of moisture content, percent passing the No. 200 sieve, and sieve analyses. The tests were performed in general accordance with test methods of the American Society for Testing and Materials (ASTM) or other applicable procedures. A brief discussion of the laboratory tests and test results is included in Appendix B.

3.0 SITE DESCRIPTION

3.1. Existing Reports

We reviewed our previous geotechnical report for the existing parking garage and the geologic map for the site, as summarized below:

■ “Report, Geotechnical Engineering Services, Proposed Parking Garage, Bellevue Community College, Bellevue, Washington,” by GeoEngineers, Inc., dated June 7, 2002.

■ “United States Geologic Survey Open File Report 93-233 titled “Geologic Map of Surficial Deposits in the Seattle 30’ x 60’ Quadrangle, Washington,” by J.C. Yount, J.P. Minard and G.R. Dembroff, dated 1993.

Our review of the geologic map for the area and our geotechnical report for the parking garage indicates that the TDI is underlain by very dense glacial till at relatively shallow depths. The glacial till generally consists of a non-sorted, non-stratified mixture of clay, silt, sand and gravel with larger constituents up to boulder-size. Glacial till is very dense and relatively impermeable, but can contain minor amounts of interbedded stratified sand and gravel.

Selected borings from our previous study for the existing parking garage are presented in Appendix C.

3.2. Surface Conditions

The TDI is located immediately north of the existing parking garage and east of Kelsey Creek Road. The site slopes down from about Elevation 405 feet on the east side of the proposed building footprint to about Elevation 393 feet on the west side of the proposed building. Most of the site is covered by landscaping including grass, small shrubs, conifer and deciduous trees and occasional dense blackberry bramble. Dense areas of conifer and deciduous trees occupy the west, south and east perimeter of the site.

3.3. Subsurface Soil Conditions

In general, the soils encountered in the explorations consisted of the following:

■ Topsoil: Borings B-1 to B-6 and test pits TP-1 to TP-3 encountered sod and topsoil to depths of approximately 6 to 12 inches.

■ Fill and Weathered Glacial Till: Approximately 2 to 5 feet of fill and/or highly weathered glacial till was observed in the explorations. The deepest area of fill/weathered glacial till (5 feet) was observed in boring B-1. Approximately 2 to 3 feet of fill and/or medium dense weathered glacial till was encountered in borings B-2 to B-6 and test pits TP-1 to TP-3. The fill and/or highly weathered glacial till generally

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consists of brown medium dense silty fine to medium sand with gravel and occasional cobbles. Bricks were observed in the fill to a depth of about 2 feet in boring B-2. The contact between the weathered glacial till and the underlying very dense relatively unweathered till is gradual.

■ Glacial Till: Very dense glacial till (weathered and unweathered) was encountered beneath the less competent soils in the explorations and to the full depth explored. The very dense glacial till was encountered at 2 to 5 feet bgs in the western portion of the site and about 2 to 3½ feet bgs in the eastern portion of the site. The very dense glacial till generally consists of gray silty fine to medium sand with variable gravel content, and occasional cobbles. The upper 2 to 3 feet of the glacial till unit is typically weathered and consists of brown, loose to dense glacial till with occasional oxidation staining.

3.4. Groundwater Conditions

Wet or moist to wet soils were observed in boring B-2 at 1 to 1½ feet bgs and represents a perched groundwater condition. Minor perched groundwater over the dense to very dense glacial till will exist in response to seasonal changes in precipitation. Dense glacial till is relatively impermeable and water that infiltrates through the ground surface typically flows down gradient over the dense till surface. Localized groundwater zones may also exist in more permeable layers within the glacial till soils.

4.0 CONCLUSIONS AND RECOMMENDATIONS

4.1. Earthquake Engineering

We evaluated the site for seismic hazards including liquefaction, lateral spreading, fault rupture and earthquake induced landsliding. Our evaluation indicates that the site does not have liquefiable soils present and therefore also has no risk of liquefaction induced lateral spreading. In addition, the site has a low risk of fault rupture and earthquake induced landsliding.

4.1.1. 2018 IBC Seismic Design Information

For the site, we recommend the International Building Code (IBC) 2018 parameters for Site Class C, mapped risk-targeted maximum-considered earthquake (MCER) spectral response acceleration at short period (Ss), mapped MCER spectral response acceleration at 1-second period (S1), short period site coefficient (Fa), long period site coefficient (Fv), design spectral acceleration at 0.2-second period (SDS) and the design spectral acceleration at 1.0-second period (SD1). Table1 summarizes recommended values for these parameters.

TABLE 1. 2018 IBC SEISMIC PARAMETERS

IBC Parameter1 Value

Site Class C

Mapped MCER Spectral Response Acceleration at Short Period, Ss (g) 1.348

Mapped MCER Spectral Response Acceleration at 1-second period, S1 (g) 0.469

Short Period Site Coefficient, Fa 1.2

Long Period Site Coefficient, Fv 1.5

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IBC Parameter1 Value

Design Spectral Acceleration at 0.2-second period, SDS (g) 1.078

Design Spectral Acceleration at 1.0-second period, SD1 (g) 0.469

Notes: 1 Parameters developed based on latitude 47.5863 and longitude -122.1478 using the Applied Technology Council (ATC) Hazards online tool (https://hazards.atcouncil.org/).

4.1.2. Liquefaction Potential

Liquefaction is a phenomenon where soils experience a rapid loss of internal strength as a consequence of strong ground shaking. Ground settlement, lateral spreading and/or sand boils may result from soil liquefaction. Structures supported on liquefied soils could suffer foundation settlement or lateral movement that could be severely damaging to the structures.

Conditions favorable to liquefaction occur in loose to medium dense, clean to moderately silty sand that is below the groundwater level. Given the density of the glacial till at the site and relatively deep static groundwater table, it is our opinion that potentially liquefiable soils are not present below the site.

4.1.3. Ground Rupture

Ground rupture from lateral spreading is associated with liquefaction. Lateral spreading involves lateral displacements of large volumes of liquefied soil and can occur on near-level ground as blocks of surface soils displace relative to adjacent blocks. In our opinion, ground rupture resulting from lateral spreading at the site is unlikely because potentially liquefiable soils are not present at the site as discussed above.

Because of the thickness of the Quaternary sediments below the site, which are commonly more than 1,000 feet thick, the potential for surface fault rupture is considered remote.

4.1.4. Landslides

Because there are no significant slopes present at this site and very dense till occurs at the shallow depths, it is our opinion that landsliding as a result of strong ground shaking is unlikely at this site.

4.2. Foundations

We recommend that the TDI be supported on shallow spread footings founded on the dense to very dense native glacial till encountered in the explorations, or on properly compacted structural fill extending down to dense glacial till. The following recommendations for the building foundations are based on the subsurface conditions observed in the borings and the site survey.

4.2.1. Foundation Design

For shallow foundation support, we recommend widths of at least 24 and 36 inches, respectively, for continuous wall and isolated column footings supporting the proposed building. Exterior footings should be founded at least 18 inches below lowest adjacent finished grade. Interior footings should be founded at least 12 inches below bottom of slab or adjacent finished grade.

Unsuitable soils consisting of topsoil, fill and/or highly weathered glacial till vary across the site and must be removed from below planned footings. Based on our borings, 2 to 5 feet of fill and/or looser weathered native soils exist on site. We anticipate that foundations will bear on dense to very dense glacial till;

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however, some overexcavation of unsuitable soils under the footings may be necessary. We recommend footings be designed using a maximum allowable bearing pressure of 8,000 pounds per square foot (psf) where foundations bear on dense to very dense native glacial till or on controlled density fill (CDF) that extends to these soils. Footings supported on suitable medium dense to dense native glacial till or on structural fill extending down to these soils may be designed using a maximum allowable bearing pressure of 3,000 psf. All existing fill and loose or otherwise unsuitable native soils must be removed from below planned footings. The allowable bearing pressure apples to the total dead and long-term live loads and may be increased up to one-third for short-term live loads such as wind or seismic forces.

Overexcavated areas below foundations designed for 8,000 psf bearing pressure should be backfilled with CDF having a design strength of at least 200 pounds per square inch (psi).Where granular structural fill is placed below footings design for 3,000 psf, the fill should extend beyond the edges of the foundations by the depth of the overexcavation.

All footings near below-grade walls should be embedded to a depth that is at least below a 1H:1V (horizontal to vertical) line projected up from the bottom of the closest section of wall, otherwise the below-grade walls need to be designed for lateral loads from the footings.

4.2.2. Foundation Settlement

We estimate that the postconstruction settlement of footings founded on the very dense glacial till or structural fill extending to the medium dense to dense till, as recommended above, will be between ½ and 1 inch. Differential settlement between comparably loaded column footings or along a 25-foot section of continuous wall footing should be less than ½ inch. We expect most of the footing settlements will occur as loads are applied. Loose or disturbed soils not removed from footing excavations prior to placing concrete will result in additional settlement.

4.2.3. Lateral Resistance

Lateral loads can be resisted by passive resistance on the sides of the footings and by friction on the base of the footings. Passive resistance should be evaluated using an equivalent fluid density of 350 pounds per cubic foot (pcf) where footings are poured neat against native soil or are surrounded by structural fill compacted to at least 95 percent of maximum dry density (MDD), as recommended. Resistance to passive pressure should be calculated from the bottom of adjacent floor slabs and paving or below a depth of 1 foot where the adjacent area is unpaved, as appropriate. Frictional resistance can be evaluated using 0.35 for the coefficient of base friction against footings. The above values incorporate a factor of safety of about 1.5.

