HomeMy WebLinkAboutT-3685 y7. S:
{g; TERRA ASSOCIATES Inc.
Consultants in Geotechnical Engineering, Geology
and
Environmental Earth Sciences
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T c p tl t c—A-- PO2L " July 10, 1997
Project No. T-3685
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Mr. Rob Purser I
Stafford Homes
16016 - 118th Place NE
Bothell, Washington 98011
Subject: Preliminary Geotechnical Report
Tharp Property
NE 36th Street and 112th Place SE
Renton, Washington
Dear Mr. Purser:
As requested, we have conducted a preliminary geotechnical engineering study for the subject project.
The attached report presents our findings and recommendations for the geotechnical aspects of project
design and construction.
Our field exploration indicates the site is generally underlain at shallow depths by medium dense to
dense silty sand. It is our opinion that the single-family residences may be constructed using
conventional spread footings placed on competent native soils or on structural fills. Slab-on-grade
floors and pavements may be similarly supported.
We trust the information presented in this report is sufficient for your current needs. If you have any
questions or need additional information, please call. �Q
Sincerely yours,
TERRA ASSOCIATES, INC. 10M
Amy Kanfi J.
Staff Engineer +c
nN,
tiGth' 7
eo ore J. Sche per, P.
Principal Engi er 2S74Z
Expms 6'][WcI'rt —�
12525 Willows Road, Suite 101, Kirkland, Washington 98034 • Phone (206) 821-7777
TABLE OF CONTENTS
Page
1.0 Project Description 1
2.0 Scope of Work 1
3.0 Site Conditions 2
3.1 Surface 2
3.2 Soils 2
3.3 Groundwater 3
4.0 Discussion and Recommendations 3
4.1 General 3
4.2 Site Preparation and Grading 3
4.3 Structural Fill 4
4.4 Slopes and Embankments 4
4.5 Excavations 5
4.6 Foundations 5
4.7 Slab-on-grade Construction 6
4.8 Lower Level Walls and Retaining Walls 6
4.9 Rockeries 6
4.10 Drainage 6
4.11 Utilities 7
4.12 Pavements 7
5.0 Additional Services 8
6.0 Limitations 8
Figures
Vicinity Map Figure 1
Exploration Location Plan Figure 2
General Slope Fill Detail Figure 3
Retaining Wall Drainage Detail Figure 4
Appendix
Field Exploration and Laboratory Testing Appendix A
ll�
Preliminary Geotechnical Report
Tharp Property
NE 36th Street and 112th Place SE
Renton, Washington
1.0 PROJECT DESCRIPTION
The project consists of a 50 to 75-lot development for single-family homes with associated utilities and
roadways. The project is in the preliminary stage and clearing and grading plans have not been
prepared at this time. We anticipate that building elevations and lot landscaping grades will blend with
the native topography. We expect that the houses will be wood-framed and one to two stories high.
Main floor levels will be framed over a crawl space with garage floors constructed as slabs-on-grade.
Structural loading will be light, ranging from one to two kips per foot for bearing walls and 20 to 30
kips for isolated columns.
The recommendations presented in the following sections of this report are preliminary. We should
review grading and stormwater drainage plans as they become available. This will allow us to
supplement our recommendations as required. We should review final design drawings and
construction specifications to verify that our recommendations have been properly interpreted and
incorporated into the project design and construction.
2.0 SCOPE OF WORK
On June 19, 1997, we explored the site soils by excavating nine test pits to depths from 9 to 13 feet
below existing grades. Using the information obtained from the subsurface exploration, we performed
analyses to develop preliminary geotechnical recommendations for project design and construction.
Specifically, this report addresses the following:
• Soil and groundwater conditions
• Site preparation and grading
r
• Suitability of native soils for use as fill
• Recommendations for import fill material
• Slopes, embankments, and excavations
July 11, 1997
Project No. T-3685
• Foundation support
• Slab-on-grade support
• Retaining walls and rockeries
• Drainage
• Utilities
3.0 SITE CONDITIONS
3.1 Surface
The project site is located southwest of the intersection of NE 36th Street and 112th Place SE in Renton.
