REVIEWED BLD2023-0460+GEO REPORT+4.12.2023_4.55.29_PM+3480102GEOTECHNICAL ENGINEERING REPORT
1 :11IN1104911 L[:Y11
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Reviewed by ;
City of Edmonds ;
Planning Division
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Prepared for:
RECEIVED
Apr 14 2023
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
Erika and Trevor Hill
PmGE&
I N C O R P O R A T E D
3213 Eastlake Avenue East
Seattle, Washington 98102
Tel: 206.262.0370 Fax: 206.262.0374
PROPOSED REMODELING
931 CAROL WAY
EDMONDS, WASHINGTON
Project No. 22-354
February 2023
Geotechnical & Earthquake
Engineering Consultants
PanGE0C O R P O R A T E D
Geotechnical & Earthquake
Engineering Consultants
February 9, 2023
Project No. 22-354
Erika and Trevor Hill
931 Carol Way
Edmonds, WA 98020
Subject: Geotechnical Engineering Report
Proposed Remodeling
931 Carol Way, Edmonds, Washington
Dear Erika and Trevor:
As requested, PanGEO Inc. completed a geotechnical engineering study to assist the design team
for the proposed remodeling project at 931 Carol Way in Edmonds, Washington. This study was
performed in general accordance with our mutually agreed scope of work outlined in our
proposal dated August 4, 2022, and subsequently approved by you on August 23, 2022. Our
service scope included reviewing readily available geologic and geotechnical data, drilling three
test borings, conducting a site reconnaissance, performing engineering analysis, and developing
the conclusions and recommendations presented in this report.
SITE AND PROJECT DESCRIPTION
The subject property is an approximately 11,760 square foot lot located at 931 Carol Way in the
City of Edmonds, Washington (see Figure 1, Vicinity Map). The site is rectangular in shape. It is
bordered to the south by Carol Way and to the other three sides by existing single-family
residences. The site is currently occupied by a two-story single-family house. The site grade
generally slopes down from east to west with a vertical relief of about 10 feet and average
gradient of about 10%. The layout of the site is shown on Figure 2, Site and Exploration Plan.
3213 Eastlake Ave E, Ste B
Seattle, WA 98102
Tel (206) 262-0370
Fax (206) 262-0374
Geotechnical Engineering Report - Proposed Remodeling
931 Carol Way, Edmonds, WA
February 9, 2023
�M1 3�'6f
Plate 1. Front view of the existing house. Looking
Plate 2. Rear view of the existing house, deck, and patio.
northwest from Carol Way.
Looking southeast from the northwest property corner.
We understand that the proposed project consists of a major interior remodel. A deck expansion
is planned for the existing desk on the north side of the house with minor grading in the back
yard. A new porch addition is also planned on the south side of the house. According to the City
of Edmonds GIS maps, the site is within an erosion geologic hazard area. As such, a
geotechnical report will be required for the building permit application.
The conclusions and recommendations outlined in this report are based on our understanding of
the proposed improvements, which is in turn based on the project information provided to us. If
the above project description is substantially different from your proposed improvements, or if
the project scope changes, PanGEO should be consulted to review the recommendations
contained in this study and make modifications, if needed.
SITE GEOLOGY
According to the Geologic Map of the Edmonds East Quadrangle (Minard, 1983), the primary
geologic unit in the vicinity of the site is Advance Outwash (Map Unit Qva). Till (Qtu) is
mapped less than one block to the west.
Vashon till (Qvt) typically consists of an unsorted mixture of clay, silt, sand, and gravel
deposited directly below the continental glacier associated with the Vashon Stade of the
Fraser Glaciation. This soil unit has been glacially overridden; as such it is typically dense to
very dense.
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Vashon advance outwash (Qva) typically consists of sand and gravel deposited by meltwater
streams emerging from an advancing glacier. This soil has also been glacially overridden
and is also typically dense to very dense.
SUBSURFACE EXPLORATION AND CONDITIONS
Three borings (PG-1 through PG-3) were drilled at the site on September 6, 2022, using a Bobcat
tracked drill rig operated by Geologic Drill Partners of Fall City, Washington under contract to
PanGEO. The borings were drilled to a maximum depth of about 8 to 161/2 feet below existing
grade. The approximate boring locations were located in the field by measuring from property
corners and site features and are shown on Figure 2.
The test borings were drilled using five -inch outside diameter hollow stem augers. Standard
Penetration Tests (SPT) were performed in the borings at 2%2-foot depth intervals using a
standard, 2-inch diameter split -spoon sampler. The sampler was advanced with a 140-pound
drop hammer falling a distance of 30 inches for each strike, in general accordance with ASTM
D-1586, Standard Test Method for Penetration Test and Split Barrel Sampling of Soils. 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.
A geologist from PanGEO was present during the field explorations to observe the drilling, assist
in sampling, and describe and document the soil samples obtained from the borings. The soil
samples were described using the system outlined on Figure A-1. The summary boring logs are
included in Appendix A as Figures A-2 through A-4.