If soils adjacent to footings are disturbed during construction, the disturbed soils must be recompacted, otherwise the lateral passive resistance value must be reduced.

4.2.4. Construction Considerations

Immediately prior to placing concrete, all debris and loose soils that accumulated in the footing excavations during forming and steel placement must be removed. Debris or loose soils not removed from the footing excavations will result in increased settlement.

If wet weather construction is planned, we recommend that all footing subgrades be protected using a lean concrete mud mat. The mud mat should be placed the same day that the footing subgrade is excavated and approved for foundation support.

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We recommend that all completed footing excavations be observed by a representative of our firm prior to placing mud mat, reinforcing steel, and structural concrete. Our representative will confirm that the bearing surface has been prepared in a manner consistent with our recommendations and that the subsurface conditions are as expected.

4.2.5. Footing Drains

We recommend that perimeter footing drains be installed around the building. The perimeter drains should be installed at the base of the exterior footings as shown on Figure 3. The perimeter drains should be provided with cleanouts and should consist of at least 4-inch-diameter perforated pipe placed on a 3-inch bed of, and surrounded by, 6 inches of drainage material enclosed in a non-woven geotextile fabric such as Mirafi 140N (or approved equivalent) to prevent fine soil from migrating into the drain material. The footing drainpipe should be installed at least 18 inches below the top of the adjacent floor slab. The drainage material should consist of “Gravel Backfill for Drains” per Section 9-03.12(4) of the 2020 Washington State Department of Transportation (WSDOT) Standard Specifications. We recommend the drainpipe consist of either heavy-wall solid pipe (SDR-35 polyvinyl chloride [PVC], or equal) or rigid corrugated smooth interior polyethylene pipe (ADS N-12, or equal). We recommend against using flexible tubing for footing drainpipes. The perimeter drains should be sloped to drain by gravity, if practicable, to a suitable discharge point, preferably a storm drain. We recommend that the cleanouts be covered, and be placed in flush mounted utility boxes. Water collected in roof downspout lines must not be routed to the footing drain lines.

4.3. Below-Grade Walls and Retaining Walls

The following recommendations should be used for the design of below-grade walls that are intended to act as retaining walls and for other retaining structures that are used to achieve grade changes.

4.3.1. Design Parameters

Lateral earth pressures for design of below-grade cast-in-place walls and retaining structures should be evaluated using an equivalent fluid density of 35 pcf provided that the walls will not be restrained against rotation when backfill is placed. If the walls will be restrained from rotation, we recommend using an equivalent fluid density of 55 pcf. Walls are assumed to be restrained if top movement during backfilling is less than H/1000, where H is the wall height. These lateral soil pressures assume that the ground surface behind the wall is horizontal and that the cast-in-place walls are backfilled with structural fill in accordance with the recommendations in Section 4.6.4. For unrestrained walls with backfill sloping up at 2H:1V, the design lateral earth pressure should be increased to 55 pcf, while restrained walls with a 2H:1V sloping backfill should be designed using an equivalent fluid density of 75 pcf. These lateral soil pressures do not include the effects of surcharges such as floor loads, traffic loads or other surface loading. Surcharge effects should be included as appropriate. Below-grade walls for buildings should also include seismic earth pressures. Seismic earth pressures should be included as a rectangular distribution determined using 7H in psf, where H is the wall height.

If vehicles can approach the tops of exterior walls to within half the height of the wall, a traffic surcharge should be added to the wall pressure. For car parking areas, the traffic surcharge can be approximated by the equivalent weight of an additional 1 foot of soil backfill (about 125 psf) behind the wall. For delivery truck parking areas and access driveway areas, the traffic surcharge can be approximated by the equivalent weight of an additional 2 feet (250 psf) of soil backfill behind the wall. These traffic surcharge loads can

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also be calculated based on a rectangular distributed load (equivalent fluid density) to the wall of 35 psf for car parking areas and 70 psf for truck parking areas. Positive drainage should be provided behind below-grade walls and retaining structures as discussed below.

These recommendations are based on the assumption that any retaining walls at this project will be provided with backdrainage. The values for soil bearing, frictional resistance and passive resistance presented above for foundation design are applicable to retaining wall design. Walls located in level ground areas should be founded at a depth of 18 inches below the adjacent grade.

4.3.2. Backdrainage

To reduce the potential for hydrostatic water pressure buildup behind the retaining walls, we recommend that the walls be provided with backdrainage. Backdrainage can be achieved by using free draining material with perforated pipes to discharge the collected water as shown on Figure 3. The zone of free-draining material should be 2 feet wide and should extend from the base of the wall to within 2 feet of the ground surface. The free draining material should be covered with 1 foot of less permeable material, such as the on-site till soil underlain by a geotextile separator such as Mirafi 140N. We recommend against using flexible tubing for wall drainage pipe. The footing drain recommended above can be incorporated into the bottom of the wall drainage zone and used for this purpose.

The pipes should be laid with minimum slopes of one-quarter percent (if possible) and discharge into the stormwater collection system to convey the water off site. The pipe installations should include a cleanout riser with cover located at the upper end of each pipe run. The cleanouts could be placed in flush mounted access boxes. Roof downspouts must not discharge into the perforated pipes intended for providing wall back drainage.

4.3.3. Other Considerations

Exterior retaining systems used to achieve grade transitions or for landscaping, can be constructed using traditional structural systems such as reinforced concrete, concrete masonry units (CMU) blocks, or rockeries. Alternatively, retaining walls can consist of mechanically stabilized earth (MSE) walls, which may be an economical alternative to traditional retaining wall systems. We can provide additional design recommendations for MSE walls, if requested.

4.4. Slab-on-Grade Floor

4.4.1. Subgrade Preparation

We recommend that concrete slabs-on-grade be constructed on a gravel layer to provide uniform support and drainage, and to act as a capillary break. We expect that slab-on-grade floors can be supported on medium dense to very dense native glacial soils encountered in our explorations, or on properly compacted structural fill extending down to these materials. Prior to placing the gravel layer, the subgrade should be proof-rolled as described in Section 4.6. The exposed subgrade should be evaluated during construction and compacted to a firm and unyielding condition, although unsuitable soils should be removed and replaced with structural fill where needed.

4.4.2. Design Parameters

A 6-inch-thick capillary break layer of 1-inch minus clean crushed gravel with negligible sand and silt (WSDOT 9-03.1(4)C, Grading No. 67) should be placed to provide uniform support and form a capillary

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break beneath the slab. For slabs designed as a beam on an elastic foundation, a modulus of subgrade reaction of 150 pounds per cubic inch (pci) may be used for subgrade soils prepared as recommended above. This value assumes the slabs are bearing directly on structural fill placed over medium dense to dense native glacial till and will require evaluation during construction.

If water vapor migration through the slabs is objectionable, the capillary break gravel layer should be covered with heavy plastic sheeting at least 10-mil thick to act as a vapor retarder. This will be desirable where the slabs are in occupied spaces or will be surfaced with tile or will be carpeted. It may also be prudent to apply a sealer to the slab to further retard the migration of moisture through the floor. The contractor should be made responsible for maintaining the integrity of the vapor barrier during construction. Additional water proofing measures that may be needed should be evaluated during design.

4.5. Pavement Recommendations


We recommend the subgrade soils in new pavement areas be prepared and evaluated as described in Section 4.6. All new pavement and hardscape areas should be supported on subgrade soils that have been proof rolled or probed as described in Section 4.6.1. If the exposed subgrade soils are loose or soft, it may be necessary to excavate localized areas and replace them with structural fill or gravel base course. Pavement subgrade conditions should be observed during construction and prior to placing the subbase materials in order to evaluate the presence of zones of unsuitable subgrade soils and the need for over-excavation and replacement of these zones.

4.5.2. New Hot Mix Asphalt Pavement

In light-duty pavement areas (e.g., automobile parking), we recommend a pavement section consisting of at least a 3-inch thickness of ½-inch hot-mix asphalt (HMA) per WSDOT Sections 5-04 and 9-03, over a 4-inch thickness of densely compacted crushed surfacing base course (CSBC) per WSDOT Section 9-03.9(3). In heavy-duty pavement areas (such as driveways, truck traffic lanes, materials delivery), we recommend a pavement section consisting of at least a 4-inch thickness of ½-inch HMA over a 6-inch thickness of densely compacted CSBC.

The base course should be compacted to at least 95 percent of the MDD obtained using ASTM D 1557. We recommend that proof rolling of the subgrade and compacted base course be observed by a representative from our firm prior to paving. Soft or yielding zones observed during proof rolling may require over-excavation and replacement with compacted structural fill.

The pavement sections recommended above are based on our experience. Thicker asphalt sections may be needed based on the actual traffic data, truck loads, and intended use. All paved and landscaped areas should be graded so that surface drainage is directed to appropriate catch basins.

4.5.3. Portland Cement Concrete Pavement

Portland cement concrete (PCC) sections may be considered for areas where concentrated heavy loads may occur. We recommend that these pavements consist of at least 6 inches of PCC over 6 inches of CSBC. A thicker concrete section may be needed based on the actual load data for use of the area. If the concrete pavement will have doweled joints, we recommend that the concrete thickness be increased by an amount

July 8, 2021 | Page 9 File No. 4598-020-00

equal to the diameter of the dowels. The base course should be compacted to at least 95 percent of the MDD.

