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April 14, 2006 0®C �tr 6 1 zimmler- 05- 01- consult
Zimmler Development, LLC
S.W. Fir Loop, Suite 100 0 7 O
Tigard, OR 97223 � RECEIVED
Email: markRzimmler.com �
Jc cl � 41
2006
CITY O TIGARD
Attention: Mark Ferris o B DVISION
GEOTECHNICAL ENGINEERING REPORT UPDATE
SW 70th and Dartmouth Project - Tigard, Oregon
INTRODUCTION
We appreciate the opportunity to present this Geotechnical Engineering Report Update for the
proposed commercial development SW 70th Avenue and SW Dartmouth Street in Tigard, Oregon. We
previously completed subsurface explorations and a geotechnical report for the site under a contract
with a previous owner. Our original geotechnical report is dated March 12, 2004 and is attached to this
letter.
We understand that the current project is an office commercial development and is being submitted to
the City of Tigard for construction permitting. Based on preliminary information provided by you and
the design team, we understand that the current development plans include one two -story building with
an approximate footprint of 15,000 square feet located in the southeast area of the site. The building
will feature steel frame construction with a brick veneer. Structural Toads were not available at the time
of this letter but based on our experience with similar structures, we assume that building loads will be
Tess than 250 kips for columns, 6 kips per foot for walls, and 250 psf for floor slabs -on- grade.
Based on our review of the proposed grading plan provided by LanPacific, site grading will consist of cuts
up to 10 feet and fills up to 14 feet relative to existing (i.e. pre - development) grades. The building will
include embedded walls up to 10 feet in height and concrete cast -in -place retaining walls up to 14 feet
tall are also planned. Underground utilities will range in depth from 3 to 10 feet below existing grades.
PURPOSE AND SCOPE
The purpose of our services was to review our previous geotechnical report, determine if our previous
recommendations are applicable to the currently proposed development, and provide updates and
revised recommendations as necessary. Our specific scope of work included the following:
• Review proposed project information including plans and drawings relevant to geotechnical
recommendations.
• Review the recommendations provided in our previous geotechnical report relative to the
currently proposed development.
• Provide a revised geotechnical report for the current project including updates relative to the
2004 Oregon Structural Specialty Code (OSSC).
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813 7 Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
April 14, 2006 zimmler -05 -01 -consult
CONCLUSIONS AND RECOMMENDATIONS
Based on our review of the aforementioned project information and our previous explorations and
analyses, the site can be developed as proposed following the recommendations provided in our
previous report and the updated /revised recommendations provided in the following sections. The
following sections should replace the corresponding sections in our previous report unless specifically
stated.
Working Blankets and Haul Roads - The following paragraph should be added as the last paragraph
to the same section on page 4 of our previous report.
The above rock and amendment thicknesses are the minimum recommended. Subgrade protection is the
responsibility of the contractor and thicker sections may be required based on subgrade conditions during
construction and type and frequency of construction equipment
Slopes — The following paragraph should be added between the first and second paragraphs of the Slopes'
section on page 4 of our previous report.
Temporary cut slopes up to 12 feet in height will be required for construction of the proposed retaining and embedded
building walls. Excavations may be completed using open cut methods in the absence of adjacent structures,
pavements, and sidewalks within 12 feet of slope crests. Temporary cuts should stand vertical to a depth of
approximately 4 feet, provided no groundwater seepage is observed Open excavation techniques may be used with
depths up to 12 feet with temporary 1 H:1 V slopes, provided groundwater seepage is not present and with the
understanding that some sloughing may occur. The excavations should be flattened if excessive sloughing occurs.
Drainage should be routed away from slope faces and no surcharges or construction equipment should be placed or
operate within 12 feet of the slope crest. Excavations where the sides cannot be sloped back as described above will
require temporary shoring.
Permanent Retaining Structures — The following sections should replace the 'Retaining/Embedded
Building Walls' section on page 6 of our previous report.
General - Our embedded building and retaining wall design recommendations are based on the following
assumptions: (I) the walls consist of conventional, cantilevered retaining walls or embedded building
walls; (2) the walls are less than 14 feet in exposed height; (3) the walls are fully drained and backfill
consists of clean granular materials; and (4) the backfill is level and no surcharges such as stockpiled soil,
equipment, or footings are located within 14 feet of the wall. Reevaluation of our recommendations will
be required if the retaining wall design criteria for the project vary from these assumptions. Footings for
retaining walls should be designed as recommended in the Shallow Foundations section of our
previous report.
Lateral Earth Pressures - For walls not restrained from rotation, with level backfill, and no surcharges,
the lateral pressure of a 35 pcf equivalent fluid should be used for design. For level backfill and no
surcharges, the lateral pressure of a 55 pcf equivalent fluid should be used for design of walls restrained
from rotation. In addition to the above appropriate static lateral earth pressures, we recommend
designing embedded walls and overall building base shear to resist a dynamic lateral force of 6H pounds
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813 7 Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
April 14, 2006 zimmler -05-0 I - consuh
per lineal foot of wall applied at 60 percent of the wall height from the wall base (where H is the total
wall height in feet).
