S12865.FINAL Subsurface Exploration.MEK.0307.pdf

FINAL

SUBSURFACE EXPLORATION

SITUK RIVER BRIDGE AREA IMPROVEMENTS

YAKUTAT, ALASKA

FINAL Subsurface Exploration Situk River Bridge Area Improvements March 2007 Yakutat, Alaska

TABLE OF CONTENTS

Page

Page ii

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 and Setting

2.2 Climate

3.0 SITE CONDITIONS

3.1 Surface

3.2 Subsurface

3.3 Groundwater

3.4 Flooding

3.5 Site Characterization

4.0 ENGINEERING ANALYSIS AND RECOMMENDATIONS

4.1 Foundations

4.2 Dewatering and Drainage

4.3 Earth Pressures

4.4 Observation

5.0 FIELD EXPLORATION

5.1 Field Exploration

6.0 LABORATORY TESTS

6.1 Visual Classification

6.2 Moisture Content

6.3 Particle Size Distribution Tests

6.4 Plasticity Index Tests

6.5 Pocket Penetrometer

7.0 REFERENCES

FIGURES

Figure 1: Vicinity Map Figure 2: Quadrant Map Figure 3: Helical Pier Detail

TABLES

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

APPENDICES

Appendix A..............................................................................................Test Pit Location Map Appendix B ....................................................................... Test Pit Logs and Descriptive Guide Appendix C ........................................................................................... Laboratory Test Results

1.0 INTRODUCTION

Atelier Landscape Architects, Inc. (Atelier) plans to design several structures and improvements to the day use areas near the Situk River Bridge in Yakutat, 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 Situk River Bridge Area Improvements project. This work was performed for

Atelier on behalf of the United States Forest Service.

1.1 Planned Development

The proposed Situk River Bridge Area Improvements project includes the following elements:

• relocation of and improvements to the boat ramp,

• parking for vehicles,

• two hole vault toilets,

• bus turnaround,

• foot bridge over overflow creek,

• log picnic shelter and day-use areas,

• six walk-in campsites with tent platforms, fire rings, picnic tables, and gravel access trails, and

• possible utility services, and improved site access to support this project.

The improvements are proposed to have finish grade elevations about two to five feet higher than existing grades.

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 project elements. This report and subsequent recommendations are based on, and valid only for, the planned development as it is currently understood. Any changes to the planned development 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 design recommendations regarding foundations, earthwork, drainage, and traffic areas.

1.3 Scope of Work

Based on the Request for Proposal dated August 4, 2006, DOWL Engineers (DOWL) proposed test pits across the site and developed a proposed scope of work. DOWL then submitted a proposal to provide geotechnical engineering services for the Situk River Bridge project.

On September 8, 2006, DOWL received Notice-to-Proceed with the project and in accordance with that proposal, the exploration was performed.

A pre-work site visit was held on September 27, 2006. Representatives from Atelier, DOWL, and the Tongass National Forest Ranger District met in Yakutat to discuss the project and visit the site. Based on the site visit, five test pits were excavated in the vicinity of planned improvements. The locations of the test pits are shown on Figure A-1, Test Pit

Location Map, Appendix A.

Figure 1: Vicinity Map

2.0 PHYSICAL SETTING

The site of the proposed Situk River Bridge Area Improvements project is located along

Forest Highway 10 (FH10) near Yakutat, Alaska. Yakutat is located approximately 700 air miles southeast of Anchorage near Yakutat Bay.

2.1 Regional Geology and Setting

The city of Yakutat is located on the Gulf of Alaska Coastline, south of Khantaak Island and east of Yakutat Bay. Yakutat is situated within the Yakutat Terrane, a part of the Gulf of

Alaska Coastal Section physiographic subprovince that borders the Gulf of Alaska. The present topography of the Yakutat area is primarily the product of glacial advances that invaded the area, as well as the effect of lacustrine (lake) and alluvial (river/creek) deposits consequent with or subsequent to the advances. The significant soils in the site area are glacial outwash deposits of Wisconsinan age silts, clays, sands, and gravels, and fluvial deposits of sands and gravels.

The geology of the Yakutat area is comprised primarily of a thick sequence of Cenezoic siliciclastic sedimentary rocks with minor amounts of coal and volcanic rocks. The Yakutat

Terrane is bounded to the east and north by the Fairweather Fault, a strike-slip fault, and the

Chugach-Saint Elias Fault, a north dipping thrust fault. To the west, the west dipping Kayak thrust fault and to south, the Transition fault system, a north dipping thrust fault.