We recommend PCC pavements incorporate construction joints and/or crack control joints spaced at maximum distances of 12 feet apart, center-to-center, in both the longitudinal and transverse directions. Crack control joints may be created by placing an insert or groove into the fresh concrete surface during finishing, or by saw cutting the concrete after it has initially set-up. We recommend the depth of the crack control joints be approximately one fourth the thickness of the concrete; or about 1½ inches deep for the recommended concrete thickness of 6 inches. We also recommend the crack control joints be sealed with an appropriate sealant to help restrict water infiltration into the joints.

4.5.4. Asphalt-Treated Base

If pavements are constructed during the wet seasons, consideration may be given to covering the areas to be paved with asphalt-treated base (ATB) for protection. Light-duty pavement areas should be surfaced with 3 inches of ATB, and heavy-duty pavement areas should be surfaced with 6 inches of ATB. Prior to placement of the final pavement sections, we recommend the ATB surface be evaluated and areas of ATB pavement failure be removed, and the subgrade repaired. If ATB is used and is serviceable when final pavements are constructed, the CSBC can be eliminated, and the design PCC or asphalt concrete pavement thickness can be placed directly over the ATB.

4.6. Earthwork

Based on the subsurface soil conditions encountered in the explorations, we expect that the soils at the site may be excavated using conventional heavy-duty construction equipment. Very dense glacial till was encountered at relatively shallow depths. Materials within the deeper portions of excavations may require a large excavator to accomplish the excavations. Cobbles were observed in some of the explorations, and glacial till deposits in the area commonly contain boulders that may be encountered during excavation. Accordingly, the contractor should be prepared to deal with boulders.

The glacial till contains sufficient fines (material passing the U.S. standard No. 200 sieve) to be highly moisture-sensitive and susceptible to disturbance, especially when wet. Ideally, earthwork should be undertaken during extended periods of dry weather when the surficial soils will be less susceptible to disturbance and provide better support for construction equipment. Dry weather construction will help reduce earthwork costs and increase the potential for using the native soils as structural fill.

Trafficability on the site is not expected to be difficult during dry weather conditions. However, the native soils will be susceptible to disturbance from construction equipment during wet weather conditions and pumping and rutting of the exposed soils under equipment loads may occur.

4.6.1. Clearing and Site Preparation

Construction of the TDI site should be cleared of surface and subsurface deleterious matter including any debris, shrubs, trees and associated stumps and roots. Graded areas should be stripped of organic soils and roots should be grubbed and removed if larger than ½-inch diameter. All existing utilities should be removed from the building footprint and rerouted if needed. Existing utility trench backfill should be removed from below planned building foundations and be replaced with CDF.

July 8, 2021 | Page 10 File No. 4598-020-00

The organic soils can be stockpiled and used later for landscaping purposes or may be spread over disturbed areas following completion of grading. If spread out, the organic strippings should be in a layer less than 1-foot thick, should not be placed on slopes greater than 3H:1V and should be track-rolled to a uniformly compacted condition. Materials that cannot be used for landscaping or protection of disturbed areas should be removed from the project site.

Some of the undocumented fill that exists on the site will be removed to accomplish the site grades for the building. Where existing undocumented fill is encountered below slab subgrade, the fill should be evaluated by GeoEngineers and removed up to 2 feet below-slab subgrade or until medium dense to dense native soils are encountered (less than 2 feet below-slab subgrade). If medium dense to dense native soils are encountered below the slab subgrade, overexcavation is not required. Excavations for slab subgrade preparation likely do not need to extend more than 2 feet below slab subgrade.


Prior to placing new fills, pavement base course materials or gravel below on-grade floor slabs, subgrade areas should be proof rolled to locate any soft or pumping soils. Prior to proof rolling, all unsuitable soils should be removed from below the building footprint. Proof rolling can be completed using a piece of heavy tire-mounted equipment such as a loaded dump truck. During wet weather, the exposed subgrade areas should be probed to determine the extent of soft soils. If soft or pumping soils are observed they should be removed and replaced with structural fill.

If deep pockets of soft or pumping soils are encountered outside the building area, it may be possible to limit the depth of overexcavation by placing a non-woven geotextile fabric such as TenCate Mirafi 500X (or equivalent) on the overexcavated subgrade prior to placing structural fill. The geotextile will provide additional support by bridging over the soft material and will help reduce fines contamination into the structural fill.

After completing the proof rolling, the subgrade areas should be recompacted to a firm condition, if possible. The degree of compaction that can be achieved will depend on when the construction is performed. If the work is performed during dry weather conditions, we recommend that all subgrade areas be recompacted to at least 95 percent of the MDD in accordance with the ASTM D 1557 test procedure (modified Proctor). If the work is performed during wet weather conditions, it may not be possible to recompact the subgrade to 95 percent of the MDD. In this case, we recommend that the subgrade be compacted to the extent possible without causing undue heaving or pumping of the subgrade soils.

Subgrade disturbance or deterioration could occur if the subgrade is wet and cannot be dried. If the subgrade deteriorates during proof rolling or compaction, it may become necessary to modify the proof rolling or compaction criteria or methods.

4.6.3. Working Pad

If construction of the building occurs during the wet weather months, generally October through May, routing of equipment on the glacial subgrade soils will be difficult and the subgrade will likely become disturbed and softened. In addition, a significant amount of mud can be produced. Therefore, to protect the subgrade soils and to provide an adequate working surface for the contractor’s equipment and labor, the contractor should consider constructing a working pad layer over the exposed subgrade soils. The working pad layer should be about 12 inches thick and should consist of 1½-inch minus clean crushed

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gravel with negligible sand or silt. The working pad layer can be placed in one lift and should be compacted to at least 95 percent of the MDD (per ASTM D 1557). If a working pad layer is used, and if relatively clean immediately prior to construction of the slab-on-grade, it may be used to replace the 6-inch capillary break layer. However, if the working pad becomes contaminated with soil, the contaminated areas should be overexcavated to a depth of 6 inches for placement of the capillary break gravel prior to constructing slabs-on-grade.

4.6.4. Structural Fill

All fill, whether existing on-site glacial till soil or imported soil, that will support floor slabs, pavement areas or foundations, or be placed against retaining walls or in utility trenches should generally meet the criteria for structural fill presented below. The suitability of soil for use as structural fill depends on its gradation and moisture content.

4.6.4.1. Materials Materials used to construct the building pad and backfill below-grade walls and surface hardscape areas are classified as structural fill for the purpose of this report. Structural fill material quality varies depending upon its use as described below:

■ Structural fill placed below foundations (designed for 3,000 psf or lower), floor slabs, or as subbase material below pavement and hardscape areas should meet the criteria for gravel borrow as described in Section 9-03.14(1) of the 2020 WSDOT Standard Specifications.

■ CDF used to support building foundations designed for bearing pressures exceeding 3,000 psf should be in accordance with 2020 WSDOT Standard Specification Section 2-09.3(1)E and should have a minimum compressive strength of 200 psi. The mix design should be adjusted to obtain this minimum compressive strength.

■ Structural fill placed to raise site grades or to backfill utility trenches should meet the criteria for common borrow as described in Section 9-03.14(3) of the 2020 WSDOT Standard Specifications during dry weather conditions (typically June through September). Common borrow materials are highly moisture-sensitive. For wet weather construction (October through May), structural fill placed to raise site grades or in utility trenches should meet the criteria for gravel borrow as described in Section 9-03.14(1) of the 2020 WSDOT Standard Specifications.

■ Structural fill placed immediately outside below-grade walls (drainage zone) should consist of washed gravel in conformance Section 9-03.12(4) of the 2020 WSDOT Standard Specifications, as shown on Figure 3.

■ Structural fill placed as CSBC below pavements should conform to Section 9 03.9(3) of the 2020 WSDOT Standard Specifications.

■ Structural fill placed as capillary break below slabs should consist of 1-inch minus clean crushed gravel with negligible sand or silt in conformance with Section 9-03.1(4)C, grading No. 67 of the 2020 WSDOT Standard Specifications.

4.6.4.2. Reuse of On-site Native Soils The till soils contain a high percentage of fines and will be sensitive to changes in moisture content and difficult to handle and compact during wet weather.

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The medium dense to very dense native glacial till deposits are expected to be suitable for structural fill in areas requiring compaction to at least 95 percent of MDD (per ASTM D 1557), provided the work is accomplished during the normally dry season (June through September) and that the soil can be properly moisture conditioned. Imported structural fill consisting of sand and gravel (WSDOT gravel borrow) should be planned under all building floor slabs and foundation elements where permitted and as wall backfill, especially if construction occurs during wet weather.

The use of existing on-site till soils as structural fill during wet weather should be planned only for areas requiring compaction to 90 percent of MDD, as long as the soils are properly protected from wet weather and not placed during periods of precipitation. The contractor should plan to cover and maintain all fill stockpiles with plastic sheeting if it will be used as structural fill. The reuse of on-site soils is highly dependent on the skill of the contractor and schedule, and we will work with the design team and contractor to maximize the reuse of on-site till soils during the wet and dry seasons.

