2021.0074.BP0005 Geotech_Report_TCOMM911_Yelm_Water_Tank_LDC_20200925
Geotechnical Report
TComm911 Yelm Water Tank
901 Rhoton Road NW
Yelm, Washington
Prepared for:
Mr. Richard Hall
RN File No. 3458-003A ● September 25, 2020
2105 South C Street 17625 130th Avenue NE, Suite 102
Tacoma, Washington 98402 www.robinson-noble.com Woodinville, Washington 98072
P: 253.475.7711 | F: 253.472.5846 P: 425.488.0599 | F: 425.488.2330
9/25/2020
Barbara A. Gallagher, PE
Senior Engineer
JHA:BAG:am
Geotechnical Report
TComm911 Yelm Water Tank
901 Rhoton Road NW
Yelm, Washington
RN File No. 3458 – 003A ● September 25, 2020
Prepared for:
Mr. Richard Hall
LDC Inc.
20210 142nd Avenue NE
Woodinville, Washington 98072
Robinson Noble, Inc.
John H. Anderson, PE
Project Engineer
TComm 911 Yelm Water Tank | Page i
RN File No. 3458-003A
September 25, 2020
TABLE OF CONTENTS
1 INTRODUCTION ....................................................................................................... 3
1.1 Project Description ......................................................................................................... 3
1.2 Scope .............................................................................................................................. 3
2 SITE CONDITIONS ................................................................................................... 4
2.1 Geologic Setting ............................................................................................................. 4
2.2 Seismic Setting ............................................................................................................... 4
2.3 Critical Areas Designations ............................................................................................. 5
2.4 Surface Conditions ......................................................................................................... 5
2.5 Field Explorations ........................................................................................................... 6
2.6 Laboratory Testing .......................................................................................................... 6
2.7 Subsurface Conditions .................................................................................................... 6
Stratigraphy/Soil Conditions ........................................................................................ 6
Hydrologic Conditions ................................................................................................. 7
Soil Resistivity ............................................................................................................. 7
3 CONCLUSIONS AND RECOMMENDATIONS ........................................................ 9
3.1 Summary of Geotechnical Considerations...................................................................... 9
3.2 Seismic Engineering ....................................................................................................... 9
Seismic Design ........................................................................................................... 9
Seismic Hazards. ....................................................................................................... 10
3.3 Erosion Hazard .............................................................................................................. 10
3.4 Foundation Design ........................................................................................................ 10
3.5 Retaining Wall Design .................................................................................................. 11
Lateral Loads ............................................................................................................. 11
3.6 Slabs-On-Grade ............................................................................................................. 12
3.7 Pavement Subgrade ..................................................................................................... 12
3.8 Drainage ....................................................................................................................... 12
3.9 Stormwater Management ............................................................................................ 12
Infiltration .................................................................................................................. 13
3.10 Earthwork and Construction Considerations ................................................................ 13
Site Preparation and Grading .................................................................................... 13
Temporary and Permanent Slopes ............................................................................ 13
Structural Fill ............................................................................................................. 14
Utilities ...................................................................................................................... 14
Wet Weather Considerations .................................................................................... 15
4 FUTURE WORK ...................................................................................................... 16
4.1 Engineering and Design ................................................................................................ 16
4.2 Construction Observation ............................................................................................. 16
5 USE OF THIS REPORT ........................................................................................... 17
6 REFERENCES ......................................................................................................... 18
TComm 911 Yelm Water Tank | Page ii
RN File No. 3458-003A
September 25, 2020
Cover sheet graphic shows western Washington geomorphology as a hillshade from Mount Rainier to the Seattle metropolitan area.
Image is derived from a compilation of Washington State DNR LIDAR surveys obtained from the Washington Lidar Portal:
http://lidarportal.dnr.wa.gov/
List of Figures
Post-text Figures
Figure 1. Vicinity Map
Figure 2. Site Plan
Figure 3. Unified Soil Classification System
Figure 4. Boring Logs – Boring 1
List of Tables
Table 1a-1d. Resistivity Data 7
Table 2. Seismic Design Inputs 9
Table 3. Seismic Design Parameters 10
Table 4. Lateral Earth Pressure Parameters 11
Table 5. Passive Resistance to Lateral Earth Pressure Parameters 12
List of Appendices
Appendix A. Soil Resistivity Data
Appendix B. Design Maps Summary Report
TComm 911 Yelm Water Tank | Page 3
RN File No. 3458-003A
September 25, 2020
1 INTRODUCTION
This report presents the results of our geotechnical engineering investigation at the TComm911
Yelm Water Tank project. The site is located at 901 Rhoton Road NW, as shown on the Vicinity
Map in Figure 1. We understand you plan to install two antennas mounted on the existing
water tank with the construction of a liquid fuel tank pad, a generator pad and an equipment
shelter.
1.1 Project Description
The project proposes to install two antennas on the existing water tank. West of the water tank
a 24-foot by 11.7-foot equipment shelter will be constructed with a concrete slab over a stem
wall foundation elevated 2 feet above grade. Two concrete pads, one for a fuel tank and one for
a generator, will be constructed north of the equipment shelter and will also be elevated 2 feet
above grade.
1.2 Scope
Our scope of services included:
Review available geologic maps for the site.
Mark the site in white paint for the public utility locating service.
Explore the subsurface soil and groundwater conditions in the area of the planned
structures with a truck mounted drill rig.
Evaluate pertinent physical and engineering characteristics of the soils encountered in
the boring.
Prepare a geotechnical report containing the results of our subsurface explorations,
and our conclusions and recommendations for geotechnical design elements of the
project.
We completed these services in general accordance with our emailed quote, dated August 18,
2020. We received notice to proceed on August 18, 2020.
TComm 911 Yelm Water Tank | Page 4
RN File No. 3458-003A
September 25, 2020
2 SITE CONDITIONS
2.1 Geologic Setting
Most of the Puget Sound Region was affected by past intrusion of continental glaciation. The
last period of glaciation, the Vashon Stade of the Fraser Glaciation, ended approximately 14,000
years ago. Many of the geomorphic features seen today are a result of scouring and overriding
by glacial ice and sediment deposition related to glacial advance and retreat. During the Vashon
Stade, areas of the Puget Sound region were overridden by over 3,000 feet of ice. Soil layers
overridden by the ice sheet were compacted to a much greater extent than those that were
not. Part of a typical glacial sequence within the area of the site includes the following soil
deposits from newest to oldest:
Artificial Fill (af) – Fill material is often locally placed by human activities, consistency
will depend on the source of the fill. The thickness and expanse of this material will be
dependent on the extent of fill required to grade land to the desired elevations. Density
of the fill will depend on earthwork activities and compaction efforts made during the
placement of the material.
