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�"'"""""'�''�� Subsurface Exploration, Geologic Hazards, and
Preliminary Geotechnical Engineering Report
Water Resources ��
PROPOSED
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BLTILDING RE-SITE
� � RENTON TECHNICAL COLLEGE
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� Renton, Washington
Solid and Hazardous Waste 11�1
Prepared for
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z �, -,��,_ _. 'P:c���-�c,,� �c�_ ._�� _sv Project No. KE05606A
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October 13, 2005
Project No. KE05606A
Renton Technical College
c/o S.M. Stemper Architects, PLLC
4000 Delridge Way SW, Suite 200
Seattle, Washington 98106 '
Attention: Ms. Sally MacGregor
Subject: Subsurface Exploration, Geologic Hazards, and
Preliminary Geotechnical Engineering Report
Proposed Maintenance and Classroom Building Re-site
Renton Technical College
3000 NE 4`� Street
Renton, Washington
Dear Ms. MacGregor:
We are pleased to present the enclosed copies of the above-referenced report. This report
summarizes the results of our subsurface exploration, geologic hazards, and preliminary
geotechnical engineering study and offers recommendations for the preliminary design and
development of the proposed project. Our recommendations are preliminary in that site
grading, structural plans, and construction methods have not been finalized at the time of this
report.
We have enjoyed working with you on this study and are confident that the recommendations
presented in this report will aid in the successful completion of your project. If you should
have any questions or if we can be of additional help to you, please do not hesitate to call.
Sincerely,
ASSOCIATED EARTH SCIENCES, INC.
Kirkland, Washington
� `
7
Kurt D. Merriman, P.E.
Principal Engineer
KDMiId-KEOi606A3-Projeccs�2005606iKE1WP
� � � _ i i . � ��f- � �. � ,
SUBSURFACE EXPLORATION, GEOLOGIC HAZARDS, AND
PRELIlVIINARY GEOTECHIVICAL ENGINEERING REPORT
PROPOSED
MAINTENANCE AND CLASSROOM
BUILDING RE-SITE
RENTON TEC�INICAL COLLEGE I
Renton, Washington
I
Prepared for:
Renton Technical College
c/o S.M. Stemper Arclutects, PLLC
4000 Delridge Way SW, Suite 200
Renton, Washington 98106
Prepared by:
Associated Earth Sciences, Inc.
911 5`� Avenue, Suite 100
Kirkland, Washington 98033
425-827-7701
Fax: 425-827-5424
October 13, 2005
Project No. KE05606A
Proposed Maintenance/Classroan Building (Building N) Subsurface Exploration, Geologic Ha<.ards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Project and Site Conditions
I. PROJECT AND SITE CONDITIONS
1.0 INTRODUCTION
This report presents the results of our subsurface exploration, geologic hazards, and
preliminary geotechnical engineering study for the proposed Maintenance/Classroom Building
(Building N) within the Renton Technical College campus located at 3000 NE 4�' Street,
Renton, Washington. The general location of the site is depicted on the Vicinity Map, Figure
l. The proposed building location and approximate locations of the explorations accomplished
for this study are presented on the Site and Exploration Plan, Figure 2. Our recommendations
are preliminary in that site grading, structural plans, and construction methods have not been
finalized at the time of this report. In the event that any changes in the nature, design, or
location of the structure are planned, the conclusions and recommendations contained in this
report should be reviewed and modified, or verified, as necessary.
1.1 Purpose and Scope
The purpose of this study was to provide subsurface data to be utilized in the preliminary
design and development of the subject project. Our study included a review of available
geologic literature, excavating an exploration pit, drilling an exploration boring, and
performing geologic studies to assess the type, thickness, distribution, and physical properties
of the subsurface sediments and shallow ground water conditions. Infiltration testing was
conducted within the exploration pit. Geologic hazard evaluations and geotechnical
engineering studies were also conducted to deternune suitable geologic hazard mitigation
techniques, the type of suitable foundation, allowable foundation soil bearing pressures,
anticipated settlements, temporary slope/shoring recommendations, basement/retaining wall
lateral pressures, floor support recommendations, and drainage considerations. This report
summarizes our current fieldwork and offers hazard mitigation, development, and infiltration
recommendations based on our present understanding of the project.
1.2 Authorization
Authorization to proceed with this study was granted by Ms. Sally MacGregor of S.M.
Stemper Architects, PLLC. Our study was accomplished in general ac�ordance with our
proposal letter dated August 25, 2005. This report has been prepared for the exclusive use of
Renton Technical College, S.M. Stemper Architects, PLLC, and their a��nts for specific
application to this project. Within the limitations of scope, schedule, and bud�et, our services
have been performed in accordance with generally accepted geotechnical engineering and
engineering geology practices in effect in this area at the time our report was prepared. No
other warranty, express or implied, is made. It must be understood that no recommendations
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Proposed Maintenance/Classroom Building (Building 1� Subsurface Fxploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Project and Site Conditions
or engineering design can yield a guarantee of stable slopes. Our observations, findings, and
opinions are a means to identify and reduce the inherent risks to the owner.
2.0 PROJECT AND SITE DESCRIPTION
This report was completed with an understanding of the project based on information provided
in a letter dated August 22, 2005 by S.M. Stemper Architects, PLLC, and an attached copy of
a portion of the Renton Technical College campus map showing the proposed location of the
maintenancelclassroom building. Present plans call for a two-story structure with daylight
basement with slab-on-grade floors planned for the basement area of the building. The lowest
level will be set at approximately the same elevation as the westerly adjacent parking area.
The second floor of the proposed new building will be at approximately the same elevation as
the easterly adjacent Building M.
The property is situated at 3000 NE 4`� Street in Renton, Washington and is the site of Renton
Technical College. The proposed new building will be situated within the northern portion of
the school campus. An asphalt concrete parking area extends along the western edge of the
proposed building area. A retaining wall, ranging in height to approximately 6 feet, extends
generally north-south within the eastern portion of the site to be developed. The retaining wall
retains an easterly adjacent play area for the child care Building M located east of the proposed
building. A moderate, 15- to 20-foot-high, grass-covered slope descends across the proposed
building area from the east retaining wall to the west parking area. A rockery wall extends
along the toe of the slope within the southern portion of the proposed building area. !,
The existing site slope is considered by the City of Renton Code to be a "Medium Landslide
Hazard," which is defined in the Renton Municipal Code, Chapter 3, Section 4-3-050,
paragraph 4.c.ii as "Areas with slopes between fifteen percent (I S%) and forty percent (40%)
and underlain by soils that consist largely of sand, gravel or glacial till." Based on
topographic information provided to us, the overall slope gradient measured from top to toe of
slope is approximately 20 to 40 percent (SH:1V [Horizontal:Vertical] to 2.SH:1V).
As proposed, site development will require temporary cuts to a height of approximately ?0 feet
along the eastern perimeter of the development. Where space limitations result in temporary ,
excavations steeper or higher than recommended herein, shoring will be required. The actual
location and configuration of the temporary cut will factor into the determination regarding
how much and where shoring will be required.
Ocrober 10, ?�S ASSOCIATED EARTH SCIE:b'CES, I�ti'C. II
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Proposed Maintenance/Classroom Building (Building N) Subsurface Exploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Project and Site Conditions
3.0 SUBSURFACE EXPLORATION
Our field study included drilling one exploration boring, excavating one exploration pit,
perfornung infiltration testing, and conducting a geologic and geologic hazard reconnaissance
to gain information about the site. The various types of sed'unents, as well as the depths where
� characteristics of the sed'unents changed, are indicated on the exploration logs presented in the
Appendix. The depths indicated on the logs where conditions changed may represent
gradational variations between sediment types in the field. If changes occurred between
sample intervals, they were interpreted. Our explorations were approximately located in the
field by estimation from known site features shown on the site plan provided to us.
The conclusions and recommendations presented in this report are based on subsurface
conditions revealed in the exploration boring and exploration pit completed for this study. The
number, locations, and depths of the explorations were completed within site and budgetary
constraints. Because of the nature of exploratory work below ground, extrapolation of
subsurface conditions between field explorations is necessary. It should be noted that differing
subsurface conditions may sometimes be present due to the random nature of deposition and
the alteration of topography by past grading and/or filling. The nature and extent of any
variations between the field explorations may not become fully evident until construction. If
vaziations are observed at that time, it may be necessary to re-evaluate specific
recommendations in this report and make appropriate changes.