The Vicinity Map, Figure 1, shows the location of the site. The property has gross dimensions of 800
feet by 1000 feet. A topographic survey of the.site was not available for us to review. In general, the
site slopes gently down. to the northeast, except adjacent to the bordering streets where the
embankments are steeply sloped. At the south end of the site, a 10 to 15-foot high hill rises sharply at
the east end and falls gently toward the west. The ridgeline is just north of Test Pits TP-7 and TP-8.
The property is bordered on the west, south, and east by scattered residences and undeveloped land.
May Creek is located 500 to 1000 feet south and west of the site. Site vegetation consists of maple,
alder, and cottonwood trees and low growth vegetation.
3.2 Soils
Surficial organic topsoil on the site ranges in thickness, from three inches or less at the south end to one
to two feet in the north end. We generally encountered roots at two to three feet below grade, with
occasional isolated roots to five feet. Underlying the topsoil, we encountered medium dense to dense,
- fine silty sand over most of the site to the depths explored. In Test Pits TP-5, TP-6, and TP-8, we
encountered a cleaner sand with silt unit from about six to ten feet to the bottom of the test pits. In Test
Pit TP-1, we encountered glacial till consisting of very dense silty sand nth gravel from seven feet to
the bottom of the test pit.
The subject property is mapped in the Soil Survey of King County Area, Washington (U.S. Soil
g Conservation Service) as Alderwood gravelly sandy loam. This classification is not consistent with
soils we observed over most of the site. In our opinion, the soils would be more representative of the
Ragnar soil series which is also mapped north of the site. A more detailed description of the subsurface
conditions we encountered is presented on the Test Pit Logs in Appendix A. The Exploration Location
Plan, Figure 2, shows the approximate test pit locations.
Page No. 2
July 11, 1997
Project No. T-3685
3.3 Groundwater
We did not encounter groundwater seepages in our test pits. However, the soils were observed to be in
a moist to very moist condition, with occasional wet seams. Fluctuations in groundwater seepage levels
should be expected on a seasonal and annual basis. The amount of seepage will be highest during
extended periods of heavy precipitation and during the wet winter months.
4.0 DISCUSSION AND RECOMMENDATIONS
4.1 General
Based on our study, in our opinion, there are no geotechnical considerations that would preclude site
development. The residences may be supported using conventional spread footing foundations bearing
on competent native soils one to three feet below existing grade or, if required, on compacted structural
fill. Pavements and floor slabs may be similarly supported.
Detailed recommendations regarding the above issues and other geotechnical design considerations are
provided in the following sections. These recommendations should be incorporated into the final design
drawings and construction specifications.
4.2 Site Preparation and Grading
In areas receiving fill and below pavements, slabs, and foundations, it will be necessary to strip and
remove vegetation and organic surface soils. Based on our study, surface stripping depths of one to two
feet in the north portion and 3 to 12 inches in the south portion should be expected to remove organic
topsoil. Stripped vegetation should be removed from the site. Organic topsoil will not be suitable for
use as structural fill, but may be used for landscaping purposes.
Prior to placing fill and to prepare building and pavement subgrades, we recommend proofrolling all
exposed surfaces to determine if any isolated soft and yielding areas are present. If excessively yielding
areas are observed, they should be recompacted in place or overexcavated to expose firm bearing soil
and replaced with structural fill to final grade. We should observe all proofrolling operations.
w
Competent bearing material for building foundations should consist of medium dense to dense native
soils. It may be necessary to carry the foundations deeper through the loose surficial soils and root mat
_ to expose competent subgrade material. Foundations may also be placed on properly placed and
compacted structural fill. Slab-on-grade floors and pavements may be constructed on any native
inorganic soil that is first compacted to a non-yielding condition or on compacted structural fill as
needed. A representative of Terra Associates, Inc. should perform field evaluations at the time of
construction to verify stable subgrades.
Page No. 3
July 11, 1997
Project No. T-3685
4.3 Structural Fill
Our study indicates that most of the native soils contain a moderate percentage of fines (silt size
particles). In general, the inorganic silty sand excavated on-site will be suitable for reuse as structural
fill material, provided it can be properly placed and compacted. However, the ability to use the native
soils as structural fill or backfill will depend on their moisture contents and the prevailing weather
conditions when site grading activities occur. Moisture conditioning may be necessary depending on
the silt and moisture content of the material.
