GRAVINA MILL ACCESS ROAD
Draft Geotechnical Engineering Report
4 March 2015
Prepared for:
Alaska Department of Transportation
& Public Facilities
6860 Glacier Highway
Juneau, AK 99801-7999
Agreement No. 0254302317
AKSAS No. 69922
Prepared by:
Amec Foster Wheeler Environment & Infrastructure, Inc.
11810 North Creek Parkway N.
Bothell, WA 98011
Under Contract to:
LEI Engineering & Surveying, LLC
310 K Street, Suite 200
Anchorage, AK 99811-2506
This page is intentionally left blank.
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
GRAVINA MILL ACCESS ROAD
Draft Geotechnical Engineering Report
4 March 2015
Prepared for:
Alaska Department of Transportation
& Public Facilities
6860 Glacier Highway
Juneau, AK 99801-7999
Prepared by:
James S. Dransfield, PE
Principal Geotechnical Engineer
William J. Lockard, LG, LEG
Senior Geologist
–I–
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
This page is intentionally left blank.
February 2016
– II –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Table of Contents
1
2
3
4
5
6
7
SUMMARY ................................................................................................................... 1
PROJECT DESCRIPTION ........................................................................................... 2
EXPLORATORY METHODS...................................................................................... 17
SITE CONDITIONS .................................................................................................... 18
4.1 Surface Conditions............................................................................................. 18
4.1.1 Topography ............................................................................................ 18
4.1.2 Surface Water ........................................................................................ 19
4.1.3 Vegetation and Other Surface Features ................................................. 19
4.2 Site Geology ...................................................................................................... 19
4.3 Soil Conditions ................................................................................................... 19
4.3.1 Site #1 .................................................................................................... 19
4.3.2 Site #2 (STA 2026+30), Site #2A (STA 2034+50), Site #3
(STA 2051+80) ....................................................................................... 20
4.3.3 Site #4 (STA 2072+70) ........................................................................... 20
4.3.4 Site #5 (STA 2083+40) ........................................................................... 20
4.4 Groundwater Conditions .................................................................................... 23
4.5 Geologic Hazard Conditions .............................................................................. 23
4.5.1 Site #1 to Site #2A (STA 2000+00 to STA 2034+50) .............................. 23
4.5.2 Site #2A to Site #3 (STA 2034+50 to STA 2051+82) .............................. 24
4.5.3 Site #3 to Site #4 (STA 2051+82 to STA 2072+70) ................................ 24
4.5.4 Site #4 to Site #5 (STA 2072+70 to STA 2083+42) ................................ 24
4.5.5 Site #5 to End of Alignment (STA 2083+42 to STA 2099+80)................. 25
4.6 Seismic Conditions ............................................................................................ 25
4.6.1 Liquefaction Analysis .............................................................................. 26
CONCLUSIONS AND RECOMMENDATIONS........................................................... 27
5.1 Site Preparation ................................................................................................. 27
5.2 Spread Footings ................................................................................................ 31
CLOSURE .................................................................................................................. 32
REFERENCES ........................................................................................................... 33
– III –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Tables
Table 1
Table 2
Table 3
Table 4
Summary of Amec Foster Wheeler Explorations .................................... 17
AASHTO LRFD Seismic Parameters ..................................................... 26
Recommended Maximum Cut Slope Inclinations ................................... 29
AASHTO LRFD Soil Design Parameters for Culvert ............................... 32
Figures
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Site Location Map .................................................................................... 3
Site and Exploration Plan, Site #1 ............................................................ 5
Site and Exploration Plan, Site #2 ............................................................ 7
Site and Exploration Plan, Site #2A .......................................................... 9
Site and Exploration Plan, Site #3 .......................................................... 11
Site and Exploration Plan, Site #4 .......................................................... 13
Site and Exploration Plan, Site #5 .......................................................... 15
Generalized Geologic Profile A-A’ at Site #4 .......................................... 21
Generalized Geologic Profile B-B’ at Site #5 .......................................... 22
Appendices
Appendix A:
Field Exploration Procedures and Logs
Appendix B:
Laboratory Testing Procedures and Results
February 2016
– IV –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
List of Acronyms
AASHTO
American Association of State Highway and Transportation Officials
DOT&PF
Department of Transportation and Public Facilities
bgs
below ground surface
LEI
LEI Engineering & Surveying
mph
miles per hour
USGS
U.S. Geological Survey
–V–
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
This page is intentionally left blank.
February 2016
– VI –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
1
SUMMARY
This summary is presented for introductory purposes and should be used only in
conjunction with the full text of this report.
Project Description: The Alaska Department of Transportation and Public Facilities
(DOT&PF) is planning improvements to the existing Gravina Mill Access Road located on
Gravina Island near Ketchikan. Existing stream crossings would be replaced at six
locations (Site #1, Site #2, Site #2A, Site #3, Site #4 and Site #5), and roadway segments
would be realigned to achieve current design standards. Arch or round culverts are planned
at Site #1, Site #2, Site #2A, and Site #3. Structural plate, open-bottom arch culverts with
strip footings are planned at Site #4 and Site #5. Bridge crossings with abutments
supported on a reinforced soil structure were also considered as an option at Site #4 and
Site #5. From site surveys conducted in 2014, the cost of bridge options at these sites was
considered too expensive, and therefore are no longer being considered.
Exploratory Methods: Subsurface conditions were investigated by means of ten test pit
explorations (TP-1 through TP-10) excavated at anticipated stream crossing locations
along the project alignment. The test pits were excavated to depths ranging from
approximately 4 to 8 feet below existing grades.
Subsurface Conditions: The test pits generally encountered a surficial organic layer,
underlain by a variable thickness of alluvial deposits. The test pits penetrated the alluvial
deposits and encountered greenschist or phyllite bedrock at depth in all but three
explorations. The alluvium consisted mostly of loose to medium dense silty sand and
gravel, but included interlayers ranging from sandy silt to clay. In one location (test pit TP-1
at Site #1) a peat layer was encountered below the alluvium. Test pit TP-1 was terminated
at 8.5 feet within the peat layer. The peat layer was measured to be at least 2.5 feet thick.
Groundwater Conditions: Groundwater seepage was encountered in most of the test pits at
depths ranging from 1 to 6 feet below existing grades. Groundwater seepage was not
encountered in test pits TP-4 and TP-5.
Recommended Foundation Support: Shallow foundation support appears feasible for
planned open-bottom arch culvert strip footings at Site #4 and Site #5. Based on
information obtained from test pits, excavations would encounter either medium dense
sands or bedrock at planned foundation elevations. A bearing pad consisting of a minimum
1-foot-thick layer of granular fill is recommended beneath all footings to provide a uniform
bearing surface. Similar subgrade preparation would be recommended to support
reinforced soil structure if the bridge option is selected. Culverts at Site #2, Site #2A, and
Site #3 can be bedded on granular fill.
Subgrade Preparation at Site #1: A compressible peat layer was encountered at the
approximate planned invert elevation for the culvert at Site #1. Options for subgrade
preparation were reviewed, and preloading in advance of culvert construction is
recommended.
–1–
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Reuse of On-site Soils: Testing indicates on-site soils would be suitable for use as Selected
Material, Type C in accordance with Alaska Highway specifications (DOT&PF 2015,
Section 703.2-07).
2
PROJECT DESCRIPTION
The Alaska Department of Transportation and Public Facilities (DOT&PF) is planning
improvements to the existing Gravina Mill Access Road located on Gravina Island
immediately west of Ketchikan, Alaska (Figure 1). Preliminary improvement plans include
re-aligning portions of the existing roadway to achieve current design standards for a 25
mile per hour (mph), gravel-surfaced roadway. The plans also include replacing stream
crossings at six locations that were identified as Site #1, Site #2, Site #2A, Site #3, Site #4
and Site #5 (listed from south to north).
The project site comprises a 9,980-foot segment of the existing road beginning adjacent to
the north end of Ketchikan International Airport and terminating at the entrance to the Seley
Mill. This segment presently consists of a one-lane, gravel-surfaced road, with six identified
stream crossings. Figures 2 through 7 illustrate the existing alignment and associated
features at each of the six stream crossing sites.
For Site #1, Site #2, Site #2A and Site #3, standard culverts are proposed, whereas for
Site #4 and Site #5, bottomless arch culverts are likely to be installed due to the extent of
the stream crossing and cost considerations. All crossings would be designed to meet the
design standards for a 40-mph roadway. Final layout plans are not complete. However,
based on the preliminary design layout, the revised alignment would incorporate portions of
the existing alignment that would be upgraded to current design standards, as well as
construction of several new segments. Widening the roadway and construction of new
segments would require at least 25 feet of fill for the two northern-most creek crossings.
DOT&PF intends to use the rock generated by planned cuts along portions of the alignment
as structural fill to raise grade for the remaining sections where fill is required. Additional fill
material generated from nearby borrow pits may also be required.
The conclusions and recommendations contained in this report are based on existing
understanding of the currently proposed improvements to the project alignment, as derived
from written information and verbal information. Consequently, any changes in the currently
proposed project may require that the conclusions and recommendations contained herein
be revised to reflect those changes.
DOT&PF specification codes cited herein refer to the 2015 edition of the Standard
Specifications for Highway Construction (DOT&PF 2015).
February 2016
–2–
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 1
Site Location Map
–3–
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 2
Site and Exploration Plan, Site #1
–5–
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 3
Site and Exploration Plan, Site #2
–7–
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 4
Site and Exploration Plan, Site #2A
–9–
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 5
Site and Exploration Plan, Site #3
– 11 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 6
Site and Exploration Plan, Site #4
– 13 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 7
Site and Exploration Plan, Site #5
– 15 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
3
EXPLORATORY METHODS
Surface and subsurface conditions at the project site were investigated during field
explorations conducted in August 2014. The exploration and testing program comprised the
following elements:

A visual surface reconnaissance of the site

Ten test pit explorations (designated TP-1 through TP-10), advanced at strategic
locations along the alignment

Hand probing along portions of the alignment and at creek crossings to determine
thickness of peat or other soft soil deposits

One grain-size analysis, performed on a selected soil sample obtained from a
strategic location beneath the project area

One Atterberg limit determination, performed on a selected sample of cohesive soil
obtained from the project area

Analytical testing performed on two representative soil samples for evaluation of
corrosivity potential of soils

A review of published geologic reports.
Table 1 summarizes the approximate locations, surface elevations, and termination depths
of the ten test pits. Figures 2 through 7 show the approximate relative locations of test pits.
Appendix A describes the field exploration procedures, and Appendix B describes
laboratory testing procedures.
Table 1
Summary of Amec Foster Wheeler Explorations
Exploration
Location
Surface
Elevation
(feet)
TP-1
TP-2
TP-3
TP-4
TP-5
TP-6
TP-7
TP-8
TP-9
TP-10
Site #1, SW quadrant of crossing
Site #2, NW quadrant of crossing
Site #2A, SW quadrant of crossing
Site #3, NW quadrant of crossing
Site #4, S side of crossing at centerline
Site #4, N side of crossing at centerline
N of Site #5, Existing road cut, 75’ E of alignment
Site #5, N side of crossing at centerline
Site #5, N side of crossing at centerline, 75’ N
Site #5, S side of crossing at centerline
127.5
185.5
185
131
55
54
50
42
52
27
Termination
Depth
(feet)
8.5
4
4.7
6
5.5
6
8
4.5
6
5.5
Elevation datum: LEI topographic survey 2014
The specific number, locations, and depths of test pit explorations were selected by LEI
Engineering and Surveying (LEI) with input by Amec Foster Wheeler. These locations were
subsequently field-adjusted to account for existing and proposed site features, constraints
of surface access, and budget considerations. The relative location of each exploration was
– 17 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
surveyed, and subsequently presented to field staff on a layout plan. The elevation of each
test pit was also determined by survey. Consequently, the data listed in Table 1 and the
locations depicted on Figures 2 through 7 should be considered accurate only to the
degree permitted by data sources and implied by the methods of measurement.
The explorations performed and used for this evaluation reveal subsurface conditions only
at discrete locations along and adjacent to the project alignment, and actual conditions in
other locations could vary. Furthermore, the nature and extent of these variations would not
become evident until additional explorations are performed or until construction activities
have begun. If significant variations are observed at that time, the conclusions and
recommendations contained in this report may need to be revised to reflect actual
conditions.
4
SITE CONDITIONS
This section presents observations, measurements, findings, and interpretations regarding
surface, soil, groundwater, and seismic conditions along the project alignment.
4.1
Surface Conditions
The existing Gravina Mill Access Road was originally constructed in the early 1960s to
access the Seley Mill, a timber processing plant located at the north end of the alignment.
No other development is present along the length of the project alignment. Several cleared
areas were observed adjacent to the roadway during the field reconnaissance. Among
these clearings, a relatively flat area north of Site #2 appeared to have been used as a
logging staging area where several large slash piles were present. Immediately south of
Site #4, a cleared area with several feet of stockpiled wood waste apparently generated by
the Seley Mill was observed.
The gravel-surfaced road generally follows existing topography. Minor stream crossings are
conveyed by galvanized steel culverts, and larger crossings consist of rail car frames
supported on log abutments. Road embankments were constructed using locally derived
bedrock. Large boulders were observed along the edges of the larger crossings, whereas
cobble-sized aggregate and crushed gravel comprised the bulk of the fill embankments.
4.1.1
Topography
The Gravina Mill Access Road project alignment is located along the eastern edge of
Gravina Island and is generally situated on a wide bench that slopes gently to moderately
downward to the east toward Tongass Narrows. To the west, grades slope gently to
moderately upward until reaching the east edge of the mountainous terrain known as the
California Ridge, which trends north-south along the length of the island. California Ridge
encompasses several peaks, including High Mountain, House Mountain, Curve Mountain,
and Nipple Mountain. Within the project limits, the topography of the alignment undulates,
rising and falling moderately, except at Site #4 and Site #5, where the streams have carved
relatively deep, steeply sloped ravines. Maximum topographic relief is on the order of
150 feet across the entire alignment, generally sloping downward to the north.
February 2016
– 18 –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
4.1.2
Surface Water
Ponded surface water was present across a substantial portion of the alignment during the
site reconnaissance and field work. Standing water within closed depressions and wetland
environments typical of muskeg was prevalent. Numerous small drainages were noted
along the alignment. Crossings had been installed where these drainages coalesced into
larger streams.
4.1.3
Vegetation and Other Surface Features
The southern two-thirds of the alignment generally traverses muskeg interspersed with
stands of moderate-sized hemlock and fir trees.
4.2
Site Geology
According to published geologic maps (Berg 1973; Berg et al. 1972), the alignment lies
within an area underlain by the Gravina Island Formation, which is composed of a bedded
unit of andesitic metavolcanic and metasedimentary bedrock of Jurassic age. Exposure of
the formation is generally poor, with neither the top nor bottom of the assemblage
observed. The unit is described as highly deformed, commonly phyllitic, and
metamorphosed to greenschist. Complex folding was observed by field staff in exposed
outcroppings at several locations, but the folding exhibited a generally eastward dip. Field
observations of bedrock exposure in road cuts and outcrops adjacent to the existing and
proposed alignment generally confirmed the mapped geology. Although no surficial
sediment mapping was readily available, Berg (1973) inferred that Gravina Island was
completely covered by the Pleistocene glacial advance, forming the U-shaped valley on the
western side of the island and rounding the peaks that make up the California Ridge.
4.3
Soil Conditions
On-site test pits revealed somewhat variable near-surface soil/rock conditions, but
generally confirmed the mapped stratigraphy. A layer of alluvial deposits that varied in
thickness was generally encountered beneath a thick root mat at the proposed stream
crossings. The alluvial soils in turn mantled bedrock in all but three explorations. Specific
subsurface conditions at each crossing location are discussed below. The exploration logs
