HomeMy WebLinkAboutRS_GEOTECHNICAL_REPORT_20250829_V1.pdfCobalt Geosciences, LLC
P.O. Box 1792
North Bend, WA 98045
www.cobaltgeo.com (206) 331-1097
October 11, 2023
Updated August 8, 2025
Faisal Muhammad
deenforlife@gmail.com
RE: Geotechnical Evaluation
Proposed Development
4108 Jones Avenue NE
Renton, Washington
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this report to
discuss the results of our geotechnical evaluation at the referenced site.
The purpose of our evaluation was to provide recommendations for foundation design, grading,
pavements, and earthwork.
Site and Project Description
The site is located at 4108 Jones Avenue NE in Renton, Washington. The site consists of two
parcels (No.’s 3345700085 and -080) with a total area of about 52,341 square feet.
The western portion of the property is developed with mobile structures and gravel parking areas.
The remainder of the site is undeveloped and vegetated with grasses, bushes, understory,
blackberry vines, ferns, and variable diameter trees.
The site is mostly level to slightly sloping downward to the west. There are local slope areas near
the east property line extending downward to the west at magnitudes of 10 to 35 percent and
relief of about 20 feet.
The site is bordered to the north and south by residential or commercial properties, to the east by
residential developments, and to the west by Jones Avenue NE.
The proposed development includes a new multi-story residential structure in the northwest
portion of the site with new parking lots south of the structure and in the western portions. We
anticipate that the new structure will be wood framed. Please notify us if concrete or masonry
structures are proposed.
Site grading may include cuts and fills of 3 feet or less and foundation loads are expected to be
moderate. We should be provided with the final plans to verify that our recommendations remain
valid and do not require updating.
Area Geology
The Geologic Map of King County indicates that this site is underlain by Alluvium.
Alluvium includes loose to medium dense mixtures and layers of sand, silt, clay, and peat. These
materials vary widely in density and were deposited by river processes (alluvium) within the
Holocene epoch. The alluvial deposits often have some potential for liquefaction and settlement
resulting from seismic activity or surcharge loads.
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In this area, the alluvium is likely underlain by Vashon Advance Outwash and/or pre-Vashon
deposits. These materials are typically dense and glacially consolidated.
Soil & Groundwater Conditions
The geotechnical field investigation program was completed in September 2023 and included
drilling and sampling two hollow stem auger borings with a limited access drill rig.
Disturbed soil samples were obtained during drilling by using the Standard Penetration Test
(SPT) as described in ASTM D-1586. The Standard Penetration Test and sampling method
consists of driving a standard 2-inch outside-diameter, split barrel sampler into the subsoil with a
140-pound hammer free falling a vertical distance of 30 inches. The summation of hammer-
blows required to drive the sampler the final 12-inches of an 18-inch sample interval is defined as
the Standard Penetration Resistance, or N-value. The blow count is presented graphically on the
boring logs in this appendix. The resistance, or “N” value, provides a measure of the relative
density of granular soils or of the relative consistency of cohesive soils.
The soils encountered were logged in the field and are described in accordance with the Unified
Soil Classification System (USCS).
A Cobalt Geosciences field representative conducted the explorations, collected disturbed soil
samples, classified the encountered soils, kept a detailed log of the exploration, and observed and
recorded pertinent site features.
The borings encountered approximately 6 inches of topsoil and vegetation or gravel underlain by
about 4.5 feet of loose to medium dense, fine to medium grained sand with gravel and silt (Fill).
This layer was underlain by approximately 13 feet of loose to medium dense, gravel with sand
trace to with silt (Alluvium). This layer was underlain by dense to very dense, fine to medium
grained sand trace to with gravel (Advance Outwash?), which continued to the termination depths
of the borings.
Groundwater was not encountered in the borings. Groundwater may become perched on the
denser outwash-like deposits, about 17 to 18 feet below site elevations in the borings. Regional
groundwater is likely close to the elevation of nearby Lake Washington, about 35 feet below site
elevations. This is a rough estimate only.
Water table elevations often fluctuate over time. The groundwater level will depend on a variety
of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and
soil permeability. Water levels at the time of the field investigation may be different from those
encountered during the construction phase of the project.
Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for King County indicate that the site
is underlain by Norma sandy loam. These soils would have a slight to moderate erosion potential
in a disturbed state depending on the slope magnitude.
It is our opinion that soil erosion potential at this project site can be reduced through landscaping
and surface water runoff control. Typically, erosion of exposed soils will be most noticeable
during periods of rainfall and may be controlled by the use of normal temporary erosion control
measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The
typical wet weather season, with regard to site grading, is from October 31st to April 1st. Erosion
control measures should be in place before the onset of wet weather.
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Seismic Hazard
The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the
International Building Code (IBC). In most areas of the site, there is a zone of liquefiable soils
which could result in a Site Class designation of E or F. If the proposed buildings have a
fundamental period of vibration of less than 0.5 seconds, it would be possible to design based on a
Site Class D. We should discuss this with the structural engineer during the design phase.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to
obtain values for SS, S1, Fa, and Fv. The USGS website includes the most updated published data
on seismic conditions. The following tables provide seismic parameters from the USGS web site
with referenced parameters from ASCE 7-16.
Seismic Design Parameters (ASCE 7-16)
Site
Class
Spectral
Acceleration
at 0.2 sec. (g)
Spectral
Acceleration
at 1.0 sec. (g)
Site
Coefficients
Design Spectral
Response
Parameters
Design
PGA/PGAM
Fa Fv SDS SD1
D 1.439 0.496 1.0 Null 0.959 Null 0.615/0.676
For items listed as “Null” see Section 11.4.8 of the ASCE.