4.6.4.3. Reuse of Existing Asphalt, Base and Concrete Rubble Existing asphalt pavement and PCC rubble may be reused as structural fill if properly crushed during demolition. Recycled PCC rubble and base course materials may be reused as structural fill throughout the project, including under the building footprint. Recycled asphalt may be used under new pavement and hardscape areas, in utility trenches, and against below-grade walls outside of the building footprint, but should not be used under the floor slabs. For use as general structural fill across the site, the asphalt and concrete rubble should be crushed or otherwise ground up and should meet the gradation requirements for gravel borrow as described in Section 9-03.14(1) of the 2020 WSDOT Standard Specifications. If recycled asphalt and/or concrete will be used under pavement areas, we recommend that it meet the gradation requirements for CSBC as described in Section 9-03.9(3) of the 2020 WSDOT Standard Specifications. Recycled asphalt and concrete should not be used in landscape areas.

4.6.4.4. Fill Placement and Compaction Criteria Structural fill should be mechanically compacted to a firm, non-yielding condition. Structural fill should be placed in loose lifts not exceeding 12 inches in thickness when using heavy compaction equipment and not more than 6 inches when using hand operated compaction equipment. The actual thickness will be dependent on the structural fill material used and the type and size of compaction equipment. Each lift should be moisture conditioned to within about 2 percent of the optimum moisture content to achieve proper compaction before placing subsequent lifts. Compaction of all structural fill at the site should be in accordance with the ASTM D 1557 (modified proctor) test method. Structural fill should be compacted to the following criteria:

1. Structural fill placed below floor slabs and foundations should be compacted to 95 percent of the MDD.

2. Structural fill placed behind below-grade walls should be compacted to between 90 to 92 percent of the MDD estimated in accordance with ASTM D 1557. Care should be taken when compacting fill near the face of below-grade walls to avoid over-compaction and hence overstressing the walls. Hand operated compactors should be used within 5 feet behind the wall. The upper 2 feet of fill below floor slab subgrade should also be compacted to at least 95 percent of the MDD. The contractor should keep all heavy construction equipment away from the top of retaining walls a distance equal to ½ the height of the wall, or at least 5 feet, whichever is greater.

July 8, 2021 | Page 13 File No. 4598-020-00

3. Structural fill in new pavement and hardscape areas, including utility trench backfill, should be compacted to at least 90 percent of the MDD, except that the upper 2 feet of fill below final subgrade should be compacted to at least 95 percent of the MDD, see Figure 4.

4. Structural fill placed as CSBC below pavements should be compacted to 95 percent of the MDD.

5. Non-structural fill, such as fill placed in landscape areas, should be compacted to at least 90 percent of the MDD.

4.6.4.5. Weather Considerations Disturbance of near surface soils should be expected if earthwork is completed during periods of wet weather. During dry weather, the soils will: (1) be less susceptible to disturbance, (2) provide better support for construction equipment, and (3) be more likely to meet the required compaction criteria.

The wet weather season generally begins in October and continues through May in western Washington; however, periods of wet weather may occur during any month of the year. For earthwork activities during wet weather, we recommend that the following steps be taken:

■ The ground surface in and around the work area should be sloped so that surface water is directed away from the work area. The ground surface should be graded so that areas of ponded water do not develop. Measures should be taken by the contractor to prevent surface water from collecting in excavations and trenches. Measures should be implemented to remove surface water from the work area.

■ Earthwork activities should not take place during periods of moderate to heavy precipitation.

■ Slopes with exposed soils should be covered with plastic sheeting.

■ The contractor should take necessary measures to prevent on-site soils and soils to be used as fill from becoming wet or unstable. These measures may include the use of plastic sheeting, sumps with pumps, and grading. The site soils should not be left uncompacted and exposed to moisture. Sealing the surficial soils by rolling with a smooth-drum roller prior to periods of precipitation will help reduce the extent that these soils become wet or unstable.

■ The contractor should cover all soil stockpiles that will be used as structural fill with plastic sheeting.

■ Construction traffic should be restricted to specific areas of the site, preferably areas that are surfaced with the existing asphalt or working pad materials not susceptible to wet weather disturbance.

■ Construction activities should be scheduled so that the length of time that soils are left exposed to moisture is reduced to the extent practical.

Routing of equipment on the native till subgrade soils during the wet weather months will be difficult and the subgrade will likely become highly disturbed and rutted. In addition, a significant amount of mud can be produced by routing equipment directly on the glacial soils in wet weather. Therefore, to protect the subgrade soils and to provide an adequate wet weather working surface for the contractor’s equipment and labor, we recommend that the contractor protect exposed subgrade soils with sand and gravel, crushed gravel, or ATB.

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4.6.5. Permanent Cut and Fill Slopes

We recommend that permanent cut or fill slopes be constructed at inclinations of 2H:1V or flatter, and be blended into existing slopes with smooth transitions. To achieve uniform compaction, we recommend that fill slopes be overbuilt slightly and subsequently cut back to expose well compacted fill. It is our experience that permanent cut slopes made in dense to very dense glacial till are difficult to establish vegetation on and difficult to place and maintain topsoil on. Therefore, 3H:1V or flatter permanent cut slopes should be considered for landscape purposes if site conditions allow for their use.

To reduce erosion, newly constructed slopes should be planted or hydroseeded shortly after completion of grading. Until the vegetation is established, some sloughing and raveling of the slopes should be expected. This may necessitate localized repairs and reseeding. Temporary covering, such as clear heavy plastic sheeting, jute fabric, or erosion control blankets (such as American Excelsior Curlex 1 or North American Green SC150) could be used to protect the slopes during periods of rainfall.

4.6.6. Utility Trenches

Trench excavation, pipe bedding, and trench backfilling should be completed using the general procedures described in the 2020 WSDOT Standard Specifications or other suitable procedures specified by the project civil engineer. The native glacial deposits and fill soils encountered at the site are generally of low corrosivity based on our experience in the Puget Sound area.

Utility trench backfill should consist of structural fill and should be placed in loose lifts not exceeding 12 inches in thickness when using heavy compaction equipment and not more than 6 inches when using hand operated compaction equipment such that adequate compaction can be achieved throughout the lift. Each lift must be compacted prior to placing the subsequent lift. Prior to compaction, the backfill should be moisture conditioned to within 2 percent of the optimum moisture content, if necessary. The backfill should be compacted in accordance with the criteria discussed above. Figure 4 illustrates recommended trench compaction criteria under pavement and non-structural areas.

4.6.7. Sedimentation and Erosion Control

In our opinion, the erosion potential of the on-site soils is low to moderate. Construction activities including stripping and grading will expose soils to the erosional effects of wind and water. The amount and potential impacts of erosion are partly related to the time of year that construction actually occurs. Wet weather construction will increase the amount and extent of erosion and potential sedimentation.

Erosion and sedimentation control measures may be implemented by using a combination of interceptor swales, straw bale barriers, silt fences and straw mulch for temporary erosion protection of exposed soils. All disturbed areas should be finish graded and seeded as soon as practicable to reduce the risk of erosion. Erosion and sedimentation control measures should be installed and maintained in accordance with the requirements of the City of Bellevue.

4.7. Excavations

We anticipate that excavations for the lowest floor level will require cuts in the eastern portion of the site. These cuts can likely be made as temporary open cut slopes depending on site constraints. Excavations are also required for underground utilities. The stability of open cut slopes is a function of soil type, groundwater seepage, slope inclination, slope height and nearby surface loads. The use of inadequately

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designed open cuts could impact the stability of adjacent work areas, existing utilities, and endanger personnel.

The contractor performing the work has the primary responsibility for protection of workmen and adjacent improvements. In our opinion, the contractor will be in the best position to observe subsurface conditions continuously throughout the construction process and to respond to variable soil and groundwater conditions. Therefore, the contractor should have the primary responsibility for deciding whether or not to use open cut slopes for much of the excavations rather than some form of temporary excavation support, and for establishing the safe inclination of the cut slope. Acceptable slope inclinations for utilities and ancillary excavations should be determined during construction. Because of the diversity of construction techniques and available shoring systems, the design of temporary shoring is most appropriately left up to the contractor proposing to complete the installation. Temporary cut slopes and shoring must comply with the provisions of Title 296 WAC, Part N, “Excavation, Trenching and Shoring.”

The excavations for the lowest floor level of the building will be completed primarily in loose to medium dense fill and medium dense to very dense glacial till deposits. The following sections summarize the general excavation recommendations. If conditions allow, the entire excavation for the proposed building may be accomplished using temporary cut slopes.

4.7.1. Temporary Cut Slopes

For planning purposes, temporary unsupported cut slopes more than 4 feet high may be inclined at 1H:1V maximum steepness within the dense to very dense glacial till (below a depth of 5 feet) and 1½H:IV maximum steepness in the overlying fill and loose to medium dense weathered till soils (upper 5 feet). If significant seepage is present on the cut face, then the cut slopes may have to be flattened. However, temporary cuts should be discussed with the geotechnical engineer during final design development to evaluate suitable cut slope inclinations for the various portions of the excavation.

The above guidelines assume that surface loads such as traffic, construction equipment, stockpiles or building supplies will be kept away from the top of the cut slopes a sufficient distance so that the stability of the excavation is not affected. We recommend that this distance be at least 5 feet from the top of the cut for temporary cuts made at 1H:1V or flatter, and no closer than a distance equal to one-half the height of the slope for cuts made steeper than 1H:IV.

Temporary cut slopes should be planned such that they do not encroach on a 1H:1V influence line projected down from the edges of nearby or planned foundation elements. New footings planned for the lowest floor level should extend through wall backfill and be embedded in native soils.

