2025.0071-2025.0463.PR0003 02 - Panda Express Yelm Ave - Geotechnical Engineering Report (269)Report Cover Page
Panda Express D37983
Geotechnical Engineering Report
April 21, 2025 | Terracon Project No. 81255065
Prepared for:
Panda Restaurant Group, Inc.
1683 Walnut Grove Ave Ste 301
Rosemead, CA 91770
6949 S. High Tech Drive
Midvale, UT 84047
P (801) 545-8500
Terracon.com
Facilities | Environmental |Geotechnical |Materials
Report Cover Letter to Sign
April 21, 2025
Panda Restaurant Group, Inc.
1683 Walnut Grove Ave Ste 301
Rosemead, CA 91770
Attn: Brian Kan
P:(626) 799-9898
E:Brian.Kan@pandarg.com
Re: Geotechnical Engineering Report
Panda Express D37983
1104 Yelm Ave E
Yelm, WA
Terracon Project No. 81255065
Dear Mr. Kan:
We have completed the scope of Geotechnical Engineering services for the above-
referenced project in general accordance with Terracon Proposal delivered via email on
March 19, 2025. This report presents the findings of the subsurface exploration and
provides geotechnical recommendations concerning earthwork and the design and
construction of foundations, floor slabs, and pavements for the proposed project.
We appreciate the opportunity to be of service to you on this project. If you have any
questions concerning this report or if we may be of further service, please contact us.
Sincerely,
Terracon
Jennifer K. Diercksen P.E. (Utah)Zachary L. Koehn, P.E.
Project Manager Geotechnical Department Manager
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials i
Table of Contents
Introduction .................................................................................................... 1
Project Description .......................................................................................... 1
Site Conditions ................................................................................................ 2
Geotechnical Characterization ......................................................................... 3
Seismic Site Class ............................................................................................ 4
Corrosivity ...................................................................................................... 5
Geotechnical Overview .................................................................................... 6
Earthwork ....................................................................................................... 7
Shallow Foundations ..................................................................................... 13
Floor Slabs .................................................................................................... 15
Stormwater Management............................................................................... 17
Pavements .................................................................................................... 19
General Comments ........................................................................................ 22
Attachments
Exploration and Testing Procedures
Site Location and Exploration Plans
Exploration and Laboratory Results
Supporting Information
Note: This report was originally delivered in a web-based format.Blue Bold text in the
report indicates a referenced section heading. The PDF version also includes hyperlinks
that direct the reader to that section and clicking on the logo will bring you
back to this page. For more interactive features, please view your project online at
client.terracon.com.
Refer to each individual Attachment for a listing of contents.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 1
Introduction
This report presents the results of our subsurface exploration and Geotechnical
Engineering services performed for the proposed restaurant to be located at 1104 Yelm
Ave E in Yelm, WA. The purpose of these services is to provide information and
geotechnical engineering recommendations relative to:
■Subsurface soil conditions
■Groundwater conditions
■Seismic site class per IBC
■Site preparation and earthwork
■Foundation design and construction
■Floor slab design and construction
■Stormwater management
■Pavement design and construction
The geotechnical engineering scope of services for this project included the advancement
of test borings, laboratory testing, engineering analysis, and preparation of this report.
Drawings showing the site and boring locations are shown in the Site Location and
Exploration Plan, respectively. The results of the laboratory testing performed on soil
samples obtained from the site during our field exploration are included on the boring logs
and/or as separate graphs in the Exploration Results section.
Project Description
Item Description
Information
Provided
MSA Task Order dated 3/19/2025 requesting geotechnical
services for new Panda Express Restaurant.
Site Plan drawing C-03.0 and ALTA Survey were provided via e-
mail on 3/18/2025.
Project
Description
Proposed new Panda Express Restaurant and associated drive
thru, drive lanes, and parking lot.
Proposed
Structure
Single-story building with footprint of approximately 2,890
square feet.
Building
Construction
Light commercial construction consisting of wood or metal
framed building on shallow foundations with slab on grade (no
basement).
Geotechnical Engineering Report
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April 21, 2025 | Terracon Project No. 81255065
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Item Description
Finished Floor
Elevation At or near existing grade.
Maximum Loads
(assumed)
Columns: 125 kips
Walls: 6 kips per linear foot (klf)
Slabs: 150 pounds per square foot (psf)
Grading/Slopes No grading is anticipated to achieve final grade.
Pavements
We assume both rigid (concrete) and flexible (asphalt)
pavement sections will be considered.
Anticipated traffic is as follows:
■Autos/light trucks: 1,000 vehicles per day
■Light delivery and trash collection vehicles: 10 vehicles per
week
■Tractor-trailer trucks: 1 vehicle per week
The pavement design period is 20 years.
Design ESALs are assumed.
Building Code 2021 International Building Code (2021 IBC)
2016 ASCE Standard ASCE/SEI 7-16 (ASCE 7-16)
Terracon should be notified if any of the above information is inconsistent with the
planned construction, especially the grading limits, as modifications to our
recommendations may be necessary.
Site Conditions
The following description of site conditions is derived from our site visit in association
with the field exploration and our review of publicly available geologic and topographic
maps.
Item Description
Parcel
Information
The project is located at 1104 Yelm Ave E, Yelm, WA.
Lot size: 1.1 acres.
Site coordinates are Latitude 46.9352° N, Longitude 122.5934°
W (approximate).
Parcel Number 22730110208.
