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GEOTECHNICAL REPORT
SOUTH SIDE TRAIL AND
PEDESTRINE BRIDGE DEVELOPMENT
MAY CREEK TRAIL PARK
Renton, Washington
PROJECT NO. 22-399
March 3, 2023
Prepared for:
City of Renton
March 3, 2023
Project No. 22-399
22-399 May Creek Trail Geotechnical Report i PanGEO, Inc.
TABLE OF CONTENTS
PROJECT DESCRIPTION ......................................................................................................... 1
SITE DESCRIPTION ................................................................................................................... 1
GEOLOGY .................................................................................................................................... 2
FIELD EXPLORATIONS ........................................................................................................... 2
LABORATORY TESTING ......................................................................................................... 2
SUBSURFACE CONDITIONS ................................................................................................... 2
SOILS ........................................................................................................................................... 2
GROUND WATER.......................................................................................................................... 4
CONCLUSIONS AND RECOMMENDATIONS ...................................................................... 4
EARTHQUAKE FAULTING ............................................................................................................. 4
SEISMIC DESIGN PARAMETERS .................................................................................................... 4
LIQUEFACTION POTENTIAL .......................................................................................................... 4
FOUNDATION RECOMMENDATIONS .............................................................................................. 5
Bridge Support ........................................................................................................................ 5
Walkway Support .................................................................................................................... 5
TRAIL CUTS AND FILLS ................................................................................................................ 6
MODULAR BLOCK & GABION WALLS .......................................................................................... 7
LIMITATIONS AND UNIFORMITY OF CONDITIONS ...................................................... 8
CLOSURE ..................................................................................................................................... 9
REFERENCES ............................................................................................................................ 10
March 3, 2023
Project No. 22-399
22-399 May Creek Trail Geotechnical Report ii PanGEO, Inc.
LIST OF FIGURES (follows text)
Figure 1 Vicinity Map
Figure 2 Site and Exploration Plan
Figure 3 Generalized Subsurface Profile, Section A-A’
APPENDIX A: FIELD EXPLORATION BORING LOGS
APPENDIX B: LABORATORY TEST RESULTS
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 1
GEOTECHNICAL REPORT
MAY CREEK TRAIL AND PEDESTRINE BRIDAGE
RENTON, WASHINGTON
PROJECT DESCRIPTION
The City of Renton plans to construct a new trail along May Creek west of I-405, which will
include a pedestrian bridge crossing May Creek (see Figures 1 & 2). Currently there is a soft
surface trail along the north bank of May Creek, which extends to the I-405 corridor and the
south bank area is undeveloped. The proposed construction will include a pedestrian bridge
crossing May Creek, some elevated boardwalks in wetland areas, and new trails above the
south bank of May Creek. Long term plans include the extension of the north bank trail
beneath I-405 to link up with already constructed trails on the east side of the corridor.
SITE DESCRIPTION
The site is located in the northernmost
extension of the City of Renton where May
Creek flows westward to Lake Washington.
The ground surface along the north or right
bank of the river at the proposed pedestrian
bridge is relatively level at an elevation of
approximately 36 feet and the area is well
wooded with fir and deciduous trees and
undergrowth (see Plate 1). Much of the north
bank is within the mapped 100-year flood
plain of May Creek.
The south or left bank ascends moderately to
steeply to the southwest at a grade of about
40% ( see Plate 1). The left bank is being
actively undercut by the creek. The left bank
is vegetated with blackberry thickets.
Plate 1 – Right bank abutment in foreground
and left bank abutment in excavated area in
background
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 2
GEOLOGY
The Washington State Geologic Information Portal suggests that the May Creek Trail Park is
underlain by alluvium.
FIELD EXPLORATIONS
Subsurface conditions at the bridge site were explored with two borings (PG-1 and PG-2) that
were drilled at the locations shown on Figure 2 using a track mounted hollow stem auger drill
rig owned and operated by Geologic Drill Partners of Bellevue, Washington. The drill was
equipped with 6-inch outside diameter hollow stem augers. Soil samples were obtained at 2½-
foot depth intervals in the top 10 feet, and at 5-foot intervals thereafter. The sampling was
conducted in general accordance with Standard Penetration Test (SPT) sampling methods
(ASTM test method D-1586) in which the samples were obtained using a 2-inch outside
diameter split-spoon sampler. The sampler was driven 18” into the soil using a 140-pound
weight freely falling 30 inches. The number of blows required for each 6-inch increment of
sampler penetration was recorded. The number of blows required to achieve the last 12 inches
of sample penetration is defined as the SPT N-value. The N-value provides an empirical
measure of the relative density of cohesionless soil, or the relative consistency of fine-grained
soils.
