HomeMy WebLinkAboutCT 2017-0003; LA COSTA TOWN SQAURE PARCEL 3 RESIDENTIAL; REVISED GEOTECHNICAL RECOMMENDATIONS FOR SLOPE EROSION MITIGATION; 2024-07-17Geotechnical C Geologic C Coastal C Environmental
18451 Collier Avenue, Suite A, Lake Elsinore, California 92530
TEL: (951) 471-0700 - FAX: (951) 471-0702
www.geosoilsinc.com
March 20, 2024
Revised July 17, 2024
W.O. 8144-B-SC
Woodside 05S, LP
1250 Corona Pointe Court, Suite 500
Corona, California 92879
Attention: Mr. Craig Moraes
Subject: Revised Geotechnical Recommendations for Slope Erosion Mitigation,
Fill Slope Above the Existing Mechanically Stabilized Earth (MSE) Retaining
Wall, La Costa Town Square Project, Carlsbad, San Diego County, California,
APN 223-050-73-00, Project ID: CT01-09, Drawing No.: DWG 474-7A
Dear Mr. Moraes:
In accordance with your request and authorization, GeoSoils, Inc. (GSI) is providing the
following revised geotechnical recommendations to mitigate erosion that may potentially
occur along the fill slope located above the existing mechanically stabilized earth (MSE)
retaining wall, near the northern margin of the subject parcel. The purpose of this letter is
to address concerns expressed by the City of Carlsbad (City) that rocks dislodged from the
face of the fill slope, due to gravity or surface runoff, may overtop the MSE retaining wall,
and result in bodily harm to the general public who may be standing or walking in proximity
to the wall. The City’s concerns were communicated to GSI during our March 4, 2024
telephone conversation with you and Mr. Jagels from your office. The scope of our
services included reviews of the referenced documents (see the Appendix), research of
debris containment and erosion control products, engineering analyses, and the
preparation of this letter. Unless specifically superseded herein, the conclusions and
recommendations contained in geotechnical reports prepared by this firm and referenced
in the Appendix are considered valid and applicable, and should be appropriately
implemented during project design and construction.
Based on our observations along the face of the subject fill slope, the slope is composed
of compacted fill materials with maximum particle dimensions generally on the order of
6 inches or less. The particles are typically angular to subangular in shape. Given the
relatively high ground surface roughness and particle angularity, it is our opinion that a
majority of the particles, should they become mobilized by gravity or surface flows, would
be captured within the concrete-lined drainage swale. The general recommendations
provided herein are intended to intercept/capture rock fragments before they overtop the
MSE retaining wall. Based on our observations, there is no evidence of shallow slope
failures or earth flows along the fill slope. Thus, recommendations for mitigating or
containing shallow slope failures or earth flows are not included herein.
Capture Netting
,.
GSi
GeoSoils,lnc. ----------___,_,~
Based on our previous letter of slope erosion mitigation/alternatives (GSI, 2024, see
Appendix) and conversations with the Client, it is our understanding that a West Coast
Netting, Inc. (WCN) K60T-1¾" knotted #60 netting has been selected to mitigate/capture
and intercept any mobilized rock particles before they can overtop the MSE retaining wall.
The netting will be affixed to the existing fall-protection fencing. Based on the new
information provided by the Client, our review of the test report by SGS North America, Inc.
(SGS, 2011), the 2002 International Standard (ISO 1806) for the determination of the
breaking force of netting, and the WCN (undated) technical specification sheet provided,
the proposed polyester filament netting by WCN appears suitable from a geotechnical
perspective. The netting consists of ultraviolet treated, knotted polyester mesh with a
1¾ square inch opening size that exhibits a breaking force with an average of
approximately 442 pounds/foot. For aesthetics, vines or climbing plants could be trained
to grow over the existing fencing and proposed netting to help conceal it. Polyester mesh
netting is subject to degradation over time. As such, periodic maintenance and ultimate
replacement will likely be necessary.
LIMITATIONS
The materials encountered on the project site and used for our analysis are believed
representative of the area; however, soil and bedrock materials vary in character between
excavations and natural outcrops or conditions exposed during mass grading.
Site conditions may vary due to seasonal changes or other factors.
Inasmuch as our study is based upon our review and engineering analyses and laboratory
data, the conclusions and recommendations are professional opinions. These opinions
have been derived in accordance with current standards of practice, and no warranty,
either express or implied, is given. Standards of practice are subject to change with time.
GSI assumes no responsibility or liability for work or testing performed by others, or their
inaction; or work performed when GSI is not requested to be onsite, to evaluate if our
recommendations have been properly implemented. In addition, this report may be
subject to review by the controlling authorities. Thus, this report brings to completion our
scope of services for this portion of the project.
Woodside 05S, LP W.O. 8144-B-SC
La Costa Town Square Project Revised July 17, 2024
File:e:\wp21\8100\8144\8144b.rgrf Page 2GeoSoils, Inc.
The opportunity to be of service is sincerely appreciated. If you should have any
questions, please do not hesitate to contact our office.
Respectfully submitted,
GeoSoils, Inc.