SOIL
The test borings advanced at the site generally encountered up to about 7 feet of loose fill
overlying medium dense to very dense silty sand with gravel (till). The following is a brief
description of the soils encountered in the test borings drilled at the site. Please refer to the
summary test boring logs in Appendix A for additional details.
UNIT 1: Fill — This soil unit extended to about 7 feet depth at PG-2 but only to about
one foot at PG-1 and PG-3. The fill encountered generally consisted of loose silty sand
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including a surficial layer of topsoil. We interpreted this soil unit as fill based on its loose
condition and disturbed appearance.
UNIT 2: Till (Qtu) — Below the fill, each boring encountered medium dense to very
dense silty sand with gravel that extended to the termination depths of the borings. We
interpreted this soil unit as the nearby mapped till deposits based on its dense condition,
diamict texture, and slight cementation. In each boring the upper 2 to 5 feet of this unit is
weathered to a medium dense condition.
GROUNDWATER
Minor groundwater seepage was observed in boring PG-1 at the depth of about 9 feet, and in
boring PG-2 at depths of about 11 and 16 feet below existing grade during drilling. The
groundwater appeared to be perched above the underlying dense till layer. No groundwater was
not encountered in boring PG-3 within the drilling depth up to about 8 feet deep. It should be
noted that groundwater levels will fluctuate depending on the season, amount of rainfall, surface
water runoff, and other factors. Generally, the water level is higher and seepage rates are greater
in the wetter, winter months (typically October through May).
GEOLOGICALLY HAZARDOUS AREAS ASSESSMENT
Based on a review of the City of Edmonds GIS map and the Edmonds Community Development
Code (ECDC), the east and west portions of the subject site are mapped within an Erosion
Hazard Area. The rockery and slopes along the east and west property lines are considered as a
steep slope (greater than 33% slope).
LANDSLIDE HAZARDS EVALUATION
Based on review of the topographic survey map provided to us and our field observations, the
site generally slopes down from the east to the west with an average slope gradient of about 10
percent. However, the rockery and slope along the east and west property lines, which are up to
approximately 5 feet in height, appear to meet the steep slope definition (33% or greater slopes).
Based on the soil data in the test borings, it is our opinion that this steep slopes are the result of
the previous grading due to street and site development. It is also our opinion that the risk for the
potential future landslide is considered minimum, and the site is not mapped as a landslide
hazard area by the Washington Department of Natural Resources.
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A site reconnaissance of the subject property was conducted on September 6, 2022. During our
site reconnaissance, we did not observe obvious evidence of past slope instability or ground
movement at the subject site. Based on our field observations and the results of subsurface data
at the subject site, in our opinion, the subject site appears to be globally stable in its current
configuration. Furthermore, it is our opinion that the proposed remodeling as currently planned
are feasible from a geotechnical engineering standpoint. It is our further opinion that the
proposed remodeling as currently planned will not adversely affect the overall stability of the site
or adjacent properties, provided the recommendations outlined herein are followed and the
proposed remodeling is properly designed and constructed.
EROSION HAZARDS EVALUATION
According to USDA Soil Conservation Service Map, the site soil is mapped as the Alderwood-
Urban land complex, 8 to 15 percent slopes. Based on the soils encountered in the test borings
and site topography, the near -surface site soils are anticipated to exhibit slight to moderate
erosion potential. However, due to very minor ground disturbance and excavations planned, in
our opinion, the potential erosion hazards at the site can be effectively mitigated with the best
management practice during construction and with properly designed and implemented
landscaping for permanent erosion control. During construction, the temporary erosion hazard
can be effectively managed with an appropriate erosion and sediment control plan, including but
not limited to installing silt fence at the construction perimeter, limiting removal of vegetation to
the construction area, placing rocks or hay bales at the disturbed/traffic areas and on the downhill
side of the project, covering stockpile soil or cut slopes with plastic sheets, constructing a
temporary drainage pond to control surface runoff and sediment trap if needed, placing rocks at
the construction entrance, etc. Permanent erosion control measures should include establishing
vegetation, landscape plants, and hardscape established at the end of project.
23.80.060 DEVELOPMENT STANDARDS — GENERAL REQUIREMENTS
According to ECDC 23.80.060, alterations of geologically hazardous areas or associated buffers
may only occur for activities that:
1. Will not increase the threat of the geological hazard to adjacent properties beyond
predevelopment conditions;
2. Will not adversely impact other critical areas;
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3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to
or less than predevelopment conditions; and
4. Are certified as safe as designed and under anticipated conditions by a qualified engineer
or geologist, licensed in the state of Washington.
Based on the site subsurface information and our understanding of the current plans, it is our
opinion that the proposed project meets the above conditions, and will not have adverse impacts
to the subject and surrounding properties during and after construction, provided that project is
constructed in accordance with the approved plans and commonly accepted practice.
