HomeMy WebLinkAboutGeotech Letter for failed wallrs.
eotech elogissGroup Northwest, Inc.• & Environmental Specialists
January 20, 2021
Mr. Bryan White
Summit Horne of Washington
16000 Christensen Road, Suite 303
Tukwila, WA 98188
Email: BryanW3@summithomeswa.com
Subject: Canyon Terrace Development
Lot 12 Retaining Wall Failure
SE 192"d Street and 1241h Avenue SE
Renton, Washington
Reference: Rob Shuey email to Scott Mitchell
RE: Canyon Terrace Lots 12 & 13 Rear Retaining Wall
Dated September 24, 2020
Dear Mr. White,
G-4003
At your request, William Chang P.E. from GEO Group Northwest, Inc. visited the site on
November 23, 2020 to evaluate the stability of the backfill in the back of the cement block wall
slope at the back of Lot 12.
Based on our site visit, we confirmed that the backfill for the block wall behind Lot 12 consisted
of silty sand with gravel (till fill) that was loose and became saturated with the rains and was
pushing the block wall out. The block wall subsequently failed around December 20, 2020. On
January 5, 2021 we went to the site again and were made aware that a broken drainage line had
contributed a large amount of water to the backfill behind the block walls.
We had recommended that the geotechnical engineer be present at the site prior to the
construction of new walls to approve subgrades, block wall materials and backfill materials. We
recommend that all of the backfill behind the proposed block walls consist of free draining clean
crushed rock.
13705 Bel -Red Road • Bellevue, Washington 98005
Phone 425/649-8757 • Fax 4251649-8758
January 20, 2021 G-4003
Canyon Terrace Development Page 2
We also recommend that the drainage be improved above the block waII area, including but not
limited to repairing the broken drainage tightline, limiting the amount of surface runoff from
driveway above by placing a berm at the edge of the driveway and directing the water to a storm
catch basin.
Sincerely
GEO Group Northwest, Inc.
William Chang, P.E.
Principal
GEO Group Northwest, Inc.