An engineering geologist from PanGEO was on site to coordinate field activities, monitor the
auger advancement, and log the materials retrieved from the sampler. Logs of the borings are
presented in Appendix A, and the underlying subsurface conditions are summarized below.
LABORATORY TESTING
To determine the index properties of the soils, selected samples were submitted for grain size
analyses and Atterberg limit testing. The results of the tests were incorporated into the
summary logs and detailed test results are presented in Appendix B.
SUBSURFACE CONDITIONS
SOILS
The soils encountered in PG-1 on the right bank, consisted of beds of alluvium overlying glacial
outwash material, with glaciolacustrine material at depth. The alluvium extends to a depth of
roughly 14 feet below the ground surface. Boring PG-2 on the left bank also encountered about 10
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 3
feet of colluvium overlying glacial outwash and glaciolacustrine beds. The subsurface conditions
at the bridge site are illustrated in Figure 3. The soil units encountered are more fully described
below.
Overbank Alluvium: Test boring PG-1 encountered 2 feet of loose, brown, non-plastic SILT with
fine sand. The soil unit was interpreted as overbank alluvium or a flood deposit.
Alluvium (Upper Bed): Underlying the overbank alluvium in PG-1 was a 3.7-foot bed of loose,
brown GRAVEL with sand and silt, which we interpreted as alluvium from May Creek.
Peat: Peat was encountered between depths of 5.7 and 8.3 feet in boring PG-1.
Alluvium (Lower Beds): below the peat in PG-1 was a 6-foot thick sequence of loose, green gray,
interbedded SILT and silty SAND. The bed was laminated, and the fines were non-plastic to
slightly plastic. Based on the low N-value of 8, this bed was also interpreted as recent alluvium.
Colluvium: In boring PG-2, the uppermost soil unit was loose, mixed brown and gray SILT with
fine sand. This soil was non-plastic, with rusty bands and a trace of organics, approximately 4.5
feet thick, and was interpreted as colluvium.
Below the uppermost soil bed in PG-2 was a 5-foot bed of medium dense, brown, silty, fine sand.
The soil was non-plastic, with rapid dilatancy and occasional silt interbeds. This unit also was
interpreted as colluvium, based on relatively low N-values and its location at the base of a steep
slope.
Glacial Outwash Gravels: Both borings penetrated a unit of medium dense to very dense, silty,
fine to medium SAND to fine to coarse SAND. Laboratory testing indicated that this unit was
classified as SW in PG-1 and SM in PG-2. It was encountered at a depth of 14 feet in PG-1 and
9.5 feet in PG-2. Based on the N-values and composition, this soil was interpreted as Glacial
Outwash. It was about 8 feet thick in both borings.
Glaciolacustrine Drift: The deepest soil unit found consisted of hard or very dense, gray to green,
gray, clayey SILT. Laboratory testing classified the soil as ML. Field examination indicated that
the soil was slightly plastic to low plastic, massive, with occasional drop stones or sandy
interbeds. This soil was interpreted as glaciolacustrine drift and was found at depths of 22 feet and
18 feet below surface in PG-1 and PG-2, respectively.
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Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 4
GROUND WATER
Groundwater was encountered at a depth of 2 feet in both borings. We anticipate that
groundwater levels will be controlled by the surface elevation of the creek and that water levels
at the abutments will be at or slightly above the creek level. Groundwater levels are expected
to fluctuate with seasonal flow changes in the creek.
CONCLUSIONS AND RECOMMENDATIONS
EARTHQUAKE FAULTING
The location of the bridge lies south of the Seattle Fault Zone which extends easterly, just north
of Mercer Island. The inferred southernmost strand of the Seattle Fault is located about a mile
north of the bridge location. In our opinion, fault rupture at the site is unlikely in a future
earthquake.
SEISMIC DESIGN PARAMETERS
In accordance with AASHTO (2019), the WSDOT Seismic Design Manual (WSDOT 2019),
and ASCE 7-16, the following provides ground acceleration design parameters (% g)
corresponding to an event having a 7 percent probability of exceedance in 1,000 years for the
site which is underlain by Site Class D soils.
As SDS (0.2 Sec) SD1 (1 Sec)
0.41 g 0.96 g 0.27 g B/C Boundary
0.47 g 1.03 g 0.47 g Site Class D
LIQUEFACTION POTENTIAL
The upper 10 to 15 feet of soil encountered in the borings are susceptible to liquefaction in the
design earthquake as based on simplified screening contained in section 6.4.2 of the
Geotechnical Design Manual (WSDOT, 2020). Consequently, the pedestrian bridge will require
pile support and the seismic design of the bridge will need to consider reduced lateral support as
a result of liquefaction.
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 5
The potential for liquefaction-induced lateral spreading is low because of the site’s relatively
level topography.
FOUNDATION RECOMMENDATIONS
Bridge Support
Considering the generally light loads on the pedestrian bridge and the desire to minimize ground
disturbance during construction, we recommend supporting the bridge on 8-inch diameter single
helical anchors drilled to a depth of about 43 feet and to a minimum torque of 3,000 ft.-lbs. as
based on our design using software from MacLean Civil Products, who is the manufacturer of
helical anchors. The anchor design is also based on the use of D6 1.5” diameter bars above the
lead helical section. The helical anchors described above would have an ultimate bearing and
tension capacity of 30 Kips. The mechanical capacity of D6 shafts and couplers is twice the
ultimate design capacity of the anchor and the buckling capacity of the shaft is greater than the
ultimate compression capacity of the anchors. At least one helical anchor at each abutment
should be load tested in tension to confirm anchor capacity.
Walkway Support
We understand that the project will also include wood platform walkways over ecologically
sensitive areas. We suggest that these walkways be supported on Diamond Piers™
(www.diamondpiers.com) or small 2 or 3 inch diameter pin piles. Recommendations for these
foundations are provided below.
Diamond Piers
Diamond Piers have been used to provide vertical support to boardwalks constructed over
environmentally sensitive terrain. The system consists of individual precast concrete elements
which are cast with sleeves that allow steel rods to be driven through the concrete elements and
into the underlying soil. Because of the geometry of the sleeves, the element is able to provide
both vertical and lateral support to the elevated boardwalk with typical vertical and lateral load
capacities of 600 pounds.
Pin Pines
Alternatively, the walkway may be supported on 2 or 3 inch diameter pin piles driven to refusal
in the glaciolacustrine beds underlying the site at depths of about 15 to 20 feet. Two inch
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 6
diameter piles Schedule-80, ASTM A-53 Grade “A” pipe driven to refusal at depths of about 20
to 30 feet may support an allowable load of 3 tons and 3-inch diameter Schedule-40, ASTM A-
53 Grade “A” pipe piles driven to refusal may be capable of supporting an allowable load of 10
tons. Refusal for 2” diameter piles is defined as less than 1-inch of penetration under
continuous driving with a 90-lb jackhammer. Refusal for 3” diameter piles is defined as the
following:
Hammer
Size
Blow per
Minute
Refusal Criteria
(3-inch pile)
600 lbs. 1000 12 seconds per inch
850 lbs. 900 10 seconds per inch
1100 lbs. 900 6 seconds per inch
At least 3% (but no more than 5) of the 3-inch pin piles should be load tested. All load tests
shall be performed in accordance with the procedure outlined in ASTM D1143. The maximum
test load shall be 2 times the design load. The objective of the testing program is to verify the
adequacy of the driving criteria, and the efficiency of the hammer used for the project.
Lateral capacity of vertical pin piles should be ignored in design calculations. Some resistance
to lateral loads may be accomplished by battering the piles to a slope of no more than
1(H):4(V).
Lateral forces from wind or seismic loading may be resisted with pile caps where passive soil
resistance may be determined using an equivalent fluid weight of 300 pounds per cubic foot
(pcf). This value includes a factor of safety of at least 1.5 assuming placement of a compacted
structural fill adjacent to the sides of the pile caps. For seismic loading, passive pressures may
be increased by one third.
TRAIL CUTS AND FILLS
Where possible, we recommend using 2(H):1(V) cut and fill slopes for new trails to minimize
slope instability and surface erosion.
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 7
MODULAR BLOCK & GABION WALLS
At locations where trails traverse steep slopes, we recommend locating the trail on a full bench
cut and installing modular blocks or gabion baskets to retain the uphill cuts.
Gabions should be constructed in accordance with WSDOT Standard Plan Sheet D-6, and
Section 8-24.3(3) Gabion Cribbing of the 2022 WSDOT Standard Specifications. Each gabion
basket should be placed horizontally and with a minimum of 6 inches of setback from the basket
below, hence creating an average wall face inclination of no steeper than 1H:6V. Dimensions of
gabion baskets may vary depending on the supplier.
Minimum Width – In general, as a minimum, all gabion baskets should have a minimum
width equal to the greater of 2½ feet or one-third the wall height.
Minimum Embedment - Walls should have a minimum of one foot of embedment. All
walls should be founded on competent native soils or on properly compacted fill.
Foundation Preparation – We recommend over excavating the footings at least 6-inches
and backfilling with Crushed Surfacing Top or Base Course (CSTC/CSBC) (WSDOT 9-
03.9(3)), or an approved equivalent. We also recommend placing a geotextile fabric at the
bottom of the over-excavation before placing structural fill. The geotextile fabric for
separation may be selected based on Table 3, Section 9-33.2(1) of the WSDOT Standard
Specifications.
Design Parameters for Gravity Walls
Soil Properties Wall Backfill1 Retained Soil2 Foundation Soil
Unit Weight (pcf) 130 130 115
Friction Angle (deg) 36 36 30
Cohesion (psf) 0 0 0
For the Service Limit State, the wall shall be designed to accommodate a maximum differential
settlement of 4 inches per 100 feet of wall length.
For the Extreme Event I Limit State, the wall shall be designed for a horizontal seismic
acceleration coefficient kh of 0.192g and a vertical seismic acceleration coefficient kv of 0.0g.
Notes: 1 – Wall backfill should be Gravel Borrow or Gravel Backfill for Walls (WSDOT, 2022).
2 – Retained material should conform to the requirements for Select or Gravel Borrow (WSDOT, 2022)
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 8
Resistance Factors for Spread Footing Design
Limit State Bearing
Shear Resistance to
Sliding
Passive Pressure
Resistance to Sliding
Strength 0.45 0.8 0.5
Service 1.0 1.0 1.0
Extreme 0.9 0.9 0.9
The recommended lateral pressure assumes that adequate wall drainage provisions will be
incorporated into the design and construction of the walls, and that properly compacted free-
draining structural fill will be used for wall backfill. On-site soils should not be used as wall
backfill because of its poor drainage characteristics.
LIMITATIONS AND UNIFORMITY OF CONDITIONS
PanGEO, Inc. (PanGEO) prepared this report for WSP America and the City of Renton. The
recommendations contained in this report are based on a site reconnaissance, a subsurface
exploration program, review of pertinent subsurface information, and our understanding of the
project.
Variations in soil conditions may exist between the locations of the explorations and the actual
conditions underlying the site. The nature and extent of soil variations may not be evident until
construction occurs. If any soil conditions are encountered at the site that are different from
those described in this report, PanGEO should be immediately notified to review the
applicability of the recommendations presented herein. Additionally, PanGEO should also be
notified to review the applicability of these recommendations if there are any changes in the
project scope.
This report has been prepared for planning and design purposes for specific application to the
proposed project in accordance with the generally accepted standards of local practice at the
time this report was written. No warranty, express or implied, is made.
This report may be used only by the client and for the purposes stated, within a reasonable time
from its issuance. Land use, site conditions (both off and on-site), or other factors including
advances in our understanding of applied science, may change over time and could materially
affect our findings. Therefore, this report should not be relied upon after 36 months from its
issuance. PanGEO should be notified if the project is delayed by more than 36 months from
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 9
the date of this report so that the applicability of the conclusions and recommendations
presented herein may be evaluated considering the time lapse.
Within the limitations of scope, schedule and budget, PanGEO engages in the practice of
geotechnical engineering and endeavors to perform its services in accordance with generally
accepted professional principles and practices at the time this report and/or its contents was
prepared. No warranty, express or implied, is made. The scope of PanGEO’s work did not
include environmental assessments or evaluations regarding the presence or absence of
wetlands or hazardous or toxic substances in the soil, surface water or ground water at this site.
PanGEO does not practice or consult in the field of safety engineering. PanGEO does not
direct the contractor’s operations, and cannot be held responsible for the safety of personnel
other than our own on the site; the safety of others is the responsibility of the contractor.
It is the client’s responsibility to see that all parties to this project, including the designer,
contractor, subcontractors, etc., are made aware of this report in its entirety. The use of
information contained in this report for bidding purposes shall be at the contractor’s sole option
and risk. Any party other than the client who wishes to use this report shall notify PanGEO of
such intended use and for permission to copy this report. Based on the intended use of the
report, PanGEO may require that additional work be performed and that an updated report be
reissued. Noncompliance with any of these requirements will release PanGEO from any
liability resulting from the use this report.
CLOSURE
PanGEO is pleased to support WSP America and the City of Renton Parks Department with
geotechnical engineering recommendations. Please call with any questions.
Stephen H. Evans, L.E.G. W. Paul Grant, P.E.
Senior Engineering Geologist Principal Geotechnical Engineer
May Creek Trail
Renton, Washington
March 3, 2023
22-399 May Creek Trail Geotechnical Report PanGEO, Inc. 10
REFERENCES
AASHTO, 2019. LRFD Bridge Design Specifications, 7th edition, American Association of State
Highway and Transportation Officials. Washington, D.C.
WSDOT, 2022. Geotechnical Design Manual (GDM), M 46-03, Washington State Department
of Transportation
WSDOT, 2012. Standard Specifications for Road, Bridge and Municipal Construction, M 41-10,
Washington State Department of Transportation
Project No.Figure No.
22-399 Fig 1.ppt 1/26/2023(12:14 PM) SHE
22-399 1
VICINITY MAP
May Creek Trail
Improvements
4260 Lake Washington
Blvd North
Renton, Washington
Base Map from the Washington
State Geological Information Portal
Not to Scale
Project Site
N
Project No.Figure No.
22-399 Fig 1.ppt 1/26/2023(12:14 PM) SHE
22-399 1
VICINITY MAP
May Creek Trail
Improvements
4260 Lake Washington
Blvd North
Renton, Washington
Base Map from WSP Survey
Vertical datum NAVD 88
Scale 1”:30’
Legend:
PanGEO Boring
PG-2
PG-1
N
0 10 20 30 40 50 60 70 80 90 100 110 120
Distance (ft.)
-20
-10
0
10
20
30
40
50
El
e
v
a
t
i
o
n
(
i
n
f
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t
)
-20
-10
0
10
20
30
40
50
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v
a
t
i
o
n
(
i
n
f
e
e
t
)
6
10
17
31
63
50/5
7
4
6
8
19
50/6
62
A A'
May Creek Trail Improvements
N 41st Street and
Lake Washington Blvd N
Renton, Washington
22-399 322
-
3
9
9
P
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i
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A
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:
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)
S
H
E
Graphics Legend:
BH-1
48
21
50/5
88
31
42
31
50/3
SPT N-valueGroundwater
Level
Soil Unit
Boundries
Groundwater Seep
Topographic Surface
SOUTH NORTH
?
?
PG-2 PG-1
MD to VD, silty
f. to m. SAND
Loose SILT
w/ f. sandl
MD silty
f. SAND
Loose interb'd
SILT and silty SAND
MD to VD,
f. - c. SAND
GENERALIZED SUBSURFACE PROFILE
PROPOSED BRIDGE SITE
SECTION A - A'
May Creek
Soft PEAT
Loose SILT w/ sand
Loose GRAVELw/ silt & SAND
Hard, clayey
SILT
?
?
?
??
?
?
?
?
?
?
??
?
Glaciolacustrine Beds
Glacial Outwash
Colluvium Alluvial Deposits
Hard, clayey
SILT
Approximate Location
of Proposed Bridge Abutment
Approximate Location
of Proposed Bridge Abutment
APPENDIX A: FIELD EXPLORATIONS
Appendix A contains written and graphical borehole logs presenting the factual and interpretive
results of our exploratory drilling program. The descriptions of the materials encountered in the
subsurface explorations are based on the soil and rock samples extracted from the borings. The
sample descriptions are augmented by observation of the drilling action and drill cuttings
brought to the surface during field operations. The paragraphs below describe the field
operations and sampling procedures used during the geotechnical field explorations.
FIELD EXPLORATIONS
The subsurface exploration program consisted of drilling two test borings at bridge site, one on
each bank. The drilling was conducted between October 20, 2023. Borings PG-1 and PG-2
were advanced to depths of 24.5 and 21 feet, respectively, where drilling refusal was met.
The approximate boring locations are shown on Figure 2. A representative of PanGEO logged
the test borings. Soil samples were collected from selected intervals in each boring. The right
bank borings were drilled with a Bobcat truck mounted drill rig provided by Geologic Drill
Partners. Both borings were drilled with hollow stem augers.
SAMPLING METHODS
Standard penetration tests were taken in both borings at 2.5-foot intervals to 10 feet, and 5-foot
intervals thereafter. Final sample in PG-2 was taken 23 feet, as practical drilling refusal had been
met The number of blows to drive the sampler each 6 inches over an 18-inch interval was
recorded and indicated on the boring logs. The number of blows to drive the sampler the final 12
inches is termed the SPT resistance, or N-value, and is used to evaluate the strength and
consistency/relative density of the soil. The hammer used to perform SPT sampling was rope
and cathead mechanism. The efficiency of the hammer mechanism is considered when
evaluating the liquefaction potential of a soil. The SPT N-values reported on the borehole logs
are field values, and are therefore not corrected for hammer efficiency, overburden stress or rod
lengths.
An engineering geologist from PanGEO was present throughout the field exploration program to
observe the borings, assist in sampling, and to prepare descriptive logs of the explorations. Soils
Proposed May Creek South Side Trail and Bridge
Renton, Washington
March 2, 2023
22-399 May Creek Trail Geotechnical Report A - 1 PanGEO, Inc
were classified in general accordance with the guidelines shown on Figure A-1. Summary
boring logs are included as Figures A-2 and A-3. The stratigraphic contacts shown on the
summary logs represent the approximate boundaries between soil types; actual stratigraphic
contacts encountered at other locations in the field may differ from the contact elevations shown
on the logs may be gradual rather than abrupt. The soil and groundwater conditions depicted are
only for the specific date and locations reported, and therefore, are not necessarily representative
of other locations and times.
MOISTURE CONTENT
2-inch OD Split Spoon, SPT
(140-lb. hammer, 30" drop)
3.25-inch OD Spilt Spoon
(300-lb hammer, 30" drop)
Non-standard penetration
test (see boring log for details)
Thin wall (Shelby) tube
Grab
Rock core
Vane Shear
Dusty, dry to the touch
Damp but no visible water
Visible free water
Terms and Symbols for
Boring and Test Pit Logs
Density
SILT / CLAY
GRAVEL (<5% fines)
GRAVEL (>12% fines)
SAND (<5% fines)
SAND (>12% fines)
Liquid Limit < 50
Liquid Limit > 50
Breaks along defined planes
Fracture planes that are polished or glossy
Angular soil lumps that resist breakdown
Soil that is broken and mixed
Less than one per foot
More than one per foot
Angle between bedding plane and a planenormaltocoreaxis
Very Loose
Loose
Med. Dense
Dense
Very Dense
SPT
N-values
Approx. Undrained Shear
Strength (psf)
<4
4 to 10
10 to 30
30 to 50
>50
<2
2 to 4
4 to 8
8 to 15
15 to 30
>30
SPT
N-values
Units of material distinguished by color and/orcomposition frommaterial unitsabove andbelow
Layers of soil typically 0.05 to 1mm thick, max. 1 cm
Layer of soil that pinches out laterally
Alternating layers of differing soil material
Erratic, discontinuous deposit of limited extent
Soil with uniform color and composition throughout
Approx. Relative
Density (%)
Gravel
Layered:
Laminated:
Lens:
Interlayered:
Pocket:
Homogeneous:
Highly Organic Soils
#4 to #10 sieve (4.5 to 2.0 mm)
#10 to #40 sieve (2.0 to 0.42 mm)
#40 to #200 sieve (0.42 to 0.074 mm)
0.074 to 0.002 mm
<0.002 mm
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS GROUP DESCRIPTIONS
Notes:
MONITORING WELL
<15
15 - 35
35 - 65
65 - 85
85 - 100
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
PT
TEST SYMBOLS
50%or more passing #200 sieve
Groundwater Level at time of drilling (ATD)Static Groundwater Level
Cement / Concrete Seal
Bentonite grout / seal
Silica sand backfill
Slotted tip
Slough
<250
250 - 500
500 - 1000
1000 - 2000
2000 - 4000
>4000
RELATIVE DENSITY / CONSISTENCY
Fissured:
Slickensided:
Blocky:
Disrupted:
Scattered:
Numerous:
BCN:
COMPONENT DEFINITIONS
Dry
Moist
Wet
1. Soil exploration logs contain material descriptions based on visual observation and field tests using a systemmodified from the Uniform Soil Classification System (USCS). Where necessary laboratory tests have beenconducted (as noted in the "Other Tests" column), unit descriptions may include a classification. Please refer to thediscussions in the report text for a more complete description of the subsurface conditions.
2. The graphic symbols given above are not inclusive of all symbols that may appear on the borehole logs.Other symbols may be used where field observations indicated mixed soil constituents or dual constituent materials.
COMPONENT SIZE / SIEVE RANGE COMPONENT SIZE / SIEVE RANGE
SYMBOLS
Sample/In Situ test types and intervals
Silt and Clay
Consistency
SAND / GRAVEL
Very Soft
Soft
Med. Stiff
Stiff
Very Stiff
Hard
Phone: 206.262.0370
Bottom of BoringBoulder:
Cobbles:
Gravel
Coarse Gravel:
Fine Gravel:
Sand
Coarse Sand:
Medium Sand:
Fine Sand:
Silt
Clay
> 12 inches
3 to 12 inches
3 to 3/4 inches
3/4 inches to #4 sieve
Atterberg Limit Test
Compaction Tests
Consolidation
Dry Density
Direct Shear
Fines Content
Grain Size
Permeability
Pocket Penetrometer
R-value
Specific Gravity
Torvane
Triaxial Compression
Unconfined Compression
Sand
50% or more of the coarsefraction passing the #4 sieve.Use dual symbols (eg. SP-SM)for 5% to 12% fines.
for In Situ and Laboratory Testslisted in "Other Tests" column.
50% or more of the coarsefraction retained on the #4sieve. Use dual symbols (eg.GP-GM) for 5% to 12% fines.
DESCRIPTIONS OF SOIL STRUCTURES
Well-graded GRAVEL
Poorly-graded GRAVEL
Silty GRAVEL
Clayey GRAVEL
Well-graded SAND
Poorly-graded SAND
Silty SAND
Clayey SAND
SILT
Lean CLAY
Organic SILT or CLAY
Elastic SILT
Fat CLAY
Organic SILT or CLAY
PEAT
ATT
Comp
Con
DD
DS
%F
GS
Perm
PP
R
SG
TV
TXC
UCC
Figure A-1
GS
Loose, brown SILT with fine sand: slightly moist, non-plastic.(Overbank Alluvium).
Loose, brown GRAVEL with silt and sand: wet. (Alluvium).
Soft, dark brown, fibrous PEAT: wet. (Peat).
Loose, green gray, interbedded SILT and silty SAND: very moist,
laminated, slightly plastic and non-plastic. (Alluvium).
Medium dense to very dense, gray, fine to coarse SAND (SW): wet,trace silt and fine gravel, homogeneous, well graded, massive to
indistinctly laminated. (Glacial Outwash).
Hard, green gray, clayey SILT (ML): moist, low plastic, homogeneous,massive, occasional drop stones. (Glaciolacustrine Drift).
Bottom of Boring.
