HomeMy WebLinkAboutCT 06-27; MUROYA SUBDIVISION; GEOTECHNICAL PEER REVIEW; 2009-11-11~ ~ l(ln90 & ~oo-re I a >-· ~
Gcotc-ct:n,ca: ,Jn(1 Env,ronmcnwl Soenc.t.'S Consultdnts
Mr. Clyde Wickham
City of Carlsbad
1635 Faraday Avenue
Carlsbad, California 92008
Subject: Geotechnical Peer Review
Proposed Muroya Residential Subdivision
Carlsbad Tract 06-27
Carlsbad, California
Dear Mr. Wickham:
November 11, 2009
Project No. 106560003
At your request and the authorization of the City of Carlsbad (the City), we have performed a third
party (or peer) review of project geotechnical docum~nts for the proposed ~uroya Residenti~l Sub
division, Carlsbad Tract 06-27; The subject tract is located along the west side of Black Rail Road
across from Songbird and Ocean Crest Avenues in Carlsbad, California. Reviewed documents pro
vided by the City included: the project geotechnical report (Geocon, 2009a); a response to review
comments letter (Geocon, 2009b); and, a review memorandum prepared by the City. Our general
scope of services was to review the materials provided and check them for compliance with mini
mum code standards, completeness, factual errors, consistency of data with the conclusions offered,
and conformance to the standards of geotechnical practice. A list of reviewed references is appended.
SCOPE OF SERVICES
Our specific scope of services included the following:
• Review of the referenced project geotechnical documents provided by the City of Carlsbad.
• Review of available published geologic and geotechnical maps and reports pertinent to the site area.
• Reconnaissance of the site by a Certified Engineering Geologist from our office.
• Preparation of this letter presenting the findings of our peer review.
REVIEW COMMENTS
From our review of the provided documents, we have developed the following review comments:
571 0 Ruffin Road • San Diego. California 92123 • Phone (858) 576-1000 • Fax {858) 576-9600
San o,ego • INine • Rancho Cucamonga • Los Angeles • Oakland • Las Vegas • Phoenix • Denver • B Paso
Proposed Muroya Residential Subdivision, Carlsbad Tract 06-27
Carlsbad, California
November 11, 2009
Project No. 106560003
• There are minor deficiencies on the cross sections. These include mislabeling T-10 as T-4 on Cross
Section A-A', not showing T-4 and T-5 on Cross Section B-B', and (also on B-B') not showing the
seepage.
• The logs for trenches T-3, T-4, and T-5 indicate that the debris fill is in an "overall poor, uncom
pacted condition." However, Page 15 of the project geotechnical report recommends that
surficial soils be considered as a Type B soil classification for temporary excavations. Due to the
poor condition of the debris fill, consideration should be given to classifying the debris fill as a
Type C soil for temporary excavations.
• Page 2 of the project geotechnical report concludes that the debris fill is "unsuitable for support
of additional fill." However, Cross Section B-B' and Pages 7 and 12 of the report indicate that
due to grading restraints for sensitive habitats, portions of the fill slope at the southeast portion
of the site will be supported on debris fill. Due to the potential instability of the underlying de
bris fill, consideration_ should be given to provide additional gradlng recommendations in this
area of the project.
• The log for trench T-4 indicates that alluvial materials may exist to depths greater than 7½ feet.
Based on the recommendations on Page 8 of the project geotechnical ~eport, the existing allu
vium should be removed and recompacted. Based on the anticipated depths of the recommended
removals at the location of trench T-8, the horizontal limits of temporary excavations niay be
limited due to the adjacent Nightshade Road. Consideration should be given to provide tempo
rary shoring recommendations for this area.
• The report does not provide a recommendation for the construction of a backdrain within the
keyway for the 1.5:1 slope at the western portion of the project. Consideration should be given
to provide such a recommendation.
• Seepage was encountered within trench T-4. This seepage was not depicted on Cross Section B-B'
or discussed as part of the slope stability analysis presented on Figure 5 of the report.
We appreciate the opportunity to be of service on this project.
Respectfully submitted,
NINYO & MOORE
£.~':!:.GE
Senior Project Engineer
JTK/RI/kh
Attachment: References
Distribution: (1) Addressee
106560003 L.doc 2
11:d:tf{~
Chief Engineering Geologist
Proposed Muroya Residential Subdivision, Carlsbad Tract 06-27
Carlsbad, California
REFERENCES
November 11, 2009
Project No. I 06560003
American Society of Civil Engineers, 2005, ASCE Standard 7, Minimum Design Loads for Buildings
and Other Structures.
California Building Standards Commission (CBSC), 2007, California Building Code (CBC), Title 24,
Part 2, Volumes 1 and 2.
City of Carlsbad Engineering Development Services, 2009, CT 06-27/CDP 06-32/CP 06-19/GPA
06-09/HDP 06-10/LCPA 06-09/ZC 06-08, Muroya Residential Subdivision Completeness &
Issues Review: dated September 8. •
Geocon, 2009a, Muroya Property, Carlsbad, California, Response to Review Comments, Project No.
07671-52-01: dated July 10.
Geocon, 2009b, Geotechnical Investigation, Muroya Property, Carlsbad, California, Project No.
07671-52-01: dated-July 14. -
Kennedy, M.P., 1996, Geologic Maps of the Northwestern Part of San Diego County, California:
California Division of Mines and Geology, Open-File Report 96-02.
Kennedy, M.P. and Tan, S.S., 2008, Geologic Map of the Oceanside 30' x 60' Quadrangle, California:
California Geological Sui:vey, Regional Geologic.Map Series. • •
Tan, S.S. and Giffen, D.G., 1995, Landslide Hazards in the Northern Part of the San Diego Metro
politan Area, San Diego County, California, California Division of Mines and Geology:
Landslide Hazards Identification Map No. 35, Open-File Report 95-04.
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