HomeMy WebLinkAboutCDP 2021-0025; SWAN RESIDENCE; GEOTECHNICAL UPDATE; 2020-10-05HETHERINGTON ENGINEERING, INC.
SOIL & FOUNDATION ENGINEERING • ENGINEERING GEOLOGY • HYDROGEOLOGY
TRE Arch.ilecture
300 Carlsbad Vi llage Drive, Suile 108-336
Carlsbad, Cali fornia 92008
Allen tion:
Subj ect:
Mr. Allan T eta
GEOTECHNICAL UPDATE
Proposed Two-Slory Single-Family Residence
2668 Ocean Street
Carlsbad, California
References: Attached
Dear Mr. Teta:
October 5, 2020
Proj ect No. 8889.1
LogNo.21160
In accordance with your request, we have performed a geoteclmical update for the
proposed single-family residence at the subject site. Our work for the update was
perfonned in September and October 2020. The purpose of our work was to updale the
previous geoteclmical work performed by Hetherington Engineering, Inc. (Reference 5).
We have been provided with architech1ral plans (Reference 12) depicting the proposed
developrnenl. This update includes seismic design criteria in accordance with the 2019
California Building Code and ASCE 7-16.
Our scope of work for this update included the following:
• Research and review of Lhe available plans and reports pertinent to the site (see
References).
• Site reconnaissance.
• Engineering and geologic analysis.
• Preparation of this repo1t providing our findings, and our conclusions and
recommendations.
5365 Avenida Encinas, Suite A• Carlsbad, CA 92008-4369 • (760) 931-1917 • Fax (760) 931-0545
333 Third Stree • Laguna Beach, CA 9265 • (949) 715-5440 • Fax (949) 715-5442
www.hetheringtonengineering.com
GEOTECHNICAL lJPDA TE
Project No. 8889. l
LogNo.21160
October 5, 2020
Page 2
The "Geo technical Tnvestigation ... " (Reference 5) should be reviewed for the results of
field at1d laboratory work previously performed and geotechnical recommendations that
are not revi sed in this report.
PROPOSED DEVELOPMENT
It is our understanding that the proposed development consists generally of a custom,
two-story, single-family residence with allached garage. We anticipate wood-frame
construction founded on conventional continuous/spread footings with slab-on-grade
ground floors. Building loads are expected to be typica l of this type of relatively light
construction.
SEISMlClTY
The site is located in a moderately acLive seismic region. Ground shaking due to
earthquakes should be anticipated during the life of the proposed improvements. The
following table lists the known active faults that would have the most significant impact
on the site:
Maximum Probable
Fault E arthquake Slip Rate
(Moment Magnitude) (mm/year)
Rose Canyon 7.0 1.5
__(5-miles/8-kilometers southwest)
Elsinore (Temecula Section) 7.3 3.0
(24-miles/39-kilometers 1101iheast)
SEISMIC EFFECTS
1. Ground Accelerations
The most significant probable earthquake to effect the site would be a 7.0 magnitude
earthquake on the Rose Canyon fault. Based on Section 1803 .5.12 of the 2019
California Building Code, peak ground accelerations (PGArv1) of 0.584g are possible
for the design earthquake.
HETHERINGTON ENGINEERING, INC.
GEOTECHNlCAL UPDATE
Project No. 8889. l
Log No. 21160
October 5, 2020
Page 3
2. Landsliding
T he risk of seismicall y induced landsliding lo affect the site is considered low due lo
the level topography of the site.
3. Ground Cracks
The ri sk or fault surface rupture due lo active faulting is considered low clue lo the
absence of an active fault on site. Ground cracks clue to shaking from seismic events
in the region arc possible, as with all southern California.
4. Liquefaction
The risk or seismically induced liquefaction to affect the site is considered low due to
the dense underlying tenace deposits and absence of shallow groundwater.
5. Tsunamis
The "Tsunami Inundation Map ... " (Reference 3) indicates the site is not located
within a tsunami inundation zone.
CONCLUSIONS /\ND RECOMMENDATIONS
1. General
Based on our site reconnaissance, the site is in a similar condition as when the
"Geolechnical Investigation ... " (Reference 5) was performed. The proposed single-
family residence is considered foasiblc from a geotechnical standpoint. Grading and
foundation plans should consider the appropriate geotechnical features of the site.
The proposed construction is not anticipated lo adversely impact the adjacent
properties from a geotechnical standpoint provided the recommendations presented in
this report, the "Geotechn.ical Investigation ... " (Reference 5), and good construction
practices are implemented during design and construction.