23.80.070 DEVELOPMENT STANDARDS — SPECIFIC HAZARDS
The portions of subject site are mapped as erosion hazard areas. However, based on the soil
conditions and proposed improvements, it is our opinion that building setback and buffer
distance are not required for the currently proposed improvements. ECDC 23.80.070 states that
alterations of an erosion or landslide area hazard area, minimum building setback and/or buffer
may only occur for activities for which a hazards analysis is submitted and certifies that:
a. The alteration will not increase surface water discharge or sedimentation to adjacent
properties beyond predevelopment conditions;
b. The alteration will not decrease slope stability on adjacent properties; and
c. Such alterations will not adversely impact other critical areas.
In our opinion, the proposed improvements as currently planned meet the above conditions.
GEOLOGIC HAZARDS MITIGATIONS
Based on the results of our evaluation of the potential geologic hazards at the site, it is our
opinion that no specific mitigation, other than the erosion measure discussed above, is required
for the proposed improvements.
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GEOTECHNICAL DESIGN RECOMMENDATIONS
SEISMIC SITE CLASS
We anticipate that the seismic design of the structures will be accomplished using the 2018
editions of the International Building Code (IBC), which specifies a design earthquake having a
2% probability of occurrence in 50 years (return interval of 2,475 years). Based on site soil
conditions, it is our opinion that Site Class D (stiff soils) should be used for this project.
CONVENTIONAL FOOTINGS
Based on the subsurface conditions encountered at the site and our understanding of the planned
remodeling, it is our opinion that the proposed deck on the north side of the building may be
supported on conventional footings. The footings should bear on medium dense to dense native
soils or on properly compacted structural fill placed on competent native soils.
Based on the boring PG-2, approximately seven feet of surficial loose fill was encountered near
the proposed porch addition on the south side of the house. As such, about five feet of over -
excavation may be required to remove the existing fill and reach the bearing soils below the
proposed porch addition. Alternatively, pin piles may be considered to support the proposed
porch addition in lieu of over -excavation.
Soil Bearing Pressure
We recommend that an allowable soil bearing pressure of 2,500 pounds per square foot (psf) be
used to size the footings, bearing on the competent native soils or structural fill/lean-mix
concrete placed on the competent native soils. The recommended allowable bearing pressure is
for dead plus live loads. For allowable stress design, the recommended bearing pressure may be
increased by one-third for transient loading, such as wind or seismic forces. Continuous and
individual spread footings should have minimum widths of 18 and 24 inches, respectively.
Exterior foundation elements should be placed at a minimum depth of 18 inches below final
exterior grade. Interior spread foundations should be placed at a minimum depth of 12 inches
below the top of slab.
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Foundation Performance
Footings designed and constructed in accordance with the above recommendations should
experience total settlement of less than one inch and differential settlement of about %2 inch.
Most of the anticipated settlement should occur during construction as dead loads are applied.
Lateral Resistance
Lateral loads on the structures may be resisted by passive earth pressure developed against the
embedded faces of the foundation system and by frictional resistance between the bottom of the
foundation and the supporting subgrade soils. For footings bearing on the firm native soil or
compacted structural fill, a frictional coefficient of 0.35 may be used to evaluate sliding
resistance developed between the concrete and the compacted subgrade soil. Passive soil
resistance may be calculated using an equivalent fluid weight of 320 pcf, assuming properly
compacted structural fill will be placed against the footings. The above values include a factor of
safety of 1.5. Unless covered by pavements or slabs, the passive resistance in the upper 12 inches
of soil should be neglected.
Perimeter Footing Drains
Footing drains, if needed, should be installed around the building perimeters, at or just below the
invert of the footings. Under no circumstances should roof downspout drain lines be connected
to the footing drain systems. Roof downspouts must be separately tightlined to appropriate
discharge locations. Cleanouts should be installed at strategic locations to allow for periodic
maintenance of the footing drain and downspout tightline systems.
Footing Subgrade Preparation
All footing subgrades should be in a firm and unyielding condition prior to setting forms and
placing rebar. Any loose or softened soil should be removed from the footing excavations. The
adequacy of the footing subgrade soils should be verified by a representative of PanGEO, prior
to placing forms or rebar.
PIPE PILES
Based on the boring PG-2, approximately seven feet of loose fill was encountered near the
proposed porch addition on the south side of the house. Depending on the final footing
elevations, estimated five feet of over -excavation may be required to reach the bearing soil. As
such, the footings for the proposed porch addition may be supported on two-inch diameter pin
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piles in lieu of over -excavation. The pin piles can avoid undermining the existing house
foundations due to over -excavation.
Nominal two-inch diameter pin piles are typically installed using portable, handheld equipment
and are suited for areas where limited site access exists. The number of piles required depends
on the magnitude of the design load. An allowable axial compression capacity of 3 tons (6 kips)
may be used per 2-inch diameter pile. Larger pin piles will require machine -mounted pile
hammer, and therefore may not be practical for this project.
The lateral capacity of 2-inch diameter pin piles should be ignored. In addition, the friction at
the base of pile -supported footings should also be ignored. An allowable passive pressure of 250
pcf may be used to calculate the lateral resistance of foundation elements. If needed, the pin
piles may be battered to provide additional lateral capacity.
