HomeMy WebLinkAboutPD 2023-0006; LA COSTA CANYON HIGH SCHOOL FITNESS CENTER; ENGINEERING AND SEISMOLOGY REVIEW; 2023-01-12~~i California ~~n ~ Department of Conservation
Y, ~ California Geological Survey
Mike Coy
Chief Facilities Officer
San Dieguito Union High School District
710 Encinitas Boulevard
Encinitas, CA 90224
Subject: Engineering Geology and Seismology Review for
Gavin Newsom, Governor
David Shabazian, Director
January 12, 2023
La Costa Canyon High School -Proposed Classroom and Weight Room
1 Maverick Way, Carlsbad, CA 92009
CGS Application No. 04-CGS5667
Dear Mr. Coy:
In accordance with your request and transmittal of documents received on November 15, 2022,
the California Geological Survey (CGS) has reviewed the engineering geology and seismology
aspects of the consulting report prepared for the subject project at La Costa Canyon High
School. It is our understanding that this project involves the construction of a single-story
classroom building and a single-story weight room building. This review was performed in
accordance with Title 24, California Code of Regulations, 2019 California Building Code (CBC)
and followed CGS Note 48 guidelines. We reviewed the following report:
Geotechnical Investigation, Fitness Center, La Costa Canyon High School,
Carlsbad, California: California: Geocon Incorporated, 6960 Flanders Drive, San
Diego, California 92121; company Project No. G 1999-42-098, report dated October 3,
2022, 21 pages, 7 figures, 3 appendices.
Based on our review, the consultants provide a thorough and well-documented assessment of
engineering geology and seismology issues with respect to the proposed project. The principal
concerns identified by the consultants are the potential for strong ground shaking and expansive
clayey soils. The consultants recommend site-specific design spectral acceleration parameters
of Sos = 0. 781g and So1 = 0.324g, which are considered reasonable. Their evaluation indicates
liquefaction, dynamic settlement, and deep-seated slope instability are not design concerns for
the project.
State of California Natural Resources Agency I Department of Conservation
Office of the State Geologist, 715 P Street, MS 19-01, Sacramento, CA 95814
conservation.ca.gov/cgs I T: (916) 445-1825
Engineering Geology and Seismology Review
La Costa Canyon High School -Proposed Classroom and Weight Room
CGS Application No. 04-CGS5667
January 12, 2023
In conclusion, the engineering geology and seismology issues at this site are adequately
assessed in the referenced reports, and no further information is requested. If you have
any further questions about this review letter, please contact the primary reviewer at
will .harris@conservation.ca.gov.
Concur:
1-1, 7Zj;
Jennifer Thornburg
Senior Engineering Geologist
PG 5476, CEG 2240
Enclosures:
Note 48 Checklist Review Comments
Respectfully submitted,
/4\//;LJ
Will Harriā/'
Senior Engineering Geologist
PG 5679, CEG 2222, CHg 750
Keyed to: Note 48 -Checklist for the Review of Engineering Geology and Seismology Reports
for California Public Schools, Hospitals, and Essential Services Buildings
Copies to:
Garry W. Cannon, Certified Engineering Geologist, and Raul R. Garcia, Registered Geotechnical
Engineer
Geocon Incorporated, 6960 Flanders Drive, San Diego, California 92121
Joe Mansfield, Architect
RNT Architects, Inc., 363 Fifth Avenue, Suite 202, San Diego, CA 92101
Geoffrey Chan, Senior Structural Engineer
Division of State Architect, 10920 Via Frontera, Suite 300, San Diego, CA 92127
Page2
Engineering Geology and Seismology Review
La Costa Canyon High School -Proposed Classroom and Weight Room
CGS Application No. 04-CGS5667
Note 48 Checklist Review Comments
January 12, 2023
In the numbered paragraphs below, this review is keyed to the paragraph numbers of California
Geological Survey Note 48 (October, 2013 edition), Checklist for the Review of Engineering
Geology and Seismology Reports for California Public Schools, Hospitals, and Essential
Services Buildings.
Project Location
1. Site Location Map, Street Address, County Name: Adequately addressed.
2. Plot Plan with Exploration Data with Building Footprint: Adequately addressed.
3. Site Coordinates: Adequately addressed. Latitude and Longitude provided in report:
33.072759°N, 117.232217°W
Engineering Geology/ Site Characterization
4. Regional Geology and Regional Fault Maps: Adequately addressed.
5. Geologic Map of Site: Adequately addressed.
6. Geologic Hazard Zones: Adequately addressed. The consultants report that the site is not
within a State of California-designated Earthquake Fault Zone.
7. Subsurface Geology: Adequately addressed. The consultants had 4 borings drilled on the
site to a maximum depth of 19.5 feet below ground surface (bgs). Fill material was
encountered in in one boring to 4 feet bgs and consisted of stiff sandy clay. The consultants
report that all borings encountered the Santiago Formation to the depth of the borings;
those earth materials were logged as dense to very dense silty sand and stiff sandy clay.