Recessional Outwash (Qvr) – These deposits were derived from the stagnating and
receding Vashon glacier and consist mostly of stratified sand and gravel, but include
unstratified ablation and melt-out deposits. Recessional deposits were not compacted
by the glacier and are typically not as dense as those that were.
Vashon Till (Qvt) – The till is a non-sorted mixture of clay, sand, pebbles, cobbles and
boulders, all in variable amounts. The till was deposited directly by the ice as it advanced
over and eroded irregular surfaces of previously deposited formations and sediments.
The till was well compacted by the advancing glacier and exhibits high strength and
stability. Drainage is considered very poor in the till.
Advance Outwash (Qva) – The advance outwash typically is a thick section of mostly
clean, pebbly sand with increasing amounts of gravel higher in the section. The
advance outwash was placed by the advancing glaciers and was overridden and well
compacted by the glacier.
The geologic units for this area are mapped on Plate 1 – Maps Showing Well Locations and
Surficial Geology, and Cross Sections, by Dion, N.P. et al. (U.S. Geological Survey, 1994). The
site is mapped as being underlain by recessional outwash deposits. Our explorations
encountered fill underlain by recessional outwash.
2.2 Seismic Setting
The Pacific Northwest is very seismically active. Off the coast, the Juan de Fuca Oceanic Plate
collides into and descends (subducts) under the North American Continental Plate. The contact
between these plates forms an approximately 600 mile long fault known as the Cascadia
Subduction Zone (CSZ). The resulting stresses generate three unique types of earthquakes that
contribute to seismic risk in the region (Cascadia Region Earthquake Workgroup, 2013):
Subduction (or Megathrust) Earthquakes: Megathrust earthquakes are formed by a rupture
of the contact between the plates along the CSZ. These events are capable of generating a
magnitude 9 or larger earthquake. These earthquakes are relatively far from the Puget Sound,
TComm 911 Yelm Water Tank | Page 5
RN File No. 3458-003A
September 25, 2020
but still pose great risk due to their extreme intensity and duration. Along the CSZ, megathrust
earthquakes are understood to have a recurrence interval of roughly every 500 years. The last
such event along the CSZ happened in 1700 AD, lowering the coastline several feet and
generating a large tsunami across the Pacific Ocean.
Shallow (or Crustal) Earthquakes: Stress from the subduction zone fractures and deforms
the continental crust across the Pacific Northwest. When these near-surface crustal faults
break, they generate earthquakes that affect smaller areas, but can locally be more intense than
the subduction events off the coast. Such faults happen to pass under some of the most
populous areas in Washington State, including the greater Seattle and Tacoma areas. Because
of their proximity and local intensity, these fault zones are often the greatest contributing factor
to seismic risk in the Puget Sound.
Deep (or Intraslab) Earthquakes: Intraslab earthquakes are associated with fractures within
the subducting Juan de Fuca plate. Because they occur at depths over 18 to 30 miles beneath
the surface, the energy of these earthquakes is dissipated over large areas of ground surface,
increasing their zone of influence but limiting their severity. However, these earthquakes are
still capable of causing significant damage to structures and are the most frequent seismic
events in the Puget Sound region. A magnitude 6.5 or larger earthquake affecting the region
can be expected, on average, every 30 years. The 2001 Nisqually earthquake was an intraslab
earthquake with over $4 billion in damages, 400 injuries, and one death. (Cascadia Region
Earthquake Workgroup, 2008).
The site is mapped on the U.S. Quaternary Faults and Folds Database web application by the
U.S. Geological Survey as located approximately 4.5 miles northeast of the Olympia Structure.
The Olympia Structure has not been firmly characterized but is speculated to be either a thrust
fault or compressional fold that begins near Shelton and trends southeast under Olympia and
the town of Rainier. It is classified as a Class B fault which indicates that there is geologic
evidence of either a fault or Quaternary deformation but insufficient data to determine potential
depth of the fault and theorization of earthquake potential.
2.3 Critical Areas Designations
The entire City of Yelm and its urban growth area are located within a high susceptibility critical
aquifer recharge area. These areas are defined in Section 18.21.070 of the Yelm Municipal
Code (YMC) as the following:
Critical aquifer recharge areas are those areas with a critical recharging effect on
aquifers used for potable water as defined by WAC 365-190-030 (2). A critical aquifer
recharge area has prevailing geologic conditions associated with infiltration rates that
create a high potential for contamination of ground water resources or contribute
significantly to the replenishment of ground water.
2.4 Surface Conditions
The project site is about 7.63 acres in size and has maximum dimensions of approximately 663
feet in the east-west direction and 509 feet in the north-south direction. Access to the site is
provided by Rhoton Road NW which borders the site to the east. The site is bordered to the
north and south by commercial acreage and to the west by residential acreage. A layout of the
site is shown on the Site Plan in Figure 2.
TComm 911 Yelm Water Tank | Page 6
RN File No. 3458-003A
September 25, 2020
The ground surface within the site is generally flat to gently sloping down to the east. The
water tank is located within the southern half of the site. This southern half of the site also
contains a large amount of stockpiled soil and compost within the western quarter. A gravel
access drive south of the water tank extends west to northwest from Rhoton Road NW to
asphalt drives and parking lots within the northern half of the site. The northern portion of the
site contains a public works building with associated access drive and parking.
The vegetation within the site generally consists of grass. Medium sized evergreen trees up to
approximately 3 feet in diameter exist west of the water tank.
2.5 Field Explorations
We explored subsurface soil and groundwater conditions within the site on August 27, 2020, by
drilling one boring with a truck mounted drill rig. The boring was drilled to a depth of
approximately 21 feet below the ground surface. The boring was sampled at 2.5-foot intervals
to a depth of 10 feet depth and then at 5-foot intervals thereafter. Samples were obtained using
the Standard Penetration Test. This test consists of driving a two-inch outside diameter split
spoon sampler with a 140-pound hammer dropping 30 inches. The number of blows required
for penetration of three 6-inch intervals was recorded. To determine the standard penetration
number at that depth the number of blows required for the lower two intervals are summed.
These numbers are then converted to a hammer energy transfer standard which is 60 percent,
N60. If the number of blows reached 50 before the sampler was driven through any 6-inch
interval, the sampler was not driven further and the blow count is recorded as 50 for the actual
penetration distance.
