Report 51:* 20oS - 000O8
Va. amerce FILE COPY
5 l awi Scvta sum
Storm Water Swale Management Plan
5 t7O; - �0003Z
Minuteman Press Facility RECEIVED
-- -Hermoso Way
Tigard, Oregon JAS! 2 2, ?tI]4
CITY OF TIGARD
PLANNm O /ENGINEERING
Site Contact: Minuteman Press
Bob Davidson 00 503- 620 -5203 �� 9.
171 :3:
Prepared By Willamette Engineering and ✓'�
Earth Sciences • = • EG.
P.O. Box 1139
5 ti.•.
Dallas, Oregon 97338
EXPIRES 06130/04
Date : January 20, 2004 Robert J. Slyh, P.E.
Principal
INTRODUCTION
The Storm Water Swale constructed as part of the site development will require periodic
inspection and maintenance to maintain the integrity and performance of the system. Visual
inspections should be performed monthly during months when run off is observed to determine if
the swale is accumulating sediment and to see that swale plantings are growing acceptably.
Sediment and debris should be removed from the swale annually, or as needed periodically to
assure that the swale storm water detention volume is maintained. Debris should be removed
periodically from the swale and inlet structure to assure that flow control orifices work as
designed.
P.O. Box 1139, Dallas, OR 97338 (503) 623 - 0304
Storm Water Swale Management Plan -0 \tis: I
City of Tigard t I FILE Copy
Approved Plans
ByP$l Date /Z'
Ve
7.2 003 —00032_
Sa a.Hd 5ant4 Seeeteed May 9, 2003
Project Number: GPC- 001.001
Mr. Mike Kezeor ECE . VED
Gray Purcell Contractors
P.O. Box 23516 DEC 9 2113
Portland, OR 97281 -3516
CITY OF TIGARD
n�V ISI �I
Re: Geotechnical Engineering Study for Minute Man Press Office St , 75 -55.5
Hermanso Way; Tigard, Oregon
Dear Mr. Kezeor:
Willamette Engineering and Earth Sciences (Willamette) is pleased to present this report
detailing the results of a geotechnical engineering study for the above referenced site. As
Willamette understands, the development will include a 7,500 square foot commercial
office structure. The structure footprint will be on the order of 40 feet by 80 feet, and will
include 3 floors, with the lower floor a basement. The proposed foundation system is a
slab -on -grade with perimeter and column footings. The site is located in the Tigard
"Triangle," as indicated on Figure 1.
The site located at the address reference above comprises a moderately sloping lot with
approximately 16 feet of vertical relief from front to back, resulting in an average 10
percent slope across the site. The existing residential structure on the site is located
approximately in the footprint of the proposed office structure. The rear of the lot includes
extensive landscape and some relatively large trees.
SITE DESCRIPTION
Surface Conditions
The site slopes moderately from east to west, with approximately 16 feet of vertical relief
from the high point at the northeast corner of the site to the northwest. The existing
structure and site landscaping are well maintained. There are a number of medium to
large deciduous and conifer trees, and mature landscape shrubs on the site.
Subsurface Conditions
Willamette observed soil conditions in three exploratory test pits and three dynamic cone
penetrometer soundings at the locations indicated on Figure 2, Exploration Locations.
The maximum depth of explorations was 11.0 feet below ground surface.
P.O. Box 1139, Dallas, OR 97338 (503) 623 -0304
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:I
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 2
In general, soil in the upper 10 feet of the site is consistent in texture and strength. Soil in
the sloping areas to the north and south, and in the relatively flat area at the rear of the
existing residence is likely fill comprised of native soil generated during the original site
development. Shallow soils at the site typically comprise a medium stiff, moist Silt (ML).
Graphical logs of the geotechnical test pits are presented in Attachment A. Graphic logs
for the dynamic cone penetrometer soundings are presented in Attachment B. The
following presents a narrative description for the respective soil units:
• Silt to Sandy Silt, 0- to 15 -feet below ground surface: Brown Silt to Clayey Silt
(ML), medium stiff to stiff with depth to 11 feet. The Silt to Sandy Silt unit was
present in all explorations. The Silt is low to moderate plasticity. Dynamic cone
penetration resistance in the shallow portions of the Silt is on the order of 0.5 blows
per inch.