2.2 Climate

Yakutat is located in a maritime climate zone with mild winters and wet summers. The climatological data presented below was taken from a range of sources; including the State of

Alaska Department of Commerce, Community, and Economic Development Community

Database, Environmental Atlas of Alaska, climate.gi.alaska.edu, and city-data.com.

Mean Annual Precipitation 160 in Mean Annual Snowfall 183 in Mean Maximum Temperature July 60°F Mean Maximum Temperature January 32°F Mean Minimum Temperature July 47°F Mean Minimum Temperature January 19°F Average Summer Temperature Range 43°F - 53°F

Average Winter Temperature Range 26°F - 41°F Freezing Degree Days (°F-day) 550 Thawing Degree Days (°F-day) 3,500 Heating Degree Days (°F-day) 9,300

Average monthly temperatures and precipitation amounts for Yakutat as recorded at the

Yakutat airport, for the period between 1917 and 2006 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) 25.8 28.4 31.5 37.2 43.6 49.7 53.6 53.3 48.2 41.1 32.4 28.6

Precipitation (including snowfall)

(in)

0.18 10.99 11.4 10.8 9.78 7.17 7.88 13.3 20.9 24 15.2 15.9

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.

3.1 Surface

The Situk River Bridge Area Improvements is segregated into the quadrants shown below and delineated by FH10 and Situk River.

Figure 2: Quadrant Map

Northwest Quadrant. The northwest quadrant is vegetated with Sitka spruce and no development is planned within this area.

Northeast Quadrant. The northeast quadrant is currently developed as a gravel parking area. Two unmarked tent campsites exist on the northeast side of the cleared area. The vegetation consists predominantly of Sitka spruce, however, alder trees and blueberry bushes occupy open vegetation areas. Three existing culverts parallel FH10 and two were observed to be situated too high to allow for proper drainage of water along FH10. A lack of access to the culverts causes flow to be diverted into the unplanned parking area and into Situk River.

Southeast Quadrant. The southeast quadrant includes the Situk River trailhead. The trailhead is located approximately 200 feet from FH10 at the end of a gravel road with a parking area large enough for two vehicles. The existing Situk River trail is a wide footpath that requires the crossing of a small creek near the trailhead. A canoe launch is present along the banks of the Situk River via a footpath from the trailhead. Vegetation surrounding the area consists of Sitka Spruce with moderate ground cover consisting of devil’s club and blueberry bushes.

Southwest Quadrant. The boat launch is located within the southwest quadrant of the project area, as well as an unplanned day use area. The boat launch is currently located near the base of the Situk River Bridge, however, the gravel access drive leading to the boat launch is improperly graded and is easily flooded during high water. The parking area adjacent to the boat ramp does not accommodate the demand of vehicle parking space or provide adequate turnaround space. The parking area is approximately ten feet below the elevation of FH10 and ponded water is often an occurrence during heavy precipitation. The access to the unplanned day use area is undeveloped and consists of vehicle paths on the forest surface. The day use area consists of a clearing with unplanned fire rings. Several footpaths lead from the day use area and boat launch to the banks of the river, and therefore, the soils of the shores have been eroded slightly. Three campsites located near the unplanned day use area are marked with brown, numbered carsonite posts.

Situk River Bridge is 30 feet wide and 100 feet long with concrete decking. Multiple footpaths are present adjacent to the bridge abutments for fishing access

3.2 Subsurface

Test Pits 1 through 3 were excavated in the southwestern quadrant where the boat ramp, parking area, toilet, campsites, and picnic shelters are planned. Test Pit 1, excavated on top of the floodplain bench, farthest from the river, yielded poorly graded sand (SP) with significant amounts of gravel below a thin peat surface. Test Pit 2 was excavated near the shore of the river, below the floodplain, and encountered poorly graded gravels (GP) with substantial amounts of sand below a surficial peat layer. Test Pit 3 was excavated near the proposed day use shelter location. Below a thin organic mat, silty gravel with sand (GM) was observed to a depth of three feet, followed by silts.

Test Pit 4 was excavated in the northeast quadrant, in the vicinity of a planned parking area.

The test pit was excavated near the shore of the river, below the floodplain and encountered a six-inch layer of poorly graded sand (SP-SM) below the peat surface. The underlying material was poorly graded gravel (GP) with sand.