Additional seismic considerations include liquefaction potential and amplification of ground
motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a
high groundwater table.
Soil liquefaction is a state where soil particles lose contact with each other and become suspended
in a viscous fluid. This suspension of the soil grains results in a complete loss of strength as the
effective stress drops to zero as a result of increased pore pressures. Liquefaction normally occurs
under saturated conditions in soils such as sand in which the strength is purely frictional.
However, liquefaction has occurred in soils other than clean sand, such as low plasticity silt.
Liquefaction usually occurs under vibratory conditions such as those induced by seismic events.
To evaluate the liquefaction potential of the site, we analyzed the following factors:
1) Soil type and plasticity
2) Groundwater depth
3) Relative soil density
4) Initial confining pressure
5) Maximum anticipated intensity and duration of ground shaking
The commercially available liquefaction analysis software, LiqSVS was used to evaluate the
liquefaction potential and the possible liquefaction induced settlement for the existing site soil
conditions. Maximum Considered Earthquake (MCE) was selected in accordance with the ASCE,
International Building Code and the U.S. Geological Survey (USGS) Earthquake Hazards
Program website.
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For this site, we used a peak ground acceleration of 0.676g and a 7.5M earthquake in the
liquefaction analyses.
The analyses yielded no significant risk of liquefaction. If groundwater were present in the upper
15 feet, there could be some potential for liquefaction and settlement. We have attached our
results with this report.
Conclusions and Recommendations
General
The site is underlain by areas of fill underlain by loose to medium dense alluvium and at depth by
very dense glacially consolidated soils. The alluvial deposits have some potential for static
consolidation under surcharge loads.
The proposed building may be supported on a shallow foundation system bearing on driven pipe
piles. Other options include rock columns (ground improvement), mat/raft foundations, or
auger-cast piles. We can provide recommendations for these options upon request.
Pin piles are steel pipes that embed in the denser soils at depth. In general, we anticipate that pin
piles may be the most cost-effective system for this project; however, feasibility will depend on
anticipated building loads.
Site Preparation
The upper 6 to 12 inches of existing topsoil, gravel, and fill should be removed prior to
preparation of the site for new fills or excavations. Note that the near surface soils will vary with
location due to the likelihood that historic grading has occurred in this area. We should be on site
during grading to determine stability of the prepared subgrades. Overexcavation should be
anticipated.
The near surface soils consist of sand with silt and gravel. These soils may be used as structural
fill if they meet compaction requirements.
Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of
3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve).
Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted
to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the
ASTM D 1557 test method.
Temporary Excavations
Based on our understanding of the project, we anticipate that the grading could include local cuts
on the order of approximately 6 feet or less for foundation and most of the utility placement. Any
deeper temporary excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in
loose native soils and fill and 1H:1V in medium dense native soils. If an excavation is subject to
heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than
2H:1V, where room permits.
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Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part
N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a
qualified person during construction activities and the inspections should be documented in daily
reports. The contractor is responsible for maintaining the stability of the temporary cut slopes
and reducing slope erosion during construction.
Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather,
and the slopes should be closely monitored until the permanent retaining systems or slope
configurations are complete. Materials should not be stored or equipment operated within 10 feet
of the top of any temporary cut slope.
Soil conditions may not be completely known from the geotechnical investigation. In the case of
temporary cuts, the existing soil conditions may not be completely revealed until the excavation
work exposes the soil. Typically, as excavation work progresses the maximum inclination of
temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental
recommendations can be made. Soil and groundwater conditions can be highly variable.
Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that
the project can proceed and required deadlines can be met.
If any variations or undesirable conditions are encountered during construction, we should be
notified so that supplemental recommendations can be made. If room constraints or
groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed
by the WAC, temporary shoring systems may be required. The contractor should be responsible
for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences
and the project structural engineer review temporary shoring designs prior to installation, to
verify the suitability of the proposed systems.
Foundation Design
Pin Piles
To mitigate the risk of total and differential settlement due to consolidation of loose alluvium,
driven pipe piles could be used to support the structure depending on the load requirements.
Auger-cast piles could also be considered if higher loads are required/anticipated.
The pile spacing will be determined by the project structural engineer during their design work.
We anticipate a pile depth on the order of 20 to 30 feet; however, the final depths will be
dependent on the loads required, building elevations, coupler type, hammer size, and soil
conditions during pile driving.
Pipe piles should consist of Schedule 40 galvanized steel with mechanical couplers for splices.
Battered piles may be necessary to provide lateral support to the structures.
The number of piles required depends on the magnitude of the design load. Allowable axial
compression capacities of 6, 10, and 15 tons may be used for the 3-, 4-, and 6-inch diameter pin
piles, respectively, with an approximate factor of safety of 2 for piles driven to refusal. Penetration
resistance required to achieve the (refusal) capacities will be determined based on the hammer
used to install the pile. Tensile capacity of pin piles should be ignored in design calculations.
It is our experience that the driven pipe pile foundations should provide adequate support with
total settlements on the order of 1/2-inch or less.
Updated August 8, 2025
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For 3-, 4-, and 6-inch pin piles, the following table is a summary of driving refusal criteria for
different hammer sizes that are commonly used:
Hammer
Model
Hammer
Weight (lb) /
Blows per
minute
3” Pile Refusal
Criteria
(s/inch
penetration)
4” Pile Refusal
Criteria
(s/inch
penetration)
6” Pile Refusal
Criteria
(s/inch
penetration)
Hydraulic
TB 325 850 / 900 10 16
Hydraulic
TB 425 1,100 / 900 6 10 20
Hydraulic
TB 725X 2,000 / 600 3 4 10
Hydraulic
TB 830X 3,000 / 500 6
Please note that these refusal criteria were established empirically based on previous load tests on
3-, 4-, and 6-inch pin piles. Contractors may select a different hammer for driving these piles and
propose a different driving criterion. In this case, it is the contractor’s responsibility to
demonstrate to the geotechnical engineer’s satisfaction that the design load can be achieved based
on their selected equipment and driving criteria.
