Concrete Wall Technical_Memorandum - GAF, PLLC.doc
GARY A. FLOWERS, PLLC
GEOLOGICAL & GEOTECHNICAL CONSULTING
Technical Memorandum
Date: May 5, 2016
To: Layne Beller Project Concrete Wall Installation
Providence Construction & Name: 704 Bell Street, Edmonds
Design BLD20151352
From: Gary Flowers Project No: 16014
Robert Pride
Subject: Rockery Replacement
At the time of our site visit a rockery along the south property line had been removed exposing a cut
slope that ranged from 3 to 4 feet tall. It is our understanding that the rockery was previously located
along the approximate western two-thirds of the slope face and the remaining approximate one-third at
the east end had been sloping ground but was cut back with the intent of extending a new rockery into
this area as well. City of Edmonds has determined that a rockery installation in this location will not be
permitted. As such, it will be necessary to install an alternative wall system. We understand that a cast
in place concrete wall will be used for this purpose. We recommend that the design include parameters
for a wall up to 5 feet tall, including about 12 inches of freeboard, which is placed at the toe of the
existing descending slope.
The exposed soils in the cut slope consist of native sand and gravely sand with little silt with some
loose organic fill soils overlying the native sediments. The native sediments are generally in a dense
condition but are looser on the east end where the recent cut was made.
With the adjacent steep slope immediately behind the wall, the new concrete wall should be designed
to resist an active equivalent fluid pressure of 60 pcf. A surcharge of 8H should be added to the wall
design for potential seismic impacts. An allowable soil bearing capacity of 2,500 psf may be used for
design purposes.
Passive resistance will be provided by the adjacent soils. All backfill soils around the foundation
should be compacted to a firm and unyielding condition. Provided the soils are suitably compacted a
passive pressure of 300 pcf should be used for design purposes. If additional passive resistance is
needed we suggest the structural engineer add a keyway to the design.
The wall should be provided with a drainage layer and footing drain. The drainage layer may be clean
crushed rock or washed drain rock that is 12 inches wide. The footing drain should be 4 inch
diameter, perforated PVC pipe surrounded by drain rock and wrapped with geotextile filter fabric.
Filter fabric should also be placed against the soil and wrapped over the top of the drainage layer.
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Phone: 206-417-7640 19532 12 Avenue NE, Shoreline, WA 98155-1106 F:206-686-3834
Technical Memorandum
704 Bell Street, Edmonds, WA
Page 2 of 2
Geotechnical inspection of the wall construction should be provided in order to verify compliance with
these recommendations. A field memo will be provided to you and the city of Edmonds following
construction of the rockery verifying suitable construction practices.
Please call if you have any questions regarding this matter.
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Phone: 206-417-7640 19532 12 Avenue NE, Shoreline, WA 98155-1106 F:206-686-3834