Water that enters the excavation must be collected and routed away from prepared subgrade areas. We expect that this may be accomplished by installing a system of drainage ditches and sumps along the toe of the cut slopes. Some sloughing and raveling of the cut slopes should be expected. Temporary covering, such as heavy plastic sheeting with appropriate ballast, should be used to protect these slopes during periods of wet weather. Surface water runoff from above cut slopes should be prevented from flowing over the slope face by using berms, drainage ditches, swales or other appropriate methods.

If temporary cut slopes experience excessive sloughing or raveling during construction, it may become necessary to modify the cut slopes to maintain safe working conditions. Slopes experiencing problems can

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be flattened, regraded to add intermediate slope benches, or additional dewatering can be provided if the poor slope performance is related to groundwater seepage.

4.8. Infiltration Considerations

Based on our review of the City’s criteria for infiltration infeasibility in the January 2017 Surface Water Engineering Standards, the planned infiltration depths, and the results of our geotechnical laboratory tests, we conclude that infiltration is not feasible at this site. We do not recommend that infiltration of storm water be planned for this site due to the presence of dense to very dense, silty native glacial till located at relatively shallow depths. Dense glacial till has very low infiltration characteristics and laboratory tests indicate a typical fines content of about 30 percent at the proposed infiltration depth and across the site. In addition, shallow perched groundwater may occur above the contact between the weathered and unweathered till, a condition which will further limit infiltration at this site.

According to the Standards, no further investigation (including pilot infiltration tests) is required for sites where groundwater seepage or a hydraulically restrictive material is encountered within the defined vertical separation depths below permeable pavement and bioretention facilities.

4.9. Drainage Considerations

We anticipate shallow groundwater seepage may enter deep excavations depending on the time of year construction takes place, especially in the winter months. However, we expect that this seepage water can be handled by digging interceptor trenches in the excavations and pumping from sumps. The seepage water if not intercepted and removed from the excavations will make it difficult to place and compact structural fill and may destabilize cut slopes.

All paved and landscaped areas should be graded so that surface drainage is directed away from the building to appropriate catch basins.

Water collected in roof downspout lines must not be routed to the footing drain lines. Collected downspout water should be routed to appropriate discharge points in separate pipe systems.

4.10. Recommended Additional Geotechnical Services

Throughout this report, recommendations are provided where we consider additional geotechnical services to be appropriate. These additional services are summarized below:

■ GeoEngineers should be notified with the building layout and finished floor elevation are finalized to determine if the recommendations in this report are still appropriate. An updated geotechnical report may be required based on final design the foundation configuration and subsurface drainage measures.

■ GeoEngineers should be retained to review the project plans and specifications when complete to confirm that our design recommendations have been implemented as intended.

■ During construction, GeoEngineers should observe temporary cut slopes, observe overexcavation of unsuitable soils (as needed), evaluate the suitability of the foundation subgrades, evaluate the suitability of floor slab and pavement subgrades, observe installation of subsurface drainage measures, observe and test structural backfill, assess temporary erosion and sediment control measures, and provide a summary letter of our construction observation services. The purposes of

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GeoEngineers construction phase services are to confirm that the subsurface conditions are consistent with those observed in the explorations and other reasons described in Appendix D, Report Limitations and Guidelines for Use.

5.0 LIMITATIONS

We have prepared this report for use by Washington State Department of Enterprise Services, Bellevue College and members of the design team for use in design of this project.

Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions, express or implied, should be understood.

Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record.

Please refer to Appendix D for additional information pertaining to use of this report.

6.0 REFERENCES

Applied Technology Council – Hazards by Location. https://hazards.atcouncil.org/#/.

GeoEngineers, 2002, “Geotechnical Engineering Services, Proposed Parking Garage, Bellevue Community College, Bellevue, Washington,” dated June 7, 2002.

International Code Council, 2018, “International Building Code.”

Washington State Department of Transportation, 2020. “Standard Specifications for Road, Bridge and Municipal Construction.”

Yount, J.C., Minard, J.P., and Dembroff, G.R., 1993. Geologic map of surficial deposits in the Seattle 30' by 60' quadrangle, Washington. 1:100000. U.S. Geological Survey, Open-File Report OF-93-233, Dated 1993.

FIGU

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WoodridgeOpen Space

InternationalSchool

NorwoodVillage

Wilburton

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SunsetCemetery

Bellevue AirfieldPark

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Lake HillsGreenbelt

RobinswoodCommunity Park

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Eastgate Park

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Vasa Creek

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Figure 1

Center for Transdisciplinary Learning & Innovation (TDI)

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features discussed in an attached document. GeoEngineers, Inc. cannotguarantee the accuracy and content of electronic files. The master file is storedby GeoEngineers, Inc. and will serve as the official record of this communication.

Data Source: Base CAD files provided by Bellevue College received 6/11/2021.

Projection: WA State Plane, North Zone, NAD83, US Foot

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Boring by GeoEngineers, Inc., 2021B-1

Test Pit by GeoEngineers, Inc., 2021TP-1

Site Boundary

Alternative Building Footprint 1

Alternative Building Footprint 2

Center for Transdisciplinary Learning & Innovation (TDI)Bellevue College, Washington

Boring by GeoEngineers, Inc., 2002B-6

Approximate Depth to Glacial Till (8,000 PSF)5'

Floor Slab

6"

12" Min. Cover OfDrainage Material (6"

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Nonwoven Geotextile

TemporaryExcavation Slope

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Retained Soil

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MATERIALS:

May consist of "Gravel Backfill for Drains" per WSDOT Standard Specification 9-03.12(4), surrounded with a non-woven geotextile suchas Mirafi 140N (or approved equivalent).

Should consist of structural fill, either on-site soil or imported. Wall backfill supporting building floor slabs should consist of importedsand and gravel per WSDOT Standard Specification 9-03.14 compacted to at least 95 percent ASTM D1557. Backfill not supportingbuilding floor slabs, sidewalks, or pavement should be compacted to 90 to 92 percent of the maximum dry density, per ASTM D1557.Backfill supporting sidewalks or pavement areas should be compacted to at least 95 percent in the upper two feet. Only hand-operatedequipment should be used for compaction within 5 feet of the walls and no heavy equipment should be allowed within 5 feet of the wall.

Should consist of a 4-inch diameter perforated heavy-wall solid pipe (SDR-35 PVC) or rigid corrugated polyethylene pipe (ADS N-12) orequivalent. Drain pipes should be placed with 0.25 percent minimum slopes and discharge to the storm water collection system.

Should consist of at least 6 inches of clean crushed gravel with a maximum size of 1-inch and negligible sand or fines, per WSDOT9-03.1(4)c Grading No. 67.

A. WALL DRAINAGE MATERIAL

B. RETAINED SOIL

C. CAPILLARY BREAK

D. PERFORATED DRAIN PIPE

Compaction Criteria for Trench Backfill

90

90 90

9590

Pipe

Varies

Varies(See Note 1)

2 Feet

Varies

(Modified Proctor)

Pipe Bedding

Trench Backfill

Base Course

Concrete or Asphalt Pavement

Maximum Dry Density, by Test Method ASTM D1557Recommended Compaction as a Percentage of

Legend

95

Not To Scale

Notes:1. All backfill under building areas should be compacted to at

least 95 percent per ASTM D1557.

Non-structuralAreas

Hardscape OrPavement

Areas

Ground Surface

P:\4

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Tech

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03-F

04.d

wg

TAB:

F04

Dat

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porte

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/21

- 15:

10 b

y hm

ara

Figure 4


AP

PE

ND

ICE

S

APPENDIX A Field Explorations

July 8, 2021 | Page A-1 File No. 4598-020-00

APPENDIX A FIELD EXPLORATIONS

Subsurface conditions at the site were explored on June 17, 2021 by drilling six borings (B-1 through B-6) and excavating three test pits (TP-1 through TP-3) at the approximate locations shown on Figure 2. Locations of the explorations were determined in the field by pacing and tape measuring distances from the exploration locations to existing site features such as sidewalks, fences, parking lot curbs, and buildings. Ground surface elevations were estimated from the site survey map provided by Bellevue College. Exploration locations should be considered accurate to the degree implied by the method used. Ground surface elevations at the exploration locations were not surveyed and were estimated from the site survey map; therefore, the elevations may only be accurate to the nearest foot.

Borings

The borings were advanced to depths of approximately 17½ to 31½ feet below ground surface (bgs). The borings were completed using a track-mounted Diedrich D50 Turbo drill rig owned and operated by Advanced Drill Technologies Inc., of Snohomish, Washington. The borings were advanced using 4½-inch inside-diameter hollow-stem augers. Drilling services were subcontracted to GeoEngineers, and the borings were advanced under the full-time observation of a representative from our firm.

The soils encountered in the borings were typically sampled at 2½ to 5-foot vertical intervals with a 2.0-inch outside-diameter split-barrel standard penetration test (SPT) sampler. The samples were obtained by driving the sampler 18 inches into the soil with a 140-pound auto-hammer free-falling 30 inches. The number of blows required for each 6 inches of penetration is recorded. The blow count (“N-value”) of the soil is calculated as the number of blows required for the final 12 inches of penetration. This resistance, or N-value, provides a measure of the relative density of granular soils and the relative consistency of cohesive soils. Where very dense soil conditions preclude driving the full 18 inches, the penetration resistance for the partial penetration is entered on the logs. The blow counts are shown on the boring logs at the respective sample depths.

