HomeMy WebLinkAboutGeoTech Assessment Review for BLD2003-01751 - BLD Engineering / Geo-tech Reports - 2/11/2004 i
MASON COUNTY
PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER
Shelton,Washington 98584
DATE: February 11`", 2004
INTER-DEPARTMENTAL COMMUNICATIONS
TO: Tammi Clark, DCD - Planner
FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. WO# PLG-04
SUBJ: Geo-Tech Assessment Review NAME: Korkendoll SFR na,Limerick Div 5, Lot#94
BLD2003-01751
Tammi,
The geotechnical assessment prepared for the proposed Kain Kirkendoll Single Family
Residence(SFR)has been received and reviewed by Public Works.
The assessment appears to dispel the need for further geotechnical investigation, conforms to
standards of engineering principles and practices for this time and place, and appears to conform
to the minimum requirements of DCD for geotechnical assessment reporting. The evaluation
raises no issues or concerns, and appears acceptable for the level of reporting required.
Recommendations contained in the report should be incorporated into the site's development.
The escape of silt or mud from the subject property constitutes a violation of both State and
County stormwater quality protection regulations, and could subject violators to fines and
penalties.
Please feel free to contact me at County extension 461 if you have any questions regarding these
comments, or if you feel any features need further discussion or attention.
Sincerely,
u�. z
ALL A. Tahja
File:H:IWPIGEOIAssessmentsIKirkendoll.doe
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Bradley-Noble Geotechnical Services
A Division of The Bradley Group, Inc.
PO Box 12267, Olympia WA 98508-2267
Phone 360-357-7883 9 FAX 360-754-4240 or 867-9307 I
e-mail: bradleynoble@juno.com
9 February 2004
Mr. Kain Kirkendoll FEB 10 2004
Washington Home Center
61 SE Ryan Road ?( rrt�trr. �, -�
Shelton, Washington 98584
Subject: Geotechnical assessment of the slope
stability and erosion potential and
their probable long-term effect on the
new residence proposed for Lot 94, Lake
Limerick No. 5 for I,VvAw c+.11 **6,1 Mason
County Tax Parcel Number 32127 54 00094 .
Dear Mr. Kirkendoll:
As requested, we visited the above lot to develop an
opinion on slope stability and erosion potential of
the site and their probable long-term influence on the
proposed construction. Our scope of work consisted of
a site visit, review of the available geologic
information, review of the proposed location of the
structure and drainfield provided to us by your firm,
and preparation of this report based on our
observations, research, and understanding of the type
of proposed construction.
The project site is located in the Lake Limerick
Development. The project includes lots served by
utilities and roadways . Storm drainage is provided by
drainage ditches constructed along the roadways . We
expect that the project was constructed in conformance
with the plans and specifications approved by Mason
County for this project at the time of project
development.
The locations of the proposed residence and drainfield
have been cleared. A crushed rock surface driveway
leads up to the building site from Kilmarock Road.
The septic design test holes were open. We found the
site to be of low relief. The grade up from
Kilmarnock Road to the building site has a slope of
about 9 to 10% . Grades in the building and drainfield
04020301
Page 1 of 3
04020301
Page 2 of 3
area are nearly level. The only steep slopes on this
property are associated with the cutting of drainage
ditches along property lines on Old Lyme Road to the
east and Kilmarnock Road to the north and west. These
cut slopes for the drainage ditches have a relief of
about four feet maximum and stand in the 1.5: 1
(horizontal to vertical) range.
Slopes on the north side of Kilmarnock Road and the
east side of Old Lyme Road are in the 15% or greater
range. There is a residence constructed on the slope
on Lot 74 . Field observation of the slopes suggest
that these slopes are presently stable and pose no
risk to this site.
Site soil profiles are exposed in the road cuts and
excavation for septic design test pits . In this area,
we find a few feet of Vashon recessional outwash sands
and gravels (Qvr) overlying Vashon subglacial till
(Qvt) . The thickness of the outwash sands and gravels
can vary, but is typically less than six feet in this
area. At this site, the exposures suggest that the
thickness of the outwash is less than four feet. The
thickness of the Vashon subglacial till varies, but we
expect in this area that it is at least thirty feet or
more.
Subglacial till is for all practical purposes
impermeable. Flows of water may develop at the
contact of the outwash sands and gravel and the
impervious subglacial till during periods of heavy or
prolonged rainfall. Seepage from cut faces can
develop during these events when the contact is
exposed. We do not expect that seepage will have any
adverse effect on the proposed construction. Ground
water is not an issue at this site.
Our interpretation of site geology is consistent with
Plate 1 of the Water-Supply Bulletin 29 for
Southeastern Mason County, Washington by John B. Noble
and Dee Molenaar. To verify our interpretation that
the slopes in the project area are stable, we reviewed
Relative Slope Stability of Southern Hood Canal Area,
Washington by Mackey Smith and R.J. Carson published
by the Washington Department of Natural Resources
1977 . We find that this area is considered to be
stable because it is underlain by subglacial till.
i
04020301
Page 3 of 3
Subglacial till has many engineering properties
similar to those of lean concrete and can stand
steeply with apparent stability and only slow erosion
occurring due to the weak cementing of the soil unit.
This opinion is consistent with our field observations
at this site.
Based on our field observations and research, it is
our opinion that the structure may be placed at the
location indicated on the site plan provided to us
with no risk of slope failure or erosion of the slope
affecting the foundations . Natural slope angles are
less than the angle of internal friction for the soils
forming the slopes in the area. When the angle of
internal friction is less than the slope angle, slope
stability is inferred.
As part of the site development work, control of storm
water from impervious surface must be addressed.
Concentrated flows can create erosion channels and
accelerate surface erosion with silt-laden water
flowing off the site. We also recommend that the
grade around the residence be constructed so that
positive drainage away from the structure is
provided. A minimum of a 2% slope for at least five
feet is recommended.
Based on our work and understanding of the area
geology and slope stability history, we do not
consider that preparation of a geotechni.cal report is
required for this project.
If you have any questions, or if we may be of
additional service to you and your client on this
project, please contact us at our Olympia office.
Cordially,
BRADLEY-NOBLE GEOTECHNICAL SERVICES
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David C. Strong, L.E.G.
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DAVID C. STRONG