Section 30 Township 17 Range 2E
See Site Location
Geotechnical Engineering Report
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April 21, 2025 | Terracon Project No. 81255065
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Item Description
Existing
Improvements Underground utilities
Current Ground
Cover Grass and weeds, bare soil
Existing
Topography Relatively flat
Geotechnical Characterization
Subsurface Conditions
We have developed a general characterization of the subsurface conditions based on our
review of the subsurface exploration, laboratory data, geologic setting, and our
understanding of the project. This characterization, termed GeoModel, forms the basis of
our geotechnical calculations and evaluation of the site. Conditions observed at each
exploration point are indicated in the individual logs. The individual logs can be found in
the Exploration Results and the GeoModel can be found in the attachments of this
report.
As part of our analyses, we identified the following model layers within the subsurface
profile. For a more detailed view of the model layer depths at each boring location, refer
to the GeoModel.
Model
Layer Layer Name General Description
1
Outwash
Deposits/Possible
Fill
Loose to medium dense, well-graded GRAVEL with
silt and sand
2
Glacially
Consolidated
Deposits
Medium dense to very dense, GRAVEL with silt and
sand or SAND with silt and gravel
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
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Groundwater
Groundwater was encountered during the subsurface exploration at approximately 18 feet
below ground surface. Groundwater observations represent groundwater conditions at the
time of the field exploration and may not be indicative of other times or at other locations.
Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall,
runoff, and other factors not evident at the time the borings were performed.
Groundwater levels during construction or at other times in the life of the structure may
be higher or lower than the levels indicated on the boring logs. The possibility of
groundwater level fluctuations should be considered when developing the design and
construction plans for the project.
Long-term groundwater monitoring was not included in the scope of services for this
project. However, it may be performed in the future as an additional service.
Seismic Site Class
The seismic design requirements for buildings and other structures are based on Seismic
Design Category. Site Classification is required to determine the Seismic Design Category
for a structure. The Site Classification is based on the upper 100 feet of the site profile
defined by a weighted average value of either shear wave velocity, standard penetration
resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7 and
the International Building Code (IBC). Based on the soil properties observed at the site
and as described in the exploration logs and results, our professional opinion is that a
Seismic Site Classification of D – Stiff Soil be considered for the project. Subsurface
explorations at this site were extended to a maximum depth of 26.5 feet. The site soil
properties below the boring depth to 100 feet were estimated based on our experience
and knowledge of geologic conditions of the general area. Additional deeper borings or
geophysical testing may be performed to confirm the conditions below the current boring
depth.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 5
Description Value 1
ASCE 7-16 Site Classification D
Site Latitude 46.9353° North
Site Longitude 122.5934° West
SS – Short Period Spectral Acceleration 1.281 g
S1 – 1-Second Period Spectral Acceleration 0.463 g
SMS – Short Period Spectral Acceleration
Adjusted for Site Class 1.281 g
SM1 – 1-Second Spectral Acceleration
Adjusted for Site Class 0.851 g
SDS – Design Short Period Spectral Acceleration 0.854 g
SD1 – Design 1-Second Spectral Acceleration 0.567 g
PGAM - ASCE 7, PGA Adjusted for Site Class 0.554 g
1.The IBC requires a site profile extending to a depth of 100 feet for seismic site
classification. Borings were extended to a maximum depth of 26.5 feet. The site
properties below the boring depth to 100 feet were estimated based on our experience
and knowledge of geologic conditions of the general area.
Surface-Fault Rupture
The hazard of damage from onsite fault rupture appears to be low based on review of the
USGS Earthquake Hazards Program Quaternary Faults and Folds Database available online
(https://usgs.maps.arcgis.com/apps/webappviewer/index.html?id=5a6038b3a168456
1a9b0aadf88412fcf) accessed on April 15, 2025. The closest mapped fault is the Olympia
Structure fault zone, which lies approximately 4 miles to the southwest.
Liquefaction
Liquefaction is the phenomenon where saturated soils develop high pore water pressures
during seismic shaking and lose their strength characteristics. This phenomenon generally
occurs in areas of high seismicity, where groundwater is shallow and loose granular soils
or relatively non-plastic fine-grained soils are present. Based on the site geology and
subsurface groundwater conditions, the hazard of liquefaction of the site soils is low.
Corrosivity
The table below lists the results of laboratory soluble sulfate, soluble chloride, electrical
resistivity, and pH testing. The values should be provided to the utility
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
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supplier/manufacturer to aid in their estimate of potential corrosive characteristics of the
on-site soils.
Corrosivity Test Results Summary
Boring
Sample
Depth
(feet)
Soil
Description
Soluble
Sulfate
(%)
Soluble
Chloride
(%)
Electrical
Resistivity
(Ω-cm)
pH
B-02 2.5
Poorly-graded
GRAVEL with
silt and sand
0.02 0.01 5335 6.98
Results of soluble sulfate testing can be classified in accordance with ACI 318 — Building
Code Requirements for Structural Concrete. Numerous sources are available to
characterize the corrosion potential to buried metals using the parameters above.
ANSI/AWWA is commonly used for ductile iron, while threshold values for evaluating the
effect on steel can be specific to the buried feature (e.g., piling, culverts, or welded wire
reinforcement) or agency for which the work is performed. Imported fill materials may
have significantly different properties than the site materials noted above and should be
evaluated if expected to be in contact with metals used for construction. Consultation with
a NACE-certified corrosion professional is recommended for buried metals on the site.