in Appendix A provide a detailed description of the soil strata encountered in test pits.
Laboratory test reports in Appendix B graphically present laboratory test results.
4.3.1
Site #1
Test pit TP-1 was excavated at Site #1 (Figure 2). TP-1 encountered a 1-foot-thick layer of
organic material (sod, root mat) that mantled 6 feet of loose to medium dense sandy gravel.
The sandy gravel was interpreted as alluvial deposits that in turn mantled peat, which
extended to at least 8.5 feet below ground surface (bgs). Deeper excavation below 8.5 feet
bgs was prevented by access and equipment limitations.
– 19 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
4.3.2
Site #2 (STA 2026+30), Site #2A (STA 2034+50), Site #3 (STA 2051+80)
Test pits excavated at proposed culvert crossings at Site #2, Site #2A, and Site #3
(Figures 3 through 5) generally encountered similar soil/rock conditions. Test Pits TP-2, TP3, and TP-4, were found to have a 1-foot to 2-foot-thick layer of organic material (sod, root
mat, or peat) over a 3-foot to 5-foot-thick layer of alluvial sediment. Texture of the alluvial
material varied from silty clay in TP-2, to silty sand and gravel, to silty gravel and cobbles
for the remaining explorations. The alluvial sediments mantled moderately weathered
bedrock, which was interpreted to be moderately to slightly weathered, medium weak
(Grade R3) based on the difficulty of excavation. However, direct observation to assess
rock type and structural characteristics was hampered by accumulation of groundwater
seeping into the base of the test pit excavations.
4.3.3
Site #4 (STA 2072+70)
Subsurface conditions at Site #4 were explored by test pits TP-5 and TP-6 (Figure 6). A
generalized cross section based on the observations from test pits excavated at Site #4 is
presented on Figure 8. Both of these test pits encountered approximately 1 foot of forest
duff and root mat mantling soft sandy silt that extended to a depth of approximately 2 to 2.5
feet bgs. Below the silt horizon, loose to medium dense silty sand was encountered
extending to approximately 3.5 feet bgs. Within TP-5 on the south/east side of the stream,
medium dense sand and gravel were present to a depth of 4 feet, transitioning to gravel
and cobbles to the full depth explored (5.5 feet bgs). TP-6 on the north/west side of the
crossing encountered a relic topsoil horizon immediately below the silty sand horizon that
extended from 2.5 to 3.5 feet bgs and then, in turn, mantled medium dense sand with some
cobbles. The cobble content of the horizon increased with depth. At a depth of
approximately 6 feet bgs, it was inferred that bedrock was encountered, which prevented
further excavation. Although the bottom of the test pit could not be observed due to
accumulation of groundwater within the test pit, it was inferred that bedrock had been
encountered. Bedrock outcroppings were noted within the stream channel 75 feet
downstream.
4.3.4
Site #5 (STA 2083+40)
Subsurface conditions on the north side of the stream crossing at Site #5 were explored by
test pits TP-7, TP-8, and TP-9; TP-10 was excavated on the south side of the stream
crossing (Figure 7). A generalized cross section based on the observations from test pits
excavated at Site #5 is presented on Figure 9. On the north side of the crossing, a 1-footthick layer of forest duff was encountered that mantled dense, silty sand with variable
gravel content. This unit extended from 1 to 4 feet bgs and was interpreted to represent
glacial till deposits. Below the till horizon, highly weathered, grading to moderately
weathered bedrock was encountered. The bedrock was interpreted as a phyllite that was
thinly foliated, with the foliations inclined at approximately 70 degrees from horizontal.
Based on the difficulty of excavation, the bedrock was interpreted to have moderate
strength. Observation of the base of the excavation was difficult due to groundwater
seepage and sidewall caving, which obscured the bottom of the test pit. As such, fracture
spacing or other discontinuities could not be readily observed.
February 2016
– 20 –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 8
Generalized Geologic Profile A-A’ at Site #4
– 21 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Figure 9
February 2016
Generalized Geologic Profile B-B’ at Site #5
– 22 –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Colluvium mantling observed in the lower portion of a road cut 75 feet east of the proposed
alignment revealed that the phyllite has completely weathered to a gravelly clay.
Excavation into the side of the cut (TP-7) disclosed the upper 2 to 3 feet of the bedrock to
be completely weathered, but grading to less weathered with depth. Below approximately
5 feet bgs, excavation of the exposed bedrock surface required substantial effort, indicating
relatively fresh and moderately strong bedrock conditions. Medium-spaced jointing was
noted. Most of the joints were filled with calcite, and the remaining exhibited little separation
but some iron-oxide staining. Foliation was inclined at 70 to 80 degrees, with the foliations
becoming wavy in the upper 4 feet of the exposed cut.
On the south side of the crossing, test pit TP-10 encountered approximately 1 foot of forest
duff and root mat mantling a 1-foot-thick layer of peat. Below the peat horizon, medium
dense silty sand was encountered to a depth of 4.5 feet bgs. At the east end of the test pit
excavation, horizontally bedded sandy gravel was noted from 2.5 to 4.5 feet bgs. Below a
depth of 4.5 feet bgs, excavation became very difficult, with little advancement of the pit.
Based on the difficulty of excavation, it was assumed that bedrock had been encountered.
However, due to groundwater accumulation within the test pit, observation of the
excavation base was not possible.
4.4
Groundwater Conditions
At the time of the subsurface exploration program (December 2014), groundwater was
encountered in all explorations, except TP-4 and TP-5 (Site #3, and Site #4 respectively),
at depths ranging from 1 to 6 feet below existing grades. Because test pits were excavated
during a generally wet period of weather, the groundwater conditions present at that time
may closely represent the yearly high levels; whereas lower levels probably occur during
summer and early fall. Throughout the year, groundwater levels would likely fluctuate in
response to changing precipitation patterns, construction activities, and site utilization.
4.5
Geologic Hazard Conditions
A visual reconnaissance of the existing alignment and proposed stream crossing locations
was conducted in December 2014. The scope of work was limited to a visual assessment
from the roadway of slopes and other site features to identify areas of potential geologic
hazards, including areas of potential slope instability, locations of previous slope failures,
and other related features that could detrimentally impact the proposed roadway alignment
and stream crossings.
4.5.1
Site #1 to Site #2A (STA 2000+00 to STA 2034+50)
This portion of the existing alignment traverses relatively gently sloping topography. The
existing alignment rises to the north from Site #1 at a slope of approximately 7 percent, with