The boring was located in the field by a geologist from this firm who also examined the soils
and geologic conditions encountered, and maintained logs of the boring. The approximate
location of the boring is shown on the Site Plan in Figure 2. The soils were visually classified in
general accordance with the Unified Soil Classification System, a copy of which is presented as
Figure 3. The log of the boring is presented in Figure 4.
2.6 Laboratory Testing
We completed moisture content testing on selected samples from our explorations. The
moisture contents are shown on the Boring Log.
2.7 Subsurface Conditions
The subsurface conditions at the site are briefly described below, based upon our completed
field explorations of soils, laboratory testing, and review of available geologic maps available for
the site. For a more detailed description of the soils encountered, review the Boring Log in
Figure 4.
Stratigraphy/Soil Conditions
Based on our completed boring, we interpret that the subsurface stratigraphy on site can be
grouped into 3 soil units: loose to medium dense surficial soils interpreted as artificial fill,
medium dense silty sand interpreted as buried topsoil, and dense to very dense silty sand
interpreted as recessional outwash.
TComm 911 Yelm Water Tank | Page 7
RN File No. 3458-003A
September 25, 2020
Artificial Fill: Artificial fill was encountered at the ground surface and extending to a depth of
approximately 15 feet. The fill generally consisted of loose to medium dense silty fine to
medium sand with gravel with varying amounts of organics.
Buried Topsoil: Buried topsoil was encountered underlying the artificial fill at a depth of
approximately 15 feet. This material consisted of medium dense dark brown to black silty sand
with gravel and organics.
Recessional Outwash: Our explorations encountered native soil interpreted to be recessional
outwash underlying the buried topsoil. This material extended to the depth explored within the
boring. The recessional outwash consisted of dense to very dense silty fine to coarse sand with
gravel and large cobbles. The large cobbles were observed within the soil cuttings removed
from the boring. It is expected that the blow counts within this material are overstated due to
driving the sampler on these cobbles.
Hydrologic Conditions
We did not observe shallow groundwater seepage while drilling the boring. The recessional
outwash interpreted to underlie the site is considered to be well draining. Depending on the
thickness of this deposit a seasonal groundwater table may exist at depth. We expect the
groundwater table generally correlates with the elevation of the Nisqually River located
approximately 1.5 miles to the east of the site and on the order of 80 feet lower in elevation
than the subject site.
Soil Resistivity
We conducted soil resistivity testing at the site on August 28, 2020 using the AMEC 6471
Digital Ground Resistance and Soil Resistivity meter. We followed the R56 Appendix B which
uses the four-point Wenner array soil resistivity method. The Wenner four-point method
requires that four metal electrodes be placed in a straight line. Each electrode is driven to a
depth of not more than 1/20 of the spacing below the ground surface. A current of know
amperage is subsequently circulated in the soil through the end electrodes and the resulting
voltage drop between the inner electrodes is measured to determine the resistance of the soil.
We performed four test lines at the site with electrode spacing as shown in the tables below.
The approximate locations of the test lines are shown on the Site Plan in Figure 1. The testing
was performed in the locations indicated due to the existing site constraints. We consider the
results of the tests to be generally representative of the soil resistivity profile at the tower
location. The graphs of the readings are included as Appendix A. The tables below summarize
the results.
Table 1a – Line 1 Soil Resistivity Profile
Distance Between Electrodes (ft) Resistance (ohms) Resistivity (Kohm-cm)
5 1,324.0 1,267.4
10 526.8 1,008.8
20 131.8 504.8
25 53.0 253.5
30 20.6 118.1
TComm 911 Yelm Water Tank | Page 8
RN File No. 3458-003A
September 25, 2020
Table 1b – Line 2 Soil Resistivity Profile
Distance Between Electrodes (ft) Resistance (ohms) Resistivity (Kohm-cm)
5 1,308.0 1,252.1
10 359.8 689.0
25 46.5 222.9
30 27.2 156.4
Table 1c – Line 3 Soil Resistivity Profile
Distance Between Electrodes (ft) Resistance (ohms) Resistivity (Kohm-cm)
5 1,615.0 1,546.5
10 771.5 1,477.5
15 401.9 1,154.5
20 163.7 626.8
Table 1d – Line 4 Soil Resistivity Profile
Distance Between Electrodes (ft) Resistance (ohms) Resistivity (Kohm-cm)
5 3,023.0 2,894.9
10 948.4 1,816.3
20 143.9 551.0
30 114.4 657.4
TComm 911 Yelm Water Tank | Page 9
RN File No. 3458-003A
September 25, 2020
3 CONCLUSIONS AND RECOMMENDATIONS
3.1 Summary of Geotechnical Considerations
The project site contains a thick layer of surficial fill and buried topsoil that extends to an
approximate depth of 16 feet. We therefore recommend that the foundations for the structures
at the site consist of drilled pier foundations. The piers should be constructed following the
placement of the structural fill pad that will be used to raise the buildings above the FEMA flood
plain requirement.
3.2 Seismic Engineering
Seismic Design
Seismic design for the 2015 International Building Code (IBC) is based on the mapped values
for the risk-targeted maximum considered earthquake (MCER). Ground motion values in these
maps include a probability of exceedance equal to 2% in 50 years, which corresponds to a
2,475-year return period. These mapped values have been prepared by the USGS in
collaboration with the FEMA-funded Building Seismic Safety Council (BSSC) and the American
Society of Civil Engineers (ASCE).
The mapped MCER spectral response accelerations are referred to as Ss for short periods (0.2
seconds) and S1 for a 1 second period. IBC 2015 directs that correction factors be applied to
these response spectra based on an evaluation of site specific subsurface conditions, referred
to as the soil site class (defined in ASCE 7 Section 20.3). The corrected MCER parameters are
referred to as SMS and SM1. IBC 2015 defines the design spectral acceleration parameters as
two-thirds of the corrected parameters, resulting in the values of SDS for short periods and SD1
for the one-second period.
Seismic design for geologic hazards including slope stability, liquefaction, seismic settlement,
lateral spreading, and other seismic risks follow ASCE 7. The seismic design procedures in this
standard are based on MCER peak ground acceleration (PGA) multiplied by a correction factor
for site-specific amplification (FPGA). This results in a site-modified peak ground acceleration
(PGAM). From the site risk category and design spectral response acceleration parameters SDS
and SD1, the site is assigned a seismic design category (ASCE 7 section 11.6).
We obtained seismic design parameters for this site from the Structural Engineers Association
of California Seismic Design Maps Tool (SEAOC). Input values based on our understanding of
the proposed project and our interpretations of subsurface conditions (described in Section 2.7)
are shown in Table 2 below. The output summary report from the SEAOC is included in this
report as Appendix B, and the seismic design parameters are shown in Table , below.