2. Seismic Parameters for Structural Design
Seismic considerations that may be used for structural design at the site, based on
Section 1613 of the 2019 California Building Code and ASCE 7-16, include Lhe
following:
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL UPDATE
Project No. 8889.l
Log No. 21 160
October 5, 2020
Page 4
a. Ground Motion -The proposed struclure should be designed and constructed to
resist the affect of seismic ground motions as provided in Section 1613 of the
2019 California Building Cod e.
Site Address: 2668 Ocean Street, Oceanside, CaUfornia
Latilude:
Longitude:
33.16077°N
11 7.35515°W
The proposed structure has a fundamental period of vibration less than 0.5s,
consequently, the exception to site response analyses in ASCE 7-l 6 (Seclion
20.3.1 .1 ) has been used. Using the Structural Engineers Association Seismic
Design Maps website, the seismic parameters Fv, Stv11, and SD1 are null and not
applicable. The Simplified Alternative Structural Design Criteria provided in
Section12.14 of ASCE 7-16 should be used.
b. Spectral Response Accelerations -Using the location of the property and data
obtained from the Earthquake Hazards Program (Reference 10), short period
Spectral Response Accelerations Ss (0.2 second period) and S, (1.0 second period)
are:
Ss = 1.099g
s, = 0.397g
c. Site Class -In accordance with Chapter 20 of ASCE 7-16 and the underlying
geologic conditions, a Site Class D is considered appropriate for the subject
property.
cl. Site Coefficients Fa and Fv -In accordance with Table 1613.3.3 and considering
the values of Ss and S1, site amplification factors are:
Fa= 1.2
Fv = Null
e. Spectral Response Acceleration Parameters Stv1s and Stv11 -In accordance with
Section 1613.3.3 and considering the values of Ss and S,, and Fa and Fv, Spectral
Response Acceleration Parameters for Maximum Considered Earthquake are:
SMs = 1.319g
S tv11 = Null
HETHERINGTON ENGINEERING. INC.
GEOTECHNlCAL UPDATE
Project No. 8889.1
Log No. 21160
October 5, 2020
Page 5
f. Design Spectral Response Acceleration Parameters Sos and S1J1 -In accordance
with Section 1613.3.4 and considering the values of SMs and SM1, Design Spectral
Response Acceleration Parameters for Maximum Considered Earthquake are:
SDs = 0.88g
So,= Null
g. Long Period Transition Period -A Long Period Transition Period of TL = 8
seconds is provided for use in San Diego County.
h. Seismic Design Category -l n accordance w ith Tables 1604.5, 1613.2.5, and
ASCE 7-16, a Risk Category II and a Seismic Design Category D are cons idered
appropriate for the subject property .
3. Grading and Foundation/Slab Recommendations
The gradi ng and foundation/slab recommendations presented 111 the "Geoteclmical
Investigation ... " (Reference 5) remain applicable.
4. Retaining Walls
Retaining walls free to rotate (cantilevered walls) should be designed for an active
pressure of 40-pounds-per-cubic-foot (equi valent fluid pressure) assunting level
backfill consisting of onsite soils. Walls restrained Crom movement at the top should
be designed for an at-rest earth pressure of 60-pou nds-per-cubic-foot (equivalent fluid
pressure). Any additional surcharge pressures behind the retaining walls should be
added to these values.
Retaining walls should be provided with adequate drainage to prevent buildup of
hydrostatic pressure and should be adequately waterproofed. The subdrain system
behind retaining wall s should consist at a minimum of 4-inch diameter Schedule 40
( or equivale nt) perforated (perforations "down") PVC pipe embedded in at least 1-
cubic-foot of 3/4-inch crushed rock per lineal foot of pipe all wrapped in approved
filter fabric . Other subdrain systems that may be contemplated fo r use behind
retaining walls due to the ultimate design and construction methodology w ill be
considered on a case-by-case basis. Recommendations for wall wateq)roofing should
be provided by the Project Architect and/or Structural Engineer.
The lateral pressure on retaining walls due to earthquake motions ( dynamic lateral
force) may be calculated as PA= 3/8 'Y H2lq, where
dynamic lateral force (pounds/fool)
HETHERINGTON ENGINEERING, INC.
GEOTECHNTCAL UPDATE
Project No. 8889.1
Log No. 211 60
October 5, 2020
Page 6
'Y
H
unit weight= 120 pounds-per-cubic-foot
he ight ol' vva ll (feet)
seismic coefficient= 0.19
The dynamic lateral force may also be expressed as 17.5-pounds-per-cubic-foot
(equivalent flu id pressure).
