D60441FINAL_sitka_geotech.pdf

ENGINEERING PLANNING SURVEYING

FINAL

SUBSURFACE EXPLORATION

AND

FOUNDATION RECOMMENDATIONS

UNITED STATES FOREST SERVICE

SITKA NEW OFFICE DESIGN

SITKA, ALASKA

Subsurface Exploration and Foundation Recommendations Sitka, Alaska United States Forest Service Sitka New Office Design W.O. D60441

TABLE OF CONTENTS

Page

Page i

1.0 INTRODUCTION

1.1 Planned Development

1.2 Purpose of Investigation

1.3 Scope of Work

2.0 PHYSICAL SETTING

2.1 Regional Geology

2.2 Climate

3.0 SITE CONDITIONS

3.1 Surface

3.2 Subsurface

3.3 Groundwater

3.4 Permafrost

4.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS

4.1 Site Response Characterization

4.2 Foundation Options

4.3 Earthwork

4.4 Dewatering and Drainage

4.5 Seasonal Frost Protection

4.6 Earth Pressures

4.7 Paved Traffic Areas

4.8 Observation

5.0 RESEARCH AND FIELD EXPLORATION

5.1 Research

5.2 Field Exploration

6.0 LABORATORY TESTS

6.1 Visual Classification

6.2 Moisture Content

6.3 Particle Size Distribution Tests

7.0 REFERENCES

TABLE OF CONTENTS (cont’d)

Page ii

FIGURES

Figure 1: Vicinity Map

Page

TABLES

Table 1: Average Monthly Temperatures and Precipitation Table 2: Observed and Measured Groundwater Levels

APPENDICES

Appendix A ........................................................................................... Test Boring Location Maps Appendix B .......................................................................Test Boring Logs and Descriptive Guide Appendix C ................................................................................................. Laboratory Test Results

1.0 INTRODUCTION

The United States Forest Service (USFS), Tongass National Forest plans to construct a two-story office building north of Cascade Creek on Halibut Point Road in Sitka, Alaska (Figure 1).

This report presents the results of our field exploration, laboratory soil testing program, and our recommendations regarding foundation design and site development in support of the proposed

USFS Sitka New Office Design project.

1.1 Planned Development

The proposed USFS Sitka New Office Design project includes the following elements:

• construction of a 2-story, up to 10,000-gross-square-foot office building,

• relocation or demolition of existing structures located in the project area,

• parking area,

• access roads,

• utilities, and

• landscaping

The facility is expected to have a finish floor elevation at or near existing grades with no basement or crawlspace.

This report documents observed subsurface geotechnical conditions at the site, and provides analyses and interpretations of anticipated site conditions within the project area. It also presents recommendations for design and construction of the foundation for the building and for earthwork required for construction of the facility. This report is valid only for the planned development as it is currently understood. Any changes to the current plans may impact the recommendations contained herein and should be evaluated by the project geotechnical engineer.

1.2 Purpose of Investigation

The purpose of this investigation was to determine subsurface soil and groundwater conditions at the site in order to provide recommendations regarding foundations, earthwork, drainage, utility installation, and paved traffic areas.

Figure 1: Vicinity Map

1.3 Scope of Work

A geotechnical exploration program was delineated in a proposal dated September 22, 2009.

Written authorization to proceed with the project was received on October 1, 2009. In accordance with that proposal, DOWL HKM performed the exploration.

Six test borings were drilled to depths of five and a half to eight and a half feet below existing grade in the area of the proposed building and improvements.

The scope of work originally proposed was essentially followed, with the following exceptions.

Shallow bedrock was encountered in every test boring and therefore reduced the depth of the test borings.

The approximate locations of the test borings are shown on Figures A-1 and A-2, Test Boring

Location Maps, Appendix A.

2.0 PHYSICAL SETTING

The city of Sitka is situated on the west coast of Baranof Island fronting the Pacific Ocean on

Sitka Sound (Figure 1). Sitka lies 95 air miles southwest of Juneau, and 185 miles northwest of

Ketchikan at approximately 57°03’N Latitude and 135°20’W Longitude. The location of the

USFS Sitka New Office Design project is at the existing USFS Cascade Creek Administrative

Site. The site is bounded by Cascade Creek to the south, Kramer Avenue to the north and northwest, Halibut Point Road to the west, and USFS trailers to the northeast.

2.1 Regional Geology

Sitka is located on an island, comprised mostly of alluvial and outwash deposits of sands and gravels overlying bedrock. The bedrock across the island ranges from Lower Cretaceous to

Upper Jurassic flysh, greenstone, graywacke, slate, argillite, volcanic detritus, and interbedded mafic volcanic rocks. Intrusive limestone, chert, granodiorite, and minor conglomerate are also present. Volcanic ash has been deposited on the island from Mount Edgecombe to the east and is at relatively shallow depths.

2.2 Climate

Sitka is located in a maritime climate zone and the channel is generally ice free. The climatological data presented below was taken from a range of sources; including the

Department of Commerce, Community, and Economic Development Community Database, and

Environmental Atlas of Alaska.

Mean Annual Precipitation 86 in

Mean Annual Snowfall 39 in

Mean Maximum Temperature July 61°F

Mean Maximum Temperature January 38°F

Mean Minimum Temperature July 51°F

Mean Minimum Temperature January 30°F

Average Summer Temperature Range 50°F – 60°F

Average Winter Temperature Range 31°F – 40°F

Freezing Degree Days (°F-day) 1

Thawing Degree Days (°F-day) 4,680

Heating Degree Days (°F-day) 8,132

Average monthly temperatures and precipitation for Sitka and vicinity, for the period between

1971 and 2000 are shown in Table 1.

