ZZ-1.pdfZipper Zeman Associates Inc.
Geotechnical and Environmental Consulting
J-2322
January 4, 2006
City of Edmonds
Development Services Department
121 Soh Avenue North
Edmond, Washington 98020
Attention: Ms. Theresa Umbaugh
Subject: Preliminary Geotechnical Review
Proposed Bui Residence
1610575 th Place West
Edmonds, Washington
Plan Review Number: 05-564
Dear Ms. Theresa Umbaugh;
As requested by the City of Edmonds, Zipper Zeman Associates, Inc. (ZZA) has begun
third -party geotechnical review for the above referenced project located within the Meadowdale
landslide hazard area in Edmonds, Washington. The purpose of this letter is to provide
preliminary review comments for response due to the complexity of the project. We were
provided with a set of the plans, including structural calculations, and the geotechnical report
prepared by LST Adapt, Inc, dated May 23, 2005.
Based on our review of the project geotechnical report, we have some concerns regarding
the slope stability analyses performed to model the existing and proposed conditions. Our
concerns are summarized below:
• It is our understanding, based on the Roger Lowe Associates (RLA) report, GeoEngineers
geotechnical report, and geotechnical reports prepared for adjacent lots within the
Meadowdale slide area, that the existing stability of the colluvial soils indicated is
marginally stable by engineering standards. GeoEngineers indicated that the existing
stability of slopes within a 30 percent probability landslide area is approximately 1.27 (up
from 1.17 by RLA). The LSI Adapt report indicates a factor of safety of 2.75, which
would correspond to over 100 percent increase in factor of safety and over 1000 percent
decrease in probability of a landslide (by methods suggested in RLA report). This would
suggest that the soils on site differ significantly from those described in the GeoEngineers
and RLA reports. We suggest that the stability analyses be reviewed and modified if
necessary.
The critical failure surface for the existing stability analysis extends into the "massive"
silt and clay. This would indicate either that the soil strength values for the colluvium
may be higher than described in the GeoEngineers and RLA reports or the limits of the
circle searches may be inhibiting the generation of more critical surfaces. We request
18905 33' Avenue West #117, Lynnwood, WA 98036 425-771-3304 Fax; 425-771-3549
Bui Residence — Edmonds, Washington
Job No. J-2322
January 4, 2006
Page 2
that additional justification of the soil values be provided and that the reasoning behind
the limits of the searchable surfaces chosen be provided.
• The Edmonds Community Development Code section 19.10.030-B refers to the site
evaluation checklist which contains geotechnical report guidelines and requires that
temporary slope conditions be considered in the stability analysis. We request that slope
stability analysis or analyses be provided for the proposed temporary slope cut
conditions.
• The factor of safety for the existing slope stability analysis was approximately 2.75, as
reported by LSI Adapt. The factor of safety for the proposed condition was
approximately 2.53. This indicates that there will be a decrease in stability; the amount
of decrease will depend on confirmation of the colluvium soil strength values referenced
above. Based on this information, it appears that additional stabilization measures need
to be undertaken such that there would be no decrease in stability. We request that this
issue be addressed by the applicant.
We trust that this letter meets your needs at this time. We will provide review comments
of the overall permit set of plans once the requested information is provided to us.
Respectfully Submitted
Zipper Zeman Associates, Inc.
VKn
StopheT. Hauck, P.E.
Project Engineer�� k
6711 -le- 6 ,
John E. Zipper, P.E
Principal
CC: LSI Adapt, Inc. — Mr. Rolf B. Hyllseth, P.E.
J-2322 Prelim Review Letter.doc