Lateral Earth Pressure Increases Due to Surcharge - Increased lateral pressures due to traffic and
slab loads, sloped backfill, and footings must be added to the above static earth pressures. For inclined
backfill slopes of up to 2H:1 V, equivalent fluid pressures used for design should be increased to 105 pcf
for walls retrained from rotation and 60 pcf for walls not restrained from rotation.
The upper retaining walls in tiered wall configurations may add additional lateral loads to the lower walls
depending on height of the lower wall and the horizontal separation between the upper and lower walls.
The same will occur with building footings located behind and above retaining walls. The induced lateral
pressure from surcharge loading from wall or building footings adjacent to retaining walls can be
calculated using the attached Induced Lateral Pressure from Strip Surcharge Loading diagram.
Building foundations and upper tier retaining walls founded at least 18 inches below a plane extending
upward at an angle of 50 degrees from the base of the lower wall will not add additional lateral
pressures to the lower wall.
Wall Backfill - Backfill should be placed and compacted as recommended for structural fill, with the
exception of backfill placed immediately adjacent to walls, which should be compacted to a lesser
standard to reduce the potential for generation of excessive pressure on the walls. Backfill located
within a horizontal distance of 3 feet from the retaining walls should be compacted to approximately 90
percent of the maximum dry density, as determined by American Society for Testing and Materials
(ASTM) D 1557 and should be compacted in lifts less than 6 inches thick using hand - operated tamping
equipment (such as "jumping jack" or vibratory plate compactors). If flat work (slabs, sidewalk, or
pavement) will be placed adjacent to the wall, we recommend that the upper 2 feet of fill be compacted
to 95 percent of the maximum dry density, as determined by ASTM D 1557. Settlements of up to I
percent of the wall height commonly occur immediately adjacent to the wall as the wall rotates and
develops active lateral earth pressures. We recommend that construction of flat work adjacent to
retaining walls be postponed at least two weeks after construction, unless survey data indicates that
settlement is complete prior to that time.
Wall Drains - As stated above, our retaining and embedded building wall recommendations apply to
fully drained conditions only. Retaining wall drains should consist of a two -foot wide zone of drain rock
encompassing a 4 -inch diameter perforated pipe, all enclosed with a non -woven filter fabric. The drain
rock should have no more than 2 percent passing a #200 sieve and should extend to within one foot of
the ground surface. The geosynthetic should have an AOS of a #70 sieve, a minimum permittivity of 1.0
sec-', and a minimum puncture resistance of 80 pounds (such as an AMOCO 4551 or equivalent). One
foot of low permeability soil (such as the on -site silt) should be placed over the fabric at the top of the
drain to isolate the drain from surface runoff. The drains must be sloped to drain and tight -lined to a
suitable discharge such as the storm system.
Pavement — The following sections should replace the 'Pavement' section on page 7 of our previous
report.
Asphalt Concrete - At the time of this report update we did not have specific information regarding
the type and frequency of expected traffic. We therefore developed asphalt concrete pavement
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813 7 Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
April 14, 2006 zimmler-05-0 I-consult
thicknesses for 2, 5 and 10 trucks per day based on a 20 -year design life and a truck factor of 0.6. We
assumed that the average truck will consist of a panel -type delivery truck. These volumes can be revised
if specific traffic data is available.
Our analyses is based on AASHTO methods and subgrade of structural fill or undisturbed medium stiff
or better native silt having a resilient modulus of 6,000 psi and prepared as recommended in our
geotechnical report. We have also assumed that construction of pavement areas will be completed
during an extended period of dry weather. The results of our analyses based on these parameters are
provided in the following table.
Trucks per day ESAL's AC (inches) CR (inches)
Passenger cars only - 2.5 6
5 32,542 3 7
10 65,084 3 9
25 162,711 4 8
The thicknesses listed in the table above are intended to the minimum acceptable during an extended
period of dry weather. Increased rock thicknesses will be required for construction during wet
conditions and the project budget and schedule should include contingencies for increased excavation
and thicker rock sections. Crushed rock should conform to ODOT base rock standards and have Tess
than 6 percent passing the #200 sieve. Asphalt concrete should be compacted to a minimum of 91
percent of a Rice Density.
Subgrade Preparation - The pavement subgrade should be prepared in accordance with the
Earthwork and Site Preparation recommendations presented in our geotechnical report and this
letter report. All pavement subgrades need to pass a proof roll prior to paving. Soft areas should be
repaired by overexcavating the areas and installing a stabilization geosynthetic. Well graded, angular
crushed rock backfill compacted as structural fill should be used to bring the aforementioned areas to-
grade. For a stabilization geosynthetic we recommend a woven geosynthetic with an AOS of #70 to
#100 sieve, and a minimum puncture resistance of 120 pounds (such as an AMOCO 2019 or
equivalent).
Seismic Design — The following sections should replace the `Seismic Design' sections on page 7 of our
previous report.