The dynamic lateral force is in addition to the static fo rce and should be applied as a
triangular distri bution at H/3 above the base of the wall. The dynamic lateral force
need not be applied to retaining walls 6-feet or less in height.
LIMITATIONS
The analyses, conclusions and recommendations contained in this report are based on site
conditions as they existed at the time of our referenced geotechnical investi gation and
further assume the excavations to be representative of the subsurface conditions
throughout the site. If different subsurface conditions from those encountered during our
exploration are observed or appear to be present in excavations, the Geotechnical
Consultant should be promptl y notified for review and reconsideration of the
recommendations.
Our wor k was performed using the degree o[ care and skill ordinarily exercised, under
similar circ umstances, by reputable Geotechnica\ Consultants practicing in this or sim ilar
localities. No other warranty, express or implied, is made as to the conclusions and
professional advice included in this report.
This opportunity to be of service is sincerely a ppreciated. If you have any questi ons,
please call this o ffice.
Sincerely,
Hetherington Engineering, Inc.
Civil Engineer 30
Geotechnical Eng
( expires 3/31 /22)
Paul A. Bogseth
Professional Geologist 3772
Certified Engineering Geologist 11
Certified Hydrogeologist 591
( expires 3/3 1/22)
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL UPDATE
Project No. 8889.1
Log No. 2 11 60
October 5, 2020
Page 7
Edwin R. Cunn ingham
Civil Engineer 81687
(expires 3/31/22)
Distribution: 4-Adclressee
I via e-mail (allan@trearch.com)
HETHERINGTON ENGINEERING. INC.
REFERENCES
1. ASCE 7-l 6, "Minimum Design Loads for Buildings and Other Stn1ctures," American
Society of Civil Engineers/Structural Engineers Insti tute, dated 2017.
2. California Building Standards Commission, California Building Code, 2019 Edition.
3. California Emergency Management Agency, ''Tsunami Tnundalion Map for Planning,
Oceanside Quadrangle/San Luis Rey Quadrangle," dated June I, 2009.
4. East Co un ty Consultation and Engineering, Inc., "Limited Geotechnical Investigation,
Proposed Single-Family Residence, 2680 Ocean Street, City of Carlsbad, CaliLornia
92008," daled March 2, 2017.
5. Helberington Engi11ccring, lnc., ''Geolechnical Investigation, Proposed Single-fam ily
Residence, 2668 Ocean Street, Carlsbad, California," dated October 9, 2019.
6. ICBO, "Maps of K.110,-vn Active Faull Near-Source Zones in California and Adjacent
Portions of Nevada," California Division of M ines and Geology, l 998.
7. Jennings, Charles W., "Fault AcLiviL·y Map of Califorrtia and Adjacent Areas,"
California Data Map Series, Map No. 6, dated 1994.
8. Palos Verdes Engineering, "Swan Residence, 2668 Ocean St., Carlsbad, CA.," dated
January 27, 2015 (Sheets S l-S4, SD1 -SD4, and SNJ).
9. Peterson, Mark P., et al, "Documentation for the 2014 Update of the Utlited States
National Seismic Hazard s Maps," USGS Open File Report 2014-109 L, dated 2014.
l 0. Structural Engineers Association, Earthquake Hazard Program, Seismic Design Maps
Website.
11 . Tan, Siang S. and Kem1edy, Michael P ., "Geologic Maps of the Northwestern Part of
San Diego County, Califorrua", California Division of Mines and Geology, Open-File
Report 96-02, dated 1996.
12. TRE Architecture, "Swan Residence, Carlsbad, California," elate of rev1s1on
September 27, 2020 (Sheets Al .1 and A2. I).
13. U.S. Geological Survey, "San Luis Rey 7.5 -Minute Quadrangle," dated 1997.
14. U.S. Geological Survey, Working Group and California Earthquake Probabilities,
"The Uniform California Earthquake Rupture Forecast", USGS Open File Report
2013-1 165 and CGS Special Report 203, dated 2013.
HETHERINGTON ENGINEERING, INC.
Project No. 8889.1
Log No. 21160
REFERENCES
15. Weber, F. Harold, "Recenl S lope Failures, Ancient Landslides, And Related Geology
of the North-Central Coastal Area, San Diego Cmmty, Cali forn.ia," California
Divis.ion of Mines and Geology, Open-F il e Report 82-12, dated 1982.
HETHERINGTON ENGINEERING. INC.
Projecl No. 8889.1
Log No.21160