3.1 Exploration Boring
The exploration boring was completed by advancing a 33/s-inch, inside-diameter, hollow-stem
auger with a track-mounted drill rig. During the drilling process, samples were obtained at
generally 2.5- or 5.0-foot-depth intervals. The boring was continuously observed and logged
by a geotechnical engineer from our firm. The exploration log presented in the Appendix is
based on the field log, drilling action, and inspection of the samples secured.
Disturbed but representative samples were obtained by using the Standard Penetration Test
(SPT) procedure in accordance with American Society for Testing and Materials (ASTM):D
1586. This test and sampling method consists of driving a standard 2-inch, outside-diameter,
split-barrel sampler a distance of 18 inches into the soil with a 140-pound hammer free-falling
a distance of 30 inches. The number of blows for each 6-inch interval is recorded and the
number of blows required to drive the sampler the final 12 inches is known as the Standard
Penetration Resistance ("N") or blow count. If a total of 50 is recorded within one 6-inch
interval, the blow count is recorded as the number of blows for the corresponding number of
inches of penetration. The resistance, or N-value, provides a measure of the relative density of
granular soils or the relative consistency of cohesive soils; these values are plotted ��n the
attached boring log.
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Proposed Maintenance/Classroom Building (Building 1� Subsurface Exploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Project and Site Conditions '
The samples obtained from the split-barrel sampler were classified in the field and
representative portions placed in watertight containers. The samples were then transported to
our laboratory for further visual classification and laboratory testing, as necessary.
3.2 Exploration Pit
The exploration pit completed for this study was excavated with a rubber-tired backhoe. The
exploration pit permitted direct, visual observation of subsurface conditions. Materials
encountered in the exploration pit were studied and classified in the field by a geotechnical i
engineer from our firm. The exploration pit was backfilled immediately after examination and
�
logging. Selected samples recovered from the exploration were transported to our laboratory
for further visual classification and testing, as necessary.
3.3 Infiltration Testing
An infiltration test was conducted at a depth of approximately 5 feet below existing ground
surface in infiltration pit IP-1 in the vicinity of the proposed storm water management structure
adjacent to the southwest corner of the proposed maintenance/classroom building. The
infiltration testing was conducted using a method generally corresponding to the procedure
� described for the Pilot Infiltration Test (PIT) in the Washington State Department of Ecology
2001 Stormwater 1l�anagement Manual for Western Washington (Ecology Manual). This test is
conducted by discharging water into a flat-bottomed pit of known dimensions for a 4-hour
"soai�ing period" to allow the receptor soils in the immediate vicinity of the pit to become
saturated. After completion of the soaking period, water is discharged into the pit at a rate
sufficient to maintain a constant head in the pit. This is continued until the discharge rate
required to maintain a constant head remains fairly consistent over a period of 1 hour. Ground
water infiltration was conducted inside a large-diameter (72-inch-diameter) iron ring embedded
into the unweathered advance outwash soil. The large-diameter ring was used in lieu of the
open pit described in the Ecology Manual to avoid or reduce testing errors due to such factors
as sidewall collapse, inaccurate measurement of open pit areas, and sidewall infiltration.
The water source used for the test consisted of a fire hydrant located near the northwest corner
of the Renton Technical College campus. Water was discharged into the pit through a fabric
diffuser to minimize turbulence and scouring of the pit bottom. A flow meter/totalizer was
'i used to monitor the water discharge rate and total flow. A staff gauge with 0.01-foot divisions
' was installed to monitor the depth of water during testing. For the constant head test, a head
� of approximately 0.53 feet was maintained in the pit. Following completion of the constant
head test, the flow of water into the pit was discontinued, and the rate of water level decline
(falling head) in the pit was monitored. Upon completion of the test, the pit was excavated to a
depth of 10 feet to allow observation of soil conditions below the elevation of the test. The
infiltration pit was backfilled immediately after examination and logging. Selected samples
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Proposed Maintenance/Classroom Building (Building N) Subsurface Fxploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Project and Site Conditions ,
recovered from the exploration were transported to our laboratory for further visual
classification and testing, as necessary.
All infiltration test data was recorded by hand in the field and subsequently transferred to an
electronic spreadsheet to allow more accurate and consistent infiltration rate calculations. The
' infiltration testing results are summarized below in Table 1.
The infiltration rate measured during the constant head test was equal to or slightly greater
than the rate measured during the falling head test. This is typical and is reflective of the
decreasing head in the pit below that maintained during the constant head test.
Table 1
Summary of Infiltration Testing Results
Infiltration Rate
Constant Head Test Falling Head Test
Test No. (in/hr)cn (in/hr)�'� '
IP-1 14.6 12
�'� in/hr = inches per hour
3.4 Laboratory Testing '
In order to provide a prelirninary infiltration rate estimate based on published correlation to
soil grain size, samples were submitted for mechanical grain size analysis testing in accordance
with ASTM:D 1140. A summary of preliminary testing results is provided below in Table 2.
Table 2
Summary of Laboratory Testing Results
Percent Silt
Infiltration Pit Sample Depth (% passing
No. (feet) Soil Type No. 200 sieve)
IP-1 0 - 5 SAND, trace silt 2.9
IP-1 5 - 7 SAND, trace silt 2.8
IP-1 7 - 10 SAND, trace silt 4.3
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Proposed Maintenance/Classroom Building (Building N) Subsurface Fzploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Project and Site Conditions
4.0 SUBSURFACE CONDITIONS
Subsurface conditions at the project site were inferred from the field explorations accomplished
for this study, visual reconnaissance of the site, and review of applicable geologic literature.
Exploration boring EB-1 was drilled within the higher elevation, eastern portion of the site;
� exploration pit EP-1 and infiltration pit IP-1 were excavated near the toe of the slope within the
southerly portion of the proposed structure. As shown on the field logs, exploration boring
EB-1 encountered approximately 2 feet of relatively loose, sandy fill overlying medium dense,
stratified, fine to coarse sand and limited silt to the bottom of the exploration boring at 21.5
feet. Infiltration pit IP-1 encountered approximately 2.5 to 3 inches of asphalt concrete
surfacing underlain by a 1-inch thickness of fine crushed gravel over medium dense, stratified,
fine to medium sand with a trace of silt to the bottom of the pit at 10 feet. A silty fine sand
lens was encountered at a depth of 7 feet within the infiltration pit. Exploration pit EP-1
encountered approxunately 1 foot of loose sand fill over medium dense, stratified, fine to
medium sand with a trace of silt to the bottom of the pit at 10 feet. The following sections
present more detailed subsurface information.
4.1 Stratigraphy
Fill
Fill soils (those not naturally placed) were encountered to a depth of approxirnately 2 feet in
exploration boring EB-1 and in exploration pit EP-1. With the exception of the asphalt
� surfacing and underlying crushed rock base, no fill was encountered in infiltration pit IP-1.
Based on the classification of the native soils encountered on-site, it is considered likely that
the fill soil was derived from on-site sources and placed during one of the phases of earlier site
I development. The fill generally consisted of a loose mixture of silt and sand. The fill soils, as
observed, are considered unsuitable for support of the proposed structure. Existing fill soil
may be considered for use as structural fill where moisture-conditioned and compacted as
recommended in the Structural Fill section of this report. Fill depth may vary across the
proposed building area. Fill is also anticipated along the east side of the retaining wall along
the eastern portion of the area to he developed.
Vashon Recessiorial Ounvash
Below the fill, a medium dense, stratified mixture of fine to coarse sand with a trace of silt
interpreted as Vashon recessional outwash was encountered. The Vashon recessional outwash
was deposited by meltwater streams that emanated from the retreating glacial ice during the
latter portion of the Vashon Stade of the Fraser Glaciation approximately 13,000 years ago.