The borings were logged by a geotechnical engineer from our firm who identified the boring locations, classified the soils encountered, obtained representative soil samples and maintained a detailed log of each boring. The soils encountered during boring operations were visually classified in the field in general accordance with the Unified Soil Classification System (USCS), ASTM D 2488, and the system described on Figure A-1. Representative soil samples were obtained from the borings, logged, placed in plastic bags, and transported to our laboratory in Redmond, Washington. The field classifications were checked in our laboratory.

In addition, pertinent information including soil sample depth, stratigraphy, and groundwater were recorded. Groundwater levels were estimated by observing soil samples and the drill rods. The drilling operation was also monitored for indication of various drilling conditions, such as hard and soft drilling. At completion of drilling, the borings were backfilled in accordance with the procedures of the Washington State Department of Ecology.

Summary boring logs are presented on Figures A-2 through A-7. A key to the symbols and terms used on the logs are included on Figure A-1. These logs are based on our interpretation of the field and laboratory data and indicate the various types of soils encountered. They also indicate the approximate depths at

July 8, 2021 | Page A-2 File No. 4598-020-00

which the soils or their characteristics change, although the change may be gradual. If a change occurred between samples in the borings, it was interpreted.

Test Pits

Test pits (TP-1 through TP-3) were excavated to depths ranging from approximately 2¾ to 3½ feet bgs. The test pits were completed using a rubber-tire Kubota L3901 Backhoe owned and operated by Bellevue College.

The test pits were monitored by a geotechnical engineer from our firm who evaluated and classified the soils encountered, obtained representative soil samples, and observed groundwater conditions. Our representative maintained a detailed log of each test pit. Disturbed samples of representative soil types were obtained from the backhoe bucket at representative depths.

Soils encountered in the test pits were classified in the field in general accordance with ASTM D 2488, the Standard Practice for Classification of Soils, Visual-Manual Procedure, which is summarized in Figure A-1. Logs of the test pits are provided in Figures A-8 through A-10.

SYMBOLS TYPICALDESCRIPTIONS

GW

GP

SW

SP

SM

FINEGRAINED

SOILS

SILTS ANDCLAYS

NOTE: Multiple symbols are used to indicate borderline or dual soil classifications

MORE THAN 50%RETAINED ONNO. 200 SIEVE

MORE THAN 50%PASSING

NO. 200 SIEVE

GRAVELAND

GRAVELLYSOILS

SC

LIQUID LIMITLESS THAN 50

(APPRECIABLE AMOUNTOF FINES)

(APPRECIABLE AMOUNTOF FINES)

COARSEGRAINED

SOILS

MAJOR DIVISIONSGRAPH LETTER

GM

GC

ML

CL

OL

SILTS ANDCLAYS

SANDS WITHFINES

SANDAND

SANDYSOILS

MH

CH

OH

PT

(LITTLE OR NO FINES)

CLEAN SANDS

GRAVELS WITHFINES

CLEAN GRAVELS

(LITTLE OR NO FINES)

WELL-GRADED GRAVELS, GRAVEL -SAND MIXTURES

CLAYEY GRAVELS, GRAVEL - SAND -CLAY MIXTURES

WELL-GRADED SANDS, GRAVELLYSANDS

POORLY-GRADED SANDS, GRAVELLYSAND

SILTY SANDS, SAND - SILT MIXTURES

CLAYEY SANDS, SAND - CLAYMIXTURES

INORGANIC SILTS, ROCK FLOUR,CLAYEY SILTS WITH SLIGHTPLASTICITY

INORGANIC CLAYS OF LOW TOMEDIUM PLASTICITY, GRAVELLYCLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS

ORGANIC SILTS AND ORGANIC SILTYCLAYS OF LOW PLASTICITY

INORGANIC SILTS, MICACEOUS ORDIATOMACEOUS SILTY SOILS

INORGANIC CLAYS OF HIGHPLASTICITY

ORGANIC CLAYS AND SILTS OFMEDIUM TO HIGH PLASTICITY

PEAT, HUMUS, SWAMP SOILS WITHHIGH ORGANIC CONTENTSHIGHLY ORGANIC SOILS

SOIL CLASSIFICATION CHART

MORE THAN 50%OF COARSE

FRACTION RETAINEDON NO. 4 SIEVE

MORE THAN 50%OF COARSE

FRACTION PASSINGON NO. 4 SIEVE

SILTY GRAVELS, GRAVEL - SAND -SILT MIXTURES

POORLY-GRADED GRAVELS,GRAVEL - SAND MIXTURES

LIQUID LIMIT GREATERTHAN 50

Continuous Coring

Bulk or grab

Direct-Push

Piston

Shelby tube

Standard Penetration Test (SPT)

2.4-inch I.D. split barrel

NOTE: The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions.Descriptions on the logs apply only at the specific exploration locations and at the time the explorations were made; they are not warranted to berepresentative of subsurface conditions at other locations or times.

Blowcount is recorded for driven samplers as the number ofblows required to advance sampler 12 inches (or distance noted).See exploration log for hammer weight and drop.

"P" indicates sampler pushed using the weight of the drill rig.

"WOH" indicates sampler pushed using the weight of thehammer.

Key to Exploration Logs

Figure A-1

Sampler Symbol Descriptions

ADDITIONAL MATERIAL SYMBOLS

NSSSMSHS

SYMBOLS

Asphalt Concrete

Cement Concrete

Crushed Rock/Quarry Spalls

Topsoil

GRAPH LETTER

AC

CC

SOD Sod/Forest Duff

CR

DESCRIPTIONSTYPICAL

TS

%F%GALCACPCSDDDSHAMCMDMohsOCPMPIPLPPSATXUCVS

Groundwater ContactMeasured groundwater level in exploration, well, or piezometer

Measured free product in well or piezometer

Graphic Log ContactDistinct contact between soil strata

Approximate contact between soil strata

Material Description ContactContact between geologic units

Contact between soil of the same geologic unit

Laboratory / Field TestsPercent finesPercent gravelAtterberg limitsChemical analysisLaboratory compaction testConsolidation testDry densityDirect shearHydrometer analysisMoisture contentMoisture content and dry densityMohs hardness scaleOrganic contentPermeability or hydraulic conductivity Plasticity indexPoint load testPocket penetrometerSieve analysisTriaxial compressionUnconfined compressionVane shear

Sheen ClassificationNo Visible SheenSlight SheenModerate SheenHeavy Sheen

tnash

Typewritten Text

Rev 09/2020

Grass at ground surface

Hard drilling at 17½ feet; refusal on boulder

11

5

8

20

Dark brown silty fine to medium sand with gravel (looseto medium dense, moist) (topsoil)

Light brown silty fine to medium sand with gravel(medium dense, moist) (fill/weathered glacial till)

Gray silty fine to medium sand with gravel (dense,moist) (glacial till)

Becomes very dense

Minor oxidation staining

1MC

2

3SA

4

5MC

6

7

9

18

0

18

6

0

11

43

64

69/11"

50/6"

50/5"

SM

SM

SM

Notes:

18YNANCRG Advance Drill Technologies, Inc. Hollow-stem Auger

Diedrich Turbo D-50DrillingEquipment

Autohammer140 (lbs) / 30 (in) Drop

WA State Plane NorthNAD83 (feet)

1316004216656

394.5NAVD88

Easting (X)Northing (Y)

Start TotalDepth (ft)

Logged ByChecked By

End

Surface Elevation (ft)Vertical Datum

Drilled

HammerData

SystemDatum

Driller DrillingMethod

Groundwater not observed at time of exploration

6/17/20216/17/2021

Note: See Figure A-1 for explanation of symbols.Coordinates Data Source: Horizontal approximated based on field measurements. Vertical approximated based on site survey.

Sheet 1 of 1Project Number:

Project Location:

Project:

4598-020-00

Log of Boring B-1

Figure A-2


Bellevue, Washington

Dat

e:7

/8/2

1 P

ath:

P:\4

\45

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TAN

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D_%

F_N

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W

REMARKS

Moi

stur

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onte

nt (%

)

Fine

sC

onte

nt (%

)

FIELD DATA

MATERIALDESCRIPTION

Sam

ple

Nam

eTe

stin

g

Rec

over

ed (i

n)

Inte

rval

Blo

ws/

foot

Col

lect

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ampl

e

Dep

th (f

eet)

0

5

10

15

Gra

phic

Log

Gro

upC

lass

ifica

tion

Elev

atio

n (f

eet)

390

385

380


16

7

6

5

30

27

Brown silty fine to medium sand with occasional gravel,fine roots (loose, moist) (topsoil)

Brown silty fine to medium sand with occasional gravel,bricks, oxidation staining (loose, wet) (fill)

Brown silty fine to medium sand with gravel (mediumdense, moist) (weathered glacial till)

Gray silty fine to medium sand with gravel (very dense,moist) (glacial till)

Becomes relatively unweathered

1%F

2A

2BSA

3

4

5MC

6

7MC

8

18

18

18

18

5

5

5.5

52

61

75

50/6"

50/5"

50/5"

50/5.5"

SM

SM

SM

SM

Notes:

26.5YNANCRG Advance Drill Technologies, Inc. Hollow-stem Auger




1316120216641

398NAVD88



Logged ByChecked By

End


Drilled

HammerData

SystemDatum



6/17/20216/17/2021



Project Location:

Project:

4598-020-00

Log of Boring B-2

Figure A-3



Dat

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/8/2

1 P

ath:

P:\4

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E_2

01

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LB/G

EI8

_GEO

TEC

H_S

TAN

DAR

D_%

F_N

O_G

W

REMARKS

Moi

stur

eC

onte

nt (%

)

Fine

sC

onte

nt (%

)

FIELD DATA

MATERIALDESCRIPTION

Sam

ple

Nam

eTe

stin

g

Rec

over

ed (i

n)

Inte

rval

Blo

ws/

foot

Col

lect

ed S

ampl

e

Dep

th (f

eet)

0

5

10

15

20

25

Gra

phic

Log

Gro

upC

lass

ifica

tion

Elev

atio

n (f

eet)

395

390

385

380

375


14

9

6

25

Brown silty fine to medium sand with occasional gravel,fine roots (loose, moist) (topsoil)

Brown silty fine to medium sand with occasional gravel,fine roots (medium dense to dense, moist)(weathered glacial till)

Brown silty fine to medium sand with gravel (dense,moist) (glacial till)

Becomes very dense, relatively unweathered

Becomes gray-brown

1MC

2A

2B

3SA

4

5

6MC

7

18

18

18

5

10

4

34

72

59

50/5"

50/4"

50/4"

SM

SM

SM

Notes:

25IKSCRG Advance Drill Technologies, Inc. Hollow-stem Auger




1316071216599

396NAVD88



Logged ByChecked By

End


Drilled

HammerData

SystemDatum



6/17/20216/17/2021



Project Location:

Project:

4598-020-00

Log of Boring B-3

Figure A-4



Dat

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ath:

P:\4

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LB/G

EI8

_GEO

TEC

H_S

TAN

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D_%

F_N

O_G

W

REMARKS

Moi

stur

eC

onte

nt (%

)

Fine

sC

onte

nt (%

)

FIELD DATA

MATERIALDESCRIPTION

Sam

ple

Nam

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stin

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Rec

over

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n)

Inte

rval

Blo

ws/

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Col

lect

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ampl

e

Dep

th (f

eet)

0

5

10

15

20

25

Gra

phic

Log

Gro

upC

lass

ifica

tion

Elev

atio

n (f

eet)

395

390

385

380

375


13

8

6

5

31

Brown silty fine to medium sand (loose to mediumdense, moist) (topsoil)

Brown silty fine to medium sand (medium dense, moist)(fill/weathered glacial till)

Brown/gray silty fine to medium sand with gravel,oxidation staining (dense, moist) (glacial till)

Becomes gray and very dense, relatively unweathered

1MC

2A

2B

3SA

4MC

5

6MC

18

18

15

5

5

35

60

82/9"

50/5"

50/5"

SM

SM

SM

Notes:

20.5IKSCRG Advance Drill Technologies, Inc. Hollow-stem Auger




1315981216548

394NAVD88



Logged ByChecked By

End


Drilled

HammerData

SystemDatum



6/17/20216/17/2021



Project Location:

Project:

4598-020-00

Log of Boring B-4

Figure A-5



Dat

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/8/2

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TD_U

S_J

UN

E_2

01

7.G

LB/G

EI8

_GEO

TEC

H_S

TAN

DAR

D_%

F_N

O_G

W

REMARKS

Moi

stur

eC

onte

nt (%

)

Fine

sC

onte

nt (%

)

FIELD DATA

MATERIALDESCRIPTION

Sam

ple

Nam

eTe

stin

g

Rec

over

ed (i

n)

Inte

rval

Blo

ws/

foot

Col

lect

ed S

ampl

e

Dep

th (f

eet)

0

5

10

15

20

Gra

phic

Log

Gro

upC

lass

ifica

tion

Elev

atio

n (f

eet)

390

385

380

375

Tree undergrowth at ground surface

Rough drilling

19

7

7

23

Brown silty fine to medium sand with gravel, fine roots(loose, moist) (topsoil)

Brown silty fine to medium sand with gravel, fine roots(medium dense, moist) (fill/weathered glacial till)

Brown silty fine to medium sand with gravel (mediumdense, moist)

Gray-brown fine to medium sand with gravel (verydense, moist) (glacial till)

Becomes gray

1MC

2A

2B

3

4

5SA

6

7MC

8

9

9

14

15

14

3

4

4

4

15

54/10"

77

57

50/3"

50/4"

50/4"

50/4"

SM

SM

SM

SM

Notes:





1316103216533

398NAVD88



Logged ByChecked By

End


Drilled

HammerData

SystemDatum



6/17/20216/17/2021



Project Location:

Project:

4598-020-00

Log of Boring B-5

Figure A-6



Dat

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EI8

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TEC

H_S

TAN

DAR

D_%

F_N

O_G

W

REMARKS

Moi

stur

eC

onte

nt (%

)

Fine

sC

onte

nt (%

)

FIELD DATA

MATERIALDESCRIPTION

Sam

ple

Nam

eTe

stin

g

Rec

over

ed (i

n)

Inte

rval

Blo

ws/

foot

Col

lect

ed S

ampl

e

Dep

th (f

eet)

0

5

10

15

20

25

30

Gra

phic

Log

Gro

upC

lass

ifica

tion

Elev

atio

n (f

eet)

395

390

385

380

375

370

Dense brush at ground surface

19

7

6

27

Brown silty fine to medium sand with gravel, fine roots(loose to medium dense, moist) (topsoil)

Brown silty fine to medium sand with gravel, occasionalfine roots (dense, moist) (weathered glacial till)

Brown silty fine to medium sand with gravel (dense tovery dense, moist) (glacial till)

Becomes gray-brown

1MC

2A

2B

3

4SA

5

6MC

7

8

18

8

18

17

4

3

5

43

50/6"

47

95/11"

50/4"

50/3"

50/5"

SM

SM

SM

Notes:





1316187216573

405NAVD88



Logged ByChecked By

End


Drilled

HammerData

SystemDatum



6/17/20216/17/2021



Project Location:

Project:

4598-020-00

Log of Boring B-6

Figure A-7



Dat

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/8/2

1 P

ath:

P:\4

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01

7.G

LB/G

EI8

_GEO

TEC

H_S

TAN

DAR

D_%

F_N

O_G

W

REMARKS

Moi

stur

eC

onte

nt (%

)

Fine

sC

onte

nt (%

)

FIELD DATA

MATERIALDESCRIPTION

Sam

ple

Nam

eTe

stin

g

Rec

over

ed (i

n)

Inte

rval

Blo

ws/

foot

Col

lect

ed S

ampl

e

Dep

th (f

eet)

0

5

10

15

20

25

30

Gra

phic

Log

Gro

upC

lass

ifica

tion

Elev

atio

n (f

eet)

400

395

390

385

380

375

Brown silty fine to medium sand, fine tree roots (loose to mediumdense, moist) (topsoil)

Brown silty fine to medium sand (medium dense to dense, moist) (fill)

Brown-gray silty fine to medium sand with gravel and cobbles (dense,moist) (weathered glacial till)

Gray silty fine to medium sand with gravel (very dense, moist) (glacialtill)

SM

SM

SM

SM

1

2%F

8

Trees and dense brush at ground surfaceProbe depth 9 inches at ground surface

Probe depth 6 inches at 1 foot

Probe depth 2 inches at 2 feet

Probe depth ½-inch at 3 feetHard digging at 3 feet

Probe depth ½-inch at 3½ feet29

Notes: See Figure A-1 for explanation of symbols.The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.Coordinates Data Source: Horizontal approximated based on field measurements. Vertical approximated based on site survey.

Dat

e:7

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7.G

LB/G

EI8

_TES

TPIT

_1P_

GEO

TEC

_%F


Project Location:

Project:

4598-020-00

Log of Boring TP-1

Figure A-8



Elev

atio

n (f

eet)

393

392

391

Dep

th (f

eet)

1

2

3

Test

ing

Sam

ple

Gra

phic

Log

SAMPLE

MATERIALDESCRIPTION

Gro

upC

lass

ifica

tion

Sam

ple

Nam

eTe

stin

g

Moi

stur

eC

onte

nt (%

) REMARKS

Fine

sC

onte

nt (%

)

DateExcavated


Coordinate SystemHorizontal Datum


TotalDepth (ft)6/17/2021 3.75

394NAVD88

1316003216596


YNAN

Checked By CRG

Groundwater not observed

Caving not observedEquipment Kubota L3901

Logged By Excavator Bellevue College

Brown silty fine to medium sand with gravel, fine roots (loose tomedium dense, moist) (topsoil)

Brown silty fine to medium sand with gravel (dense to very dense,moist) (weathered glacial till)

Gray silty fine to medium sand with occasional gravel and oxidationstaining (dense, moist to wet) (glacial till)

Gray silty fine to medium sand with gravel (very dense, moist)

SM

SM

SM

SM

1

2%F

3

18

Tree undergrowth at ground surfaceProbe depth 7 inches at ground surface

Probe depth 3 inches at 1 foot

Probe depth 1-inch at 2 feet

Probe depth ½-inch at 3 feet

33


Dat

e:7

/8/2

1 P

ath:

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Log of Boring TP-2

Figure A-9



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TotalDepth (ft)6/17/2021 3.5

395.5NAVD88

1316039216550


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Checked By CRG




Brown silty fine to medium sand with gravel (medium dense, moist)(topsoil)

Brown-gray silty fine to medium sand with gravel, oxidation staining,weathered (dense, moist) (weathered glacial till)

Gray silty fine to medium sand with gravel (very dense, moist) (glacialtill)

SM

SM

SM

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2%F

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Grass at ground surfaceProbe depth 1-inch at ground surface

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Log of Boring TP-3

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APPENDIX B Laboratory Testing

July 8, 2021 | Page B-1 File No. 4598-020-00

APPENDIX B LABORATORY TESTING

Soil samples obtained from the explorations were transported to our laboratory and evaluated to confirm or modify field classifications, as well as to evaluate engineering properties of the soil. Representative samples were selected for laboratory testing that consisted of moisture content determinations and sieve analysis. The tests were performed in general accordance with test methods of the ASTM or other applicable procedures.