S-1
S-2
S-3
S-4
S-5
S-6
S-7
4
3
4
4
3
1
3
3
3
3
4
4
7
9
10
50/6
32
22
40
Remarks:
0.0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5
25.0
The stratification lines represent approximate boundaries. The transition may be gradual.
MATERIAL DESCRIPTION
Figure A-2
Ot
h
e
r
T
e
s
t
s
Sa
m
p
l
e
N
o
.
Completion Depth:
Date Borehole Started:
Date Borehole Completed:
Logged By:
Drilling Company:
De
p
t
h
,
(
f
t
)
May Creek Trail Improvements
22-399
N41st Street and Lake Washington Blvd. N, Renton, WA
Northing: , Easting:
24.5ft
10/20/22
10/20/22
S. Evans
Geologic Drill Partners
Sheet 1 of 1
Project:
Job Number:
Location:
Coordinates:
Sy
m
b
o
l
Sa
m
p
l
e
T
y
p
e
Bl
o
w
s
/
6
i
n
.
HSA
SPT
Surface Elevation:
Top of Casing Elev.:
Drilling Method:
Sampling Method:
LOG OF TEST BORING PG-1
N-Value
0
Moisture LL
50
PL
RQD Recovery
100
>>
GS
GS
Loose, brown and gray SILT with fine sand: wet, non-plastic,homogeneous, rusty bands, trace organics. (Colluvium).
Medium dense, brown, silty, fine SAND (SM): wet, non-plastic, rapiddilatancy, one silt interbed with rusty band at lower contact,
homogenous. (Colluvium).
Dense to very dense, brown, silty, fine to medium SAND (SM): wet,non-plastic, homogeneous, laminated, occasional gravel, one silt
rip-up clast. (Glacial Outwash).
Brown gray, occasional rusty bands, one light brown clayey siltinterbed.
Hard, gray, clayey SILT: moist, low plastic, homogeneous, massive,occasional sand interbeds. (Glaciolacustrine Drift).
Bottom of Boring.
S-1
S-2
S-3
S-4
S-5
S-6
3
3
3
3
5
5
7
8
9
9
13
19
13
23
40
20
50/5
Remarks:
0.0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5
25.0
The stratification lines represent approximate boundaries. The transition may be gradual.
MATERIAL DESCRIPTION
Figure A-3
Ot
h
e
r
T
e
s
t
s
Sa
m
p
l
e
N
o
.
Completion Depth:
Date Borehole Started:
Date Borehole Completed:
Logged By:
Drilling Company:
De
p
t
h
,
(
f
t
)
May Creek Trail Improvements
22-399
N41st Street and Lake Washington Blvd. N, Renton, WA
Northing: , Easting:
20.9ft
10/20/22
10/20/22
S. Evans
Geologic Drill Partners
Sheet 1 of 1
Project:
Job Number:
Location:
Coordinates:
Sy
m
b
o
l
Sa
m
p
l
e
T
y
p
e
Bl
o
w
s
/
6
i
n
.
HSA
SPT
Surface Elevation:
Top of Casing Elev.:
Drilling Method:
Sampling Method:
LOG OF TEST BORING PG-2
N-Value
0
Moisture LL
50
PL
RQD Recovery
100
>>
22-399 May Creek Trail Geotechnical Report A - 1 PanGEO, Inc.
APPENDIX B: LABRATORY TESTING
Appendix B contains the results of laboratory testing conducted on selected samples for
classification purposes, according to Unified Soil Classification system. Tests done included
natural moisture, grainsize and Atterberg tests.
0
10
20
30
40
50
60
0 20 40 60 80 100
CL
MH
CH
Specimen Identification
PG-1
MLCL-ML
PLA
STI
CIT
Y
IND
EX
Classification
104131
M LL
24.0 25
ATTERBERG LIMITS
FinesPIPL
LIQUID LIMIT
Figure
B-2
Project: May Creek Trail Improvements
Job Number: 22-399
Location: N41st St. and Lk. Wash. Blvd. N, Renton, WAPhone: 206.262.0370
AT
T
E
R
B
E
R
G
L
I
M
I
T
S
2
2
-
3
9
9
L
O
G
S
.
G
P
J
P
A
N
G
E
O
.
G
D
T
2
/
6
/
2
3