HomeMy WebLinkAboutCDP 2017-0074; STAINBACK RESIDENCE; SECOND REVIEW OF GEOTECHNICAL REPORT; 2019-09-03NV 5
City of Carlsbad
1635 Faraday Avenue
Carlsbad, California 92008
Attention: Mr. David Rick, PE
Subject: Second Review of Geotechnical Report
Project: Proposed Stainback Residence
5360 Los Robles Drive
Carlsbad, California
City Project ID:
City GR No.:
CDP2017-0074
GR2019-0008
September 3, 2019
Project No.: 226816-00 IO 1.53
Refe rences: I) "Comments and Responses", received in an email from Mr. Jay K. Heiser of Geotechnical
Exploration, [nc. (jheiser@ge i sd .com), dated August 19, 2019, and also received in a
separate email from Ms. Cecelia Fernandez of the City of Carlsbad
(Cecelia.Fe rnandez@carlsbad.gov), dated August 20, 2019.
2) "Review of Geotechnical Report, Proposed Stainback Residence, 5360 Los Robles Drive,
Carlsbad, California", prepared by NV 5 West, lnc. Project No. 226816-00 IO 1.53, dated
March 28, 2019.
3) "Preliminary Geotechnical Investigation, Eaton-Stainback Residence, 5360 Los Robles
Drive, Carlsbad, California", prepared by Geotechnical Exploration, Inc., Project No. 17-
11606, dated September 28, 2017.
4) "Technical Guidelines for Geotechnical Rep orts ", issued by the City of Carlsbad, dated
January 1993.
5) "CGS Note 41 , Guidelines for Reviewing Geologic Rep orts", prepared by the State of
California, Department of Conservation, California Geological Survey, dated 2017.
Dear Mr. David Rick:
As requested, NV5, West Inc. (NV5) has conducted a second geotechnical review of the above-referenced
geotechnical report and associated geotechnical addendum (comment responses) for the proposed residence
located at 5369 Los Robles Drive in Carlsbad, California. Our initial review (reference 2) was prepared for the
preliminary geotechnical investigation report (reference 3) prepared for the project. The purpose of the second
review was to provide an opinion on whether the geotechnical aspects of the project have been identified and
appropriately addressed in the geotechnical Engineers response (reference I) to NV5's initial review of the
project geotechnical report (reference 3). NV5 's second geotechnical review is based on geotechnical
information presented in the referenced geotechnical engineer response and geotechnical report (references I
and 3), the guidelines for geotechnical and geologic reports (references 4 and 5), and experience with the
geotechnical conditions in the general site area. NV5 has not performed an independent geotechnical
investigation at the project site and therefore does not offer or imply any guarantee or warranty as to future site
performance. The opinions presented below are limited. Other consultants could arrive at different conclusions.
This report presents a summary of the review.
OF'"FlCES NATIONW10£
I 5092 AVENUE OF S CIENCE, S UITE 200 SAN DIEGO, CA 9 2 I 28 WWW.NV5 .COM OFFICE 858 . .385,0500 FAX 858 . .385.0400
CONSTRUCTION 0UA1.ITY ASSURANCE • INP'RASTRUCTIJRE • ENERGY • PROGRAM MANAGEMENT • (NvlRONMENTA~
Second Review ofGeotechnical Report
Proposed Stainback Residence
5360 Los Robles Drive
Carlsbad, California
Review Summary
Project No.: 2268 I 6-00 IO 1.53
As indicated above, this is NV S's second review of the referenced project geotechnical repo,ts. NV S's first
review (reference 2, above), provided comments and requested additional information be provided. In
response to NV S's first review, the appli cant submitted reference 1, above which, based on NV S's second
review, has appropriately responded to most ofNVS's comments of the first review. However, one of the
responses was incomplete as indicated below.
Comment 4 ofNVS's first review suggested that the geotechnical report should include a geologic map,
and since the property has significant fill , should include a scaled cross section depicting the subsurface
geology. These are essential to the understanding of the report and site geology.
The response from Geotechnical Exploration, Inc. stated that:
We provided a site plan to show the location of our test
pits and the test pits show that the entire lot is underlain by fill soil over old paralic
deposits and a geology map is not warranted for this simple geology.
The City of Carlsbad Geotechnical Review Checklist requires that a geologic map and cross section be
submitted in geotechnical reports. It does not matter if the geology is "simple", it is a requirement of the
City of Carlsbad. If the geology is not complicated, a simple geologic map based on published geologic
mapping may be acceptable.
For reference, the City of Carlsbad Geotechnical Report Review Checklist (Checklist) was attached to
NVS's first review. The Checklist outlines item that are typically required to be addressed in a project
geotechnical report prior to approval by the City of Carlsbad. It is noted that not all of the items on the
Checklist may be applicable or pertinent to every project, but the Checklist does present list of items that
are checked by City reviewers. The Checklist is also attached hereto.
NV5 appreciates the opportunity to be of service to you on this project. If you have any questions regarding
this report, please do not hesitate to contact our office.
Respectfully submitted,
NV5 West, Inc.
Carl Henderson, PhD, GE 2886
CQA Group Director (San Die o)
GC/CH:ma
Attachment: City of Carlsbad Geotechnical Report Review Checklist
Distribution: ( 1) Addressee, via email
NIVIS
OFFlCES NATIONWIDE
CONSTRUCTION QUALITY ASSURANCE • INFRASTRUCTURE ENCINEERIHG • MUNICIPAL OUTSOURClNG -ASSET MANAGEMENT • ENVIRONMENTAL SERVICES
.,
GEOTECHNICAL REPORT REVIEW CHECKLIST
Plan Check Number:
Location / Address :
City Plan Checker: Date: _______ _
GEOTECHNICAL REPORT -GENERAL
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Signed by CEG (Required for Hillside Area) □ □ □
Project Address □ □ □
Location Index Map with reference north, scale, etc. □ □ □
Site Description (topography, vegetation, existing structures/improvements, drainage) □ □ □
Description of Proposed Development (grading, structures/improvements, drainage, use, foundation □ □ □ type, estimated structural loads)
GEOTECHNICAL REPORT-FIELD INVESTIGATION
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Site Specific Subsurface Investigation □ □ □
Description of Investigative and Sampling Methods □ □ □
Boring/Test Pit Logs (Soil/Bedrock descriptions with depth, type and depth indicated for sampling , □ □ □ real or assumed elevation indicated, qroundwater conditions)
Sampling performed to anticipated depth of foundations and/or deepest excavation □ □ □
Boring/Test Pits located on Geotechnical Map/Plot Plan □ □ □
Revised 5/10/2018 Page 1 of 7
GEOTECHNICAL REPORT -LAB TESTING
Description of lab test performed with referenced test method (ASTM, EPA, etc)
Soil Strength (Shear)
Expansion
Sulfate
Gradation
Classification of soil in accordance with ASTM D 2487 (when using California Building Code values
for lateral load)
Moisture/Density
Consolidation
Atterberg Limits
Maximum Dry Density/Optimum Moisture Content
GEOTECHNICAL REPORT-EARTH MATERIALS
Description and designation of geologic units (surficial soils and bedrock, including depth, thickness)
Geologic structure (bedding, fracturing , faulting of bedrock material)
Description of regional geologic conditions (including reported regional trends of bedding and
faultinq)
GEOTECHNICAL REPORT -SEISMICITY
General description of regional and local faulting
Site Class
Mapped Spectral Acceleration Parameters (Ss, S1)
Site Coefficients (Fa, Fv)
Design Spectral Acceleration Parameters (Sos, So1)
Geotechnical Report Checklist
Revised 5/10/2018 Page 2 of 7
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Seismic Design Category
GEOTECHNICAL REPORT -GEOLOGIC HAZARDS
Landslide
Expansive Soils
Surficial Slope Instability
Slope Creep
Groundwater
Total and Differential Settlement
Sulfate
Liquefaction
Affect of liquefiable soils on utilities and lifeline services outside of structural mitigation
Seismic Induced Landsliding
Tsunami Potential
GEOTECHNICAL REPORT-ILLUSTRATIONS
Geotechnical Map / Plot Plan
Existing topography/ improvements
Proposed topography/ improvements
Location of subsurface exploration (borings, test pits, etc.)
Geologic Contacts
Geologic Structure
Location of fill key / buttress
Geologic Cross-Section
Existing topography/ improvements
Geotechnical Report Checklist
Revised 5/10/2018 Page 3 of 7
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Proposed topography/ improvements
Location of subsurface exploration (borings, test pits, etc.)
Geologic Contacts
Geologic Structure
Slope setbacks
Temporary cuts/ shoring
Fill Key / buttress
Slope benching
GEOTECHNICAL REPORT-CONCLUSIONS/ RECOMMENDATIONS
Statement as to feasibility of project
Statement as to impact on adjacent properties
Statement of the condition of slopes with respect to stability
Slope stability analysis provided to support conclusion/recommendations
Statement regarding liquefaction potential
Liquefaction analysis provided to support conclusion/recommedations
Grading Recommendations
Remedial grading
Compaction standards
Groundwater Mitigation
Temporary excavation (backcuts, slopes) with time limit recommendations
Shoring
Benching
Keys / buttresses
Canyon/Key Subdrains
Foundation Recommendations
Geotechnical Report Checklist
Revised 5/10/2018 Page 4 of 7
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Expansive soil mitigation (CBC 1805) -
Description of approved embedment material (i.e. compacted fill , terrace deposits, etc)
Minimum depth of embedment (into approved material) for foundations
Minimum width of footings
Minimum diameter of caissons
Bearing capacity (end bearing for caissons)
Coefficient of friction (caisson skin friction)
Lateral bearing
Down drag forces (liquefiable soils,)
Lateral Spread forces (liquefiable soils)
Foundation slope/trench setback
Minimum reinforcement requirements
Minimum slab thickness and reinforcement
Slab underlayment
Soluable Sulfate exposure mitigation (typically cement type)
Conventional Retaining Wall Recommendations
Active pressures (level, sloping)
Retaining wall backdrain or recommendation of additional hydrostatic pressure
Backfill
Surcharges
MSE Wall Recommendatior:is (facing material, grid, backfill, stability analysis)
Flatwork / Hardscape recommendations including driveways (subgrade preparation, minimum slab
thickness, reinforcement and joint spacinq)
Roadway Pavement recommendations (section design, subgrade preparation)
Swimming Pool recommendations
GEOTECHNICAL REPORT -OBSERVATION/TESTING DURING CONSTRUCTION
Geotechnical Report Checklist
Revised 5/10/2018 Page 5 of 7
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Footing Excavations
Subdrains
Caisson / Drilled Pier excavations (CBC Table 1704.9)
Pool Excavations
Benching
Keyways
Temporary excavations
Geologic mapping of bedrock excavations
Retaining wall backfill
Utility trench backfill
Engineered fill
Hardscape subgrade (driveways, patios, walkways , etc .)
Import soils
GEOTECHNICAL REPORT -REFERENCES
Current/ City adopted Building Code
Grading Code
Geotechnical reports/ publications/ geologic maps
Ariel photographs
Websites
GEOTECHNICAL REPORT -COASTAL BLUFF
Top of bluff designation (presented on geologic map and cross-sections)
Geotechnical Report Checklist
Revised 5/10/2018 Page 6 of 7
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Arial photograph of site showing top of bluff
Bluff retreat rate and total estimated retreat for a 50 year period
Codified Bluff top setback (presented on geologic map and cross-sections)
Slope stability analysis
References for bluff retreat rate
Slope Stability Setback presented on geologic map (surface expression of 1.5 FS)
Total Setback presented on geologic map (greater of A: Slope Stability Setback + 50 yr bluff retreat
or B: 10-feet buffer+ 50 yr bluff retreat)
Explanation and justification of 40-feet setback deviation
Geotechnical Report Checkli st
Revised 5/10/2018 Page 7 of 7
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