4-2010 - Hillside Evaluation and Preliminary Design.pdf

031710dl_final waga hillside rpt.docx

HILLSIDE EVALUATION AND

PRELIMINARY DESIGN

OLYMPIA CAPITOL CAMPUS,

OLYMPIA, WASHINGTON

(08-076)

Submitted To: Washington State Department of General Administration 210 West 11 th Street SE nd

Floor, Room 206 Olympia, Washington 98504-1012

Submitted By: Golder Associates Inc.

18300 NE Union Hill Road, Suite 200 Redmond, Washington 98052

March 17, 2010 083-93287.400

R E

P O

R T

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Table of Contents

1.0 INTRODUCTION

1.1 Scope of Services

1.1.1 Research

1.1.2 Stability Assessment

1.1.3 Reporting

1.2 Report Outline

2.0 SITE CONDITIONS

2.1 Site Basemap and LiDAR

2.1.1 Site Basemap and Datum

2.1.2 LiDAR

2.2 Site Visits and Observations

2.2.1 Site Development

2.2.2 Topography and Vegetation

2.2.3 Surface Water

2.3 Site Data and Document Review

2.3.1 Plan Review - Campus Structures and Infrastructure

2.3.1.1 Site Development History

2.3.1.2 Buildings

2.3.1.3 Infrastructure

2.3.2 Report Reviews

3.0 SUBSURFACE EXPLORATIONS AND CONDITIONS

3.1 Field Exploration

3.1.1 Drilling

3.1.2 Installations

3.2 Laboratory Testing

3.3 Explorations by Others

3.4 Campus Geology

3.5 Subsurface Conditions

3.5.1 Observed Soil

3.5.2 Groundwater

4.0 SLOPE STABILITY ANALYSES AND RISK EVALUATION

4.1 Qualitative Slope Stability

4.2 Quantitative Slope Evaluations

4.2.1 Methodology

4.2.2 Results of Stability Analyses

4.3 Slope Risk Evaluation

4.3.1 Likelihood of Failure

4.3.2 Consequences

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4.3.3 Risk

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 Causes of Slope Failures

5.2 Slope Setbacks

5.3 Recommended Maintenance Activities

5.3.1 Storm Drain Systems

5.3.2 Other Utilities

5.3.3 Landscaping and Pavements

5.3.4 Soldier Pile Wall

5.4 Recommended Monitoring

5.5 Potential Stabilization Alternatives

6.0 SCHEMATIC AND FINAL DESIGNS

6.1 Schematic Design

6.2 Selected Stabilization Alternative for 2010

7.0 CLOSING

8.0 REFERENCES

List of Figures

Figure 1 Vicinity Map Figure 2 Project CAD Database Plan (11x17 and oversize in pocket) Figure 3 Historic Explorations Figure 4 Shaded Relief Map of Capitol Campus (11x17 and oversize in pocket)

List of Appendices

Appendix A Field Explorations Procedures, Data, and Logs A-1 Golder Explorations A-2 Explorations by Others

Appendix B Laboratory Testing

Appendix C Inclinometers and Piezometers C-1 Golder Installed Inclinometers and Piezometers C-2 Existing Inclinometers and Piezometers by Others C-3 Inclinometer Measurements C-4 Groundwater Measurements

Appendix D Instrumentation Monitoring Program

Appendix E Technical Memorandums E-1 Ivy Management at the Capitol Campus, Olympia, Washington (2/16/09) E-2 Stability and Risk Evaluation Update (11/12/2009) E-3 Schematic Design Alternatives (12/18/2009)

Appendix F Annotated Bibliography and CAD Database F-1 Annotated Bibliography F-2 Project Database

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1.0 INTRODUCTION

The purpose of the Hillside Evaluation Project (Project) was to evaluate slopes on the Capitol Campus in

Olympia for stability, risk of failure, and consequences of slope failure with respect to managing the campus assets such as buildings and infrastructure. The project was planned with three phases that included research, stability assessment, and reporting.

The Project was originally defined to include slopes from the south boundary of the campus to the north legislative parking area slopes extending to (but not including) Heritage Park. During a meeting with

General Administration (GA) personnel on August 6, 2009, an expansion of the study area was discussed to encompass slopes near the Greenhouse and the GA Building. The slopes of the Heritage Park Trail have been extensively evaluated by others and are not included within the Project evaluation area.

However, information related to the Heritage Park Trail is discussed when applicable to other project areas.

1.1 Scope of Services

The scope of services for this project consisted of three primary phases: Research, Stability Assessment, and Reporting. A brief description of the activities performed for each phase is discussed in the following sections.

1.1.1 Research

Visits to the General Administration (GA) archives were completed on several occasions (September 10 and December 4, 2008 and January 8, February 20, and September 16, 2009) to gather information related to geotechnical studies and construction of campus buildings. Information collected included historic borings, site plans, records of slope failures, and construction plans. Approximate boring locations from the reviewed reports were added to a project database in CAD format. The working project spatial database was developed in CAD using a CAD base file provided by Blair Prigge of Parametrix in

December 2008.

A qualitative evaluation of the campus slope stability was also performed. The evaluation was performed during site visits by Golder geologists. Slope conditions and key slope features were documented during these visits.

1.1.2 Stability Assessment

Services performed under the Stability Assessment phase of the campus slopes included drilling two geotechnical borings, installing inclinometers to monitor slope movements, installing vibrating wire piezometers to monitor ground water conditions, and performing slope stability analyses. One boring was advanced behind the Pritchard Building; the other boring was advanced behind the Governor’s Mansion.