Geotechnical Overview
The glacial outwash deposits commonly include large, coarse-granular particles such as
cobbles and boulders. The presence of cobbles and boulders immediately below the
foundations could lead to cracking and influence long-term performance. Partial
overexcavation of the subgrades to reduce the risk of stress-concentration from cobbles
and boulders is recommended. The Earthwork and Shallow Foundations section
addresses support of the building bearing on native and compacted structural fill. The
Floor Slabs section addresses slab-on-grade support of the building.
The site is relatively level; therefore, we do not anticipate significant quantities of cutting
and filling to produce level building pads and paving areas. Effective drainage should be
completed early in the construction sequence and maintained after construction to avoid
potential issues. If possible, earthwork should be performed during the warmer and dryer
times of the year. If grading is performed during the winter months, fill placement and
compaction may be more difficult. Additional site preparation recommendations are
provided in the Earthwork section. Based on the conditions encountered in the borings,
the proposed structures can be supported on conventional spread footings bearing on
structural fill over native soils. Foundation areas should be prepared per the
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 7
recommendations provided in the Earthwork section. The Floor Slabs section addresses
slab-on-grade support of the building.
Our opinion of pavement section thickness design has been developed based on our
understanding of the intended use, assumed traffic, and subgrade preparation
recommended herein. The Pavements section includes minimum pavement component
thickness.
The recommendations contained in this report are based on the results of field and
laboratory testing (presented in the Exploration Results), engineering analyses, and our
current understanding of the proposed project. The General Comments section provides
an understanding of the report’s limitations.
Earthwork
Earthwork is anticipated to include clearing and grubbing, excavations, and engineered fill
placement. The following sections provide recommendations for use in the preparation of
specifications for the work. Recommendations include critical quality criteria, as
necessary, to render the site in the state considered in our geotechnical engineering
evaluation for foundations, floor slabs, and pavements.
Site Preparation
Prior to placing fill, any existing vegetation, topsoil, and root mats should be removed.
Complete stripping of the topsoil should be performed in the proposed building and
parking/driveway areas.
Although no evidence of fill or underground facilities (such as septic tanks, cesspools, or
basements) was observed during the exploration and site reconnaissance, such features
could be encountered during construction. If unexpected fills or underground facilities are
encountered, such features should be removed, and the excavation thoroughly cleaned
prior to backfill placement and/or construction.
Subgrade Preparation
We recommend that the soils beneath the footings of the proposed structure be removed
to a minimum depth of 2 feet below existing grades, or as necessary to reach the dense
granular native soil. Structural Fill placed beneath foundations should extend horizontally
as shown in the figure in the Foundation Construction Considerations Section.
Large-area subgrades should be proofrolled with an adequately loaded vehicle such as a
fully loaded tandem-axle dump truck. The proofrolling should be performed under the
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 8
observation of the Geotechnical Engineer or their representative. Areas excessively
deflecting under the proofroll should be delineated and subsequently addressed by the
Geotechnical Engineer. Such areas should either be removed or modified by scarifying and
recompacting. Excessively wet or dry material should either be removed or moisture
conditioned and recompacted.
Based on the subsurface conditions determined from the geotechnical explorations,
subgrade soils exposed during construction are anticipated to be relatively workable;
however, the workability of the subgrade may be affected by precipitation, repetitive
construction traffic, or other factors. If unworkable conditions develop, workability may
be improved by scarifying and drying.
Fill Material Types
Fill required to achieve design grade should be classified as Structural Fill and Common
Fill. Structural Fill is material used below, or within 10 feet of structures and apertures,
pavements, and constructed slopes. Common Fill is material used to achieve grades
outside of these areas.
Import and On-Site Soil: Excavated on-site soil from Soil Layer 1 and 2 may be
selectively reused as structural fill with some handling to remove particles over 3-inches
in diameter.
Imported fill materials should meet the following material property requirements.
Regardless of its source, compacted fill should consist of approved materials that are free
of organic matter and debris. Frozen material should not be used, and fill should not be
placed on a frozen subgrade.
Material property requirements for on-site soil for use as general fill and structural fill are
noted in the table below:
Fill Type Recommended Materials Acceptable Location
for Placement
Structural Fill
9-03.9(3)Crushed Surfacing Base Course 1
9-03.12(1)A Gravel Backfill for Foundations
Class A 1
9-03.14(1)Gravel Borrow 1
On-site Native Soils (Soil Layer 2)2, 3
Beneath and adjacent to
structural slabs,
foundations, building
appurtenances, and
pavement subgrades
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 9
Fill Type Recommended Materials Acceptable Location
for Placement
Common Fill
Section 9-03.14(3)Common Borrow 1
On-site Native Soils (GeoModel Layers 1
and 2)2, 3
Grade filling, utility
trench backfill outside
the building foundation,
and appurtenances
Free-Draining
Granular Fill
Structural Fill 4
9-03.12(2)Gravel Backfill for Walls 1
9-03.12(4)Gravel Backfill for Drains 1
Backfilling in wet
weather, drainage
layers for walls, sump
drains, footing drains 5
1.WSDOT Standard Specifications
2.Structural and common fill should consist of approved materials free of organic
matter and debris. After removing the organic materials, native soils may be
reused as Common Fill and as backfill within the pavement subgrade areas in
accordance with the Fill Material Types section. Frozen material should not be
used, and fill should not be placed on a frozen subgrade. A sample of each
material type should be submitted to the Geotechnical Engineer for evaluation
prior to use on this site.
3.High fines content in the on-site soils could make this material moisture sensitive
and may be difficult to achieve compaction when the moisture content is more
than about 2 percentage points above or below the optimum. Particles with a
nominal diameter greater than about 3 inches should be removed.