Test Pit 5 was excavated in the southeast quadrant, in the vicinity of a planned parking area.

The test pit was excavated near the shore of the river, below the floodplain and encountered a two-foot layer of silty gravel (GM) below the peat surface. The underlying material was poorly graded gravel (GP) with sand.

The native poorly graded gravels (GP) have varying amounts of sand and are non-frost susceptible (NFS). The in situ moisture contents of the range from three to six percent.

The silty gravel (GM) observed in Test Pits 3 and 5, have low frost susceptibility (F1) and contain nonplastic fines.

The poorly graded sands (SP) observed in Test Boring 1 are NFS with an in situ moisture content of four percent.

The silts observed beneath the gravels in Test Pit 3 are nonplastic and contain varying amounts of sand and organics, such as grass and plants. These silts have high frost susceptibility (F4) and the in situ moisture content ranges from 34 to 47 percent.

The soil descriptions contained herein and the classifications shown on the test pit 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.

Refer to the test pit logs in Appendix B For a more detailed presentation of the soil conditions encountered in each of the test pits. Refer to the Test Pit Log - Descriptive Guide, which consists of six pages following the pit logs for definitions of the frost classifications and soil types discussed.

3.3 Groundwater

Groundwater was observed in each of the test pits while excavating at depths ranging from one to four and a half feet. The water level will tend to fluctuate two to three feet seasonally, especially during periods of heavy precipitation and spring “breakup.” Larger fluctuations in the water table will occur closest to the river and in wetland areas.

The groundwater level observed while excavating is shown on each test pit log and summarized in Table 2 below.

Table 2: Observed Groundwater Levels

While Excavating (September 27, 2006)

Test Pit No.

Depth to Water (ft)

1 4.5 2 1.5 3 2 4 1 5 3

3.4 Flooding

At the time of the investigation, heavy rains had caused the river level to rise approximately three feet overnight. The water level of the river, according to the United States Geological

Survey stream gauge read an elevation of approximately 70 feet during the field investigation. This was a fairly large event but does occur on an annual basis.

3.5 Site Characterization

Site characterization under the 2000/2003 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 1615.1.1 of the IBC. In our opinion, the appropriate soil profile type for this site is D.

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 Foundations

There are a number of different structures planned for this area; covered picnic shelters, vault toilet, parking areas, and a boat ramp. The foundation systems for each of these planned improvements are addressed below. A sketch of the proposed improvements is shown on

Figure A-2, Proposed Improvements.

Picnic Shelter. The site of the proposed picnic shelter is in the vicinity of Test Pit 3. The groundwater depth was observed at two feet below the ground surface. Excavating for the footings will encounter water, requiring dewatering. Raising the site grades by two to three feet instead is recommended.

Spread footings, timber or concrete, founded on a minimum of two feet of structural fill and designed for a maximum allowable soil bearing pressure of 2,000 pounds per square foot may be used to support the shelters. 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 minimum width of each footing should be 24 inches and founded at a minimum depth of

24 inches below the adjacent exterior grade.

Restroom. It is expected that the restroom will be a Sweet Smelling Toilet. Our understanding is that this will be a two hole toilet. This is essentially a concrete vault toilet with two underground holding tanks and cross ventilation above grade. Conventional spread footings, concrete mat, or concrete blocks could be used to support the structure. The concrete should be founded on structural fill or on the native sands below the fill material and designed for a maximum allowable soil bearing pressure of 2,000 pounds per square foot.

The site of the proposed restroom is in the vicinity of Test Pit 1. The groundwater depth was observed at 4.5 feet below the ground surface while excavating. Excavation will encounter water, requiring dewatering. Raising the site grades by two to three feet instead is recommended. The structure should also be designed to resist the buoyant forces of the groundwater during periods of heavy rainfall.

Boat Ramp. The site of the proposed boat ramp is in the vicinity of Test Pit 2. The groundwater depth was observed at 1.5 feet below the ground surface while excavating. It is our understanding that the boat ramp will consist of a precast concrete structure about 14 feet wide. The structure will be placed directly on the ground surface. All organics should be removed from below the boat ramp. Armor rock (riprap) should be placed adjacent to the boat ramp to reduce the potential for scour.

Footbridge. A small footbridge is planned to be constructed over the overflow creek in the southeast corner of the site. There are a number of foundation systems that could be used to support the bridge. These include concrete spread footings, a concrete block, driven piles or helical piers.