The slope stability analyses were performed to identify areas with the greatest likelihood of slope failure.

The slope stability analyses consisted of a relative ranking of the slopes by factor of safety for the static

March 2010 2 083-93287.400 condition. Subsurface conditions were modeled using information from borings completed by others on the campus and information from the borings advanced by Golder for this project. The slope locations analyzed for stability included:

Slopes west of the Pritchard Building

Slopes west of the O’Brien Building

Slopes west of the Governor’s Mansion

Slopes east of the Powerhouse (both south and north of the steam lines)

Slopes north of legislative parking area (North Parking Lot)

Slopes west the Greenhouse

Slopes west of the GA Building

Based on the results of the slope stability analyses, potential slope stabilization projects were identified.

1.1.3 Reporting

The Final Reporting task was to provide a summary report document that incorporates project findings, evaluations, and completed technical memorandums. The final project bibliography and spatial database(s) were completed under this task. The reporting task also included preparation of a campus monitoring report.

1.2 Report Outline

This report documents the methods, results, conclusions, and recommendations of our geotechnical site investigation and slope stability analyses of the slopes on the Capitol Campus. The report is organized as follows:

Section 1 (Introduction) this section.

Section 2 (Site Conditions) outlines the physical setting of the project and provides a summary of our understanding of the history of the Capitol Campus slopes and nearby buildings and infrastructure.

Section 3 (Subsurface Explorations and Conditions) describes the methods used to complete the field investigation, discusses the general geologic setting of the project, and summarizes the subsurface soil and groundwater conditions encountered during the field investigation; this section also describes laboratory testing and installation and monitoring.

Section 4 (Slope Stability and Risk Evaluation) describes the results of our slope stability analyses and presents an overview of the risk evaluation and the results.

Section 5 (Conclusions and Recommendations) summarizes conclusions about the causes of campus slope failures and presents recommendations to address stability issues.

Section 6 (Schematic and Final Designs) presents an overview of the schematic designs and associated cost estimates.

Section 7 (Closing) presents our closing statements.

Section 8 (References) documents the outside resources referred to in performing the investigation and analyses.

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The following appendices are also included with this report:

Appendix A (Field Explorations Procedures, Data, and Logs) presents a summary of the various explorations completed for this project and other projects in the vicinity.

Appendix B (Laboratory Testing and Analysis) presents the detailed results of the laboratory testing.

Appendix C (Inclinometers and Piezometers) presents monitoring results of the inclinometers and piezometers.

Appendix D (Instrumentation Monitoring Program) presents the recommended monitoring program and manuals for the instruments.

Appendix E (Technical Memorandums) presents copies of memorandums submitted during previous phases of the project.

Appendix F (Annotated Bibliography).

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2.0 SITE CONDITIONS

The project limits include slopes extending north and northeast from state owned property near the south edge of the Pritchard Building to the slopes west of the GA Building. Down slope project limits extend to the water’s edge or the railroad tracks and up slope limits extend to approximately 100 feet beyond the top edge of campus slopes. Structures of interest include the Pritchard Building, the O’Brien Building, the

Governor’s Mansion, the Powerhouse, the Greenhouse, the soldier pile wall, and the GA Building. This report section provides a discussion of data sources, research findings, and observations related to site conditions.

2.1 Site Basemap and LiDAR

Basic project information used for evaluations included a site basemap provided by Parametrix and topographic information from LiDAR (Light Detection and Ranging).

2.1.1 Site Basemap and Datum

An electronic site basemap showing key exploration locations and other site features was created by

Parametrix based on a site utility survey and provided by Parametrix in December 2008. Golder updated the basemap to include the approximate location of selected geotechnical explorations (borings) identified during review of reports from the GA archives.

The approximate locations of the explorations are shown on the AutoCAD basemap provided as

Figure 2 and Figure 3; an oversize version of Figure 2 is also provided as a foldout drawing in Appendix F at the end of this document. In the electronic basemap file, an image of the boring log is hyperlinked to the boring location; right clicking (assuming a right-hand mouse) on the boring location will open an image of the boring log. Copies of the boring logs linked in the AutoCAD file are presented in Appendix A. The basemap can serve as a resource for campus personnel to identify previous explorations on the site. The basemap can be updated to include future explorations.

Important Note: the project basemap horizontal datum is NAD1983 and the vertical datum is NAVD88.

Most of the historic drawings appear to have been completed using City of Olympia Vertical Datum

(COVD). The correlations between these two datums is variable – estimated to be between about

13.4 and 13.8 feet (e.g., 100 foot City Olympia Vertical Datum = approximately 113.4 to 113.8 feet

NAVD88 datum). The elevations presented in this report will indicate the datum that is referenced.

2.1.2 LiDAR

LiDAR data were used in the project for multiple purposes. The LiDAR was flown in early winter

2002, and the bare earth data was downloaded from a publically accessible site in June 2008 (Puget

Sound LiDAR Consortium 2008). These data were processed in GIS to produce a shaded topographic version of the data (Figure 4) as well as topographic information that was imported to the CAD basemap.

The shaded topographic image was used to support geomorphic interpretations, and the topographic

March 2010 5 083-93287.400 information imported to CAD was used for stability evaluations and design. The LiDAR data is provided on Washington State Plane North Zone, NAD 1983 horizontal datum and NAVD88 vertical datum. It is generally not possible to determine the accuracy of public LiDAR data without a topographic survey.