Table 1: Average Monthly Temperatures and Precipitation

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Temperature

(°F) 34.1 36 37.6 42 47.4 52.4 56 57.1 53 46 39.5 36

Precipitation

(in) 7.23 6.29 5.93 4.75 4.56 3.32 4.26 6.77 11.02 13.16 9.83 8.74

3.0 SITE CONDITIONS

This section reports interpretations and opinions concerning the surface and subsurface soil and groundwater conditions at the site. The site conditions described are valid for the data collected within the scope of work. If additional data becomes available, some or all of the interpretations and opinions expressed herein could change. We should be notified immediately if the conditions found at the site are different from those encountered during this investigation.

The soil descriptions contained herein and the classifications shown on the test boring logs are the project geotechnical engineer's interpretation of the field logs, the visual soil classification performed in the laboratory, and the results of the laboratory soil testing. The largest particle size that can be recovered with standard drill hole samplers is often smaller than the maximum particle size in a gravelly soil deposit. Therefore, the soil descriptions and test results for gravelly soils tend to be biased toward the finer particle sizes.

Refer to the Test Boring Log - Descriptive Guide in Appendix B immediately following the test boring logs for a more detailed presentation on sample sizes, sample quality, frost classifications, soil types, and the soil classification procedures.

3.1 Surface

The project area has been partially developed with a maintenance facility, warehouse, crew-house, garage, house, and two trailers. The site is relatively flat in the developed areas with a gradual increase in elevation towards the east. The majority of the area is covered by gravel parking and existing buildings. Landscaped areas are present near the existing house, trailers, and along Halibut Point Road. The site drains towards the west.

3.2 Subsurface

The subsurface soils across the site are generally consistent. Below an organic mat or gravel surface, the native mineral soils consist of poorly and well graded sands and gravel to bedrock.

Bedrock was consistently encountered at depths of 5.3 to 8.5 feet.

The poorly and well graded gravels (GW, GP, GW-GM, GP-GM) have low frost susceptibility

(non-frost susceptible [NFS] to F1), are medium dense to very dense, and have in situ moisture contents of 10 to 29 percent.

Well graded sand (SW-SM) was observed in Test Boring 5 at a depth of 4.5 to 8.5 feet. The well graded sands have low frost susceptibility (F2), are very dense, and have in situ moisture contents of 15 to 20 percent.

3.3 Groundwater

Groundwater was observed in five of the test borings while drilling at depths of one to five feet and was not encountered in Test Boring 3. Groundwater elevations observed during drilling often differ from water levels measured after drilling depending on the permeability of the surrounding soils. A slotted PVC standpipe was installed in each of the test borings and the water levels were measured prior to leaving the site. The water levels will tend to fluctuate two to three feet seasonally, especially during periods of heavy precipitation and spring “breakup.”

The groundwater level observed while drilling is shown on each test boring log and measured groundwater levels are noted at the end of each boring log. In addition, Table 2 summarizes our observations of the groundwater within the project area. “N.E.” indicates the groundwater table was “not encountered” while the test boring was drilled or during subsequent measurements through the standpipes.

Table 2: Observed and Measured Groundwater Levels

Depth to Water (ft)

Test Boring

While Drilling (March 22 through March 23, 2010)

Measured Depth (March

23, 2010) 1 2 0.8 2 5 4.7 3 N.E. N.E.

4 2.5 3 5 1 1.2 6 5 7.2

3.4 Permafrost

No permafrost was encountered in any of the test borings nor is any known to exist in the general vicinity of the site. In addition, no unusually cold soils were observed in the samples.

Therefore, we believe the risk of permafrost being present on this site is low. The contractor should be aware that if any evidence of frozen soil is encountered in any of the excavations, we should be notified immediately to evaluate the situation.

4.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS

This section of the report includes interpretations and opinions concerning the interaction of the planned development with the surface and subsurface conditions detected by the field exploration and laboratory tests. It reflects an evaluation of the data collected during the field exploration and soil laboratory tests, and an understanding of the planned development. The analysis is valid for the data collected within the scope of work. The collection of additional data, or a change in the development plans, could provide information, which would alter some or all the interpretations and opinions expressed herein.

These recommendations are based on professional judgment and experience and the data collected during the site exploration and soil laboratory tests. These recommendations generally are not the only design options available; there may be several acceptable alternatives. These recommendations are not intended to represent the only way, but rather to indicate one appropriate option based on the information available.

4.1 Site Response Characterization

Site characterization under the 2006 International Building Code (IBC) is based on an evaluation of the soils in the upper 100 feet of the soil profile. The site class ranges from A to F, and is defined in Table 1613.5.2 of the IBC. In our opinion, the appropriate soil profile type for this site is B.

4.2 Foundation Options

Spread Footings. Spread footings founded on the undisturbed native granular soils, on properly compacted structural fill, or on competent bedrock, and designed for a maximum allowable soil bearing pressure of 5,000 pounds per square foot may be used to support the building. The fill, debris, organics, or disturbed soils at this site are not suitable for support of the structure. They must be removed and replaced with controlled structural fill. The total and differential elastic settlements of properly constructed spread footings founded on the soils recommended herein, and designed for the recommended allowable soil bearing pressure, should not exceed one-inch and three-fourths-inch, respectively.

The allowable soil-bearing pressure may be increased by one-half for wind and seismic forces.

The minimum width of continuous strip footings should be 16 inches and the minimum width of isolated rectangular footings should be 18 inches.

Perimeter footings of warm buildings should be founded at least 36 inches below the adjacent exterior grade. Additionally, all interior footings should be founded at least 18 inches below the lowest adjacent grade unless constrained by the floor slab.

These recommendations are predicated on the assumption that the building will be continually heated during the life of the structure. If the ground floor of the building, or portions of the ground floor of the building will not be heated, the footings in the unheated areas should be founded at a minimum depth of four feet. Any footings extending more than five feet outside the heated building line should be considered cold footings.