Disturbed torvane shear strengths were measured at 1,100 pounds per square foot (psf)
up to 1,500 psf . Undisturbed vane shear measurements yield a peak shear strength on
the order of 3,000 psf. Subgrade modulus information based. on DCP tests range from
less than 100 pounds per cubic inch (pci) for the suspected fill areas to on the order of
200 pci for the stiffer native deposits.
Groundwater was encountered at a depth of approximately 7.0 feet bgs in the the western
test pits. The depth to groundwater in the area is expected to vary considerably with
seasonal fluctuations in rainfall, with highest winter levels likely represented by those
observed in the field exploration.
Seismic Considerations
There is an inferred fault (see Figure 3) in the general vicinity of the site as identified by
Wong et. al.' The local seismic regime for the 500 -year event in this area appears to be
dominated by the local faults.
Seismic design for the structure requires definition of the seismic zone, soil profile type,
and estimated peak site acceleration. The seismic zone for the site based on the Uniform
Building Code (UBC) is zone 3. The soil profile type is based on soil stiffness and
thickness.
I. Wong, W. Silva, J. Bott, D. Wright, P. Thomas, N. Gregor, S. Li, M. Mabey, A. Sojourner, and Y.
Wang, IMS — 16, Earthquake Scenario and Probabilistic Ground Shaking Maps for Portland, Oregon,
Metropolitan Area, Oregon Department of Geology and Mineral Industries
Vilamette
Sviaeert.49 a.Kd Sand 5eieHeed
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:I
.
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 3
Willamette also reviewed United States Geological Survey (USGS) seismic mapping to
estimate site peak ground acceleration (PGA). USGS indicates a PGA of 0.23 gravities
(g) with a 90- percent chance of not being exceeded in 50- years, while Wong et. al.
indicated a PGA of 0.25 g with a frequency of occurrence of once in 500 -years (10- pecent
chance of occurrence in 50- years). Willamette believes the 0.25 g estimate based on the
USGS data is appropriate and reasonably conservative.
Seismic Hazards
The primary seismic risk at the site is earthquake induced lateral accelerations on the
structure. The site is moderately sloping, but should not be susceptible to earthquake
induced landslides. There is a small chance of subsidence due to earthquake induced
accelerations based on the presence of some sands identified in off -site borings, although
that type of behavior would be expected to extend over a very large area. There are no
known active faults at the site, although fault rupture always remains a remote possibility.
Tsunami impacts at the site are unlikely.
2 USGS National Seismic Hazard Mapping Project, 1997.
Seefiaeeiria9 ewe Send S
7545 Hermanso Geotechnical Engineering Report-03 \rjs: I
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 4
Foundation Recommendations
General
In general, the site appears to be acceptable for the proposed development. There will
likely be some cutting and filling required to achieve desired building and parking lot
grades. Shallow soil conditions are soft in the north and south of the structure, probably
as a result of fill placement, and may require some mitigation to achieve acceptable
pavement subgrade. Site soils are moisture sensitive, and will become difficult, if not
impossible to work in wet weather. Willamette believes that the proposed structure may
be supported by a standard spread footing system
Clearing and Stripping
All surficial materials and pavements contaminated with organic debris, concrete or
asphalt rubble, and loose or damaged asphalt and rubble, should be cleared from areas
beneath footings, slabs, and paved areas, and disposed outside of building and pavement
areas, at an approved disposal site.
Once stripping is complete other disturbed soil exposed during stripping should be
removed or recompacted, and the finished surface should be graded to drain. Significant
ponding of surface water on the stripped finish surface may cause soil conditions to
deteriorate. Total depth of stripping is estimated at about 6 inches. Over - excavation may
be required in some areas to remove the soft surficial fill.