We recommend that the following specifications be included on the foundation plan for two-inch
diameter pin piles:
1. 2-inch diameter piles should consist of Schedule-80, ASTM A-53 Grade "A" pipe.
2. 2-inch diameter piles shall be driven to refusal with a minimum 90-lb jackhammer.
Refusal is defined as no more than 1 inch of penetration for 1 minute of continuous
driving.
3. Piles shall be driven in nominal sections and connected with compression fitted sleeve
couplers (see detail next page — Courtesy of McDowell Pile King, Kent, WA). We
discourage welding of pipe joints, particularly when galvanized pipe is used, as we have
frequently observed welds broken during driving.
4. The geotechnical engineer of record or his/her representative shall provide full time
observation of pile installation.
The quality of a pin pile foundation is dependent, in part, on the experience and professionalism
of the installation company. We recommend that a company with experienced personnel be
selected to install the piles.
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Pipe LD.
2" touu6"
�l
New Steel Pipe Section
10" to 1 1 1/4" to 2" wide X-Strong Steel Ring
1/4" filet welded to pipe sleeve
Driven Steel Pipe Section
Beveled End to aid insertion
CONCRETE SLAB -ON -GRADE
Conventional slab -on -grade concrete floors, if needed, may be used for this project. The floor
slabs should be supported on competent native soil or structural fill placed on competent native
soils. Any over -excavations, if needed, should be backfilled with structural fill.
For the interior living space, the concrete slab -on -grade floors should be underlain by at least 4
inches of capillary break, which consists of free -draining, clean crushed rock or well -graded
gravel compacted to a firm and unyielding condition. The capillary break material should have
no more than 20 percent passing the No. 4 sieve and less than 5 percent by weight of the material
passing the U.S. Standard No. 100 sieve. We also recommend that a minimum 10-mil
polyethylene vapor barrier be placed below the proposed floor slabs.
RETAINING WALL DESIGN PARAMETERS
Retaining walls, if needed, should be designed to resist the lateral earth pressures exerted by the
soils behind the wall. Proper drainage provisions should also be provided behind the walls to
intercept and remove groundwater that may collect behind the walls.
Lateral Earth Pressures
Cantilever walls should be designed for an equivalent fluid pressure of 35 pcf for a level backfill
condition behind the walls assuming the walls are free to rotate. If the walls are restrained at the
top from free movement, such as basement walls with a floor diaphragm, an equivalent fluid
pressure of 45 pcf should be used for a level backfill condition behind the walls. Permanent
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walls should be designed for an additional uniform lateral pressure of 8H psf for seismic loading,
where H corresponds to the height of the buried depth of the wall.
The recommended lateral pressures assume the backfill behind the walls consists of a free
draining and properly compacted fill with adequate drainage provisions.
Surcharge
Surcharge loads, where present, should also be included in the design of retaining walls. We
recommend that a lateral load coefficient of 0.3 be used to compute the lateral pressure on the
wall face resulting from surcharge loads located within a horizontal distance of one-half wall
height.
Lateral Resistance
Lateral forces from seismic loading and unbalanced lateral earth pressures may be resisted by a
combination of passive earth pressures acting against the embedded portions of the foundations
and by friction acting on the base of the wall foundation. Passive resistance values may be
determined using an equivalent fluid weight of 320 pcf. This value includes a factor of safety of
1.5, assuming the footing is backfilled with structural fill. A friction coefficient of 0.35 may be
used to determine the frictional resistance at the base of the footings. The coefficient includes a
factor of safety of 1.5.
Wall Drainage
Provisions for wall drainage should consist of a 4-inch diameter perforated drainpipe behind and
at the base of the wall footings, embedded in 12 to 18 inches of clean crushed rock and pea
gravel wrapped with a layer of filter fabric. A minimum 18-inch wide zone of free draining
granular soils (i.e. pea gravel or washed rock) is recommended to be placed adjacent to the wall
for the full height of the wall. Alternatively, a composite drainage material, such as Miradrain
6000, may be used in lieu of the clean crushed rock or pea gravel. The drainpipe at the base of
the wall should be graded to direct water to a suitable outlet.
Wall Backfill
Retaining wall backfill should consist of free draining granular material. In our opinion, the site
soils have high fines content and would not meet the requirements for wall backfill. We
recommend importing a free draining granular material, such as Seattle Type 17 or a soil
meeting the requirements of Gravel Borrow as defined in Section 9-03.14(1) of the WSDOT
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Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT, 2023). In
areas where space is limited between the wall and the face of excavation, pea gravel may be used
as backfill without compaction.
Wall backfill should be properly moisture conditioned, placed in loose, horizontal lifts less than
12 inches in thickness, and compacted to a dense and unyielding condition. If density tests will
be performed, the test results should show at least 95 percent of the maximum dry density, as
determined using test method ASTM D-1557 (Modified Proctor). Within 5 feet of the wall, the
backfill should be compacted with hand -operated equipment to at least 90 percent of the
maximum dry density.
