HomeMy WebLinkAboutMS 2020-0003; HEMLOCK COAST HOMES; RESPONSE TO THIRD-PARTY REVIEWER; 2021-05-03GHi Geotechnical Exploration, Inc.
3W SOIL AND FOUNDATION ENGINEERING e GROUNDWATER e ENGINEERING GEOLOGY
03 May 2021
Mr. John Norum
KMJ Real Estate
1446 Front Street, Suite 300
San Diego, CA 92101
Subject: Resnonse to Third-Party Reviewer
Hemlock Coastal Homes Residential Project
320 Hemlock Avenue
Carlsbad, California
Dear Mr. Norum:
Job No. 20-12842
As requested and as required by the City of Carlsbad third-party geotechnical
reviewer, Hetherington Engineering, Inc., in a letter dated April 7, 2021, we herein
respond to the review comments. The third-party reviewer has reviewed our "Report
of Preliminary Geotechnical Investigation" for the subject project dated August 24,
2020, and a set of undated grading plans "Grading Plans for Hemlock Avenue" by
Pasco Laret Suiter and Associates (Sheets 1 through 6).
REVIEW COMMENTS OF GEOTECHNICAL REPORT
Comment: The consultant should provide recommendations for temporary
excavations (backcuts, slopes).
GEl Response: Temporary excavations during grading are anticipated not to exceed
5 feet in the area of HP-4 where a trash pit was encountered during exploratory work
at the site. Most of the temporary excavations will be in the range of 3 feet. These
temporary excavations will not require shoring and can be vertical. During
construction, the excavations are anticipated to be in firm recompacted soils and
formational soil, and not expected to exceed 4 feet. A vertical cut up to 3 feet can
be made in the lower part of the excavation, and at 0.5:1.0 (horizontal: vertical) in
the upper backcut.
RECE WED
MAY 17 2021
LAND DEVELOPMENT
ENGINEERING
7420 TRADE STREETO SAN DIEGO, CA. 921210 (858) 5497222 0 FAX: (858) 549-1604 0 EMAIL: geotech@gei-sd.com
Hemlock Coastal Homes Job No. 20-12842
Carlsbad, California Page 2
Comment: The consultant should provide a statement regarding the impact of the
proposed grading and construction on adjacent properties and improvements.
GE! Response: It is our professional opinion that the proposed grading and
construction should not have any adverse impact on the adjacent properties from a
geotechnical engineering viewpoint.
Comment: 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.
GE! Response: On April 28, 2021, we collected two representative soil samples
from the upper 2 feet of each half of the site and obtained soluble sulfate tests (refer
to Appendix A). Test results of 30 and 40 parts per million indicate that the soluble
sulfate of the on-site soils should have negligible potential for attacking concrete, and
Type II cement may be used. There is no other special concrete requirement on the
project based on the test results and ACI 318.
Comment: The consultant should provide a statement as to whether the site is a
Near Fault Site.
GE! Response: On page 12 of our report dated August 24, 2020, we reference the
Kennedy and Tan 2007 Geological Map which indicates no fault is shown to be
crossing the site. It is our professional opinion that the site is not underlain by a
fault. We indicate in our report that the Rose Canyon Fault, which is mapped
approximately 8 miles to the west of the site is the closest active fault
Comment: The consultant should provide a list of recommended geotechnical
observations and testing to be performed during grading and construction.
GE! Response: All "recommended geotechnical observations and testing to be
performed during grading and construction" was provided in our project specific
report dated August 24, 2020, reportedly reviewed by the third-party geotechnical
reviewer. We are providing the following summary of that information.
During grading we should:
observe the bottom of the excavation of removed soils to consist of firm
adequate bearing soils;
perform field density tests of placed and compacted soils at least every 2 feet
in thickness;
Hemlock Coastal Homes Job No. 20-12842
Carlsbad, California Page 3
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, and verify adequacy and moisture
content of subgrade soils to receive pavement or flatwork improvements.
In public street areas, we should obtain soil samples and perform R-value tests as
required by the City of Carlsbad in areas to receive pavement in order to verify
adequacy of pavement cross sections, verify adequacy of compaction of asphalt
concrete, and verify adequacy of grain size of base material to be specified by the
City of Carlsbad.
We should also determine the maximum dry density in the laboratory as well as
relative compaction in the field, and observe the bottom of foundation excavations
and evaluate soil compaction adequacy of bearing soils.
Comment: Foundation and slab design criteria for 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.
GEl Response: We performed Expansion Index (El) tests on two representative soil
samples collected on April 28, 2021, from the upper 2 feet of each half of the site,
and confirmed our visual soil classification regarding soil expansivity. The results
indicated that the on-site soils are very low expansive, with EI=0 and EI=7, and do
not require any expansive soil design per Section 1808.6 of the 2019 CBC. Therefore,
our foundation and slab design recommendations remain applicable as presented in
our geotechnical report dated August 24, 2020.
Hemlock Coastal Homes Job No. 20-12842
Carlsbad, California Page 4
If you have any questions regarding this letter, please contact our office. Reference
to our Job No. 20-12842 will help expedite a response to your inquiry.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
R.C.E. 34422/G.E. 2007
Senior Geotechnical Engineer
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Lzz-ew'7 eiie D. Reed, President
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CERTIFIED IP ENGINEERING
9
APPENDIX A
SOLUBLE SULFATE TEST RESULTS
I BORATORY REP k T
Telephone (619) 425-1993 Fax 425-7917 Established 1928
CLARKSON LABORATORY AND SUPPLY INC.
350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com
ANALYTICAL AND CONSULTING CHEMISTS
Date: April 29, 2021
Purchase Order Number: 20-12842
Sales Order Number: 51550
Account Number: GEOE.R
To:
* -------------------------------------------------*
Geotechnical Exploration, INC.
7420 Trade Street
San Diego, Ca 92121
Attention: Cathy Ganze
Laboratory Number: S08216 Customers Phone: 858-549-7222
Fax: 858-549-1604
Sample Designation:
* -------------------------------------------------
Two soil samples received on 04/26/21 at 1:50pm,
from 320 Hemlock Ave marked as follows:
ANALYSIS: Water Soluble Sulfate (SO4) California Test 417
Sample SO4%
#1 HP-i
#2 HP-2 0.004
Rosa "ernal