Letter from Geotech Engineer.pdfMCOBALT
GEOSCIENCES
Date: November 12, 2019
Contractor: -
Observations:
Project: 17123 69th Place W
Location: Edmonds
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
Job No.: 2019-199
Weather: Clouds 55
At your request and authorization, Cobalt Geosciences, LLC was on site to observe the side sewer
extending from 69th Place W. toward the residence.
We understand that the side sewer has a steep pipe slope (20 percent) toward the street and that
the City requires some type of hold-down for the pipe. In this case, the trench backfill is about 2
feet over the pipe and in proposed landscaped areas.
There are several options to secure pipes in sloped areas. We recommend either utilizing 2 inch
diameter driven pipe piles with galvanized or other straps designed for this purpose, or concrete
dead man anchors (collar) over the pipe.
For option 1, two inch diameter Schedule 8o pin piles driven to refusal would be located on either
side of the pipe with mechanical or welded connections to a strap that extends over the top of the
pipe. Refusal is achieved with 3 cycles of 6o seconds per inch of embedment using a 140 pound
pneumatic hammer. We anticipate a pile depth of less than 5 feet in the glacial till.
For option 2, a collar of poured concrete may be used to secure the pipe. We recommend a
minimum collar width (along the pipe length) of 6 inches, extending at least 4 inches over the top
of the pipe and on the bedding materials on either side of the pipe. Concrete could consist of
3,000 psi mix or a minimum 2 sack lean mix.
We recommend spacing the anchor systems at no greater than 20 feet on center along the pipe
run in areas where backfill thickness is less than 3 feet.
Sincerely,
Cobalt Geosciences, LLC
�r
Phil Haberman, PE, LG, LEG
Principal
PH/sc