REVIEWED BLD2023-1421+Geotechnical_Letter+11.8.2023_9.25.16_AM+3888201RECEIVED
Nov 09 2023
CITY OFEDMONDS BLD2023-1421 vo
DEVELOPMENT SERVICES
DEPARTMENT
September21, 2023 Earth Solutions NW LLC
ES-7291.02 Geotechnical Engineering, Construction
Observation/Testing and Environmental Services
Krista Carlson
7824 — 175t" Street Southwest
Edmonds, Washington 98026
Subject: Geotechnical Addendum II
Proposed Patio Block Wall
7824 — 175t" Street Southwest
Edmonds, Washington
Dear Krista:
As requested, Earth Solutions NW, LLC (ESNW) has prepared this letter for the proposed patio
block wall to be constructed adjacent to the recently constructed deck and building addition, and
for the restoration of the original slope grades. This letter is provided as an addendum to the
referenced geotechnical evaluation that was prepared for the recently constructed deck and
building addition.
Project Description
We understand that a new block wall is proposed to support a level patio area immediately
adjacent to the recently constructed building and deck addition. The retaining wall will be about
six feet in exposed height.
If the above design assumptions are incorrect or change, ESNW should be contacted to review
the recommendations provided in this addendum. ESNW should review the final design to verify
the geotechnical recommendations provided in this letter have been incorporated into the plans.
Proposed Block Wall
The proposed block wall will be installed immediately adjacent to the recently constructed deck
and building addition. Based on the referenced site plans, the grading will involve minor fills to
establish a level patio; the fill will be supported by the new block wall. The grading and
construction should be completed in general accordance with the recommendation in this letter,
the attached modular block wall design, and the referenced structural details. The design
recommendations include the following items:
• Proposed grading area should be bench cut into native soil.
• Engineered geofoam lightweight fill should be used for majority of fill placed in patio area.
• Up to two feet (in height) of structural fill can be placed at the top of the patio fill area.
• The top layer of geogrid should be anchored to the existing foundation per the referenced
structural details.
15365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 0 (425) 449-4704 • FAX (425) 449-4711
Krista Carlson ES-7291.02
September 21, 2023 Page 2
Based on the results of slope stability analysis (attached) and provided the construction is
completed in accordance with the design documents, the proposed project will not negatively
affect the factor of safety within the site and slope hazard area; additionally, there will be no new
geological hazards adjacent to the property related to this construction.
Restoration of Original Slope Grades
We understand that the recently constructed terraced block walls will be removed and the
backyard area of the subject property will be restored to the original slope grades per the
referenced demolition plan. We recommend the following for removal of the block walls and
restoration of the original slope grades:
• The terraced block walls should be removed from the top down.
• The facing blocks and reinforced soil zone should be removed concurrently; we
recommend not removing more than two feet of blocks (in height) or two feet of soil (in
height) prior to removing the other.
• The remaining original slope grades should be compacted to a firm and unyielding
condition.
• If fill placement is necessary to restore the original slope grades, the slope should be
bench cut to allow the fill to be placed and compacted on a level grade and in accordance
with the requirements of structural fill.
• The restored slope grades should be vegetated.
• Jute -matting (or similar) should be staked across the restored slope grade to provide
surficial erosion stability while the vegetation and root system is being established.
• Demolition and restoration work should not occur during periods of extended wet weather.
I imitatinnc
The recommendations and conclusions provided in this letter are professional opinions consistent
with the level of care and skill that is typical of other members in the profession currently practicing
under similar conditions in this area. A warranty is not expressed or implied.
Earth Solutions NW. LLC
Krista Carlson
September 21, 2023
ES-7291.02
Page 3
We trust this letter meets your current needs. Should you require additional information, or have
questions, please call.
Sincerely,
EARTH SOLUTIONS NW, LLC
.,'2023
Henry T. Wright, P.E.
Associate Principal Engineer
cc: Michel Construction, Inc.
Attention: Rob Michel
References:
• Geotechnical Evaluation, prepared by ESNW, ES-7291, dated September 9, 2020
• Modular Block Wall Designs and Notes, prepared by ESNW, dated March 13, 2023
• Hamby Addition and Demolition Plans, prepared by Michel Construction, Inc., Sheets A3
and P1, dated August 9, 2022
• Structural Details, prepared by Sound Structural Solutions Engineers, dated March 13,
2023
Earth Solutions NW. LLC