Floor Slab. The floor slab should be supported on a minimum of six inches of properly compacted structural fill. The structural fill below the floor slab should consist of gravel no larger than two inches in diameter.

Bridge Foundation. It is expected the bridge will consist of a glu-lam slab bridge situated on a

24-inch glu-lam grade beam. The bridge will be situated on undisturbed native granular soils or on properly compacted structural fill, and designed for a maximum allowable soil bearing pressure of 3,000 pounds per square foot.

Any surficial organics, debris, or disturbed soils at this site are not suitable for support of the bridge must be removed and replaced with structural fill.

4.3 Earthwork

Excavation. Any organic material, debris, and existing fill must be removed from beneath the building footprint area and all load bearing areas and replaced with structural fill. Some of the removed fill can be reused as structural fill if it meets the requirements for structural fill as described herein.

Excavations should be done utilizing an excavator with a smooth-bladed bucket from outside the excavation to minimize disturbance of the subgrade soils. Soils that are disturbed, pumped, or rutted by construction activity should be redensified, if possible, or completely removed and replaced with structural fill.

Geotextiles. A separation geotextile is used to permanently separate two distinct layers of soil in an excavation. For this project, the soils at depth are expected to be dense and granular, not requiring a geotextile. If any soft, silty material is encountered, a geotextile should be used to separate the backfill from the soft material.

Rock. Drilling encountered cobbles, boulders, and bedrock. Any excavations or subsurface work may be impacted by the presence of the cobbles, boulders, and bedrock. The contractor should be aware of these conditions and use appropriate equipment.

Running Sands. Clean sands can present difficulties when excavating below the water table.

The sands may be stable when confined by surrounding soils, but seepage forces can create a

“quick” condition and wash the sands into the excavation, resulting in slumping and caving of the sides. This phenomenon is locally referred to as a running sand or heaving sand condition, and can greatly increase the size of an excavation.

The condition can be controlled by drawing the elevation of the water table down to below the bottom of the planned excavation, and with an appropriate dewatering system prior to excavation, and maintaining the dewatering until the backfill is above the level of the water table.

Cut Slopes. Temporary cut slopes for utility trenches and for foundation excavations in both granular and fine-grained soils have been known to stand temporarily at very steep angles;

however, they also have been known to fail suddenly, without warning, claiming lives. It is the responsibility of the contractor to determine appropriate temporary cut slopes or shoring for excavations and trenches for the site soils, and surface loading conditions. As a minimum, the contractor should be in full compliance with all federal, state, and local safety requirements for trenching and shoring.

Structural Fill. Structural fill is defined as load-bearing fill placed under footings, structural slabs, roads, and parking areas. All structural fill should consist of NFS, sound and durable sand or gravel and contain no lumps, frozen material, organic matter, or other deleterious matter.

Structural fill shall meet the following gradation requirements:

Sieve Size 3”

Percent Finer 100*

1-1/2” 70-100 3/4” 30-100 ½” 25-100

No. 4 20-49 No. 40 0-25 No. 200 0-6 0.02mm 0-3

* The fill may contain up to 10 percent cobbles.

The upper six inches of structural fill below spread footings, grade beams, slabs, and pavements should not contain particles larger than two inches to facilitate fine grading.

Other NFS fill material, which does not meet this gradation requirement, may be acceptable for use. However, the gradation of such material should be evaluated by the project geotechnical engineer prior to its use.

Limits of Fill and Backfill. Structural fill and backfill should extend laterally from the edge of footings, slabs-on-grade, and pavements one-foot for each foot of fill beneath the footing, slab or pavement.

Utility Trench Backfill. A suitable granular bedding material meeting the gradation requirements below should be placed and compacted to a depth of at least six inches below all utility lines. This bedding material should extend six inches above the top of pipe, and should be compacted to 95 percent of the maximum index density, determined in accordance with ASTM

D1557. The remainder of the trench should be backfilled with the excavated material free of debris and organics if it can be compacted. This material should be compacted in lifts not exceeding one foot in thickness to 95 percent of the maximum index density determined in accordance with ASTM D1557.

Sieve Size 1”

Percent Finer

3/8” 60-100 No. 4 40-85 No. 10 25-70 No. 40 5-40 No. 200 0-6*

*Shall not be greater than 35 percent of that fraction passing the No. 40 sieve.

Fill Placement. Structural fill should be placed and compacted in lifts not exceeding 12 inches in loose thickness if a large vibratory compactor is used, or not exceeding 6 inches in loose thickness if a hand-operated compactor is used. Each lift of structural fill should be compacted throughout its entire depth to a density of at least 95 percent of the maximum index density determined in accordance with ASTM D1557. All excavations should be completely dewatered before placement of structural fill.

Fill Testing. Frequent, in-place density tests should be performed in each lift of fill to verify that the fill has been properly compacted prior to placing subsequent lifts. The number of tests performed in each lift should be commensurate with the size of the area worked by the contractor, the variability of the soil types used as fill, and the amount of time an inspector spends on site observing the work.

4.4 Dewatering and Drainage

Final grades and temporary construction grades should be constructed and maintained to rapidly drain surface runoff away from the area. Based on the measured depth of the groundwater table and the planned construction, construction dewatering will be necessary. It is the contractor's responsibility to determine the appropriate dewatering techniques for the construction methods he chooses and for the soil and water conditions encountered. As a minimum, the contractor should be in compliance with any permits for discharge of water, given the proximity of Cascade

Creek.

With a finish floor elevation near existing grades and groundwater encountered between one and seven feet beneath the existing ground surface, a footing drain should be considered for this project. The footing drain should consist of a six-inch diameter perforated pipe surrounded with

“sewer rock” or “pea gravel,” which is all enclosed in a geotextile. The roof drains should not be tied into the footing drains.