If site grading takes place during the wet winter season or begins in the fall and extends into winter, it
may be necessary to import suitable wet weather structural fill. For this purpose, we recommend
importing a clean granular material that meets the following grading requirements.
Maximum Aggregate=3 inches
U.S. Sieve Size Percent Passing
No. 4 75 maximum
No. 200 5 maximum*
*Based on the 3/4 inch fraction
Before use, Terra Associates, Inc. should examine and test all materials imported to the site for use as
structural fill.
Structural fill should be placed in uniform loose layers not exceeding 12 inches and compacted to a
minimum of 95 percent of the soil's maximum dry density, as determined by ASTM Test Designation
D-698 (Standard Proctor). The moisture content of the soil at the time of compaction should be within
two percent of its optimum, as determined by this ASTM standard. In non-structural areas, the degree
of compaction could be reduced to 90 percent.
4.4 Slopes and Embankments
All permanent cut and fill slopes should be graded with a finished inclination of no greater than 2:1
(Horizontal:Vertical). Interior detention pond slopes should be graded to 3:1 below the maximum
detained water level. When grading is complete, slope faces should be thoroughly compacted and
" track-walked and then appropriately vegetated or provided with other physical means to prevent
erosion. All fill placed for embankment construction should meet the requirements described in the
Structural Fill section. Subgrades should be prepared as discussed in the Site Preparation and Grading
section. Structural fills placed over existing slopes of 20 percent or greater should be keyed and
benched into competent native slope soils. A typical slope key and bench configuration is shown on
Figure 3.
Page No.4
July 11, 1997
Project No. T-3685
Final grades at the top of the slopes must promote surface drainage away from the slope crest. Water
should not flow uncontrolled over the slope face. If it is necessary to direct surface runoff towards the
slope, it should be controlled at the top of the slope, piped in a closed conduit or an appropriately lined
channel installed on the slope face, and taken to an approved point of discharge beyond the slope toe.
4.5 Excavations
All excavations at the site associated with confined spaces, such as utility trenches and lower building
levels, must be completed in accordance with local, state, or federal requirements. Based on current
Occupational Safety Health Administration (OSHA) regulations, the majority of the site soils consisting
of silty sand outwash would be classified as Group C soils. The glacial till encountered at Test Pit TP-1
is considered Group A soil.
For excavations more than four feet and less than 20 feet in depth, side slopes should be laid back at a
minimum slope inclination of 1.5:1. Where till is encountered underlying the sand deposits,
excavations in the till may be sloped at .75:1. If there is insufficient room to complete excavations in
this manner, you may need to consider using temporary shoring to support the excavations.
The above information is provided solely for the benefit of the owner and other design consultants, and
should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. It
is understood that job site safety is the sole responsibility of the project contractor.
4.6 Foundations
Foundations may be supported on competent native soils or on structural fills placed and compacted on
competent native soils as described in the Site Preparation and Grading section. Foundations exposed
to the weather should be a minimum of 18 inches below final exterior grades. Interior foundations can
be constructed at any convenient depth below the floor slab.
M Foundations can be dimensioned for a net allowable bearing capacity of 2,000 pounds per square foot
(psf). For short-term loads, such as wind and seismic, a 1/3 increase in this allowable capacity can be
used. With structural loading as anticipated and this bearing stress applied, estimated total settlements
are about one inch and less.
For proportioning foundations to resist lateral loads, a base friction coefficient of 0.4 can be used.
" Passive earth pressure development acting on the side of the footing and buried portion of the
foundation stem wall can also be considered. We recommend calculating this lateral resistance using an
equivalent fluid weight of 350 pounds per cubic foot(pcf). We recommend not including the upper one
foot of soil in this computation because it can be affected by weather or disturbed by future grading
activity. This value assumes the foundation will be constructed neat against competent native soil or
backfilled with structural fill as described in the Site Preparation and Grading section. The passive
value recommended includes a safety factor of 1.5.
Page No. 5
July 11, 1997
Project No. T-3685
4.7 Slab-on-grade Construction
Slab-on-grade floors may be supported on a subgrade prepared as recommended in the Site Preparation
and Grading section. Immediately below the floor slab, we recommend placing a four-inch layer of
clean, free-draining sand or gravel that has less than three percent fines passing the No. 200 sieve. This
will prevent wetting of the floor slab due to capillary movement of water through the underlying soil.