4.Material provided must be specified to be less than 5-percent passing the #200
sieve for the portion of material passing the #4 sieve.
5.Minimum particle size must be greater than drainpipe perforations.
Other earthen materials may be suitable for use in addition to the options presented in
the table above. All materials should be approved by the Geotechnical Engineer prior to
use.
Fill Placement and Compaction Requirements
Structural Fill and Common Fill should meet the following compaction requirements.
Item Structural Fill Common Fill
Maximum Lift
Thickness
8 inches or less in loose thickness when heavy,
self-propelled compaction equipment is used
4 to 6 inches in loose thickness when hand-
guided equipment (i.e., jumping jack or plate
compactor) is used
Same as
Structural Fill
Geotechnical Engineering Report
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April 21, 2025 | Terracon Project No. 81255065
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Item Structural Fill Common Fill
Minimum
Compaction
Requirements1
95% of maximum below foundations and floor
slabs and within 1-foot of pavement subgrades
92% of maximum above foundations, and
below the upper 1-foot of pavement subgrade
92% of maximum
dry density
Water Content
Range1 Typically, within 2% of optimum
As required to
achieve min.
compaction
requirements
1.Maximum density and optimum water content as determined by the Modified
Proctor test (ASTM D 1557).
Utility Trench Backfill
Any soft or unsuitable materials encountered at the bottom of utility trench excavations
should be removed and replaced with structural fill or bedding material in accordance with
public works specifications for the utility be supported. This recommendation is particularly
applicable to utility work requiring grade control and/or in areas where subsequent grade
raising could cause settlement in the subgrade supporting the utility. Trench excavation
should not be conducted below a downward 1:1 projection from existing foundations
without engineering review of shoring requirements and geotechnical observation during
construction.
On-site materials are considered suitable for backfill of utility and pipe trenches from 1
foot above the top of the pipe to the final ground surface, provided the material is free of
organic matter and deleterious substances.
All trenches should be wide enough to allow for compaction around the haunches of the
pipe. If water is encountered in the excavations, it should be removed prior to fill
placement. The presence of cobbles and boulders may present challenges with respect to
trench stability. Nested cobbles and boulders in trench side walls may become loosened
during trench that could influence trench stability. The utility contractor should be
prepared to contend with the likely presence of cobbles and boulders in utility trench
alignments.
Trench backfill should be mechanically placed and compacted as discussed earlier in this
report. Compaction of initial lifts should be accomplished with hand-operated tampers or
other lightweight compactors. Where trenches are placed beneath slabs or footings, the
backfill should satisfy the gradation and expansion index requirements of engineered fill
discussed in this report. Flooding or jetting for placement and compaction of backfill is not
recommended.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 11
Grading and Drainage
All grades must provide effective drainage away from the building during and after
construction and should be maintained throughout the life of the structure. Effective
drainage will be essential during construction to limit the extent of soil disturbance during
the wet season.
Water retained next to the building can result in soil movements greater than those
discussed in this report. Greater movements can result in unacceptable differential floor
slab and/or foundation movements, cracked slabs and walls, and roof leaks. Gutters and
downspouts should be routed into tightline pipes that discharge either directly into a
municipal storm drain or to an alternative drainage facility. Splash-blocks should also be
considered below hose bibs and water spigots.
Site grades should be established such that surface water is directed away from foundation
and pavement subgrades to prevent an increase in the water content of the soils. Adequate
positive drainage which diverts water from structures, open cuts, and slopes should be
established to prevent erosion, ground loss, and instability. Locally, flatter grades may be
necessary to transition ADA access requirements for flatwork. After building construction
and landscaping, final grades should be verified to document that effective drainage has
been achieved. Where paving or flatwork abuts the structure a maintenance program
should be established to effectively seal and maintain joints to prevent surface water
infiltration.
Earthwork Construction Considerations
Shallow excavations for the proposed structure are anticipated to be accomplished with
conventional construction equipment; however, removal of large boulders or zones of
cobbles and boulders may require specialty equipment for removal. Upon completion of
filling and grading, care should be taken to maintain the subgrade water content prior to
construction of grade-supported improvements such as floor slabs and pavements.
Construction traffic over the completed subgrades should be avoided. The site should also
be graded to prevent ponding of surface water on the prepared subgrades or in
excavations. Water collecting over or adjacent to construction areas should be removed.
If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should
be removed, or the materials should be scarified, moisture conditioned, and recompacted
prior to floor slab construction.
As a minimum, excavations should be performed in accordance with WAC Chapter 296-
155 Part N “Excavation, Trenching, and Shoring”, OSHA 29 CFR, Part 1926, Subpart P,
“Excavations” and its appendices, and in accordance with any applicable local regulations.
Construction site safety is the sole responsibility of the contractor who controls the means,
methods, and sequencing of construction operations. Under no circumstances shall the
Geotechnical Engineering Report
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information provided herein be interpreted to mean Terracon is assuming responsibility
for construction site safety or the contractor's activities; such responsibility shall neither
be implied nor inferred.
Construction Observation and Testing
The earthwork efforts should be observed by Terracon. Observation should include
documentation of adequate removal of vegetation, deleterious materials, and soils, as well
as proofrolling and mitigation of unsuitable areas delineated by the proofroll.
Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as
recommended by Terracon prior to placement of additional lifts. Each lift of fill should be
tested for density and water content.
In areas of foundation excavations, the bearing subgrade should be evaluated by Terracon.