no evidence of slope instability noted. Bedrock outcrops along the west side of the existing
roadway consisted of slightly to moderately weathered slate varying to greenschist, which
was found to be medium weak to strong (Grade R3 to R4). A relatively low risk of rock fall
or other rock mass instability was inferred for this slope due to the generally low relief of the
outcrops; the strength of the exposed rock; the favorable orientation of observed
– 23 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
discontinuities, fractures and foliation; and the moderate slope. Probing along selected
sections of the east side of the alignment and at the creek crossing revealed less than
2 feet of soft surficial sediments (topsoil and/or peat). As previously discussed, a peat layer
was encountered at Site #1 at a depth of 6 feet, extending to at least 8.5 feet below existing
grades. The presence of the peat layer presents a risk of differential settlement to the
proposed crossing.
Conditions at Site #2 (STA 2026+30) are favorable, with no geologic hazards identified.
Topography from Site #2 to Site #2A was generally flat, with only minor grade changes.
Probing of the surficial sediments within this section of the alignment disclosed soft peat
deposits (muskeg) varying from 2 feet to 4 feet thick before encountering refusal.
4.5.2
Site #2A to Site #3 (STA 2034+50 to STA 2051+82)
Approximately 300 feet north of Site #2A, the proposed alignment crosses a moderate to
steep east-facing slope, while the current roadway alignment skirts around the toe of the
slope. Observation of the slope conditions did not disclose any evidence of slope instability,
such as scarps, slumps, or bowed tree trunks. Hand probing the surficial soils disclosed a
relatively thin soil horizon mantling bedrock. The remaining portion of this section was
relatively flat, with only minor topographic relief. Peat approximately 2 to 5 feet thick was
noted.
4.5.3
Site #3 to Site #4 (STA 2051+82 to STA 2072+70)
Gentle grades typify the majority of this portion of the alignment, which slopes downward at
approximately 1 to 2 percent until approximately 200 feet from Site #4. At this approximate
location, wood waste (shavings, bark, and log debris) was noted to be stockpiled on the
east side of the alignment. A portion of this wood waste extends onto the footprint of the
proposed alignment.
At Site #4, the existing stream channel lies within a moderately incised valley with steeply
sloping side slopes and an approximate overall relief of 15 feet on the south side of the
creek. The slope terminates on a gently sloping bench, with the stream channel lying
approximately 3 to 5 feet below. The slopes on the north side of the stream valley rise
gently to moderately from the channel up to a flat plateau. Due to the moderate to steep
side slopes of the stream valley, a moderate risk of slope instability and erosion exists at
this crossing. The terrace on the south side of the channel indicates that the stream
periodically floods and channel migration has occurred in the past.
4.5.4
Site #4 to Site #5 (STA 2072+70 to STA 2083+42)
The alignment continues sloping gently downward from Site #4 toward Site #5 at a slope of
less than 5 percent. No significant geologic hazards were identified in the segment of the
alignment between the two sites. Near Site #5, wood waste (shavings, bark, and log debris)
was noted to be stockpiled on the east side of the alignment. A portion of the wood waste
extends onto the footprint of the proposed alignment. Hand probing within the muskeg
disclosed peat and soft sediments varying from approximately 2 to 5 feet thick. Similar to
Site #4, the alignment crosses a moderately to steeply incised stream valley at Site #5, with
February 2016
– 24 –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
total vertical relief of at least 15 feet, On the south side of the stream, the slope inclined
down at nearly 100 percent to a 50-foot wide bench, which lies approximately 5 to 8 feet
above the current stream channel. No evidence of recent or historic slope instability was
noted. On the north side of the stream, bedrock is exposed at the base of the slope. At the
stream edge, the near-vertical outcrop extends upward approximately 15 to 20 feet before
flattening somewhat. Measurements of the orientation of foliation and discontinuities within
bedrock outcrop exposed at the stream edge indicated it to be dipping to the east, nearly
perpendicular to the slope. The rock mass appeared relatively stable, with the exposed
rock estimated to be slightly weathered and moderately weak to strong (Grade R3 to R4).
4.5.5
Site #5 to End of Alignment (STA 2083+42 to STA 2099+80)
After crossing the stream valley, the alignment gently rises at a slope of approximately 5 to
7 percent for a distance of approximately 500 feet, where it flattens and remains nearly flat
until reaching the end of the alignment. Within the heavily wooded stream crossing area,
hand probing disclosed less than 2 feet of soft sediments (topsoil or peat). Beyond the
forested area where grades flattened, peat thickness was found to increase to 4 to 5 feet
before encountering refusal. No other hazards were noted.
4.6
Seismic Conditions
Analysis of subsurface exploration logs and review of published geologic maps were used
to interpret on-site soil conditions. Conditions were interpreted to correspond to Site
Class C (very dense soil and soft rock) where alluvial soils overlie bedrock, and Site
Class B (rock) where bedrock is exposed at the ground surface, as defined by the
American Association of State Highway and Transportation Officials (AASHTO 2012). Site
Class C has been applied as a conservative assumption for analysis of site conditions.
A summary of the assumed seismic parameters is presented in Table 2. AASHTO (2012)
specifies the 1,000-year return interval (7 percent probability of exceedance in 75 years)
ground motion as the design earthquake for transportation projects. For this site latitude
and longitude, the U.S. Geological Survey (USGS 2014) provides a peak ground
acceleration coefficient of 0.085g, where g is the acceleration due to gravity. This value is
multiplied by the coefficient FPGA (equal to 1.2) to obtain the resultant As (equal to 0.102g)
to assess the potential for liquefaction and estimate seismic earth pressures and inertial
forces for retaining wall and slope design.
– 25 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Table 2
4.6.1
AASHTO LRFD Seismic Parameters
Design Parameter
Recommended Value
Site Class
PGA
Ss
S1
FPGA
AS = FPGA x PGA
FA
FV
C
0.085g
0.185
0.143
1.2
0.102g
1.2
1.657
Liquefaction Analysis
Liquefaction is a sudden increase in porewater pressure and a sudden loss of soil shear
strength caused by shear strains, as could result from an earthquake. Research has shown
that saturated, loose sands with a fines (silt and clay) content less than about 25 percent
are most susceptible to liquefaction. Although other soil types are generally considered to
have a lower susceptibility, liquefaction may still occur during a strong earthquake. Review
of site conditions resulted in the following conclusions regarding liquefaction potential:

Where bedrock is present, the risk of liquefaction is negligible.

On-site subsurface explorations revealed potentially saturated, near-surface, loose
silty sand layers or lenses that may be subject to liquefaction under moderate to
strong shaking. However, based on the planned excavation depths for culvert
structures, these upper soil layers would be removed from beneath planned culvert
locations.

Some of the test pits encountered medium dense saturated sand layers that may
remain in place beneath culvert structures. At Site #4 (test pit TP-5), bedrock was not
encountered below the medium dense saturated silty sand. A conservative estimate
of liquefaction potential was made assuming the same soil type extended to depths
of as much as 50 feet below ground surface. Modeling using SHAKE 2000 software
predicted soils to have a field standard penetration test blow count of 10 to a depth of
35 feet bgs, increasing to 15 blows per foot to a depth of 50 feet bgs. Fines content
of the sand was conservatively assumed to be 15 percent based on visual
observation, and the groundwater table was assumed to be at the ground surface.
For the AASHTO design earthquake with a 1,000-year return interval, applied as
AS = 0.102g, analysis indicates that all or most of the soils beneath the groundwater
table have low susceptibility to liquefaction, with a safety factor above 1.5.
Liquefaction settlement for this hypothetical profile was also minimal.
February 2016
– 26 –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
5
CONCLUSIONS AND RECOMMENDATIONS
DOT&PF is planning improvements to the existing Gravina Mill Access Road. These
improvements include replacing existing stream crossings at six locations and realigning
the road to achieve current design standards. Arch or round culverts are planned at Site #1,
Site #2, Site #2A, and Site #3. Structural plate, open-bottom arch culverts with strip footings
are planned at Site #4 and Site #5. Bridge crossings were also considered an option at
Site #4 and Site #5, with abutments supported on a reinforced soil structure.
Geotechnical exploration and analysis for this project have resulted in the following general
conclusions and recommendations:

Feasibility: Based on field explorations, research, and analyses, the proposed
roadway improvements appear feasible from a geotechnical standpoint, contingent
on the recommendations presented herein.

Foundation Options: The proposed culvert structures can be supported by
conventional spread footings that bear on medium dense native soils or bedrock. All
structures should be constructed upon a granular bedding to provide a uniform
bearing surface.