However, the accuracy of the data can be estimated from the return signal density and an understanding of the ground condition effect on LiDAR returns. Typically, horizontally accuracy is much greater than vertical accuracy. Based on experience with similar data, the relative accuracy of vertical data for the project should be considered no better than +/- 5 feet.

Geomorphic features identified from LiDAR interpretation, ground surface observations, and literature reviews are shown on the LiDAR image, Figure 4. The LiDAR image shows an upland area that is heavily modified, surrounded by natural and modified slopes on the west and north edges of the campus.

All slopes around campus have geomorphic evidence of smaller, surficial slope failures that are usually visible on LiDAR. These smaller features are typically about 30 to 80 feet wide and about 50 to 100 feet long. Multiple west-facing scallops at the southwest edge of the campus reflect a series of very large, ancient, natural landslides that were likely initiated several thousand years ago, after the Vashon-age glaciers retreated and the Deschutes River down cut its channel. These large slides show a steeper edge or “scarp” at the top of the slope and a flatter accumulation zone near the middle to lower parts of the slope. The ancient landslide features are about 500 to 900 feet wide (north to south) and about 300 to

400 feet long (east to west, direction of movement).

Slopes west of the O’Brien and Pritchard Buildings are moderate to steeply inclined and show evidence of large-scale ancient landslides as well as artificial modification such as an apparent fill slope in the area adjacent to O’Brien and Pritchard Buildings. Very small, shallow slope failures are also visible on these slopes.

Slopes west of the Governor’s Mansion, above the Powerhouse, and on the north side of campus are steep and irregularly sloped. On these slopes there are no current geomorphic features indicating large-scale post-glacial landsliding like the features that are visible west of the Pritchard and O’Brien Buildings.

The steep slopes below the Governor’s Mansion, Powerhouse, and north campus areas do show evidence of smaller-scale landsliding as shown on Figure 4. The slopes north and east of the Law

Enforcement Memorial show a series of overlapping features possibly a combination of recent human-induced and older natural landslides. The slopes from the Powerhouse to the north part of the campus have been much more heavily modified by human activities such as historical grading, the Powerhouse construction, parking areas, the railroad embankment, Heritage Park Trail, and park construction along

Capitol Lake.

2.2 Site Visits and Observations

Several site visits were performed to document campus slope conditions, observe geotechnical borings, and monitor instrumentation. The dates and purpose of site visits are summarized below:

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Site Visit

Date of Visit Purpose

7/31/08

Completed field reconnaissance to observe surface and slope conditions, document key slope features. Slopes observed included near Prichard and O’Brien Buildings, Governor’s Mansion, north side of Powerhouse, and north parking area.

9/23/08 Completed field reconnaissance to observe surface and slope conditions, document key slope features; completed additional observations near north parking area and Heritage Park.

1/8/09 Observed slope conditions following a large storm event and high lake levels; focus on slopes north of parking area.

2/20/09 Met to discuss proposed activities and observe liner around the diesel tank. Also completed reconnaissance of slope above south side of the Powerhouse.

5/29/09 Drilled and installed inclinometers and piezometers, GB-1 and GB-2.

7/1/09 Completed baseline inclinometer and piezometer reading for GB-1 and

GB-2.

8/27/09 Completed first reading of inclinometer and piezometer at GB-1 and GB-2.

Baseline inclinometer reading for DH-1 and DH-2. Trained GA staff on inclinometer monitoring procedures.

12/2/09

Completed second reading of inclinometer and piezometer at GB-1 and GB-2. Completed first reading of inclinometer at DH-1 and DH-2.

Completed initial reading of piezometers DH-7P, HC-2, HC-3, HC-5, HC-6, and HC-7. Trained GA staff on inclinometer and piezometer monitoring procedures. Observed condition of soldier pile wall.

2.2.1 Site Development

Observations of developed conditions were made during campus site visits as described in this section.

Pritchard Building

The Pritchard Building is approximately 11 feet from the slope edge at the southeast part of the building.

The building is a multi-story structure, clad in sandstone panels, with a basement; no notable foundation cracking was observed. The southeast edge of the building is surrounded by concrete sidewalks and landscape areas. There is a shallow (4- to 6-inch-deep) trough visible on the outer side of the sidewalk near the southeast part of the building, extending about 40 feet. According to campus maintenance personnel, this trough could be related to installation of a storm drain system aligned with the edge of the sidewalk and trending toward the O’Brien Building. There is also some minor tilting and separation of nearby sidewalk slabs.

O’Brien Building

At the time of our initial site visits in 2008, the west side of the O’Brien Building was approximately 25 feet from the slope edge. Subsequent to those visits, a new basement addition was constructed that is located as close as approximately 6 feet from the slope edge. A lawn area is present between the

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O’Brien Building and the slope edge. We understand that a below-grade soldier pile shoring wall was constructed between the new addition and the slope as part of the basement structure.

Governor’s Mansion

The Governor’s Mansion is an older brick structure that is located on a small hill above other campus buildings. The mansion is surrounded by landscaped areas and naturally vegetated areas. The southwest corner of the mansion is approximately 25 feet from the slope edge. No evidence of ground cracking or movement was observed near the mansion.