If concrete is used, the concrete should be founded at least two feet below the existing ground surface for frost considerations. Bearing capacity and minimum sizes as outlined for the platforms can be used for the bridge. Another option is to support the bridge with a helical pier foundation installed to a minimum embedment of ten feet. The lead section at a minimum, should be 1.5-inch square solid steel. The piers should consist of a minimum of two helical plates as shown in Figure 3.

Figure 3: Helical Pier Detail

The helical piers should be spaced a minimum of three diameters apart from the outer edge of the largest helical plate. The expected ultimate loads that the piers will be required to support are shown below. To determine allowable loads, the ultimate capacity should be divided by a factor of safety of 2.0.

• Ultimate Axial Capacity - 21 kips (estimated)

• Ultimate Lateral Capacity - 1 kip (estimated)

• Ultimate Uplift Capacity - 4 kips (estimated)

The axial capacities of single piers shown above may be assumed for piers installed ten degrees or less from vertical. Alternate pier configurations could be utilized, but the contractor should submit the configuration and calculations to the project engineer for approval prior to installation.

For the lateral capacity of the shaft, a pipe sleeve or larger diameter shaft should be used.

The pipe sleeve is typically a four-inch diameter hollow steel pile that slips over the shaft and is then rigidly connected to the pier. The sleeves do not provide axial capacity but additional lateral bracing. A pipe sleeve or 2.5-inch diameter shaft will provide the lateral capacity as shown above.

Installation should be performed by an experienced contractor using the proper equipment and with a minimum of three years of local experience with docks/platforms/boardwalk-type structures. Proof of experience should be requested. The helical piers should be constructed under ISO 9000 and 9001 standards and a list of equipment and components that have been demonstrated to meet or exceed these specifications should be provided.

Test borings were not performed at this site and penetration test values were not obtained.

Assumptions regarding typical values associated with the observed soils in the area were used to develop the helical pier configuration. Depending on the soils encountered at depth, alternate configurations may be more appropriate. The contractor should be required to install and test one pier configuration prior to installing all piers.

During installation, the contractor should make a log of installation torque versus depth.

Qualitative observations of performance during installation should also be recorded. The ultimate capacity should be verified in the field with one load test performed in general accordance with ASTM D1143, “Piles under Static Axial Compressive Load.” The load test should be performed early in the project to allow the results to be incorporated into the bridge foundation system. The load test should be observed by a qualified representative working for the design team or owner. A qualified engineer should review the pile load test data.

Large stone or riprap could be placed around the piers for added protection during high flow events.

Parking Areas/Access Roads. It is our understanding that the parking areas and access roads will be gravel covered. Parking areas and gravel access roads should be constructed by removing all peat and organic silt (estimated to be less than one foot). The road section would then consist of the following:

• a minimum of 6 inches of crushed aggregate, over

• a minimum of 12 inches of structural fill.

Trails. The gravel trails should be constructed as follows after complete removal of the surficial organic mat.

• a minimum of 3 inches of crushed aggregate, over

• a minimum of six inches of structural fill.

Excavation. Generally, all unsuitable soils must be removed and replaced with structural fill where specified. Unsuitable soils are peat, organic silt, existing fill, debris, or frozen soil.

Some of the native sands and gravels may be suitable for reuse if they meet the requirements for structural fill as described below. Any existing soils that do not meet the requirements for structural fill as discussed herein must be removed and replaced with structural fill.

Site Grades. Given the shallow depth to groundwater, large fluctuations in the groundwater table, and periodic flooding, we recommend that site grades be raised wherever possible.

This will assist with the long-term performance of all the planned structures and improvements.

Frozen Soils. Do not place fill over frozen soils. Do not fill or backfill with frozen soils.

All frozen soils encountered must be removed.

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. Any excavations will likely encounter this condition.

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, maintain the dewatering until the backfill is above the level of the water table.

Cut Slopes. Temporary cut slopes and utility trenches 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.

Permanent Cut and Fill Slopes. Permanent cut and fill slopes should not be steeper than

2 horizontal to 1 vertical. Erosion protection, such as topsoil and seeding should be placed as soon as practical after slopes are constructed.

