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. HAFDMAN
wit-tizo`ko GEOTECHNICAL
SERVICpS INC.
4 -Efli Gsote6iricaf Solutions
March 25,2016
HGSI Project No. 16-1992
rrr rr r c c < < r
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Dan Grimberg/Miriam Wilson
West Hills Development r r. ` r r r r
735 SW 158th Street
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Beaverton,Oregon 97006 � �C C
0 NOV 1 i 2016
Copy: Mike Peebles, Otak,Inc.
ARpVia e-mail with hard copies mailed on request 1j >1 oly, �
Subject: GEOTECHNICAL ENGINEERING REPORT
RIVER TERRACE EAST-MULTIFAMILY SITE
TIGARD,OREGON
This report presents the results of a geotechnical engineering study conducted by Hardman Geotechnical
Services Inc. (HGSI)for the above-referenced project. The purpose of this study was to evaluate subsurface
conditions at the site and to provide geotechnical recommendations for site development.
SITE DESCRIPTION AND PROPOSED DEVELOPMENT
The site consists of a 2.5 acre irregularly shaped property located southeast of the intersection of SW Scholls
Ferry Road and SW Roy Rogers Road in Sherwood, Oregon(see Vicinity Map,Figure 1). This multifamily
site is in the southwest portion of the overall River Terrace East neighborhood. A single family home with
barn currently occupies the site. The site is gently sloping to the south and is covered by a pasture and a few
trees.
A preliminary layout plan for the multifamily site indicates nine separate buildings will be constructed,with
appurtenant underground utilities,driveways and parking. Site access will be from River Terrace East
interior streets, from the east. Planned grading includes cuts and fills up to about 6 feet deep.
REGIONAL GEOLOGY AND SEISMIC SETTING
The subject site lies within the Portland Basin, a broad structural depression situated between the Coast Range
on the west and the Cascade Range on the east. The Portland Basin is a northwest-southwest trending
structural basin produced by broad regional downwarping of the area. The Portland Basin is approximately 20
miles wide and 45 miles long and is filled with consolidated and unconsolidated sedimentary rocks of late
Miocene,Pliocene and Pleistocene age.
Gannet and Caldwell(1998)map the site area as being underlain by Pleistocene-age Alluvium and Glacial-
Outburst Flood Sediments and Holocene Alluvial Deposits. These materials are described as"silt, sand and
gravel deposited primarily by late Pleistocene glacial-outburst floods,but also including glaciofluvial
sediments from the Cascade Range"and"sand,gravel,and silt deposits along channels and flood plains of the
present day drainage system",respectively. The catastrophic flood deposits are associated with repeated
glacial outburst flooding of the Willamette Valley, the last of which occurred about 10,000 years ago(Madin,
1990). The lower,eastern portion of the site is mapped as Continental Sedimentary Rocks. This geologic unit
10110 SW Nimbus Avenue,Suite B-5 Tel(503)530-8076
Portland,Oregon 97223 Cell(503)575-5634
}
March 25,2016 0 ,.
HGSI Proje t No.16-1992'
is the main basin fi11in,unit of the Willairctte Lowland and consists of sand, gravel,sandstone,conglomerate
siltstone,once mudstone derived primari'y from the Cascade Range and Columbia River drainage (Gannett and
Caldwell, 1998).
At least three.ngLjor seismic source zoncc capable of generating damaging earthquakes are known to exist in
the region. TneFe irclude the Fort and Hills Fault Zone,Gales Creek-Newberg-Mt. Angel Structural Zone, and
the Cascadia Subduction Zone. These potential earthquake source zones are included in the determination of
seismic design values for structures,as presented in the Seismic Design section.
FIELD EXPLORATION
The site-specific exploration for this study was conducted on March 14, 2016 and consisted of seven test pits
(designated TP-1 through TP-7)excavated to depths of approximately 10 feet below ground surface(bgs)at
the approximate locations shown on the attached Site Plan,Figure 2. It should be noted that exploration
locations were determined in the field by pacing or taping distances from apparent property corners and other
site features shown on the plans provided. As such,the locations of the explorations should be considered
approximate.
Explorations were conducted under the full-time observation of HGSI personnel. Soil samples obtained from
the borings were classified in the field and representative portions were placed in relatively air-tight plastic
bags. These soil samples were then returned to the laboratory for further examination. Pertinent information
including soil sample depths,stratigraphy, soil engineering characteristics,and groundwater occurrence was
recorded. Soils were classified in general accordance with the Unified Soil Classification System.
Summary test pit logs are attached to this report. The stratigraphic contacts shown on the individual
borehole logs represent the approximate boundaries between soil types. The actual transitions may be more
gradual. The soil and groundwater conditions depicted are only for the specific dates and locations reported,
and therefore,are not necessarily representative of other locations and times.
