HomeMy WebLinkAboutMS 2020-0004; ADAMS STREET HOMES; GEOTECHNICAL RESPONSE TO COMMENTS FOR PROPOSED ADAMS STREET HOMES; 2022-04-13Geotechnical Exploration, Inc.
SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY
13 April 2022
Rincon Real Estate Group
3005 S. El Camino Real
San Clemente, CA 92672
Attn: Mr. Kevin Dunn
Job No. 20-12852
Subject: Response to Third-Party Reviewer csecond), Project No.
9537.1 Loa No. 21787
Rincon Residential Project
3745 Adams Street
Carlsbad, California
GR2021-004 l/MS2020-0004
Dear Mr. Dunn:
As requested and required by the City of Carlsbad third-party geotechnical reviewer
(Hetherington Engineering, Inc.) in a letter dated March 1, 2022, we herein respond
to their review comments. It is our understanding that the third-party reviewer has
reviewed our "Report of Preliminary Geotechnical Investigation" dated September 14,
2020. The consultant has also reviewed Reference 2, "Grading Plans for Adams
Street, 3745 Adams Street, Carlsbad, California" by Pasco Laret Suiter and
Associates, undated (Sheets 1 through 6); Reference 3, "Improvement Plans for
Adams Street Homes, 3745 Adams Street, by Pasco Laret Suiter and Associates,
undated (Sheets 1 through 3); Reference 4, "Third Party Geotechnical Review (First),
3745 Adams Street, Carlsbad, California, GR2021-0041/MS2020-0004" by Hethering
Engineering Inc., dated November 1, 2021; and Reference 5," Plan Review, Proposed
Adams Street Homes, 3745 Adams Street, Carlsbad, California," by Geotechnical
Exploration, Inc., dated January 17, 2022.
REVIEW COMMENTS & RESPONSES
1. The consultant should provide an updated geotechnical map utilizing the
current grading plan for the project to clearly show (at minimum): a) existing
site topography, b) proposed structures/improvements, c) proposed finished
grades, d) geologic conditions, e) locations of the subsurface exploration, f)
temporary construction slopes, g) remedial grading, etc.
7420 TRADE STREET• SAN DIEGO, CA. 92121 • (858) 549-7222 • FAX: (858} 549-1604 • EMAIL: geotech@gei-sd.com
Rincon Adams Street Project
Carlsbad, California
Job No. 20-12852
Page 2
GEi Response: As previously stated in our letter dated March 4, 2022, we
have included an updated Plot Plan (see Appendix A) based on the undated
grading plans, showing the existing and proposed structures and
improvements, proposed finish grades, locations of subsurface exploration,
and geologic contacts on the included topographic base map. No temporary
construction slopes are required on the site as it is relatively flat and no
basement walls are proposed. Some proposed retaining walls or property line
walls on the west side may need temporary construction (excavation) slopes
if the retaining walls are built after rough grading is completed. If that is the
case, the recommendations presented in our report for temporary excavations
should be followed. Otherwise, any grading adjacent to existing structures on
the property line should be made using a slot alternating (A-B-C) excavation
method, with slots not exceeding 8 feet in width. These excavations should
not exceed 3 feet in height.
2. Foundation and slab design criteria for expansive soils should be consistent
with Section 1808.6 of the 2019 California Building Code. The consultant
should provide expansion index test results and update foundation
recommendations, as necessary.
GEi Response: As previously stated in our letter dated March 4, 2022, we
recently performed expansion index tests on two samples retrieved from the
site. One sample was from the eastern half and the other from the western
half of the site. The tests results yielded expansion indices of zero for both
tests. Therefore, no special or updated recommendations are needed for
foundations or slabs on-grade due to soil expansivity.
3. The consultant should specify the sulfate exposure category (ACI 318) based
on soluble sulfate testing and provide recommendations for sulfate resistant
concrete, if necessary, or default to a severe exposure category, if testing is
not available.
GEi Response: As stated in our letter dated March 4, 2022, soluble sulfate
and chloride test results also indicated SO exposure classification (negligible)
for sulfate attack potential to the concrete; and negligible for chloride attack
to the concrete. See the attached test results in Appendix B.
4. The Consultant should provide a list of recommended testing and observation
during grading and construction.
Rincon Adams Street Project
Carlsbad, California
Job No. 20-12852
Page 3
GEi Response: As previously stated in our letter dated March 4, 2022, during
grading, our firm should observe the bottom of excavations, perform field
density tests of placed and compacted soils at least every 2 feet in thickness,
verify the adequacy of soil moisture content and relative compaction, obtain
and verify the maximum dry density of the soils being placed as fill material,
and verify the adequacy of imported soils by performing sieve tests and
expansion index tests as well as maximum dry density and optimum moisture
tests.
In addition, we should verify soil moisture content and compaction of on-site
soils being used for trench and retaining wall backfill, verify adequacy and
moisture content of subgrade soils to receive pavement or flatwork
improvements, in public street areas obtain soil samples and perform R-value
tests in areas to receive pavement (if required to verify adequacy of pavement
cross sections), verify adequacy of compaction of asphalt concrete, verify
adequacy of base material grain size as well as determination of maximum dry
density in the laboratory and relative compaction in the field.
If you have any questions regarding this letter, please contact our office. Reference
to our lob No. 20-12852 will help expedite a response to your inquiry.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
. . . C.E.G. 999/P.G. 3391
Senior Geotechnical Engineer
at
APPENDIX A
Updated Plot Plan
INF-2Approximate Location of Infiltration TestApproximate Location of Proposed Biofiltration BasinScale: 1” = 10’(approximate)LEGENDGEOLOGY LEGENDApproximate Locationof Exploratory TrenchT-9Artificial FillOld Paralic Deposits( units 2-4 )INF-2INF-1T-2T-4T-6T-7T-5T-8T-1T-3T-920-12852-24X36-P.aiMarch 2022Adams Street Homes3745 Adams StreetCarlsbad, CA.Figure No. IIJob No. 20-12852PLOT PLAN ANDSITE SPECIFICGEOLOGIC MAPNOTE: This Plot Plan is not to be used for legalpurposes. Locations and dimensions are approximate.Actual property dimensions and locations of utilitiesmay be obtained from the Approved Building Plansor the “As-Built” Grading Plans.REFERENCE: This Plot Plan was prepared from an existing undatedGRADING PLAN by PASCO LARET SUITER & ASSOCIATESand from on-site field reconnaissance performed by GEI.QopQaf2-4QopQaf2-4QopQaf2-4QopQaf2-4QopQaf2-4
APPENDIX B
Soluble Sulfate and Chloride Test
Results
i;&
LABORATORY REPORT
Telephone (619) 425-1993 Fax 425-7917 Established 1928
CLARKSON LABORATORY AND SUPPLY INC.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S
Date: February 22, 2022
Purchase Order Number: 20-12852
Sales Order Number: 54708
Account Number: GEOE.R
To: *-------------------------------------------------* Geotechnical Exploration, INC.
7420 Trade Street
San Diego, Ca 92121
Attention: Jaime Cerros
Laboratory Number: SO8619 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation: *-------------------------------------------------* Two soil samples received on 02/18/22 at 12:00pm,
taken from Adams Homes Job 20.12852 marked as follows:
ANALYSIS: Water Soluble Sulfate (SO4) California Test 417
(Turbidity Method)
Water Soluble Chloride (Cl) California Test 422
{Titration Method)
Sample
#1 East Side
#2 West Side
Rosa Bernal
RMB/arr
0.003
0.005
Cl%
0.002
0.003