Report (27) 112013 -
RECEIVED o o° z`{
S E P 5 2013
CITY OF TIGARD
BUILDING DIVISION
PRELIMINARY GEOTECHNICAL ENGINEERING REPORT
PROPOSED 4-STORY BUILDING
7148 SW GONZAGA STREET
TIGARD, OREGON
Prepared for:
Steve Leasure
Centrex Construction
8250 SW Hunziker Street
Tigard, Oregon 97223
January 28, 2013
Project No 528-001
TERRA DOLCE CONSULTANTS, INC.
TERRA DOLCE CONSULTANTS,INC.
4706 NE 757"AVE
PORTLAND,OREGON 97218
503-502-5114
January 28, 2013
Project No. 528-001
Steve Leasure
Centrex Construction
8250 SW Hunziker Street
Tigard, Oregon 97223
PRELIMINARY GEOTECHNICAL ENGINEERING REPORT
PROPOSED 4-STORY BUILDING
7148 SW GONZAGA STREET
TIGARD, OREGON
Dear Steve:
Terra Dolce Consultants, Inc. (TDC) is pleased to present our report summarizing
our evaluation of the referenced property. The purpose of our work was to conduct
a site investigation and provide geotechnical recommendations for the proposed
building. Our work was completed under the terms of our January 15, 2013
proposal.
SITE DESCRIPTION
The site is located on the eastside of SW 72nd Avenue, just north of Highway 217 in
Tigard, Oregon (see Figure 1). Presently, the 0.47-acre site is undeveloped except
for a small shed that is located in the western portion of the site. The site is covered
in grass and has one or two trees in the southeast corner. Based on our fieldwork,
the site is mantled with 3 to 4 feet of undocumented Fill.
PROJECT UNDERSTANDING
TDC understands that the site will be developed with a 4-story building in the
eastern half of the site and a paved parking lot in the western portion. At the time of
our investigations, the layout for the proposed building footprint and parking was
not available. It is our understanding, however, that the anticipated loads will most
likely be 4 kips per lineal foot for the wall loads and 50 to 70 kips for the column
loads.
GEOLOGIC SETTING
Review of the geologic maps of the area indicates that the site is underlain with the
Fine-grained Facies of the Catastrophic Flood Deposits (www.portlandmaps.com).
The fine-grained deposits typically consist of coarse sand to silt-size material. The
finer sediments are predominantly quartz and feldspar and also contain white mica.
The coarser sediments are predominantly Columbia River basalt fragments. Poorly
defined beds 1 to 3 feet thick are observed in outcrop. Locally, beds are separated
by accumulations of brown clay and iron oxide 2 inches thick, which are probably
paleosols. Soil development commonly introduces significant clay into the upper 2-3
5-10 feet of the deposits. The fine sediments are typically mantle slopes up to
elevation 400 feet.
FIELD INVESTIGATIONS
On January 18, 2013, TDC conducted a site investigation to evaluate the surface and
subsurface conditions of the site. The following observations were made:
Surface Conditions.
On the day of our site investigation, a portion of the proposed parking lot had been
overexcavated and replaced with 2-inch crushed rock (see Figure 2). The
overexcavated material was stockpiled on the site and covered with Visqueen (see
Figure 2). The remainder of the site was covered with grass. There were one or two
trees in the eastern portion of the site. The location of the trees might be within the
footprint of the proposed building.
Subsurface Conditions
Subsurface conditions of the site were evaluated by drilling two borings,
(designated B-1 and B-2, see Figure 2) to 22.5 feet below ground surface (bgs) and
20 feet bgs, respectively. Soil samples were collected at 2.5-foot-intervals to 10 feet
bgs and 5-foot-intervals to the extent of the borings using the Standard Penetration
Test (ASTM 1587). For each test, an 18-inch-long split-spoon sampler was driven
with a 140-pound hammer. The number of blows required to drive the sampler 18
inches are recorded in 6-inch intervals. The last two blow counts are added together
to determine the blows per foot (bpf). The blows per foot are used to determine the
in-place consistency of the soil.
The following subsurface conditions were encountered at the site:
Undocumented Fill. Three (3) to four (4) feet of undocumented fill was
encountered throughout the site. The fill consisted of soft, moist Silt with trace
organics.
