162ndStPark_ResubmitReviewTM.pdf
PR
LANEVIEW
We reviewed therevisedplans for the park development to assess their consistency with:our
May 5, 2008 review comments;geotechnicalrecommendations contained in the HWA Geosciences, Inc.
(HWA) report; and with the provisions of ECDC 19.10 and ECDC 23.80.The issues that we had
previously identified and their resolutions are outlined below:
·
The plans show a retaining wall andup to 10 ft of fill placedabove existing gradeson and
near the base of the slope on the park property. The park development plan considered in the
originalgeotechnical report did notaddress the effect of the proposed retaining wall and fill
on the slope stability.TherevisedHWA reportuses the results of slope inclinometer
monitoring and slope stability analyses to analyze the existing slope configuration and the
effect of a proposed buttress fill at the toe of the slope that has shown recent slope movement.
The stability analyses demonstrate an improvement in slope stability. Although the
configuration of the wall and fill currently planned is somewhat different than the slope
configuration analyzed in the revised geotechnical report, the beneficial effectof placing fill
near the toe of the slope should still be beneficial.
·
Theplans indicate that the retaining wall planned on the park property would be supported on
2-ft diameter augercast piles installed to a depth of 10 ft.The original submittal provided
limited information related to this design. The revised HWA report and the HWA
Memorandum dated April 1, 2008 address the geotechnical recommendations for the wall
support and those recommendations have been incorporated into the plans.
·
Theplannedretaining wallas shown on the original plansis composed of amodular block
wall, but thegeogrid or geotextile reinforcementof the backfill behind the wallthat was
recommended in the original HWA report was not shown.The resubmitted plans nowshow
geogrid reinforcement consistent with the HWA geotechnical report recommendations.
·
The original retaining wall details did not show how the drainage pipe behind the wall will be
connected to the site drainage system. This information is now shown on the resubmitted
plans.
·
Theoriginalgeotechnical report recommends a deep trench subdrain (8 to 10 ft deep) near the
toe of the eastern slope on the park property.The revised geotechnical report recommends a
4 to 5 ft deep trench drain.A subdrain is shown on the plans (Sheet L-4) with a note to see
the Civil Plansfor the invert elevations. The invert elevation information was not apparent
on the plan sheets that we were providedfor the original submittal and we are not able to find
that information in our current review of the resubmittal.Confirm that the slope drain is at
an appropriate location and depth consistent with the geotechnical report recommendations,
and provide invert elevations on the plans.
·
City requirements for retaining wall permits (see City Handout B62)and the provisions for
permits as contained in the City’s ESLHA documents outline the requirements for calling for
Building Inspections by the City during construction, and Special Inspection Requirements
that call for the Geotechnical Engineer of Record to monitor the construction to verify the site
conditions and construction and to submit Field Reports to the City.The requirements for
City Building Inspections and Special Inspections by the Geotechnical Engineer of Record
should be included on the design plans.
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·
PlansheetsL-14 through L-16 relate to irrigation. However, the City has identified that site
improvements that introduce water into the ground within the ESLHA (including watering or
irrigations systems) are prohibited (ECDC 19.10.070.D).The plans should be revised to
reflect this requirement.
GRR
EOTECHNICALEPORTEVIEW
Theoriginal geotechnical report did not reference or address the specific requirements of ECDC
19.10 or ECDC 23.80 related to projects within the North Edmonds ESLHA.We had recommended that
the HWA report be updated to address the landslide hazard discussion and background as required by
ECDC 19.10.The revised geotechnical report is not substantially different than the original report and
does not specifically reference or address the specific requirements of ECDC 19.10 or ECDC 23.80.
TherevisedHWA reporthasconsidered the results ofrecent slopeinclinometer readings and
addressedslope stability at the parkby specific analyses of the slope before andafter construction, as
requested in our previous review comments.
C
LOSURE
This technical memorandum has been prepared for use by the City of Edmonds in evaluating the
nd
adequacy ofconstruction documentsresubmitted forthe City’s 162 Street Park. Thefocus of this
review was the geotechnical aspects of the documents. The purpose of the review was to assess the
adequacy of the documents for compliance with City requirements contained inECDC 19.10,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.
DRS/rgm
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