Liquefaction Considerations: Liquefaction analysis indicated a low risk of
liquefaction-induced settlement in the medium dense alluvium, and little to no risk of
liquefaction within the underlying bedrock.

On-Site Soil Reuse: Visual soil classifications and laboratory testing indicate that the
nonorganic alluvium and bedrock would be suitable for reuse as Selected Materal,
Type C, inaccordance with standard specifications (DOT&PF 2015, section 2032.07). Most of the on-site soils are moderately to highly moisture-sensitive and
susceptible to disturbance when wet. To maximize the potential for reusing on-site
soils as structural fill, earthwork should be scheduled for periods of dry weather, such
as usually occur during the summer and early fall months.

Subgrade Protection: Due to the moisture-sensitive nature of the on-site soils, the
contractor should (1) install appropriate temporary drainage systems to keep water
out of construction areas, and (2) minimize traffic over any subgrades prepared
within these soils.
The following sections present specific geotechnical conclusions and recommendations
concerning site preparation and structural fill.
5.1
Site Preparation
Preparation of the project site would involve demolition, temporary drainage and
dewatering, clearing, stripping, cutting, filling, excavations, erosion control, and subgrade
compaction. The paragraphs below present geotechnical recommendations and comments
concerning site preparation.
Temporary Drainage: Potential sources of surface or near-surface water within the
construction zones should be intercepted and diverted before stripping begins. Because the
selection of an appropriate drainage system depend on the water quantity, season, weather
– 27 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
conditions, construction sequence, and contractor's methods, final decisions regarding
drainage systems should occur in the field at the time of construction.
In addition to control of surface water, temporary diversion of streams at each of the six
crossings would likely be required. These diversions may involve temporary damming of
smaller drainage channels and then pumping the streamflow over the roadway
embankment. A new diversion channel or large temporary pipeline may be required to
accommodate diversion flow from the larger flows at Site #4 and Site #5.
Clearing and Stripping: After surface and near-surface water sources are controlled, the
construction areas should be cleared and stripped of all trees, bushes, sod, and topsoil.
Geotechnical explorations indicate that the thickness of sod, root mat, topsoil, and peat
ranged from about 0.5 to 2 feet. An average thickness of 1 foot is estimated across the site,
but significant variations could exist for removal of wood waste piles, corduroy log roads,
tree stumps, or other accumulations of organic material. Furthermore, if the stripping
operation proceeds during wet weather, a generally greater stripping depth might be
necessary to remove disturbed moisture-sensitive soils; therefore, stripping is best
performed during a period of dry weather.
Demolition: Demolition and removal of the old bridge structures (rail cars and logs) would
be required. Associated underground culverts or utilities should be exhumed as part of this
demolition operation. Logs from former corduroy roads may exist at bridge abutments and
at other low-lying areas along the existing road alignment.
Erosion Control Measures: Particular attention should be given to stripped surfaces and soil
stockpiles, which are typically a source of runoff sediments. If earthwork occurs during wet
weather, all stripped surfaces should be covered with straw or other mulch to reduce
erosion. Similarly, soil stockpiles and cut slopes should be covered with mulch or plastic
sheeting for erosion protection. A staked silt fence should be installed around the area to
be disturbed. The base of the silt fence should be buried so that sediment cannot pass
beneath it, and the silt fence should be inspected and maintained on a periodic basis during
the time that site soils are exposed, and after any major rainstorm event. It may be prudent
to maintain a berm and swale around the downslope side of stripped areas and stockpiles
in order to capture runoff water and thereby reduce the downslope sediment transport. In
addition, stripped areas should be revegetated as soon as possible to reduce the potential
for erosion.
Site Excavations: Proposed grading plans call for cuts alongside the alignment. Based on
geotechnical explorations and site reconnaissance, these cuts would be expected to
encounter soil over bedrock in most areas. The upper soils can likely be cut with
conventional earthworking equipment, such as scrapers and trackhoes. However, drilling
and blasting would likely be needed to complete the excavations where bedrock is present.
Conclusions and recommendations regarding reuse of on-site soils are presented below.
Temporary Dewatering: Geotechnical explorations encountered groundwater seepage at
depths of about 1 to 6 feet below grade at the time of test pit excavation. In some locations,
February 2016
– 28 –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
rapid seepage and caving made it infeasible to view the base of the excavation. During
construction, a temporary dewatering system should be provided that lowers the
groundwater surface sufficiently to allow for visual verification of firm and non-yielding
native subgrade conditions to support all culvert foundations and granular bedding. The
subgrade surface at the bottomless culvert strip footing locations should be maintained in a
drained and dewatered condition throughout the process of excavation, subgrade
verification, forming, concrete placement, and curing. At the other culvert locations, the
subgrade surface should be maintained in a drained and dewatered condition throughout
the process of excavation, subgrade verification, placement of bedding, placement of the
culvert on the bedding, and placement of pipe zone backfill around the culvert. Where
groundwater is encountered above a bedrock surface during construction, a system of
ditches, sumpholes, and pumps should be adequate to temporarily dewater the excavation.
In areas where deeper soil deposits occur at subgrade elevation, additional well points or
drilled dewatering wells may be required. An experienced dewatering contractor should
design such a dewatering and drainage system after being allowed to review the test pit
logs (Appendix A).
Temporary Cut Slopes: All temporary cut slopes associated with site regrading or
excavations should be adequately inclined to prevent sloughing and collapse. Table 3
provides maximum cut slope inclinations tentatively recommended for the various soil
layers that would likely be exposed in on-site cuts.
Table 3
Recommended Maximum Cut Slope Inclinations
Soil Type
Expected Depth Interval
Maximum Inclination
Loose, Silty SAND
0 to 2 feet
1.5H:1V
Medium-Dense to Dense Gravelly SAND
2 to 5 feet
1H:1V
Bedrock
2 to 5+ feet
0.5H:1V
However, appropriate inclinations would ultimately depend on the actual soil conditions
exposed during earthwork.
Subgrade Compaction: Exposed subgrades for culvert footings and for the roadway
alignment prior to filling should be compacted to a firm, unyielding state using a large
vibratory roller. Any localized zones of loose granular soils observed within a subgrade
should be compacted to a density commensurate with the surrounding soils. In contrast,
any organic, soft, or pumping soils observed within a subgrade should be overexcavated
and replaced with a suitable structural fill material.
Subgrade Preparation at Site #1: At Site #1, a buried peat layer was encountered at
planned invert elevation. The total thickness and lateral extent of the peat layer beneath the
culvert and approach embankment are not known. Differential settlement can be minimized
using one of the following treatment options (from most effective to less effective):
– 29 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT

Preload: Temporarily bypass the creek flow, place a full-height embankment across
the creek (to serve as the preload). Leave in place for about 1 month, then excavate
the creek channel again and install the culvert.