Load testing of at least 3 percent of the piles should be performed (one pile minimum) if required
by the permitting authority. The load test should be performed in 25 percent increments of the
design load up to 200 percent. Deflections should be measured with dial gauges to determine
suitability.
A passive pressure of 250 pcf may be used in the design, neglecting the upper 12 inches. Any fill
used to create the passive resistance should be compacted as structural fill. Battered piles could
be considered to increase passive resistance, if required. A typical batter is 1H:6H.
A structural engineer shall perform the structural design of the pile including spacing and
reinforcing steel. The structural engineer also should determine the buckling load for the slender
piles and make sure that is not exceeded.
Slab-on-Grade
If the owner accepts some risk of settlement over time, a minimum depth of overexcavation,
geotextile placement, and structural fill replacement may be suitable to support new slab areas.
We recommend that the areas be overexcavated 12 inches below subgrade followed by
replacement with 1-1/4 to 2 inch minus crushed rock placed on Tensar TX150 geogrid.
If unstable soils are present at the 1-foot overexcavation depth during construction, we should be
notified so that we may provide location specific recommendations. We should be notified of the
planned loads so that we may provide specific recommendations.
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Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor
barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture
typically requires the usage of a vapor barrier. A materials or structural engineer should be
consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs
typically do not utilize vapor barriers.
The American Concrete Institutes ACI 360R-06 Design of Slabs on Grade and ACI 302.1R-04
Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier
selection and floor slab detailing.
Slabs on grade may be designed using a coefficient of subgrade reaction of 150 pounds per cubic
inch (pci) assuming the slab-on-grade base course is underlain by structural fill placed and
compacted as outlined above. A 4- to 6-inch-thick capillary break layer should be placed over the
prepared subgrade. This material should consist of pea gravel or 5/8 inch clean angular rock.
A perimeter drainage system is recommended unless interior slab areas are elevated a minimum
of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should
consist of a 4-inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain
rock wrapped in a non-woven geosynthetic filter fabric to reduce migration of soil particles into
the drainage system. The perimeter drainage system should discharge by gravity flow to a
suitable stormwater system.
Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate
surface water flow away from the building and preferably with a relatively impermeable surface
cover immediately adjacent to the building.
Stormwater Management Feasibility
The site is underlain by fill and at depth by coarse grained alluvium. Infiltration is suitable in the
alluvial soil deposits. Groundwater was not encountered in the explorations. Groundwater may
become perched about 17 to 18 feet below grade during winter months. It would be necessary to
install monitoring wells to confirm/determine fluctuations and seasonal high levels.
Upon application of King County SWDM and City of Renton Stormwater Manual correction
factors of 0.5 for testing, 1.0 for geometry (can be modified by civil engineer for system shape),
and 0.8 for plugging, the design rate is 7.5 inches per hour. This may be adjusted by the civil
engineer for geometry.
Systems could also be designed using the Coarse Sand or Gravel designation from the King
County SWDM and Renton manual.
Any fine grained soils or interbeds of fine grained soils must be removed prior to rock placement.
We should verify soil conditions during excavation work.
We should be provided with final plans for review to determine if the intent of our
recommendations has been incorporated or if additional modifications are needed. Verification
testing of infiltration systems should be performed during construction by the geotechnical
engineer.
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Erosion and Sediment Control
Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to
wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment
control measures should be implemented, and these measures should be in general accordance
with local regulations. At a minimum, the following basic recommendations should be
incorporated into the design of the erosion and sediment control features for the site:
Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance
of the site soils, to take place during the dry season (generally May through September).
However, provided precautions are taken using Best Management Practices (BMP’s), grading
activities can be completed during the wet season (generally October through April).
All site work should be completed and stabilized as quickly as possible.
Additional perimeter erosion and sediment control features may be required to reduce the
possibility of sediment entering the surface water. This may include additional silt fences, silt
fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration
systems.
Any runoff generated by dewatering discharge should be treated through construction of a
sediment trap if there is sufficient space. If space is limited other filtration methods will need
to be incorporated.
Utilities
Utility trenches should be excavated according to accepted engineering practices following OSHA
(Occupational Safety and Health Administration) standards, by a contractor experienced in such
work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent
to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be
avoided. Depending upon the location and depth of some utility trenches, groundwater flow into
open excavations could be experienced, especially during or shortly following periods of
precipitation.
In general, sandy and gravelly soils were encountered at shallow depths in the explorations at this
site. These soils have low cohesion and density and will have a tendency to cave or slough in
excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations
greater than 4 feet deep.
All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility
trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at
least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5
feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent
of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench
backfill in pavement areas should be compacted to at least 90 percent of the maximum dry
density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe
manufacturer's recommendations.
The contractor is responsible for removing all water-sensitive soils from the trenches regardless of
the backfill location and compaction requirements. Depending on the depth and location of the
proposed utilities, we anticipate the need to re-compact existing fill soils below the utility
structures and pipes. The contractor should use appropriate equipment and methods to avoid
damage to the utilities and/or structures during fill placement and compaction procedures.
Updated August 8, 2025
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Flexible connections for utilities could be utilized to reduce the risk of static consolidation of fill
and/or settlement associated with liquefaction. These would typically be located near the
buildings to allow movement of the exterior areas. The buildings will be supported by piles and
not apt to have significant movement while the exterior areas may experience settlement.