The fill is not suitable as a subgrade for building or the proposed parking lot. The
material should be overexcavated and replaced with compacted structural fill in an
area 5 feet outside of the proposed building footprint and the parking area. The
undocumented fill is appropriate only for the landscaped areas.
Fine-grained Flood Deposits. The Fine-grained Flood Deposits were encountered
below the Undocumented Fill to 19 feet bgs in B-1 and in B-2. The Fine-grained
deposit was fine-grained Silt to Sandy Silt, brown, medium stiff, with trace micas and
slightly cemented. Measured blow count in the Silty Sand ranged from 8 to 11 bpf.
Columbia River Basalt. Columbia River Basalt was encountered at 20 feet bgs in
both borings. In B-1, the basalt had a 2-foot-thick weathered layer that we were able
to drill through. Directly below that, however, we encountered refusal.
Groundwater. Groundwater was encountered at 9 feet bgs in the borings.
Centrex Construction January 28,2012 Page 2
Geotechnical Evaluation
7148 SW Gonzaga St
Tigard,Oregon
Project No.528-001
CONCLUSIONS AND RECOMMENDATIONS
The conclusions and recommendations presented in this report are based on the
information provided by Centrex Construction, results of the field investigation, and
professional judgment. We have observed only a small portion of the pertinent soil
and groundwater conditions. The recommendations presented in this report are
preliminary and are based on the assumption that the soil and groundwater
conditions do not deviate appreciably from the conditions encountered during our
field investigation. Once the design of the building is completed, we'll finalize our
recommendations and submit a Final Geotechnical Engineering Report. If during
construction of the building undesirable conditions are encountered, then we should
be consulted for further recommendations.
General
Field data indicate that the site is mantled with 3 to 4 feet of Undocumented Fill
overlying 16 feet of medium stiff Silt on top of dense basalt. In our opinion, the site is
geotechnically suitable for the proposed development. This conclusion is based on
the assumptions that the recommendations presented in this report are followed,
and that during construction site conditions change from what is presented in this
report, that we will be consulted for updated recommendations for developing the
site.
Site Preparation and Earthwork
The site should be stripped of the grass and other vegetation within 5 feet of the
building and parking lot footprint. The stripped material should be removed from
the site or stockpiled for use as cover in the landscaped area. This material is not
suitable for Structural Fill within 5 feet of the building footprint or parking area. If
the onsite trees need to be removed, then the rootballs should be overexcavated
and replaced with Structural Fill.
The Undocumented Fill is not suitable within 5 feet of the building or parking lot
subgrade. This material shall be overexcavated to firm-native soils and removed
from the site. If soft spot or wet areas are encountered below the Undocumented
Fill, then those areas should be overexcavated and replaced with Structural Fill. Due
to the fine-grained nature of the silts, care should be taken that the subgrade is not
disturbed or rutted during site preparation.
Wet Weather or Wet Soil Construction
During wet weather or soil conditions, the exposed soils may be disturbed by
construction traffic. Such disturbance will structurally weaken the soil and render it
unsuitable for uses in foundation bearing, for subgrade of compacted structural fills,
and for subgrades of asphalt.
If construction occurs during wet weather, construction traffic should be rounded to
avoid areas of exposed fine-grained soils and should be protected by at least 18
inches of 3-inch-minus crushed rock underlain with woven geotextile, such as LINQ
GTF 300 or equivalent. In addition, care should be taken to minimize disturbance of
native silty soil, which may become "pumped" and weakened by repeated loading
and vibratory compaction and wheeled equipment. Should soils become disturbed,
Centrex Construction January 28,2012 Page 3
Geotechnical Evaluation
7148 SW Gonzaga St
Tigard,Oregon
Project No.528-001
the soils should be removed to firm native subgrade and replaced with compacted
structural fill placed in accordance with the recommendations below.
• Structural Fill
TDC recommends that structural fill shall consist of 1 1/2 to 3/4-inch crushed rock
containing less than 10 percent fines. The imported fill shall be placed in 8- to 12-
inch-thick lifts and compacted to 95 percent of the maximum dry density as
determined by a Modified Proctor (ASTM D1557). The material should be within 3
percent of the optimum water content.
Preliminary Shallow Footings Recommendations
TDC recommends an allowable bearing pressure of 2,000 pounds per square foot
(psf) for dead loads. The allowable bearing pressure may be increased by one-third
for transitory live loads, such as loads and seismic loading.
