HomeMy WebLinkAboutRS_GeoTechnical Report - 212 S. 20th Place, Renton - Karen Lang_v1
13705 Bel-Red Road · Bellevue, Washington 98005
Phone 425/649-8757 · Fax 425/649-8758
August 10th, 2020 G-5204
Ms. Karen Lang
212 – S 20th Pl
Renton, WA
Subject: Geotechnical Evaluation
Backyard Deck
212 – S 20th Pl
Renton, WA
Dear Ms. Lang,
Per your request, GEO Group Northwest, Inc. has completed a geotechnical evaluation of the
backyard deck at the above-subject property in Renton, Washington.
SITE DESCRIPTION
The above-subject property is a currently occupied, single-family residence southwest of the
interchange of SR-167 and I-405, in Renton, Washington, as illustrated in Plate 1 – Site location
Map. The property is pentagon shaped. It comprises 5,011 square feet, and generally slopes
down to the north, with inclinations increasing near the north property line. The northern
property line borders a parcel approximately 2-acres in size. The west and east property lines
border single-family residences and the southern property line opens South 20th Place.
Construction of a deck located at the northern extent of the site has been started earlier this year,
but is currently halted per the direction of the City of Renton.
GEOLOGIC OVERVIEW
According to published geologic mapping of the area, the site is underlain by shallow bedrock
known as the Renton Formation. The formation is composed of arkosic sandstone, mudstone,
and shale, and is interpreted to be of continental origin.
SITE RECONNAISSANCE
On July 22nd, 2020, Mr. William Chang, Principal Engineer from our firm, visited the site to
perform a visual reconnaissance of the property and investigate the subsurface soil conditions.
August 10th, 2020 G-5204
212 – S 20th Pl, Renton, WA Page 2
GEO Group Northwest, Inc.
We evaluated the deck construction during our visit. The deck is well-built and is supported by
timber posts and cylindrical concrete footings which are underlain by shallow bedrock. No signs
of settling were observed at the new deck or in the house when laser level measurements were
conducted. A plan of the deck can be found in Appendix A.
SUBSURFACE CONDITIONS
We observed dense soils at the surface within the subject site. A ½-inch diameter probing rod
was used to confirm the density of the soils. We interpret the dense soils in the area as
weathered bedrock from the Renton Formation.
CONCLUSIONS
We understand that construction of the subject backyard deck has been halted as of June 22nd,
2020 due to the lack of a building permit. After investigation of the deck construction and
subsurface condition, it is our opinion that the deck is well-supported and bears on dense,
shallow bedrock. The risk of the backyard deck adversely affecting the subject or neighboring
properties is very low.
LIMITATIONS
The findings and recommendations stated herein are based on field observations, our experience
on similar projects and our professional judgment. The recommendations presented herein are
our professional opinions derived in a manner consistent with the level of care and skill
ordinarily exercised by other members of the profession currently practicing under similar
conditions in this area and within the project schedule and budget constraints. No warranty is
expressed or implied. In the event that site conditions are found to differ from those described in
this report, we should be notified so that the relevant recommendations in this report can be
reevaluated and modified if appropriate.
August 10th, 2020 G-5204
212 – S 20th Pl, Renton, WA Page 3
GEO Group Northwest, Inc.
CLOSING
We appreciate the opportunity to provide you with geotechnical engineering services for this
project. Please do not hesitate to contact us if you have any questions regarding this report.
Sincerely,
GEO Group Northwest, Inc.
Garrett Dean, G.I.T. William Chang, P.E.
Staff Engineering Geologist Principal Engineer
Plates and Attachment:
Plate 1 – Site Location Map
Appendix A – Deck Plan
Source: King County iMap
SCALE NONE DATE 8/10/2020 MADE GD CHKD WC JOB NO.G-5204 PLATE 1
SITE LOCATION MAP
SINGLE-FAMILY RESIDENCE
212 - S 20TH PL
RENTON, WA
Geotechnical Engineers, Geologists, &
Environmental Scientists
GEO Group Northwest, Inc.
PROJECT SITE
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