If unanticipated conditions are observed, Terracon may recommend mitigation options.
In addition to the documentation of the essential parameters necessary for construction,
the continuation of Terracon as the Geotechnical Engineer into the construction phase of
the project provides the continuity to maintain our evaluation of subsurface conditions,
including assessing variations and associated design changes.
Wet Weather Earthwork
The suitability of soils used for Structural Fill depends primarily on their grain-size
distribution and moisture content when they are placed. As the fines content (the soil
fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small
changes in moisture content. Soils containing more than about 5 percent fines (by weight)
cannot be consistently compacted to a firm, unyielding condition when the moisture
content is more than 2 percentage points above or below optimum. Optimum moisture
content is the moisture content at which the maximum dry density for the material is
achieved in the laboratory by the ASTM D1557 test procedure. Due to the presence of
fines, on-site soils may be sensitive to disturbance from construction activity and
increased moisture. Drainage ditches installed early in construction will aid in reducing the
amount of free water in the soil. If precipitation occurs prior to or during construction, the
near-surface soil could increase in moisture content and become more susceptible to
disturbance.
If inclement weather or in situ soil moisture content prevent the use of on-site material
as structural fill, we recommend the use of materials specified in Fill Material Types for
free-draining granular fill.
Stockpiled soils should be protected with polyethylene sheeting anchored to withstand
local wind conditions and to preserve the soil’s moisture content.
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Shallow Foundations
If the site has been prepared in accordance with the requirements noted in Earthwork,
the following design parameters are applicable for shallow foundations.
Design Parameters — Compressive Loads
Item Description
Maximum Net Allowable Bearing Pressure1, 2
2-feet overexcavation and replacement with structural
fill as described in Earthwork
3,000 psf
Required Bearing Stratum3
Undisturbed native granular soils
(Soil Layer 2) under 2-feet
structural fill
Minimum Foundation Dimensions 24 inches for Spread Footing
18 inches for Wall Footing
Ultimate Passive Resistance4
(equivalent fluid unit weight)
440 pcf (compacted granular
backfill)
Sliding Resistance5 0.4 allowable coefficient of
friction — granular material
Minimum Embedment Below
Finished Grade6 18 inches
Estimated Total Settlement from Structural
Loads2 < 1 inch
Estimated Differential Settlement2, 7 About 2/3 of total settlement
1.The maximum net allowable bearing pressure is the pressure in excess of the minimum
surrounding overburden pressure at the footing base elevation.
2.Values provided are for maximum loads noted in Project Description. Additional
geotechnical consultation will be necessary if higher loads are anticipated.
3.Unsuitable, loose, or soft soils should be overexcavated and replaced per the
recommendations presented in Earthwork.
4.Use of passive earth pressures requires the sides of the excavation for the spread
footing foundation to be nearly vertical and the concrete placed neat against these
vertical faces or that the footing forms be removed and compacted Structural Fill be
placed against the vertical footing face. Assumes no hydrostatic pressure. Passive
resistance in the upper 2 feet should be neglected.
5.Can be used to compute sliding resistance where foundations are placed on suitable
soil/materials. Frictional resistance for granular materials is dependent on the bearing
pressure which may vary due to load combinations.
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Item Description
6.Embedment necessary to reduce the effects of frost and/or seasonal water content
variations. For sloping ground, maintain depth below the lowest adjacent exterior grade
within 5 horizontal feet of the structure.
7.Differential settlements are noted for equivalent-loaded foundations and bearing
elevation as measured over a span of 40 feet.
Foundation Construction Considerations
As noted in Earthwork, the footing excavations should be evaluated under Terracon’s
observation. The base of all foundation excavations should be free of water and loose soil,
prior to placing concrete. Concrete should be placed soon after excavating to reduce
bearing soil disturbance. Care should be taken to prevent wetting or drying of the bearing
materials during construction. Excessively wet or dry material or any loose/disturbed
material in the bottom of the footing excavations should be removed/reconditioned before
foundation concrete is placed.
Overexcavation for Structural Fill placement below footings should be conducted as
shown below. The overexcavation should be backfilled up to the footing base elevation,
with Structural Fill placed, as recommended in the Earthwork section.
If prepared foundation subgrades become disturbed prior to casting the foundation, the
disturbed materials should be removed and replaced with compacted structural fill.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 15
Foundation Drains
We recommend the building be encircled with a perimeter foundation drain to collect
exterior seepage water. This drain should consist of a 4-inch diameter perforated pipe
within an envelope of washed rock, extending at least 6 inches on all sides of the pipe.
The washed rock should conform to WSDOT Section 9-03.12(4), Gravel Backfill for Drains
or 9-03.12(5), Gravel Backfill for Drywells. The washed rock envelope should be wrapped
with filter fabric (such as Mirafi 140N, or equal) to reduce the migration of fines from the
surrounding soil. Ideally, the drain invert would be installed no more than 8 inches above
or below the base of the perimeter footings. The perimeter foundation drain should not be
connected to roof downspout drains and should be constructed to discharge into the site
stormwater system or other appropriate outlets. These recommendations are summarized
in the figure below.
Floor Slabs
Design parameters for floor slabs assume the requirements for Earthwork have been
followed. Specific attention should be given to positive drainage away from the structure
and positive drainage of the aggregate base beneath the floor slab.