4.5 Seasonal Frost Protection

Frost protection is a significant consideration in the design and construction of this facility. Frost action in seasonally frozen ground can subject foundations and structures to large uplift forces and destructive movements. Furthermore, freezing and thawing of structural fill can reduce its density to less than the minimum required for adequate support of structural loads. Seasonal frost can be expected to penetrate as deep as three feet at this site during a cold winter.

The soil frost classification is only an indication of the potential for the growth of ice lenses in the soil and the stability during thaw. It has no relationship to the rate of freezing or thaw penetration. NFS soil can expand when frozen if moisture is present, and can exert significant frost heave and jacking forces. A saturated, clean soil will expand in volume about two to four percent upon freezing. Silty soils will expand significantly more upon freezing and also have the potential for ice lens formation.

Based on our understanding of the site soils and the planned development, one appropriate frost protection scheme is presented below. Other frost protection schemes may be appropriate for this project. Typical methods for dealing with seasonal frost problems include keeping the bearing soils thawed by heating, insulating, and/or using an appropriate depth of bury; designing the structure to resist frost heaving or jacking forces; and/or designing the structure to accommodate the anticipated frost heave.

Building. The ground floor in heated portions of the structure must remain uninsulated to allow heat to escape into the foundation soils. We also recommend installing a two-inch-thick layer of non-water absorbing, closed-cell, extruded-polystyrene insulation on the outboard face of exterior footings in those areas to direct heat flow down and through the soils beneath the building. Where the foundation wall extends above the exterior finish grade, that portion of the insulation may be placed on the inboard face of the wall and lapped at least 12 inches beyond the exterior insulation. This approach to foundation insulation serves two purposes:

1) to provide a frost bond break to prevent uplift forces on the side of the foundation walls, and

2) to allow building heat to flow downward below footings and keep the bearing soils thawed.

The foundation design recommendations are predicated on the foundation soils in the heated portion of the building remaining thawed throughout the construction period and over the life of the structure. The recommendations above accomplish this with heat from the building’s permanent heating system. If the building is not enclosed and its permanent heating system is not operative prior to the advent of freezing weather, other methods should be employed to prevent freezing of the foundation soils and the structural fill within the building area. The effectiveness of any construction frost protection scheme should be monitored closely.

4.6 Earth Pressures

Lateral earth pressures against foundation walls may be relied upon to resist lateral loads against the building. The magnitude of lateral earth pressure is a function of the type and density of the soil adjacent to the subgrade wall or footing; the height of the groundwater table adjacent to the structure; and the allowable movement of the structure with respect to the backfill. Design values for the classic "active,” "at rest,” and "passive" earth pressure conditions are presented below.

Movement is needed to develop the full active or passive earth pressure states. The sketch below shows the general relationship between the earth pressure coefficients and wall movement.

Effect of Deformation or Tilt on the

Magnitude of Earth Pressure

2.0

1.0

3.0

Kp

Ko Ka

Into Soil MassAway from Soil Mass

Tilt or Movement of Wall

La te ra l E ar th

P re ss ur e C oe ffi ci en ts

Drainage must be provided behind all retaining-type walls - especially those that are also exterior building walls. Subgrade building walls should be waterproofed above interior floor grades.

All soil retaining structures and subgrade walls should be designed to withstand the lateral pressures imposed by the backfill soils, groundwater, and any surcharge or point loads behind the wall.

Level Backfill. The walls with level, sand/gravel backfill should be designed for the following equivalent fluid soil pressures:

Active Case: Cantilevered Walls 40 pcf - above the groundwater table

82.4 pcf - below the groundwater table (0.002 H minimum wall deflection away from the backfill, where H - the height of the soil above the base of the wall)

At Rest Case: Basement Walls or Walls Restrained from Movement at the Top 60 pcf - above the groundwater table

92.4 pcf - below the groundwater table (no wall deflection)

Passive Case: Walls Moving into the Soil

300 pcf - above the groundwater table 150 pcf - below the groundwater table (.01 H minimum wall deflection toward the backfill)

Unfactored coefficient of friction between concrete spread footings and structural fill = 0.7 Note: Drainage should always be provided behind retaining structures. A typical drainage system would consist of clean, free-draining gravel (protected by a geotextile) draining to a perforated subdrain and/or weep holes. The drainage system should be designed by a qualified engineer and reviewed by the project geotechnical engineer. If drainage is not provided, then the maximum possible hydrostatic pressure against the wall should be included in the structural design of the wall.

4.7 Paved Traffic Areas

Paved areas experience differential frost heave due to variations in the subsoil and the availability of water for forming ice lenses. This phenomenon can be particularly pronounced at backfilled utility trenches. If the trench backfill is less frost susceptible than the surrounding undisturbed soil, the trench area will tend to heave less and create a depression. Conversely, if the trench backfill is more frost susceptible than the surrounding undisturbed soil, then the trench area will tend to heave more and create a hump in the pavement. Differential heave of six inches or more at the trench section can occur when there is a shallow groundwater table and a wide difference in frost susceptibility between the trench backfill and the surrounding soils.

It is imperative that cracks that form during winter freezing be filled each spring to maintain the integrity of the pavement section and subgrade.

All of the existing organic material and fill should be completely removed from the traffic areas, parking areas, and driveways, and be replaced with properly compacted structural fill. This will result in the best performing traffic section. The thickness of the pavement section is shown in the table below and is based on the frost classification of the subgrade soils.

Based on the anticipated traffic loads and the variation in frost classification of the native and fill soils, we recommend the following minimum pavement section for the parking and driveway areas:

• 2 inches of asphalt pavement, over

• 2 inches of base course, over

• a minimum of 20 inches of subbase.

