HomeMy WebLinkAboutParcel 12228-44-00020 Deleted SPL95-00058 - GEO General - 8/24/1985 N
GARY YANDO,DIRECTOR
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DEPARTMENT OF COMMUNITY DEVELOPMENT
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z o T z PLANNING - SOLID WASTE - UTILITIES
y BLDG. I • 411 N. 5TH ST. • P.O. BOX 578 N Y
1864 SHELTON,WA 98584 • (360) 427-9670
August 24, 1995
To: Jerry Hauth/Alan Tahja
From: Randy Neff
RE: Geo-assessment for Robin Coleman
The Mason County Department of Community Development
required a geo-whatever for this site due to its location within
a landslide hazard area, per Ord.#777 -93 . Would you please
review this document.
Thank You
Randy Neff
Recycled �'�v
Bradley-Noble Geotechnical Services
A Division of The Bradley Group, Inc.
2401 Bristol Court SW, PO Box 10267, Olympia WA 98502
Phone 360-357-7883 FAX 360-754-4240
21 August 1995 (4'
a
Robin & Helene Coleman
1720 Union Street
Shelton, Washington 98584 -
Subject: Evaluation of your proposed large lot
subdivision, Mason County Tax Parcel
Number. ;2228--44-00020, as being in a
Landslide Hazard Area as defined in
Section 17 . 01 . 100 of the Interim
Resource Ordinance adopted by Mason
County.
Dear Mr. & Mrs . Coleman:
As requested, we have conducted a reconnaissance level
survey of the above property to determine the
possibility that it might be affected by future soil
movements . This letter will present our observations
and opinions based on this survey and on our research.
From our field discussion, we understand that part of
the property extends west of State Highway 302 and is
between the highway and Puget Sound. We also
understand that this property will be held for joint
access to the beach by the property owners of your
four lot subdivision and that no construction is
proposed on this piece of the property. The area of
u
�_11 tl�f. riu Cis N?. _ si f:^ -4 S?'?to
__ :.V r• s L•G {.��n111 � s`l
Highway 302 .
Construction of the highway has resulted in the
creation of artificially oversteepened slopes at the
west boundary lines for Lots 2 , 3, and 4 . We also
observed settling and sliding of the roadway in this
area. We expect that the cause of the roadway failure
is the result of poor construction practices during
the initial grading and also lack of drainage. This
failure is not expected to affect the upland area of
the project, although the common area to the west of
the roadway may be affected, especially if subgrade
stabilization work is done by the Washington State
Department of Transportation in the future.
95080801
Page 1 of 3
95080801
Page 2 of 3
Our on-site observations of the soils and slopes did
not indicate that the upland area comprising the four
lots is unstable. We found, exposed in the test pits,
soils that have high natural angles of internal
friction. We expect that the slopes are less than the
angle of internal friction for these soils, and thus
stability is inferred. The steep road cut for Highway
302 did not indicate that mass wasting processes other
than sheet washing were active.
Examination of the trees growing on this and adjacent
properties did not show that any significant soil
creep or mass wasting had occurred in the past. No
land forms associated with mass wasting were observed
on this or adjacent upland property. From the soils
exposed, we expect that this site has good
near-surface internal drainage which aids slope
stability.
The Coastal Zone Atlas, published by the Department of
Ecology in March 1980 , map MA-12 presents general
information on the site geology and an evaluation of
apparent slope stability. This area is considered to
be stable, a classification with which we are in
agreement .
We expect that construction of residences on these
lots will proceed by cutting benches into the slope.
We recommend a minimum setback of the foundation for
the structures of 50 feet from the present top of the
roadway embankment cut.
We also recommend that all storm water from impervious
su_faces be : ollected in-Lo a storm .eater disposal
system. Point discharge of storm water between the
residences and the top of the roadway cut is
discouraged, as it can create areas of localized
saturation and induce slope instability. Discharging
collected storm water into the existing roadway
drainage ditch on the east side of Highway 302 may
accelerate the settling and sliding of the roadway.
We did not observe any cross culvert under the
roadway, and the failure of the roadway may be in part
the result of saturation from water collected in this
ditch.
It is our opinion, based on our on-site observations
95080801
Page 3 of 3
and research, that this four large lot subdivision is
not in a landslide hazard area. Good construction
practices are required to ensure that construction
does not cause future slope instability. Collection
and disposal of storm water from impervious surfaces
is required to protect the slope from point discharge.
We do not believe that single-family residences,
constructed at the minimum recommended setback, will
be at risk of being adversely affected by soil
T1?O`Ie71''AI?tS on the S1C' ,c?. Tr:c '"1Sk' .::+i. tiiio c3i-LC wcjlliu
be no greater than the risk for existing residences
already constructed on the slopes and adjacent to this
property.
If you have any questions, or if we may be of
additional service to you, please contact us at our
Olympia office.
Cordially,
BRADLEY-NOBLE GEOTECHNICAL SERVICES
David C. Strong
Engineering Geologist