HomeMy WebLinkAboutEx14_Geotechnical_Letter_23081115365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 • (425) 449-4704 • FAX (425) 449-4711
Earth Solutions NW LLC
Geotechnical Engineering, Construction
Observation/Testing and Environmental Services
August 11, 2023
ES-4044.01
Charles Jackson
12815 Northeast 126th Place
Kirkland, Washington 98034
Subject: Response to Comments and Geotechnical Update
2223 Northeast 23rd Street
Renton, Washington
Reference: Earth Solutions NW, LLC
Infiltration Evaluation, ES-4044, dated July 15, 2016
City of Renton
Engineering Consolidated Comment Email, Jackson Short Plat, dated July 5, 2022
Renton Project Number PRE19-000170
Client Provided, Storm Drainage and Grading Plan, Sheets C1.0 through C2.3,
Dated January 18, 2022
Greetings, Charles:
In accordance with your request, Earth Solutions NW, LLC (ESNW) has prepared this letter
providing a response to comments provided by the City of Renton representatives. The comment
from the reviewer is cited, and the ESNW response follows.
City of Renton Comment – COR Maps indicates there are sensitive slopes on the property and
landslide hazard areas within 50 feet of the project site. The geotechnical report does not address
these items.
ESNW Response – City of Renton municipal code 4-3-050F (Submittal Requirements and Fees)
requires a geotechnical study shall be required where a geologic hazard is present on the site or
within 50 feet of the subject site. The site is not described as possessing an erosion hazard on
the city mapping for erosion hazards. The site is mapped as possessing a steep slope hazard
within the southern portion of the site, but sits at the toe-of-slope which ascends approximately
15 feet to the south. As the subject site is located at the toe-of-slope, there will be no increase
in surcharge on the slope which is described on the steep slope map.
EXHIBIT 14
RECEIVED
PLANNING DIVISION
05/29/2024AVanGordon
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Charles Jackson ES-4044.01
August 11, 2023 Page 2
Earth Solutions NW, LLC
The site is sited within 50 feet of a medium landslide hazard as described for west of the subject
project area. ESNW has provided the following assessment where City of Renton Code requires
the following:
ii. The required studies shall demonstrate the following review criteria can be met:
(a) The proposal will not increase the threat of the geological hazard to adjacent or abutting
properties beyond pre-development conditions;
(b) The proposal will not adversely impact other critical areas; and
(c) The development can be safely accommodated on the site.
ESNW prepared the referenced report for the site which included a project description,
subsurface conditions, geologic setting, groundwater observations, and an infiltration evaluation.
ESNW has reviewed the referenced maps demonstrating the subject steep slope complex off-
site (west) being of moderate landslide hazard. There are no critical areas mapped for the subject
site with the exception of the steep slope in the southern portion of the site which ascends to the
south and off-site. The subject site sits at the toe of a slope where in our opinion there is no
necessity for analysis of a critical area for the subject site as the planned re-development will not
result in an increase in loading on slopes on or around the subject site per ESNW review of the
site plans.
ESNW anticipates the site soils will adequately infiltrate vertically with little to no lateral migration
of the stormwater being introduced to the drywell based on observations of the subsurface.
ESNW should be retained to confirm the conditions within three to five feet of the bottom-of-
facility are free from silt lensing. ESNW recommends a note be added to the project plans stating
subsurface condition confirmation of the drainage characteristics of the receptor soils within
infiltration facilities must be undertaken during construction.
Were water to migrate laterally, the rockery drainage elements will intercept and vector away
from any downslope elements and outlet to an appropriate discharge point. This will act in some
ways as redundancy for site drainage.
A provision for overflow (catch basin) is provided in the design of the drywell based on our review.
In our opinion this is prudent and will aid to minimize the potential for overflow and sheeting of
water towards any downslope elements on and around the subject site.
In our opinion, if the subject infiltration facility performs as expected there will be no increase in
the threat of geological hazard adjacent or abutting properties beyond the pre-development
conditions. The proposed infiltration will not adversely impact other critical areas and can be
safely accommodated on the site given ESNW is provided the opportunity to observe the
installation of the subject facility and confirm the subsurface conditions as mentioned above.
City of Renton Comment – The provided geotechnical report was authored in 2016. Please
provide an updated report. If conditions have not changed an addendum authored by a
professional engineer is acceptable.
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Charles Jackson ES-4044.01
August 11, 2023 Page 3
Earth Solutions NW, LLC
ESNW Response – The subject site has not been changed in such a manner as to render the
subsurface information in the referenced infiltration evaluation as non-applicable since the time
of site exploration. As the referenced document was an infiltration evaluation it did not include a
seismic site class determination or foundation design parameters. As such, seismic and
foundation design recommendations are presented below.