SUBSURFACE CONDITIONS
The following discussion is a summary of subsurface conditions encountered in our explorations. For more
detailed information regarding subsurface conditions at specific exploration locations,refer to the attached
test pit logs. Also,please note that subsurface conditions can vary between exploration locations,as
discussed in the Uncertainty and Limitations section below.
Soil
On-site soils are anticipated to consist of clayey silt belonging to the Willamette Formation as described
below.
Clayey Silt—Underlying approximately 10 inches of topsoil,all test pits encountered clayey silt.
These soils were typically medium stiff to hard stiff and were brown to light brown with gray and
orange mottling. The test pits terminated in this soil unit at roughly 10 feet.This silt unit was
interpreted as belonging to the Willamette Formation.
Groundwater
At the time of our explorations,groundwater was not encountered beneath the site. Minor to moderate
seepage was encountered at depths ranging from about 3 to 6 feet in TP-2 through TP-6. This is perched
groundwater resulting from the unusually wet winter months prior to our field exploration. Regional
16-1992 River Terrace East Multifamily-GR 2 HARDMAN GEOTECHNICAL SERVICES INC.
March 25, 2016 •
HGSI Project No. 16-1992
geologic mapping(Snyder,2008)indicates that static groundwaterrisrp ;sent at i death of about<1CO feet
below the existing ground surface at the site. In our experience, it:s notpcomr or to encounter thin
perched groundwater zones within the Willamette Formation in this'area,particularlyduring the wet season.
The groundwater conditions reported above are for the specific date and 13,datioils indic tzrl,girl therefore
may not necessarily be indicative of other times and/or locations. Fuahert tori,it iF.intk,ipat2c1 that
groundwater conditions will vary depending on the season, local subsh fac corxiitions, ,hon s in land use
and other factors.
CONCLUSIONS AND RECOMMENDATIONS
Results of this study indicate that the proposed development is geotechnically feasible,provided that the
recommendations of this report are incorporated into the design and construction phases of the project.
Recommendations are presented below regarding site preparation,engineered fill, wet weather earthwork,
spread footing foundations,below grade structural retaining walls, concrete slabs-on-grade,perimeter footing
drains, seismic design,excavating conditions and utility trench backfill,and erosion control considerations.
Site Preparation
The areas of the site to be graded should first be cleared of vegetation and any loose debris;and debris from
clearing should be removed from the site. Organic-rich topsoil should then be removed to competent native
soils. We anticipate that the average depth of topsoil stripping will be 6 to 12 inches over most of the site.
The final depth of stripping removal may vary depending on local subsurface conditions and the contractor's
methods, and should be determined on the basis of site observations after the initial stripping has been
performed. Stripped organic soil should be stockpiled only in designated areas or removed from the site and
stripping operations should be observed and documented by HGSI. Existing subsurface structures(tile
drains,old utility lines,septic leach fields, etc.)beneath areas of proposed structures and pavement should be
removed and the excavations backfilled with engineered fill.
There is potential for old fills to be present on site in areas beyond our explorations. Where encountered
beneath proposed structures,pavements,or other settlement-sensitive improvements,undocumented fill
should be removed down to firm inorganic native soils and the removal area backfilled with engineered fill
(see below). HGSI should observe removal excavations(if any)prior to fill placement to verify that
overexcavations are adequate and an appropriate bearing stratum is exposed.
In construction areas,once stripping has been verified,the area should be ripped or tilled to a depth of 12
inches,moisture conditioned,and compacted in-place prior to the placement of engineered fill. Exposed
subgrade soils should be evaluated by HGSI. For large areas,this evaluation is normally performed by
proof-rolling the exposed subgrade with a fully loaded scraper or dump truck. For smaller areas where
access is restricted,the subgrade should be evaluated by probing the soil with a steel probe. Soft/loose soils
identified during subgrade preparation should be compacted to a firm and unyielding condition or over-
excavated and replaced with engineered fill,as described below. The depth of overexcavation, if required,
should be evaluated by HGSI at the time of construction.
If present, existing drywells should be removed or demolished in place. Portions of a drywell deeper than 8
feet should be backfilled with controlled density fill(CDF),which is essentially a lean mix concrete
consisting of water, sand and cement. We recommend use of"excavatable"CDF so that future excavations
can be made through the dry well backfill if any new utilities or other excavations are needed in the affected
areas. Above a depth of 8 feet,at the contractor's option,backfill may consist of granular material such as
"reject rock,"recycled concrete or similar material approved by HGSI. The granular backfill should be
placed in lifts no thicker than about 18 inches and compacted with a"hoe-pac"excavator attachment to a
16-1992 River Terrace East Multifamily-GR 3 HARDMAN GEOTECHNICAL SERVICES INC.
March 2'.1,2016
HGSI Project No. 16-1992
minimum;ef 90 percent raf Modified Proctor(ASTM D-1557). This backfill specification should also be
used for alp/basemen:s or other depressions that require fill during the demolition process.