Table 2: Seismic Design Inputs
Seismic Design Maps Tool Inputs Value
Site Latitude 46.949651
Site Longitude -122.601797
Site Class D
Risk Category I-III
TComm 911 Yelm Water Tank | Page 10
RN File No. 3458-003A
September 25, 2020
Table 3: Seismic Design Parameters
Seismic Hazards.
Aside from the direct impact of ground shaking on structures, additional seismic hazards to be
considered in a seismic event include ground surface displacement from fault rupture,
liquefaction and amplification of ground motion, and landslides.
Surface Displacement: Due to the distance from the site to the nearest known strand
(discussed in Section 2.2) and the lack of evidence of past fault displacement onsite, we
expect the site to have a low risk for surface displacement.
Liquefaction: The liquefaction potential is highest for loose sand with a high groundwater
table. The underlying dense recessional outwash is considered to have a very low potential for
liquefaction and amplification of ground motion and seismically induced lateral spread.
3.3 Erosion Hazard
The erosion hazard criteria used for determination of affected areas includes soil type, slope
gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to
vegetative cover and the specific surface soil types (group classification), which are related to
the underlying geologic soil units. We reviewed the Web Soil Survey by the Natural Resources
Conservation Service (NRCS) to determine the erosion hazard of the on-site soils. The site
surface soils were classified using the SCS classification system as Spanaway gravelly sandy
loam, 0 to 3 percent slopes. The corresponding geologic unit for these soils is gravelly outwash,
which is in agreement with the soils encountered in our site explorations. The erosion hazard
for the soil is listed as being slight for the gently sloping conditions at the site.
3.4 Foundation Design
We recommend that foundations for the structures at the site consist of drilled pier
foundations. We recommend that the drilled piers be constructed following the placement of
the structural fill pad to raise the structures above the FEMA flood plain requirements.
The piers should be founded on undisturbed, medium dense or firmer soil. All loose or
disturbed soil should be removed from the foundation excavation prior to placing concrete. If
the soil at the planned bottom of footing elevation is not suitable, it should be overexcavated to
expose suitable bearing soil.
We recommend the piers penetrate into the medium dense or better native outwash deposits
to allow the development of full point resistance. The native soils were encountered at a depth
of about 16 feet. The minimum drilled pier depth should be 21 feet, or 5 feet into native soil.
2012/15 IBC Design Parameter Recommended Value
Seismic Design Category D
PGAM (2% in 50 years – 2,475 year event) 0.517
SDS 0.834
SD1 0.498
TComm 911 Yelm Water Tank | Page 11
RN File No. 3458-003A
September 25, 2020
Based on an anticipated drilled pier diameter of 1.5 feet, we recommend using an allowable
design bearing pressure of 7,000 psf. As plans develop, we are available to provide design soil
values under specific pier diameter and load conditions.
We expect that settlement of drilled pier foundations that are designed and constructed as
recommended will not exceed ½ inch. The majority of this settlement should take place
immediately after pile loading. The International Building Code (IBC) allows a one third increase
in allowable soil stresses for wind and seismic loads for certain load combinations. If the
appropriate load combinations are used, the allowable axial pile capacity recommended above
can be increased by one third when considering wind and seismic loads. The pipe piles should
not be used for consideration of resistance to lateral loads.
3.5 Retaining Wall Design
Lateral Loads
The lateral earth pressure acting on retaining walls is dependent on the nature and density of
the soil behind the wall, the amount of lateral wall movement, which can occur as backfill is
placed, and the inclination of the backfill. Walls that are free to yield at least one-thousandth of
the height of the wall are in an “active” condition. Walls restrained from movement by stiffness
or bracing are in an “at-rest” condition.
We recommend design earth pressure values as given in Table below. H represents the wall
height. These values assume that the on-site soils or imported granular fill are used for backfill,
and that the wall backfill is drained. The given values do not include the effects of surcharges,
such as due to foundation loads or other surface loads. Surcharge effects should be considered
where appropriate. Seismic lateral loads are a function of the site location, soil strength
parameters and the peak horizontal ground acceleration (PGA) for a given return period. We
used the seismic design parameters discussed in Section 3.2, above, to compute the additional
seismic lateral loads for the site.
Table 4: Lateral Earth Pressure Parameters
*Kicker is to be applied at 60% of the wall height
The above lateral pressures may be resisted by friction at the base of the wall and passive
resistance against the foundation. We recommend resistance values as given in Table 5 below.
To achieve these values of passive resistance pressure, the foundations should be poured
“neat” against the native dense soils, or compacted fill should be used as backfill against the
front of the footing, and the soil in front of the wall should extend a horizontal distance at least
equal to three times the foundation depth. A resistance factor of 0.67 has been applied to the
passive pressure to account for required movements to generate these pressures.
Earth Pressure
Condition Backslope Angle Equivalent Fluid
Density (pcf)
Seismic Earth
Pressure Kicker (psf)
Active (Ka) Level 35 8H
At-Rest (Ko) Level 55 8H
TComm 911 Yelm Water Tank | Page 12
RN File No. 3458-003A
September 25, 2020
Table 5: Passive Resistance to Lateral Earth Pressure Parameters
All wall backfill should be well compacted. Care should be taken to prevent the buildup of
excess lateral soil pressures due to overcompaction of the wall backfill.
3.6 Slabs-On-Grade
Slab-on-grade areas should be prepared as recommended in Section 3.10.1. Slabs should be
supported on medium dense or firmer native soils, or on structural fill extending to these soils.
Where moisture control is a concern, we recommend that slabs be underlain by 6 inches of pea
gravel for use as a capillary break. A suitable vapor barrier, such as heavy plastic sheeting,
should be placed over the capillary break. An additional 2-inch-thick damp sand blanket can be
used to cover the vapor barrier to protect the membrane and to aid in curing the concrete. This
will also help prevent cement paste bleeding down into the capillary break through joints or
tears in the vapor barrier. The capillary break material should be connected to the footing drains
to provide positive drainage.
3.7 Pavement Subgrade
The performance of roadway pavement is critically related to the conditions of the underlying
subgrade. We recommend that the subgrade soils within the roadways be prepared as
described in Section 3.10.1. Prior to placing base material, the subgrade soils should be
compacted to a non-yielding state with a vibratory roller compactor and then proof-rolled with a
piece of heavy construction equipment, such as a fully-loaded dump truck. Any areas with
excessive weaving or flexing should be overexcavated and recompacted or replaced with a
structural fill or crushed rock placed and compacted in accordance with recommendations
provided in Section 3.10.3.
