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be affected by disturbances caused during construction. In particular, erosion due to de-vegetation likely
poses the greatest risk at the site. We agree with Merit that risks due to erosion increase significantly
during the wet season.In our opinion, more detail is required regarding the type and extent of vegetation
restoration on the slope and this information should be incorporated directly into the project documents.
Merit may also want to consider delineating “no-work”zones on the slope in order to limit the extent of
vegetation removal and damage to existing vegetation that would need to be replaced. Given the
steepness of the slope and limited growing season before winter, the erosion control approach may need
to include fabricated erosion control products placed at key locations on the slope to inhibit erosion until
vegetation becomes reestablished.
Merit’s response does not specifywhatadditional repairswill be conducted, if any,forthe
undermined portions of a concrete pad located above the slide that is mentioned in their December 7,
2007 letter.
A specific erosion control and re-vegetation program(consistent with the requirements listed in
the“Site Drainage and Erosion Control” comments of our August 4, 2008 technical memorandum)
should be incorporated into the project documents. Repair recommendations for undermined portions of
the concrete slab should be developed, if warranted.
Pin Piles
Merit’s response includes specific pin pile refusal criteria and a minimum pile embedment length.
This response adequately addresses pin pilecomments raised in our August 4, 2008 technical
memorandum.
Soil Anchors
Weraised constructabilityconcerns in our August 4, 2008 technical memorandum regarding the
closely spaced soil anchors specified in Merit’s design.Constructability of the proposed design is
ultimately the responsibility of Merit, and is largely determined by the equipment and skill of the selected
contractor and construction sequence.
Slide Debris Removal
Merit’s response indicates that slide debris at the toe of the slope was removed. We agree that
this condition likely results in a lower factor of safety against sliding and makes repairs to the slope more
urgent.
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Site Drainage and Erosion Control
Based upon the documents we received during our peer review,it appears that Merit concluded
during their field reconnaissance thatsite drainagemay have played a significant role in causingthe
recently documentedslope instability at the subject propertiesOriginal permit documents, as well as
current requirements outlined in ECDC 23.80, prohibit stormwater discharge to the slope.
As discussed in our August 4, 2008 technical memorandum, correspondence between the City
Engineering andBuilding Departmentsrelated to the original building permit seems toindicate that site
drainage at 1205 Viewland Way was to be routed to the storm sewer locatedat the southwest corner of
that property. Based upon drainage pipes exposed in the slide, it appears that those requirements were
likely not met during original construction. In our opinion, it would be prudent to assess the routing and
dischargelocations for thevarious drains at 1201 and 1205Viewland Way in order to determine: 1)
whetherthose drains satisfy original or current permit requirements,and2)ifany of those drains in their
currentconfigurations pose additional risks to long term slope stability. It maybe prudent to extend this
evaluationto the irrigation system located at the topof the slope.Merit’s response does not indicate the
appropriateness or adequacy of the drain and discharge location for long-term use.
The adequacy of existing drainage installationsand their conformance to original or current
permit requirements should be established. If drainage installations are inadequate or not in
conformance with permit requirements, the design documents should include a permanent drainage
system that includes size, type, and location of collectors (such as catch basins or collection troughs),
pipe materials, pipe anchorage, energy dissipation fixtures, and an appropriate long-term discharge
location.
As recommended in our August 4, 2008 technical memorandum, the design plans should include
temporary erosion and sediment control measures to be employed during and after construction in
accordance with Chapter 18.30 ECDC.
Inspections
Merit acknowledgedtheowner requirements for arranging City inspections and for additional
special inspections by the Geotechnical Engineer of Record.
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LOSURE
This technical memorandum has been prepared for use by the City of Edmonds in evaluating the
adequacy of design documents and related correspondence submitted by Merit for a permit related to the
proposed retaining walls for landslide repairs and slope stabilization at 1201 and 1205 Viewland Way in
Edmonds, Washington. The focus of this technical memorandum was to review responses and additional
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information provided in a letter by Meritto the City dated August 7, 2008.The purpose of this continued
geotechnical review was to assess the adequacy of the application documents for compliance with City
requirements contained in ECDC 23.80, City Retaining Wall Permit Submittal Requirements, and
conformance with conventionally accepted engineering practices. This peer review 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.
DRS/CTM/rgm
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