Engineered Fill
In general,wz gnt:mate thatcn-s,te soils will be suitable for use as engineered fill in dry weather conditions,
provided they e ce;at,ve y free o`organics and are properly moisture conditioned for compaction. Imported
fill material must be approved by the geotechnical engineer prior to being imported to the site. Oversize
material greater than 6 inches in size should not be used within 3 feet of foundation footings,and material
greater than 12 inches in diameter should not be used in engineered fill.
Engineered fill should be compacted in horizontal lifts not exceeding 8 inches using standard compaction
equipment. We recommend that engineered fill be compacted to at least 90 percent of the maximum dry
density determined by ASTM D1557 (Modified Proctor)or equivalent. On-site soils may be wet or dry of
optimum;therefore,we anticipate that moisture conditioning of native soil will be necessary for compaction
operations.
Proper test frequency and earthwork documentation usually requires daily observation and testing during
stripping,rough grading,and placement of engineered fill. Field density testing should conform to ASTM
D2922 and D3017,or D1556. Engineered fill should be periodically observed and tested by the project
geotechnical engineer or his representative. Typically,one density test is performed for at least every 2
vertical feet of fill placed or every 500 yd3,whichever requires more testing.
Wet Weather Earthwork
The on-site soils are moisture sensitive and may be difficult to handle or traverse with construction
equipment during periods of wet weather. Earthwork is typically most economical when performed under
dry weather conditions. Earthwork performed during the wet-weather season will probably require
expensive measures such as cement treatment or imported granular material to compact fill to the
recommended engineering specifications. If earthwork is to be performed or fill is to be placed in wet
weather or under wet conditions when soil moisture content is difficult to control,the following
recommendations should be incorporated into the contract specifications.
• Earthwork should be performed in small areas to minimize exposure to wet weather. Excavation or
the removal of unsuitable soils should be followed promptly by the placement and compaction of
clean engineered fill. The size and type of construction equipment used may have to be limited to
prevent soil disturbance. Under some circumstances, it may be necessary to excavate soils with a
backhoe to minimize subgrade disturbance caused by equipment traffic;
• The ground surface within the construction area should be graded to promote run-off of surface
water and to prevent the ponding of water;
• Material used as engineered fill should consist of clean,granular soil containing less than about 7
percent fines. The fines should be non-plastic. Alternatively,cement treatment of on-site soils may
be performed to facilitate wet weather placement;
• The ground surface within the construction area should be sealed by a smooth drum vibratory roller,
or equivalent,and under no circumstances should be left uncompacted and exposed to moisture.
Soils which become too wet for compaction should be removed and replaced with clean granular
materials;
• Excavation and placement of fill should be observed by the geotechnical engineer to verify that all
unsuitable materials are removed and suitable compaction and site drainage is achieved; and
16-1992 River Terrace East Multifamily-GR 4 HARDMAN GEOTECHNICAL SERVICES INC.
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HGSI Project No. 16-1992
• Bales of straw and/or geotextile silt fences should be strat¢gi a ly lopat(d t¢ c-ntrdi(erosion.
If cement or lime treatment is used to facilitate wet weather construction; iGS'should be contacted to
provide additional recommendations and field monitoring
Spread Footing Foundations
Shallow, conventional isolated or continuous spread footings maybe sed to support ih6
p".'opused structures,
provided they are founded on competent native soils,or compacted engineered fill placed directly upon the
competent native soils. We recommend a maximum allowable bearing pressure of 2,500 pounds per square
foot(psf)for designing spread footings bearing on undisturbed native soils or engineered fill. The
recommended maximum allowable bearing pressure may be increased by a factor of 1.33 for short term
transient conditions such as wind and seismic loading. All footings should be founded at least 18 inches
below the lowest adjacent finished grade. Minimum footing widths should be determined by the project
engineer/architect in accordance with applicable design codes.
Assuming construction is accomplished as recommended herein,and for the foundation loads anticipated,we
estimate total settlement of spread foundations of less than about 1 inch and differential settlement between
two adjacent load-bearing components supported on competent soil of less than about 1/2 inch. We anticipate
that the majority of the estimated settlement will occur during construction, as loads are applied.
Wind,earthquakes,and unbalanced earth loads will subject the proposed structure to lateral forces. Lateral
forces on a structure will be resisted by a combination of sliding resistance of its base or footing on the
underlying soil and passive earth pressure against the buried portions of the structure. For use in design, a
coefficient of friction of 0.5 may be assumed along the interface between the base of the footing and
subgrade soils. Passive earth pressure for buried portions of structures may be calculated using an equivalent
fluid weight of 390 pounds per cubic foot(pcf),assuming footings are cast against dense,natural soils or
engineered fill. The recommended coefficient of friction and passive earth pressure values do not include a
safety factor. The upper 12 inches of soil should be neglected in passive pressure computations unless it is
protected by pavement or slabs on grade.