Structural Fill. Structural fill is defined as load bearing fill consisting of NFS sand or gravel meeting the following gradation requirements for the minus three-inch fraction:

Sieve Size Percent Finer 3" 100*

1-1/2" 70 - 100 3/4" 30 - 100 1/2" 25 - 100

No. 4 20 - 49 No. 40 0 - 25 No. 200 0 - 6

0.02 mm 0 - 3

*The fill may contain up to ten percent cobbles.

Fill Placement. Where structural fill may be required, the 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 six 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

D4253. All excavations should be completely dewatered before placement of structural fill.

Fill Testing. 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.

4.2 Dewatering and Drainage

It likely will be necessary to dewater excavations unless site grades are raised. However, this will depend on:

• the final grading plan,

• the contractor’s approach to the work, and

• the weather at the time of construction.

It is important that any water be removed from excavations until they are properly backfilled.

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 Situk River.

Finish floor elevations should be established and site grades should be constructed and maintained to rapidly drain surface and roof runoff away from the picnic shelters and toilet subgrade soils.

4.3 Earth Pressures

All soil retaining structures 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

34 pcf - above the groundwater table 80 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: Walls Restrained from Movement at the Top

53 pcf - above the groundwater table 90 pcf - below the groundwater table (no wall deflection)

Passive Case: Walls Moving into the Soil

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

Note: Drainage should always be provided behind retaining walls whenever possible.

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.

4.4 Observation

It is important for the performance of the planned improvements that any organic soils are removed where specified, and that structural fill consist of proper materials and are adequately compacted. All excavation and backfill should be observed by qualified inspection/testing personnel under the supervision of the project 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 his representative, and not the contractor, to avoid any inherent conflict of interest and to better ensure that the required level of quality assurance is provided.

5.0 FIELD EXPLORATION

This section presents the technical data obtained from 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 Field Exploration

The test pit exploration for the Situk River Bridge Area Improvements project was conducted on September 27, 2006. The test pits were excavated using a Case 580 Super L rubber tire backhoe owned by Pate Construction and operated by Donnie Pate of Yakutat, Alaska. The test pits were excavated in the vicinity of the proposed improvements. A geologist supervised the test pit exploration and obtained samples of the distinct soil layers.

Each test pit was located in the field measuring distances from existing control points or topographic features. A hand-held Garmin Global Positioning System 12 unit was used to record the locations. The test pit locations were then surveyed horizontally and vertically using standard survey techniques.

General Material Site Evaluation. Two possible gravel sources exist near the project site:

Pate Construction’s material site in Yakutat, Alaska and a private pit of unknown ownership approximately one half mile from the edge of the pavement leading from Yakutat on FH10.

Bulk samples were acquired from each of these sites to determine the quality of the gravel for potential use in future road development. Speaking with Bob Pate, owner of Pate

Construction, most of the material for use in construction in the Yakutat area is used from the

Pate Construction material site.

The gravel pit owned by Pate Construction is located near the Glacier Bear Lodge approximately one-quarter mile east of the community. Currently, one pond covers the site and several stockpiles of material are present on all sides of the pond. Material is obtained by dredging and stockpiling. Material of various sizes were stockpiled across the site, ranging in size from sands to a maximum of eight-inch diameter cobbles. A crusher is located on-site. A bulk sample was obtained of the material from one of the stockpiles and the test results indicate a well graded sand (SW) with gravel.

The private gravel pit consisted of numerous stockpiles of material. A sample of material was obtained from one of the stockpiles. The material test results indicate a poorly graded sand (SP). The results of the tests are shown in Appendix C, Laboratory Test Results.

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 May 1, 2007, 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 pit logs, Appendix B.

6.3 Particle Size Distribution Tests

Four 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.

6.4 Plasticity Index Tests

One plasticity index test was performed in accordance with ASTM D4318, Standard Test

Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils. The liquid limit, plastic limit, and plasticity index numbers obtained from the test are plotted and used to classify the cohesive soil as silts or clays. In addition, the limits are used to estimate strength and settlement characteristics of these soils.

The liquid limit is the water content (in percent) of a soil passing the boundary between the liquid and plastic states. If the in situ moisture of the soil is higher than the liquid limit, the soil will be difficult to work with, and will not be able to be compacted.

The plastic limit of a soil is the lowest water content at which the soil is plastic. The difference between the liquid and plastic limits is the plasticity index or the range of water contents where a soil will behave plastically. The result of the plasticity index test is presented in Figure C-1, Appendix C, Laboratory Test Results.