General Fill Placement
General fill will be placed as backfill around the building perimeter, behind retaining
walls, in landscape areas, and may support sidewalks around the building perimeter. In
general, the fill should meet the following specifications:
Percent of Compaction: 90 percent:
Maximum Slope: 3:1 (Horizontal : Vertical)
Fill or backfill materials can consist of either suitable on -site fill or select fill. On -site fill
is soil generated from excavation and grading which can, in the opinion of the
geotechnical engineer, be satisfactorily placed and compacted as fill. Select fill is
N eiameete
Sofa cefiru y aocd gaged SueKeed
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:I
MIL
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 5
imported material consisting of aggregate or combinations of aggregate and soil that can
be successfully compacted.
If grading is performed during the wet winter months, generally October through May,
Willamette recommends that on -site fill only be used if it has been drained sufficiently
well to achieve the required compaction.
Fill material should be placed in layers twelve inches or less in loose thickness, moisture
conditioned if necessary, and compacted to 90- percent of the maximum Standard Proctor
density, ASTM D698. Fill should not be placed against retaining walls until concrete has
had sufficient curing time.
If field density tests indicate the required percentage of compaction has not been obtained,
the fill material shall be recompacted, or scarified and moisture conditioned as necessary
and recompacted to the required Percent Compaction before placing any additional
material.
Structural Fill Placement
Structural fill will be placed beneath structure foundations and will support parking and
roadway areas. In general, the structural fill should meet the following specifications:
Percent of Compaction: 92 percent:
Maximum Slope: 2:1 (Horizontal : Vertical)
Structural fill materials can consist of either select aggregate fill in wet or dry weather
conditions, or approved on -site fill during dry weather conditions. On -site fill is soil
generated from excavation and grading which can, in the opinion of the geotechnical
engineer, be satisfactorily placed and compacted as fill.
If grading is performed during the wet winter months, generally October through May,
Willamette recommends that on -site fill only be used if it has been drained sufficiently
well to achieve the required compaction.
Fill material should be placed in layers twelve inches or less in loose thickness, moisture
conditioned if necessary, and compacted to 92- percent of the maximum Modified Proctor
density, ASTM D1557. Fill should not be placed against retaining walls until concrete has
had sufficient curing time.
Nb arett`e
gos ateenuu acrd Saei Sci&scea
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:1
MIL
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 6
If field density tests indicate the required percentage of compaction has not been obtained,
the fill material shall be re- compacted, or scarified and moisture conditioned as necessary
and recompacted to the required Percent Compaction before placing any additional
material.
Utility Trench Excavation
Utility line excavations beneath paved or floor slab areas, should be properly backfilled
with compacted aggregate fill, placed to the specified degree of compaction, or better.
Figure 4 provides a pictorial representation of Willamette's recommended design. Utility
lines that will be located in the vicinity of the buildings must be installed after site grading
and fill placement. On -site soils should not be used as backfill for utility lines, except in
landscape areas where some backfill settlement is tolerable. Shoring will be required in
all excavations greater than 4 -feet in depth, or as required by Oregon Occupational Health
and Safety Construction standards.
Spread and Continuous Footings
Spread and continuous footings should be founded on mini piles. Footings should not be
constructed at locations and elevations such that the slope down from the edge of the
footing is at an inclination greater than 2:1 (horizontal:vertical) without the approval of the
engineer.
Bearing Material
Mini pile foundation elements driven to refusal in the lower Sand unit.
Footing Lateral Load Resistance
Passive Resistance: 300 pounds per cubic foot (pcf)
equivalent fluid density
Coefficient of Friction at Footing Base: 0.35
Note: These values do NOT include a load factor; the structural engineer should
provide this factor. These values do, however, assume that all footing backfill has
been placed and compacted to a maximum density equivalent to 95 percent of the
maximum Modified Proctor density, ASTM D1557.
Periamette
Eg94teece:49 aKd Eantli Seee# eed
7545 Hermanso Geotechnical Engineering Report- 03\rjs:1
•
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 7
Allowable Bearing Pressure
1,750 -psf for all dead and live loads bearing on approved subgrade or compacted
select fill placed in accordance with the structural fill recommendations.
One -third increase allowable for temporary short-term wind and seismic loads.
Subgrade Stiffness
175 pounds per cubic inch (pci) bearing on approved subgrade or compacted select
fill placed in accordance with the structural fill recommendations.
Lateral Load Resistance
Passive Resistance: 300 pounds per cubic foot (pcf) equivalent
fluid density
Coefficient of Friction at Mat Base: 0.35
Note: These values do NOT include a load factor; the structural engineer should
provide this factor. These values do, however, assume that all footing backfill has
been placed and compacted to a maximum density equivalent to 95 percent of the
maximum Modified Proctor density, AS TM D1557.
Seismic Design
To design for seismic forces in accordance with Division Iv and V, Earthquake Design,
Sections 1626 through 1636 of the 1997 Uniform Building Code.
Seismic zone 3
Soil Profile Type SD - Stiff Soil Profile, N avg > 15, < 50
Site Acceleration 0.25 g, 90 percent chance of not being
exceeded in 50 years
V cria zet>te
Sagureenia9 a#10( Sand Scieacat
7545 Hermanso Geotechnical Engineering Report- 03\rjs:1
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
•
Page 8
Slab -on -Grade Floors
Subgrade
4 inches compacted structural fill
Capillary Break
Minimum of 2 inches of free - draining sand and gravel containing less than 3
percent fines (materials passing No. 200 mesh sieve) based on fraction passing the
No. 4 mesh sieve. (Not necessary if Select Fill is used and meets this requirement)
Vapor Barrier
In areas where moisture would be detrimental to equipment, floor coverings or
furnishings inside the building, a vapor barrier should be placed beneath the
concrete floor slab. Reinforced plastic sheeting is satisfactory for this purpose.
Protection Measures
A layer of sand, approximately 2 inches thick, may be placed over the vapor barrier
membrane to protect it from damage, to act as an aid in curing of the concrete slab,
and also to help prevent cement paste bleeding down into the underlying capillary
break.
Footing Drains
Install perimeter- footing drains adjacent to all continuous exterior footings, basement
walls, and thickened slabs. Footing drains should not be connected to the downspout or
roof drain system. A typical footing drain schematic is presented in Figure 5.
Settlement
Shallow soils on the site appear somewhat settlement sensitive, however over - excavation
of unsuitable native soil should reduce post construction settlement on a mat slab
foundation to a tolerable level. Mini Pile foundation systems will virtually eliminate
potential foundation settlement.
Veil m a re
S 944evr y aocl Sandi Se a seed
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:1
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 9
Provided over - excavation recommendations are followed, foundation settlements should
be within the following limits:
Total Settlement: less than 0.75 inch
Differential Settlement: less than 0.25 inch over 50 feet
Time Rate: approximately 90 percent in first
month after loads applied; remainder
within one year of completion of
construction.
Lateral Earth Pressures
Lateral earth pressures either apply active loads to retaining walls or buried structure walls
such as basement walls, or provide passive resistance to lateral loads being carried in
structure foundations. Active and passive lateral earth pressures are based on material
friction angles estimated from the field testing program, and the proposed footing or wall
backfill material. Compacted aggregate structural fill has been assumed for all footing and
retaining wall backfill.
Design active lateral pressures
Wall free to rotate at top: 35 -pcf equivalent fluid density
Wall fixed at top: 55 -pcf equivalent fluid density
Floor surcharge: 40 -psf uniformly distributed over
entire height of wall where applicable
Traffic Surcharge: 80 -psf uniformly distributed over
entire height of wall where applicable
Hydrostatic Pressure Reduction: Include footing drains to reduce
hydrostatic pressures on basement or
retaining walls.
Design passive lateral pressures
Wall: 300 -pcf equivalent fluid density
SK9iureenuu1 a.Kd Sands Sec teed
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:I
•
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 10
Floor surcharge: 150 -psf uniformly distributed over
entire buried portion of the wall
where applicable
Note: These values assume that all wall backfill has been placed and compacted
to a maximum density equivalent to 92 percent of the maximum Standard Proctor
density, ASTM D1557.