Footing excavations should be trimmed neat and the bottom of the excavation should be carefully prepared.
Loose,wet or otherwise softened soil should be removed from the footing excavation prior to placing
reinforcing steel bars. HGSI should observe foundation excavations prior to placing crushed rock,to verify
that adequate bearing soils have been reached. Due to the high moisture sensitivity of on-site soils,
construction during wet weather may require overexcavation of footings and backfill with compacted,
crushed aggregate.
Below-Grade Structural Retaining Walls
Lateral earth pressures against below-grade retaining walls will depend upon the inclination of any adjacent
slopes,type of backfill, degree of wall restraint,method of backfill placement,degree of backfill compaction,
drainage provisions,and magnitude and location of any adjacent surcharge loads. At-rest soil pressure is
exerted on a retaining wall when it is restrained against rotation. In contrast,active soil pressure will be
exerted on a wall if its top is allowed to rotate or yield a distance of roughly 0.001 times its height or greater.
If the subject retaining walls will be free to rotate at the top,they should be designed for an active earth
pressure equivalent to that generated by a fluid weighing 35 pcf for level backfill against the wall. For
restrained walls,an at-reset equivalent fluid pressure of 54 pcf should be used in design,again assuming
level backfill against the wall. These values assume that the recommended drainage provisions are
incorporated,and hydrostatic pressures are not allowed to develop against the wall.
During a seismic event,lateral earth pressures acting on below-grade structural walls will increase by an
incremental amount that corresponds to the earthquake loading. Based on the Mononobe-Okabe equation
16-1992 River Terrace East Multifamily-GR 5 HARDMAN GEOTECHNICAL SERVICES INC.
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HGSI Project No. 16-1992
and peak horizontal acceleratiors apprcrpr.iate for the site location, seismic loading should be modeled using
the active of at-)est eaifh pressures>eccmmended above,plus an incremental rectangular-shaped seismic
load of magnitude 5H,where H is the total height of the wall.
For design of retaini,ig wall footings,the allowable bearing pressure and friction coefficient values listed
above in Structt'r'l ro,in'Ia,ions bre applicable.
We assume relatively level ground surface below the base of the walls. As such,we recommend passive
earth pressure of 390 pcf for use in design,assuming wall footings are cast against competent native soils or
engineered fill. If the ground surface slopes down and away from the base of any of the walls,a lower
passive earth pressure should be used and HGSI should be contacted for additional recommendations.
The above recommendations for lateral earth pressures assume that the backfill behind the subsurface walls
will consist of properly compacted structural fill,and no adjacent surcharge loading. If the walls will be
subjected to the influence of surcharge loading within a horizontal distance equal to or less than the height of
the wall,the walls should be designed for the additional horizontal pressure. For uniform surcharge
pressures,a uniformly distributed lateral pressure of 0.3 times the surcharge pressure should be added.
The recommended equivalent fluid densities assume a free-draining condition behind the walls so that
hydrostatic pressures do not build up. This can be accomplished by placing a 12-inch wide zone of crushed
drain rock containing less than 5 percent fines against the walls. A 3-inch minimum diameter perforated,
plastic drain pipe should be installed at the base of the walls and connected to a sump to remove water from
the crushed drain rock zone. The drain pipe should be wrapped in filter fabric(Mirafi 140N or other as
approved by the geotechnical engineer)to minimize clogging. The above drainage measures are intended to
remove water from behind the wall to prevent hydrostatic pressures from building up. Additional drainage
measures may be specified by the project architect or structural engineer,for damp-proofing or other reasons.
HGSI should be contacted during construction to verify subgrade strength in wall keyway excavations,to
verify that backslope soils are in accordance with our assumptions,and to take density tests on the wall
backfill materials.
Concrete Slabs-on-Grade
Preparation of areas beneath concrete slab-on-grade floors should be performed as recommended in the Site
Preparation section. Care should be taken during excavation for foundations and floor slabs,to avoid
disturbing subgrade soils. If subgrade soils have been adversely impacted by wet weather or otherwise
disturbed,the surficial soils should be scarified to a minimum depth of 8 inches,moisture conditioned to
within about 3 percent of optimum moisture content,and compacted to engineered fill specifications.
Alternatively,disturbed soils may be removed and the removal zone backfilled with additional crushed rock.
For evaluation of the concrete slab-on-grade floors using the beam on elastic foundation method,a modulus
of subgrade reaction of 200 kcf(115 pci)should be assumed for the soils anticipated at subgrade depth. This
value assumes the concrete slab system is designed and constructed as recommended herein,with a
minimum thickness of crushed rock of 8 inches beneath the slab.
Interior slab-on-grade floors should be provided with an adequate moisture break. The capillary break
material should consist of ODOT open graded aggregate per ODOT Standard Specifications 02630-2. The
minimum recommended thickness of capillary break materials on re-compacted soil subgrade is 8 inches.
The total thickness of crushed aggregate will be dependent on the subgrade conditions at the time of
construction,and should be verified visually by proof-rolling. Under-slab aggregate should be compacted to
at least 90%of its maximum dry density as determined by ASTM D1557 or equivalent.
16-1992 River Tenace East Multifamily-OR 6 HARDMAN GEOTECHNICAL SERVICES INC.
March 25,2016
HGSI Project No. 16-1992
In areas where moisture will be detrimental to floor coverings or equrprsent ins Je t e,pi opo.ed structure,
appropriate vapor barrier and damp-proofing measures should be itnpleix ented.;-A eoxnmonly,applied vapor
barrier system consists of a 10-mil polyethylene vapor barrier placed directly over the capillary break
material. With this type of system,an approximately 2-inch thick layer of sand is often placed over the vapor
barrier to protect it from damage,to aid in curing of the concrete,an4;als'o to help prevent,;,ement from
bleeding down into the underlying capillary break materials. Other damp/vaporba_ris,r-,gste n$may also be
feasible. Appropriate design professionals should be consulted regarding vapor bairitr and damp proofing
systems,ventilation,building material selection and mold prevention issues,which are outside HGSI's area
of expertise.
Perimeter Footing Drains
Due to the potential for perched surface water above fine grained deposits such as those encountered at the
site,we recommend the outside edge of perimeter footings be provided with a drainage system consisting of
4-inch minimum diameter perforated PVC pipe embedded in a minimum of 1 ft3 per lineal foot of clean,
free-draining sand and gravel or 1"- 'A"drain rock. The drain pipe and surrounding drain rock should be
wrapped in non-woven geotextile(Mirafi 140N, or approved equivalent)to minimize the potential for
clogging and/or ground loss due to piping. Water collected from the footing drains should be directed into
the local storm drain system or other suitable outlet. A minimum 0.5 percent fall should be maintained
throughout the drain and non-perforated pipe outlet. The footing drains should include clean-outs to allow
periodic maintenance and inspection.
Down spouts and roof drains should collect roof water in a system separate from the footing drains in order
to reduce the potential for clogging. Roof drain water should be directed to an appropriate discharge point
well away from structural foundations. Grades should be sloped downward and away from buildings to
reduce the potential for ponded water near structures.
Seismic Design
Structures should be designed to resist earthquake loading in accordance with the methodology described in
the 2009 International Residential Code(IRC)for One-and Two-Family Dwellings,with applicable Oregon
Structural Specialty Code(OSSC)revisions. We recommend Site Class D be used for design per the OSSC,
Table 1613.5.2. Design values determined for the site using the USGS(United States Geological Survey)
Seismic Design Tool utility are summarized below in Table 1.
Table 1. Recommended Earthquake Ground Motion Parameters (2009 IRC)
Parameter Value
Location(Lat,Long),degrees 45.424,-122.853
Mapped Spectral Acceleration Values
(MCE, Site Class B):
Short Period, SS 0.955 g
1.0 Sec Period, Si 0.425 g
Soil Factors for Site Class D:
Fa 1.118
Fv 1.575
SD,=2/3xFax SS 0.712g
SDI=2/3xF„xSi 0.446 g
16-1992 River Terrace East Multifamily-GR 7 HARDMAN GEOTECHNICAL SERVICES INC.
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HGSI Project No. 16-1992
Potential seismic urpa�te also inch e secondary effects such as soil liquefaction,fault rupture potential,and
other hazards as discussed below:
• Soil Liquefaction Potential—Soil liquefaction is a phenomenon wherein saturated soil deposits
temporggly;o$E strength,andbehave as a liquid in response to earthquake shaking. Soil
liquefaction-is,geilerally bmite1 to loose, granular soils located below the water table. On-site
soils consist of generally of vex.),stiff to hard clayey silt,underlain by basalt bedrock.
Permanent ground water table lies about 100 feet below ground surface,and,therefore,soils
under the project site are not considered susceptible to liquefaction. It is our opinion that special
design or construction measures are not required to mitigate the effects of liquefaction.
• Fault Rupture Potential—Based on our review of available geologic literature,we are not
aware of any mapped active(demonstrating movement in the last 10,000 years)faults on the site.
During our field investigation,we did not observe any evidence of surface rupture or recent
faulting. Therefore,we conclude that the potential for fault rupture on site is low.
• Seismic Induced Landslide—We anticipate that engineered retaining walls will be used to
support the existing cut slope along the northeast property line. Such retaining walls should be
designed using the seismic ground motion parameters tabulated above. With the engineered
wall(s)in place,the potential for slope instability and seismic induced landslide on site is
considered low to very low.
• Effects of Local Geology and Topography—In our opinion,no additional seismic hazard will
occur due to local geology or topography. The site is expected to have no greater seismic hazard
than surrounding properties and the Tigard area in general.
Excavating Conditions and Utility Trench Backfill
We anticipate that on-site soils can be excavated using conventional heavy equipment such as trackhoes.
Weathered bedrock was not encountered to the maximum depth of our test pit explorations, 10 feet bgs.
Maintenance of safe working conditions,including temporary excavation stability,is the responsibility of the
contractor. Actual slope inclinations at the time of construction should be determined based on safety
requirements and actual soil and groundwater conditions. All temporary cuts in excess of 4 feet in height
should be sloped in accordance with U.S. Occupational Safety and Health Administration(OSHA)
regulations(29 CFR Part 1926),or be shored. The existing native soils classify as Type B Soil and
temporary excavation side slope inclinations as steep as 1H:1 V may be assumed for planning purposes. This
cut slope inclination is applicable to excavations above the water table only. Flatter temporary excavation
slopes will be needed if groundwater is present,or if significant thicknesses of sandy soils are present in
excavation sidewalls.
Perched groundwater conditions often occur over fine-grained native deposits such as those beneath the site,
particularly during the wet season. If encountered,the contractor should be prepared to implement an
appropriate dewatering system for installation of the utilities. At this time,we anticipate that dewatering
systems consisting of ditches, sumps and pumps would be adequate for control of groundwater where
encountered during construction conducted during the dry season. Regardless of the dewatering system
used,it should be installed and operated such that in-place soils are prevented from being removed along
with the groundwater.
Vibrations created by traffic and construction equipment may cause some caving and raveling of excavation
walls. In such an event,lateral support for the excavation walls should be provided by the contractor to
prevent loss of ground support and possible distress to existing or previously constructed structural
improvements.
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' March 25, 2016
HGSI Project No. 16-1992
Utility trench backfill should consist of 3/4"-0 crushed rock, compacted to at leas.90% of the maximum dry
density obtained by Modified Proctor(ASTM D 1557)or equivalent. Initial backfill lift thicknesses for a
3/4"-0 crushed aggregate base may need to be as great as 4 feet to reduce the risk of flattening underlying
flexible pipe. Subsequent lift thickness should not exceed 1 foot. I:`imported ganular fill material is used,
then the lifts for large vibrating plate-compaction equipment(e.g. hoe compactor a tach r e nt ) 'nay be up to
2 feet,provided that proper compaction is being achieved and each lift is tasted. the of large vibrating
compaction equipment should be carefully monitored near existing structures and improvements due to the
potential for vibration-induced damage.
Adequate density testing should be performed during construction to verify that the recommended relative
compaction is achieved. Typically,one density test is taken for every 4 vertical feet of backfill on each 200-
lineal-foot section of trench.
Erosion Control Considerations
Fine grained soils on steep slopes are susceptible to erosion. Erosion during construction can be minimized
by implementing the project erosion control plan,which should include judicious use of bio-bags, silt fences,
or other appropriate technology. Where used, erosion control devices should be in place and remain in place
throughout site preparation and construction.
Erosion and sedimentation of exposed soils can also be minimized by quickly re-vegetating exposed areas of
soil, and by staging construction such that large areas of the project site are not denuded and exposed at the
same time. Areas of exposed soil requiring immediate and/or temporary protection against exposure should
be covered with either mulch or erosion control netting/blankets. Areas of exposed soil requiring permanent
stabilization should be seeded with an approved grass seed mixture, or hydroseeded with an approved seed-
mulch-fertilizer mixture.
UNCERTAINTIES AND LIMITATIONS
We have prepared this report for the owner and his/her consultants for use in design of this project only.
This report should be provided in its entirety to prospective contractors for bidding and estimating purposes;
however,the conclusions and interpretations presented in this report should not be construed as a warranty of
the subsurface conditions. Experience has shown that soil and groundwater conditions can vary significantly
over small distances. Inconsistent conditions can occur between explorations that may not be detected by a
geotechnical study. If,during future site operations, subsurface conditions are encountered which vary
appreciably from those described herein,HGSI should be notified for review of the recommendations of this
report,and revision of such if necessary.
Sufficient geotechnical monitoring, testing and consultation should be provided during construction to
confirm that the conditions encountered are consistent with those indicated by explorations.
Recommendations for design changes will be provided should conditions revealed during construction differ
from those anticipated,and to verify that the geotechnical aspects of construction comply with the contract
plans and specifications.
Within the limitations of scope, schedule and budget,HGSI executed these services in accordance with
generally accepted professional principles and practices in the field of geotechnical engineering at the time
the report was prepared. No warranty, expressed or implied, is made. The scope of our work did not include
environmental assessments or evaluations regarding the presence or absence of wetlands or hazardous or
toxic substances in the soil,surface water,or groundwater at this site.
16-1992 River Terrace East Multifamily-GR 9 HARDMAN GEOTECHNICAL SERVICES INC.
March 25,2016
HGSI Project No. 16-1992
0.0
We appreciate this opportunity to be of service.