6.5 Pocket Penetrometer

Pocket penetrometers are commonly used on split-spoon and thin-walled tube samples to evaluate the estimated unconfined compressive strength of saturated cohesive soils. They may also be used for the same purpose in freshly excavated trenches. Pocket penetrometer results are shown on the individual test pit logs located in Appendix B.

7.0 REFERENCES

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.

Plafker, G. and Berg, H.C. (Eds.), 1994, The Geology of North America, The Geology of

Alaska, v. G-1, Geological Society of America, Boulder, Colorado, 1055 p.

Staff, 1996, Community Information Summary - Yakutat, 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 Pit Location Map

TEST PIT LOCATION

EDGE OF WATER

EDGE OF VEGETATION

EXISTING CAMPSITE LOCATION

EXISTING FIRE PIT LOCATION

EXISTING BUILDING SITE

CONTOUR INTERVAL IS 1 FOOT

EXISTING ROAD/ TRAIL

Test Pit Location Map- Existing Condition

SITUK RIVER BRIDGE IMPROVEMENTS

Yakutat, Alaska

FIGURE A-1

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Test Pit Location Map- Proposed Improvements

SITUK RIVER BRIDGE IMPROVEMENTS

Yakutat, Alaska

FIGURE A-2

FUTR.scr SCALE: AS SHOWN

APPENDIX B

Test Pit Logs and Descriptive Guide

POORLY GRADED SAND, brown, about 5% gravel, 5% silt, gravel subrounded to 1", medium sand, damp

POORLY GRADED SAND WITH GRAVEL, gray, 41% gravel, 1% silt, gravel subrounded to 2", medium sand, wet to saturated

Groundwater encountered at 4.5' while excavating

TEST PIT COMPLETED ON 9-27-06

Fr os t C la ss

14MA

LO

G

O F

E X

P

LO

R A

TI

O

N

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J B

LA

N

K 2.

G D

T

/7 /0

DEPTH

D

EP

TH

(F

EE

T)

M oi st ur e C on te nt

PT

SP

SP

TD=6.0'

0.2FOREST SURFACE

PEAT, brown, damp

6.0

F4

NFS

NFS

1.0

So il

C la ss

BORING COMPLETED: 9-27-06

FIGURE B-1

Sa m pl e

N o.

LOCATION: N59822.3 / E30018.7

ELEVATION: 75.1 FT

PROJECT: Situk River Bridge

Sa m pl e

Ty pe

LOG OF TEST PIT 1

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

340# weight, 30" fall

O th er T es ts

LOGGED BY: Keri A. Nutter

So il

G ra ph

EXCAVATOR: Pate Construction

EQUIPMENT: Case 580 Super L

OPERATOR: Donnie Pate

METHOD: Extendahoe

W.O. S12865

TEST PIT 1

MA

TD

Fr os t D ep th

KEY

= Mechanical Analysis = Total Depth

CLIENT: Atelier ps

Groundwater encountered at 1.5' while excavating

DEPTH

D

EP

TH

(F

EE

T)

Fr os t C la ss

LO

G

O F

E X

P

LO

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O

N

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N

K 2.

G D

T

/7 /0

W.O. S12865

NFS

PT

GP

TD=4.5'

0.2

4.5

TEST PIT COMPLETED ON 9-27-06

F4 becoming more gravelly, about 30% sand, 5% silt, saturated

GRASS SURFACE

PEAT, brown, damp

POORLY GRADED GRAVEL WITH SAND, gray, about 40% sand, 5% silt, gravel subrounded to 3", medium sand, wet to saturated, cobbles to 4"

FIGURE B-2

So il

C la ss

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

340# weight, 30" fall

M oi st ur e C on te nt

LOGGED BY: Keri A. Nutter

LOCATION: N59809.9 / E30120.0

ELEVATION: 70.5 FTSa m pl e Ty pe So il G ra ph

Sa m pl e

N o.

EXCAVATOR: Pate Construction

EQUIPMENT: Case 580 Super L

OPERATOR: Donnie Pate

METHOD: Extendahoe

LOG OF TEST PIT 2

CLIENT: Atelier ps

TD

Fr os t D ep th

O th er T es ts

PROJECT: Situk River Bridge KEY = Total Depth

TEST PIT 2

BORING COMPLETED: 9-27-06

Groundwater encountered at 2' while excavating

SANDY SILT, gray, about 30% sand, nonplastic, fine sand, saturated, ORGANICS present to 30% by volume, (grass, in situ plants, PP= .25 TSF

SILT WITH SAND, gray, about 20% sand, nonplastic, fine sand, saturated, ORGANICS present to 30% by volume, (grass, in situ plants, PP= .4 TSF

TEST PIT COMPLETED ON 9-27-06

DEPTH

LO

G

O F

E X

P

LO

R A

TI

O

N

.G P

J B

LA

N

K 2.