Powerhouse

The campus Powerhouse lies at the base of a slope on the west side of campus and provides steam heat to the campus. The Powerhouse is accessed by a stairway from the North Parking Lot and a maintenance road along Capitol Lake. The Powerhouse also includes a large (approximately

350,000 gallons) diesel oil tank south of the Powerhouse that is used for backup steam generation. The diesel oil tank is in a containment enclosure lined with a synthetic membrane. The tank may be drained in the future and used to store reclaimed water for reuse. Several utilities are present near the Powerhouse including: a sanitary sewer pump station north of the Powerhouse; a primary natural gas line feed near the top of the stairway; and multiple other utilities including several storm drain lines from the campus to the base of the slope, a steam line, a condensate line, chilled water supply and return lines, a communications line, and a potable water line.

North Parking Area

A large paved parking area is present east of the Powerhouse; this parking area extends north to near the top of the slope. Several utilities lie beneath the parking area including multiple storm drain lines, a natural gas line near the north edge of the lot; sanitary sewer; and power and communications lines. Also present are utilities associated with the Powerhouse, including the utilidor tunnel and steam, condensate, chilled water supply and return, communications, and potable water lines. The lot pavement is in generally good to fair condition; no cracks or settlement related to slope instability were observed during our visits.

Greenhouse

The Greenhouse is an “L” shaped two story structure east of the Heritage Park Trail. A second smaller shed-like structure is also present in the Greenhouse area. The Greenhouse structure is about 15 feet from the slope edge and the shed is less than 10 feet from the slope edge. The structures appear to be lightly loaded and are likely supported by shallow spread footings. Some cracking of foundations has been reported by others. The Greenhouse area includes a paved drive, parking, and storage area. No signs of ground or pavement cracking suggesting slope instability were observed during our visits.

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Soldier Pile Wall

An approximately 230-foot-long soldier pile wall is located along the slope near and north of the

Greenhouse. The wall supports a parking area on the north side of the Greenhouse and a lawn and parking area west of the GA building. The wall is approximately 30 feet from the paved parking area.

The soldier pile wall condition was observed during the site visit on December 2, 2009. Due to the vegetation cover (e.g., ivy extending up the wall and thick blackberry bushes on the slope below the wall), our access was limited to observations from the top of the wall and from approximately 30 feet west of the toe of the wall.

Our observations did not show any visible deterioration of the soldier pile wall. The soil loss at the toe of the wall appears to be less than 1 to 2 feet, although this observation was limited by heavy vegetation.

The original wall design by GeoEngineers (1988) neglected the upper 9 feet of soil at the toe of the wall, permitting up to 9 feet of ground loss or small slope failures to occur at the toe of the wall without impacting the overall wall performance.

The condition of the wood lagging boards appears to be satisfactory. Specifically, the wood lagging boards do not exhibit signs of rotting or breaking. Portions of the wall are heavily covered with vegetation, and the condition of the boards covered by the vegetation could not be observed. Gaps between lagging boards were observed at approximately three locations (the gaps appeared to be approximately

3 to 6 inches in width). There was no evidence of soil sloughing out of the gaps between lagging boards.

However, because of shadows, the presence or absence of voids could not be confirmed. No signs of ground subsidence were observed at the top of the soldier pile wall.

GA Building

The GA Building is a five-story building on the northwest edge of the Capitol Campus. A road and parking area are present west of the building. The building is approximately 40 feet from the slope edge on the northwest corner and 90 to 100 feet from the soldier pile wall on the west side of the building. Pavement on the nearby road and parking area is cracked and potholed, but there is no cracking that appears to be related to slope or wall movement.

2.2.2 Topography and Vegetation

Topography on and near the campus varies between relatively flat developed areas to steep slopes on the edge of campus above Capitol Lake. The west campus area slopes slightly downward to the north.

Elevations vary from about 140 feet at the Governor’s Mansion to about 20 feet at the base of slopes

(NAVD88).

Pritchard and O’Brien Building Slopes

The slopes adjacent to Pritchard and O’Brien Buildings are about 110 feet high and are inclined from about 1.7H:1V in the upper part of the slope to flatter than 6H:1V at the lower part of the slope. The

March 2010 9 083-93287.400 upper part of the slope is very evenly inclined reflecting a zone of fill that was placed in this area as part of site development; the lower part of the slope appears to reflect the deposition zone from ancient landslide features.

Governor’s Mansion Slopes

The slopes west of the mansion are about 120 feet high and generally sloped at about 1.2 to 1.3H:1V.

Flatter slopes inclined at about 2.5H:1V are present near Capitol Lake reflecting a landslide run out zone potentially associated with 1996 and older landslides.

Slopes Powerhouse and Vicinity

The slopes east of the Powerhouse are about 90 feet high and vary from about 2.5 H:1V in regraded areas at the top of the slope to about 1.3H:1V in natural parts of the slope, with slopes steeper than about

1H:1V near the lower part of the slopes north and south of the Powerhouse structure. Parts of the slope north of the Powerhouse have been reconstructed as a reinforced slope inclined at about 1H:1V.

Slopes North Parking Lot (and Heritage Park)

The slopes adjacent to the North Parking Lot are about 90 feet high and inclined at about 1.25H:1V, with some steeper slopes at landslide scarps inclined at about 0.5H:1V. Slopes in the Heritage Park Trail area are inclined at about 2.5H:1V.

Slopes Greenhouse, Soldier Pile Wall, GA Building

Slopes west of the Greenhouse and GA Building are up to about 80 feet high and are inclined at about

1.25H:1V to 2.5 H:1V.

2.2.3 Surface Water

Other than Capitol Lake, there are no major surface water features on or near the campus. During site visits in late summer 2008, minor seepage (< ½ gpm) was observed near the base of the slope adjacent to the Pritchard and O’Brien Buildings. During these visits, low seepage (between about ½ and 1 gpm) was also observed at the base of slopes north of the North Parking Lot and at several slope locations near Heritage Park.

Palmer and Gerstel (1996a) noted small seeps and springs on landslide scarps near the south end of the

Governor’s Mansion during their field visits. Golder personnel did not observe these seeps during field visits to this area in summer 2009.

2.3 Site Data and Document Review

The project included research of the Capitol Campus development records and previous studies that could relate to campus slopes. Visits to the GA archives were completed on several occasions

(September 10 and December 4, 2008 and January 8, February 20, and September 16, 2009) to gather information related to geotechnical studies for historical campus projects. Information collected included

March 2010 10 083-93287.400 historic borings, site plans, records of slope failures, and construction plans. Our studies and information review focused on structures, infrastructure, and other features close to the campus slopes that could be impacted by slope failure. An annotated bibliography of reviewed information is provided in Appendix F.

Over 60 geotechnical and geologic related reports and documents were reviewed for the Project. The reports were generally related to building improvements, slope failures, or other campus studies.

2.3.1 Plan Review - Campus Structures and Infrastructure

Historic design and construction plans were reviewed in the State archives to gather information about campus development that could be pertinent to the project. These plans are provided in the bibliography in Appendix F; key reviewed plans included:

Site and foundation plans for the Pritchard Building

Historic grading and foundation plans for the O’Brien Building

Foundation and shoring wall plans for a 2009 addition to the O’Brien Building

Limited plans for the Governor’s Mansion

A series of design plans for the Powerhouse including original construction, tank and containment area construction, and seismic upgrades

Design plans for a soldier pile wall near the GA Building

Design plans for the GA Building

Other plans for the west campus that showed infrastructure or other features

2.3.1.1 Site Development History

Original site grades on the west campus are not fully known. Grading in parts of campus reportedly began in the late 1800s and early 1900s with construction of the Governor’s Mansion and the Legislative

Building. Grading occurred after approximately 1911 to fill in an old ravine west of the current location of

Water Street (Palmer and Gerstel 1995; Author Unknown 1911). Additional grading appears to have occurred with construction of the Governor’s Mansion in 1908 and the Powerhouse and the Temple of

Justice in the early 1920s. Grading near O’Brien, Pritchard, and the Governor’s Mansion occurred in

1937 – 1938, associated with O’Brien Building construction. This grading included placing fill on the slope west of O’Brien and Pritchard Buildings to create an access road and lawn area. Minor additional grading occurred in the early 1950s associated with the GA Building construction and in the late 1950s associated with Pritchard Building construction.

2.3.1.2 Buildings

Design drawings were found for the Pritchard building, O’Brien building, the Governor’s Mansion, the

Powerhouse, and the GA Building. Design plans were not found for the Greenhouse.

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Pritchard Building

Based on a design drawing (Plot Plan by Paul Thiry Architect 1957a) showing existing site grades prior to building construction, there appears to have been relatively little grading of the slope near the Pritchard

Building. This drawing shows the slope edge approximately 10 ft from building at the closest point; the current distance from the building to the slope edge is similar to that shown on the 1957 plan. Design and construction plans (Paul Thiry Architect 1957b) also showed foundations bearing at about 108 feet COVD and the basement floor at 110.8 feet (COVD). Original ground surface elevations appeared to range from about 115 feet COVD at the SW corner of Pritchard Building to about 130 feet COVD at the east side of the building (Jos H. Wohleb 1938a). Based on this information, it appears that the Pritchard foundations are likely bearing 7 to 12 feet below original site grades on the west side of the building closest to the slope.

O’Brien Building

Site plans for grading associated with O’Brien (Jos H. Wohleb 1938a) indicate that up to about 25 feet

(measured vertically) of fill may have been placed on the edge of the slope to widen the area around the building. Plans show foundations extended to native soils with basement foundations at 99 to 105 feet

COVD feet when the ground surface was at about 115 to 117 feet COVD (Jos H. Wohleb 1938b). The design drawings (Jos H. Wohleb 1938a) showed a distance from the original building to the slope edge varying from about 70 feet at the southern end to about 45 feet at the northern end. The current distance to the slope edge from the corner nearest the slope is approximately 25 feet, indicating that potentially

20 feet (horizontal) of the edge of the slope may have failed sometime in the past. However, no records of this failure were found during our research. The current slope configuration is very evenly inclined, potentially indicating repair or regrading of any failure that may have occurred.

In 2009, a new addition was added to the west side of O’Brien Building resulting in a building edge approximately 6 feet from the slope edge. This building addition included a basement similar to the existing structure with footings at approximately 98 to 100 feet COVD. The addition was constructed using soldier pile shoring that was left in place, and the new basement walls were cast against the shoring. The soldier piles along the northwest side of the addition (closest to the slope) extend to approximately 38 feet below the adjacent ground surface, to an elevation of approximately 90 feet

NAVD88.