TDC recommends that continuous footings and individual spread footings should
have a minimum width of 24 inches and a minimum embedment of 18 inches.
Subgrades for the shallow foundations should be firm and free of organics and
deleterious debris as determined by the geotechnical engineer. Soft soils or
undocumented fills encountered during excavation of the footings should be
removed to firm soils and backfilled with imported granular structural fill, as
described above.
Lateral loads on the building foundations may be resisted using an allowable
frictional coefficient of 0.35. In addition, passive resistance may be considered using
an allowable equivalent fluid weight of 300 pound per cubic foot (pcf). For
consideration of passive resistance, the upper 1 foot of embedment should be
disregarded.
Estimated Total and Differential Settlements
Total and differential settlements were calculated for the spread footings using an
estimated structural load, allowable bearing pressures, and laboratory data. For the
spread footing foundations, designed in accordance with the above
recommendations, the estimated total static settlement will be less than 1 inch, with a
differential settlement less than '/2 inch.
Slab-on-Grade Recommendations
The slab-on-grade floor should be designed for an allowable subgrade reaction
modulus of approximately 150 pounds per cubic inch. The subgrade soils must be
in a firm, non-yielding conditional at the time of slab construction. Soft areas
encountered during the preparation of the slab subgrade should be overexcavated
and replaced with structural fill.
A capillary break consisting of at least 6 inches of clean gravel should be placed
underneath the floor slab. The gravel should consist of '/4-inch to 3/4-inch rock with
no more than 2 percent passing the No. 200 sieve (washed analyses). Suitable
material is PCC course aggregated specified in Section 02690.20 of the Oregon
Department of Transportation "Standard Specification Highway Construction".
Centrex Construction January 28,2012 Page 4
Geotechnical Evaluation
7148 SW Gonzaga St
Tigard,Oregon
Project No.528-001
For wet weather conditions, care must be taken to reduce the potential of rainwater
ponding on the slab-on-grade rock section. If the slab is to be covered with a
moisture-sensitive flooring, and wet-weather conditions are anticipated,
consideration should be given to use of a water retarding admixture added to the
concrete or sealing of the finished slab. In addition, a 4-inch thick life of 1/4-inch to
3A-inch, open graded, angular drain rock placed below the capillary break,
discussed above, may be substituted for vapor barrier if approve by the
geotechnical engineer or project architect and used in conjunction with an approved
water proofing admixture.
It is our experience that concrete slab-on-grade commonly exhibit shrinkage cracks
despite the presence of steel reinforcing or fiber strands. This cracking can be
reduced by using a low-slump concrete, properly designed and constructed joints
and by properly curing the concrete.
Flexible Pavement Design
As noted above, up to 4 feet of Undocumented Fill was encountered across the site.
TDC recommends that the Undocumented Fill be overexcavated to firm, non-
yielding Silty material and removed from the site. Once the subgrade is exposed,
then a woven geotextile, such as LINQ-GTF 300 or equivalent should be placed on
the subgrade. The area should be brought to subgrade level and 8 inches of 3/4-inch
crushed rock should be place. The parking lot should be paved with a minimum of 3
inches of PG-64-22, Level 2 - 1/2" Hot Mix Asphalt Concrete (HMAC) Dense Graded.
As stated above, pavement sections assume that the subgrade is unyielding. The
pavement subgrades should be proof-rolled, under the observation of the
geotechnical engineer, with a heavy roller or a loaded 10-cubic-yard dump truck
before placement of crushed rock base material.
Utility Excavation and Backfill
It is anticipated that the excavation for utilities may be up to 4 feet deep. If utility
trenches deeper, then proper shoring should be incorporated into the construction
plans. Excavation for utilities may generate soils that are impacted with
hydrocarbons.
Only imported granular fills should be used as utility trench backfill. Imported
granular backfill should consist of sand, sand and gravel, or crushed rock up to 1 1/2-
inch in dimension and less than 5 percent passing the No. 200 sieve (washed
analyses). The bedding material used for the pipes should conform to the
manufacturer's recommendations for the type of pipe selected. The granular
backfill should be placed in maximum 12-inch loose lifts and compacted to at least
90 percent of the maximum dry density as determined by Modified Proctor (ASTM
D-1557) using a vibratory plate compactors attached to backhoes ("hoepacts").