Where moisture by vapor transmission is undesirable, a durable polyethylene vapor barrier should also
be installed. This vapor barrier should be placed on the capillary break layer and then covered with one
to two inches of clean, moist sand to prevent damage during construction and to aid in uniform curing
of the concrete floor.
4.8 Lower Level Walls and Retaining Walls
The magnitude of earth pressures developing on lower level walls or retaining walls will partly depend
on the wall backfill. We recommend placing and compacting wall backfill as structural fill. To prevent
development of hydrostatic pressure, subsurface drains must be installed behind all walls. Figure 4
shows a typical recommended retaining wall drainage detail.
With proper wall backfill and drainage, we recommend designing unrestrained walls for an active earth
pressure imposed by an equivalent fluid weighing 35 pcf. For restrained walls, an additional uniform
lateral pressure of 100 psf should be added. These values assume a horizontal backfill condition and
that no other surcharge loading, such as traffic, sloping embankments, or adjacent buildings will act on
the wall. If such conditions will exist, the imposed loads must be included in the wall design. Friction
at the base of foundations and passive earth pressures will provide resistance to these lateral loads.
Values for these parameters are provided in the Foundations section.
4.9 Rockeries
In general, rockeries are not considered engineered retaining wall features. They are primarily used to
face soils exposed along inherently stable cuts and protect them from erosion.
In our opinion, soil conditions at the site would not be suitable to face with rockery construction at a
height of greater than four feet. If planned grading results in vertical grade breaks greater than four
feet, they should be supported with retaining wall construction designed in accordance with
recommendations outlined in the preceding section.
4.10 Drainage
Final exterior grades should promote free and positive drainage away from the building sites at all
times. Water must not be allowed to pond or collect adjacent foundations or within immediate building
areas.
Page No. 6
July 11, 1997
Project No. T-3685
We recommend providing a minimum drainage gradient of three percent for a minimum distance of ten
feet from building perimeters, except in paved locations. In paved locations, a minimum gradient of
two percent should be provided unless provisions are included for collection and disposal of surface
water adjacent the structures.
Roof gutter drains should be tightlined away from the structure and not tied to the wall or perimeter
foundation drains. Drains and surface runoff collected from impervious surfaces should be tightlined to
discharge at an approved location, taking care not to impact adjacent slopes and properties.
4.11 Utilities
Utility pipes should be bedded and backfilled in accordance with American Public Works Association
(APWA) or City of Renton specifications. At minimum, trench backfill should be placed and
compacted as structural fill, as described in the Structural Fill section.
4.12 Pavements
Pavements should be constructed on subgrades prepared as described in the Site Preparation and
Grading section. However, regardless of the degree of relative compaction achieved, the subgrade must
be in a firm and relatively unyielding condition prior to paving. The subgrade should be proofrolled
with heavy construction equipment to verify this condition.
Tile pavement design section is dependent on the supporting capability of the subgrade soils and the
traffic conditions to which it will be subjected. For traffic consisting mainly of light passenger and
commercial vehicles with only occasional heavy traffic in the form of moving trucks and trash removal
vehicles, and with a stable subgrade prepared as recommended, we recommend the following pavement
sections:
• Two inches of asphalt concrete(AC) over six inches of crushed rock base (CRB)
• Two inches of AC over four inches of asphalt treated base(ATB)
Paving materials used should conform to Washington State Department of Transportation (WSDOT)
specifications.
Long-term pavement performance will depend on surface drainage. A poorly-drained pavement section
will be subject to premature failure as a result of surface water infiltrating into thesubgrade soils and
reducing their supporting capability. For optimum pavement performance, we recommend surface
drainage gradients of no less than two percent. Also, some degree of longitudinal and transverse
cracking of the pavement surface should be expected over time. Regular maintenance should be
planned to seal cracks when they occur.
Page No. 7
July 11, 1997
Project No. T-3685
5.0 ADDITIONAL SERVICES
Terra Associates, Inc. should review the final design and specifications in order to verify that earthwork
and foundation recommendations have been properly interpreted and incorporated into the project
design and constriction. We should also provide geotechnical services during construction in order to
observe compliance with the design concepts, specifications, and recommendations. This will allow for
design changes if subsurface conditions differ from those anticipated before the start of construction.