Governor’s Mansion

Limited plans were available for the Governor’s Mansion. The 1908 plans show that the south and southwest side of the mansion were originally excavated approximately 7 to 10 feet below existing grades to construct footings and a basement. A concrete retaining wall with a maximum height of approximately

13 feet was constructed around the south side of the Governor’s Mansion in 1937-1938 in association with O’Brien Building construction. A new addition was added to the south and west part of the mansion in about 1974; the elevation of the footings for this addition is currently not known

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(Ibsen Nelsen & Associates 1974). The garage was relocated to its current location during this renovation. There are also other smaller outbuildings, including a guard station and a soil shed, on the grounds of the Governor’s Mansion.

Powerhouse

Site drawings dated 1920 (Wilder & White Architects 1920) show that the Powerhouse is founded on a combination of spread footings and piles. The spread footings were used on the east part of the building, which was excavated about 3 to 10 feet below existing grades on the adjacent slope to construct footings.

The west part of the building is supported on a pile mat (number of piles, pile type, depth, and spacing unknown). Other major improvements to the Powerhouse facility included:

The addition of an oil storage tank and containment area in about 1976 (Noel Adams PE & Associates 1976)

Installation of a sewer pump station in 1980 (Howard Godat & Associates, 1980 a, b), placement of a synthetic liner in about 1993 (Anderson & Boone Architects 1993 a, b)

A seismic upgrade in 1993 (ABAM Consulting Engineers 1993 a, b, c, d, e)

Limited site repairs associated with the Nisqually Quake in 2003 and later (JWM&A 2003 a, b)

The drawings indicate that the oil storage tank and the outer containment wall are supported on piles of unknown depth (ABAM Consulting Engineers 1993). The containment wall on the east side of the tank consists of unreinforced concrete (sack grout) that has been placed against the soil slope (this part of the wall is not an engineered structure). The seismic upgrade activities included extensive soil anchors that were installed into the slope east of the building as well as a sheet pile wall driven along the west edge of the building to address liquefaction (GeoEngineers 1992 and ABAM Consulting Engineers 1993).

Greenhouse

No drawings were found in the archives for the Greenhouse. Based on the type of structure, it is likely that this building is supported on shallow footings. Review of historical drawings and exploration logs by others (Gerstel 1996) indicate that the Greenhouse is likely underlain by uncontrolled fill that was historically placed in a ravine that trended southward to the “Winged Victory” area. Settlement of the

Greenhouse reportedly occurred starting in the 1960s.

Soldier Pile Wall

A soldier pile wall was constructed in about 1988 to address a slope failure that occurred west of the GA

Building in 1986. The soldier pile wall extends southward to the edge of the parking area on the north side of the Greenhouse. These design drawings (Sverdrup Corporation 1988 a, b, c, d) show a soldier pile wall with piles approximately 50 feet long with up to 2 rows of tiebacks and an exposed wall face height of greater than 25 feet in some areas.

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GA Building

The GA Building was constructed in the 1950s with a basement level that extends approximately one story below adjacent site grades. Based on site observations and plans review, the GA Building appears to be founded on spread footings supported by native soils.

2.3.1.3 Infrastructure

Campus infrastructure includes utilities, parking lots, sidewalks, and drive areas. Our evaluations focused on infrastructure that serves a larger part of the campus and that was located in areas that could be impacted by landsliding. Our understanding of site infrastructure is based on site maps completed by

Parametrix (2008) and discussions with campus personnel. In some cases, we supplemented information provided by Parametrix with information from the archive files. Identified infrastructure includes:

A large storm drain on the slope west of O’Brien Building that is tightlined to a discharge point downslope (near elevation 60 feet NAVD88)

Steam lines and a gas line on the slope above the Powerhouse

A sewer line from the pump station near the Powerhouse to the north parking area

A gas line on the north edge of the north parking area that is within a few feet of the slope edge in some areas

Several other storm drains with associated collection systems, including a large storm drain south of the Powerhouse

2.3.2 Report Reviews

Golder reviewed several reports and other documents directly related to campus slope stability. Key reports and documents included:

Capitol Campus Bluff Slope Stability Analysis (Gerstel 1996a)

Slope Stability Analysis of the Bluffs along the Washington State Capitol Campus (Gerstel 1996b)

Capitol Campus Greenhouse Soil Stability Investigation Status Report.

(Palmer and Gerstel 1995)

Capital Campus Conservatory Soil and Slope Stability Investigation Final Report.

(Palmer and Gerstel 1997)

Design Memorandum, Geotechnical Consultation, Slide Correction, General Administrative Building (GeoEngineers 1988)

These documents provided a description of campus history and geologic and geomorphic conditions.

One of the reports (Gerstel 1996b) was completed after a series of landslides in early February 1996.

These reports described a history that included slope failures on most slopes around the Capitol Campus.

A summary of these documented slope failures is provided below; other undocumented slides have probably occurred.

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History of Slope Failures on Campus

Date Location Comments

Slope in front of Temple of Justice Near current Heritage Park Trail; winter 58-59

1965 – 1972 Campus-wide Period of higher slope failure activity

1981 Campus-wide Period of higher slope failure activity

1986/87 Slope west of GA building Remediated by soldier pile wall in 1988

1990 Campus-wide Period of higher slide activity

1990 Slope north of Powerhouse Failure covered access road and RR; damaged NE corner of plant; remediated by reinforced slope

Slope west of Pritchard Building Slope failure estimated < 20 years old in 1997

Slope west of Governor's Mansion

Slope failure estimated active last 30 years (as reported in 1996)

1996 Slope north of Powerhouse Flow into lake related to heavy February rains

Slope west of Governor's Mansion

Slopes west / southwest of mansion; failures extended to top of slope related to heavy February rains

1996 North slopes Series of smaller failures related to heavy February rains

2002 Heritage Park Trail Slope failure during construction (December)

2003 Heritage Park Trail Slope failure during construction (October)

2009 Slope North of Parking Area Small slope failure after heavy rain in early January

The reviewed documents provided information about subsurface explorations, slope stability analyses, and causes of slope failures. The subsurface information and data from currently existing monitoring instrument installations have been incorporated into this Capitol Campus study. Geologic conditions were similar to those observed in Golder explorations, and very little groundwater was observed. General causes of recent slope failures were identified as being related to saturation of loose/soft surface soils that mantle most campus slopes and small rotational failures initiating in the upper parts of slopes. The weak surface soils have formed through natural and human-caused processes, including remobilized soils from slope failures, soil creep, and sidecast fill or landscaping debris. The previous studies showed that stability of the surface soil mantle is very low when the layer is saturated – a condition that often occurs during and following heavy rainfall. The authors noted that the small rotational slope failures appeared to be related to small springs and seeps at the landslide headwalls.

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3.0 SUBSURFACE EXPLORATIONS AND CONDITIONS

Golder personnel completed field explorations and reviewed explorations by others in order to assess the subsurface conditions that impact the campus slopes.

3.1 Field Exploration

The Golder field investigation was completed on May 26 through May 29, 2009 and consisted of advancing two geotechnical borings (GB-1 and GB-2). The approximate boring locations are shown on the Site and Exploration Plan, Figures 2 and 3. Locations are based on field measurements from existing buildings and a site survey by Parametrix (Parametrix 2008). Boring locations were selected based on existing site conditions, existing utilities, and accessibility by the drill rig. Boring logs and a summary of the field exploration procedures are provided in Appendix A.

3.1.1 Drilling

The borings were advanced using mud rotary drilling methods with a B-61, truck-mounted drill rig equipped with an autohammer. The drill rig was operated by Holocene Drilling Inc. under the full-time observation of a Golder geologist, Alison Dennison. The borings GB-1 and GB-2 were advanced to depths of approximately 103 and 104 feet below the existing ground surface (bgs), respectively. Logging and sampling of soils were performed in general accordance with Golder Associates procedures for field identification of soils, based on the Unified Soil Classification System (USCS). A summary of the soil classification terminology is presented on the Soil Classification Legend in Appendix A. The collected soil samples were returned to our Redmond, Washington laboratory for further classification; laboratory testing was performed by Soil Technology, of Bainbridge Island, Washington.

The stratigraphic contacts indicated on the boring logs represent the approximate depths to boundaries between soil units; actual transitions between soil units may be more gradual. The subsurface descriptions are based on the conditions encountered at the time of exploration. Subsurface conditions between exploration locations may vary from those encountered, and groundwater may be present during certain times of the year.

3.1.2 Installations

After completing each exploration, an inclinometer casing and vibrating wire piezometer (a type of electronic device to measure groundwater pressure) were installed in each boring. The inclinometers extend approximately 98 feet bgs in boring GB-1 and 102 feet bgs in boring GB-2. The vibrating wire piezometer was installed at 80 feet bgs in GB-1 and 50 feet bgs in GB-2. The inclinometer and vibrating wire piezometer installation details are presented in Appendix A.

3.2 Laboratory Testing

Geotechnical laboratory testing was conducted by Soil Technology on representative samples from the borings for the purpose of classification and evaluation of pertinent engineering properties. Laboratory

March 2010 16 083-93287.400 tests included natural moisture content determination, sieve analyses, percent fines content, and

Atterberg limits. The field soil classifications were revised where applicable based on laboratory testing results. Laboratory test methods and results are provided in Appendix B.

3.3 Explorations by Others

Exploration logs were gathered from reviewed reports in the GA archives and from other sources. A summary table of explorations and copies of these explorations completed by other consultants are provided in Appendix A-2. Approximate locations of these explorations are shown on Figures

2 and 3. Please note that these explorations vary greatly in age, ranging from 1937 through 2008, and the classification system used on logs is different between consultants and over time. The approximate locations of these explorations were often determined from reproduced site plans within reports, sometimes without scales or defined site features. No exploration locations are based on surveying.

3.4 Campus Geology

The recent geologic history of the Puget Sound region has been dominated by several glacial episodes.

The most recent episode, the Vashon Stade of the Fraser Glaciation (about 12,000 to 20,000 years ago), is responsible for most of the visible geologic and topographic conditions in the region. The regional

Puget Sound landscape is characterized by elongated north-south oriented uplands and intervening valleys associated with this glacial advance and retreat. Older (Pre-Vashon) deposits are seen in some areas at the base of coastal bluffs; these deposits include glacial and nonglacial sediments deposited during repeated glacial and interglacial periods during the past two million years.

The Puget lobe of the Vashon Stade advanced south from British Columbia into the Puget Sound lowland reaching maximum extent south of Olympia about 17,000 years ago (Haugerud and Greenberg 2003).