Depending on the finished floor elevation, loose soils may be observed at the floor slab
subgrade level. These soils should be scarified and recompacted under the observation of
the geotechnical engineer. Removal and replacement with properly compacted Structural
Fill be necessary.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 16
Floor Slab Design Parameters
Design parameters for floor slabs assume the requirements for Earthwork have been
followed. Specific attention should be given to have positive drainage away from the
structure along with positive drainage of the aggregate base beneath the floor slab.
Floor Slab Design Parameters
Item Description
Floor Slab Support 1
Minimum 6 inches of free-draining of either of the following:
■Washed drain rock
■9-03.12(1)A Gravel Backfill for Foundations Class A
(compacted to at least 95% of ASTM D 1557)2, 3
Estimated Modulus
of Subgrade
Reaction 4
150 pounds per square inch per inch (psi/in) for point loads
80 psi/in for distributed loads
1.Floor slabs should be structurally independent of building footings or walls to
reduce the possibility of floor slab cracking caused by differential movements
between the slab and foundation.
2.WSDOT Standard Specification.
3.Values of modulus of subgrade reaction are estimated for the subgrade conditions
stated.
4.The floor slab design should include a capillary break, comprised of compacted
material with less than 12% passing the No. 40 sieve and less than 5% fines
(material passing the No. 200 sieve).
The use of a vapor retarder should be considered beneath concrete slabs on grade covered
with wood, tile, carpet, or other moisture sensitive or impervious coverings, when the
project includes humidity-controlled areas, or when the slab will support equipment
sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab
designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding
the use and placement of a vapor retarder.
Saw-cut contraction joints should be placed in the slab to help control the location and
extent of cracking. For additional recommendations, refer to the ACI Design Manual. Joints
or cracks should be sealed with a waterproof, non-extruding compressible compound
specifically recommended for heavy duty concrete pavement and wet environments.
Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or
other construction objectives, our experience indicates differential movement between the
walls and slabs will likely be observed in adjacent slab expansion joints or floor slab cracks
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 17
beyond the length of the structural dowels. The Structural Engineer should account for
potential differential settlement through the use of sufficient control joints, appropriate
reinforcing, or other means.
Floor Slab Construction Considerations
Finished subgrade, within and for at least 10 feet beyond the floor slab, should be
protected from traffic, rutting, or other disturbance and maintained in a relatively moist
condition until floor slabs are constructed. If the subgrade should become damaged or
desiccated prior to construction of floor slabs, the affected material should be removed,
and structural fill should be added to replace the resulting excavation. Final conditioning
of the finished subgrade should be performed immediately prior to placement of the floor
slab support course.
Terracon should observe the condition of the floor slab subgrades immediately prior to
placement of the floor slab support course, reinforcing steel, and concrete. Attention
should be paid to high traffic areas that were rutted and disturbed earlier, and to areas
where backfilled trenches are located.
Stormwater Management
The subsurface conditions generally appear appropriate for stormwater management via
infiltration. Infiltration rates were estimated using two methodologies: percolation
testing and grain-size analysis.
Percolation Testing
Terracon completed two percolation tests to estimate the infiltration rates for the
management of stormwater runoff via pervious pavements. Percolation tests were
conducted in general accordance with the methodology for the Falling Head Percolation
Test Procedure (U.S. EPA, On-site Wastewater Treatment and Disposal Systems, 1980).
Tests were conducted adjacent to explorations which were advanced to approximately
11½ feet below ground surface to determine the presence of groundwater. The results of
the field percolation tests are summarized in the following table.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 18
Infiltration Rate from Grain-Size Analysis
Currently, the stormwater management testing requirements are unknown. For planning
purposes, we evaluated infiltration potential based on grain size analysis. These should be
used for preliminary sizing of the infiltration facility only. In situ testing via pilot infiltration
testing (PIT) may be required by local jurisdictions to confirm the values herein.
Using the grain-size correlation presented in the Department of Ecology Manual for
Western Washington, a unfactored infiltration rate of 15 inches per hour is estimated.
Applying the reduction factors of 1.0, 0.4, and 0.9 for site variability, test method, and
siltation/bio-buildup, respectively, estimated design infiltration rate is 5½ inches per hour.
The civil engineer should review the reduction factors assumed and revise the estimated
result, as needed, if lower reduction factors are realized.
Preliminary Stormwater Management Design Recommendations
The estimated design infiltration rate of 5½ in/hr is valid under the following
recommendations:
■If soil units of lower permeability are observed, perform over-excavation as needed
to hydraulically connect the infiltration system with an infiltrating soil unit.
■If over-excavation is necessary, backfilling should use granular fill with a fines
content less than 5% (i.e. percent passing the #200 sieve).
■Retain Terracon to observe the base of the infiltration system, once excavated, to
help identify soils units that may be of lower permeability than the soil unit of which
infiltration testing was performed.
■Earthwork is performed using low to moderate ground pressure excavation
equipment for leveling and grading soils beneath the base of the infiltration facility.
Compacting within the infiltration area will reduce the infiltration rate.
Boring ID Approximate
Depth (ft)
USCS
Classification
Percolation Rate
(in/min)1
Measured Rate
(in/hr)1
B-03 2.5 GW-GM 0.25 15
B-06 2.5 SW-SM 0.52 31
1.Unfactored, measured infiltration rate. We recommend multiplying the measured rates by
at least 0.5 to estimate the design infiltration rate.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 19
Pavements
General Pavement Comments
Pavement designs are provided for the traffic conditions and pavement life conditions as
noted herein. A critical aspect of pavement performance is site preparation. Pavement
designs noted in this section must be applied to the site which has been prepared as
recommended in the Earthwork section.