We request a notice of two working days minimum be given to schedule our services during
construction.
6.0 LIMITATIONS
This report is the property of Terra Associates, Inc. and was prepared in accordance with generally
accepted geotechnical engineering practices. This report is intended for specific application to the
Tharp Property project and for the exclusive use of Stafford Homes and their authorized representatives.
No other warranty, expressed or implied, is made.
The analyses and recommendations presented in this report are based upon data obtained from the test
pits excavated on-site. Variations in soil conditions can occur, the nature and extent of which may not
become evident until construction. If variations appear evident, Terra Associates, Inc. should be
requested to reevaluate the recommendations in this report before proceeding with construction.
Page No. 8
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REFERENCE: THE THOMAS GUIDE, KING COUNTY, WASHINGTON, PAGES 596 AND 626, 1997 EDITION.
VICINITY MAP
gTERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
•' Geotechnical Consultants Proj. No.3685 Date JUNE 1997 Figure 1
NE. 36th Street
TP-1 I I TP-2
t I i I
I I
� I
' TIP-3
I TP-4 \ APPROXIMATE SCALE
120 0 120 240 feet
I
I \� LEGEND:
I �
j APPROXIMATE TEST PIT LOCATION
I
TP-5 i I
I I �
TP-9
REFERENCE:
UNTITLED AND UNDATED PLAT MAP PROVIDED
BY CLIENT
I
® i i
I NOTE:
TP-6 I TP-7 THIS PLAN WAS PREPARED USING THE REFERENCED
TP-8 SITE PLAN AS A BASE. ALL LOCATIONS AND
DIMENSIONS SHOULD BE CONSIDERED APPROXIMATE.
i I THIS PLAN IS NOT TO BE USED FOR CONSTRUCTION
PURPOSES.
I
I
EXPLORATION LOCATION PLAN
TERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants 1proj. No.3685 Date JUNE 1997 Figure 2
SLOPE TO DRAIN
NEW STRUCTURAL FILL
MAXIMUM SLOPE GRADIENT: 2:1(H:V) —
2
EXISTING
GRADE i
TYPICAL BENCH —
,,�:. MAY REQUIRE SUBDRAIN IF SEEPAGE
CONDITIONS ARE INDICATED
GRADE AFTER THE REMOVAL OF
• . TOPSOIL AND OTHER LOOSE SOILS
KEY CUT AND TOE DRAIN —
4" DIAMETER PERFORATED PIPE ENVELOPED
IN 1 cu.ft. 3/4" DRAINAGE GRAVEL
NOT TO SCALE
NOTES:
1. SLOPE SHOULD BE STRIPPED OF TOPSOIL AND UNSUITABLE SOILS PRIOR TO PLACING ANY FILL.
2. "BENCHES" SHOULD BE A MINIMUM OF 8 FEET WIDE.
3. "KEY" SHOULD BE MINIMUM 2 FEET DEEP AND 8 FEET WIDE, EXTENDING THE FULL LENGTH OF
THE SLOPE FACE.
4. FINAL SLOPE FACE SHOULD BE DENSIFIED BY COMPACTION.
5. PLANT OR HYDROSEED SLOPE FACE TO REDUCE EROSION POTENTIAL.
6. ALL STRUCTURAL FILL SHOULD BE COMPACTED TO 95% OF SOILS MAXIMUM DRY DENSITY PER
ASTM D-698 (STANDARD PROCTOR).
GENERAL SLOPE FILL DETAIL
9OTERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No.3685 Date JUNE 1997 1 Figure 3
12" MINIMUM WIDE
FREE—DRAINING GRAVEL
SLOPE TO DRAIN
1 r
17
EXCAVATED SLOPE
(SEE REPORT FOR
= APPROPRIATE
' INCLINATIONS)
COMPACTED STRUCTURAL
BACKFILL
�•r
.......... % % 1 r OVER THE PIPE
4 DIAMETER PVC Y BELOW THE PIPE
PERFORATED PIPE
NOT TO SCALE
RETAINING WALL DRAINAGE DETAIL
TERRA THARP PROPERTY
ROGeotechnical
ASSOCIATES
RENTON, WASHINGTON
Consultants Proj. No. 3685 Date JUNE 1997 figure 4
APPENDIX A
FIELD EXPLORATION AND LABORATORY TESTING
Tharp Property
NE 36th Street and 112th Place SE
Renton,Washington
On June 19, 1997, we performed our field exploration using a trackhoe. We explored subsurface soil
conditions at the site by excavating nine test pits to a maximum depth of 13 feet below existing grade.