The upper portion of the recessional outwash sediments encountered during our exploration
typically contained substantial quantities of silt. The weathered recessional outwash horizon
was typically limited to the portion of this unit located within approximately 4 feet of the
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Proposed Maintenance/Classroom Building (Building N) Subsurface�rploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Reraon, Washington Project and Site Condirions
ground surface. Where encountered during our exploration, the Vashon recessional outwash
sediments extended to depths in excess of the maximum depth explored.
', 4.2 Hydrology
No ground water/seepage was encountered in our explorations. It should be noted that
fluctuations in the level of the ground water may occur due to the tune of the year, variations
in rainfall, irrigation, on- and off-site land usage, and other factors.
4.3 Site Inf'iltration
The Ecology Manual defines three methods for detemuning long-term infiltration rate. The
methods are identified in the following paragraphs and results, as related to the project site, are
presented.
Method 1
The results of grain size analyses conducted on soil samples obtained from IP-1 excavated in
the vicinity of the proposed storm water facility indicate a silt content ranging between 0.6 and
4.7 percent. Using the United States Department of Agriculture (USDA) Textural Triangle
presented as Figure 7.1 in the Ecology Manual, the texture of the samples tested is determined
to be sand. Using this texture classification in conjunction with Table 7.1 in the Ecology
Manual, an estimated long-term (design) infiltration rate of 2 inches per hour, whieh includes a
correction factor (CF) of 4, is considered appropriate for site soils.
Method 2
The second method, Method 2, presented in the Ecology Manual, allows estunation of long-
term (design) infiltration rate directly from soil gradation data. This method requires a
determination of the effective size of the grains comprising tbe soil. The effective size (D�o) is
defined as the size corresponding to 10 percent on the grain size curve. The effective size of
soil within samples obtained from the site ranges from approximately 0.15 millimeter (mm}
(IP-1 at 7 to 10 feet) to 0.25 mm (IP-1 at 5 to 7 feet). Using the effective size determined for
samples tested and Table 7.2 presented in the Ecology Manual, the corresponding estimated
long-term (design) infiltration rate for site soil ranges from 2 to 3.5 inches per hour.
Method 3
As described in Section 3.3 Infiltration Testing, a PIT was conducted in general conformance
with Method 3 presented in the Ecology Manual. The results of the test indicated an
infiltration rate of 14.6 inches per hour.
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Proposed Mainrenance/Classroom Building (Building N) Subsurface Exploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton. Washington Project and Site Conditions
Infiltration Design (Long-Term) Rate
Subsurface conditions encountered during site exploration indicated soil stratification and
relatively minor fine soil lenses within the soil underlying the site. Based on observations
during site exploration in combination with the results of the PIT and the long-term infiltration
" rate determined by the two methods described above, we recommend a maximum design
infiltration rate of 2 inches per hour.
To enhance the performance of the proposed infiltration system so that a design rate of 2
inches per hour can be used without additional reduction factors, we recommend construction
of vertical gravel drains to extend beneath the base of the system through any silty soil layer to
allow for a vertical hydraulic connection between the system and the underlying sand stratum.
It is our understanding that Stormtech chambers will be used for the site infiltration system.
Typical gravel drains for the proposed system would consist of trenches measuring 10 feet
deep, 2 feet wide, and 4 feet long filled with pea gravel and covered with filter fabric. For
preliminary planning, approximately one gravel drain is recommended beneath each Stormtech
SC-740 chamber group (nominal chamber dimensions: 48 inches deep, 51 inches wide, and
90.7 inches long). Placement of recommended drains effectively doubles the storage capacity
of the system, provides greater surface area for infiltration to occur, and significantly improves
vertical infiltration preventing adverse ground water mounding effects.
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Proposed Maintenance/Classroom Building (Building N) Subsurface Exploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Geologic Hazards and Mitigarions
II. GEOLOGIC HAZARDS AND MITIGATIONS
The following discussion of potential geologic hazards is based on the geologic, slope, and
ground water conditions as observed and discussed herein. The discussion will be limited to
seismic, landslide or mass wasting, and erosion, including sed'unent transport.
5.0 SEISMIC HAZARDS AND RECOMMENDED MITIGATION
�
Earthquakes occur in the Puget Lowland with great regularity. The vast majority of these
', events are small and are usually not felt by people. However, large earthquakes do occur as
evidenced by the 1949, 7.2-magnitude event; the 1965, 6.5-magnitude event; and the 2001 6.9-
magnitude event. The 1949 earthquake appears to have been the largest in this area during
recorded history. Evaluation of earthquake return rates indicates that an earthquake of the
magnitude between 5.5 and 6.0 is likely within a given approximate 20-year period.
Generally, there are four types of potential geologic hazards associated with large seismic
events: 1) surficial ground rupture; 2) liquefaction; 3) ground motion; and 4) seismically
induced landslides. The potential for each of these hazards to adversely impact the proposed
project is discussed below.
5.1 Surficial Ground Rupture
Generally, the largest earthquakes that have occurred in the Puget Sound area are sub-crustal
events with epicenters ranging from 50 to 70 kilometers in depth. For this reason, no surficial
faulting or earth rupture as a result of seismic activity has been documented to date within at
least 5 miles of the site. Therefore, it is our opinion, based on existing geologic data, that the
risk of surface rupture impacting the proposed project is low, and no mitigations are necessary.
5.2 Liquefaction
Liquefaction is a process through which unconsoli�iated soil loses strength as a result of
vibratory shaking, such as that which occurs during a seismic event. During normal
conditions, the weight of the soil is supported by both grain-to-grain contacts and by the
pressure within the pore spaces of the soil below the water table. Extreme vibratory shaking
can disrupt the grain-to-grain contact, increase the pore pressure, and result in a decrease in
soil shear strength. The soil is said to be liquefied when nearly all of the weight of the soil is
supported by pore pressure alone. Liquefaction can result in deformation of the sediment and
settlement of overlying structures. Areas most susceptible to liquefaction include those areas
underlain by coarse silt and sand with low relative densities accompanied by a shallow water
table. '
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Proposed Maintenance/Classroom Building (Building N) Subsurface Fxploration, Geologic Hazards, I
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Geologic Hazards and Mitigations
The majority of the soils encountered in our explorations were in a medium dense to dense ;
condition and therefore do not present a significant liquefaction hazard. Based on soil density ',
and the absence of ground water, site soils are considered to have a low potential for
,, liquefaction.
5.3 Ground Motion
Based on site stratigraphy and visual reconnaissance of the site, it is our opinion that any
earthquake damage to the proposed structure founded on suitable bearing strata would be
caused by the intensity and acceleration associated with the event and not any of the impacts
discussed in the Seismic Hazards and Recommended Mitigation section of this report.
Structural design of the building should take into consideration stress caused by seismically
induced earth shaking.
Due to the thickness and consistency of the sediments underlying the site, amplification of
seismic motion upward through this soil column is possible. The approximate proposed
building period should be compared to the estimated soil column period of vibration to check
for resonant conditions. It is these conditions that result in our recommendation for the more
stringent Site Class D for use with the International Building Code (IBC), as discussed below.
Guidelines presented in the 2003 IBC, Section 1615, may be used. Information presented in �
Figure 1615(1) indicates a mapped spectral acceleration for short periods of S5 = 1.37. I
Information presented in Figure 1615(2) indicates a mapped spectral acceleration for a 1- II
second period of S� = 0.47. Based on the results of subsurface exploration and on an !,
estimation of soil properties at depth utilizing available geologic data, Site Class D in li
conformance with Table 1615.1.1 may be used. Site coeff'icients Fa = 1.0 and F� = 1.5 in '
conformance with IBC Tables 1615.1.2(1) and 1615.1.2(2), respectively, may be used. �
5.4 Seismically Induced Landslides I
The existing slope within the building area is to be removed and replaced with a retaining wall
as a part of site development. Therefore, the potential risk of seismically induced landslides
affecting the proposed structure is eliminated. No mitigations are recommended regarding
seismically induced landslides. Slope stability is discussed further in the following section.
6.0 LANDSLIDE HAZARDS AND MITIGATION
Generally, there are two rypes of landslides that commonly occur in the Puget Sound region.
The first type is termed Earth Slump or Slump-Earth Flow. This type of earth movement is
deep-seated and usually involves the regolith (topsoil) and the underlying sedimentary units.
Slides of this type can be very large.
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Renton Technical College and Preliminary Geotechnical Engineering Repon
Renton, Washington Geologic Hazards and Mitigations
The second type is termed Debris Slump or Debris Flow and usually involves the upper few
feet of the regolith. This type of slide is very dependent on local drainage patterns and the
resulting moisture content of the soils.
Based on the site stratigraphy and visual geologic reconnaissance, the slope areas appear to be
� more susceptible to a shallow debris flow due to the presence of the medium dense outwash
soil encountered below the surficially disturbed fill/topsoil horizon. A slope stability analysis
was beyond the scope of this study, and therefore the stability risks cannot be quantified by this
study. However, it is our opinion, based on previous similar studies and similar slope and soil
types, that the seismic and static factors of safety would lie within generally accepted limits
and that the deep-seated landslide risks on the site are low under both static and seismic
conditions. The proposed development should not increase the risk of deep-seated movements
provided the recommendations presented in this report are followed.
As discussed earlier in this report, proposed development will eliminate the existing slope
within the building area and will eliminate the potential risk of landslides affecting the
proposed structure. Slopes will remain north and south of the proposed structure and adjacent
to pedestrian walkways. Based on observed evidence of weathering and disturbance due to I
burrowing rodents, it is our opinion that shallow movement on the slope areas to remain north I
and south of the proposed structure presents a low risk under current site conditions. Since
local drainage, slope steepness, slope height, and vegetation cover largely influence the
shallow stability and soil erosion, the planned development will require specific mitigation
measures to avoid increasing the shallow earth movement risk. These mitigations include
controlling runoff, establishing vegetation cover, and following the recommendations as
outlined in this report. In our opinion, by following these recommendations, the risk of
shallow earth movement on the site or on surrounding properties will not be increased by the
proposed construction.
7.0 EROSION HAZARDS AND MITIGATION
As defined by the City of Renton, "Erosion hazard areas are identified by the presence of
vegetative cover, soil texture, slope, and rainfall patterns, or human-induced changes to such
characteristics which create site conditions which are vulnerable to erosion. Erosion hazard
areas are classified as having moderate to severe, severe, or very severe erosion potential by
the Soil Conservation Service, United States Department of Agriculture (USDA). "
Soils in the vicinity of the project are mapped by the USDA as Alderwood gravelly sandy loam
on slopes of 6 to 15 percent. Site-specific information from our explorations is in general
agreement with the USDA mapping. Some areas of Alderwood soils on slopes of 15 to 30
percent may be encountered, but are not mappable at the USDA map scale. Surface runoff and
erosion hazards soil characteristics of these soil types are presented in Table 4.
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Proposed Maintenance/Classroom Building (Building N) Subsurface Fxploration, Geologic Hazards,
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Renton, Washington Geologic Hazards and Mitigalions
Table 4
Surface Runoff and Erosion Hazard Soil Characteristics
Soil Type Percent Slope Surface Runoff Erosion Hazard
Alderwood 6 to 15 Medium Moderate
Alderwood 15 to 30 Medium to Rapid Moderate to Severe
The on-site soils contain a significant amount of fines and are considered moisture-sensitive.
Therefore, all permanent and temporary slopes should be protected from erosion. The
following general erosion mitigation measures are recommended for use throughout the site.
1. All storm water from impermeable surfaces should be tightlined into approved storm
water drainage systems.
2. To reduce the amount of sediment transport from the proposed construction area, silt
fencing should be placed along the lower elevations of the cleared areas.
3. Temporary sediment catchment facilities, interceptor drainage swales, and surface
conveyance swales should be installed to intercept runoff and eroded sediment prior to
site work. Check dams should be installed, as necessary.
4. Earthwork should proceed during the drier summer periods of the year and disturhed
areas should be revegetated as soon as possible. Temporary erosion control measures
should be maintained until permanent erosion control measures are established.
5. All devices used to collect surface runoff should be directed into a tightline or swale
system designed to convey the collected drainage to discharge within an approved storm
drain system.
6. Soils that are to �:. reused around the site should be stored in such a manner as to
reduce erosion. Protective measures may include, but are not necessarily limited to,
covering with plastic sheeting, the use of low stockpiles in flat areas, or the use of
straw bales/silt fences.
7. Prior to the onset of winter, any exposed subgrade should be hydroseeded, covered
with plastic sheeting, or otherwise protected. Seed should be planted soon enough to ',
have the grass established by October 31. If suitable ground-cover vegetation is not I
' established prior to the wet season, mulch cover or plastic sheeting should be used. '
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Proposed Maintenance/Classroom Building (Building 11� Subsurface Fxploration, Geologic Hazards, I�,
Renron Technical College and Preliminary Geotechnical Engineering Repon ,
Renton, Washington Geologic Hazards and Mitigations ��i
8. At the end of each workday, disturbed areas should be sloped to drain into a storm '
conveyance and seal-rolled to promote surface drainage.
9. A temporary, rock-surfaced construction entrance and staging areas should be I
established early in the project sequence.
10. All storm water from impermeable surfaces, including driveways and roofs, should be
tightlined into approved facilities and not directed onto or above steeply sloping areas. ,
11. As much of the natural vegetation on the slopes as is possible should be left intact i
during construction. Sloping areas without sufficient vegetation and areas stripped of
vegetation during construction should be planted as soon as possible or otherwise
protected.
12. Erosion control measures should be inspected regularly and maintained/improved as
necessary to maintain function.
13. The surface of the slopes to remain adjacent to the proposed building and associated
hardscape should be scarified, moisture-conditioned as necessary, and compacted. The
resulting slope gradient should be as uniform as possible and should match that of the
surrounding areas.
14. Regular pest control services should be employed to maintain the site free of burrowing
rodents.
Associated Earth Sciences, Inc. (AESI) would be available to provide site-specific
recommendations upon request. We recommend that an erosion control inspector or the
geotechnical engineer make on-site inspections as needed to monitor performance of the
erosion control system. In this way, site-specific recommendations, modifications, and
construction sequencing decisions can be made during the construction phase.
October 10, 200J ASSOCIATED EARTN SCIENCES, INC.
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Proposed Maintenance/Classroom Building (Building 1� Subsurface Exploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Preliminary Design Recommendations
III. PRELIMINARY DESIGN RECOMMENDATIONS
8.0 INTRODUCTION �
: Our exploration indicates that, from a geotechnical standpoint, the project azea is suitable for
the proposed development provided that the recommendations contained herein are properly
followed. It is our understanding that column loads will be on the order of 100 to 150 kips.
Subsurface conditions disclosed by our explorations revealed medium dense to dense advance
outwash sediments at a depth of approximately 1 to 2 feet below existing ground surface. ,
Given the loose nature of the fill and disturbed advance outwash soil, it is not recommended
for support of building foundations. The existing fill and disturbed advance outwash materials
may be suitable for reuse as structural fill provided the moisture content is maintained within
the compactable range.
Site development will require temporary cuts to a height of 20 feet (maximum) along the
eastern, northern, and southern perimeters of the proposed structure. Where space limitations
result in temporary excavations steeper or higher than recommended herein, shoring will be
required. The actual location and configuration of the temporary cut will be factors in how
much and where shoring will be required. Recommendations are presented in the Shoring -
Soldier Pile Walls section of this report.
9.0 SITE PREPARATION
Site preparation within the planned building area should include removal of all trees, landscape
structures, pavements, brush, debris, and any other deleterious material. Additionally, any
organic topsoil should be removed and the remaining roots grubbed.
Any buried structures and/or utilities should be removed or relocated if they are encountered
under/within the area to be developed. The resulting depressions that extend below or outside
the plann�d excavation envelope should be backfilled with structural fill, as discussed under the
Structural Fill section of this report.
9.1 Temporary Cut Slopes
In our opinion, stable construction slopes should be the responsibility of the contractor and
should be determined during construction based on the conditions encountered at a particular
location and time. For estimating purposes, however, we anticipate that temporary,
unsupported cut slopes in the sandy fill and advance deposit soil can be planned at a maximum
slope of 1.SH:1V. To provide additional protection, the top of a cut slope should begin no
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Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Preliminary Design Recommendations
closer than 5 feet from existing structures such as light poles/hardscape to remain. To reduce
the potential for loose, unstable zones on the cut face, we recommend that the surface be
recompacted using a backhoe-mounted plate compactor ("hoepac") as the excavation proceeds.
Compaction should be performed under the observation of a representative of AESI. As is
typical with earthwork operations, some sloughing and raveling may occur and cut slope
' gradient may have to be adjusted in the field. In addition, WISHA/OSHA regulations should
' be followed at all times.
Where space limitations result in temporary cuts steeper or higher than recommended herein,
shoring will be required. The actual location and configuration of the temporary cut will
. factor into determination of how much and where shoring will be required. Recommendations
' are presented in the Shoring - Soldier Pile Walls section of this report.
9.2 Erosion/Piping Protection for Temporary Cuts �
Cuts in sandy advance outwash sediments may be prone to localized erosion due to seepage if I
encountered. During earthwork, areas determined by the project geotechnical engineer ar
geologist to be potentially unstable due to seepage/erosion may require removal of the
unstable/saturated soil and placement of a stabilizing rock blanket. If necessary, a rock blanket
would typically consist of a minunum, 2-foot-thick prism of 2- to 4-inch-sized crushed quarry ,
rock embedded in the seepage zone. A layer of filter fabric (Mirafi 140N, or equivalent)
should be provided between the rock and the subgrade soil to prevent the migration of fines �
through the rock. The requirement for and extent of rock protection for seepage zones can be
determined in the field during site earthwork as seepage areas are exposed. In general, late,
dry season construction is anticipated to minimize the seepage quantities and the requirements !
for erosion/piping protection.
9.3 Site Disturbance
A portion of the on-site soils contains a high percentage of fine-grained material, which makes �,
them moisture-sensitive and subject to disturbance when wet. The contractor must use care !,I
during site preparation and excavation operations so that the underlying soils are not softened.
If disturbance occurs, the softened soils should be removed and the area brought to grade with
structural fill. Consideration should be given to protecting any unpaved access and staging
areas with an appropriate section of crushed rock or asphalt treated base (ATB). ,
, If crushed rock is used for the access and staging areas, it should be underlain by engineering I�
� stabilization fabric to reduce the potential of fine-grained materials pumping up through the
;� rock and turning the area to mud. The fabric will also aid in supporting construction
equipment, thus reducing the amount of crushed rock required. We recommend that at least 10
inches of rock be placed over the fabric; however, due to the variable nature of the near-
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Proposed Mainlenance/Classroom Building (Building 1� Subsurface Exploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Preliminary Design Recommendations
surface soils and differences in wheel loads, this thickness may have to be adjusted by the
contractor in the field. ,
No information regarding the pavement section existing along the east, west, and south sides of
the proposed building area was available to AESI as of the date of this report. It is considered
likely that repetitive heavy loading, such as that anticipated by construction traffic, including
loaded dump trucks, could cause damage to existing pavement. Repair of these areas as
necessary should be included in construction scope and budgets.
10.0 SHORING - SOLDIER PILE WALLS
To achieve design daylight basement elevation, an excavation ranging in depth to 20 feet is
currently anticipated for this project. Some form of temporary shoring will be required to
support the temporary excavation where open cuts in conformance with recommended
gradients are not feasible. This section of the report presents preliminary design
considerations and criteria that should be considered in the design of the shoring for the
excavation. With this information and other pertinent data, it should be the responsibility of
the shoring subcontractor(s) to determine the appropriate design, construction methods, and
procedures for installation of the shoring system. ',
The most common method of shoring used in the area consists of a conventional soldier I
pile/waler shoring system utilizing steel soldier piles, sometunes in conjunction with an
internally braced or tieback system. Soldier piles, which are wide-flange beams, are placed in
pre-drilled holes that extend beyond the bottom of the excavation. The portion of each soldier
pile extending below the bottom of the excavation is grouted in place with sufficient-strength
concrete to transmit the vertical loads of the soldier beams to the soil below the excavation
level. The upper portion of the soldier pile is then backfilled with a relatively weak grout so
that it may be removed for placement of lagging. We recommend that lagging be backfilled
with sand slurry pumped into place behind shoring walls to minimize the potential for
movement of the cut soil.
10.1 Shoring Wall Retained Earth Pressures
For cantilever walls, we recommend that the shoring system be designed to withstand lateral
soil pressures based on "active" conditions. This design pressure, based on a level back�ll, is
in the form of an equivalent fluid equal to 35 pounds per cubic foot (pc fl triangular distribution
acting over the pile spacing above the excavation level. Below the level of excavation, the 35
pcf may be considered to act only over the diameter of the grouted soldier pile section. Any
applicable surcharges from adjacent structures, stockpiled materials, construction equipment,
or sloping ground must be added to the above values. Where supporting a backslope of
1.SH:1V, an equivalent fluid equal to 60 pcf triangular distribution may be used. Again,
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Renton Technical College and Preliminary Geotechnical Engineering Repon �
Renton, Washington Preliminary Design Recommendations
�
below the level of excavation, the 60 pcf may be considered to act only over the diameter of
the grouted soldier pile section. The use of active pressure for the shoring system assumes
sufficient deformation if the soil occurs to develop an active condition-- typically on the order
of 0.001 to 0.002 times the height of the excavation. Any settlement-sensitive structures
should be set back a minimum horizontal distance equal to the shoring wall height so that wall
` deflections/soil movement do not impact adjacent foundations.
A combination of temporary 1.SH:1 V slopes and shoring may be utilized to reduce the overall
height of shoring. Once the shoring/slope configuration is developed, AESI should be I�
consulted to review the design parameters, as necessary.
10.2 Shoring Wall Passive Earth Pressure
The soldier piles must be located a sufficient depth below the base of the excavation to provide
adequate lateral resistance to horizontal loads. The lateral resistance may be computed on the
basis of passive pressure in the form of an equivalent fluid equal to 300 pcf. The upper 2 feet
of passive soil resistance should be ignored due to disturbance. This pressure may be
considered to be acting against twice the diameter of the grouted soldier pile section. Piles �
should extend at least 10 feet below the excavation level. 'i
10.3 Shoring Inspections
�
Shoring installation should be observed by a representative of AESI to verify that subsurface
conditions are as anticipated and that the shoring elements are installed in conformance with
the shoring plan. Inspections should include pile installation, excavation and lagging
placement, lagging backfill, and drainage. Survey monitoring of the piling and adjacent
structures may also be required.
10.4 Tiebacks
Tieback anchors may be used to aid in resisting lateral loading on the shoring system. A
tieback system consists of drilling behind the soldier pile wall at an angle to the horizontal and
installing rods or cables with a grout anchor. The anchor loads are transmitted to the
surrounding soil by side friction or adhesion with the soil. If requested, recommendations for
design and testing of tieback anchors can be provided.
11.0 STRUCTURAL FILL
Structural fill will be necessary for wall backfill, utility backfill, and beneath hardscape. All
references to structural fill in this report refer to subgrade preparation, fill type, placement,
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Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Preliminary Design Recommendations
and compaction of materials, as discussed in this section. If a percentage of compaction is
specified under another section of this report, the value given in that section should be used.
If fill is to be placed on slopes steeper than SH:1V, the base of the fill should be tied to firm,
stable subsoil by appropriate keying and benching, which would be established in the field to
� suit the particular soil conditions at the time of grading. The keyway will act to embed the toe
of the new fill into the hillside. Generally, the keyway for hillside fills should be at least 4 feet
wide and cut into medium dense sand or stiff silt. Level benches would then be cut
' horizontally across the hill following the contours of the slope. No specific width is required
for the benches, although they are usually at least 4 feet wide. All fills proposed over a slope
should be reviewed by our office prior to construction.
After stripping, planned excavation, and any required overexcavation have been performed to
-- the satisfaction of the geotechnical engineer/engineering geologist, the exposed ground should
be recompacted to 90 percent of the modified Proctor maximum density using ASTM:D 1557
as the standard. If the subgrade contains too much moisture, adequate recompaction may be
difficult or impossible to obtain and should probably not be attempted. In lieu of
' recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to
act as a capillary break between the new fill and the wet subgrade. Where the exposed ground
remains soft and further overexcavation is impractical, placement of an engineering
stabilization fabric may be necessary to prevent contamination of the free-draining layer by silt
migration from below.
After recompaction of the exposed ground is tested and approved or a free-draining rock
course is laid, structural fill may be placed to attain desired grades. Structural fill is defined as
non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts
with each lift being compacted to 95 percent of the modified Proctor maximum density using
ASTM:D 1557 as the standard. The top of the compacted fill should extend horizontally
' outward a minimum distance of 3 feet beyond the location of footings ar pavement edges
before sloping down at an angle of 2H:1V.
The contractor should note that any proposed fill soils must be evaluated by AESI prior to their
use in fills. This would require that we have a sample of the material 72 hours in advance to
perform a Proctor test and determine its field compaction standard. Soils in which the amount
of fine-grained material (smaller than the No. 200 sieve) is greater than approximately 5
percent (measured on the minus No. 4 sieve size) should be considered moisture-sensitive.
Use of moisture-sensitive soil in structural fills should be 1'united to favorable dry weather
conditions. The on-site soils generally contained significant amounts of silt and are considered
moisture-sensitive. In addition, construction equipment traversing the site when the soils are
wet can cause considerable disturbance. If fill is placed during wet weather or if proper
compaction cannot be obtained, a select import material consisting of a clean, free-draining
� gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the
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Proposed Maintenance/Classroom Building (Building 1� Subsurface Exploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Preliminary Design Recommendations
amount of fine-grained material limited to 5 percent by weight when measured on the minus
No. 4 sieve fraction with at least 25 percent retained on the No. 4 sieve.
An AESI representative should inspect the stripped subgrade and be present during placement
of structural fill to observe the work and perform a representative number of in-place density
tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses and
any problem areas may be corrected at that time. It is important to understand that taking
random compaction tests on a part-time basis will not assure uniformity or acceptable
performance of a fill. As such, we are available to aid the owner in developing a suitable I
monitoring and testing frequency. �
I
i
I
12.0 FOUNDATIONS i
�I
Spread footings may be used for building support when founded directly on suitable outwash
soil or on structural fill placed as previously discussed. Footings founded on suitable outwash
sand or on structural fill above the outwash sand may be designed for an allowable foundation ;
soil bearing pressure of 2,500 pounds per square foot (ps�, including both dead and live loads. ',
An increase of one-third may be used for short-term wind or seismic loading. Based on the �
anticipated dense condition of the granular soils at the base of the excavation along the east
perimeter of the proposed structure, a higher allowable bearing capacity of 6,000 psf may be
used in design of the footing for the eastern retaining wall. All foundations must penetrate to
the prescribed bearing stratum and no foundations should be constructed in or above loose,
organic, or existing fill soils. In addition, all footings must have a minimum width of 18
inches.
Perirneter footings should be buried at least 18 inches below lowest adjacent grade for frost
protection; interior footings require only 12 inches burial.
Considering the granular nature of the site soils, settlements are expected to be small and occur
rapidly during the initial application of dead load. Anticipated settlement of footings founded
as described above should be on the order of 3/a inch with differential movement about half of
that total. However, disturbed soil not removed from footing excavations prior to footing
placement could result in increased settlements. Installation of settlement-sensitive surfaces
should be delayed as long as practical. All footing areas should be inspected by AESI prior to
placing concrete to verify that the design bearing capacity of the soils has been attained and
that construction conforms to the recommendations contained in this report. The City of
Renton may require such inspections. Perimeter footing drains should be provided, as
discussed under the section on Drainage Considerations.
It should be noted that the area bounded by lines extending downward at 1H:1V from any
footing must not intersect another footing or intersect a filled area that has not been compacted
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Renton Technical College and Preliminary Geotechnical Engineering Report
Renlon, Washington Preliminary Design Recommendations
to at least 95 percent of ASTM:D 1557. In addition, a 1.SH:1V line extending down from any
footing must not daylight because sloughing or raveling may eventually undermine the footing.
Thus, footings should not be placed near the edge of steps or cuts in the bearing soils.
13.0 LATERAL WALL PRESSURES
All backfill behind walls or around foundation units should be placed as per our
recommendations for structural fill and as described in this section of the report. Horizontally
backfilled walls, which are free to yield laterally at least 0.1 percent of their height, may be
designed using an equivalent fluid equal to 35 pcf. Fully restrained, horizontally backfilled
rigid walls that cannot yield should be designed for an equivalent fluid of 55 pcf. An
incremental dynamic lateral load of 6H and 8H psf for the active and at-rest loading cases,
respectively, may be used where determining seismic earth pressure in conformance with the
2003 IBC. Where driveway or parking areas are adjacent to walls, a surcharge equivalent to 2
feet of soil should be added to the wall height in determining lateral design forces.
The lateral pressures presented above are based on the conditions of a uniform, level backfill
consisting of free-draining soil compacted to 90 percent of ASTM:D 1557. A higher degree of
compaction is not recommended as this will increase the pressure acting on the wall. A lower
compaction may result in settlement of any slab-on-grade or other structures above the walls.
Thus, the compaction level is critical and must be tested by our firm during placement.
Surcharges from adjacent footings, heavy construction equipment, or sloping ground must be
added to the above values. Footing drains should be provided for all retaining walls, as
discussed under the section on Drainage Considerations.
It is irnperative that proper drainage be provided so that hydrostatic pressures do not develop
against the walls. This would involve installation of a minimum, 1-foot-wide blanket drain to
within 1 foot of the top of the wall using imported, washed gravel against the walls. Less
permeable on-site soil may be used as a cap over the gravel. Filter fabric (Mirafi 140N, or
equivalent) should be placed over the gravel drain prior to soil cap placement to reduce the
potential for migration of fines.
13.1 Passive Resistance and Friction Factors
Retaining wall footings/keyways cast directly against undisturbed, dense outwash sediments in
a trench may be designed for passive resistance against lateral translation using an equivalent
fluid equal to 300 pcf. The passive equivalent fluid pressure diagram begins at the top of the
footing; however, total lateral resistance should be summed only over the ciepth of the actual
key (truncated triangular diagram). These values apply only to footings/keyways where
concrete is placed directly against the trench sidewalls without the use of forms.
Octoher 10, 2005 ASSOCIATED F_ARTH SCIE,'�'CES, LtiC.
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Proposed Maintenance/Classroom Building (Building NJ Subsurface Fxploration, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report
Renton, Washington Preliminary Design Recommendations
If footings are placed on suitable advance outwash sediments and then backfilled, the top of the
compacted backfill must be horizontal and extend outward from the footing for a minimum
lateral distance equal to three times the height of the backfill before tapering down to grade.
' With backfill placed as discussed, footings may be designed for passive resistance against
lateral translation using an equivalent fluid equal to 250 pcf and the truncated pressure diagram
E discussed above. Passive resistance values include a factor of safery equal to 3 in order to
�
reduce the amount of movement necessary to generate passive resistance.
The friction coefficient for footings cast directly on undisturbed, dense outwash sediments or
structural fill may be taken as 0.35. This value includes a safety factor of at least 1.5.
14.0 FLOOR SUPPORT
The slab-on-grade floor may be founded on structural fill or unweathered outwash sediments.
The floor should be cast atop a minimum of 4 inches of washed pea gravel to act as a capillary
break. It should also be protected from dampness by a minimum 10-mil-thick vapor retarder
membrane.
15.0 DRAINAGE CONSIDERATIONS
All retaining and perimeter footing walls should be provided with a drain at the footing
elevation. Drains should consist of minimum, 6-inch-diameter, rigid, perforated, polyvinyl
chloride (PVC) pipe surrounded by washed pea gravel. The level of the perforations in the
pipe should be at least 12 inches below the bottom of the floor slab, and the drains should be
constructed with sufficient gradient to allow gravity discharge away from the building. �
Footing drains should be provided with cleanouts to allow periodic future '�
cleaning/maintenance. '
All retaining walls should be lined with a minimum, 12-inch-thick, washed gravel blanket to
within 1 foot of the top of the wall and which ties into the footing drain. Less permeable on-
site soil may be used as a cap over the gravel. Filter fabric should be placed over the gravel
prior to soil cap placement to reduce the potential for migration of fines into the wall drain.
Roof and surface runoff should not discharge into the footing drain system, but should be
handled by a separate, rigid, tightline drain. In planning, exterior grades adjacent to walls
should be sloped downward away from the structure (minimum 2 percent slope) to achieve
surface draina�e.
October]0, 2005 ASSOCIATED EARTH SCIENCES, INC.
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Proposed Maintenance/Classroom Building (Building NJ Subsurface Explorarion, Geologic Hazards,
Renton Technical College and Preliminary Geotechnical Engineering Report I
Renton, Washington Preliminary Design Recommendations
16.0 PROJECT DESIGN AND CONSTRUCTION MONITORING j
At the time of this report, site grading, structural plans, and construction methods have not �I,
; � been fmalized, and the recommendations contained herein are preliminary. We are available to i
� provide additional geotechnical consultation as the project design develops and possibly ''
changes from that upon which this report is based. We recommend that AESI perform a �I
geotechnical review of the plans prior to final design completion. In this way, our earthwork ''�
�
and foundation recommendations may be properly interpreted and implemented in the design. '
I ,
We are also available to provide geotechnical engineering and monitoring services during ;
construction. The integrity of the foundation depends on proper site preparation and
construction procedures. In addition, engineering decisions may have to be made in the field �
in the event that variations in subsurface conditions become apparent. Construction monitoring �
services are not part of this current scope of work. If these services are desired, please let us
know and we will prepare a cost proposal.
We have enjoyed working with you on this study and are confident that these recommendations
will aid in the successful completion of your project. If you should have any questions or �
require further assistance, please do not hesitate to call.
,
Sincerely,
ASSOCIATED EARTH SCIENCES, INC. ,
Kirkland, Washington �. M E j�
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��� ���-�, EXPIRES 11�2���(p
Maire Thornton, P.E. Kurt D. Merrirnan, P.E.
Senior Project Engineer Principal Engineer
Attachments: Figure l: Vicinity Map
Figure 2: Site and Exploration Plan
Appendix: Exploration Logs
October 10, 2005 ASSOCIATED EARTH SCIENCES, INC. ,
MTild-KE05606A2-Projectsi2IX1560h!KEI44P P$ge 22
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RENTON, WASHINGTON PROJ.NO. KE05606A
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� Associated Earth Sciences, (f1C. FIGURE 2
� SITE AND EXPLORATION PLAN
' Q � � � � � PROPOSED MAINTENANCE AND CLASSROOM BUILDING DATE 10/05
o RENTON, WASHINGTON PROJECT N�. KE05606A I
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� 'o� Well-graded gravei and Terms Describing Relative Density and Consisfency
" o'o' GW 9ravel with sand,little to Densi SPTmblowsJfoot
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y LL 'o � no fines Very l.00se 0 ro 4
` m Coarse- �se 4 to 10
m i0 ' ='o�o° Poorly-graded gravel Grained Soils
m � � �a D o D o Gp t�edium Dense �o to 3o Test Symbals
and gravel with sand, Dense 3o to 50
o � a °'°'� Very Dense >50 G =Grain Size
,o,o, fittle lo no fines
Z o � ����o Consisten SP T��blows/foot M=Moisture Content
,� o �1/ A=Aflerberg Limits
Silry gravel and silty
� c � Very Soil 0 to 2 C=Chemical
o L � � • �M gravel with sand Fine- Sott 2 to a DD = Ory Density
� d !fl � - Grained Sats t�tedium Slif( 4 to 8 K =Permeability
C N jy
� g � : $liti 8101$
� � � Clayey gravel and very St�rt 15 l0 30
� � � Gc Uayey gravel with sand Hard >"a0
„� � Componenf Defcnitions
' L o Well-graded sand 2nd Descriptive Term Size Range and Sieve Number
� � --: Syy sand with gravel,6ttle Bou�ders Larger than 12'
1O " '�'�'�''� to no fines Cobbles 3'to 17
`o � d .
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� m " """'�" Grave! 3'to No.4(4.75 mm)
y ` ='�'���'•" Poor - raded sand
� > � •- �g Coarse Gravel 3'to 3/4'
in U� •. SP and Sand with g�2vel, Fine Grave! 3/4'fo No.4(4.75 mm)
m a v little to no fines
c d Sand No.4(4.75 mm)to No.200(0.075 mm)
� � z Coarse Sand No.4(4.75 mm)to No.10(2.00 mm)
'" Silly Sand and Medium Sand No.70(2.00 mm)lo No.40(0.425 mm)
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� � N • S M Sllly Sand with Fine Sand No.40(0.425 mm)to No.200(0.075 mm)
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o LL :. g�ave� Silt and Clay Smaper Ihan No.200(0.075 mm)
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� � sc Clayey sand and �3�Estimated Percentage Moisture Content
� ^' : clayey sand with gravel Percentage by Dry-Absence of masture,
`n Component dusty,dry to the touch
We�ght
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m o ML silt with sand or gravel Fe`"' S to�o masture
m � Little 1 S l0 25 Moist-Damp but no visible
v� H � With -Nm-primary coarse water
o `D � Clay of low to medium constituents: > 15% Very Moist-Water visible but
`�' v � -Fines conterri between not(ree draining
o � � plasticity; silty,sandy,or
I Z �= CL 5%and 15% Wet-Vsible tree water,usua
gravelty clay,lean clay �Y
o °=� irom below water�able
N (n � — —
a � =— Organic clay or silt of low Symbols
� � _— o� plastiCity etows/6'or
� Sam lef
� = P poAlOn of G Cement grwt
o — TYpe / surface seal
Elastic silt,clayey silt,siit { Sampler Type
2.0'OD Brstonile
e with micaceous or : � DescripGon
o „ MH SpGt-Spoon , (•) seal
� o diatomaceous fine sand or S�P�� 3.0'OD S lit-S Sam Ier
H �� Silt S P P� P - - '_Fdter padc wi�h
o m o � � 3.25'OO Spfit-Spoon Ring Sampler �.> : _= blank casing
� � o Clay oi high plasticity,
� �� sand or ravell cla fa[ Bulksample _ '-• seciion
m c= CH Y 9 y y' 3.0"OD Thin-Wall Tube Sampler - =' Screened casing
� y J clay with sand or gravel ' (ncluding She�by tube) �� °f�`o�'�
�j — � Grab Sample ':w+th filtel pack
m �� �iii� -• End cap
c � �i��i� Organic cfay or silt of o Portion not recwered
"- J %;;:; aH medium to high �» ,
������ Percentage hy dry weight �� Depth of ground water
����� plasticity �1 (gp7�5tandard Penetration Test
(ASTM 0-1586) 1 ATD=At time af drilfmg
>. `—' Peat, muck and other �� Q StaGc water level(date)
c � In Genera!Accordance with
=o�o p'� highly ofganiC sOils Standard Practice for Description �� Combined USCS symhols used for
and Identificalion of Soils(/ISTM D-2488) fines belween S%and 15%
Cfassifications of soils in this repoA are based on visual field and/or laboratory o�servations,which indude density/consistency,masture condiGon,grain size,and
ptasticity eslimales and should not be construed to imply field or laboratory lesting unless presented herein.VisuaRmanual and/or laboralory dassificalion
a methods of ASTM 0-2487 and 0-2488 were used as an idenlificalion guide for lhe Unified Soil Classificalion System.
0
_ p
3
> Associated Earth Sciences, Inc. F�cuRe
� � � � � � IExploration Log Key A-,�
�a
I
- �Associated Earth Sciences, Inc. Ge010 ic & Monitorin Well Construction Lo
Project Number Weil Number Sheet
; � � � � � KE05606A EB-1 1 of 1 '
' Project Name Renton Technical College Location Renton, WA
Elevation(Top of Well Casing) Surface Elevation(ft)
Water Level Elevation Date StaNFinish /��,g/�3/�5
DrillinglEquipment Davies Driiling Hole Diameter(in)
Hammer WeighUDrop 140#/30��
; V O
- m.� � � m E
� o�
� � � WELL CONSTRUCTION 'T� m �� DESCRIPTION
, �
Surface Monument 15 Fill '
i 14 Moist,dark brown to light brown,silty SAND,roothairs.
Cement 14
------------ -- - ------ -
Outwash
Bentonite
5 , � Moist,gray,fine SAND/coarse SAND,stratified.
� 12 � '
�2
�� Well Screen � Moist,gray,fine SAND/coarse SAND, stratified.
s
�s
,
15 ; I �
y Moist,gray,fine SAND/coarse SAND,stratified.
12
15 I
Zp End Cap
i 7 Moist,gray,fine SAND/coarse SAND,stratfied.
24 �
; 30 ! goring terminated at 21.5 feet on 9/13/05
� No ground water.
I
25
I
30 I
�
!
0 35
�,
o�
�I �
0
�
t7
2
� I
m � I
a' �
¢ Sampler Type(ST):
� � 2"OD Split Spoon Sampler(SPT) � No Recovery M - Moisture Logged by: MT
�
� J �j 3"OD Split Spoon Sampler(D&M) � Ring Sample � Water Level Q Approved by:
�� � Grab Sample � Shelby Tube Sample 1 Water Level at time of drilling(ATD) i
_ -�
I
LOG OF EXPLORATION PIT NO. EP-1
� This log is part of the report prepared by Associated Earth Sciences, Inc.(AESI)for the named project and should be
� read together with that report for complete interpretation.This summary applies oniy to the location of this trench at the
� time of excavation.Subsurface conditions may change at this location with the passage of time.The data presented are
o � a simpification of actual conditions encountered.
� ;; DESCRIPTION
Topsoil �
Loose, damp, light brown, silty fine SAND.
r... 1
� ----------------------
---------------------
Outwash
Medium dense, damp, light brown, silty fine SAND, slight stratification.
2 �
3
4 �
Medium dense, damp to moist, light brown, fine to medium SAND, coarser with depth.
, 5
I
6
7 �
�
8 �
9
I , �
10
Bottom of exploration pit at depth 10 feet
11 No ground water/seepage. No caving.
12
�
13 -t
i
14 ,
15
16 '
E !
17
18
19
� ,
��
N
LV _ -
O
O
N
m Renton Technical College Maintenance/Classroom Building
a
o Renton, WA
a
< Associated Earth Sciences, Inc.
� Logged by: MT Project No. KE05606A
N � � � � �
-� � Approved by � 9/26105
a
J
Y
LOG OF INFILTRATION PIT NO. IP-1
� This log is part of the report prepared by Associated Earth Sciences, Inc. (AESp for the named project and should be I
� read together with that report for com�lete interpretation.This summary applies only to the locafion of this trench at the
� time of excavation.Subsurface conditions may change at this location with the passage of time.The data presented are
o a simplfication of actual conditions encountered. I
� DESCRIPTION
, -' _ _____ 2 112"to 3"Asphalt Concrete on surface over 1"thick Fine Crushed Gravel _ �
_ , � Outwash
�'� ,
� � I
� ' ! '�
2 Medium dense, damp, light brown, silty fine SAND, slight stratification. ',
I� 3
I
� ---- ------- -------- ------ -----
4 Medium dense, damp, light brown, fine to medium SAND, slight stratification. I
5
6
7 ----------------------- -- -------- ---
Medium dense, moist, I�ht brown, silty fine SAND._ �
------------ ------------------------
8 �
� Medium dense, damp, light brown, fine to medium SAND, slight stratification.
9 �
I ,
, 10 I
� Bottom of exploration pit at depth 10 feet I�
� 1 1 No ground water/seepage. No caving.
12
, 13
�: 14
,
J 15
; '
16 -
17 —
18
19
� �
��
�
L
0
0
N
m Renton Technical College Maintenance/Classroom Building
n
o Renton, WA
a
a Associated Earth Sciences, ItIC. pro ect No. KE05606A
N Logged by: MT 1
� Approved by: � � � � � 9/26/05
U
Y
Associated Earth Sciences, Inc.
� � � � �
Ce�r,�y�r�fi��2��eav��of S'eyvice
February 28, 2006
Project No. KE05606A
Renton Technical College
clo S.M. Stemper Architects, PLLC
4000 Delridge Way SW, Suite 200
Seattle, Washington 98106
Attention: Ms. Sally MacGregor-Crone
Subject: Protected Slope Area Within Proposed Building Area
Maintenance and Classroom Building Re-Site
Renton Technical College
3000 NE 4'" Street
Renton, Washington
Dear Ms. MacGregor-Crone:
It is our understanding that the location for the proposed maintenance and classroom building
has been revised since the date of our referenced report and letter. Based on information
presented on the "Maintenance and Classroom Re-Bid" dated February 2, 2006 by S.M.
Stemper Architects, PLLC (Stemper Architects), the currently proposed building location is
situated farther north and east than originally planned. The currently proposed location
removes most of the protected slope azea, as defined by the Renton Municipal Code (slopes
higher than 15 feet and over 40 percent grade), in the vicinity of the proposed building.
As requested, this letter presents our geotechnical recommendations for the proposed revised
building location and addresses the impact of the revised building location on the protected
slope area mapped on the site. Figure 2, attached to this letter, depicts the revised location of
the proposed maintenance and classroom building based on information presented on the ,
"Maintenance and Classroom Re-Bid" dated February 2, 2006 by Stemper Architects. A�s �
proposed, the excavation for the proposed building will remove the protected slope within the �
building footprint and retain resulting cuts by permanent, drained retaining walls. '
Recommendations presented in our referenced report and letter remain applicable and should
be incorporated into site development plans. It is our opinion that by eliminating the protected
slope, the intent of the geologic hazard requirements (Renton Municipal Code Section 4-3-050)
is satisfied.
i ICirl:land Office•911 Eifth Avenue,Suite 100•ICirldand,V(�A 98033°P�(425)827-7?01•F�(42>)82%-5424 �
E��erett Office•2911 1/2 He�ti�tt Aveiiue,Suite 2•Everett,Wt1 98201�P�(425)259 05?2•F�(�251252-3�i08
' �titiv�vaesgeo.com
;
i
;
The proposed exterior stairway to be located along the south side of the new building is
anticipated to protect underlying soil from surface weathering and resulting surficial slope
deterioration. An interceptor drain is recommended along the southern edge of the stairway to
reduce the potential for erosion due to concentrated flow along the unpermeable concrete
stairway. Figure 3 presents a typical detail for use in designing the interceptor drain.
We have enjoyed our continued work with you on this project. If you have questions or
require any additional information, please do not hesitate to call.
Sincerely, ,
( ASSOCIATED EARTH SCIENCFS, INC.
� Kirkland, Washington ,
�
ME �
,�,�.���w�s R ,� ''
� � c� �
' x �
i - 2 G'
I f
i . :��,�235'�80��
faNAL�
EXPIRES �1�ZOI (p
� '
' Kurt D. Meniman, P.E. �
Principal Engineer I
I ',
I ',
Attachments: List of References '
Figure 1: Vicinity Map i
Figure 2: Revised Site and Exploration Plan ',
Figure 3: Typical Interceptor Trench Detail ,
�
I
�
KDMlsn �
' KFA5606A6 i
Projcctsl?00506061KE\N P
- 2
i
� ' List of References
Subsurface Exploration, Geologic Hazards, and
Preliminazy Geotechnical Engineering Report
Proposed Maintenance and Classroom Building Re-Site
Renton Technical College
3000 NE 4'� Street
Renton, Washington
Report Date: October 13, 2005 ,
Recommendations for Temporary Shoring
Proposed Maintenance and Classroom Building Re-Site
Renton Technical College
3000 NE 4'� Street
Renton, Washington
Letter Date: January 13, 2006
I
KDMlsn
KE05606A6
Proj ects��0U50G06'�K E�.w'P
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v
" FIGURE 1 I
t Associated Earth Sclenees, Inc. VICINITY MAP
a � � � � � PROPOSED MAINTENANCE AND CLASSROOM BUILDING DATE 2/06
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a REVISED SITE AND EXPLORATION PLAN
a � � � � � PROP05ED MAINTENANCE AND CLASSROOM BUILDING RE-SITE DATE 2/06
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a RENTON TECHNICAL COLLEGE RE-SITE DATE 2/O6
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� PROJ.NO KE05606A
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