Sediments deposited with this glacial event typically include proglacial lacustrine silt and clay, advance outwash, and lodgment till. These sediments were overridden by thick glacial ice and are typically overconsolidated and strong. As the Puget Lobe of the Vashon Stade glacier retreated northward, it deposited a discontinuous veneer of recessional outwash and other local deposits that are normally consolidated and weaker than older glacial deposits (e.g., ice did not override these deposits). Post-glacial deposits include alluvium deposited within active stream channels, modern lacustrine (i.e., lake) deposits, marine and deltaic deposits, localized organic silt and peat deposits, landslide deposits, and volcanic deposits such as pyroclastic flows and lahars associated with post-glacial activity.

The Geologic Map of the Tumwater 7.5-minute Quadrangle, Thurston County, Washington

(Walsh, Logan, Schasse, and Polenz 2003) covers the Capitol Campus. The geologic map shows all of the Capitol Campus mapped as Latest Vashon recessional sand and minor silt (Qgos). This unit is described as moderately well sorted, moderately- to well-rounded, fine- to medium-grained sand with minor silt. Based on boring observations, Latest Vashon fine-grained sediments (Qgof) may also be present. Qgof is less than 10 feet thick and is associated with small lakes that formed during the glacial

March 2010 17 083-93287.400 recession. Interpreted pre-Vashon deposits (Qps and Qpg) were observed in exposures near the base of west facing slopes and in both Golder borings; however, these units are not distinctly shown on the geologic maps. Geologic mapping describes Qps as thin- to thick-bedded to cross-bedded sand interbedded with laminated silt and minor peat and gravel. Qpg is described as gravel and sand from non-local sources, commonly tinted orange with iron oxide staining, moderately to poorly sorted, and commonly cross-bedded. The Vashon and pre-Vashon age deposits are interpreted to be underlain by bedrock at depth.

The geologic map also contains a cross-section view of units near the project. The cross-section shows a thick sequence (potentially up to 400 feet thick) of Qgos underlying the project area and most of downtown Olympia. This deposit is the result of a large outwash channel in the Olympia area that occurred as the glacier retreated. The deposits associated with this channel are laterally discontinuous and have wide-ranging grain size and characteristics.

3.5 Subsurface Conditions

Subsurface conditions were observed by Golder in limited exposures during site visits and from soil samples during drilling. Interpreted subsurface soil conditions were generally consistent with reports and exploration logs by other consultants. Soils observed in Golder explorations included late Vashon recessional deposits overlying Pre-Vashon deposits. The recessional strata were deposited in a very active fluvial environment resulting in interbedded soil units that are discontinuous between borings.

3.5.1 Observed Soil

A layer of topsoil and undocumented fill was encountered at the ground surface in both borings, GB-1 and

GB-2, extending 7.5 to 4.5 feet bgs, respectively. Below the topsoil and fill, both borings encountered soil consistent with the geologic map descriptions of the Latest Vashon recessional sand and minor silt

(Qgos), Pre-Vashon sandy deposits (Qps), pre-Vashon lacustrine deposits (Qpf), and Pre-Vashon gravel

(Qpg). Summary information about soil units is presented in the table below; additional information is shown on the boring logs provided in Appendix A.

Topsoil/Fill (Qf)

Topsoil is a soil unit that contains a relatively high percentage of organics. The observed topsoil was relatively thin and consisted of loose, dark brown, silty fine to medium sand with little fine to coarse gravel and some organics. Fill is a soil unit placed by man; the observed fill is considered undocumented because there are no specific records that document the amount of compaction effort that was used to place the fill. The observed undocumented fill was variable in character, consisting of moist, loose to compact, yellow brown to brown gray, fine to medium sand with silt to stiff sandy silt. Fill was observed in

Golder borings to depths of between 4.5 and 7.5 feet.

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Latest Vashon recessional sand and minor silt (Qgos) and Latest Vashon fine-grained sediments

(Qgof)

These deposits were encountered beneath fill at borings GB-1 and GB-2. The deposits included alternating layers of stratified silt, sandy silt, silty fine to medium sand, and fine to medium sand with little silt. Consistency and density of the layers ranged from very soft / loose to hard / dense. The deposits were in moist condition.

Pre-Vashon sandy deposits (Qps) and lacustrine deposits (Qpf), and gravel (Qpg)

These units were deposited in fluvial and lacustrine environments before the advance of the Vashon glacier and were subsequently over-ridden by the glacier. These soil units were over-consolidated by the weight of glacial ice; the soil units are relatively strong in comparison to the younger, overlying normally consolidated Qgos and Qgof. Both borings terminated in these Pre-Vashon deposits. At boring GB-1, an interbedded sequence of silt and sand interpreted to be Qpf and Qps was encountered at 86 feet below the ground surface (bgs). At boring GB-2, Qps was observed at 91 feet bgs. The Qpf observed in Golder borings was typically a hard, yellow brown to gray silt; the observed Qps was a very dense dark gray brown stratified fine to coarse sand with little to trace silt and some fine gravel. Pre-Vashon gravel (Qpg) was encountered in GB-1 at 91 feet bgs and was observed in an exposure near the base of the slope near the Powerhouse. At the exposure, the unit consisted of stratified, iron oxide-stained sandy fine to coarse gravel.

3.5.2 Groundwater

No free groundwater was observed by the driller during the advancement of either GB-1 or

GB-2. However, based on observed soil types that are likely to hold free groundwater, vibrating wire piezometers (VWPs) were installed in both borings. The installation depths of the VWPs were based on the soil types, relative moistures, and general stratigraphy that would tend to accumulate groundwater, if present.