The test pit locations are shown on Figure 2. The test pit locations were approximately determined by
pacing and visual references from existing property lines and site features. The Test Pit Logs are
presented on Figures A-2 through A-6.
A geotechnical engineer from our firm conducted the field exploration and classified the soil conditions
encountered, maintained a log of each test pit, obtained representative soil samples, and observed
pertinent site features. All soil samples were visually classified in accordance with the Unified Soil
Classification System described on Figure A-1.
Representative soil samples obtained from the test pits were placed in closed containers and taken to our
laboratory for further examination and testing. The moisture content of each sample was measured and
is reported on the Test Pit Logs. Grain size analyses were performed on selected samples, the results of
which are shown on Figures A-7 through A-10.
Project No. T-3627
MAJOR DIVISIONS LETTER TYPICAL DESCRIPTION
SYMBOL
Clean GW Well-graded gravels, gravel-sand mixtures, little or no
GRAVELS Gravels fines.
CD (less than GP Poorly-graded gravels, gravel-sand mixtures, little or
O 2 N More than 5/a fines) no fines.
U) in 50% of coarse
Silty gravels, gravel-sand-silt mixtures, non-plastic
0 m fraction is Gravels GM fines.
W a) > larger than No. with fines
Z Co �, 4 sieve
Q E o GC Clayey gravels, gravel-sand-clay mixtures, plastic fines.
N Clean SW Well-graded sands, gravelly sands, little or no fines.
o SANDS Sands
� Z (less than Poorly-graded sands or gravelly sands, little or no
c More than 5% fines) SP fines.
Q 50% of coarse
Q o"- fraction is SM Silty sands, sand-silt mixtures, non-plastic fines.
U smaller than Sands
No. 4 sieve with fines
SC Clayey sands, sand-clay mixtures, plastic fines.
Inorganic silts, rock flour, clayey silts with slight
� o SILTS AND CLAYS ML plasticity.
(Do
O CU N CL Inorganic clays of low to medium plasticity, (lean clay).
E o a) Liquid limit is less than 50%
0 �Z N
0
OL Organic silts and organic clays of low plasticity.
Z LOMa)
< `.(D M H Inorganic silts, elastic.
O = aD SILTS AND CLAYS
W m E CH Inorganic clays of high plasticity, fat clays.
_Z 0 En Liquid limit is greater than 50%
ILLOH Organic clays of high plasticity.
HIGHLY ORGANIC SOILS PT Peat.
DEFINITION OF TERMS AND SYMBOLS
w Standard Penetration 2" OUTSIDE DIAMETER SPLIT
Density Resistance in Blows/Foot I SPOON SAMPLER
ty
G Very loose 0-4 2.4" INSIDE DIAMETER RING SAMPLER
o Loose 4-10 T OR SHELBY TUBE SAMPLER
Medium dense 10-30
z Dense 30-50 1 WATER LEVEL (DATE)
Q Very dense >50
Tr TORVANE READINGS, tsf
Standard Penetration Pp PENETROMETER READING, tsf
Consistency Resistance in Blows/Foot DD DRY DENSITY, pounds per cubic foot
o�
v Very soft 0-2 LL LIQUID LIMIT, percent
o` Soft 2-4
I— Medium stiff 4-8 PI PLASTIC INDEX
_J
0) Very stiff 6-2 N STANDARD PENETRATION, blows per foot
Hard >32
- UNIFIED SOIL CLASSIFICATION SYSTEM
TERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants
Proj. No. T-3685 Date JUNE 1997 Figure A-1
Test Pit No. TP-1
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content
0 Forest Duff, roots to 2 feet.
Brown SILTY SAND, fine, scattered gravel and cobbles, medium dense
to dense,very moist. Till-like. (SM)
5 Sand is more cemented from 5 feet.
Gray-brown silty SAND with gravel,fine,very dense, very moist.