Groundwater was not encountered in the borings.
8. Geologic Cross Sections: Adequately addressed.
9. Geotechnical Testing of Representative Samples: Adequately addressed.
10. Consideration of Geology in Geotechnical Engineering Recommendations: Adequately
addressed.
11. Conditional Geotechnical Topics: Not applicable.
Seismology & Calculation of Earthquake Ground Motion
12. Evaluation of Historic Seismicity: Adequately addressed. The consultants provide a
summary of historical seismicity in the region.
13. Classify the Geologic Subgrade (Site Class): Adequately addressed. The consultants
classify the site soil profile as Site Class C based on blowcount data. This appears to be
the appropriate designation given the formational material encountered and generally
increasing blowcounts with depth.
14. General Procedure Ground Motion Analysis: Adequately addressed. The consultants report
the following parameters derived from a map-based analysis:
Ss = 0.963 and S1 = 0.351
Sos= 0.771 and So1 = 0.351
Ts was not provided by consultants but can be calculated as So1/Sos.
15. Site-Specific Ground Motion Hazard Analysis: Adequately addressed. The consultants'
probabilistic MCE spectra appear reasonable based on comparison with results from the
National Seismic Hazard Model (from Petersen and others, 2014). The consultants did not
conduct a deterministic analysis in accordance with ASCE, Supplement 1, Section 21 .2.2,
based on the probabilistic response spectrum, with the largest response acceleration being
Page 3
Engineering Geology and Seismology Review
La Costa Canyon High School -Proposed Classroom and Weight Room
CGS Application No. 04-CGS5667
January 12, 2023
less than 1.2Fa. The consultants report their site-specific seismic design parameters are:
Sos= 0.781g and S01 = 0.324g. Alternatively, Sa values presented in the "Site-Specific
Design Earthquake" column in Figure 10 of the consultants' report may be used with the
equivalent lateral force procedure, per ASCE 7, Section 21.4. The site-specific ground
motion analysis presented appears to be reasonable and in accordance with ASCE 7-16.
16. Deaggregated Seismic Source Parameters: Not applicable.
17. Time-Histories of Earthquake Ground Motion: Not applicable.
Fault Rupture Hazard Evaluation
18. Active Faulting & Coseismic Deformation Across Site: Adequately addressed. The
consultants note that based on their review of published mapping and their own site
reconnaissance, active faulting does not cross the site and so the potential for ground
surface rupture to occur at the site is considered low. This appears to be a reasonable
conclusion .
Liquefaction/Seismic Settlement Analysis
19. Geologic Setting for Occurrence of Seismically Induced Liquefaction: Adequately
addressed. The consultants conclude that based on the dense nature of the native earth
materials encountered during exploration, the risk associated with seismically induced
liquefaction is low, which appears to be a reasonable conclusion.
20. Seismic Settlement Calculations: Not applicable.
21 . Other Liquefaction Effects: Not applicable.
22. Mitigation Options for Liquefaction: Not applicable.
Slope Stability Analysis
23. Geologic Setting for Occurrence of Landslides: Adequately addressed. The consultants
note that no evidence of landsliding was encountered during their investigation and no
landslides are mapped on the site or in areas that would potentially impact the site. They
conclude that the risk associated with ground movement hazard due to landsliding is low.
This appears to be a reasonable conclusion.
24. Determination of Static and Dynamic Strength Parameters: Not applicable.
25 . Determination of Pseudo-Static Coefficient (Keq): Not applicable.
26. Identify Critical Slip Surfaces for Static and Dynamic Analyses: Not applicable.
27. Dynamic Site Conditions: Not applicable.
28 . Mitigation Options/Other Slope Failure: Not applicable.
Other Geologic Hazards or Adverse Site Conditions
29. Expansive Soils: Adequately addressed. Based on laboratory testing, the consultants state
that on-site surficial soils are expansive.
30. Corrosive/Reactive Geochemistry of the Geologic Subgrade: Adequately addressed. The
consultants report that testing of on-site soils indicate the soils have a moderate to high
corrosion potential for ferrous metals. Water soluble sulfate content of site materials was
tested. It was determined the tested materials have "SO" and "S2" sulfate exposure to
concrete structures as defined by 2019 CBC Section 190, and ACI 318-14 Chapter 19.
31. Conditional Geologic Assessment: Adequately addressed. No significant conditional
hazards of potential concern were identified by the consultants.
Page 4
Engineering Geology and Seismology Review
La Costa Canyon High School -Proposed Classroom and Weight Room
CGS Application No. 04-CGS5667
Report Documentation
January 12, 2023
32. Geology, Seismology, and Geotechnical References: Adequately addressed.
33. Certified Engineering Geologist: Adequately addressed.
Garry W. Cannon, Certified Engineering Geologist #2201
34. Registered Geotechnical Engineer: Adequately addressed.
Raul R. Garcia, Registered Geotechnical Engineer #2842
Page 5