Pavement Sections
Pavement design and capacity recommendations for the parking areas have been
developed based on site conditions and material properties developed from the field test
program, and our experience with similar soils. Based on the soils in the shallow
subsurface, all pavement repair areas should include a sub -base lift consisting of 6- inches
of 11/2 -inch to 0 -inch crushed aggregate over a structural geotextile fabric as a base for the
design pavement section.
The design pavement sections should consist of either a layer of Crushed Rock Base
(CRB) or Asphalt Treated Base (ATB) material placed on the compacted subgrade and
overlain at a later date by an Asphaltic Concrete Pavement (ACP). The design pavement
section should consist of one of the following:
Parking and Light Traffic Areas
For areas that will support primarily automobile traffic. The upper 12- inches of
aggregate fill will be compacted to not less than 95 Percent compaction verified by
proof rolling as described above.
Geotextile Fabric: Mirafi 200 X or approved equal
Minimum Sub Base Layer Thickness: 6 inches 11/2 - 0 CRB
Minimum Base Layer Thickness: 6 inches of % - 0 CRB or 2 inches of
ATB
Minimum Surfacing Thickness: 2.5 inches of Class B ACP
Zieel mette
Seviozezig9 awe Ewa% Sae-44a
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:1
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 11
Heavy Traffic Areas
For areas that will support primarily truck traffic. Upper 12- inches of aggregate fill
compacted to not less than 95 Percent compaction verified by proof rolling as
described above.
Geotextile Fabric: Mirafi 200 X or approved equal
Minimum Sub Base Layer Thickness: 12 inches 1' /2 - 0 CRB
Minimum Base Layer Thickness: 6 inches of of 3 /4 - 0 CRB or 4 inches
of ATB
Minimum Surfacing: 3.5 inches of Class B ACP
Vbanetfe
Stejame�curg afcd Sang Seietee4
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:1
1111111 ,
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 12
SUMMARY
•
Willamette appreciates the opportunity to be of service in this matter. Willamette should
be requested to observe the foundation preparation prior to placement of foundations or
structural fill, and to review the fill placement procedures to verify the execution of the
design intent.
If you have any questions, please call me at (503) 623 -0304, or (503) 871 -4984 (mobile).
Sincerely,
Wiliamate
S 9ureecuuf awe Swim Seiegeed
r c o PROp.,, .
��G I •E .
/ X70,3 �`'
W• REGO
d i e �N . 18
Ojai J J.
EXPIRES 06/30/04
Robert J. Slyh, P.E.
Principal
Attachments: Limitations
Figures 1 through 5
Attachments A, B, and C
7e/deamette
S ile f awe Sand se eweed
7545 Hermanso Geotechnical Engineering Report- 03 1rjs:1
Mr. Mike Kezeor Project Number: GPC- 001.001
May 9, 2003
Page 13
•
LIMITATIONS
This report has been prepared for the exclusive use of our Client and their other
consultants, for this project only. The conclusions and recommendations in this report are
based on conditions encountered at the time of our field visit, data and information you
provided, and our experience and engineering judgment.
Willamette Engineering and Earth Sciences cannot be responsible for the interpretation of
the data described herein by others. Our work has been performed in a manner consistent
with that level of care and skill ordinarily exercised by members of the profession
currently practicing under similar conditions in the area. No other warranty, express or
implied, is made.
Willamette Engineering and Earth Sciences must presume the conditions observed are
representative of the entire property. However, you should be aware that subsurface
conditions may vary, and unanticipated conditions can and often do occur. The
interpretations provided do not warrant subsurface conditions except in the specific
exploration and sample locations, at the time of the investigation. If differing conditions
are exposed during construction or the design is modified, Willamette Engineering and
Earth Sciences should be requested to reevaluate our recommendations and to provide a
written confirmation or modification, as necessary. We cannot be responsible for the
applicability of our recommendations if not afforded this opportunity.
V &amette
50196ree tuuy aace gana .S cte e-eQ
7545 Hermanso Geotechnical Engineering Report- 03 \rjs:1