Soil Classifications

All soil samples obtained from the explorations were visually classified in the field and/or in our laboratory using a system based on the Unified Soil Classification System (USCS) and ASTM classification methods. ASTM test method D 2488 was used to visually classify the soil samples, while ASTM D 2487 was used to classify the soils based on laboratory tests results. These classification procedures are incorporated in the exploration logs shown in Figures A-2 through A-10, in Appendix A.

Moisture Content Determinations

Moisture contents were determined in general accordance with ASTM D 2216 for numerous samples obtained from the explorations. The results of these tests are presented on the exploration logs at the respective sample depth in Appendix A.

Percent Passing U.S. No. 200 Sieve

Selected samples were “washed” through the U.S. No. 200 mesh sieve to determine the relative percentage of coarse- and fine-grained particles in the soil. The percent passing value represents the percentage by weight of the sample finer than the U.S. No. 200 sieve. These tests were conducted in general accordance with ASTM D 1140, and the results are shown on the exploration logs at the representative sample depths.

Sieve Analysis

Sieve analyses were performed on ten samples obtained from the explorations. The analyses were conducted in general accordance with ASTM D 422. The wet sieve analysis method was used to determine the percentage of soil greater than the U.S. No. 200 mesh sieve. The results of the sieve analyses were plotted, classified in general accordance with the USCS, and presented in Figures B-1 and B-2

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Silty fine to medium sand with occasional gravel (SM)



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4598-020-00 Date Exported: 06/25/2021

Note: This report may not be reproduced, except in full, without written approval of GeoEngineers, Inc. Test results are applicable only to the specific sample on which they were

performed, and should not be interpreted as representative of any other samples obtained at other times, depths or locations, or generated by separate operations or processes.

The grain size analysis results were obtained in general accordance with ASTM C 136. GeoEngineers 17425 NE Union Hill Road Ste 250, Redmond, WA 98052

#2001” #140

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4598-020-00 Date Exported: 06/25/2021

Note: This report may not be reproduced, except in full, without written approval of GeoEngineers, Inc. Test results are applicable only to the specific sample on which they were

performed, and should not be interpreted as representative of any other samples obtained at other times, depths or locations, or generated by separate operations or processes.

The grain size analysis results were obtained in general accordance with ASTM C 136. GeoEngineers 17425 NE Union Hill Road Ste 250, Redmond, WA 98052

#2001” #140

APPENDIX C Boring Logs from Previous Studies

July 8, 2021 | Page C-1 File No. 4598-020-00

APPENDIX C BORING LOGS FROM PREVIOUS STUDIES

Appendix C includes selected boring logs from the following previous study completed in the immediate vicinity of the project site:

■ “Report, Geotechnical Engineering Services, Proposed Parking Garage, Bellevue Community College, Bellevue, Washington,” by GeoEngineers, Inc., dated June 7, 2002.

APPENDIX D Report Limitations and Guidelines for Use

July 8, 2021 | Page D-1 File No. 4598-020-00

APPENDIX D REPORT LIMITATIONS AND GUIDELINES FOR USE1

This appendix provides information to help you manage your risks with respect to the use of this report.

Read These Provisions Closely

It is important to recognize that the geoscience practices (geotechnical engineering, geology and environmental science) rely on professional judgment and opinion to a greater extent than other engineering and natural science disciplines, where more precise and/or readily observable data may exist. To help clients better understand how this difference pertains to our services, GeoEngineers includes the following explanatory “limitations” provisions in its reports. Please confer with GeoEngineers if you need to know more how these “Report Limitations and Guidelines for Use” apply to your project or site.

Geotechnical Services Are Performed for Specific Purposes, Persons and Projects

This report has been prepared for use by Bellevue College, Washington State Department of Enterprise Services, and their authorized agents. The information contained herein is not applicable to other sites or projects.

GeoEngineers structures its services to meet the specific needs of its clients. No party other than the party to whom this report is addressed may rely on the product of our services unless we agree to such reliance in advance and in writing. Within the limitations of the agreed scope of services for the Project, and its schedule and budget, our services have been executed in accordance with our Agreement with the Washington State Department of Enterprise Services and generally accepted geotechnical practices in this area at the time this report was prepared. We do not authorize, and will not be responsible for, the use of this report for any purposes or projects other than those identified in the report.

A Geotechnical Engineering or Geologic Report is Based on a Unique Set of Project-Specific Factors

This report has been prepared for the Center of Transdisciplinary Learning and Innovation (TDI) at Bellevue College. GeoEngineers considered a number of unique, project-specific factors when establishing the scope of services for this project and report. Unless GeoEngineers specifically indicates otherwise, it is important not to rely on this report if it was:

■ Not prepared for you,

■ Not prepared for your project,

■ Not prepared for the specific site explored, or

■ Completed before important project changes were made.

1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org.


For example, changes that can affect the applicability of this report include those that affect:

■ The function of the proposed structure;

■ Elevation, configuration, location, orientation or weight of the proposed structure;

■ Composition of the design team; or

■ Project ownership.

If changes occur after the date of this report, GeoEngineers cannot be responsible for any consequences of such changes in relation to this report unless we have been given the opportunity to review our interpretations and recommendations. Based on that review, we can provide written modifications or confirmation, as appropriate.

Subsurface Conditions Can Change

This geotechnical or geologic report is based on conditions that existed at the time the study was performed. The findings and conclusions of this report may be affected by the passage of time, by man-made events such as construction on or adjacent to the site, new information or technology that becomes available subsequent to the report date, or by natural events such as floods, earthquakes, slope instability or groundwater fluctuations. If more than a few months have passed since issuance of our report or work product, or if any of the described events may have occurred, please contact GeoEngineers before applying this report for its intended purpose so that we may evaluate whether changed conditions affect the continued reliability or applicability of our conclusions and recommendations.

Geotechnical and Geologic Findings Are Professional Opinions

Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies the specific subsurface conditions only at those points where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field and laboratory data and then applied its professional judgment to render an informed opinion about subsurface conditions at other locations. Actual subsurface conditions may differ, sometimes significantly, from the opinions presented in this report. Our report, conclusions and interpretations are not a warranty of the actual subsurface conditions.

Geotechnical Engineering Report Recommendations Are Not Final

The recommendations included in this report are preliminary and should not be considered final. GeoEngineers’ recommendations can be finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers cannot assume responsibility or liability for the recommendations in this report if we do not perform construction observation.

We recommend that you allow sufficient monitoring, testing and consultation during construction by GeoEngineers to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes if the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork activities are completed in accordance with our recommendations. Retaining GeoEngineers for construction observation for this project is the most effective means of managing the risks associated with unanticipated conditions.


A Geotechnical Engineering or Geologic Report Could Be Subject to Misinterpretation

Misinterpretation of this report by members of the design team or by contractors can result in costly problems. GeoEngineers can help reduce the risks of misinterpretation by conferring with appropriate members of the design team after submitting the report, reviewing pertinent elements of the design team’s plans and specifications, participating in pre-bid and preconstruction conferences, and providing construction observation.

Do Not Redraw the Exploration Logs

Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. The logs included in a geotechnical engineering or geologic report should never be redrawn for inclusion in architectural or other design drawings. Photographic or electronic reproduction is acceptable, but separating logs from the report can create a risk of misinterpretation.

Give Contractors a Complete Report and Guidance

To help reduce the risk of problems associated with unanticipated subsurface conditions, GeoEngineers recommends giving contractors the complete geotechnical engineering or geologic report, including these “Report Limitations and Guidelines for Use.” When providing the report, you should preface it with a clearly written letter of transmittal that:

■ Advises contractors that the report was not prepared for purposes of bid development and that its accuracy is limited; and

■ Encourages contractors to confer with GeoEngineers and/or to conduct additional study to obtain the specific types of information they need or prefer.

Contractors Are Responsible for Site Safety on Their Own Construction Projects

Our geotechnical recommendations are not intended to direct the contractor’s procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on-site personnel and adjacent properties.

Biological Pollutants

GeoEngineers’ Scope of Work specifically excludes the investigation, detection, prevention or assessment of the presence of Biological Pollutants. Accordingly, this report does not include any interpretations, recommendations, findings or conclusions regarding the detecting, assessing, preventing or abating of Biological Pollutants, and no conclusions or inferences should be drawn regarding Biological Pollutants as they may relate to this project. The term “Biological Pollutants” includes, but is not limited to, molds, fungi, spores, bacteria and viruses, and/or any of their byproducts.

A Client that desires these specialized services is advised to obtain them from a consultant who offers services in this specialized field.

This appendix provides information to help you manage your risks with respect to the use of this report.

Attachment 6b: Geotech Report

Documents

Transcript of Attachment 6b: Geotech Report