Pavement loading was not provided to us. We have assumed the following traffic volume
for estimating the minimum pavement thickness. If traffic volume will exceed the assumed
values, Terracon should be notified in order to provide pavement sections designed for
higher levels of traffic.
■1,000 passenger cars/pick-up trucks and vans/recreational vehicles per day
■10 delivery trucks and garbage/dumpster trucks per week
■1 tractor-trailer truck per day (for heavy duty areas only)
For design purposes, we have assumed a CBR value of at least 10. Any imported or borrow
source fill placed below the proposed pavements should have a CBR value of at least 10.
A modulus of subgrade reaction of 200 lbs. per cubic inch (pci) was assumed for compacted
subgrade for concrete pavement design.
Pavement Section Thicknesses
Design of Asphaltic Concrete (AC) pavements is based on the 1993 AASHTO guidelines.
Minimum recommended pavement section thicknesses are presented below:
Asphaltic Concrete (AC) Design
Layer Light Duty AC
Thickness (inches)
Heavy Duty AC
Thickness (inches)
Compacted Subgrade 1 12 12
Crushed Aggregate Base 2 6 6
Asphalt Thickness 3, 4 3 4
1.May vary based on observations following proof-rolling and the requirements
specified in the Earthwork section.
2.Aggregate base meeting WSDOT:9-03.9(3) Base Course specifications.
3.Aggregates for asphalt surface meeting WSDOT: 9-03.8(2) ½-inch HMA.
4.PG58H-22 asphalt binder.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 20
Portland Cement Concrete (PCC) Design
Layer Light Duty PCC
Thickness (inches)
Heavy Duty PCC
Thickness (inches)
Compacted Subgrade 1 12 12
Crushed Aggregate Base 2 6 6
Portland Cement Concrete
Thickness 5 6
1.May vary based on observations following proof-rolling and the requirements
specified in the Earthwork section.
2.Aggregate base meeting WSDOT:9-03.9(3) Base Course specifications.
We recommend that Portland cement concrete (PCC, rigid) pavement be used where rigid
pavements are appropriate. These areas include but are not limited to entrance and exit
sections, dumpster pads, or any areas where extensive wheel maneuvering or repeated
loading is expected. The rigid pavement pads should be large enough to support the
wheels of the truck which will be bearing the haul load. Adequate reinforcement and
number of longitudinal and transverse control joints should be placed in the rigid pavement
in accordance with ACI requirements. Although not required for structural support, the
base course layer is recommended to help reduce the potential for slab curl, shrinkage
cracking, subgrade “pumping” through joints, and to provide a workable surface. These
thicknesses assume the subgrade is properly prepared and compacted as noted above.
Proper joint spacing will also be required to prevent excessive slab curling and shrinkage
cracking. All joints should be sealed to prevent entry of foreign material and dowelled
where necessary for load transfer.
The minimum pavement sections outlined above were determined based on post-
construction traffic loading conditions. These pavement sections do not account for heavy
construction traffic during development. A partially constructed structural section that is
subjected to heavy construction traffic can result in pavement deterioration and premature
distress or failure. Our experience indicates that this pavement construction practice can
result in pavements that will not perform as intended. Considering this information,
several alternatives are available to mitigate the impact of heavy construction traffic prior
to pavement construction. These include using thicker sections to account for the
construction traffic after paving; using some method of soil stabilization to improve the
support characteristics of the pavement subgrade; routing heavy construction traffic
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 21
around paved areas; or delaying paving operations until as near the end of construction
as is feasible.
Pavement Drainage
Pavements should be sloped to provide rapid drainage of surface water. Water allowed to
pond on or adjacent to the pavements could saturate the subgrade and contribute to
premature pavement deterioration. In addition, the pavement subgrade should be graded
to provide positive drainage within the granular base section. Appropriate sub-drainage or
connection to a suitable daylight outlet should be provided to remove water from the
granular subbase.
We recommend drainage be included at the bottom of the crushed aggregate base (when
used) at the storm structures to aid in removing water that may enter this layer. Drainage
could consist of small diameter weep holes excavated around the perimeter of the storm
structures. The weep holes should be excavated at the elevation of the crushed aggregate
base and soil interface. The excavation should be covered with crushed aggregate
encompassed in Mirafi 140NL, or an approved equivalent, which will aid in reducing the
amount of fines that enter the storm system.
Pavement Maintenance
The pavement sections represent minimum recommended thicknesses and, as such,
periodic maintenance should be anticipated. Therefore, preventive maintenance should be
planned and provided for through an ongoing pavement management program.
Maintenance activities are intended to slow the rate of pavement deterioration and to
preserve the pavement investment. Maintenance consists of both localized maintenance
(e.g. crack and joint sealing and patching) and global maintenance (e.g. surface sealing).
Preventive maintenance is usually the priority when implementing a pavement
maintenance program. Additional engineering observation is recommended to determine
the type and extent of a cost-effective program. Even with periodic maintenance, some
movements and related cracking may still occur, and repairs may be required.
A pavement’s performance is affected by its surroundings. In addition to providing
preventive maintenance, the civil engineer should consider the following recommendations
in the design and layout of pavements:
■Final grade adjacent to paved areas should slope down from the edges at a
minimum 2%.
■Subgrade and pavement surfaces should have a minimum 2% slope to promote
proper surface drainage.
■Install joint sealant and seal cracks immediately.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 22
■Seal all landscaped areas in or adjacent to pavements to reduce moisture migration
to subgrade soils.