CONSTRUCTION CONSIDERATIONS
TEMPORARY EXCAVATIONS
As currently planned, the proposed construction may require excavations up to eight feet below
the existing grade. We anticipate the excavations to mainly encounter loose fill over medium
dense to dense native soils. All temporary excavations should be performed in accordance with
Part N of WAC (Washington Administrative Code) 296-155. The contractor is responsible for
maintaining safe excavation slopes and/or shoring.
All temporary excavations deeper than a total of 4 feet should be sloped or shored. Based on the
soil conditions at the site, for planning purposes, it is our opinion that temporary excavations for
the proposed construction may be sloped 1H:1V (Horizontal:Vertical) or flatter. Based on our
current understanding of the anticipated building layout and finished floor elevation, it appears
that sufficient space is available for unsupported open cuts. Where space may be limited, the use
of L-shaped footings may be required to conserve space for the temporary cuts. In event that
sufficient space is not available for unsupported open cuts, temporary shoring will be needed to
support the temporary excavations.
The temporary excavations and cut slopes should be re-evaluated in the field during construction
based on actual observed soil conditions, and may need to be flattened in the wet seasons and
should be covered with plastic sheets. We also recommend that heavy construction equipment,
building materials, excavated soil, and vehicular traffic should not be allowed within a distance
equal to 1/3 the slope height from the top of any excavation.
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MATERIAL REUSE
The soils underlying the site primarily consist of silty sand, are moisture sensitive, and will
become disturbed and soft when exposed to inclement weather conditions. We do not
recommend reusing the native soils as structural fill. If it is planned to use the native soil in non-
structural areas, the excavated soil should be stockpiled and protected with plastic sheeting to
prevent it from becoming saturated by precipitation or runoff.
STRUCTURAL FILL PLACEMENT AND COMPACTION
In the context of this report, structural fill is defined as compacted fill placed under footings,
concrete stairs and landings, and slabs, or other load -bearing areas. Structural fill, if needed,
should consist of imported, well -graded, granular material, such as City of Seattle Type 17,
WSDOT Section 9-03.9(3) Crushed Surfacing Base Course (WSDOT 2023), or an approved
equivalent.
Structural fill should be properly moisture conditioned, placed in loose, horizontal lifts less than
12 inches in thickness, and compacted to a dense and unyielding condition. The adequacy of
compaction should be verified by a PanGEO representative. Alternatively, if density tests will
be performed, the test results should indicate a minimum 95 percent relative compaction level as
determined using ASTM D-1557 (Modified Proctor).
The procedure to achieve proper density of a compacted fill depends on the size and type of
compaction equipment, the number of passes, thickness of the lifts being compacted, and certain
soil properties. If the excavation to be backfilled is constricted and limits the use of heavy
equipment, smaller equipment can be used, but the lift thickness will need to be reduced to
achieve the required relative compaction.
Generally, loosely compacted soils are a result of poor construction technique or improper
moisture content. Soils with high fines contents are particularly susceptible to becoming too wet
and coarse -grained materials easily become too dry, for proper compaction. Soils with a
moisture content too high for adequate compaction should be dried as necessary, or moisture
conditioned by mixing with drier materials, or other methods.
WET WEATHER EARTHWORK
In our opinion, the proposed construction may be accomplished during wet weather (such as in
winter) without adversely affecting the site stability. However, earthwork construction
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performed during the drier summer months likely will be more economical. Winter construction
will require the implementation of best management erosion and sedimentation control practices
to reduce the chance of off -site sediment transport. Some of the site soils contain a high
percentage of fines and are moisture sensitive. Any footing subgrade soils that become softened
either by disturbance or rainfall should be removed and replaced with structural fill, Controlled
Density Fill (CDF), or lean -mix concrete. General recommendations relative to earthwork
performed in wet conditions are presented below:
• Site stripping, excavation and subgrade preparation should be followed promptly by the
placement and compaction of clean structural fill or CDF;
• The size and type of construction equipment used may have to be limited to prevent soil
disturbance;
• The ground surface within the construction area should be graded to promote run-off of
surface water and to prevent the ponding of water;
• Geotextile silt fences should be strategically located to control erosion and the movement
of soil;
• Structural fill should consist of less than 5% fines; and
• Excavation slopes should be covered with plastic sheets.
SURFACE DRAINAGE AND EROSION CONSIDERATIONS
Surface runoff can be controlled during construction by careful grading practices. Typically, this
includes the construction of shallow, upgrade perimeter ditches or low earthen berms in
conjunction with silt fences to collect runoff and prevent water from entering excavations or to
prevent runoff from the construction area from leaving the immediate work site. Temporary
erosion control may require the use of hay bales on the downhill side of the project to prevent
water from leaving the site and potential storm water detention to trap sand and silt before the
water is discharged to a suitable outlet. All collected water should be directed under control to a
positive and permanent discharge system.