G D

T

/7 /0

PI=NP

PP

PP

GM

ML

ML

TD=6.0'

3.0

SILTY GRAVEL WITH SAND, brown, about 35% sand, 15% silt, nonplastic, gravel subrounded to 3", medium sand, wet to saturated

6.0

GRASS SURFACE, ORGANIC MAT

F1

F4

F4

4.0

So il

C la ss

O th er T es ts

PROJECT: Situk River Bridge

TEST PIT 3

D

EP

TH

(F

EE

T)

PI

LL

PP

TD

KEY

= Plasticity Index = Liquid Limit = Pocket Penetrometer = Total Depth

Sa m pl e

Ty pe

LOG OF TEST PIT 3

LOCATION: N59734.0 / E30124.6

ELEVATION: 71.0 FT

LOGGED BY: Keri A. Nutter= Grab Sample = SPT Sample = Shelby Tube - pushed = 2.5" I.D. Spoon Sample

340# weight, 30" fall

So il

G ra ph

M oi st ur e C on te nt

Fr os t C la ss

FIGURE B-3

W.O. S12865

Fr os t D ep th

BORING COMPLETED: 9-27-06

EXCAVATOR: Pate Construction

EQUIPMENT: Case 580 Super L

OPERATOR: Donnie Pate

METHOD: Extendahoe

CLIENT: Atelier ps

Sa m pl e

N o.

POORLY GRADED SAND WITH SILT AND GRAVEL, brown, about 15% gravel, 10% silt, gravel subrounded to 1.5", medium sand, wet, trace of ORGANICS (roots) Groundwater encountered at 1' while excavating

POORLY GRADED GRAVEL WITH SAND, gray, 38% sand, 1% silt, gravel subrounded to 2", medium sand, saturated

TEST PIT COMPLETED ON 9-27-06

D

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(F

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TD=5.0'

0.5 PEAT, brown, damp

5.0

ALDER SURFACE

F4 F2

NFS

1.0

So il

C la ss

LOGGED BY: Keri A. Nutter

PROJECT: Situk River Bridge

TEST PIT 4

BORING COMPLETED: 9-27-06

M oi st ur e C on te nt

Fr os t D ep th

So il

G ra ph

MA

TD

Sa m pl e

Ty pe

LOCATION: N60131.6 / E30363.6

ELEVATION: 72.5 FT

LOG OF TEST PIT 4

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

340# weight, 30" fall

O th er T es ts

KEY

= Mechanical Analysis = Total Depth

EXCAVATOR: Pate Construction

EQUIPMENT: Case 580 Super L

OPERATOR: Donnie Pate

METHOD: Extendahoe

Fr os t C la ss

FIGURE B-4

W.O. S12865

CLIENT: Atelier ps

Sa m pl e

N o.

PEAT, brown, damp

SILTY GRAVEL WITH SAND, brown, about 30% sand, 15% silt, nonplastic, gravel subrounded to 2", medium sand, damp, trace of ORGANICS (roots)

Groundwater encountered at 3' while excavating

POORLY GRADED GRAVEL WITH SAND, gray, about 35% sand, 5% silt, gravel subrounded to 3", wet to saturated

TEST PIT COMPLETED ON 9-27-06

Fr os t C la ss

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TH

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TD=5.0'

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FOREST SURFACE

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F4

F1

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il C la ss

BORING COMPLETED: 9-27-06

FIGURE B-5

Sa m pl e

N o.

LOCATION: N59656.0 / E30599.4

ELEVATION: 71.4 FT

PROJECT: Situk River Bridge

Sa m pl e

Ty pe

LOG OF TEST PIT 5

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

340# weight, 30" fall

O th er T es ts

LOGGED BY: Keri A. Nutter

So il

G ra ph

W.O. S12865

TEST PIT 5

EXCAVATOR: Pate Construction

EQUIPMENT: Case 580 Super L

OPERATOR: Donnie Pate

METHOD: Extendahoe

TD

Fr os t D ep th

KEY

= Total Depth

CLIENT: Atelier ps

Sheet 1 of 5

TEST PIT LOG - DESCRIPTIVE GUIDE

Soil Descriptions - The soil description on the pit log is based on an interpretation of the field and laboratory visual classifications, along with the results of laboratory particle-size distribution analyses and Atterberg Limits tests which may have been performed.