Seismic Class Determination
The 2018 IBC recognizes the most recent edition of the Minimum Design Loads for Buildings and
Other Structures manual (ASCE 7-16) for seismic design, specifically with respect to earthquake
loads. Based on the soil conditions encountered at the test pit locations, the parameters and
values provided below are recommended for seismic design per the 2018 IBC.
Parameter Value
Site Class D
Mapped short period spectral response acceleration, SS (g) 1.434
Mapped 1-second period spectral response acceleration, S1 (g) 0.492
Short period site coefficient, Fa 1.000
Long period site coefficient, Fv 1.808
Adjusted short period spectral response acceleration, SMS (g) 1.434
Adjusted 1-second period spectral response acceleration, SM1 (g) 0.889
Design short period spectral response acceleration, SDS (g) 0.956
Design 1-second period spectral response acceleration, SD1 (g) 0.593
*Assumes medium dense soil conditions, encountered to a maximum depth of five feet bgs during the field
exploration, remain medium dense to dense to at least 100 feet bgs. Based on our experience with the project
geologic setting across the Puget Sound region, soil conditions are likely consistent with this assumption.
Foundations
Based on the subsurface information in the referenced ESNW letter, the proposed residential
structure can be supported on conventional spread and continuous footings bearing on
competent native soils, competent existing fill or new structural fill. Based on the soil conditions
encountered at the test sites, competent native soils suitable for support of foundations should
be encountered at depths of approximately two feet below existing grades in most areas. Where
loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction
of the soils to the specifications of structural fill, or overexcavation and replacement with structural
fill, may be necessary. ESNW should be retained during construction to confirm the suitability of
the new foundation subgrade and offer recommendations as necessary.
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Charles Jackson ES-4044.01
August 11, 2023 Page 4
Earth Solutions NW, LLC
Provided foundations will be supported as described above, the following parameters can be
used for design of new foundations:
Allowable soil bearing capacity 2,500 psf
Passive earth pressure 300 pcf (equivalent fluid)
Coefficient of friction 0.40
A one-third increase in the allowable soil bearing capacity can be assumed for short-term wind
and seismic loading conditions. The above passive pressure and friction values include a factor-
of-safety of 1.5. With structural loading as expected, total settlement in the range of one inch and
differential settlement of about one-half inch is anticipated. The majority of the settlements should
occur during construction, as dead loads are applied.
Limitations
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. Our recommendations are based on the information
available at the time of this letter preparation. A warranty is not expressed or implied.
We trust this letter meets your current needs. If you have any questions, or if additional
information is required, please call.
Sincerely,
EARTH SOLUTIONS NW, LLC
Stephen H. Avril Kyle R. Campbell, P.E.
Project Manager Senior Principal Engineer
Attachment: Earth Solutions NW, LLC
Infiltration Evaluation, ES-4044, dated July 15, 2016
cc: Merrick Lentz Architect
Attention: Jason Beagle
08/11/2023
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Drwn.
Checked Date
Date Proj.No.
Plate
Earth Solutions NWLLC
Geotechnical Engineering,Construction Monitoring
EarthSolutionsNWLLC
EarthSolutionsNWLLC and Environmental Sciences
Vicinity Map
N.E.23rd Street
Renton,Washington
GLS 07/13/2016 4044
BJP July 2016 1
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
Reference:
King County,Washington
Map 626
By The Thomas Guide
Rand McNally
32nd Edition
NORTH
SITE
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Drwn.
Checked Date
Date Proj.No.
Plate
Earth Solutions NWLLC
Geotechnical Engineering,Construction Monitoring
EarthSolutionsNWLLC
EarthSolutionsNWLLC and Environmental Sciences
Test Pit Location Plan
N.E.23rd Street
Renton,Washington
MRS
BJP
07/13/2016
July 2016
4044
2
NORTH
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
NOTE:The graphics shown on this plate are not intended for design
purposes or precise scale measurements,but only to illustrate the
approximate test locations relative to the approximate locations of
existing and /or proposed site features.The information illustrated
is largely based on data provided by the client at the time of our
study.ESNW cannot be responsible for subsequent design changes
or interpretation of the data by others.
NOT -TO -SCALE
LEGEND
Approximate Location of
ESNW Test Pit,Proj.No.
ES-4044,June 2016
Subject Site
Existing Building
N.E. 22ND STREET
TP-1
TP-2
TP-3
TP-1
N.E. 23RD STREET
CAMAS
AVENUE
N.E.
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E
Docusign Envelope ID: E59390F3-F590-4F4B-85CA-AE9BC959928E