Permanent control of surface water should be incorporated in the final grading design. Adequate
surface gradients and drainage systems should be incorporated into the design such that surface
runoff is directed away from structures. Potential problems associated with erosion may also be
reduced by establishing vegetation within disturbed areas immediately following grading
operations.
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ADDITIONAL SERVICES
To confirm that our recommendations are properly incorporated into the design and construction
of the proposed remodeling, PanGEO should be retained to conduct a review of the final project
plans and specifications, and to monitor the construction of geotechnical elements. Modifications
to our recommendations presented in this report may be necessary, based on the actual
conditions encountered during construction.
CLOSURE
We have prepared this report for Erika and Trevor Hill and the project design team.
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. The study was performed using a mutually agreed -upon scope of work.
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, we should be notified immediately to review the applicability of our
recommendations. Additionally, we should also be notified to review the applicability of our
recommendations if there are any changes in the project scope.
The scope of our work does not include services related to construction safety precautions. Our
recommendations are not intended to direct the contractors' methods, techniques, sequences or
procedures, except as specifically described in our report for consideration in design.
Additionally, the scope of our work specifically excludes the assessment of environmental
characteristics, particularly those involving hazardous substances. We are not mold consultants
nor are our recommendations to be interpreted as being preventative of mold development. A
mold specialist should be consulted for all mold -related issues.
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
22-354 931 Carol Way Edmonds Page 15 PanGEO, Inc.
Geotechnical Engineering Report - Proposed Remodeling
931 Carol Way, Edmonds, WA
February 9, 2023
affect our findings. Therefore, this report should not be relied upon after 24 months from its
issuance. PanGEO should be notified if the project is delayed by more than 24 months from the
date of this report so that we may review the applicability of our conclusions considering the
time lapse.
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 should be done at the contractor's
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.
We appreciate the opportunity to be of service.
Sincerely,
PanGEO, Inc.
0210912023
Chien -Lin (Johnny) Chen, P.E.
Senior Geotechnical Engineer
22-354 931 Carol Way Edmonds Page 16 PanGEO, Inc.
Geotechnical Engineering Report - Proposed Remodeling
931 Carol Way, Edmonds, WA
February 9, 2023
Attachments:
Figure 1 Vicinity Map
Figure 2 Site and Exploration Plan
Appendix A — Summary Test Boring Logs
Figure A-1
Terms and Symbols for Boring and Test Pit Logs
Figure A-2
Log of Test Boring PG-1
Figure A-3
Log of Test Boring PG-2
Figure A-4
Log of Test Boring PG-3
22-354 931 Carol Way Edmonds Page 17 PanGEO, Inc.
Geotechnical Engineering Report - Proposed Remodeling
931 Carol Way, Edmonds, WA
February 9, 2023
REFERENCES
ASTM International (ASTM), 2021, Annual book of standards, Section 04.08 Soil and Rock (I):
D420-D5876: West Conshohocken, Pennsylvania.
International Code Council, 2018, International Building Code (IBC).
Minard, J.P., 1983, Geologic map of the Edmonds East and part of the Edmonds West
Quadrangles, Washington: U.S. Geological Survey Miscellaneous Field Studies Map MF-
1541, scale 1:24000.
City of Seattle, 2020, Standard Specifications for Road, Bridges, and Municipal Construction.
Washington State Department of Transportation (WSDOT), 2023, Standard Specifications for
Road, Bridge and Municipal Construction, M 41-10.
Washington Administrative Code (WAC), 2019, Chapter 296-155 - Safety Standards for
Construction Work, Part N - Excavation, Trenching, and Shoring, Olympia, Washington.
22-354 931 Carol Way Edmonds Page 18 PanGEO, Inc.
Legend:
Approx. Test Boring Location
(Approx. Depth to Bearing Soil, ft)
i
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________ ________
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W_C• 1:
Approx. Scale
ill =25'
Note: Base map modified from Site Plan by
H2D Architecture & Design dated 8/25/2022
APPENDIX A
SUMMARY TEST BORING LOGS
RELATIVE DENSITY / CONSISTENCY
SAND / GRAVEL
SILT / CLAY
SPT
Approx. Relative
SPT Approx. Undrained Shear
DensityN-values
Density (%)
Consistency
N-values
Strength (psf)
Very Loose
<4
<15
Very Soft
<2
<250
Loose
4 to 10
15.35
Soft
2 to 4
250.500
Med. Dense
10 to 30
35.65
Med. Stiff
4 to 8
500.1000
Dense
30 to 50
65.85
Stiff
8 to 15
1000.2000
Very Dense
>50
85.100
Very Stiff
15 to 30
2000.4000
Hard
>30
>4000
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GROUP DESCRIPTIONS
•�'
GW:
Well -graded GRAVEL
Gravel
GRAVEL (<5% fines)
''
•••••I......................................................
50% or more of the coarse
GP :
Poorly -graded GRAVEL
fraction retained on the #4
sieve. Use dual symbols (eg.
.............................
o °
.....:......................................................
GM
Silty GRAVEL
GP -GM) for 5% to 12% fines.
o
GRAVEL(>12/ofines)
••••••••••••••••••••••••••••••
GC :
........................•••
Clayey GRAVEL
......................................................................
..........................................................
SW:
Well -graded SAND
""
Sand
SAND (<5/o fines)
50% or more of the coarse
SP
Poorly -graded SAND
fraction passing the 94 sieve.
Use dual symbols SP-SM)
•• ••� �•
;; ;
SM :
Silty SAND
for 5%to12%fines.
o
•SAND(>12/o fines)
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••
SC :
Clayey SAND
•• ...............................••
.............................
............................................................
MIL :
:
SILT
Liquid Limit < 50
CL :
............................................................
......................................................
Lean CLAY
Silt and Clay
=—
_—
OL :
Organic SILT or CLAY
50%or more passing #200 sieve
:..................................
.........................................................
MH :
Elastic SILT
Liquid Limit > 50
CH
Fat CLAY
..............................-.................................
OH
............................................................
Organic SILT or CLAY
_ ,
HighlyOrganic Soils
PT :
PEAT
Notes: 1. Soil exploration to s contain material descriptions based on visual observation and field tests using a system
modified from the Uniform Soil Classification System (USCS). Where necessary laboratory tests have been
conducted (as noted in the "Other Tests" column), unit descriptions may include a classification. Please refer to the
discussions 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.
DESCRIPTIONS OF SOIL STRUCTURES
Layered: Units of material distinguished by color and/or
Fissured: Breaks along defined planes
composition from material units above and below
Slickensided: Fracture planes that are polished or glossy
Laminated: Layers of soil typically 0.05 to 1 mm thick, max. 1 cm
Blocky: Angular soil lumps that resist breakdown
Lens: Layer of soil that pinches out laterally
Disrupted: Soil that is broken and mixed
Interlayered: Alternating layers of differing soil material
Scattered: Less than one per foot
Pocket: Erratic, discontinuous deposit of limited extent
Numerous: More than one per foot
Homogeneous: Soil with uniform color and composition throughout
BCN: Angle between bedding plane and a plane
normal to core axis
COMPONENT DEFINITIONS
COMPONENT
SIZE / SIEVE RANGE
COMPONENT
SIZE / SIEVE RANGE
Boulder:
> 12 inches
Sand
Cobbles:
3 to 12 inches
Coarse Sand:
#4 to #10 sieve (4.5 to 2.0 mm)
Gravel
Medium Sand:
#10 to #40 sieve (2.0 to 0.42 mm)
Coarse Gravel:
3 to 3/4 inches
Fine Sand:
#40 to #200 sieve (0.42 to 0.074 mm)
Fine Gravel:
3/4 inches to #4 sieve
Silt
0.074 to 0.002 mm
Clay
<0.002 mm
TEST SYMBOLS
for In Situ and Laboratory Tests
listed
in "Other Tests" column.
ATT
Atterberg Limit Test
Comp
Compaction Tests
Con
Consolidation
DID
Dry Density
DS
Direct Shear
%F
Fines Content
GS
Grain Size
Perm
Permeability
PP
Pocket Penetrometer
R
R-value
SG
Specific Gravity
TV
Torvane
TXC
Triaxial Compression
UCC
Unconfined Compression
SYMBOLS
Sample/In Situ test types and intervals
®2-inch
OD Split Spoon, SPT
(140-lb. hammer, 30" drop)
B3.25-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
MONITORING WELL
SZ
Groundwater Level at
time of drilling (ATD)
1
Static Groundwater Level
Cement / Concrete Seal
Bentonite grout / seal
Silica sand backfill
Slotted tip
Slough
Bottom of Boring
MOISTURE CONTENT
Dry
Dusty, dry to the touch
Moist
Damp but no visible water
Wet
Visible free water
PanGEO Terms and Symbols for
I N C O R P O R A T E D Boring and Test Pit Logs Figure A-1
Phone: 206.262.0370
Project: Proposed Remodeling
Surface Elevation: 135.0ft
Job Number: 22-354
Top of Casing Elev.: N/A
Location: 931 Carol Way, Edmonds, WA
Drilling Method: HSA
Coordinates: Northing: 47.81596, Easting:-122.3659
Sampling Method: SPT
..
v
CL p
p
Z
fn
a>
n
H
U)
C
CD
3
m
N
O
p
MATERIAL DESCRIPTION
N-Value A
PL Moisture LL
El RecoveryEl
0 50 100
0
`` Grass and sod over loose, brown, silty SAND; moist; poorly graded
[Topsoil/Fill].
Medium dense, orange -brown, slightly gravelly, silty SAND; moist; poorly
graded, iron obde staining [Weathered Till].
2
9
S-1
31
4
48
--becomes gravelly; blow count maybe inflated.
12
6
S-2
X
15
14
---------------------------
Dense, gray -brown, slightly gravelly, silty fine SAND; moist; poorly graded,
...... : N:
8
S-3
X
15
21
slightly cemented [Qtu - Till]........
.........
....... . . . . . . .
25
--becomes wet.
10
10
S-4
X
21
27
--becomes moist.
12
14
21
--becomes very dense.
16
S-5
32
33
Boring terminated at about 16.5 feet below ground surface. Static
groundwater was not encountered during drilling; thin wet sandy interlayers
were observed at about 9-11 feet depth during drilling.
18
.........
.........
20
Completion Depth: 16.5ft
Remarks: Boring drilled using a Bobcat track drill rig. Standard penetration test (SPT) sampler
Date Borehole Started: 9/6/22
Date Borehole Completed: 9/6/22
driven with a 140 lb. safety hammer. Hammer operated with a rope and cathead mechanism.
Surface elevation estimated from City of Edmonds GIS Map.
Logged By: B. Weitering
Drilling Company: Geologic Drill Partners
�
nGE R ® LOG OF TEST BORING PG-1
I N C O R P O R A T E D Figure A-2
The stratification lines represent approximate boundaries. The transition may be gradual. Sheet 1 of 1
Project: Proposed Remodeling
Surface Elevation: 135.0ft
Job Number: 22-354
Top of Casing Elev.: N/A
Location: 931 Carol Way, Edmonds, WA
Drilling Method: HSA
Coordinates: Northing: 47.8158, Easting:-122.36595
Sampling Method: SPT
..
v
CL p
p
Z
U)
a>
n
H
U)
C
CD
3
m
N
O
p
MATERIAL DESCRIPTION
N-Value A
PL Moisture LL
El RecoveryEl
0 50 100
0
`` Grass and sod over loose, brown, silty SAND; moist; poorly graded
[Topsoil/Fill].
' Loose, dark brown to orange -brown, slightly gravelly, silty SAND; moist;
poorly graded, iron obde staining, disturbed appearance [Fill].
2
3
S-1
3
4
2
2
6
S-2
2
3
' Medium dense, gray -brown, slightly gravelly, silty fine SAND; moist; poorly
8
S-3
5
11
graded [Qtu - Till].
11
10
11
--becomes dense.
S-4
X
21
21
--becomes wet.
12
Very dense, interlayered gray -brown and gray, silty fine SAND interlayered
with fine SAND; moist to wet in sandy layers; poorly graded [Qtu - Till].
14
10
16
S-5
35
36
Boring terminated at about 16.5 feet below ground surface. Static
groundwater was not encountered during drilling; thin wet sandy interlayers
were observed at about 11 and 16 feet depth during drilling.
18
.........
.........
20
Completion Depth: 16.5ft
Remarks: Boring drilled using a Bobcat track drill rig. Standard penetration test (SPT) sampler
Date Borehole Started: 9/6/22
Date Borehole Completed: 9/6/22
driven with a 140 lb. safety hammer. Hammer operated with a rope and cathead mechanism.
Surface elevation estimated from City of Edmonds GIS Map.
Logged By: B. Weitering
Drilling Company: Geologic Drill Partners
RnGBR) LOG OF TEST BORING PG-2
I N C O R P O R A T E D Figure A-3
The stratification lines represent approximate boundaries. The transition may be gradual. Sheet 1 of 1
Project: Proposed Remodeling
Surface Elevation: 138.0ft
Job Number: 22-354
Top of Casing Elev.: N/A
Location: 931 Carol Way, Edmonds, WA
Drilling Method: HSA
Coordinates: Northing: 47.81584, Easting:-122.3657
Sampling Method: SPT
..
v
CL p
p
Z
fn
a>
n
H
U)
C
CD
3
m
N
O
p
MATERIAL DESCRIPTION
N-Value A
PL Moisture LL
El RecoveryEl
0 50 100
0
``
Grass and sod over loose, brown, silty SAND; moist; poorly graded
[Topsoil/Fill].
Medium dense, orange -brown, slightly gravelly, silty SAND; moist; poorly
graded, iron obde staining [Weathered Till].
2
S 1
13
50/6
Very dense, gray -brown, slightly gravelly, silty fine SAND; moist; poorly
graded, slightly cemented [Qtu - Till].
4
S-2
X
50/6
6
8
S-3
50/6
: »
Boring terminated at about 8 feet below ground surface due to practical
drilling refusal. Groundwater was not encountered during drilling.
10
12
14
16
18
.........
.........
20
Completion Depth: 8.0ft
Remarks: Boring drilled using a Bobcat track drill rig. Standard penetration test (SPT) sampler
Date Borehole Started: 9/6/22
Date Borehole Completed: 9/6/22
driven with a 140 lb. safety hammer. Hammer operated with a rope and cathead mechanism.
Surface elevation estimated from City of Edmonds GIS Map.
Logged By: B. Weitering
Drilling Company: Geologic Drill Partners
RnGBR) LOG OF TEST BORING PG-3
I N C O R P O R A T E D Figure A-4
The stratification lines represent approximate boundaries. The transition may be gradual. Sheet 1 of 1