Overexcavate: While preparing for the culvert, provide temporary shoring and
dewatering and continue excavation deeper to remove greater thickness of peat. The
greater the depth of overexcavation, the less post-construction settlement that would
be anticipated.

Subgrade Reinforcement: Place geogrid and/ or geotextile across the subgrade prior
to placing backfill.
Given the great depth of the layer and the unknown thickness and extent, the preloading
option is recommended.
Site Filling: Proposed grading plans call for filling in the topographically low areas of the site
to achieve design subgrades for the new roadway. Conclusions and recommendations
regarding reuse of on-site soils and comments regarding wet-weather filling are presented
below.
On-Site Soils: Because large cuts are planned for the project, large quantities of on-site
soils are anticipated to be generated during earthwork activities. Evaluation of these on-site
soils in relation to potential use as structural fill is presented below.
Surficial Organic Soils: The sod, duff, topsoil, and organic-rich soils mantling most of the
alignment are not suitable for use as structural fill under any circumstances, due to their
long-term compressibility. Consequently, these materials can be used only for nonstructural purposes, such as landscaping.
Alluvium: The silty sands and gravels underlying the surficial organic soils appear
marginally suitable for reuse as structural fill at their present moisture contents. This
material generally conforms to the requirements for Selected Material Type C (DOT&PF
2015, Section 703-2.07). However, portions of these granular soils may become difficult to
reuse during wet weather, due to their moderately high silt content. The sandy silt and clay
interlayers within the alluvium would likely not be suitable for use as structural fill due to
high fines content, and should be removed.
Bedrock: The excavated phyllite and greenschist bedrock would be suitable for reuse as
Selected Material Type C (DOT&PF 2015, Section 703-2.07). However, the maximum
particle size may need to be reduced in order to use this material as embankment fill where
maximum lift thickness should be 8 inches or less. The durability testing of the bedrock
suggests it would also be a suitable source for Subbase (DOT&PF 2015, Section 7032.09). However, this material would need to be screened and or washed to remove the
fines to meet gradation requirements.
Wet-Weather Considerations: As discussed above, most or all of the on-site soils would be
difficult to reuse as structural fill during wet weather. Consequently, the project
specifications should include provisions for using imported, clean, granular fill in case site
February 2016
– 30 –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
filling must proceed during wet weather. For general structural fill purposes, Selected
Material Type A (DOT&PF 2015, Section 703-2.07) is recommended. This same material is
specified as bedding and pipe zone backfill for pipes (DOT&PF 2015, Section 204-2.01).
Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined
to minimize long-term raveling, sloughing, and erosion. For planning purposes, no slopes
steeper than 2H:1V are recommended, but cut slopes in bedrock and similarly coherent
soils can be inclined as steep as 1H:1V. Steeper slopes are likely feasible in bedrock, but
may be subject to weathering over the design life of the project. In soils, the use of flatter
slopes (such as 3H:1V) would further reduce long-term erosion and facilitate revegetation.
Slope Protection: Construction of a permanent berm, swale, or curb is recommended along
the top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative
groundcover should be established as soon as feasible to further protect slopes from runoff
water erosion. Alternatively, permanent slopes could be armored with quarry spalls or a
geosynthetic erosion mat.
5.2
Spread Footings
Foundation Type: The culverts (or optional bridge) at Site #4 and Site #5 can be supported
on shallow foundations. The foundation can bear directly either on the bedrock or native
medium dense sand. A granular fill bearing pad layer is recommended beneath all
foundations to provide uniform bearing conditions, since mixed rock/soil subgrade
conditions might be encountered.
Bearing Pad Materials: Bearing pads composed of well-graded sands and gravels are
recommended for all footings (such as Selected Material Type A, DOT&PF 2015,
Section 703-2.07). If the bottom of the excavation is in saturated conditions, Subbase
(DOT&PF 2015, Section 703-2.09, Grading D [3/4-inch maximum size]) would provide a
workable subgrade.
Bearing Pad Dimensions: The thickness of bearing pads would vary, depending on the
required overexcavation depth. Because foundation stresses are transferred outward, as
well as downward, into the bearing soils, all bearing pads composed of structural fill soil
should extend horizontally outward from the edge of each footing a distance equal to the
bearing pad thickness. Therefore, an overexcavation that extends 12 inches below the
footing base should also extend 12 inches outward from the footing edges.
Footing Depths and Widths: For frost protection, the bottoms of all footings should bear at
least 18 inches below adjacent grades. The top of all foundations should be buried at least
12 inches below grade. In addition, greater embedment may be required to prevent
undermining due to scour.
Culvert Design Considerations: For precast culvert design with strip footings bearing upon
the dense native gravel or a compacted bearing pad constructed above the native gravel,
the AASHTO Load Resistance Factor Design (LRFD) soil design parameters presented in
– 31 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
Table 4 are recommended. The lateral pressures acting on a culvert or wing wall depend
on backfill type. The parameters in Table 4 apply to use of on-site soil as backfill, assuming
that compaction to at least 90 percent of AASHTO T180 compaction can be achieved.
According to AASHTO, no dynamic surcharge (expressed as Kae) acts on the wall with
clay backfill, owing to the low seismic loading and the slight cohesive strength of the on-site
silty soils during short-term seismic loading.
Table 4 also includes parameters for imported granular (sand) backfill, such as Selected
Material Type A (DOT&PF 2015), compacted to 90 percent density.
Table 4
AASHTO LRFD Soil Design Parameters for Culvert
Design Parameter
Recommended
Value
Backfill Soil Density (pcf) (on-site backfill)
Coefficient of active earth pressure Ka (on-site backfill)
Coefficient of at-rest earth pressure Ko (on-site backfill)
Coefficient of dynamic active pressure Kae (on-site backfill)
125
0.35
0.52
0.0
Backfill Soil Density (pcf) (sand backfill)
Coefficient of active earth pressure Ka (sand backfill)
