20080512095245.pdf" LANDAU
ASSOCIATES
14
TECHNICAL MEMORANDUM 11WRONMENTAL I GE=HMCAL I NATURAL RESOURCES
TO: Jeannine Graf, Building Official
City of Edmonds Building Department
FROM: Dermis R. Stettler, P.E.
Chad McMullen, P.E.
DATE: May 9, 2008
RE: GEOTECHNICAL PEER REVIEW
COOPER RETAINING WALLS - RESUBMITTAL
7306164T" PLACE SW
EDMONDS, WASHINGTON
INTRODUCTION
This technical memorandum provides our geotechnical peer review comments for a resubmittal of
technical documents and plans submitted to the City of Edmonds (City) for the proposed retaining walls
at the Cooper single family residence. Landau Associates provided a geotechnical peer review of the
original submittal and our comments are summarized in a technical memorandum dated April 8, 2008.
The purpose of the geotechnical peer review was to review portions of the submittal package and
assess its compliance with City development and building permit requirements as contained in Edmonds
Community Development Code (ECDC) Chapter 23.80, and City of Edmonds Retaining Wall Permit
Submittal Requirements (as contained in City Handout B62). This geotechnical peer review was
accomplished in accordance with Task Order No. 08-05 of Landau Associates' On -Call Geotechnical
Engineering Services Agreement with the City.
We have received the following additional information that addresses our April 8, 2008 review
comments:
• Responses to Comments in Landau Associates 418108 Memo, Landslide Investigation and
Stabilization Recommendations, John Cooper Residence, 7306 - 164`h Place SW, Edmonds,
Washington, L & A Job No. 8,4010 letter report prepared by Liu & Associates, Inc. for John
Cooper, dated April 14, 2008.
• Slide Repair and Slope Stabilization, Plan Sheet SS -1 of 1, Revision 1 prepared by Liu &
Associates, Inc. for John Cooper Residence, dated April 14, 2008.
TECHNICAL REVIEW R Ek
, v
The following summarizes our technical review comments related to the resubmittal.
130 2nd Avenue South • Edmonds, WA 98020 (425) 778-0907 fax (425) 778-6409 www.landauinc.com
Slope Stability
Liu & Associates has provided additional information related to their opinions regarding the
cause of the landslide, the potential for deep-seated landslides, their understanding of landslide history on
the property, and their opinion on the improved condition following the proposed stabilization work. We
take no exception to this additional information.
Earth Pressures
Liu & Associates has provided additional information regarding the basis for their design.
However, the issue of available passive resistance raised in our April 8, 2008 review letter was not
addressed in their comments. The passive resistance question is copied from our April 8, 2008 letter and
is repeated below.
"The geometry of the passive wedges at the bottom of each wall tier is of
concern. The passive earth pressure provided in the geotechnical report and used for wall
design is consistent with level ground conditions only. For the lower wall, the ground
slopes steeply away from the wall and the available passive pressure would be
substantially reduced. In addition, because of the close proximity of the upper wall to the
lower wall, the passive pressure wedge of the upper wall would intersect with the lower
wall, potentially inducing greater load on the lower wall. The available passive
resistance should reflect the slope geometry within the passive wedge and the influence of
the nearby lower retaining wall".
Helical Anchors
No comments.
Site Drainage and Erosion Control
Liu & Associates has provided revisions to the plans to provide a permanent tightline connection
to the roof drain. It is not clear whether the tightline outfall will be connected to a public storm sewer
system or just discharge at the toe of the slope beyond the Cooper property line. If the tightline does not
discharge directly to the storm sewer system, the downslope conditions should be evaluated to confirm
that discharge of this water will not adversely impact downslope property.
The requirements for temporary erosion and sedimentation control measures, as required by the
provisions of ECDC 18.30, have not been fully addressed. Provisions for temporary erosion and
sedimentation control are not included in the retaining wall design plans. In accordance with ECDC
18.30.050, temporary erosion and sediment control measures need to address a number of issues in
519!08 k%Edmdatakprojects1074NI48 Cooper Ret WallkFi[eRmkRlCooper_PearReview-Resubmital_TM.doc LANDAU ASSOCIATES
2
addition to hydroseeding and temporary protection with plastic sheeting. For example, the plans have no
provision for sediment trapping (ECDC 18.30.050 ESC Minimum Requirement 9). The design plans
should include temporary erosion and sediment control measures to be employed during and after
construction, until permanent vegetation is established.
Inspections
Liu & Associates asks that the City outline the requirements for geotechnical inspection. These
requirements are already outlined in the Retaining Wall Permit Submittal Requirements (see City
Handout B62).
CLOSURE
This technical memorandum has been prepared for use by the City of Edmonds in evaluating the
adequacy of design documents submitted for a permit related to the proposed retaining walls for landslide
stabilization at the Cooper single family residence at 7306 164']'Place SW. The focus of this review was
the geotechnical aspects of the documents. The purpose of the review was to assess the adequacy of the
application documents for compliance with City requirements contained in ECDC 23.80, City of
Edmonds Retaining Wall Permit Submittal Requirements, and conformance with conventionally accepted
geotechnical engineering practices. This geotechnical peer review by Landau Associates does not lessen
the requirements for the applicant's geotechnical consultant and other design professionals to prepare an
appropriate design for the site conditions.
We appreciate this opportunity to be of service to the City. Please contact us if you have any
questions, or if we may be of further service.
DRSICTMIrgm
519108 15Edmdatalprojects%0741148 Cooper Ret WallkFi[eRmlRlCooper_PeerReview-Resubmital_TM.dor LANDAU ASSOCIATES
3