Pavements
The near surface subgrade soils generally consist of sand trace to with silt and gravel. These soils
are rated as fair to poor for pavement subgrade material (depending on silt content and moisture
conditions). We estimate that the subgrade will have a California Bearing Ratio (CBR) value of 10
and a modulus of subgrade reaction value of k = 200 pci, provided the subgrade is prepared in
general accordance with our recommendations.
We recommend that at a minimum, 18 inches of the existing subgrade material be moisture
conditioned (as necessary) and re-compacted to prepare for the construction of pavement
sections. Deeper levels of recompaction or overexcavation and replacement may be necessary in
areas where fill and/or very poor (soft/loose) soils are present. Note that re-compaction may not
be possible unless the soils are aerated and dried to the proper moisture levels. Overexcavation
will likely be the most suitable method of mitigation.
If the work occurs during the wet season, additional overexcavation could be required as soils
typically degrade more rapidly in wet weather conditions.
The subgrade should be compacted to at least 95 percent of the maximum dry density as
determined by ASTM Test Method D1557. In place density tests should be performed to verify
proper moisture content and adequate compaction. If unstable soils are present prior to fill
placement for the sections, we should be notified so that we may provide location specific
recommendations. These could include additional overexcavation or stabilization with geotextiles.
The recommended flexible and rigid pavement sections are based on design CBR and modulus of
subgrade reaction (k) values that are achieved, only following proper subgrade preparation. It
should be noted that subgrade soils that have relatively high silt contents will likely be highly
sensitive to moisture conditions. The subgrade strength and performance characteristics of a silty
subgrade material may be dramatically reduced if this material becomes wet.
Based on our knowledge of the proposed project, we expect the traffic to range from light duty
(passenger automobiles) to heavy duty (delivery trucks, forklifts). The following tables show the
recommended pavement sections for light duty and heavy duty use.
ASPHALTIC CONCRETE (FLEXIBLE) PAVEMENT
LIGHT DUTY
Asphaltic Concrete Aggregate Base* Compacted Subgrade* **
2.5 in. 6.0 in. 18.0 in.
Updated August 8, 2025
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HEAVY DUTY
Asphaltic Concrete Aggregate Base* Compacted Subgrade* **
3.5 in. 6.0 in. 18.0 in.
PORTLAND CEMENT CONCRETE (RIGID) PAVEMENT
Min. PCC Depth Aggregate Base* Compacted Subgrade* **
6.0 in. 6.0 in. 18.0 in.
* 95% compaction based on ASTM Test Method D1557
** A proof roll may be performed in lieu of in place density tests
The asphaltic concrete depth in the flexible pavement tables should be a surface course type
asphalt, such as Washington Department of Transportation (WSDOT) ½ inch HMA. The rigid
pavement design is based on a Portland Cement Concrete (PCC) mix that has a 28 day
compressive strength of 4,000 pounds per square inch (psi). The design is also based on a
concrete flexural strength or modulus of rupture of 550 psi.
CONSTRUCTION FIELD REVIEWS
Cobalt Geosciences should be retained to provide part time field review during construction in
order to verify that the soil conditions encountered are consistent with our design assumptions
and that the intent of our recommendations is being met. This will require field and engineering
review to:
Monitor and test structural fill placement and soil compaction
Verify foundation support system placement and load testing (pin piles)
Observe slab-on-grade preparation
Monitor foundation drainage placement
Observe excavation stability
Geotechnical design services should also be anticipated during the subsequent final design phase
to support the structural design and address specific issues arising during this phase. Field and
engineering review services will also be required during the construction phase in order to
provide a Final Letter for the project.
CLOSURE
This report was prepared for the exclusive use of Faisal Muhammad and his appointed
consultants. Any use of this report or the material contained herein by third parties, or for other
than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC.
The recommendations contained in this report are based on assumed continuity of soils with
those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with
final architectural and civil drawings when they become available in order that we may review our
design recommendations and advise of any revisions, if necessary.
Updated August 8, 2025
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Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is
the responsibility of Faisal Muhammad who is identified as “the Client” within the Statement of
General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences
should any of these not be satisfied.
Sincerely,
Cobalt Geosciences, LLC
8/8/2025
Phil Haberman, PE, LG, LEG
Principal
Updated August 8, 2025
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Statement of General Conditions
USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its
agent and may not be used by any third party without the express written consent of Cobalt
Geosciences and the Client. Any use which a third party makes of this report is the responsibility
of such third party.
BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this
report are in accordance with Cobalt Geosciences present understanding of the site specific
project as described by the Client. The applicability of these is restricted to the site conditions
encountered at the time of the investigation or study. If the proposed site specific project differs
or is modified from what is described in this report or if the site conditions are altered, this report
is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the
report to reflect the differing or modified project specifics and/or the altered site conditions.
STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in
accordance with the normally accepted standard of care in the state of execution for the specific
professional service provided to the Client. No other warranty is made.
INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and
statements regarding their condition, made in this report are based on site conditions
encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or
sampling locations. Classifications and statements of condition have been made in accordance
with normally accepted practices which are judgmental in nature; no specific description should
be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in
situ conditions can only be made to some limited extent beyond the sampling or test points. The
extent depends on variability of the soil, rock and groundwater conditions as influenced by
geological processes, construction activity, and site use.
VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be
encountered that are different from those described in this report or encountered at the test
locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected
conditions are substantial and if reassessments of the report conclusions or recommendations are
required. Cobalt Geosciences will not be responsible to any party for damages incurred as a result
of failing to notify Cobalt Geosciences that differing site or sub-surface conditions are present
upon becoming aware of such conditions.
PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and
specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next
project stage (property acquisition, tender, construction, etc), to confirm that this report
completely addresses the elaborated project specifics and that the contents of this report have
been properly interpreted. Specialty quality assurance services (field observations and testing)
during construction are a necessary part of the evaluation of sub-subsurface conditions and site
preparation works. Site work relating to the recommendations included in this report should only
be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be
responsible for site work carried out without being present.
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
SITE MAP
FIGURE 1
N
Proposed Development
4108 Jones Avenue NE
Renton, Washington
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
SITE
PLAN
FIGURE 2
Proposed Development
4108 Jones Avenue NE
Renton, Washington
Attachment
Cobalt Geosciences, LLC
PO Box 1792
North Bend, WA 98045
(206) 331-1097
www.cobaltgeo.com
phil@cobaltgeo.com
PT
Well-graded gravels, gravels, gravel-sand mixtures, little or no fines
Poorly graded gravels, gravel-sand mixtures, little or no fines
Silty gravels, gravel-sand-silt mixtures
Clayey gravels, gravel-sand-clay mixtures
Well-graded sands, gravelly sands, little or no fines
COARSE
GRAINED
SOILS
(more than 50%
retained on
No. 200 sieve)
Primarily organic matter, dark in color,
and organic odor Peat, humus, swamp soils with high organic content (ASTM D4427)HIGHLY ORGANIC
SOILS
FINE GRAINED
SOILS
(50% or more
passes the
No. 200 sieve)
MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION
Gravels
(more than 50%
of coarse fraction
retained on No. 4
sieve)
Sands
(50% or more
of coarse fraction
passes the No. 4
sieve)
Silts and Clays
(liquid limit less
than 50)
Silts and Clays
(liquid limit 50 or
more)
Organic
Inorganic
Organic
Inorganic
Sands with
Fines
(more than 12%
fines)
Clean Sands
(less than 5%
fines)
Gravels with
Fines
(more than 12%
fines)
Clean Gravels
(less than 5%
fines)
Unified Soil Classification System (USCS)
Poorly graded sand, gravelly sands, little or no fines
Silty sands, sand-silt mixtures
Clayey sands, sand-clay mixtures
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
or clayey silts with slight plasticity
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays,
silty clays, lean clays
Organic silts and organic silty clays of low plasticity
Inorganic silts, micaceous or diatomaceous fine sands or silty soils,
elastic silt
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
Organic clays of medium to high plasticity, organic silts
Moisture Content Definitions
Grain Size Definitions
Dry Absence of moisture, dusty, dry to the touch
Moist Damp but no visible water
Wet Visible free water, from below water table
Grain Size Definitions
Description Sieve Number and/or Size
Fines <#200 (0.08 mm)
Sand
-Fine
-Medium
-Coarse
Gravel
-Fine
-Coarse
Cobbles
Boulders
#200 to #40 (0.08 to 0.4 mm)
#40 to #10 (0.4 to 2 mm)
#10 to #4 (2 to 5 mm)
#4 to 3/4 inch (5 to 19 mm)
3/4 to 3 inches (19 to 76 mm)
3 to 12 inches (75 to 305 mm)
>12 inches (305 mm)
Classification of Soil Constituents
MAJOR constituents compose more than 50 percent,
by weight, of the soil. Major constituents are capitalized
(i.e., SAND).
Minor constituents compose 12 to 50 percent of the soil
and precede the major constituents (i.e., silty SAND).
Minor constituents preceded by “slightly” compose
5 to 12 percent of the soil (i.e., slightly silty SAND).
Trace constituents compose 0 to 5 percent of the soil
(i.e., slightly silty SAND, trace gravel).
Relative Density Consistency
(Coarse Grained Soils) (Fine Grained Soils)
N, SPT, Relative
Blows/FT Density
0 - 4 Very loose
4 - 10 Loose
10 - 30 Medium dense
30 - 50 Dense
Over 50 Very dense
N, SPT, Relative
Blows/FT Consistency
Under 2 Very soft
2 - 4 Soft
4 - 8 Medium stiff
8 - 15 Stiff
15 - 30 Very stiff
Over 30 Hard
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Soil Classification Chart Figure C1
Grass/Topsoil
Log of Boring B- 1
Date: September 29, 2023
Contractor: Geologic
Method: Hollow Stem Auger
Depth: 2 ’ 0.5
Elevation: N/A
Logged By: Checked By: KK PH
Initial Groundwater: None
Sample Type: Split Spoon
Final Groundwater: None
Material Description
SPT N-Value
Moisture Content (%)Plastic
Limit
Liquid
Limit
10 20 30 400 50
2
4
6
8
10
12
14
16
18
Medium dense becoming loose fine to medium , grained sand with
gravel, dark yellowish brown,
dry to moist.
(Fill)
SP
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Proposed Development
4108 Jones Avenue NE
Renton, Washington
Boring
Log
8
11
8
3
5
3
5
2
1
Loose to medium dense, gravel with sand trace silt,
Alluviumyellowish brown to grayish brown to yellowish brown, moist. ( )
End of Boring 20.5’ Refusal in dense soils
20
22
24
26
28
11
15
17
50/5
GP
30
SP Dense to very dense, fine to medium grained sand trace
to with gravel, grayish brown to olive gray, moist.
(Advance Outwash?)
Log of Boring B- 2
Date: September 29, 2023
Contractor: Geologic
Method: Hollow Stem Auger
Depth: 2 ’ 0.5
Elevation: N/A
Logged By: Checked By: KK PH
Initial Groundwater: None
Sample Type: Split Spoon
Final Groundwater: None
Material Description
SPT N-Value
Moisture Content (%)Plastic
Limit
Liquid
Limit
10 20 30 400 50
2
4
6
8
10
12
14
16
18
Medium dense becoming loose fine to medium , grained sand with
gravel, dark yellowish brown,
dry to moist.
(Fill)
SP
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Proposed Development
4108 Jones Avenue NE
Renton, Washington
Boring
Log
7
5
5
4
5
5
8
6
4
Loose to medium dense, gravel with sand trace silt,
Alluviumyellowish brown to grayish brown to yellowish brown, moist. ( )
End of Boring 20.5’ Refusal in dense soils
20
22
24
26
28
13
20
30
50/5
GP
30
SP Dense to very dense, fine to medium grained sand trace
to with gravel, grayish brown to olive gray, moist.
(Advance Outwash?)
SPT BASED LIQUEFACTION ANALYSIS REPORT
:: Input parameters and analysis properties ::
Analysis method:
Fines correction method:
Sampling method:
Borehole diameter:
Rod length:
Hammer energy ratio:
NCEER 1998
NCEER 1998
Standard Sampler
65mm to 115mm
3.30 ft
1.00
G.W.T. (in-situ):
G.W.T. (earthq.):
Earthquake magnitude M w:
Peak ground acceleration:
Eq. external load:
Project title : Jones Ave NE
Location : Renton WA
SPT Name: SPT #1
30.00 ft
17.00 ft
7.50
0.70 g
0.00 tsf
Raw SPT Data
SPT Count (blows/ft)
5 04 03 02 01 00
D
e
p
t
h
(
f
t
)
2 1
2 0
1 9
1 8
1 7
1 6
1 5
1 4
1 3
1 2
1 1
1 0
9
8
7
6
5
4
3
2
1
0
Raw SPT Data
Insitu
CSR - CRR Plot
CSR - CRR
10. 80. 60. 40. 20
D
e
p
t
h
(
f
t
)
2 0
1 9
1 8
1 7
1 6
1 5
1 4
1 3
1 2
1 1
1 0
9
8
7
6
5
4
3
2
1
CSR - CRR Plot
During earthq.
FS Plot
Factor of Safety
210
D
e
p
t
h
(
f
t
)
2 0
1 9
1 8
1 7
1 6
1 5
1 4
1 3
1 2
1 1
1 0
9
8
7
6
5
4
3
2
1
FS Plot
During earthq.
LPI
Liquefaction potential
0
D
e
p
t
h
(
f
t
)
2 0
1 9
1 8
1 7
1 6
1 5
1 4
1 3
1 2
1 1
1 0
9
8
7
6
5
4
3
2
1
LPI
During earthq.
CRR 7.50 clean sand curve
Corrected Blow Count N1(60),cs
5 04 54 03 53 02 52 01 51 050
C
y
c
l
i
c
S
t
r
e
s
s
R
a
t
i
o
*
0. 8
0. 7
0. 6
0. 5
0. 4
0. 3
0. 2
0. 1
0. 0
CRR 7.50 clean sand curve
Liquefaction
No Liquefaction
F.S. color scheme
Almost certain it will liquefy
Very likely to liquefy
Liquefaction and no liq. are equally likely
Unlike to liquefy
Almost certain it will not liquefy
LPI color scheme
Very high risk
High risk
Low risk
Project File:
Page: 1LiqSVs 1.3.3.1 - SPT & Vs Liquefaction Assessment Software
This software is registered to: Cobalt Geosciences
Raw SPT Data
SPT Count (blows/ft)
5 04 03 02 01 00
D
e
p
t
h
(
f
t
)
2 1
2 0
1 9
1 8
1 7
1 6
1 5
1 4
1 3
1 2
1 1
1 0
9
8
7
6
5
4
3
2
1
0
Raw SPT Data
Insitu
CSR - CRR Plot
CSR - CRR
10. 80. 60. 40. 20
D
e
p
t
h
(
f
t
)
2 0
1 9. 5
1 9
1 8. 5
1 8
1 7. 5
1 7
1 6. 5
1 6
1 5. 5
1 5
1 4. 5
1 4
1 3. 5
1 3
1 2. 5
1 2
1 1. 5
1 1
1 0. 5
1 0
9. 5
9
8. 5
8
7. 5
7
6. 5
6
5. 5
5
4. 5
4
3. 5
3
2. 5
2
1. 5
1
CSR - CRR Plot
During earthq.
FS Plot
Factor of Safety
210
D
e
p
t
h
(
f
t
)
2 0
1 9. 5
1 9
1 8. 5
1 8
1 7. 5
1 7
1 6. 5
1 6
1 5. 5
1 5
1 4. 5
1 4
1 3. 5
1 3
1 2. 5
1 2
1 1. 5
1 1
1 0. 5
1 0
9. 5
9
8. 5
8
7. 5
7
6. 5
6
5. 5
5
4. 5
4
3. 5
3
2. 5
2
1. 5
1
FS Plot
During earthq.
Vertical Liq. Settlements
Cuml. Settlement (in)
0
D
e
p
t
h
(
f
t
)
2 0
1 9. 5
1 9
1 8. 5
1 8
1 7. 5
1 7
1 6. 5
1 6
1 5. 5
1 5
1 4. 5
1 4
1 3. 5
1 3
1 2. 5
1 2
1 1. 5
1 1
1 0. 5
1 0
9. 5
9
8. 5
8
7. 5
7
6. 5
6
5. 5
5
4. 5
4
3. 5
3
2. 5
2
1. 5
1
Vertical Liq. Settlements
During earthq.
Lateral Liq. Displacements
Cuml. Displacement (ft)
0
D
e
p
t
h
(
f
t
)
2 0
1 9. 5
1 9
1 8. 5
1 8
1 7. 5
1 7
1 6. 5
1 6
1 5. 5
1 5
1 4. 5
1 4
1 3. 5
1 3
1 2. 5
1 2
1 1. 5
1 1
1 0. 5
1 0
9. 5
9
8. 5
8
7. 5
7
6. 5
6
5. 5
5
4. 5
4
3. 5
3
2. 5
2
1. 5
1
Lateral Liq. Displacements
During earthq.
:: Overall Liquefaction Assessment Analysis Plots ::
Project File:
Page: 2LiqSVs 1.3.3.1 - SPT & Vs Liquefaction Assessment Software
This software is registered to: Cobalt Geosciences
Test
Depth
(ft)
:: Field input data ::
SPT Field
Value
(blows)
Fines
Content
(%)
Unit
Weight
(pcf)
Infl.
Thickness
(ft)
Can
Liquefy
1.00 19 0.00 110.00 4.00 Yes
5.00 3 0.00 110.00 5.00 Yes
10.00 8 0.00 110.00 5.00 Yes
15.00 32 0.00 110.00 5.00 Yes
20.00 50 0.00 115.00 5.00 Yes
Abbreviations
Depth:
SPT Field Value:
Fines Content:
Unit Weight:
Infl. Thickness:
Can Liquefy:
Depth at which test was performed (ft)
Number of blows per foot
Fines content at test depth (%)
Unit weight at test depth (pcf)
Thickness of the soil layer to be considered in settlements analysis (ft)
User defined switch for excluding/including test depth from the analysis procedure
:: Cyclic Resistance Ratio (CRR) calculation data ::
CRR 7.5Depth
(ft)
SPT
Field
Value
CN CE CB CR C S (N 1)60 (N 1)60csαβFines
Content
(%)
σ v
(tsf)
u o
(tsf)
σ'vo
(tsf)
Unit
Weight
(pcf)
1.00 19 1.70 1.00 1.00 0.75 1.00 24 0.00 1.00 24 4.0000.00110.00 0.06 0.00 0.06
5.00 3 1.51 1.00 1.00 0.75 1.00 3 0.00 1.00 3 4.0000.00110.00 0.28 0.00 0.28
10.00 8 1.28 1.00 1.00 0.85 1.00 9 0.00 1.00 9 4.0000.00110.00 0.55 0.00 0.55
15.00 32 1.11 1.00 1.00 0.85 1.00 30 0.00 1.00 30 4.0000.00110.00 0.82 0.00 0.82
20.00 50 0.98 1.00 1.00 0.95 1.00 46 0.00 1.00 46 4.0000.00115.00 1.11 0.00 1.11
σ v:
u o:
σ'vo:
CN:
CE:
CB:
CR:
CS:
N1(60):
α, β:
N1(60)cs:
CRR7.5:
Total stress during SPT test (tsf)
Water pore pressure during SPT test (tsf)
Effective overburden pressure during SPT test (tsf)
Overburden corretion factor
Energy correction factor
Borehole diameter correction factor
Rod length correction factor
Liner correction factor
Corrected N SPT to a 60% energy ratio
Clean sand equivalent clean sand formula coefficients
Corected N1(60) value for fines content
Cyclic resistance ratio for M=7.5
Abbreviations
σ v,eq
(tsf)
r d CSR MSF CSR eq,M=7.5 K sigma CSR *
:: Cyclic Stress Ratio calculation (CSR fully adjusted and normalized) ::
Depth
(ft)
Unit
Weight
(pcf)
u o,eq
(tsf)
σ'vo,eq
(tsf)
FSα
1.00 110.00 0.06 0.00 0.06 1.00 0.455 1.00 0.455 1.00 0.455 2.0001.00
5.00 110.00 0.28 0.00 0.28 0.99 0.451 1.00 0.451 1.00 0.451 2.0001.00
10.00 110.00 0.55 0.00 0.55 0.98 0.446 1.00 0.446 1.00 0.446 2.0001.00
15.00 110.00 0.82 0.00 0.82 0.97 0.441 1.00 0.441 1.00 0.441 2.0001.00
20.00 115.00 1.11 0.09 1.02 0.96 0.475 1.00 0.476 1.00 0.476 2.0001.00
Project File:
Page: 3LiqSVs 1.3.3.1 - SPT & Vs Liquefaction Assessment Software
This software is registered to: Cobalt Geosciences
σ v,eq
(tsf)
r d CSR MSF CSR eq,M=7.5 K sigma CSR *
:: Cyclic Stress Ratio calculation (CSR fully adjusted and normalized) ::
Depth
(ft)
Unit
Weight
(pcf)
u o,eq
(tsf)
σ'vo,eq
(tsf)
FSα
σv,eq:
uo,eq:
σ'vo,eq:
rd :
α:
CSR :
MSF :
CSR eq,M=7.5:
Ksigma:
CSR *:
FS:
Total overburden pressure at test point, during earthquake (tsf)
Water pressure at test point, during earthquake (tsf)
Effective overburden pressure, during earthquake (tsf)
Nonlinear shear mass factor
Improvement factor due to stone columns
Cyclic Stress Ratio (adjusted for improvement)
Magnitude Scaling Factor
CSR adjusted for M=7.5
Effective overburden stress factor
CSR fully adjusted (user FS applied)***
Calculated factor of safety against soil liquefaction
Abbreviations
1.00*** User FS:
:: Liquefaction potential according to Iwasaki ::
Depth
(ft)
FS F Thickness
(ft)
wz IL
1.00 2.000 0.00 9.85 0.004.00
5.00 2.000 0.00 9.24 0.004.00
10.00 2.000 0.00 8.48 0.005.00
15.00 2.000 0.00 7.71 0.005.00
20.00 2.000 0.00 6.95 0.005.00
0.00
IL = 0.00 - No liquefaction
IL between 0.00 and 5 - Liquefaction not probable
IL between 5 and 15 - Liquefaction probable
IL > 15 - Liquefaction certain
Overall potential I L :
:: Vertical settlements estimation for dry sands ::
Depth
(ft)
(N 1)60 τav p Gmax
(tsf)
α b γ ε 15 Nc εNc
(%)
ΔS
(in)
Δh
(ft)
1.00 24 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0004.00
5.00 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0005.00
10.00 9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0005.00
15.00 30 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0005.00
Abbreviations
τav:
p:
Gmax:
α, b:
γ:
ε15:
Nc:
εNc:
Δh:
ΔS:
Average cyclic shear stress
Average stress
Maximum shear modulus (tsf)
Shear strain formula variables
Average shear strain
Volumetric strain after 15 cycles
Number of cycles
Volumetric strain for number of cycles Nc (%)
Thickness of soil layer (in)
Settlement of soil layer (in)
0.000Cumulative settlemetns:
Project File:
Page: 4LiqSVs 1.3.3.1 - SPT & Vs Liquefaction Assessment Software
This software is registered to: Cobalt Geosciences
:: Vertical settlements estimation for saturated sands ::
Depth
(ft)
D 50
(in)
q c/N e v
(%)
Δh
(ft)
s
(in)
20.00 0.01 2.10 0.00 5.00 0.000
Abbreviations
0.000Cumulative settlements:
D50:
qc/N:
ev:
Δh:
s:
Median grain size (in)
Ratio of cone resistance to SPT
Post liquefaction volumetric strain (%)
Thickness of soil layer to be considered (ft)
Estimated settlement (in)
:: Lateral displacements estimation for saturated sands ::
Depth
(ft)
(N 1)60 Dr
(%)
γ max
(%)
dz
(ft)
LDI LD
(ft)
1.00 24 68.59 0.00 4.00 0.000 0.00
5.00 3 24.25 0.00 5.00 0.000 0.00
10.00 9 42.00 0.00 5.00 0.000 0.00
15.00 30 76.68 0.00 5.00 0.000 0.00
20.00 46 100.00 0.00 5.00 0.000 0.00
0.00
Abbreviations
Cumulative lateral displacements:
Dr:
γmax:
dz:
LDI:
LD:
Relative density (%)
Maximum amplitude of cyclic shear strain (%)
Soil layer thickness (ft)
Lateral displacement index (ft)
Actual estimated displacement (ft)
Project File:
Page: 5LiqSVs 1.3.3.1 - SPT & Vs Liquefaction Assessment Software
References
⦁ Ronald D. Andrus, Hossein Hayati, Nisha P. Mohanan, 2009. Correcting Liquefaction Resistance for Aged Sands Using Measured
to Estimated Velocity Ratio, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 135, No. 6, June 1
⦁ Boulanger, R.W. and Idriss, I. M., 2014. CPT AND SPT BASED LIQUEFACTION TRIGGERING PROCEDURES. DEPARTMENT OF
CIVIL & ENVIRONMENTAL ENGINEERING COLLEGE OF ENGINEERING UNIVERSITY OF CALIFORNIA AT DAVIS
⦁ Dipl.-Ing. Heinz J. Priebe, Vibro Replacement to Prevent Earthquake Induced Liquefaction, Proceedings of the Geotechnique-
Colloquium at Darmstadt, Germany, on March 19th, 1998 (also published in Ground Engineering, September 1998), Technical
paper 12-57E
⦁ Robertson, P.K. and Cabal, K.L., 2007,Guide to Cone Penetration Testing for Geotechnical Engineering. Available at no cost at
http://www.geologismiki.gr/
⦁ Youd, T.L., Idriss, I.M., Andrus, R.D., Arango, I., Castro, G., Christian, J.T., Dobry, R., Finn, W.D.L., Harder, L.F., Hynes , M.E.,
Ishihara, K., Koester, J., Liao, S., Marcuson III, W.F., Martin, G.R., Mitchell, J.K., Moriwaki, Y., Power, M.S., Robertson, P.K.,
Seed, R., and Stokoe, K.H., Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF
Workshop on Evaluation of Liquefaction Resistance of Soils, ASCE, Journal of Geotechnical & Geoenvironmental Engineering,
Vol. 127, October, pp 817-833
⦁ Zhang, G., Robertson. P.K., Brachman, R., 2002, Estimating Liquefaction Induced Ground Settlements from the CPT, Canadian
Geotechnical Journal, 39: pp 1168-1180
⦁ Zhang, G., Robertson. P.K., Brachman, R., 2004, Estimating Liquefaction Induced Lateral Displacements using the SPT and CPT,
ASCE, Journal of Geotechnical & Geoenvironmental Engineering, Vol. 130, No. 8, 861 -871
⦁ Pradel, D., 1998, Procedure to Evaluate Earthquake-Induced Settlements in Dry Sandy Soils, ASCE, Journal of Geotechnical &
Geoenvironmental Engineering, Vol. 124, No. 4, 364-368
⦁ R. Kayen, R. E. S. Moss, E. M. Thompson, R. B. Seed, K. O. Cetin, A. Der Kiureghian, Y. Tanaka, K. Tokimatsu, 2013. Shear-
Wave Velocity–Based Probabilistic and Deterministic Assessment of Seismic Soil Liquefaction Potential, Journal of Geotechnical
and Geoenvironmental Engineering, Vol. 139, No. 3, March 1
LiqSVs 1.3.3.1 - SPT & Vs Liquefaction Assessment Software