General - In accordance with the International Building Code (IBC) 2003 as adapted by State of Oregon
Structural Specialty Code (SOSSC) and based on our explorations and experience in the site vicinity, the
subject project should be evaluated using the parameters associated with Site Class D. The relative
earthquake hazard map of the Lake Oswego quadrangle (DOGAMI GMS -91) indicates that the site is in
an area of low overall seismic hazard. This overall rating includes low liquefaction and moderate
amplification hazards.
Liquefaction - Liquefaction occurs in loose, saturated, granular soils. Strong shaking, such as that
experienced during earthquakes, causes the densification and the subsequent settlement of these soils.
Given the site topography and soil type and consistency encountered in our explorations, the risk of
liquefaction and related settlement is low.
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813 7"' Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
April 14, 2006 zimmler -05-0 I- consult
LIMITATIONS AND OBSERVATION DURING CONSTRUCTION
We have prepared this report update for our original project geotechnical report dated March 12, 2004
for use by Zimmler Development, LLC and the design and construction teams for this project only. The
information herein could be used for bidding or estimating purposes but should not be construed as a
warranty of subsurface conditions. We have made observations only at the aforementioned locations
and only to the stated depths. These observations do not reflect soil types, strata thicknesses, water
levels or seepage that may exist between observations. We should be consulted to observe all
foundation bearing surfaces, installation of structural fill and backfill, and subsurface drainage. We should
be consulted to review final design and specifications in order to see that our recommendations are
suitably followed. If any changes are made to the anticipated locations, Toads, configurations, or
construction timing, our recommendations may not be applicable, and we should be consulted. The
preceding recommendations should be considered preliminary, as actual soil conditions may vary. In
order for our recommendations to be final, we must be retained to observe actual subsurface
conditions encountered. Our observations will allow us to interpret actual conditions and adapt our
recommendations if needed.
Within the limitations of scope, schedule and budget, our services have been executed in accordance
with the generally accepted practices in this area at the time this report was prepared. No warranty,
expressed or implied, is given.
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We appreciate the opportunity to work with you on this project and look forward to our continued
involvement. If you have any questions, please call.
Sincerely,
�p PR
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Christopher J. Palmer, MS, PE I 72 849
Senior Project Engineer �`/
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Don Rondema, MS, PE, GE I E)ff'IRES:12/31 /0(
Principal
Attachments — Induced Lateral Pressure from Strip Surcharge Loading
Geotechnical Engineering Report by Geotech Solutions, Inc. dated March 12, 2004.
cc: Brian Frey, Myhre Group — email: BrianF(5 myhregroup.com
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813 7 Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fox 503.722.9946
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~ a STRIP LOAD, q
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NOTES:
I. THESE GUIDELINES APPLY TO RIGID WALLS WITH POISSON'S
RATIO ASSUMED TO BE 0.5 FOR BACKFILL MATERIALS.
2. STRIP LOAD PARALLEL TO WALL
} INDUCED LATERAL PRESSURE FROM STRIP SURCHARGE LOADING
G� `l li o n s Inc 1 zimmler -05 -0I - consult
SW Dartmouth and SW 70 Project
Tigard, Oregon
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Voiustions Incl
March 12, 2004
GSI Project bissett- 04 -01 -gi
March 12, 2004 bissett Iii
Spectrum Development
do Westlake Consultants
151 15 SW Sequoia Parkway, Suite I50
Tigard, OR 97224
Ien_ schelsky @westlakeconsultants.com
. (.)) 4 ..\
Attention: Len Schelsky
0 �
GEOTECHNICAL ENGINEERING REPORT `
SW 70th and Dartmouth Commercial Development - Tigard, OR
- appreciate the opportunity to present this geotechnical report for the proposed project. We
and - stand the site will be developed with four small office buildings, incorporating cuts and fills of up to
10 feet , height, asphalt driveway and parking areas, utilities, and landscaping. Building loads are
expected t• • e Tess than 250 kips for columns, 6 kips per foot for walls, and 250 psf for floors.
The purpose of ou work was to evaluate subsurface conditions to provide geotechnical
recommendations for • -sign and construction. Specifically, our scope of work included the following
• Provide principal level prof -. t management including management of field and subcontracted
services, report writing, analys - , and invoicing.
• Review previous reports, geologic , aps, and vicinity geotechnical information as indicators of
subsurface conditions.
• Complete a site reconnaissance to obsery - surface features relevant to geotechnical issues, such as
topography, vegetation, presence and conditi • , of springs, exposed soils, and evidence of previous
grading.
• Identify exploration locations and coordinate possib - ocation conflicts with utilities.
• Explore subsurface conditions by excavating eight test pi , to depths of up to 15 feet using a large
excavator.
• Classify and sample the materials encountered and maintain a d - iled log of the explorations.
• Determine the moisture content of selected samples obtained fro e explorations and conduct
soil classification testing as necessary.
• Provide recommendations for earthwork including seasonal material usage, se of granular working
pads, cut and fill slope inclinations, and fill preparation and compaction.
• Provide recommendations for foundation support, including suitable soils, bearin ressures, sliding
coefficients, seismic coefficients, and construction considerations.
• Provide recommendations for subsurface drainage including perimeter and underslab dra age, as
well as cut slope toe drains.
• Provide recommendations for retaining wall design including lateral earth pressures, drainage, a
foundations.
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813 7 Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
March 12, 2004 Bissett- 04 -01-gi
• Provide recommendations for slab support, including settlement estimates, underslab rock thickness,
and materials.
• Provide recommendations for site pavements including subgrade preparation as well as asphalt
concrete and base rock thickness using traffic data provided by others.
• Provide a written report summarizing the results of our geotechnical evaluation.
SITE OBSERVATIONS AND CONDITIONS
Surface Conditions
The approximate I.9 -acre site is located along the north side of SW Dartmouth Street west of the SW
70th Avenue right -of -way in Tigard, Oregon. The site topography slopes gently to the southwest from
an approximate elevation of 260 feet along the eastern site boundary to an elevation of 225 feet at the
southwest corner of the site. A cut slope approaching 2H:1 V to 3H:1 V (horizontal:vertical) is present
along the southern border of the site (i.e. along SW Dartmouth). Site topography is shown on the
attached Site Plan.
An existing residence is located at the northeast corner of the property. The residence is surrounded
with numerous abandoned vehicles, machinery, trailers, and debris piles. Driveway and access roads to
the east and south of the residence are partially covered with organic debris (wood chips), crushed
rock, and crushed concrete debris. Areas to the immediate southeast and west of the residence have
been disturbed by vehicle traffic during the wet season and tire ruts up to 8- inches were observed.
Occasional debris (e.g. lumber and car batteries) were observed in the central area of the site and a pile
of car bumpers and wood debris was observed at the northwest corner of the site.
The site is moderately forested with mature conifer and deciduous trees. Thick blackberry bushes and
undergrowth is present over most of the site with the exception of areas immediately surrounding the
residence.
Subsurface Conditions
The site was explored on March 10, 2004 by excavating 8 test pits (TP -1 through TP -8) to depths of up
to 15.0 feet below the existing ground surface (bgs) using a track mounted excavator. Geology maps of
the area (DOGAMI GMS -59, Open File Report 0 -90 -2) indicate that the site is underlain by fine- grained
soils which may be underlain by Boring Lava. Boring Lava consists of basalt that is generally weathered
and friable near the surface, becoming less weathered with increasing depth.
Surficial fill and piles of debris were observed in the area of the existing residence. The thickness of
surficial fill encountered in TP -2 was approximately 8 inches.
Soil conditions at the site generally consisted of medium stiff silt with trace organics to 2.0 feet,
becoming stiff to very stiff at depths below 2 to 5 feet, and becoming medium stiff with trace fine sand
below depths of 8 to 14.5 feet. A layer of soft silt was observed between 2.0 and 3.0 feet in TP-4 and
soft to medium stiff silt with trace fine sand was observed below 12.0 feet in TP -6. Caving was not
observed in out test pits except for TP -5 where minor caving was observed below 1.0 feet. Laboratory
testing indicates that moisture contents of the silt were between 23 and 30 percent.
Ground Water — Ground water seepage was observed in only one test pit exploration. Slow seepage
was observed between I 0 and 10.5 feet in TP -4. We anticipate that groundwater levels will vary with
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813 7 Street Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
March 12, 2004 Bissett- 04-0 1 -gi
the seasons and perched groundwater could exist near the ground surface. Moist to wet soil was
present at the ground surface at the top of the cut slope along SW Dartmouth (i.e. in the area from TP-
4 to the southwest corner of the site) and may indicate a slow seep or spring in the area.
CONCLUSIONS AND RECOMMENDATIONS
General
Based on the results of our explorations and analyses, the site can be developed as proposed following
the recommendations herein. The near surface soils at the site consist of fine- grained silt which is easily
disturbed when wet. Dry season grading is therefore recommended. If construction is planned for wet
conditions, measures should be taken to minimize disturbance.
Earthwork
Preparation - Prior to earthwork the site should be prepared by removal of existing structures,
utilities, debris, and surficial fill. Site preparation for earthwork will also require removal of vegetation
and topsoil from pavement and fill areas, and a 5 -foot perimeter around those areas. In all but the driest
summer weather, stripping using an excavator equipped with a smooth bucket is recommended.
Average combined thickness of duff and topsoil in our explorations was about I0 to 12 inches and may
be as thick as 2 feet in heavily treed areas. Root balls from trees may extend several feet, and generally
roots greater than one inch in diameter should be removed. Resulting excavations should be brought
back to grade with structural fill.
The test pit excavations were backfilled using relatively minimal compactive effort. Therefore, soft spots can
be expected at these locations. We recommend that these relatively uncompacted soils be removed from the
test pits located within the proposed building and paved areas to a depth of 3.0 feet below finished subgrade.
The resulting excavation should be brought back to grade with structural fill. If located beneath a footing, the
uncompacted soils should be completely removed and replaced with structural fill.
Stabilization and Soft Areas - After stripping, we should be contacted to evaluate the exposed
subgrade for soft areas. This evaluation can be done by proof rolling in dry conditions or probing in wet
conditions. Extensive soft areas could be created if the exposed subgrade is directly trafficked and /or
improperly stripped. Soft areas will require overexcavation and installation of a stabilization
geosynthetic. Well graded, angular crushed rock backfill compacted as structural fill should be used to
bring the aforementioned areas to- grade. For a stabilization geosynthetic we recommend a woven
geosynthetic with an AOS of #70 to # 100 sieve, and a minimum puncture resistance of 120 pounds
(such as an AMOCO 2019, or equivalent).
Alternatively, stabilization could likely be accomplished by soil amendment. This requires experienced
use of specialty spreading and mixing equipment. Typically 5 to 6 percent cement is used for
amendment with a mix depth of 12 inches. However, the materials used and quantities can vary based
on moisture contents, presence of organics, and plasticity. Grading of amended soils should be
completed within 4 hours of mixing, and the amended soil should be allowed to cure for 4 days prior to
J �t
trafficking. Mixed particle size should generally have at least 50 percent passing a No. 4 sieve.
Working Blankets and Haul Roads - Construction equipment should not directly traffic the site soils, 5 1 �w
as they are very susceptible to disturbance and softening. Rock working blankets and haul roads placed ( V\ \'‘
over a stabilization geosynthetic in a thickened advancing pad can provide this protection. For working a V\z,
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813 7' Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
March 12, 2004 Bissett-04-01 -gi
blanket and haul road rock, we recommend sound, angular, pit run or crushed basalt with no more than
6 percent passing a #200 sieve. Working blankets should be at least 12 inches thick, and haul roads at
least 18 inches thick. Alternatively, the soils could be cement amended to a depth of 12 inches and
covered with 4 inches of crushed rock. Some repair of working blankets and haul roads should be
expected.
Erosion Protection - Site soils are easily eroded by wind and water. Therefore, erosion control
measures should be planned and in place prior to construction, with native vegetation left in place
outside the grading limits. Erosion protection should be provided in accordance with City of Tigard,
Washington County and Clean Water Services Standards. Erosion can be reduced with the use of silt
fences, hay bales, buffer and zones of natural growth. Additionally, cut and fill slopes should be
protected immediately upon completion. All stormwater should be tight -lined to suitable discharges
such as approved, protected outlets and infiltration systems.
j s 4 ) 4 9 1
Slopes - For all permanent and temporary cut slopes, the slope should be excavated with a smooth QC
bucket excavator with the surface repaired if disturbed. In addition, upslope surface runoff should be „ V �
rerouted so that it does not run down the face of the slopes. Equipment should not be allowed to 7
induce vibration or infiltrate water above the slopes, and no surcharges are allowed within 20 feet of the 0 1 J'�
slope crest.
,Permanent cut slopes up to 10 feet high can be inclined at 2H:1 V in the medium stiff or better silt. The
presence of slow seepage may require drainage in the form of a 1 2-inch thick blanket of 9 -inch minus
angular pit run rock or a suitably revegetated reinforced erosion control blanket (such as North
American Green SCI 50 or equivalent). Faster seepage may require improved erosion control
measures, including additional drainage elements, and/or flatter slopes, and we should be consulted.
Exposed soils which are soft or loose may also require such measures. To reduce saturation and
seepage near the toe, we recommend a toe drain at the base of permanent cuts where seepage is
observed. It is possible that deep cuts could encounter Boring Lava (refer to Rock Excavation section
of this report).
Fill slopes should be inclined no steeper than 2H:1 V for slopes up to 10 feet high, and should be
benched into existing slopes that are steeper than 5H:1 V. The face of the fill slope should be cut back
into compacted materials with a smooth bucket excavator. If steeper fill slopes are desired, we should
be consulted to evaluate use of amended soils or grid reinforcement. Erosion control is critical to
maintaining fill slopes, and should be as described for cut slopes.
Fill — The on site soil beneath the topsoil can be used for structural fill if properly moisture conditioned.
This will not be feasible in wet conditions. Even in dry summer conditions the soil will require drying by
discing in thin lifts and frequently turning the materials. In these conditions once moisture contents are
within 3 percent of optimum, compaction should take place with a tamping foot or sheeps foot type
compactor and reach 92 percent relative to ASTM D 1557. Fill should be placed in lifts no greater than
10 inches in loose thickness. Fill will also need to pass a proof roll. Fill on slopes steeper than 5H:1 V
requires benching.
In wet conditions fill should be imported granular soil with less than 5 percent fines, such as clean sand
or rock. This material should be compacted to 95 percent relative to ASTM D 1557. Alternatively, fills
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813 7 Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
March 12, 2004 Bissett-04 -01-gi
can be amended. We should be consulted to evaluate amendment of fills, as the amendment materials,
quantities, and processes need to be adapted to actual conditions. Amending fill soils is more difficult
than amending soils in situ due to equipment access on very soft material. Typically, all wheel drive
spreading equipment with off road tires, a high powered mixer, 6 percent cement, and a mixing depth 2
inches greater than the lift thickness would be a starting point. For building fills with cement
amendment, all lifts except the final lift may be placed consecutively without significant cure time. If
intact basalt is encountered at subgrade elevations in cut areas, amendment will not be feasible.
Trenches — Utility trenches may encounter ground water seepage and possibly weathered rock (refer
to the following section). Caving is expected in the silt if seepage is encountered. Shoring of utility
trenches will be required for depths greater than 4 feet. Groundwater seepage in the silt unit can likely
be accommodated with sump pumps. Stabilization with at least 12 inches of clean, angular pit run rock
may be necessary where seepage is present and the trench is based in the silt unit. Pipe bedding should
be in accordance with the pipe manufacturers' recommendations. Trench backfill above the pipe zone
should consist of well graded, angular crushed rock with no more than 7 percent passing a #200 sieve.
Trench backfill should be compacted to 92 percent relative to ASTM D -1557, with paving not occurring
within one week of backfilling.
Rock Excavation - Although rock was not encountered in our explorations, geologic maps indicate the
area is underlain by basalt (Boring Lava). We were unable to complete explorations in the northeast
area of the site where the house is present. In areas where cuts or utility excavations are greater than
10 feet, or in the northeast corner of the property, basalt rock may be encountered. Due to the
possible presence of rock at the site, we recommend including a contingency in the project budget and
schedule for rock excavation and increased excavation and backfill volumes for trenches in those area.
Shallow Foundations
Footings should be embedded at least 18 inches below the lowest adjacent, exterior grade. Footings can
be designed for an allowable bearing pressure of 2,500 psf for medium stiff or better native silt. The
lower brown silt unit may require some overexcavation and replacement with crushed rock if exposed
at footing subgrades. The preceding bearing pressure can be increased to 5,000 psf for temporary wind
and seismic loads. Continuous footings should be no less than 18 inches wide, and pad footings should
be no less than 24 inches wide. Resistance to lateral loads can be obtained by a passive equivalent fluid
pressure of 300 pcf against suitable footings, ignoring the top 12 inches of embedment, and by a footing
base friction coefficient of 0.35. Properly founded footings are expected to settle less than a total of I
inch, with less than % inch differentially.
Slabs
Floor slab Toads of less than 250 psf are expected to induce less than one inch of settlement. A
minimum of six inches of clean, angular crushed rock with no more than 5 percent passing a #200 sieve
is recommended for underslab rock. Prior to slab rock placement the subgrade will need to be
evaluated by us by probing or will need to pass a proof roll with a fully loaded truck. Underslab rock
should be compacted to 92 percent compaction relative to ASTM D 1557, and should be proof rolled as
well. In addition, any areas contaminated with fines must be removed and replaced with clean rock. If
the base rock is saturated or trapping water, this water must be removed prior to slab placement.
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813 7 Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fox 503.722.9946
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March 12, 2004 ki (X Bissett-04-0 1 -gi
' etaining/Embedded Building Walls
G. eral - The following recommendations are based on the assumptions that (1) Wall backfill cons'.ts
of - II- drained, angular, granular material, (2) Walls are less than 10 feet in height, and (3) No
surch. ges such as stockpiled soil or equipment is placed within 10 feet of the wall.
For level b: ckfill, walls restrained against rotation should be designed using an equivalent • id pressure
of 55 pcf; thi can be reduced to 35 pcf for walls not restrained against rotation. For b.. dl slopes of
2H:1 V, walls r- trained against rotation should be designed using an equivalent fluid p -ssure of 105 pcf;
this can be reduc; d to 60 pcf for walls not restrained against rotation. For embed • ed building walls
with a daylight base - ent configuration, a superimposed seismic lateral force, equ' alent to 9.2H (where
H is the total wall heir t) should be applied at a height of 0.6H above the base the wall footing.
These forces can be res ted by passive pressure at the toe of the wall using . equivalent fluid pressure
of 350 pcf (this should exc de the top 12 inches of embedment) and fricti • along the base using a
friction coefficient of 0.35.
Backfill - Retaining walls should • - backfilled with clean, imported, : . nular soil with Tess than 6 percent
fines, such as clean sand or rock. 's material should also be co •acted to a minimum of 92 percent
relative to ASTM D -1557 (modified p actor). Within 3 feet of - wall, backfill should be compacted to
not more than 90 percent relative to AS D -1557 using han • operated equipment.
Drainage - All walls should be drained with a • rain install.: immediately behind the wall. The wall
drain should consist of a 2 -foot wide chimney o • rain r• k or clean, open - graded crushed rock
extending to within 1 -foot of the ground surface, ''th . 6 -inch diameter perforated pipe enclosed in a
1 -foot wide zone of drain rock, wrapped in a non -w• en geosynthetic and should be sloped to drain and
tight -lined to a suitable discharge such as the existi • g st• rm system.
The rock should have no more than 6 percent •assing a #2' ' sieve. The geosynthetic should have an
AOS of a #70 sieve, with a minimum permitt' ity of 1.0 sec -1 , a • a minimum puncture resistance of 80
pounds (such as an AMOCO 4551 or equi . lent).
Drainage
General - The perimeter ground su ce and hard - scaping should be slo • -d to drain away from all
structures. Gutters should be tigh ined to a suitable discharge and mainta • ed as free - flowing.
Perimeter Foundation Drains We recommend installing perimeter foundatio drains around all
exterior foundations for buil •• gs constructed in cut areas of the site. The founda •• n drains should
consist of a two -foot wide • ne of drain rock encompassing a 4 -inch diameter perfo . ed pipe, all
enclosed with a non -wov filter fabric. The drain rock should have no more than 2 pe ent passing a
#200 sieve and should , end to within one foot of the ground surface. The geosyntheti hould have
an AOS of a #70 siev a minimum permittivity of 1.0 sec- and a minimum puncture resista e of 80
pounds (such as a • MOCO 4551 or equivalent). One foot of low permeability soil (such as the on -site
silt) should be p . ced over the fabric at the top of the drain to isolate the drain from surface runoff.
Foundation d , ins should be routed to a suitable discharge.
6/8
813 7 Street Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
March 12, 2004 4 )0 2 Bissett-04-01 -gi
ai l , e
9, (1 ,), (L
Pavement
Asp . It Concrete - We have developed asphalt concrete pavement thickness at the site for 5, 10, and
25 trucks • - day and a 20 -year design life. These volumes can be revised if specific traffic is
available. Our a - ses is based on AASHTO methods and subgrade of structural fill ndisturbed
medium stiff or bette 4ative silt having a resilient modulus of 6,000 psi. We harealso assumed that
roadway construction wi = - completed during an extended period of dry weather. The results of our
analyses based on these param - - rs are provided in the following t��
/
/'
Trucks ESAL's 'AC (inches) CR (inches)
5 32542 / 3 7
I 65084 3 9
25 1 � 627J ,1� 4 8
The thicknesses listed in the to Icsabove are intended to the mini m acceptable. Crushed rock should
conform to ODOT baser standards and have less than 6 percent . - sing the #200 sieve. Asphalt \
concrete should be c patted in one lift to 91 percent of a Rice Density, • to 98 percent of the
maximum densi om a test strip.
/ \ J
Seis is esign / l '
Gen T he project site is currently located in Seismic Zone 3 with a soil profile Wpe So and should 0‘ a 7
. be designe using seismic coefficient of C. = 0.36. The relative earthquake hazard'map of the Lake `
Oswego qua ngle (DOGAMI GMS-9 I) indicates that the site is in an area of I6w overall seismic y ��
hazard. This oll rating includes low liquefaction and moderate amplification hazards. V
Liquefaction - Liquefaction occurs in loose, saturated, granular soils. Strong shaking, such as that
experienced during eart' • uakes, causes the densification and the sul sequent settlement of these soils.
Given the site topography . d soil type and consistency encountered in our explorations, the risk of
liquefaction and related settle =. ent is low.
LIMITATIONS AND OBSERV .,\ ION DURING CONSTRUCTION
We have prepared this report for use • \ Spectrum Development and members of the design and
construction teams for this project only. a informafron herein could be used for bidding or estimating
purposes but should not be construed as a .my/of subsurface conditions. We have made
observations only at the aforementioned locati.' n- . nd only at the stated depths. These observations do
not reflect soil types, strata thicknesses, water,,eVejs seepage that may exist between observations.
We should be consulted to observe all foundation bearin; surfaces, proof rolling of pavement subgrades, -
installation of structural fill, and any cut slopes. We should ; ; consulted to review final design and
specifications in order to see that our re ommendations are sui • ly followed. If any changes are made
to the anticipated locations, loads, con gurations, or construction ti • ing, our recommendations may
not be applicable, and we should be onsulted. The preceding recomm - dations should be considered
preliminary, as actual soil conditi s may vary. In order for our recomme .ations to be final, we must
be retained to observe actual s surface conditions encountered. Our obse tions will allow us to
interpret actual conditions d adapt our recommendations if needed.
7/8
813 7"' Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
March 12, 2004 Bissett-04-0 1-gi
Within the limitations of scope, schedule and budget, our services have been executed in accordance
with the generally accepted practices in this area at the time this report was prepared. No warranty,
express or implied, is given.
< >
We appreciate the opportunity to work with you on this project and look forward to our continued
involvement. If you have any questions, please do not hesitate to call.
Sincerely,
FA PRof
I*/ Al
Christopher Palmer, MS, PE
Project Engineer ✓ �
` lOs n 15 A �
AHER 3.
1 EXPIRES: 12/31 /oy 1
•
Don Rondema, MS, PE
Principal
Attachments - Site Plan, Test Pit Logs, Moisture Contents
8/8
813 7"' Street, Suite 202, Oregon City, OR 97045 ph 503.657.3487 fax 503.722.9946
SW 70th AVE.
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• I 1 inch = 50 feet
BASE DRAWING PROVIDED BY WESTLAKE CONSULTANTS, INC.
G t c SITE PLAN
out uons 1 ncl bissett- 04 -0 I_ i
S
Test Pit # Depth (ft) Soil Description
Explorations completed on March 10, 2004 with a JCB 220L (48,000 pound) trackhoe.
TP -1 Location: Southeast corner of site.
Surface conditions: Thick blackberries and undergrowth.
0.0 — 15.0 Medium stiff, brown, SILT with trace organics (8- to 10 -inch thick root zone); moist.
- becomes stiff without organics at 2.0 feet.
- becomes stiff to very stiff at 5.0 feet.
- grades to with trace fine sand at 9.0 feet.
- becomes medium stiff, orange - mottled, with some fine sand at 14.5 feet.
No groundwater seepage observed.
No caving observed.
TP -2 Location: Central- eastern border of site.
Surface conditions: Wood chips and crushed concrete debris.
0.0 — 0.75 Soft to medium stiff, dark brown, SILT FILL with wood chips and crushed concrete
debris; moist.
0.75 — 14.5 Medium stiff, brown, SILT with trace organics; moist.
• - becomes stiff without organics at 2.0 feet.
• No groundwater seepage observed.
No caving observed.
TP -3 Location: North - central area of site.
Surface conditions: Blackberry vines and ivy.
0.0 — 12.0 Medium stiff, brown, SILT with trace organics (6- to 8 -inch thick root zone); moist.
- becomes stiff without organics at 2.0 feet.
- becomes medium stiff at 10.0 feet.
No groundwater seepage observed.
No caving observed.
GentpCn TEST PIT LOGS
utions I nCl bissett- 04 -0I -gi
•
Test Pit # Depth (ft) Soil Description
TP -4 Location: South - central area of site.
Surface conditions: Thick blackberries.
0.0 — 15.0 Medium stiff, dark brown, SILT with trace organics (8- to I0 -inch thick root zone);
moist.
- becomes soft at 2.0 feet.
- grades to without organics at 2.5 feet.
- becomes medium stiff, orange - mottled brown at 3.0 feet.
- becomes stiff to very stiff at 4.0 feet.
- becomes soft to medium stiff, brown -gray, with trace fine sand at 14.0 feet.
Slow groundwater seepage observed between 10.0 and 10.5 feet.
No caving observed.
TP -5 Location: Central area of site.
Surface conditions: Thick blackberries.
0.0 — 12.0 Medium stiff, orange- brown, SILT with trace organics (8- to I0 -inch thick heavy
root zone); moist.
- becomes stiff without organics at 3.0 feet.
- becomes medium stiff with trace fine sand at 8.0 feet.
No groundwater seepage observed.
Minor to moderate caving observed below 1.0 feet.
TP -6 Location: Southwest corner of site.
Surface conditions: Blackberries and underbrush.
0.0 — 12.5 Medium stiff, brown, SILT with trace organics (1 6-inch thick root zone); moist.
- grades to without organics at 2.0 feet.
- becomes stiff at 4.0 feet.
- grades to with trace fine sand at 9.0 feet.
- grades to with some fine sand at 1 1.0 feet.
- becomes soft to medium stiff, medium plasticity at 12.0 feet.
No groundwater seepage observed.
No caving observed.
p � TEST PIT LOGS
G S O h i l i o n s I n c l bissett- 04 -0I -gi
Test Pit # Depth (ft) Soil Description
TP -7 Location: Western - central area of site.
Surface conditions: Thick blackberries.
0.0 — 12.0 Medium stiff, brown, SILT with trace organics (8- to 10 -inch thick root zone); moist.
- grades to without organics at 2.0 feet.
- becomes stiff at 3.0 feet.
- becomes medium stiff with trace fine sand at 8.0 feet.
No groundwater seepage observed.
No caving observed.
TP -8 Location: Northwest corner of site.
Surface conditions: Thick blackberries.
0.0 — 12.0 Medium stiff, brown, SILT with trace organics (8- to 10 -inch thick root zone); moist.
- grades to without organics at 2.0 feet.
- becomes stiff at 3.0 feet.
- becomes medium stiff with trace fine sand at 11.5 feet.
No groundwater seepage observed.
No caving observed.
G Q n t c tj TEST PIT LOGS
solutions n c l bissett- 04 -0I -gi
Test Pit Depth, ft Moisture Content
TP-1 1.0 25%
.. ------ - • 3.0 _
34% ...
TP-1 9.0 30%
TP-1 14.5 32%
TP4----- _
___..
23°i0
.___... 2.0
TP-2 — 9.0 30%
. -- • TP-3 14.0 28%
• ..__. ........._
2.0 24%
TP-3 4.0 30%
TP-3 10.0 31%
TP-4 -- _ 2.5 ......_ .._.. _
TP-4 5.0 36%
.._
1
TP-4 10.0 -----------------
31%
..._
TP-4------- --- 14.5 33%
........
TP-5 2.0 24%
.__
TP-5 5.0 34%
• ..._
TP-5 11.0
TP-6 ..._
9.0 _ _ 31%
32%
....___. __.. ..... ..__
TP-6 12.0 6 /0 --
.... _ 33
...___ .._ _....
3
TP-7 2.0 30%
___.. ..__
TP-7 11.0 31%
...__.
TP-8 6.0 32%
TP-8 • 10.0 32%
. -
G MOISTURE CONTENTS
G en t� Incl bissett-04-01-gi
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