Todd A. Greer Stephen J. Coover
Engineering Geologist, CEG 2377 Geotechnical Engineer, GE 2057
TAG/SJC/ef
Attachment: Appendix - References
Distribution: (1) Addressee (PDF via email)
Woodside 05S, LP W.O. 8144-B-SC
La Costa Town Square Project Revised July 17, 2024
File:e:\wp21\8100\8144\8144b.rgrf Page 3GeoSoils,lnc.
APPENDIX
REFERENCES
GeoSoils, Inc., 2024, Geotechnical recommendations for slope erosion mitigation, fill slope
above the existing Mechanically Stabilized Earth (MSE) retaining wall, La Costa
Town Square project, Carlsbad, San Diego County, California, APN 223-050-73-00,
Project ID: CT2017-0003, Grading Permit No.: GR2022-0001, W.O. 8144-B-SC,
dated March 20.
_____, 2023a, Responses to third-party review comments regarding building setbacks from
the existing mechanically stabilized earth wall, La Costa Town Square Project,
Carlsbad, San Diego County, California, APN 223-050-73-00,
Project ID: CT2017-0003, Grading Permit No.: GR2022-0001, W.O. 8144-B-SC,
dated October 25.
_____, 2023b, Geotechnical update and response to City of Carlsbad Engineering
Department plan check comment regarding building setbacks from the existing
mechanically stabilized earth retaining wall, La Costa Town Square project,
Carlsbad, San Diego County, California, APN 223-050-73-00,
project ID: CT2017-0003, grading permit no.: GR2022-0001, W.O. 8144-B-SC,
dated September 21.
_____, 2023c, Summary of geotechnical observation and testing services during repair of
existing Anchor Retaining Wall No. 1, La Costa Town Square Project, Carlsbad,
San Diego County, California, APN 223-050-73-00, Project ID: CT2017-0003,
Grading Permit No.: GR2022-0001, W.O. 8144-F-SC, dated August 3.
_____, 2023d, Memorandum: Review of construction change no. 2 rough grading plans,
La Costa Town Square project, City of Carlsbad, San Diego County, California,
APN 223-050-73-00, project no.: CT 2017-0003, drawing no.: 536-1A,
W.O. 8144-B-SC, dated August 1.
_____, 2023e, Standalone geotechnical report and response to City of Carlsbad
Geotechnical Review Memorandum dated July 7, 2023, proposed repairs to existing
Anchor Retaining Wall No. 1, La Costa Town Square Project, Carlsbad, San Diego
County, California, APN 223-050-73-00, project ID: CT2017-0003, grading permit
no.: GR2022-0001, W.O. 8144-B-SC, dated July 12.
_____, 2023f, Memorandum: Geotechnical review of post tension plans, La Costa Town
Square affordable project, City of Carlsbad, California APN 223-050-73-00,
W.O. 8144-A-SC, dated July 10.
_____, 2023g, Memorandum: Review of construction change rough grading plans,
La Costa Town Square project, City of Carlsbad, California, APN 223-050-73-00,
project no.: CT 2017-0003, drawing no.: 536-1A, W.O. 8144-B-SC, dated June 29.
GeoSoils, Inc.
_____, 2023h, Geotechnical update and addendum to “Geotechnical Due Diligence Report
and Attachments, La Costa Town Square Project, City of Carlsbad, California
APN 223-050-73-00,” W.O. 8144-A-SC, dated February 9, 2023, W.O. 8144-A-SC,
dated June 20.
_____, 2023i, Memorandum: Geotechnical recommendations for subdrain construction
north of planned building pads for Lots 6 through 16 and Private Driveways “C”
through “H”, La Costa Town Square project, City of Carlsbad, California
APN 223-050-73-00, project no.: CT 2017-0003, drawing no.: 536-1A,
W.O. 8144-B-SC, dated May 30.
_____, 2023j, Memorandum: Review of precise grading plans, La Costa Town Square
project, City of Carlsbad, California APN 223-050-73-00, project no.: CT 2017-0003,
drawing no.: 536-1A, W.O. 8144-B-SC, dated May 30.
_____, 2023k, Memorandum: Geotechnical due diligence report and attachments,
La Costa Town Square project, City of Carlsbad, California, APN 223-050-73-00,
W.O. 8144-A-SC, dated February 9.
_____, 2022, Review and response to third party geotechnical review comments, La Costa
Town Square townhome site (APN 223-050-73-00), La Costa Boulevard, City of
Carlsbad, California, W.O. 8144-A-SC, dated March 24.
_____, 2021, Geotechnical due diligence evaluation of the La Costa Town Square
townhome site, APN 223-050-73-00, La Costa Avenue, City of Carlsbad, San Diego
County, California 92011, W.O. 8144-A-SC, dated June 17.
International Standard, 2002, ISO 1806, Fishing nets - determination of mesh breaking
force of netting, 14 pgs., dated December 1.
SGS North America, Inc., 2011, Test Report, knotted #60 treated twisted polyester,
K60T-1¾”, 2 pgs, dated August 3.
West Coast Netting, Inc., Technical specification sheet, 1 pg, undated.
Woodside 05S, LP Appendix
File:e:\wp21\8100\8144b.rgrf Page 2GeoSoils, Inc.