Base course shall conform to the requirements of the State of Alaska Department of

Transportation and Public Facilities (DOT&PF) Aggregate Base Course, Grading D-1 as defined in the 2004 Standard Specification for Highway Construction. The base course shall be compacted to 95 percent of the maximum index density determined in accordance with ASTM

D1557. Subbase shall meet the requirements of structural fill as defined in Section 4.4, Earthwork.

4.8 Observation

It is important to the performance of the planned USFS Sitka New Office Design that any organic soils are removed where specified, and that structural fill consists of proper materials and is adequately compacted. All excavation and backfill should be observed by qualified inspection/testing personnel under the supervision of a geotechnical engineer. Several in-place density tests should be performed in each lift of the structural fill to verify that minimum fill densities are being attained.

The inspection/testing personnel should be employed by the owner or owner’s representative, not by the contractor, to avoid any inherent conflict of interest and to better ensure that the required level of quality assurance is achieved.

5.0 RESEARCH AND FIELD EXPLORATION

This section presents the technical data obtained from office research and the field investigation.

The methods and procedures used in obtaining the data are presented. The data should be considered accurate only at the locations specified and only to the degree implied by the methods used. The data presented was obtained specifically to address the needs of the design, and may not be adequate for construction purposes.

5.1 Research

DOWL HKM began the geotechnical investigation by researching existing soils information in the project area. Our in-house files indicated in 2008 20 test pits were excavated by others for development of the adjacent Whitcomb Heights Subdivision. This investigation was reviewed in order to determine likely subsurface conditions, and to help establish an appropriate drilling program and is not included in this report.

5.2 Field Exploration

The test boring exploration for the USFS Sitka New Office Design Project was conducted on

March 22 and March 23, 2010. Six test borings were drilled, sampled, and logged in the vicinity of the proposed building footprint and other improvements to depths of eight and a half feet.

The test borings were located in the field by swing tying off existing landmarks using a fiberglass tape. This method is only as accurate as implied. The approximate locations of the current and previous test borings are shown on Figure A-1 and A-2, Test Boring Location Maps, located in Appendix A.

The test borings were drilled using a CME-55 Nodwell-mounted drill rig fitted with continuous flight, hollow stem auger. The drill rig is owned and operated by Denali Drilling, Inc. The drilling was supervised and the samples logged by a geologist with our firm.

Grab samples were obtained at a depth of two feet if cuttings were available. A heavy concentration of gravel and cobbles prevented most of the material from migrating to the surface.

Disturbed samples were obtained at two and a half foot intervals to bedrock using a split-spoon sampler. Standard Penetration Tests (SPT) were performed in each of the test borings. The results are an indication of the relative density or consistency of the subsoil.

The SPT was performed in all of the test borings by driving a 2-inch outside-diameter, split-spoon sampler a distance of 18 inches ahead of the auger with a 140-pound hammer falling

30 inches in accordance with ASTM D1586. The standard penetration resistance (N) value shown on the test boring logs indicates the number of blows required to drive the sampler the last

12 inches. The N-values shown in the logs are raw data from the field and have not been adjusted for sampling equipment type or overburden pressure.

As the soil samples were recovered, they were visually classified and sealed in plastic bags to preserve the natural water content. The samples were then transported to DOWL HKM’s laboratory in accordance with ASTM 4220, for further testing.

A slotted PVC standpipe was installed in each of the test borings and the depth to the groundwater was measured after the drilling was completed.

No environmental testing or monitoring was conducted as a part of this investigation.

6.0 LABORATORY TESTS

This section of the report presents the technical data obtained during the soil laboratory testing in narrative, tabular, and graphic form. The methods and procedures used in obtaining the data are described herein. The data should be considered accurate only to the degree implied by the methods used.

An engineering technician visually classified each sample recovered and the natural water content was measured. Index tests were performed on selected samples and consisted of grain size analyses.

Soil samples will be stored until July 1, 2010 after which time they will be discarded unless other arrangements are made.

6.1 Visual Classification

In the laboratory, an engineering technician visually classified each soil sample obtained from the field exploration. The visual classification procedure consists of:

• identifying the color of the soil,

• estimating the percentages of gravel, sand, and minus No. 200 particle sizes,

• estimating the maximum particle size,

• estimating the size range of the sand particles,

• identifying the shape of the particles,

• estimating the dry strength of the soil when a water content test is performed,

• estimating the plasticity description of the soil and plasticity index,

• comparing the natural water content with respect to the Atterberg limits, and

• identifying the Unified Soil Classification System group.

6.2 Moisture Content

The natural water content of each sample was determined in accordance with ASTM D2216, Standard Test Method for Laboratory Determination of Water (Moisture) Content of Soil and

Rock. The water contents are reported on the graphic test boring logs under Appendix B.

6.3 Particle Size Distribution Tests

Five particle-size distribution tests were performed on selected soil samples in accordance with

ASTM D422. These tests consisted of mechanical sieving, the results of which are presented graphically as Appendix C.

7.0 REFERENCES

Golder, 2008, Geotechnical Investigation for the Whitcomb Heights Subdivision, Sitka, Alaska, Golder Associates Inc., 57p.

Johnson & Hartman, 1984, Environmental Atlas of Alaska, 2nd Ed. Revised: Institute of Water

Resources, University of Alaska, Fairbanks, 95p.

Pewe, T.L., 1975, Quaternary Geology of Alaska, U.S. Geological Survey, Professional

Paper 835, U.S. Government Printing Office, Washington, 145p., 1 map, 2 tables in pocket.

Staff, 1996, Community Information Summary - Sitka, Department of Commerce, Community, and Economic Development, Research and Analysis Section, Anchorage, Alaska.