The stability of the excavation and the design, installation, and dewatering of
shoring for the excavation is the responsibility of the contractor. Workers should not
be allowed to enter excavation of 4 feet or deeper unless the excavations have been
Centrex Construction January 28,2012 Page 5
Geotechnical Evaluation
7148 SW Gonzaga St
Tigard,Oregon
Project No.528-001
properly shored and dewatered. All excavation and shoring systems should be in
compliance with current local, state, and federal worker safety codes and practices.
2010 Oregon Structural Specialty Code Seismic Design Recommendations
Table 1
Seismic Design Recommendations
Seismic Variables Recommended Values
Site Classification: D 1
Latitude/Longitude 45.42828/-122.75073
Maximum Considered Spectral Accelerations:
Short Period: Ss = 0.949g
Residential Design Information:
Residential Site Value: 2/3 x Fa x Ss
2/3(0.981) (1.121) = 0.709g
PGA= 0.709/2.5 0.28
kh= 0.14
Document Review and Construction Monitoring
TDC should be retained to review final plans and specifications. This review will
allow us to examine the documents to determine whether the intent of our
recommendations presented in this report was incorporated into the design of the
building.
TDC should be retained to provide construction monitoring and testing services
during the earthwork and foundation construction activities. The purpose of our
field monitoring services is to confirm that the site conditions are as anticipated and
to provide field recommendations as required based on the conditions encountered.
TDC should provide Special Inspections for the following project construction
activities:
• Site stripping;
• Foundation and parking lot subgrade preparation; and
• Slab-on-grade subgrade.
A Materials Testing Company, (i.e., ACS Testing) should be contracted directly with
the owners to provide field and laboratory compaction tests for the Structural Fill,
asphalt base rock, and asphalt testing.
Centrex Construction January 28,2012 Page 6
Geotechnical Evaluation
7148 SW Gonzaga St
Tigard,Oregon
Project No.528-001
IMITATIONS
Geotechnical review is of paramount importance in engineering practice. The poor
performance of many foundations has been attributed to inadequate construction
review. On-site grading and earthwork should be observed and, where necessary,
tested by a qualified engineering firm to verify the compliance with the
recommendations contained in this report. Foundation excavation should also be
observed to compare the generalized site conditions assumed in this report with
those found on the site at the time of construction. If the plans for site development
are changed, or if various or undesirable geotechnical conditions are encountered
during construction, the geotechnical engineer should be consulted for further
recommendations.
This report is issued with the understanding that it is the responsibility of the Client
to ensure that the recommendations are incorporated in the plans and the necessary
steps are taken to see that the contractor and subcontractors carry out such
recommendations in the field. Geotechnical engineering is characterized by a
certain degree of uncertainty. Professional judgments presented are based partly
on our understanding of the proposed construction and partly on our general
experience. Our engineering work and judgments rendered meet current
professional standards; no other warranties, either expressed or implied are made.
This report is subject to review and should not be relied upon after a period of 3
years.
Sincerely,
Terra Dolce Consultants, Inc.
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Cynthia L. Hovind, P.E., G.E.
Professional Geotechnical Engineer, OR-17857PE
Attachments
Figure 1 -Vicinity Map
Figure 2 -Site Plan
Boring Log
Centrex Construction January 28,2012 Page 7
Geotechnical Evaluation
7148 SW Gonzaga St
Tigard,Oregon
Project No.528-001
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Terra Dolce Consultants, Inc. Proposed New Building
4706 NE 75th Ave 7148 SW Gonzaga St
Portland, Oregon 97218
Phone 503.502.5114 Tigard, Oregon
Project No. 528-001 I January 28, 2013 I Vicinity Map I Figure 1
a� • GRAVELED AREA
SW Gonzaga St COVERED
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Terra Dolce Consultants, Inc. Proposed New Building 1
4706 NE 75th Ave 7148 SW Gonzaga St
Portland, Oregon 97218
• Phone 503.502.5114 Tigard, Oregon
,
' Project No. 528-001 I January 28, 2013 I Site Map I Figure 2
BORING LOGS
Terra Dolce Consultants, Inc. Boring Log No. B-1
7148 SW Gonzaga St
Location:7148 SW Gonzaga St WO#:528-001
Method:Solid Stem Ground EL:
•Hammer:Safety Hammer Hammer weight(lb):140 Hole depth(ft):22.5
Sampler:SS Drop(in):30 G.W.T.@ Drilling(ft):10 Sampled by:CLH
- Driller:Dan Fischer Excavating,Inc. Drill Date:January 18,2013 Logged by:CLH
w m �n u) ■ SPT.blow/ft
o z° m a j Soil Description 0 Moisture% Notes
S 20 40 60
Fill(ML)Brown,moist,medium Stiff,medium 0
- 1 .\ 1-2-3 plasticity,with organics(Silty Fill) -
0
2 \ 2-3-4
ML Silt to Sandy Silt(ML)Gray mottled brown,moist,
rn —5 medium stiff to stiff,trace micas,trace fine-grained 5 —
• - 3 3-4-5 sand(Fine-grained Flood Deposits) -
o - _
0 .