Glacial Till. SM
10 Test pit terminated at 9 feet.
No groundwater seepage encountered.
15
Test Pit No. TP-2
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content
0
Forest Duff and roots.
Brown silty SAND,fine, loose to medium dense, moist to very moist. (SM)
5 Gray-brown and rust-mottled silty SAND, fine, medium dense to dense,
very moist. (SM)
Becomes wet and increasingly siltier.
10
" Test pit terminated at 11.5 feet.
No groundwater seepage encountered.
15
_ TEST PIT LOGS
TERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3685 Date JUNE 1997 Figure A-2
Test Pit No. TP-3
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content
Forest Duff, roots to 3 feet.
Brown and slightly rust-mottled silty SAND, fine, occasional boulder and
scattered gravel, many seams of cleaner sand, some cementation,
medium dense, moist to very moist. (SM)
5 Gray-brown silty SAND, fine, occasional silt seam, medium dense to
dense,very moist to wet. (SM)
10
Test pit terminated at 10 feet.
No groundwater seepage encountered.
15
Test Pit No. TP-4
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content
Q Forest Duff, 3 inches. Brown silty SAND with organics, loose to medium
dense, moist. SM
Brown to gray-brown silty SAND,fine,trace gravel,some cementation,
medium dense, moist to very moist. Till-like. (SM)
5
+ Gray-brown silty SAND,fine,occasional seams of silt with perched water
in sand seam above, medium dense to dense, moist.
10
Test pit terminated at 12 feet.
No groundwater seepage encountered.
15
_. TEST PIT LOGS
TERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3685 Date JUNE 1997 Figure A-3
Test Pit No. TP-5
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content
Forest Duff and roots,consisting of organic soilty sand, loose to medium
dense, moist to very moist. (SM)
Gray and brown and mottled silty SAND,fine, occasional gravel, medium
dense,very moist to wet. (SM)
5
Gray SAND with silt,fine, medium dense to dense,very moist to wet.
(SP-SM)
10
Test pit terminated at 10 feet.
No groundwater seepage encountered.
15
Test Pit No. TP-6
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content
0
Brown SAND with silt, fine, roots to 3 feet, loose to medium dense,
moist to very moist. (SP-SM)
5— Gray and mottled SILT,trace to little sand, stiff to very stiff,moist to
very moist. (ML)
Gray SAND with silt,fine to medium, medium dense, moist. (SP-SM)
10
Test pit terminated at 12 feet. -
No groundwater seepage encountered.
15
TEST PIT LOGS
TERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3685 Date JUNE 1997 Figure A-4
Test Pit No. TP-7
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content
Forest Duff, 3 inches.
Brown silty SAND,fine, roots to 2 feet, one tree root at 5 feet, occasional
silt seams, loose to medium dense, moist to very moist. (SM)
5 Becomes brown to gray-brown and medium dense to dense,
one boulder at 8 feet.
Becomes gray.
10
Test pit terminated at 12 feet.
No groundwater seepage encountered.
15
Test Pit No. TP-8
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content
0
Brown silty SAND,fine, roots and organics to 3 feet,one root stump at
5 feet, loose,very moist.
5
Light-brown silty SAND,fine, medium dense to dense, moist to
very moist. (SM)
Few seams of silt.
10
Gray SAND with silt, fine, medium dense to dense, moist. (SP-SM)
.+r
Test pit terminated at 13 feet.
15
TEST PIT LOGS
TERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
Geotechnical Consultants Proj. No. T-3685 Date JUNE 1997 Figure A-5
Test Pit No. TP-3
Logged by: ABK
Date: 6/19/97
Depth Moisture
(ft.) Soil Description Content(%)
Forest Duff, 2 inches.
Gray-brown silty SAND, fine, medium dense, moist. (SM)
5
Medium dense to dense, moist to very moist.
10
Test pit terminated at 10.5 feet.
No groundwater seepage encountered.