Sincerely, °" i°,9. -°°
HARDMAN GEOTECHNICAL SERVICES INC.
L ,
- 64,,2 'C
•
44;4/BER S �P 3 2..c-I
�'L. HP
EXPIRES: 06-30-20\1
Scott L. Hardman,P.E.,G.E.
Principal Geotechnical Engineer
Attachments: References
Figure 1 —Vicinity Map
Figure 2—Site Plan
Logs of Test Pits TP-1 through TP-7
REFERENCES
Gannett,M.W. and Caldwell,R.R., 1998,Geologic framework of the Willamette Lowland aquifer system,
Oregon and Washington:U.S.Geological Survey Professional Paper 1424-A,32 pages text, 8 plates.
Madin,LP., 1990, Earthquake hazard geology maps of the Portland metropolitan area,Oregon: Oregon
Department of Geology and Mineral Industries Open-File Report 0-90-2,scale 1:24,000,22 p.
Snyder,D.T.,2008,Estimated Depth to Ground Water and Configuration of the Water Table in the Portland,
Oregon Area:U.S.Geological Survey Scientific Investigations Report 2008-5059,41 p., 3 plates.
16-1992 River Terrace East Multifamily-CR 10 HARDMAN GEOTECHNICAL SERVICES INC.
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Legend Approx. Scale: 1 inch =2000 feet
Base Map: USGS Beaverton Quadrangle Map, from US Topo, 2014
Project: River Terrace East
Tigard, Oregon Project No. 16-1992 I FIGURE 1
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Practical,Cost Effettive Gw:otech1 L al SoI tions
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Legend Base map provided by:
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TP-7 Test Pit Designation and
'�..� Approximate Location
Project: River Terrace East Project No. 16-1992 FIGURE 2
Tigard,Oregon
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LOG OF BACKHOE / EXCAVATORS }TEST PIT
Project: River Terrace East C • ��
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Tigard, Oregon Project No. 16-7.992 ,THst Ply Nr). , TP-1
Qt ly Qt (a = 2 Ov
E eL -a 03M
Q� Eat E _ � = v r -
a o _ o o Material Des ri,Qt�nn
0
d 0 C7
Medium stiff, Silt, dark brown, moist, many fine roots (top soil)
1 — 1.00 Medium stiff to very stiff, Clayey Silt, brown, moist
2— 2.75
3— >4
Hard, Clayey Silt, light brown with orange and gray mottling, slightly moist
4— >4
5-
6-
7-
8-
9-
10
Test pit terminated at 10 feet
No groundwater or seepage encountered
11-
12-
13-
14-
15-
16-
17—
IICS1CFIICAL. LEGEND
SERVICES INC. Date Excavated: 3-14-16
cost-Wk..al)Gec ttech'dcal saANa n Z
S-1
10110 SW Nimbus Avenue,Suite 8-5 Logged By: IDM
Portland,OR 97223 Soil Sample Depth Water Level at
(503)530-8076 Interval and Designation Time of Excavation
LOG Or BACKHOE / EXCAVATOR TEST PIT
Project: Ri?rer,Terra-;eEast
T;ga:C Oregon _ Project No. 16-1992 Test Pit No. TP-2
w I = Cd 11'
N ci ,2 '6 W T,IT, E'-� 1 t0 1
�, o„ � Material Description
at as co= ■ wQ gU o
0
_Medium stiff, Silt, dark brown, moist, many fine roots(top soil _
Stiff to very stiff, Clayey Silt, brown, moist
1 - 1.75
2- 2.5
3— 3.5 Very stiff, Clayey Silt, light brown with orange and gray mottling, slightly moist
4— 2.5
5-
6-
7-
8-
9-
10 Test pit terminated at 10 feet
-- Low seepage encountered at 3 feet
11-
12—
_
13--
14—
15--
16-
17—
HOS! HARMAN
GEOTECHNICAL
LEGEND
Date Excavated: 3-14-16
SERVICES INC. ® S-1
aCost.trMane ca« swwns Logged By: IDM
10110 SW Nimbus Avenue,Suite B-5
Portland,OR 97223 Soil Sample Depth Water Level at
(503)530-8076 Interval and Designation Time of Excavation
LOG OF BACKHOE / EXCAVATOR TEST PiT
Project: River Terrace East
Tigard, Oregon Project No. 16-1932 TPst P(t TP- 3
c
•• a r N N O e o N
s YE nm 3
a 2 o u_ c o o Material DosFri�lion
a.