3.8 Drainage
We recommend that runoff from impervious surfaces, such as roofs and access roadways, be
collected and routed to an appropriate storm water discharge system. The finished ground
surface should be sloped at a gradient of 5 percent minimum for a distance of at least 10 feet
away from the buildings, or to an approved method of diverting water from the foundation, per
IBC Section 1804.4. Surface water should be collected by permanent catch basins and drain
lines, and be discharged into a storm drain system.
3.9 Stormwater Management
It should be noted that the site is located within a Category 1 critical aquifer recharge area. The
stormwater management for the site must be designed in such a way as to meet the
performance standards described in Section 18.21.070.C of the Yelm Municipal Code (YMC).
These requirements are as follows:
Soil Type Coefficient of
Friction
Equivalent Fluid
Density (pcf)
Recessional Outwash (native/structural fill) 0.5 260
TComm 911 Yelm Water Tank | Page 13
RN File No. 3458-003A
September 25, 2020
1. Activities may only be permitted in a critical aquifer recharge area if the applicant can
show that the proposed activity will not cause contaminants to enter the aquifer and
that the proposed activity will not adversely affect the recharging of the aquifer.
2. The proposed activity must comply with the water source protection requirements of
the U.S. Environmental Protection Agency, Washington State Department of Health,
and the Thurston County environmental health division.
3. All new development, redevelopment and small parcel development shall meet the
water quality requirements of the stormwater manual as adopted by the City of Yelm.
Infiltration
We understand that the City of Yelm has adopted the 2012 Department of Ecology Stormwater
Management Manual for Western Washing as Amended in December 2014 (DOE) This manual
provides feasibility criteria for the use of infiltration best management practices (BMPs) for roof
downspouts in in Volume III, Section 3.1.1. Infiltration facilities serving roof downspouts must
have a minimum of 3 feet of permeable soil from the final grade to the seasonal high
groundwater table and have at least 1 foot of clearance from the expected bottom elevation of
the infiltration trench or drywell. Feasibility criteria for infiltration BMPs used for flow control are
provided in Volume III, Section 3.3.7. The existing soil conditions must provide a minimum of 5
feet of native permeable soil and vertical separation to an impermeable soil layer or seasonal
high groundwater table.
Our site explorations encountered fill soils to a depth of approximately 16 feet before
encountering native recessional outwash. We do not consider the existing fill soils suitable for
infiltration.
3.10 Earthwork and Construction Considerations
Site Preparation and Grading
The first step of site preparation should be to strip the vegetation, topsoil, or loose soils to
expose medium dense or firmer soils in equipment shelter, generator and fuel tank areas. The
excavated material should be removed from the site, or stockpiled for later use as landscaping
fill. The resulting subgrade should be compacted to a firm, non-yielding condition. Areas
observed to pump or yield should be repaired prior to placing hard surfaces.
Temporary and Permanent Slopes
Temporary cut slope stability is a function of many factors, such as the type and consistency of
soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains
open, and the presence of surface or groundwater. It is exceedingly difficult under these
variable conditions to estimate a stable temporary cut slope geometry. Therefore, it should be
the responsibility of the contractor to maintain safe slope configurations, since the contractor is
continuously at the job site, able to observe the nature and condition of the cut slopes, and able
to monitor the subsurface materials and groundwater conditions encountered.
For planning purposes, we recommend that temporary cuts in the near-surface soils be no
steeper than 1.5 Horizontal to 1 Vertical (1.5H:1V). ). If groundwater seepage is encountered,
we expect that flatter inclinations would be necessary.
TComm 911 Yelm Water Tank | Page 14
RN File No. 3458-003A
September 25, 2020
We recommend that cut slopes be protected from erosion. Measures taken may include
covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut
slopes. We do not recommend vertical slopes for cuts deeper than 4 feet, if worker access is
necessary. We recommend that cut slope heights and inclinations conform to local and
WISHA/OSHA standards.
Final slope inclinations for granular structural fill and the native soils should be no steeper than
2H:1V. Lightly compacted fills, common fills, or structural fill predominately consisting of fine
grained soils should be no steeper than 3H:1V. Common fills are defined as fill material with
some organics that are “trackrolled” into place. They would not meet the compaction
specification of structural fill. Final slopes should be vegetated and covered with straw or jute
netting. The vegetation should be maintained until it is established.
Structural Fill
All fill placed beneath buildings, pavements or other settlement sensitive features should be
placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed
methods and standards, and is observed by an experienced geotechnical professional or soils
technician. Field observation procedures would include the performance of a representative
number of in-place density tests to document the attainment of the desired degree of relative
compaction.
Materials: Imported structural fill should consist of a good quality, free-draining granular soil,
free of organics and other deleterious material, and be well graded to a maximum size of about
3 inches. Imported, all-weather structural fill should contain no more than 5 percent fines (soil
finer than a Standard U.S. No. 200 sieve), based on that fraction passing the U.S. 3/4-inch sieve.
The use of on-site soil as structural fill will be dependent on moisture content control. Some
drying of the native soils may be necessary in order to achieve compaction. During warm,
sunny days this could be accomplished by spreading the material in thin lifts and compacting.
Some aeration and/or addition of moisture may also be necessary. We expect that compaction
of the native soils to structural fill specifications would be difficult during wet weather.
Fill Placement: Following subgrade preparation, placement of the structural fill may proceed.
Fill should be placed in 8- to 10-inch-thick uniform lifts, and each lift should be spread evenly
and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying
building areas, and within a depth of 2 feet below pavement and sidewalk subgrade, should be
compacted to at least 95 percent of its maximum dry density. Maximum dry density, in this
report, refers to that density as determined by the ASTM D1557 compaction test procedure. Fill
more than 2 feet beneath sidewalks and pavement subgrades should be compacted to at least
90 percent of the maximum dry density. The moisture content of the soil to be compacted
should be within about 2 percent of optimum so that a readily compactable condition exists. It
may be necessary to overexcavate and remove wet surficial soils in cases where drying to a
compactable condition is not feasible. All compaction should be accomplished by equipment of
a type and size sufficient to attain the desired degree of compaction.
Utilities
Our explorations indicate that deep dewatering will not be needed to install standard depth
utilities. Anticipated groundwater is expected to be handled with pumps in the trenches. We
also expect that some groundwater seepage may develop during and following the wetter
TComm 911 Yelm Water Tank | Page 15
RN File No. 3458-003A
September 25, 2020
times of the year. We expect this seepage to mostly occur in pockets. We do not expect
significant volumes of water in these excavations.