15
y
TEST PIT LOGS
TERRA THARP PROPERTY
ASSOCIATES RENTON, WASHINGTON
�` Geotechnical Consultants Proj. No. T-3685 Date JUNE 1997 Figure A-6
SIEVE ANALYSIS HYDROMETER
SIZE OF OPENING IN INCHES • •1GRAIN SIZE IN MM
gm�Olfmm�MEOW, R111mim
Moisture
•
•
® :• •.• 1 • ® Description
Content
• 1silty SAND
• : 1silty SAND
SIEVE ANALYSIS HYDROMETER
SIZE OF I• GRAIN SIZE IN MM
Im
• .I �Hr�r�H■r■r1■�r!•H�����5:��11■H�r��■H■■H��H�
.1 �rrr■r�r�rr■■r■H■rrir■fir■�������■r■Hrr��■■■■■Hr�rl•HH �1 .•
. 1 �����■ter■■�����������■����■■■■■���� /
��r■r��■r/r■����r�����u��■110 HM�■■■■■HMMDescription Moisture
• • • • •• • • • • • • •
Content (%) ,im
•
•
•
® :• ••• 1 .
1silty SAND
• 1silty SAND with gravel
SIEVE ANALYSIS HYDROMETER ANALYSIS
SIZE OF WHIJ!f:IR TOR>ORMOMMIJ.ItIMMORTIM •.
MUM a
CD
mm�l OM
MMM
•
Description
Content Mim
• 1:: �d�1�9��1►1�<d�L•1:r9��Il�IIll11,'��W�
•
® :• •.• 1 •
1 with silt
. 1 1
SIEVE ANALYSIS HYDROMETER ANALYSIS
-SIZE1 1•
•
•
® i• ••• 1 • ® Description
•Moisture- m�
1
mom
silty SAND
TERRA A. , t SSOCIAI rS, Inc.
Consultants in Geotechnical Engineering, Geology
and
Environmental Earth Sciences
July 10, 1997
Project No. T-3685
Mr. Rob Purser
Stafford Homes
16016 - 118th Place NE
Bothell, Washington 98011
Subject: Site Observations RFCFivFn
Tharp Property
NE 36th Street and 112th Place SE NOV �99�
Renton, Washington
D6VELUf-tvitN7 PLANNING
CITY OF RLNTON
Dear Mr. Purser:
As requested, we visited the subject property which is located southwest of the intersection of NE 36th Street and
1 12th Place SE in Renton. The purpose of our work was to complete a site evaluation to determine if wetland
conditions are present. Our scope of work included a site visit on June 19, 1997, at which time we completed our
site evaluation.
The subject property is an irregularly shaped parcel of approximately 12.8 acres located on the southwest corner
of the intersection of 112th Place SE and NE 36th Street in Renton. The site is presently undeveloped. Adjacent
properties to the north, west, and south are also undeveloped and forested. There are existing single-family
residences on properties to the west. Topographically, the property generally slopes down from the southeast
corner toward the north. A low ridge oriented in a north-south direction crosses the middle of the property. A
broad topographic swale runs along the west property line.
The site is forested in a mixed deciduous stand of big leaf maple and red alder with a sparse shrub understory
beneath the closed forest canopy. Indian plum, hazelnut, and vine maple are common understory shrubs with
some patches of Himalayan blackberry. Stinging nettle is the predominant herbaceous cover on the western
section of the property with sword fern common on the eastern section.
Soils on the property are mapped as Alderwood gravelly sandy loam. This mapping is not consistent with our site
observations. Soils we observed consisted of fine to medium silty sand to sand with silt. These soils are more
consistent with the Ragnar soils series which is also mapped north of the site. Soil colors are generally brown
(10YR4/4 or 10YR4/3).
12525 Willows Road, Suite 101, Kirkland, Washington 98034 • Phone (206) 821-7777
Mr. Rob Purser
July 11, 1997
These conditions are consistent across the property and within the topographic swale along the west property line
and in other shallow depressions. At the lowest point on the property in the base of theswale near the northwest
property corner, soils were brown (10YR4/4) with no mottling. Soils were moist to dry with no evidence of
surface water. Vegetation at this location is a dense patch of hazelnut with Himalayan blackberry.
It is our conclusion that there are no wetland conditions or other surface water features on the property or within
200 feet of the property boundaries.
If you have any questions or need additional information,please call.
Sincerely yours,
TERRA ASSOCIATES,INC.
-,I'."t P. %�U�
Garet P. Munger
Project Scientist
Project No. T-3685
Page No. 2