3 —
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4 2-3-5 _
g- _
-10 y 10—
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—20 r,. , 20 Weathered Basalt,Gray,soft(R2), 20—
- ti...r 7 \ 8-26-26 (Columbia River Basalt) -
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1 - N 'Fresh Basalt,Gray,Hard(R4),(Columbia River / II
8 50/1" Basalt)
- Boring completed at depth of 22.5
i —25 25—'
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8
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Remarks:
Refusal at 22.5 feet.
Plate 1
Boring Log No. B-2
Terra Dolce Consultants, Inc. 7148 SW Gonzaga St
Location:7148 SW Gonzaga St WO#:528-001
Method:Solid Stem Ground EL:
-Hammer:Safety Hammer Hammer weight(lb):140 Hole depth(ft):20
Sampler:SS Drop(in):30 G.W.T.@ Drilling(ft):11 Sampled by:CLH
•Driller:Dan Fischer Excavating,Inc. Drill Date:January 18,2013 Logged by:CLH
r u u) ■ SPT.blow/ft
d `� z° r o , Soil Description 0 Moisture% Notes
o in C7 m a D
N —0 0 20 40 60 0 —
Fill(ML)Brown,moist,medium Stiff,medium
2
i - 1 \ 1-5-6 plasticity,with organics(Silty Fill) I -
c
;, 2 1-2-3
ML Silt to Sandy Silt(ML)Gray mottled brown,moist,
a —5 medium stiff to stiff,trace micas,trace fine-grained 5 —
i- 3 \ 2-4-6 sand(Fine-grained Flood Deposits) -
2
0 — -
C, -
3
a _ 4 3-3-4
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c —10 '.:,SM Silty Sand(SM)Brown,loose to medium dense 10—
- ,:' 5 3-5-5 (Fine-grained Flood Deposits) --
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a_ 6 ` 44-5
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" 20 ti...� Fresh Basalt,Gray,hard(R4)(Columbia River
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7 6 31-50/4" \Basalt) /
c Boring completed at depth of 22.5
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g -25 25—
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—35 35—
Remarks:
Refusal at 22.5 feet.
Plate 2
TUALATIN VALLEY WATER DISTRICT Test #: 868
FIRE HYDRANT FLOW TEST REPORT Hydrant ID #: 2S1W01A40H50
Location: 7070 SW GONZAGA ST. Date: 8/31/2009
Test made by: HERB & KEVIN
Witness: Time: 11:00
Project name:
Discharge coefficient: .54816
Inside dia. of outlet = 4.5 inches
Pitot reading = 41 psi Pitot 2 = 0 psi
Observed flow rate = 2119.5 gpm
Flow method: HOSE MONSTER
Static pressure: 110 psi Residual pressure: 80 psi Di
5
Flow at 20psi residual pressure (calculated): 3836 gpm G'
Location map: To be attached to test report and to show which hydrants were
used to monitor residual pressure and flow.
Gaye information:
Static and residual pressure gage: 120997-2C Pitot gage: 9864E1
Hydrant information:
Hydrant ID Year Make Notes
Flow hydrant: 2S1W01A40H50 1999 WATEROUS see map for location
Read hydrant: 2S1W01A39H50 2000 WATEROUS see map for location
Remarks:
The mapping, flow or pressure information contained herein reflects conditions on the date
and time of the test. Tualatin Valley Water District makes no representation as to the system's
ability to meet specific fire flow requirements. Future system capability may differ from the
flows reported herein because of subsequent modifications to the district's system and/or
because flow and pressure may vary by time of day and season. Test gage callibration
information available upon request.
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