General Comments
Our analysis and opinions are based on our understanding of the project, the geotechnical
conditions in the area, and the data obtained from our site exploration. Variations will
occur between exploration point locations or due to the modifying effects of construction
or weather. The nature and extent of such variations may not become evident until during
or after construction. Terracon should be retained as the Geotechnical Engineer, where
noted in this report, to provide observation and testing services during pertinent
construction phases. If variations appear, we can provide further evaluation and
supplemental recommendations. If variations are noted in the absence of our observation
and testing services on-site, we should be immediately notified so that we can provide
evaluation and supplemental recommendations.
Our Scope of Services does not include either specifically or by implication any
environmental or biological (e.g., mold, fungi, or bacteria) assessment of the site or
identification or prevention of pollutants, hazardous materials, or hazardous conditions. If
the owner is concerned about the potential for such contamination or pollution, other
studies should be undertaken.
Our services and any correspondence are intended for the sole benefit and exclusive use
of our client for specific application to the project discussed and are accomplished in
accordance with generally accepted geotechnical engineering practices with no third-party
beneficiaries intended. Any third-party access to services or correspondence is solely for
information purposes to support the services provided by Terracon to our client. Reliance
upon the services and any work product is limited to our client and is not intended for
third parties. Any use or reliance of the provided information by third parties is done solely
at their own risk. No warranties, either express or implied, are intended or made.
Site characteristics as provided are for design purposes and not to estimate excavation
cost. Any use of our report in that regard is done at the sole risk of the excavating cost
estimator as there may be variations on the site that are not apparent in the data that
could significantly affect excavation cost. Any parties charged with estimating excavation
costs should seek their own site characterization for specific purposes to obtain the specific
level of detail necessary for costing. Site safety and cost estimating including excavation
support and dewatering requirements/design are the responsibility of others.
Construction and site development have the potential to affect adjacent properties. Such
impacts can include damage due to vibration, modification of groundwater/surface water
flow during construction, foundation movement due to undermining or subsidence from
excavation, and noise or air quality concerns. Evaluation of these items on nearby
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials 23
properties is commonly associated with contractor means and methods and is not
addressed in this report. The owner and contractor should consider a
preconstruction/precondition survey of the surrounding development. If changes in the
nature, design, or location of the project are planned, our conclusions and
recommendations shall not be considered valid unless we review the changes and either
verify or modify our conclusions in writing.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials
Attachments
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials
Exploration and Testing Procedures
Field Exploration
Number of Borings Approximate Boring
Depth (feet)Location
2 21.5 building
1 (with monitoring well)26.5 pavement / utilities
3 11.5 pavement / utilities
Boring Layout and Elevations: Terracon personnel provided the boring layout using
handheld GPS equipment (estimated horizontal accuracy of about ±10 feet) with
reference to existing site features. Approximate ground surface elevations were
estimated using Google Earth. If elevations and a more precise boring layout are
desired, we recommend borings be surveyed.
Subsurface Exploration Procedures: We advanced the borings with a track-mounted
drill rig using a continuous flight hollow stem auger. Four samples were obtained in the
upper 10 feet of each boring and at intervals of 5 feet thereafter. In the split-barrel
sampling procedure, a standard 2-inch outer diameter split-barrel sampling spoon was
driven into the ground by a 140-pound hammer falling a distance of 30 inches. The
number of blows required to advance the sampling spoon the last 12 inches of a normal
18-inch penetration is recorded as the Standard Penetration Test (SPT) resistance value.
The SPT resistance values, also referred to as N-values, are indicated in the boring logs
at the test depths. We observed and recorded groundwater levels during drilling and
sampling. For safety purposes, all borings were backfilled with bentonite after
completion, with the exception of B-03, which was completed as a monitoring well with a
protective steel cover.
We also observed the boreholes at the completion of drilling for the presence of
groundwater. The groundwater levels are shown in the attached boring logs.
The sampling depths, penetration distances, and other sampling information were
recorded on the field boring logs. The samples were placed in appropriate containers and
taken to our soil laboratory for testing and classification by a Geotechnical Engineer. Our
exploration team prepared field boring logs as part of the drilling operations. These field
logs included visual classifications of the materials observed during drilling and our
interpretation of the subsurface conditions between samples. Final boring logs were
prepared from the field logs. The final boring logs represent the Geotechnical Engineer's
interpretation of the field logs and include modifications based on observations and tests
of the samples in our laboratory.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials
Percolation Testing:
A 6.75-inch OD soil boring was drilled to approximately 2.5 feet below the existing site
grade. A four-inch-diameter solid PVC pipe was inserted, and the hole was backfilled with 6
inches of gravel and sand to keep the pipe in place. The pipe was then filled with water and
the soil allowed to saturate. The time required for the water level to drop incrementally was
measured over the course of the field exploration (approximately 6 hours).
Laboratory Testing
The project engineer reviewed the field data and assigned laboratory tests. The
laboratory testing program included the following types of tests:
■Moisture Content
■Atterberg Limits
■Grain Size Distribution
■Corrosivity Testing
The laboratory testing program often includes examination of soil samples by an
engineer. Based on the results of our field and laboratory programs, we described and
classified the soil samples in accordance with the Unified Soil Classification System.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials
Site Location and Exploration Plans
Contents:
Site Location Plan
Exploration Plan
Note: All attachments are one page unless noted above.
Geotechnical Engineering Report
Panda Express D37983 | Yelm, WA
April 21, 2025 | Terracon Project No. 81255065
Facilities |Environmental |Geotechnical | Materials
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Site Location
DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS