Report Main Office Salem Office Bend Office
P.O. Box 23814 4060 Hudson Ave., NE P.O. Box 7918
a Tigard, Oregon 97281 Salem, OR 97301 Bend, OR 97708
Carlson S �Y� � �1 l 1^1 Q f J C o Phone (503) 684-3460 Phone (503) 589 -1252 Phone (541) 330 -9155
1l i!l il In FAX (503) 684 -0954 FAX (503) 589 1309 FAX (541) 330 -9163
Special Inspection
FINAL SUMMARY LETTER
July 29, 2004
T0303660
City of Tigard
13125 SW Hall Blvd., FILE C
Tigard, OR 97223 -8199
Attn: Building Department
Re: Metzger Elementary School Replacement
10350 SW Lincoln Street- Tigard, OR
Permit No.: BUP2003 -00443
Dear Sir or Madam:
This is to certify that in accordance with Section 1701 of the Uniform Building Code, Title 24, we have
performed special inspection of the following item(s) per our inspection reports only:
Reinforced Concrete
Installation of Adhesive Anchors and /or Wedge Anchors
Structural Masonry
Structural Steel- Fabrication & Erection, includes verification of welder certifications, weld procedures and material certifications
All inspections and tests were performed and reported according to the requirements of Project Documents
and, to the best of our knowledge, the work was in conformance with the approved plans and
specifications, approved change orders and applicable workmanship provisions of the State Building Code
and Standards, as well as the structural engineer's design changes, approvals and verbal instructions.
* This final letter now includes the Covered Play Structure. All work has been completed.
Our reports pertain to the material tested /inspected only. Information contained herein is not to be
reproduced, except in full, without prior authorization from this office.
If the are any further questions regarding this matter, please do not hesitate to contact this office.
Res ctfully s •f
CA SO " STING, INC.
J - 0 1 . Hietpas
— rations Manager
J • H /ks
c: Tigard - Tualatin School District #23J- Stephen Poage
' Nishkian Dean Structural Engineers- Gerald Gotchall
SLX Architects- Xavier Rueda
Robinson Constructin Co (Job Site)- Mike Flannery
Cornerstone Construction Management- Brian Radabaugh
P 1WOR0\RE PORTS\F INLTR \T
Main Office Salem Office Bend Office
P.O. Box 23814 4060 Hudson Ave., NE P.O. Box 7918
Tigard, Oregon 97281 — Salem, OR 97301 Bend, OR 97708
Carlson Testing Inc. Phone (503) 684 -3460 — Phone (503) 589 -1252 Phone (541) 330 9155
FAX (503) 684 -0954 FAX (503) 589-1309 FAX (541) 330 -9163
Special Inspection
FINAL SUMMARY LETTER
"PARTIAL"
June 16, 2004 .
T0303660
City of Tigard
13125 SW Hall Blvd.,
Tigard, OR 97223 -8199
Attn: Building Department
Re: Metzger Elementary School Replacement
10350 SW Lincoln Street- Tigard, OR
Permit No.: BUP2003 -00443
Dear Sir or Madam:
This is to certify that in accordance with Section 1701 of the Uniform Building Code, Title 24, we have
performed special inspection of the following item(s) per our inspection reports only:
Reinforced Concrete
Installation of Adhesive Anchors and /or Wedge Anchors
Structural Masonry
Structural Steel- Fabrication & Erection, includes verification of welder certifications, weld procedures and material certifications
All inspections and tests were performed and reported according to the requirements of Project Documents
and, to the best of our knowledge, the work was in conformance with the approved plans and
specifications, approved change orders and applicable workmanship provisions of the State Building Code
and Standards, as well as the structural engineer's design changes, approvals and verbal instructions.
* This "Partial Final" is excluding the Covered Play Structure. To this date, the covered play
structure has not been completed.
Our reports pertain to the material tested /inspected only. Information contained herein is not to be
reproduced, except in full, without prior authorization from this office.
If there�e any further questions regarding this matter, please do not hesitate to contact this office.
Respp tfully submitted,
CARLON TESTING, INC.
Jar s'F. Hietpas
/ . rations Manager
J H /ks
Vcc: Tigard - Tualatin School District #23J- Stephen Poage
Nishkian Dean Structural Engineers- Gerald Gotchall
SLX Architects- Xavier Rueda
Robinson Constructin Co (Job Site) Mike Flannery
Cornerstone Construction Management- Brian Radabaugh
P:\WORD REPORTSTINLTR\T
I [ . OFFICE COPY
RECEIVED
/AUG 2 u ?no
GEOTECHNICAL A',`,,;,vis►ATION
SITE - SPECIFIC SEISMIC
HAZARD EVALUATION
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METZGER ELEMENTARY SCHOOL
TIGARD, OREGON
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PREPARED FOR
TIGARD - TUALATIN DISTRICT
TIGARD, OREGON
FEBRUARY 2003
GEOCON
N O R T H W E S T, I N C.
GEOTECHNICAL CONSULTANTS 4,-,)
Project No. P1191 -05 -01
February 28, 2003
Tigard - Tualatin School District 23J
Larry Hibbard Administration Center
• 6960 SW Sandburg Street
Tigard, Oregon 97223
Attention: Mr. Stephen Poage
Subject: NEW METZGER ELEMENTARY SCHOOL
TIGARD, OREGON
GEOTECHNICAL INVESTIGATION AND
SITE - SPECIFIC SEISMIC HAZARD EVALUATION
Dear Mr. Poage;
In accordance with our proposal number P03- 05 -08, dated January 31, 2003, and your
authorization, we have performed a geotechnical investigation for the proposed New
Metzger Elementary School site in Tigard, Oregon. The accompanying report presents the
findings of the geotechnical investigation and conclusions and recommendations regarding
the geotechnical aspects of the proposed facility. Based on the results of this investigation,
it is our opinion that the site can be developed as proposed, provided the recommendations
of this report are followed. The primary geotechnical concerns associated with the
development are near surface perched water and high moisture content of near surface
soils.
If you have questions regarding this report, or if we may be of further service, please contact
the undersigned at your convenience.
Sincerely,
GEOCON NORTHWEST, INCORPORATED
Heather Devine, P.E. Wesley S- -ng, ° .
Geotechnical Engineer President
,�� PR
,EO OFF
�
HLD:AWS .��"c'l8281 F9 Uh l
cc: Mr. Brian Radabaugh, Cornerstone Construction Management
Mr. Xavier Rueda, Selig Lee Rueda Architects OREGON
Mr. Gerald Gotchall, Nishkian Dean
►I C•• 1. .:r •. s• o• m-- V./. N g9 6
8380 SW Nimbus Avenue Beaverton, Oregon 97008 • Telephone (503) 626 -9889 • Fax (503) 62. , 6 cs`ey sw4C-
EFP)RATION DATE: 6/30i O Y
TABLE OF CONTENTS
1. PURPOSE AND SCOPE 1
2. SITE AND PROJECT DESCRIPTION - 1
3. REGIONAL GEOLOGY - 2
4. SUBSURFACE EXPLORATION AND CONDITIONS 3
4.1. SITE EXPLORATION 3
4.2. SUBSURFACE CONDITIONS 4
5. SITE - SPECIFIC SEISMIC HAZARD EVALUATION 5
5.1 SEISMIC SETTING 5
5.2. GROUND SHAKING CHARACTERISTICS 7
5.3. FAULT DISPLACEMENT AND SUBSIDENCE 8
5.4. SLOPE INSTABILITY 8
5.5. LIQUEFACTION 9
5.6. LATERAL SPREADING 9
5.7. SEICHE AND TSUNAMI INUNDATION 9
6. LABORATORY TESTING 9
7. CONCLUSIONS AND RECOMMENDATIONS 10
7.1. GENERAL 10
7.2. SITE PREPARATION 10
7.3. PROOF ROLLING 12
7.4. FILLS 13
7.5. CUT AND FILL SLOPES 14
7.6. SURFACE AND SUBSURFACE DRAINAGE 14
7.7. FOUNDATIONS 14
7.8. CONCRETE SLAB -ON -GRADE 15
7.9. UTILITY EXCAVATIONS 16
7.10. PAVEMENT DESIGN 17
8. FUTURE GEOTECHNICAL SERVICES 18
9. LIMITATIONS 18
REFERENCES
TABLES
Table 1,Crustal Faults
Table 2, Asphalt Concrete Pavement Design
Table 3, Portland Cement Concrete Pavement Design
MAPS AND ILLUSTRATIONS
Figure 1, Vicinity Map
Figure 2, Site Plan
APPENDIXA
FIELD INVESTIGATION
APPENDIX B
LABORATORY TESTING
GEOTECHNICAL INVESTIGATION
1. PURPOSE AND SCOPE
This report presents the results of the geotechnical investigation and site - specific seismic
hazard evaluation for the proposed New Metzger Elementary School. The site is located
south of the existing school building located at 10255 SW 90 Avenue in Tigard, Oregon, as
shown in Figure 1, Site Vicinity Map. The purpose of the geotechnical investigation was to
evaluate subsurface soil and geologic conditions at the site and, based on the conditions
encountered,' provide conclusions and recommendations pertaining to the geotechnical
aspects of the construction of the replacement school. The site - specific seismic hazard
evaluation was completed in general accordance with the 1997 Uniform Building Code and
Oregon Structural Specialty Code 1804.2.1 and 1804.3.
The scope of the field investigation consisted of a site reconnaissance, review of published
geological literature, five exploratory borings and two dilatometer soundings. A detailed
discussion of the field investigation is presented in Section 4 of this report. Exploratory logs
are presented in Appendix A.
Laboratory tests were performed on selected soil samples obtained during the investigation
to evaluate pertinent physical properties. Appendix B presents a summary of the laboratory
test results, with the exception of in situ moisture content results. The results of laboratory
moisture content tests are presented on the exploratory boring and trench logs, located in
Appendix A.
The recommendations presented herein are based on an analysis of the data obtained
during the investigation, laboratory test results and our experience with similar soil and
geologic conditions. This report has been prepared for the exclusive use of the Tigard -
Tualatin School District and their agents, for specific application to this project, in
accordance with generally accepted geotechnical engineering practice. This report may not
contain sufficient information for purposes of other parties or other uses.
2. SITE AND PROJECT DESCRIPTION
The project site is located within T.1 S, R.1 W, Section 35, in Tigard, Oregon, at 10255 SW
90 Street. The approximate location is shown in the Site Vicinity Map, Figure 1. The
development site is south of the existing school, and is currently used as a playing field.
Project No. P1191 -05 -01 1 February 28, 2003
The proposed project consists of the construction of a new replacement elementary school
with associated access drives, parking lots and playing fields. The existing school is slated
for demolition following the completion of the new building. Playing fields will be relocated
to the area now occupied by the school. Based on discussions with project structural
engineer, Nishkean Dean, the maximum column and wall loads for the replacement school
are estimated at 160 kips and 5 kips /foot, respectively.
3. REGIONAL GEOLOGY
Based on the State of Oregon Department of Geology and Mineral Industries' (DOGAMI)
Open File Report 0 -90 -2, the site is mapped within an area of Pleistocene age fine - grained
facies to a depth of less than 30 feet bgs. These Pleistocene age deposits are characterized
by brown to buff, unconsolidated beds and lenses of coarse - grained sand to silt. The fine -
grained facies are slack water fluvial and/or lacustrine deposits resulting from repeated
temporary inundation of the Willamette Valley by Late - Pleistocene glacial outburst floods.
These glacial floods originated in the Missoula Valley of Montana, passed through eastern
Washington, . and followed the Columbia River downstream. When these large floods
entered the Portland Basin they flowed up the Willamette River and its tributaries, flooding
most of the Willamette and Tualatin Valleys up to an approximate elevation of 350 feet MSL.
The last of these glacial floods, also thought to be one of the largest, occurred about 12,400
years ago, establishing the minimum age of the silt deposit. Below the surface deposit is a
Pliocene age sandstone and conglomerate of inundated beds and lenses of well sorted
sand and gravel, typically referred to as the Troutdale Formation. The Troutdale Formation
occurs primarily in the valleys of the Willamette, Clackamas and Sandy Rivers, as well as
along many of their tributaries. Older bedrock units are mapped at a depth of approximately
150 feet below the ground surface.
The USDA Soil Conservation Service "Soil Survey of Washington County, Oregon" (1982)
maps the site as Aloha Silt loam. The Aloha Series is characterized as somewhat poorly
drained soils with reported permeability rates of 0.2 to 0.6 inches per hour. Frost
penetration depth is less than 18 inches.
2
Project No. P1191 -05 -01 February 28, 2003
. r.
4. SUBSURFACE EXPLORATION AND CONDITIONS
4.1. Site Exploration
The subsurface soil conditions at the Metzger Elementary School site were determined
based on the literature review, field exploration and laboratory testing. The field exploration
was completed on February 6, 2003 and consisted of two dilatometer (DMT) soundings and
five exploratory borings. The soundings and borings were completed in the approximate
locations shown in Figure 2, Site Plan.
4.1.1. Dilatometer Test
The dilatometer test provides a rational, cost - effective method to determine
'engineering parameters for the design of earthworks and structural foundations. It is
particularly useful in silts and sands that can be difficult to sample or test by other
methods. The DMT is performed in situ by pushing a blade- shaped instrument into
the soil. The blade is equipped with an expandable membrane on one side that is
" y pressurized until the membrane moves horizontally into the surrounding soil.
Readings of the pressure required to move the membrane to a point that is flush with
the blade (A — pressure) and to a point 1.1 mm into the surrounding soil (B —
pressure) are recorded. The pressure is subsequently released and, in permeable
s iw.r'
soils below the groundwater table, a pressure reading is recorded as the membrane
returns to the flush position (C — pressure). In addition, the thrust required to
advance the blade to the desired test depth is recorded. The test sequence is
performed at 0.2 -meter intervals to obtain a comprehensive soil profile. A material
index (l a horizontal stress index (Ko) and a dilatometer modulus (E are obtained
directly from the dilatometer data.
Marchetti (1980) developed a soil classification system based on the material index.
According to this system, soils with ID values less than 0.35 are classified as clay.
Soils classified as sand have an ID value greater than 3.3. Material index values
between 0.35 — 3.3 indicate silty clay to silty sand soils.
Empirical relationships between the horizontal stress index and the coefficient of
lateral earth pressure (K have been developed by Lunne et al. (1990) for clays and
by Schmertmann (1983) for uncemented sands. While Lunne's method makes use
of dilatometer data exclusively, Schmertmann utilizes both DMT and cone
penetration data to estimate K
3
Project No. P1191 -05 -01 February 28, 2003
Since the DMT is strain - controlled, the measured difference between the B- pressure
and A- pressure readings (corrected for membrane stiffness) and cavity expansion
theory, can be used to directly measure the soil stiffness. Assuming a Poisson's
ratio, the dilatometer modulus is correlated to shear modulus, Young's modulus, and
constrained modulus.
The dilatometer soundings completed at this site were advanced to a depth of
approximately 13 feet below the ground surface, where refusal on weathered rock
was encountered. A member of Geocon Northwest's engineering staff recorded
thrust and pressure readings every eight inches as the dilatometer blade was
advanced.
4.1.2. Borings
Four borings, located within the footprint of the proposed school building, were
advanced to depths of approximately 16.5 feet bgs, where, in general, refusal in
weathered rock was encountered. One shallow boring was completed in the location
of the proposed parking. The borings were completed with a trailer - mounted drill rig
equipped with solid stem auger. A member of Geocon Northwest's geology staff
logged the subsurface conditions encountered - within the borings. Standard
penetration tests (SPT) were performed in each boring by driving a 2 -inch outside
diameter split spoon sampler 18 inches into the bottom of the boring, in general
accordance with ASTM D 1586. The number of blows required to drive the sampler
the last 12 of the 18 inches (blow count) are reported on the boring logs located in
Appendix A at the end of this report. Disturbed bag samples were obtained from SPT
testing. Service providers subcontracted by Geocon Northwest completed the
borings.
Exploration logs describing the subsurface conditions encountered are presented in
Appendix A at the end of this report.
4.2. Subsurface Conditions
The subsurface explorations were widely spaced across the site and it is possible that some
local variations and possible unanticipated subsurface conditions exist. Based on the
conditions observed during the reconnaissance and field exploration, the : subsurface
conditions, in general, consisted of the following:
4
Project No. P1191 -05 -01 February 28, 2003
TOPSOIL AND /OR PAVEMENT — Approximately six inches of organic topsoil was
encountered within the exploratory borings and soundings completed in the playing field
area. Boring B -3 was completed within the existing west parking lot where approximately
2.5 inches of a/c pavement underlain by crushed rock was encountered.
FILL — A very stiff silt fill was encountered below the pavement section to a depth of
approximately four feet below the ground surface within Boring. B -3. The fill material
appeared to be consistent with native soil type and relatively free of debris.
WILLAMETTE SILT- In general, a moist to wet, medium stiff to stiff, brown silt with varying
amounts of clay was encountered below the topsoil or fill layer, The Willamette Silt deposit
extended to an approximate depth of 12 feet to 15 feet below the ground surface.
WEATHERED ROCK- Hard, wet, brown to gray, severely weathered rock was encountered
below the Willamette Silts.
Subsurface conditions encountered during the field investigation appear to be consistent
with geologic conditions mapped within the region. -
a4 GROUNDWATER — Groundwater was encountered at depths ranging from five to nine feet
below the ground surface in the playing field. Groundwater was encountered at a depth of
15 feet in Boring B -3, completed in the west parking area.
5. SITE- SPECIFIC SEISMIC HAZARD EVALUATION
5.1 Seismic Setting
5.1.1. Earthquake Sources
The seismicity of the Portland Region, including Metzger Elementary School site, is
controlled by three separate fault mechanisms. These include the Cascadia
Subduction Zone (CSZ), the mid -depth intraplate zone, and relatively shallow crustal
faults.
The Cascadia Subduction Zone is located offshore and extends from Northern
California to British Columbia. Within this zone the oceanic Juan De Fuca Plate is
being subducted beneath the continental North American Plate to the east. The
interface between these two plates is located at a depth of approximately 15 to 20
kilometers. The seismicity of the CSZ is subject to several uncertainties, including
the maximum earthquake magnitude and the recurrence intervals associated with
5
Project No. P1191 -05 -01 February 28, 2003
various magnitude earthquakes. Anecdotal evidence of previous CSZ earthquakes
has been observed within, coastal marshes along the Oregon coast (Peterson et al.
1993). Sequences of interlayered peat and sands have been interpreted to be the
result of large subduction zone earthquakes occurring at intervals on the order of
300 to 500 years, with the most recent event taking place approximately 300 years
ago. A recent study by Geomatrix (1995) suggests that the maximum earthquake
associated with the CSZ is moment magnitude (M 8 to 9. This is based on an
empirical expression relating moment magnitude to the area of fault rupture derived
from earthquakes which have occurred within subduction zones in other parts of the
world.
The intraplate or intraslab zone encompasses the portion of the subducting Juan De
Fuca Plate located at a depth of approximately 20 to 40 km below Western Oregon.
Very low levels of seismicity have been observed within the intraplate zone in
Oregon. However, much higher levels of seismicity within this zone have been
recorded in Washington and California. Several reasons for this seismic quiescence
in Oregon were suggested in the Geomatrix (1995) study and include changes in the
direction of subduction between Oregon and British Columbia as well as the effects
of volcanic activity along the Cascade Range. Historical activity associated with the
intraplate zone includes the 1949 Olympia (magnitude 7.1), the 1965 Puget Sound
(magnitude 6.5), and the more recent 2001 Nisqually (magnitude 6.8) earthquakes.
Both Geomatrix (1995) and Wong et al (2000) present estimates of Mw of 7.0 to 7.2
for the maximum moment magnitude of the intraslab zone
The third source of seismicity that can result in ground shaking at the Metzger
Elementary School site is near - surface crustal earthquakes occurring within the
North American Plate. The historical seismicity of crustal earthquakes in western
Oregon is higher than the seismicity associated with the CSZ and the intraplate
zone. The 1993 Scotts Mills (magnitude 5.6) and Klamath Falls (magnitude 6.0)
were crustal earthquakes. Individual faults or fault zones, which have been mapped
by the Oregon Department of Geology and Mineral Industries (1991), Geomatrix
(1995) and Wong et al (2000) within the near - vicinity of the site, are indicated on
Table 1: Crustal Faults (all tables are presented at the end of the report). As
discussed within Wong et al (2000), the estimated maximum moment magnitude for
each crustal fault was determined using empirical relationships developed by Wells
and Coppersmith (1994) between rupture length, rupture area, and earthquake
magnitude.
6
Project No. P1191 -05 -01 , February 28, 2003
Seismic and geologic parameters such as slip rate, horizontal and vertical offset,
rupture length, and geologic age have not been determined for the majority of the
faults in Table 1. This is primarily due to the lack of surface expressions or
exposures of faulting because of urban development and the presence of late
Quaternary soil deposits that overlie the faults. The low level of historical seismicity
(particularly for earthquakes greater than magnitude 5) and lack of paleo- seismic
data results in large uncertainties when evaluating individual crustal fault maximum
magnitude earthquakes and recurrence intervals, and limits the available knowledge
of characteristic motions of estimated maximum moment earthquakes.
5.1.2. Historical Seismicity
The historical seismicity of the site and the vicinity was determined based upon the
review of the September 1993 and November 1995 issues of Oregon Geology and
on the analysis of the 150 year Oregon earthquake catalog, DOGAMI Open -File
Report 0 -94 -4. OFR 0 -94 -4 is a database of 15,000 Oregon earthquakes that
occurred between 1833 and October 25, 1993. In order to establish an estimated
Richter Magnitude for those seismic events that do not have such a recording, the
Gutenberg and Richter, 1965 relationship, M = (2/3) MMI +1, was applied to those
earthquakes that only had a reported Modified Mercalli Intensity (MMI). The MMI
scale is a means of estimating the size of an earthquake using human observations
and reactions to the earthquake. The MMI scale ranges from I to XII, with Xll
representing the highest intensity., A search of the database was conducted to
determine the number and estimated magnitude of earthquakes that have taken
place within 50 kilometers of the site. The information derived from the Oregon
earthquake catalog indicates that ten magnitude M5.0 and greater earthquakes
occurred within the search zone. Three of these ten were greater than M5.0. M5.7
in 1877 was the largest recorded magnitude within the 50 -km search area.
5.2. Ground Shaking Characteristics
5.2.1. Several studies have been published which present probability -based levels of
ground motion for Western Oregon. Studies reviewed for this report include
Geomatrix (1995) and United States Geological Survey (1996). These probabilistic
studies incorporate the seismic characteristics of faults and seismic zones,
including fault location and geometry, slip rate, and magnitude, to develop
estimates of ground or bedrock shaking for different return periods (or probability of
exceedance at different time periods). Within Western Oregon large uncertainties
7
Project No. P1191 -05 -01 February 28, 2003
exist in probabilistic analyses due to the lack of significant historical seismicity and
the uncertainty associated with seismic source characterization.
The study by Geomatrix (1995) estimated peak bedrock horizontal accelerations in
the site vicinity of 0.20g, 0.27g, and 0.38 for return periods of approximately 500
years, 1,000 years, and 2,500 years, respectively.
The United States Geological Survey "National Seismic Hazard Mapping Project"
(1996) estimated peak bedrock horizontal accelerations of 0.19g, 0.27g, and 0.39g
also for return periods of approximately 500, 1,000, and 2,500 years, respectively.
5.2.2. Design Ground Shaking Parameters
For buildings designed in accordance with the current Uniform Building Code
(UBC) a soil characteristic called "Soil Profile Type" is used to account for the
effect of the underlying soil conditions on bedrock motion.
Based on the subsurface data information obtained at the site, supplemented with
deep . boring and seismic cone penetrometer data recorded in DOGAMI Open File
Report 0 -95 -7, the soil profile type was determined in accordance with the
procedures outlined in UBC Section 1636 "Site Categorization Procedure."
Subsurface characteristics place the site within Soil Profile Type SD. It is
recommended that, a seismic zone factor of 0.3 for UBC Zone 3 be used for
structural seismic analysis of the proposed building. Seismic design coefficients of
Ca equal to 0.36 and equal to 0.54 are recommended based on Soil Profile
Type S
5.3. Fault Displacement and Subsidence
Based on the literature review, identified faults were not mapped within the boundaries of
the site or within adjacent properties. Evidence was not encountered during the field
investigation to suggest the presence of faults within the property. The potential for fault
displacement and associated ground subsidence at the site is considered remote.
5.4. Slope Instability
Earthquake induced landslides generally occur on steep slopes composed of weak soil or
bedrock. Among the factors that influence seismic induced landsliding include earthquake
8
Project No. P1191 -05 -01 February 28, 2003
intensity, topographic relief, ground water, and soil or bedrock type. Earthquakes can also
reactivate existing landslides. Based on the relatively flat site topography and field
observations, the site is estimated to have a low earthquake induced slope instability
hazard.
5.5. Liquefaction
Liquefaction can cause aerial and differential settlement, lateral spreading, and sudden loss
of soil shear strength. Soils prone to liquefaction are typically loose (with SPT blow counts
less than 20), saturated sands and, to a lesser degree, silt. Liquefaction susceptible soils
typically consist of geologically young alluvial deposits and man -made fills. Recent studies
(Andrews, 2000) indicate that soils with 10% or more grainsize less than 0.002mm and a
liquid limit greater than or equal to 32 are not susceptible to liquefaction. Laboratory test
results of samples collected show the Willamette Silts at this site to have a liquid limit
between 33 and 37 with 25% to 30% grainsize less than 0.002 and are considered non -
liquefiable.
5.6. Lateral Spreading _
Lateral spreading is a liquefaction related seismic hazard that may adversely impact some
sites. Areas subject to lateral spreading are underlain by liquefiable sediments and are
iA sloping sites or are flat sites adjacent to an open face. Based upon a review of the site
subsurface conditions and flat topography, it is determined that the site has negligible
potential for lateral spreading.
5.7. Seiche and Tsunami Inundation
There is not a potential for seiche- and tsunami - related damage at the site due to the
distance of the site from waterways, lakes, and coastal areas.
6. LABORATORY TESTING
Laboratory testing was performed on selected soil samples to evaluate moisture content,
grain size distribution, plasticity, and compaction characteristics. Visual soil classification
was performed both in the field and laboratory, in general accordance with the Unified Soil
Classified System. Moisture content determinations (ASTM D 2216) were performed on soil
samples to aid in classifying the soil. Grain size analyses were performed on selected
samples using procedures ASTM D 1140 and ASTM D 422. The plasticity index was
determined in general accordance with ASTM D 4318. ASTM D 1557 (Modified Proctor)
procedures were used to evaluate the compaction characteristics for the near surface soils.
9
Project No. P1191 -05 -01 February 28, 2003
Moisture contents are indicated on the boring logs, which are located in Appendix A of this
report. Other laboratory test results for this project are summarized in Appendix B.
7. CONCLUSIONS AND RECOMMENDATIONS
7.1. General
7.1.1. It is our opinion that the proposed project is geotechnically feasible, provided the
recommendations of this report are followed. The primary geotechnical concerns
associated with the project development are the presence of groundwater at near
surface elevations and the high moisture content of the near - surface, moisture
sensitive, soils.
7.1.2. Moisture contents of near- surface soils were wet of optimum at the time of the
investigation. Recommendations for both dry weather site preparation and wet
weather site preparation in moisture - sensitive soils are provided, however, dry
weather construction at this site is recommended. It is recommended that the
project budget include costs for wet weather construction, regardless of the time of
year construction is scheduled to occur.
7.1.3. Groundwater was encountered at a depth of approximately 5 to 9 feet below the
ground surface in borings completed in the building footprint area currently
occupied by playing fields. Groundwater was encountered at approximately 15
feet below the ground surface in Boring B -3, located in the west parking lot.
Recommendations regarding drainage and vapor retarders are provided in
subsequent sections of this report.
7.2. Site Preparation
7.2.1. Prior to beginning construction, the areas of the site to receive . fill, footings or
pavement should be stripped of vegetation, topsoil, non - engineered fill, previous
subsurface improvements, debris, and otherwise unsuitable material, down to firm
native soil. Topsoil thickness of approximately six inches was encountered in the
playing fields during the investigation. Approximately 2.5 inches of a/c pavement
was encountered within the west parking lot. Any structures not to be incorporated
into the development, including the modular structures within the proposed building
footprint, should be removed in their entirety. It is understood that the main
building associated with the existing school will be demolished following the
completion of the new school. Excavations made to remove previous subsurface
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Project No. P1191-05-01 February 28, 2003
improvements or unsuitable soils in structural areas should be backfilled with
structural fill per Section 7.4 of this report.
7.2.2. Recommendations for both dry weather and wet weather site preparation are
provided in the following sections. However, due to the moisture sensitive near
surface soils, it is recommended that the site be prepared during dry weather.
7.2.3. Dry Weather Site Preparation
Subgrades in pavement and structural areas that have been disturbed during
stripping or cutting operations should be scarified to a depth of at least eight
inches. The scarified soil should be moisture conditioned as necessary to achieve
the proper moisture content, then compacted to at least 92% of the maximum dry
density as determined by ASTM D- 1557. Minimum compaction for the eight inches
immediately underlying pavement sections should be 95 %. Even during dry
weather it is possible that some areas of the subgrade will become soft or may
"pump," particularly in poorly drained areas or where soft clay is encountered. Soft
or wet areas that cannot be effectively dried and compacted should be prepared in
accordance with Section 7.2.4.
7.2.4. Wet Weather Preparation
•
During wet weather, defined as whenever adequate soil moisture control is not
possible, it may be necessary to install a granular working blanket to support
construction equipment and provide a firm base on which to place subsequent fills
and pavements. Commonly, the working blanket consists of a bank run gravel or
pit run quarry rock (six to eight inch maximum size with no more than 5% by weight
passing a No. 200 sieve). A member of Geocon Northwest's engineering staff
should be contacted to evaluate the suitability of the material before installation.
The working blanket should be installed on a stripped subgrade in a single lift with
trucks end - dumping off an advancing pad of granular fill. It should be possible to
strip most of the site with careful operation of track - mounted equipment. However,
during prolonged wet weather, or in particularly wet locations, operation of this type
of equipment may cause excessive subgrade disturbance. In some areas final
stripping and /or cutting may need to be accomplished with a smooth - bucket
trackhoe, or similar equipment, working from an advancing pad of granular fill.
After installation, the working blanket should be compacted by a minimum of four
complete passes with a moderately heavy static steel drum or grid roller. It is
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Project No. P1191 -05 -01 February 28, 2003
recommended that Geocon Northwest be retained to observe granular working
blanket installation and compaction.
The working blanket must provide a firm base for subsequent fill installation and
compaction. Past experience indicates that about 18 inches of working pad is
normally required. This assumes that the material is placed on a relatively
undisturbed subgrade prepared in accordance with the preceding
recommendations. Areas used as haul routes for heavy construction equipment
or construction staging areas may require a work pad thickness of two feet or
more.
In particularly soft areas, a heavy - grade, non - degradable geotextile fabric installed
on the subgrade may reduce the thickness of working blanket required. The fabric
should have a minimum puncture resistance of 80 pounds and a minimum Mullen
Burst strength of 300 psi.
Construction practices can affect the amount of work pad necessary. By using
tracked equipment and special haul roads, the work pad area can be minimized.
The routing of dump trucks and rubber tired construction equipment across the site
can require extensive areas and thicknesses of work pad. Normally, the design,
installation and maintenance of a work pad are the responsibility of the contractor.
Lime or cement treatment may be a suitable alternative wet - weather construction
technique for the subgrade conditions encountered at this site. Successful lime or
cement treatment is dependent upon moisture content of the subgrade soils,
weather conditions at the time of treatment, and adequate mixing of the soil and
lime or cement. It is recommended that cement treated soils have a three -day,
unconfined compressive strength of 250 psi. Cement or lime treatment design is
typically the responsibility of the contractor.
7.3. Proof Rolling
7.3.1. Regardless of which method of subgrade preparation is used (i.e. wet weather or
sdry weather), it is recommended that, prior to fill placement or base course
installation, the subgrade or granular working blanket be proof - rolled with a fully -
loaded 10- to 12 -yard dump truck. Areas of the subgrade that pump, weave or
appear soft or muddy should be scarified, dried and compacted, or overexcavated
and backfilled with structural granular fill per Section 7.4. If a significant length of
time passes between fill placement and commencement of construction
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Project No. P1191 -05 -01 February 28, 2003
•
operations, or if significant traffic has been routed over these areas, the subgrade
should be similarly proof - rolled before final placement of asphalt or concrete. It is
recommended that a member of our geotechnical engineering staff observe the
proof -roll operation.
7.4. Fills
7.4.1 Structural fills should be constructed on a subgrade that has been prepared in
accordance with the recommendations in Section 7.2 of this report. Structural fills
should be installed in horizontal lifts not exceeding about eight inches in thickness,
and should be compacted to at least 92% of the maximum dry density for the
native silt soils, and 95% for imported granular material. Compaction should be
referenced to ASTM D -1557 (Modified Proctor). The compaction criteria may be
reduced to 85% in landscape, planter or other non - structural areas.
7.4.2. During dry weather when moisture control is possible, structural fills may consist of
native material, free of topsoil, debris and organic matter, which can be compacted
•;••• to the preceding specifications. However, if excess moisture causes the fill to
tr pump or weave, those areas should be scarified and allowed to dry, and then be
recompacted, or removed and backfilled with compacted granular fill as discussed
in Section 7.2 of this report.
7.4.3. The native, non - organic silt would generally be acceptable for structural fills if
properly moisture conditioned. Near - surface moisture contents at the time of the
field investigation were wet of optimum and ranged from approximately 26% to
31 %. Based on laboratory test results, the optimum moisture content for
compaction is approximately 16% at a maximum dry density of approximately 112
pcf. Moisture conditioning operations, including discing and aeration, should be
anticipated for the native soils (even during dry months).
7.4.4 During wet - weather grading operations, Geocon Northwest recommends that fills
consist of well - graded granular soils (sand or sand and gravel) that do not contain
more than 5% material by weight passing the No. 200 sieve. In addition, it is
usually desirable to limit this material to a maximum three inches in diameter for
future ease in the installation of utilities.
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Project No. P1191 -05 -01 February 28, 2003
7.5. Cut and Fill Slopes
7.5.1. Cut slopes should be sloped no steeper than 2H:1 V. These values assume that
the slopes will be protected from erosion and that significant drainage will not occur
over the face of the slope. They further assume that no loads will be imposed
within a horizontal distance of one -half of the slope height measured from the top
of the slope face. Cut slopes should be constructed with a smooth bucket
excavator to minimize subgrade disturbance. Slope drainage may be required if
springs, seeps, or groundwater are encountered.
7.5.2. Fill slopes should be obtained by placing and compacting material beyond the
design slope and then excavated back to the desired grade or by other means that
will result in a dense, compacted sloped face. Fill compaction should be as stated
in Section 7.4. Filled slopes should not be graded steeper than 2H:1 V and no
loads should be imposed within a horizontal distance of one -half of the slope
height.
7.5.3. The face of the constructed slope should be protected from erosion by applying
vegetation or other approved erosion control material as soon as practicable after
construction.
7.6. Surface and-Subsurface Drainage
7.6.1. During site contouring, positive surface drainage should be maintained away from
foundation and pavement areas. Additional drainage or dewatering provisions may
be necessary If soft spots, springs, or seeps are encountered in subgrades.
Where possible, surface runoff should be routed independently to a storm water
collection system.
7.6.2. Drainage systems should be sloped to drain by gravity to a storm sewer or other
positive outlet.
7.6.4. Drainage and dewatering systems are typically designed and constructed by the
contractor. Failure to install necessary subsurface drainage provisions may result
in premature foundation or pavement failure.
•
7.7. Foundations
7.7.1. The following foundation recommendations are based on estimated maximum
column and wall loads of 160 kips and 5 kips /foot, respectively.
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Project No. P1191 -05 -01 February 28, 2003
7.7.2. Spread and perimeter foundation support for proposed structures may be obtained
from the near - surface, non - organic, native silt soil or from structural fill installed in
accordance with our recommendations.
7.7.3. Spread and perimeter footings should be at least 12 inches wide and should
extend at least 18 inches below the lowest adjacent pad grade. Foundations
having these minimum dimensions that are founded on firm native soils or
engineered fill may be designed for an allowable soil bearing pressure of 3,000
pounds per square foot (psf).
7.7.4. When encountered at bottom of foundation elevation, soft and /or saturated soils
may require overexcavation.
7.7.5. Gravel or lean concrete may need to be placed in the bottom of the footing
excavation to reduce soil disturbance during foundation forming and construction.
7.7.6. The allowable bearing pressure given above may be increased by one -third for
short term transient loading, such as wind or seismic forces.
7.7.7. Lateral loads may be resisted by sliding friction and passive pressures. A base
friction of 40% of the vertical load may be used against sliding. An equivalent fluid
weight of 300 pcf may be used to evaluate passive resistance to lateral loads.
7.7.8. Foundation settlements for the loading conditions expected for this project are
estimated to be less than one inch, with not more than one -half inch occurring as
differential settlement.
7.7.9. Geocon Northwest recommends that foundation drains be installed at or below the
elevation of perimeter footings to intercept potential subsurface water.
7.8. Concrete Slab -on -Grade
7.8.1. Subgrades in floor slab areas should be prepared in accordance with Section 7.2
of this report. Floor slab areas should be proof - rolled with a fully loaded 10- to 12-
yard dump truck to detect areas that pump; weave, or appear soft or muddy.
When detected these areas should be overexcavated and stabilized with
compacted granular fill.
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Project No. P1191 -05 -01 February 28, 2003
7.8.2. A minimum six -inch thick layer of compacted 3 /4 -inch minus material should be
installed over the prepared subgrade to provide a capillary break and to minimize
subgrade disturbance during construction. The crushed rock or gravel material
should be poorly - graded, angular and contain no more than 5% by weight passing
the No. 200 Sieve.
7.8.3. A modulus of subgrade reaction of 100 pci is recommended for design.
7.8.4. The fine- grained near - surface soils at the site have high natural moisture contents
and low permeability. These characteristics indicate that high ground moisture
may develop under floor slabs during the life of the project. The difference in
moisture content between the air in the subgrade soil and the air in the finished
building may cause water vapor to travel upward. The resulting water vapor
pressure will force migration of moisture through the slab. This migration can
result in the loosening of flooring materials attached with mastic, the warping of
wood flooring, stain concrete, and in extreme cases, mildewing of carpets and
building contents. To retard the migration of moisture through the floor slab,
Geocon Northwest recommends installing a 10 -mil polyethylene vapor retarding
membrane below the concrete slab. Installation of the membrane should be in
conformance with product manufacturer's specifications. A minimum 6 -inch under-
slab section of crushed rock, as recommended in Section 7.8.2, should be placed
as a capillary break above the subgrade and below the vapor retarder. Any
moisture that has accumulated on the vapor retarding membrane should be
removed prior to the concrete pour. Concrete with a minimum compressive
strength of 4000 psi and a water /cement ratio of less than 0.48 is recommended.
Wet curing of the concrete slab is recommended.
7.9. Utility Excavations
7.9.1. Based on the subsurface explorations, difficult excavation characteristics are not
anticipated above a depth of approximately 15 feet. Severely weathered rock was
encountered at approximately 15 feet.
7.9.2. Excavations deeper than four feet, or those that encounter groundwater, should be
sloped or shored in conformance with OSHA regulations. Shoring systems are
typically contractor designed.
7.9.3. Groundwater was encountered at approximately four to nine feet bgs. Near -
surface perched groundwater may be encountered during construction.
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Project No. P1191 -05 -01 February 28, 2003
Excavation dewatering may be necessary if substantial flow of groundwater is
encountered. Water removed from excavations should be routed to non- structural
areas of the site. Dewatering systems are typically designed and installed by the
contractor.
7.9.4. Utilities should be bedded in sand within one conduit diameter in all directions,
prior to the placement of coarser backfill. Trench backfill should be lightly
compacted within two diameters or 18 inches, whichever is greater, above
breakable conduits. The remaining backfill, to within 12 inches of finished grade,
should be compacted to 92% of the maximum dry density as determined by ASTM
D1557. In structural areas, the upper foot of backfill should be compacted to 95%
of the maximum dry density.
7.9.5. Backfill in utility trenches that will be spanned by building foundations should be
compacted to 95% of the maximum dry density as determined by ASTM D1557
above the conduit zone.
•
7.10. Pavement Design
7.10.1. Near surface soil samples were evaluated to determine pavement design
parameters. A CBR of 3 at 95% compaction and a resilient modulus of 4,500 psi
were used for pavement design.
7.10.2. Alternate pavement designs for both asphalt and portland cement concrete (pcc)
are presented in Tables 2 and 3. Pavement designs have been prepared in
accordance with accepted AASHTO design methods. A range of pavement
designs for various traffic conditions is provided in the tables. The designs assume
that the top eight inches of pavement subgrade will be compacted to 95% ASTM
D -1557. Specifications for pavement and base course should conform to current
Oregon State Department of Transportation specifications. Additionally, the base
rock should contain no more than 5% by weight passing a No. 200 Sieve, and the
asphaltic concrete should be compacted to a minimum of 91% of ASTM D2041.
7.10.3. Pavement sections were designed using AASHTO design methods, with an
assumed reliability level (R) of 90 %. Terminal serviceability of 2.0 for asphaltic
concrete, and 2.5 for portland cement concrete were assumed. The 18 kip design
axle loads are estimated from the number of trucks per day using State of Oregon
17
Project No. P1191 -05 -01 February 28, 2003
typical axle distributions for truck traffic and AASHTO load equivalency factors, and
assuming a 20 year design life. The concrete designs were based on a modulus of
rupture equal to 550 psi, and a compressive strength of 4000 psi. The concrete
sections assume plain jointed or jointed reinforced sections with no load transfer
devices at the shoulder.
7.10.4. In areas where construction traffic and staging areas are anticipated, 18 inches of
rock underlain by a geotextile fabric are recommended, regardless of the final
design section.
8. FUTURE GEOTECHNICAL SERVICES
The analyses, conclusions and recommendations contained in this report are based on site
conditions as they presently exist, and on the assumption that the subsurface investigation
locations are representative of the subsurface conditions throughout the site. It is the nature
of geotechnical work for soil conditions to vary from the conditions encountered during a
normally acceptable geotechnical investigation. While some variations may appear slight,
their impact on the performance of structures and other improvements can be significant.
Therefore, it is recommended that Geocon Northwest be retained to observe portions of this
project relating to geotechnical engineering, including site preparation, grading, compaction,
foundation construction and other soils related aspects of construction. This will allow
correlation of investigative observations and findings to actual soil conditions encountered
during construction and evaluation of construction conformance to the recommendations put
forth in this report.
A copy of the plans and specifications should be forwarded to Geocon Northwest so that
they may be evaluated for specific conceptual, design, or construction details that may
affect the validity of the recommendations of this report. The review of the plans and
specifications will also provide the opportunity for Geocon Northwest to evaluate whether
the recommendations of this report have been appropriately interpreted.
9. LIMITATIONS
Unanticipated soil conditions are commonly encountered during construction and cannot
always be determined by a normally acceptable subsurface exploration program. The
recommendations of this report pertain only to the site investigated and are based upon the
assumption that the soil conditions do not deviate from those disclosed in the investigation.
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Project No. P1191 -05 -01 February 28, 2003
•
If variations or undesirable conditions are encountered during construction, or if the
proposed construction will differ from that anticipated herein, Geocon Northwest should be
notified so that supplemental recommendations can be given.
This report is issued with the understanding that the owner, or his agents, will ensure that
the information and recommendations contained herein are brought to the attention of the
architect and engineer for the project and incorporated into the plans.
The findings of this report are valid as of the present date. However, changes in the
conditions of a property can occur with the passage of time, whether they be due to natural
processes or the works of man on this or adjacent properties. In addition, changes in
applicable or appropriate standards may occur, whether they result from legislation or the
broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly
or partially by changes outside our control. Therefore, this report is subject to review should
such changes occur.
,,.., If you have any questions regarding this report, or if you desire further information, please
contact the undersigned at (503) 626 -9889.
GEOCON NORTHWEST, INC.
‘lt 4_
Heather Devine,
P.E. Wesley - Spang, P h.D., P.E.
Geotechnical Engineer President
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Project No, P1191 -05 -01 February 28, 2003
REFERENCES
Andrews, D.C., Martin, G.R., 2000, Criteria for Liquefaction of Silty Soils, World Conference
on Earthquake Engineering.
Bott, D.J., Wong, I.G., September 1993, "Historical Earthquakes in and Around Portland,
Oregon," Oregon Geology, Vol. 55, No. 5.
Geomatrix, 1995, "Seismic Design Mapping, State of Oregon," prepared for Oregon
Department of Transportation.
Lunne, T., Robertson, P.K., Powell, J.J.M., 1997, Cone Penetration Testing In Geotechnical
Engineering Practice, E & FN Spon Publishers.
Mabey, M. A., Madin, l.P., 1995, Open -File- Report 0 -95 -7, "Downhole and Seismic Cone
Penetrometer Shear -Wave Velocity Measurements for the Portland Metropolitan
Area, 1993 and 1994," Oregon Department of Geology and Mining Industries.
Marchetti, S., 1980, "In Situ Tests by Flat Dilatometer,: Journal of Geotechnical Engineering,
ASCE, Vol. 106, No. GT3, Proc. Paper 15290, March, pp 299 -321
National Center For Earthquake Engineering Research, 1997, "Proceedings of the NCEER
Workshop on Evaluation of Liquefaction Resistance of Soils," Technical Report
NCEER 97 -0022.
Oregon Department of Geology and Mineral Industries, 1994, Open -File Report 0 -94 -4.
Peterson, C.D., Darienzo, M.E., Burns, S.F., and Burris, W.K., September 1993, "Field Trip
to Cascadia Paleoseismic Evidence Along the Northern Oregon Coast: Evidence of
Subduction Zone Seismicity in the Central Cascadia Margin," Oregon Geology, Vol.
55, No. 5,
Schmertmann, J.H., 1983, "DMT Digest No. 1," Internal Report of GPE inc., April
Seed, H.B., and Idriss, I.M., 1982 Ground Motions and Soil Liquefaction During
Earthquakes, Earthquake Engineering Research Institute.
Stark, T.D., Olson, S.M., 1995, "Liquefaction Resistance Using CPT and Field Case
Histories," Journal of Geotechnical Engineering, Vol. 121, No. 12.
United States Geologic Survey, 1996, "National Seismic Hazard Mapping Project."
http : / /geohazards.cr.usgs.gov /eq /.
Wong, I.G., Bott, D.J., November 1995, "A look Back at Oregon's Earthquake History, 1841-
1994," Oregon Geology, Vol. 57, No. 6.
•
Table 1: Crustal Faults
Mapped Fault Probability of Fault Type Maximum Approx.
or Fault Zone Activity Geomatrix Moment Horizontal
Wong (2000) (1995) Magnitude Distance From
Wong (2000) Site to Surface
Fault Trace
(miles)
Portland Hills 0.8 Strike -slip (1) 6.8 6.5
Fault
Oatfield Fault ' 0.8 Strike -slip (1) 6.8 4
East Bank Fault 0.8 Strike -slip (1) 6.8 8.5
Bolton Fault 0.2 Reverse (1) 6.3 6
Grant Butte, 0.5 Lateral slip (1) 6.4 14
Damascus -
Tickle Creek -
Fault Zone
Helvetia Fault 0.2 Reverse (1) 6.3 10
Lacamas Lake 0.5 Strike -slip, 6.5 21
Fault Oblique -slip (1)
Sandy River 0.1 Dip -slip, Strike- 6.4 27
Fault slip (1)
Mount Angel 0.9 Strike -slip (1) 6.6 20
Fault
Newberg Fault 0.7 Strike -slip (1) 6.2 12
Gales Creek 0.7 Strike -slip (1) 6.4 15
Fault
Table 2: Asphalt Concrete Pavement Design
Approx. Approx, Asphalt Crushed Rock
Number of Number of 18 Concrete Base Thickness
Trucks per Day Kip Design Axle Thickness (inches)
. (each way) Load (1000) (inches)
Auto Parking 10 2.5 8
5 22 3.0 8
10 44 3.0 10
15 66 5 66 3.5 10
25 110 4.0 10
50 220 4.0 12
100 440 4.5 12
150 660 5.0 .13
Table 3: Portland Cement Concrete Pavement Design
Approx. Approx: P.C.C. Crushed Rock
Number of Number of 18 Thickness Base Thickness
Trucks per Day Kip Design Axle (inches) (inches)
(each way) Load (1000)
25 110 6.0 6
50 220 7.0 6
100 440 8.0 6
150 660 8.5 6
200 880 8.5 6
250 1100 9.0 6