Medium stiff, Silt, dark brown, moist, many fine roots(top soil)
1 — 1.75 Medium stiff to very stiff, Clayey Silt, brown, moist
2— 3.25
3— >4 Hard, Clayey Silt, light brown with orange and gray mottling, slightly moist
4— >4
5-
6-
7-
8-
9-
10—
Test pit terminated at 10 feet
Low seepage encountered at 2.5 to 3 feet
11—
12-
13-
14-
15-
16-
17—
1 HH RDIVI
SAL LEGEND
SERVICES INC. Date Excavated: 3-14-16
Practcal Cost-Weave Geotedriml SaitatsS-1
10110 SW Nimbus Avenue,Suite 6-5 Logged By: IDM
Portland,OR 97223 Soil Sample Depth Water Level at
(503)530-8076 Interval and Designation Time of Excavation
LOG OF BACKHOE / EXCAVATOR TEST PIT
Project: River Terrace East Project No. 16-1992 Test Pit No. TP-4
Tiga a, Oregon
r a� E H E ani , a
Material Description
,� Y � L � 'C I "J� G
0 tl N o C 7 �' E. 77 7 .
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Medium stiff, Silt, dark brown, moist, many fine roots(top soil)
1 -- 1.75 Medium stiff to stiff, Clayey Silt, brown, moist
2- 1.0
3 >4 Hard, Clayey Silt, light brown with orange and gray mottling, slightly moist
4— >4
5--
6—
7-
--
8-
--
9-
10- -
--
8-
9-10 Test pit terminated at 10 feet
Moderate seepage encountered at 3 feet
11-
12-
13-
14—
15--
16--
17----
IsmHARDMAN LEGEND
GEOTECH�9CAL Date Excavated: 3-14-16
SERVICES INC. ® 5-1
w c .Err«uveceasor,00 Logged By: IDM
10110 SW Nimbus Avenue,Suite B-5
Portland,OR 97223 Soil Sample Depth Water Level at
(503)530-8076 Interval and Designation Time of Excavation
LOG OF BACKHOE / EXCAVATOR `TEST PiT
:oJ:;t
, gProject No. 151922 MistPtNeiTP-N E N NN� f6
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2-(75 Eco Ec �c
o a= o _ Material Ds( r pfior
0 0 0 ,,
Medium stiff, Silt, dark brown, moist, many fine roots(top soil)
1 — 1.75
2— 1.5
Medium stiff to hard, Clayey Silt, brown, moist to slightly moist
3— 3.0
4— >4
5-
6-
7-
8-
9-
10—
11— Test pit terminated at 10.5 feet
Moderate seepage encountered from 2-6 feet
12-
13-
14-
15-
16-
17—
CC:FICAL LEGEND
INC.I SERVICES Date Excavated: 3-14-16
Cost-Weave Z
S-1
10110 SW Nimbus Avenue,Suite B-5 Logged By: IDM
Portland,OR 97223 Soil Sample Depth Water Level at
(503)530-8076 Interval and Designation Time of Excavation
LOG OF BACKHOE / EXCAVATOR TEST PIT
Project: River.Teirace Est ,
Tiga-d, Oregon < Project No. 16-1992 Test Pit No. TP- 6
ol45I
y„^ N y x N ,c...
- titi o_ o ^Et g-z5 , o.. , Material Description
0 d o.� - r cn Q 2 0 p
d O 0 0
Medium stiff, Silt, dark brown, moist, many fine roots(top soil)
1 - 1.25 Medium stiff to very stiff, Clayey Silt, brown, moist
2- 3.25
3- '4 Hard, Clayey Silt, light brown with orange and gray mottling, slightly moist
4- >4
5-
6-
7-
8--
9-
10 Test pit terminated at 10 feet
Low seepage encountered at 3 feet
11-
12-
13-
14-
15-
16 --
17-
HOW' HAFIDMAN LEGEND
coreccaL Date Excavated: 3-14-16
SERVICES we S-1
E' �G°°°�" ® Logged By: IDM
10110 SW Nimbus Avenue,Suite B-5
Portland,OR 97223 Soil Sample Depth Water Level at
(503)530-8076 Interval and Designation Time of Excavation
ri -vvviv- mv Am(mv am.
LOG OF BACKHOE / EXCAVATOR TEST PIT
Project: River Terrace East
Tigard, Oregon Project No. 1'5-1922 Test Ft No. TP- 7
wN C L
• Nr Ef0 �.Q o (0
o� Eur E � v, � a
o a o o MaterialaDas+:rFp4ion
CO
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Medium stiff, Silt, dark brown, moist, many large roots (top soil)
1 1.5 Medium stiff to very stiff, Clayey Silt, brown, moist
2— 3.5
3 >4
Hard, Clayey Silt, light brown with orange and gray mottling, slightly moist
4— >4
5—
6—
7—
8—
9—
10— Test pit terminated at 9.5 feet
No groundwater or seepage encountered
11-
12-
13-
14-
15-
16-
17—
RCS! HH AC NINOTEAL LEGEND
tSERVICES INC.s,a ® S-1 Date Excavated: 3-14-16
10110 SW Nimbus Avenue,Suite B-5 Logged By: IDM
Portland,OR 97223 Soil Sample Depth Water Level at
(503)530-8076 Interval and Designation Time of Excavation