The soils likely to be exposed in utility trenches after site stripping are considered moisture
sensitive. We recommend that they be considered for trench backfill during the drier portions
of the year. Provided these soils are within 2 percent of their optimum moisture content, they
should be suitable to meet compaction specifications. During the wet season, it may be difficult
to achieve compaction specifications.
Wet Weather Considerations
The on-site fill and recessional outwash likely to be exposed during construction will disturb
easily when wet. We expect these soils would be difficult, if not impossible, to compact to
structural fill specifications in wet weather. We recommend that earthwork be conducted
during the drier months. Additional expenses of wet weather or winter construction could
include extra excavation and use of imported fill or rock spalls. During wet weather, alternative
site preparation methods may be necessary. These methods may include utilizing a smooth-
bucket trackhoe to complete site stripping and diverting construction traffic around prepared
subgrades. Disturbance to the prepared subgrade may be minimized by placing a blanket of
rock spalls or imported sand and gravel in traffic and roadway areas. Cutoff drains or ditches
can also be helpful in reducing grading costs during the wet season. These methods can be
evaluated at the time of construction.
TComm 911 Yelm Water Tank | Page 16
RN File No. 3458-003A
September 25, 2020
4 FUTURE WORK
4.1 Engineering and Design
The intent of this geotechnical report is to provide LDC, Inc. with a professional evaluation of
existing subsurface conditions at the site and to provide recommendations for geotechnical
design elements of the proposed project.
Once LDC, Inc. has determined how to proceed with the project, we may be retained to
provide additional services including engineering, design work, and project management
specific to their chosen design.
4.2 Construction Observation
We should be retained to provide observation and consultation services during construction to
confirm that the conditions encountered are consistent with those indicated by the
explorations, and to provide recommendations for design changes, should the conditions
revealed during the work differ from those anticipated. As part of our services, we would also
evaluate whether or not installation activities comply with contract plans and specifications.
We recommend that Robinson Noble perform the following tasks:
Review contractor submittals
Observe foundation installation
Perform compaction tests
Perform laboratory tests as needed
Attend meetings as needed
Provide geotechnical consultation
TComm 911 Yelm Water Tank | Page 17
RN File No. 3458-003A
September 25, 2020
5 USE OF THIS REPORT
We have prepared this report for LDC, Inc. and their agents, for use in planning and design of
this project. The data and report should be provided to prospective contractors for their bidding
and estimating purposes, but our report, conclusions and interpretations should not be
construed as a warranty of subsurface conditions.
The scope of our services does not include services related to construction safety precautions,
and 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. There are possible variations in subsurface conditions. We recommend that project
planning include contingencies in budget and schedule, should areas be found with conditions
that vary from those described in this report.
Within the limitations of scope, schedule and budget for our services, we have strived to take
care that our services have been completed in accordance with generally accepted practices
followed in this area at the time this report was prepared. No other conditions, expressed or
implied, should be understood.
We appreciate the opportunity to be of service to you. If there are any questions concerning
this report or if we can provide additional services, please call.
TComm 911 Yelm Water Tank | Page 18
RN File No. 3458-003A
September 25, 2020
6 REFERENCES
City of Yelm Municipal Code. January 28, 2020
Dion, N.P., Turney, C.G., Jones, M.A. Plate 1 – Maps Showing Well Locations and Surficial
Geology, and Cross Sections. U.S. Geological Survey.,
International Code Council. 2015 International Building Code. June 5, 2014.
Structural Engineers Association of California (2019). Seismic Design Maps (web application).
https://seismicmaps.org/
United States Geological Survey (2019). Quaternary Fault and Fold Database of the United
States: Interactive Fault Map. https://earthquake.usgs.gov/hazards/qfaults/
Washington State Department of Natural Resources. 2012-2013. Understanding Earthquake
Hazards in Washington State: Modeling a Magnitude 5.7 Earthquake on the Olympia
Fault in Thurston County .
Washington Department of Ecology, 2012. Stormwater Management Manual for Western
Washington as Amended December 2014
Note:
Basemap taken
from McKenna 7.5
minute series.
USGS 2020.LDC, Inc: TComm911 Yelm Water Tank
Vicinity Map
Figure 1
PM: BAG
September 2020
3458-003A
Project
Site
RHOTON ROADG R AV E L PA R K I N G A R E A
G R A S S
G R A S S
G R A S S
G R A S S GATEPAD MOUNTED
TRANSFORMER
GENERATOR ON
CONCRETE PAD
TELEPHONE PEDESTAL
CCTV PEDESTAL
HANDHOLE
IRRIGATION
CONTROL VALVES
WHEEL STOP
(TYPICAL)
GRAVEL ROADWAY
GRAVEL
SIGN
TANK SUPPORT LEG
ON CONCRETE FOOTING
(TYPICAL)GATEASPHALT DRIVEWAY
WATER, BURIED POWER AND
TELEPHONE PAINTED LOCATES
VERTICAL PIPE
DRAIN
POWER OUTLET AT
EDGE OF FOOTING
G R A S S
G R A S S
G R A S S
G R A S S &
G R AV E L
G R A S S &
G R AV E L
VERTICAL
PVC PIPE
FLAG POLE
POWER OUTLET AT
EDGE OF FOOTING
APPROXIMATE FLOOD ZONE DELINEATION
LINE SCALED FROM FEMA FIRMETTE
SET HUB
(TYPICAL)
WATER TANK
(TO REMAIN)
EXISTING SITE
ACCESS ROAD
EXISTING TREES,
TYP (TO REMAIN)
EXISTING SITE
ACCESS GATE
1
A-1.2
PROPOSED TCOMM911 ELECTRICAL SERVICE
ORIGINATING FROM AN EXISTING 480Y/277, PSE
XFRM (559640/147526) AND CONTINUING VIA
BURIED CONDUIT WITHIN UNDERGROUND
TRENCH TO TCOMM911 EQUIPMENT SHELTER
(WITH POSSIBLE 25KVA STEP-DOWN
TRANSFORMER LOCATED WITHIN SHELTER)
DELIVERING 200A, 120/240 1PH, SERVICE TO
DISCONNECT AND DISTRIBUTION
PROPOSED TCOMM911 ANTENNAS MOUNTED
ON EXISTING WATER RESERVOIR WITH THE
ADDITION OF GROUND EQUIPMENT
PROPOSED
TCOMM911 25'-0"
SETBACK FROM ALL
IGNITION SOURCES,
BUILDINGS, &
PROPERTY LINES
140'-0"
ANTENNA SETBACK
Figure 2
Site Plan
LDC, Inc: TComm911 Yelm Water Tank
PM: BAG
September 2020
3458-003A
Note: Basemap taken
from Sheet A-1.1 Overall
Site Plan prepared by
LDC, Inc. dated
5/28/2020.
B-1
B-1
Scale 1" = 50'
0 50 100
0 30 60
Scale 1" = 30'
Number and Approximate
Location of Soil Boring
LEGEND
Approximate Location
of Resistivity Test
1
1
2
3
4
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS GROUP
SYMBOL GROUP NAME
WELL-GRADED GRAVEL, FINE TO COARSE GRAVEL
POORLY-GRADED GRAVEL
SILTY GRAVEL
CLAYEY GRAVEL
WELL-GRADED SAND, FINE TO COARSE SAND
GW
GP
GM
GC
SW
SP POORLY-GRADED SAND
SILTY SAND
CLAYEY SAND
SILT
CLAY
ORGANIC SILT, ORGANIC CLAY
SILT OF HIGH PLASTICITY, ELASTIC SILT
CLAY OF HIGH PLASTICITY, FAT CLAY
ORGANIC CLAY, ORGANIC SILT
PEATPTHIGHLY ORGANIC SOILS
GRAVEL
CLEAN GRAVEL
GRAVEL
WITH FINES
SAND CLEAN SAND
SAND
WITH FINES
INORGANIC
INORGANIC
ORGANIC
ORGANIC
COARSE -
GRAINED
SOILS
MORE THAN 50%
RETAINED ON
NO. 200 SIEVE
MORE THAN 50% OF
COARSE FRACTION
RETAINED ON NO. 4
SIEVE
MORE THAN 50% OF
COARSE FRACTION
PASSES NO. 4 SIEVE
SM
SC
ML
CL
OL
MH
CH
OH
FINE -
GRAINED
SOILS
MORE THAN 50%
PASSES NO. 200 SIEVE
SILT AND CLAY
SILT AND CLAY
LIQUID LIMIT
LESS THAN 50%
LIQUID LIMIT
50% OR MORE
NOTES:
1) Field classification is based on
visual examination of soil in general
accordance with ASTM D 2488-93.
2) Soil classification using laboratory
tests is based on ASTM D 2487-93.
3) Descriptions of soil density or
consistency are based on
interpretation of blowcount data,
visual appearance, of soils, and/or
test data.
SOIL MOISTURE MODIFIERS
Dry- Absence of moisture, dusty, dry
to the touch
Moist- Damp, but no visible water
Wet- Visible free water or saturated,
usually soil is obtained from
below water table
KEY TO BORING LOG SYMBOLS
*
*
*Modifications have been applied to ASTM
methods to describe sit and clay content.
SM
ML
Letter symbol for soil type
Ground water level
DD = Dry Density
MC ( ) = % Moisture =
Blows required to drive
sample 12 in. using SPT (converted to N )60
Contact between soil strata
(Dashed line indicates approximate
contact between soils)
Letter symbol for soil type
(Weight of water)
(Weight of dry soil)
NOTE: The stratification lines represent the approximate boundaries between soil types and the transition may be gradual
PM: BAG
September 2020
3458-003A LDC, Inc: TComm 911 Yelm Water Tank
Figure 3
N = N *C *C *C *C 60 M E B R S
N = blows/foot, measured in field M
C = ER /60, convert measured hammer energy E m
to 60% for comparison with design charts.
C = adjusts borehole diameterB
C = rod length, adjusts for energy loss in rodsR
C = Sample liner = 1.0S
Date 8/27/2020 Hole dia. (in) 6
Logged by ATB Hole depth (ft) 20'
Driller Holt Well dia. (in) N/A
Page 1 of 1 Elevation (ft) - Well depth N/A
Sample Liner Yes Hammer Eff. 86%
Dark brown silty fine to medium sand with gravel and SM 4/18 3
organics (loose, moist) (Fill)3
3
Dark brown silty fine to medium sand with gravel and SM 10/18 4
organics (medium dense, moist) (Fill)9
9
Dark brown silty fine to medium sand with gravel (loose, SM 6/18 1
moist) (Fill)2
3
Dark grayish-rown silty fine to medium sand with gravel SM 7/18 15
(medium dense, moist) (Fill)15
3
Dark brown to black silty sand with gravel and organics SM 7/18 11
medium dense, moist) (Buried Topsoil)10
10
Grayish-brown silty fine to coarse sand with gravel and
large cobbles (dense to very dense, moist) SM 11/12 50
(Recessional Outwash) Blowcounts may be overstated. 50/6"
Boring completed at 21 feet on August 27, 2020
25
Phone: 425-488-0599 Phone: 253-475-7711
Fax: 425-488-2330 Fax: 253-472-5846
17625 130th Ave NE, Suite 102 2105 South C Street
Woodinville, Washington 98072 Tacoma, Washington 98402
19
22
17
7
Standard Penetration Resistance
(140 lb. weight, 30" drop)
SPT N60 (blows/ft)
2
5
18
15
12
9
10
16
13
LITHOLOGY / DESCRIPTION
Moisture Content (%) Static Water Level14
3
4
6
1
B-1
U.S.C.Sample Recovery/ Driven Interval (in)N- Blow Counts (blows/6")8 Depth (feet)11
3548-003A Figure 4
24
23
20
21
TComm 911 - Yelm Water Tank
0 10203040506065+
RN File No. 3458-003A
September 2020
Appendix A
Resistivity Data
Name Date Time
Combined Distance Chart AC 4-Pole Wenner (Rho) 8/27/2020 12:07:29.000 PM
100k
200k
300k
400k
500k
600k
700k
800k
900k
1000k
1.1M
1.2M
1.3M
Ohm-cm
5.0000 Feet 30.000 Feet25.000 Feet
5.0000 Feet/Div
Distance d (Feet)Rho (Ohm-cm)R Y-Xv (Ohms)I Z-X (A)V Y-Xv (V)V.H-E (Z-X)
5 1267414.45 1324 0.00047 0.599 31.80
10 1008811.04 526.8 0.00041 0.209 31.90
20 504849.56 131.8 0.0004 0.0509 31.90
25 253573.73 52.96 0.00046 0.0234 31.90
30 118134.42 20.56 0.00053 0.0103 31.90
R P-Z (Ohms)R P-Y (Ohms)R P-Xv (Ohms)R P-X (Ohms)
40804 24087 38413 26105
Test Frequency (Hz)V Noise Y-Xv (V)Freq Noise Y-Xv (Hz)Test Voltage Output Limit (V)
128.1 0.02 - - -32
GroundTesterResult (Resistivity 8 27 2020 12 07 29 PM) - Wenner, 1 of 1
Line 1
Name Date Time
Combined Distance Chart AC 4-Pole Wenner (Rho) 8/27/2020 12:41:20.000 PM
200k
300k
400k