Wahrhaftig, Clyde, 1965. Physiographic Divisions of Alaska, US Geological Survey

Professional Paper 482, US Government Printing Office, Washington D.C., 52p., 6 plates.

APPENDIX A

TEST BORING LOCATION MAPS

TB-1

TB-4

TB-6

TB-3

APPROXIMATE TEST BORING LOCATIONTB-1

TB-2

TB-5

P:\Projects\D60441\GEO\GTB-SITKA-CASCADE.dwg 2010-4-8

Test Boring Location Map

USFS SITKA NEW OFFICE DESIGN

Sitka, Alaska

FIGURE A-1

SCALE: AS SHOWN

TB-1

TB-4

TB-6

TB-3

APPROXIMATE TEST BORING LOCATIONTB-1

TB-2

PROPOSED

OFFICE BUILDING

TB-5

P:\Projects\D60441\GEO\GTB-SITKA-CASCADE.dwg 2010-11-4

Proposed Improvements

USFS SITKA NEW OFFICE DESIGN

Sitka, Alaska

FIGURE A-2

SCALE: AS SHOWN

APPENDIX B

TEST BORING LOGS AND DESCRIPTIVE GUIDE

D

EP

TH

(F

EE

T)

GW

TD=5.4'

19/6"

44/5"

MA

DEPTHB

lo w s

/ F oo t

M oi st ur e C on te nt

FIGURE B-1

LO

G

O F

E X

P

LO

R A

TI

O

N

.G P

J B

LA

N

K 2.

G D

T

/9 /1

5.4

NFS

GRASS SURFACE

Groundwater encountered at 2' while drilling

WELL GRADED GRAVEL WITH SAND, brown, 35% sand, 3% silt, gravel subrounded to 3", medium sand, saturated, medium dense, bouncing on a rock

TEST BORING COMPLETED ON 3-23-10

PVC STANDPIPE INSTALLED TO 5.4'

GROUNDWATER MEASURED AT 0.8' ON 3-23-10

W.O. 1122.60441.01 becoming siltier, about 35% sand, 5% silt, bouncing on bedrock

Fr os t C la ss

So il

C la ss

TEST BORING COMPLETED: 3-23-10

So il

G ra ph

CLIENT: USFS, Tongass National Forest

KEY

= Mechanical Analysis = Total Depth = Groundwater After Drilling

MA

TD

DRILLING CO.: Denali Drilling, Inc.

EQUIPMENT: CME-55 Nodwell

OPERATOR: Kelly Hill

METHOD: 8 in. OD hollow-stem auger

LOCATION: SEE TEST BORING LOCATION MAP

ELEVATION:Sa m pl e N

o. TEST BORING 1

Sa m pl e

Ty pe

PROJECT: USFS Sitka New Office Design

Fr os t D ep th

= Grab Sample = SPT Sample = Shelby Tube - pushed = Direct Push Sample = 2.5" I.D. Spoon Sample

340# weight, 30" fall

O th er T es ts

LOGGED BY: Callie J. Keller

LOG OF TEST BORING 1

GP

GM

TD=7.5'

DEPTH

D

EP

TH

(F

EE

T)

M oi st ur e C on te nt

LO

G

O F

E X

P

LO

R A

TI

O

N

.G P

J B

LA

N

K 2.

G D

T

/9 /1

FIGURE B-2

W.O. 1122.60441.01

50/0" no sample recovered - bouncing on bedrock 7.5

F1

GRAVEL SURFACE

auger action indicates cobbles

POORLY GRADED GRAVEL WITH SILT AND SAND, brown, 34% sand, 12% silt, gravel subangular to 2", medium sand, damp, dense, rock stuck in catcher becoming more gravelly, about 30% sand, 10% silt, saturated, very dense, bouncing on a rock20

TEST BORING COMPLETED ON 3-22-10

PVC STANDPIPE INSTALLED TO 7.5'

GROUNDWATER MEASURED AT 4.7' ON 3-23-10

Fr os t C la ss

Groundwater encountered at 5' while drilling So il G ra ph

B lo w s

/ F oo t

Sa m pl e

N o.

Sa m pl e

Ty pe

TEST BORING COMPLETED: 3-22-10

So il

C la ss

CLIENT: USFS, Tongass National Forest

KEY

= Mechanical Analysis = Total Depth = Groundwater After Drilling

OPERATOR: Kelly Hill

METHOD: 8 in. OD hollow-stem auger

Fr os t D ep th

PROJECT: USFS Sitka New Office Design

TEST BORING 2

LOCATION: SEE TEST BORING LOCATION MAP

ELEVATION:

LOG OF TEST BORING 2

LOGGED BY: Callie J. Keller

O th er T es ts

= Grab Sample = SPT Sample = Shelby Tube - pushed = Direct Push Sample = 2.5" I.D. Spoon Sample

340# weight, 30" fall

FIGURE B-3

40/0"

DEPTH

D

EP

TH

(F

EE

T)

B lo w s

/ F oo t

Fr os t D ep th Fr os t C la ss

TD=5.6'

W.O. 1122.60441.01

5.6

LO

G

O F

E X

P

LO

R A

TI

O

N

.G P

J B

LA

N

K 2.

G D

T

/9 /1

M oi st ur e C on te nt

F1

GRAVEL SURFACE

auger action indicates cobbles

POORLY GRADED GRAVEL WITH SILT AND SAND, brown, about 35% sand, 10% silt, gravel subrounded to 3", medium sand, damp, dense, cobbles to 4" (~ 5%)

4.75' to 5' - boulder or weathered bedrock, as indicated by drillers no sample recovered - bouncing on bedrock

38 128

GP

GM

TEST BORING COMPLETED ON 3-23-10

NO GROUNDWATER ENCOUNTERED WHILE DRILLING

PVC STANDPIPE INSTALLED TO 5.6'

NO MEASURABLE GROUNDWATER ON 3-23-2010

CLIENT: USFS, Tongass National ForestDRILLING CO.: Denali Drilling, Inc.

EQUIPMENT: CME-55 Nodwell

OPERATOR: Kelly Hill

METHOD: 8 in. OD hollow-stem auger

So il

G ra ph

KEY

= Total DepthTD

TEST BORING COMPLETED: 3-23-10

= Grab Sample = SPT Sample = Shelby Tube - pushed = Direct Push Sample = 2.5" I.D. Spoon Sample

340# weight, 30" fall

Sa m pl e

N o.

So il

C la ss

LOGGED BY: Callie J. Keller

O th er T es ts

LOCATION: SEE TEST BORING LOCATION MAP

ELEVATION:

TEST BORING 3

PROJECT: USFS Sitka New Office Design

LOG OF TEST BORING 3

Sa m pl e

Ty pe

D

EP

TH

(F

EE

T)

GW

TD=5.3'

35/0"

DEPTHB

lo w s

/ F oo t

M oi st ur e C on te nt

Fr os t C la ss

FIGURE B-4

LO

G

O F

E X

P

LO

R A

TI

O

N

.G P

J B

LA

N

K 2.

G D

T

/9 /1 no sample recovered - bouncing on a bedrock 5.3

NFS

GRAVEL SURFACE

auger action indicates gravel

FILL, WELL GRADED GRAVEL WITH SAND, brown, 27% sand, 5% silt, gravel subangular to 2", medium sand, saturated, dense

DEBRIS present (wood)

MA

TEST BORING COMPLETED ON 3-23-10

PVC STANDPIPE INSTALLED TO 5.25'

GROUNDWATER MEASURED AT 3' ON 3-23-10

Groundwater encountered at 2.5' while drilling

So il

G ra ph

W.O. 1122.60441.01

Sa m pl e

N o.

TEST BORING COMPLETED: 3-23-10

So il

C la ss

CLIENT: USFS, Tongass National Forest

KEY

= Mechanical Analysis = Total Depth = Groundwater After Drilling

OPERATOR: Kelly Hill

METHOD: 8 in. OD hollow-stem auger

Fr os t D ep th TEST BORING 4

Sa m pl e

Ty pe

LOCATION: SEE TEST BORING LOCATION MAP

ELEVATION:

= Grab Sample = SPT Sample = Shelby Tube - pushed = Direct Push Sample = 2.5" I.D. Spoon Sample

340# weight, 30" fall

O th er T es ts

LOGGED BY: Callie J. Keller

LOG OF TEST BORING 4

PROJECT: USFS Sitka New Office Design

TD=8.5'

MA

MA

DEPTH

SW

SM

76/7"

LO

G

O F

E X

P

LO

R A

TI

O

N

.G P

J B

LA

N

K 2.

G D

T

/9 /1

GW

GM

becoming sandier, 42% gravel, 5% silt, gravel subangular to 1.5"

4.5

8.5

F1

F2

GRASS SURFACE

Groundwater encountered at 1' while drilling

FILL, WELL GRADED GRAVEL WITH SILT AND SAND,

gray, 43% sand, 6% silt, gravel subangular to 3", medium sand, saturated, ORGANICS present to 10% by volume, (roots), ORGANIC odor

WELL GRADED SAND WITH SILT AND GRAVEL, brown, about 40% gravel, 10% silt, gravel subrounded to 2", medium sand, saturated, very dense no sample recovered - bouncing on bedrock

TEST BORING COMPLETED ON 3-23-10

PVC STANDPIPE INSTALLED TO 8.5'

GROUNDWATER MEASURED AT 1.2' ON 3-23-10

gray to brown, becoming siltier, about 40% sand, 10% silt, gravel subangular to 2", medium dense, trace of ASH, trace of ORGANICS, (rootlets)

= Grab Sample = SPT Sample = Shelby Tube - pushed = Direct Push Sample = 2.5" I.D. Spoon Sample

340# weight, 30" fall

O th er T es ts

LOGGED BY: Callie J. Keller

D

EP

TH

(F

EE

T)

25/0"

Sa m pl e

Ty pe

TEST BORING COMPLETED: 3-23-10

DRILLING CO.: Denali Drilling, Inc.

EQUIPMENT: CME-55 Nodwell

OPERATOR: Kelly Hill

METHOD: 8 in. OD hollow-stem auger

So il

C la ss

So il

G ra ph

Sa m pl e

N o.

CLIENT: USFS, Tongass National ForestMA

KEY

= Mechanical Analysis = Total Depth = Groundwater After Drilling

B lo w s

/ F oo t

M oi st ur e C on te nt

Fr os t C la ss

W.O. 1122.60441.01

Fr os t D ep th

PROJECT: USFS Sitka New Office Design

TEST BORING 5

LOCATION: SEE TEST BORING LOCATION MAP

ELEVATION:

LOG OF TEST BORING 5 FIGURE B-5

GP

TD=8.5'

W.O. 1122.60441.01

D

EP

TH

(F

EE

T)

LO

G

O F

E X

P

LO

R A

TI

O

N

.G P

J B

LA

N

K 2.

G D

T

/9 /1

M oi st ur e C on te nt

Fr os t C la ss

FIGURE B-6

68/11" no sample recovered - bouncing on bedrock 8.5

NFS

GRAVEL SURFACE

auger action indicates gravel

POORLY GRADED GRAVEL WITH SAND, gray, about 35% sand, 5% silt, gravel subangular to 2", medium sand, damp, medium dense

Groundwater encountered at 5' while drilling becoming sandier, about 35% sand, 5% silt, very dense, HYDROCARBON ODOR

TEST BORING COMPLETED ON 3-23-10

PVC STANDPIPE INSTALLED TO 8.5'

GROUNDWATER MEASURED AT 7.2' ON 3-23-10

B lo w s

/ F oo t becoming more gravelly, about 20% sand, 5% silt, saturated So il C la ss

So il

G ra ph

Sa m pl e

N o.