Coefficient of at-rest earth pressure Ko (sand backfill)
Coefficient of dynamic active earth pressure Kae (sand)
135
0.24
0.38
0.371
Strength Limit bearing resistance (psf) on bedrock
Service Limit bearing resistance (psf) on bedrock
23,000
14,000
Strength Limit bearing resistance (psf) on bearing pad
Service Limit bearing resistance (psf) on bearing pad
16,500
5,300
Resistance factor – bearing on gravel bearing pad
Ultimate coefficient of friction, gravel to cast-in-place concrete
Ultimate coefficient of friction, gravel to precast concrete
Resistance factor – sliding, gravel to cast-in-place concrete
Resistance factor – sliding, gravel to precast concrete
0.45
0.55
0.50
0.802
0.902
1
Assumes level backslope using one-half of the peak ground acceleration.
2
These factors apply to strength limit state – use 1.0 for service limit state.
6
CLOSURE
The conclusions and recommendations presented in this report are based, in part, on the
explorations performed for this study; therefore, if variations in the subgrade conditions are
observed at a later time, this report may need to be modified to reflect those changes.
Because the future performance and integrity of the project elements depend largely on
proper initial site preparation, drainage, and construction procedures, monitoring and
testing by experienced geotechnical personnel should be considered an integral part of the
construction process.
February 2016
– 32 –
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
7
REFERENCES
Alaska Department of Transportation and Public Facilities (DOT&PF). 2015. Standard
Specifications for Highway Construction, 2015 Edition. Juneau.
American Association of State Highway and Transportation Officials (AASHTO). 2012.
AASHTO LRFD Bridge Design Specifications. Washington, D.C.
Berg, Henry, C., Jones, D.L., and Richter, D.H. 1972. Gravina-Nutzotin Belt – Tectonic
Significance of Upper Mesozoic Sedimentary and Volcanic Sequence in Southern
and Southeastern Alaska. Geological Survey Professional Paper 800-D, Geologic
Survey Research 1972 Chapter D.
Berg, Henry, C. 1973. Geology of Gravina Island, Alaska. Geological Survey Bulletin 1373.
United States Geological Survey (USGS). 2014. USGS Seismic Design Maps web tool.
http://earthquake.usgs.gov/designmaps/us/application.php
– 33 –
February 2016
GRAVINA MILL ACCESS ROAD
GEOTECHNICAL ENGINEERING REPORT
This page is intentionally left blank.
February 2016
– 34 –
Appendix A
Field Exploration Procedures and Logs
The following paragraphs describe procedures used for field explorations and field tests
conducted for this project. Descriptive logs of geotechnical explorations are included in this
appendix.
Test Pit Procedures
Exploratory test pits were excavated using a John Deere 130 G trackhoe excavator
provided and operated by a representative from LEI. A qualified geologist continuously
observed the test pit excavations, logged subsurface conditions, and obtained
representative soil and rock samples. All samples were stored in watertight containers and
later transported to the laboratory for further visual examination and testing. After each test
pit was logged, the test pit was backfilled with the excavated soils, and the surface was
compacted by tamping the surface with the trackhoe.
The test pit logs indicate the vertical sequence of soils and materials encountered in each
test pit, based primarily on field classifications and supported by subsequent laboratory
examination and testing. Where a soil contact was observed to be gradational or
undulating, test pit logs indicate the average contact depth. The relative density and
consistency of in situ soils were estimated by means of the excavation characteristics and
the stability of the test pit sidewalls. Test pit logs also indicate the approximate depths of
any sidewall caving or groundwater seepage observed in the test pits, as well as all sample
numbers and sampling locations.
Appendix A
Appendix B
Laboratory Testing Procedures and Results
The following paragraphs describe laboratory test procedures. Geotechnical laboratory testing
was performed by Krazan Associates in their Lynnwood, Washington, laboratory. Graphical
results of certain laboratory tests are included in this appendix.
Visual Classification Procedures
Visual soil classifications were conducted on all samples in the field and on selected samples
in the laboratory. All soils were classified in general accordance with the Unified Soil
Classification System, which includes color, relative moisture content, primary soil type (based
on grain size), and any accessory soil types. The resulting soil classifications are presented on
the exploration logs in Appendix A.
Moisture Content Determination Procedures
Moisture content determinations were performed on representative samples to aid in
identification and correlation of soil types. All determinations were made in general accordance
with ASTM D-2216. The results of these tests are shown on the exploration logs in Appendix A.
Atterberg Limit Determination Procedures
Atterberg limits are used primarily for classifying and indexing cohesive soils. The liquid and
plastic limits, which are defined as the moisture contents of a cohesive soil at arbitrarily
established limits for liquid and plastic behavior, were determined for selected samples in
general accordance with ASTM D-4318. The results of these tests are presented on the
enclosed Atterberg limit graphs and on the exploration logs in Appendix A.
Degradation Value of Aggregates
This test is used to determine the durability of aggregate or bedrock proposed for use as
aggregate. The degradation value indicates the relative resistance of an aggregate to produce
detrimental clay-like fines when subjected to a prescribed abrasion process in the presence of
distilled or demineralized water. Representative samples of bedrock were collected and
submitted to the laboratory for testing in accordance with Alaska Test Method 313. Results of
the tests are presented on the enclosed laboratory test results sheet.
Los Angeles Abrasion
The Los Angeles Abrasion test is a measure of degradation of mineral aggregates. The test
was performed in accordance with ASTM C-131, which involves placing a known volume of the
aggregate into a rotating steel drum with steel spheres. The drum revolves at the specified rate
for 500 revolutions, after which the sample is removed from the drum. The resulting volume of
material of a specified size is compared to the original sample to determine the difference,
which is termed the percent loss. Test results are presented in this appendix.
Analytical Testing
For use in determining corrosion potential of the site soils, soil samples from Test Pits TP-2 and
TP-5 were analyzed for pH, resistivity, chloride, and sulfate. Samples were submitted to
AmTest, Inc., in Kirkland, Washington. Test results are presented in this appendix.
Appendix B