The soil classification is based on ASTM Designation D2487 "Standard Test Method for Classification of Soils for Engineering Purposes" and ASTM D2488 "Standard Practice for Description and Identification of Soils (Visual - Manual Procedure)" and the soil frost classification is based on the system developed by the U.S. Army Corps of Engineers.

Outlines of these classification procedures are presented on the following pages.

The soil color is the subjective interpretation of the individual logging the test pit.

The plasticity of the minus No. 40 fraction of the soil is described and the fine-grained soils are identified from manual tests using the following table as a guide:

Soil Symbol Dry Strength Dilatancy Toughness ML none to low slow to rapid low or thread cannot be formed CL medium to high none to slow medium MH low to medium none to slow low to medium CH high to very high none high

Plasticity Description

Criteria

Nonplastic A 1/8" (3.2mm) thread cannot be rolled at any water content.

Low A thread can barely be rolled and the lump cannot be formed when drier than the plastic limit.

Medium The thread is easy to roll and not much time is required to reach the plastic limit. The thread cannot be rerolled after reaching the plastic limit. The lump crumbles when drier than the plastic limit.

High It takes considerable time rolling and kneading to reach the plastic limit. The thread can be rerolled several times after reaching the plastic limit. The lump can be formed without crumbling when drier than the plastic limit.

Laboratory Atterberg Limits tests usually are performed on a few of the plastic soils and results are reported on the test pit log. These laboratory tests are performed in accordance with ASTM D4318 "Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils."

The shape of the gravel particles is described based on this guide:

Angular: particles have sharp edges and relatively plane sides with unpolished surfaces.

Subangular: particles are similar to angular but have somewhat rounded edges.

Subrounded: particles exhibit nearly plane sides but have well-rounded corners and edges.

Rounded: particles have smoothly curved sides and no edges.

Sheet 2 of 5 The size of gravel and sand particles is described using this guide:

Gravel Sand

Coarse: Passes 3" (75 mm) sieve, retained on 3/4" (19 mm) sieve

Passes No. 4 sieve, retained on No. 10 sieve

Medium: N/A Passes No. 10 sieve, retained on No. 40 sieve

Fine: Passes 3/4" (19 mm) sieve, retained on No. 4 sieve

Passes No. 40 sieve, retained on No. 200 sieve

The soil moisture is described as:

dry: powdery, dusty, no visible moisture.

damp: enough moisture to affect the color of the soil; moist.

wet: water in pores but not dripping; capillary zone above water table.

saturated: dripping wet, contains significant free water, or sampled below water table.

Soil Layer Boundaries - Generally, there is a gradual transition from one soil type to another in a natural soil deposit, and it is difficult to determine accurately the boundaries of the soil layers.

• A diagonal line between soil layers on the graphic pit log indicates the general region of transition from one soil layer to another.

• A horizontal line between soil layers indicates a relatively distinct transition between soil types was observed in the recovered samples and from a visual examination of the pit walls.

Sample Interval - The sample interval is shown graphically on the test pit log and generally is accurate to about 0.5 foot (0.15 meter).

Frost Depth and Soil Temperatures - If frozen ground is encountered during excavating, the interval of frozen soil is shown graphically on the test pit log. Generally, the temperature of a few soil samples is measured and shown on the pit log. These sample temperatures only give a qualitative indication of the in situ soil temperatures. The temperature of samples can be influenced significantly by the ambient air temperature.

Soil Moisture Content - Generally, laboratory soil moisture content tests are performed on all recovered samples. Only about 30 grams of the minus No. 4 material typically is used for the moisture content test, so results reported on the log may not reflect accurately the in situ moisture content of gravelly soils.

Groundwater - The depth to groundwater observed during excavating generally is shown on the test pit log. The depth to groundwater observed during excavating can differ significantly from the depth to the actual groundwater table, particularly in fine-grained soils.

Grab Samples - Grab samples are obtained of the distinct soil layers. The sample depth and interval indicated on the test pit log should be considered an approximation.

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