500k
600k
700k
800k
900k
1000k
1.1M
1.2M
1.3M
Ohm-cm
5.0000 Feet 30.000 Feet25.000 Feet
5.0000 Feet/Div
Distance d (Feet)Rho (Ohm-cm)R Y-Xv (Ohms)I Z-X (A)V Y-Xv (V)V.H-E (Z-X)
5 1252153.42 1308 0.00025 0.301 32.00
10 689021.04 359.8 0.00016 0.0545 32.00
25 222976.64 46.57 0.00045 0.0201 31.90
30 156445.01 27.23 0.00035 0.00875 32.00
R P-Z (Ohms)R P-Y (Ohms)R P-Xv (Ohms)R P-X (Ohms)
Overflow Overflow 50332 58328
Test Frequency (Hz)V Noise Y-Xv (V)Freq Noise Y-Xv (Hz)Test Voltage Output Limit (V)
128.1 0.17 180 32
GroundTesterResult (Resistivity 8 27 2020 12 41 20 PM) - Wenner, 1 of 1
Line 2
Name Date Time
Combined Distance Chart AC 4-Pole Wenner (Rho) 8/27/2020 1:54:27.000 PM
600k
700k
800k
900k
1000k
1.1M
1.2M
1.3M
1.4M
1.5M
1.6M
1.7M
Ohm-cm
5.0000 Feet 20.000 Feet15.000 Feet
3.0000 Feet/Div
Distance d (Feet)Rho (Ohm-cm)R Y-Xv (Ohms)I Z-X (A)V Y-Xv (V)V.H-E (Z-X)
5 1546564.26 1615 0.00021 0.309 32.00
10 1477596 771.5 0.00035 0.247 32.00
15 1154538.38 401.9 0.00018 0.0689 32.10
20 626872.66 163.7 0.0004 0.059 32.00
R P-Z (Ohms)R P-Y (Ohms)R P-Xv (Ohms)R P-X (Ohms)
59353 Overflow Overflow Overflow
Test Frequency (Hz)V Noise Y-Xv (V)Freq Noise Y-Xv (Hz)Test Voltage Output Limit (V)
128.1 0.2 0 32
GroundTesterResult (Resistivity 8 27 2020 1 54 27 PM) - Wenner, 1 of 1
Line 3
Name Date Time
Combined Distance Chart AC 4-Pole Wenner (Rho) 8/27/2020 2:23:55.000 PM
600k
800k
1000k
1.2M
1.4M
1.6M
1.8M
2M
2.2M
2.4M
2.6M
2.8M
3M
Ohm-cm
5.0000 Feet 30.000 Feet25.000 Feet
5.0000 Feet/Div
Distance d (Feet)Rho (Ohm-cm)R Y-Xv (Ohms)I Z-X (A)V Y-Xv (V)V.H-E (Z-X)
5 2894997.85 3023 0.00008 0.244 32.10
10 1816385.94 948.4 0.00012 0.101 32.10
20 551043.31 143.9 0.00029 0.0379 32.00
30 657470.21 114.4 0.00016 0.0163 32.50
R P-Z (Ohms)R P-Y (Ohms)R P-Xv (Ohms)R P-X (Ohms)
45293 33583 69836 Overflow
Test Frequency (Hz)V Noise Y-Xv (V)Freq Noise Y-Xv (Hz)Test Voltage Output Limit (V)
128.1 0.14 - - -32
GroundTesterResult (Resistivity 8 27 2020 2 23 55 PM) - Wenner, 1 of 1
Line 4
RN File No. 3458-003A
September 2020
Appendix B
Design Maps Summary Report
9/14/2020 U.S. Seismic Design Maps
https://seismicmaps.org 1/2
Latitude, Longitude: 46.949651, -122.601797
Date 9/14/2020, 10:40:53 AM
Design Code Reference Document IBC-2015
Risk Category II
Site Class D - Stiff Soil
Type Value Description
SS 1.25 MCER ground motion. (for 0.2 second period)
S1 0.498 MCER ground motion. (for 1.0s period)
SMS 1.25 Site-modified spectral acceleration value
SM1 0.748 Site-modified spectral acceleration value
SDS 0.834 Numeric seismic design value at 0.2 second SA
SD1 0.498 Numeric seismic design value at 1.0 second SA
Type Value Description
SDC D Seismic design category
Fa 1 Site amplification factor at 0.2 second
Fv 1.502 Site amplification factor at 1.0 second
PGA 0.517 MCEG peak ground acceleration
FPGA 1 Site amplification factor at PGA
PGAM 0.517 Site modified peak ground acceleration
TL 16 Long-period transition period in seconds
SsRT 1.25 Probabilistic risk-targeted ground motion. (0.2 second)
SsUH 1.268 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration
SsD 1.5 Factored deterministic acceleration value. (0.2 second)
S1RT 0.498 Probabilistic risk-targeted ground motion. (1.0 second)
S1UH 0.528 Factored uniform-hazard (2% probability of exceedance in 50 years) spectral acceleration.
S1D 0.6 Factored deterministic acceleration value. (1.0 second)
PGAd 0.6 Factored deterministic acceleration value. (Peak Ground Acceleration)
CRS 0.986 Mapped value of the risk coefficient at short periods
CR1 0.942 Mapped value of the risk coefficient at a period of 1 s
9/14/2020 U.S. Seismic Design Maps
https://seismicmaps.org 2/2
DISCLAIMER
While the information presented on this website is believed to be correct, SEAOC /OSHPD and its sponsors and contributors assume no responsibility or
liability for its accuracy. The material presented in this web application should not be used or relied upon for any specific application without competent examination
and verification of its accuracy, suitability and applicability by engineers or other licensed professionals. SEAOC / OSHPD do not intend that the use of this
information replace the sound judgment of such competent professionals, having experience and knowledge in the field of practice, nor to substitute for the
standard of care required of such professionals in interpreting and applying the results of the seismic data provided by this website. Users of the information from
this website assume all liability arising from such use. Use of the output of this website does not imply approval by the governing building code bodies responsible
for building code approval and interpretation for the building site described by latitude/longitude location in the search results of this website.