DEPTH

DRILLING CO.: Denali Drilling, Inc.

EQUIPMENT: CME-55 Nodwell

OPERATOR: Kelly Hill

METHOD: 8 in. OD hollow-stem auger

PI

D

(p pm

CLIENT: USFS, Tongass National Forest

KEY

= Photoionization Detector = Total Depth = Groundwater After Drilling

PID

TEST BORING COMPLETED: 3-23-10

TEST BORING 6

LOCATION: SEE TEST BORING LOCATION MAP

ELEVATION:

PROJECT: USFS Sitka New Office Design

Sa m pl e

Ty pe

= Grab Sample = SPT Sample = Shelby Tube - pushed = Direct Push Sample = 2.5" I.D. Spoon Sample

340# weight, 30" fall

O th er T es ts

LOGGED BY: Callie J. Keller

LOG OF TEST BORING 6

Fr os t D ep th

APPENDIX C

LABORATORY TEST RESULTS

Maria E. Kampsen, P.E • 4041 B Street • Anchorage • Alaska • 99503 • 907/562-2000 • Fax 907/563-3953

Client:

Project:

Work Order:

USFS, Tongass National Forest

USFS Sitka New Office Design

D60441

3/29/2010

2010-241Lab Number

Received

Reported 4/8/2010

#200 2.9%

#100 4%

#60 6%

#40 7%

#20 12%

#10 25%

Total Weight of Fine Fraction: 70.94g

#4 38%

Ȩ" 53%

½" 67%

¾" 85%

1" 100%

1½" 100%

2" 100%

3" 100%

Total Weight of Coarse Fraction: 187.92g

Size Passing Specification

ASTM D422

Particle Size Distribution

Engineering Classification:

Frost Classification:

Well Graded Gravel with Sand, GW

Not Measured

Location: Boring 1

Sample 1

Depth 2.5'-3.5'

Maria E. Kampsen, P.E • 4041 B Street • Anchorage • Alaska • 99503 • 907/562-2000 • Fax 907/563-3953

Project:

Work Order:

USFS, Tongass National Forest

USFS Sitka New Office Design

D60441

3/29/2010

2010-242Lab Number

Received

Reported 4/8/2010

#200 12%

#100 15%

#60 18%

#40 22%

#20 26%

#10 34%

Total Weight of Fine Fraction: 137.16g

#4 46%

Ȩ" 61%

½" 68%

¾" 81%

1" 86%

1½" 100%

2" 100%

3" 100%

Total Weight of Coarse Fraction: 301.74g

Size Passing Specification

ASTM D422

Particle Size Distribution

Engineering Classification:

Frost Classification:

Poorly Graded Gravel with Silt and Sand, GP-GM

Not Measured

Location: Boring 2

Depth 2.5'-4'

Maria E. Kampsen, P.E • 4041 B Street • Anchorage • Alaska • 99503 • 907/562-2000 • Fax 907/563-3953

Project:

Work Order:

USFS, Tongass National Forest

USFS Sitka New Office Design

D60441

3/29/2010

2010-243Lab Number

Received

Reported 4/8/2010

#200 4.8%

#100 6%

#60 8%

#40 9%

#20 13%

#10 21%

Total Weight of Fine Fraction: 111.79g

#4 32%

Ȩ" 44%

½" 52%

¾" 72%

1" 91%

1½" 100%

2" 100%

3" 100%

Total Weight of Coarse Fraction: 344.73g

Size Passing Specification

ASTM D422

Particle Size Distribution

Engineering Classification:

Frost Classification:

Well Graded Gravel with Sand, GW

Not Measured

Location: Boring 4

Depth 2.5'-4'

Maria E. Kampsen, P.E • 4041 B Street • Anchorage • Alaska • 99503 • 907/562-2000 • Fax 907/563-3953

Project:

Work Order:

USFS, Tongass National Forest

USFS Sitka New Office Design

D60441

3/29/2010

2010-244Lab Number

Received

Reported 4/8/2010

#200 6.1%

#100 9%

#60 12%

#40 15%

#20 20%

#10 32%

Total Weight of Fine Fraction: 437.12g

#4 49%

Ȩ" 65%

½" 72%

¾" 83%

1" 89%

1½" 95%

2" 100%

3" 100%

Total Weight of Coarse Fraction: 1735.68g

Size Passing Specification

ASTM D422

Particle Size Distribution

Engineering Classification:

Frost Classification:

Well Graded Gravel with Silt and Sand, GW-GM

Not Measured

Location: Boring 5

Depth 0'-2'

Maria E. Kampsen, P.E • 4041 B Street • Anchorage • Alaska • 99503 • 907/562-2000 • Fax 907/563-3953

Project:

Work Order:

USFS, Tongass National Forest

USFS Sitka New Office Design

D60441

3/29/2010

2010-245Lab Number

Received

Reported 4/8/2010

#200 5.1%

#100 6%

#60 8%

#40 10%

#20 14%

#10 33%

Total Weight of Fine Fraction: 238.52g

#4 58%

Ȩ" 70%

½" 74%

¾" 90%

1" 92%

1½" 100%

2" 100%

3" 100%

Total Weight of Coarse Fraction: 409.31g

Size Passing Specification

ASTM D422

Particle Size Distribution

Engineering Classification:

Frost Classification:

Well Graded Sand with Silt and Gravel, SW-SM

Not Measured

Location: Boring 5

Sample 4

Depth 7'-8.1'