HomeMy WebLinkAboutCDP 2020-0018; FORESTER RESIDENCE; GEOTECHNICAL ADDENDUM AND RESPONSES TO THIRD PARTY GEOTECHNICAL REVIEW; 2021-12-17 ADVANCED GEOTECHNICAL SOLUTIONS, INC.
485 Corporate Drive, Suite B
Escondido, California 92029
Telephone: (619) 867-0487 Fax: (714) 786-5661
ORANGE AND L.A. COUNTIES INLAND EMPIRE SAN DIEGO AND IMPERIAL COUNTIES
(714) 786-5661 (619) 867-0487 (619) 867-0487
John Forester December 17, 2021
300 Carlsbad Village Drive, Suite 108a-335 P/W 1901-03
Carlsbad, California 92008 Report No. 1901-03-B-3
Attention: Mr. John Forester
Subject: Geotechnical Addendum and Response to Third-Party Geotechnical Review,
Proposed Single-Family Residence, 4464 Adams Street, Carlsbad, California
References: 1) Advanced Geotechnical Solutions, 2020, Geotechnical Investigation and Preliminary
Design Recommendations for Proposed Single-Family Residence, 4464 Adams Street,
Carlsbad, California, dated December 31, 2019, Report No. 1901-03-B-2.
2) Fusion Eng Tech, 2021, Grading and Improvement Plans for Forester Residence, 4464
Adams Street, plot dated September 1, 2021.
3) Hetherington Engineering, 2021, Third-Party Geotechnical Review Comments (First) 4464
Adams Street, Carlsbad, California, GR2021-0037/CDP2021-0037, their Project No.
9541.1, Log No. 21675, dated November 11, 2021.
Gentlepersons:
In accordance with your request, Advanced Geotechnical Solutions, Inc. (AGS) has prepared this response
to third party geotechnical review comments issued by Hetherington Engineering (2021) on behalf of the
City of San Carlsbad regarding the geotechnical investigation report prepared by AGS (2020) for the
proposed single-family residence project to be located on 4464 Adams Street. The review comments are
presented below followed by our responses. A copy of the review comment sheet is appended.
Comment 1: Due to the age of the geotechnical investigation, the Consultant should update the project
seismic, grading and foundation recommendations to comply with requirements of the 2019 California
Building Code and ASCE 7-16.
AGS Response – As noted in the project geotechnical investigation report by AGS (2020), the site
may be classified as Seismic Site Class D consisting of a stiff soil profile. Site coordinates of
Latitude 33.1456°N and Longitude 117.3272°W were utilized in conjunction with the USGS
Seismic Design Maps web-based ground motion calculator (https://seismicmaps.org/) to obtain the
2019 CBC seismic design parameters presented in Table 1.
~GS
December 17, 2021 Page 2
P/W 1901-03 Report No. 1901-03-B-3
ADVANCED GEOTECHNICAL SOLUTIONS, INC.
TABLE 1 - 2019 CBC SEISMIC DESIGN PARAMETERS
Seismic Site Class D
Mapped Spectral Acceleration Parameter at Period of 0.2-Second, Ss 1.058g
Mapped Spectral Acceleration Parameter at Period 1-Second, S1 0.383g
Site Coefficient, Fa 1.077
Site Coefficient, Fv N/A3
Adjusted MCER1 Spectral Response Acceleration Parameter at Short Period, SMS 1.139g
1-Second Period Adjusted MCER1 Spectral Response Acceleration Parameter, SM1 N/A3
Short Period Design Spectral Response Acceleration Parameter, SDS 0.759g
1-Second Period Design Spectral Response Acceleration Parameter, SD1 N/A3
Peak Ground Acceleration, PGAM2 0.528g
Seismic Design Category N/A3
Notes: 1 Risk-Targeted Maximum Considered Earthquake
2 Peak Ground Acceleration adjusted for site effects
3 Requires Site Specific Ground Motion Hazard Analysis per ASCE 7-16 Section 11.4.8 except if CS is determined
by Equation 12.8-2 for values of T 1.5TS and taken as equal to 1.5 times the values computed with either
Equation 12.8-3 for TL ≥ T > 1.5Ts or Equation 12.8-4 for T > TL.
Comment 2: The Consultant should review the project grading and improvement plans (Reference 2), and
foundation plans, provide any additional geotechnical analyses/recommendations considered necessary,
and confirm that the plans have been prepared in accordance with the geotechnical recommendations.
AGS Response - AGS has reviewed the project grading and improvement plans prepared by Fusion
Eng Tech (2021). Based on our review, the project grading and improvement plans have been
prepared in accordance with the recommendations provided by AGS (2020) in the geotechnical
report for the project. Foundation and structural plans have not been provided to AGS for review
but will be reviewed when available.
Comment 3: 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.
AGS Response - AGS has prepared the attached Plate 1, Geologic Map and Exploration Location
Plan based on the current rough grading plan by Fusion Eng Tech (2021) which depicts the existing
site topography, proposed structures/improvements, proposed rough grades, geologic conditions
and locations of subsurface exploration by AGS. Recommendations for remedial grading were
provided by AGS (2020) in Section 6.1.2 of the geotechnical report as follows: “Topsoil, artificial
fill, and highly weathered old paralic deposits are considered to be compressible in their current
condition and should be removed in areas to receive fill and where settlement sensitive
improvements are planned...In general, it is anticipated that unsuitable soil removals will be on the
order of 2 to 5 feet deep. Localized areas may require deeper removals. The extent of removals can
best be determined in the field during grading when observation and evaluation can be performed
by the soil engineer and/or engineering geologist.” Recommendations for temporary slopes were
provided by AGS (2020) in Section 6.3 of the geotechnical report.
December 17, 2021 Page 3
P/W 1901-03 Report No. 1901-03-B-3
ADVANCED GEOTECHNICAL SOLUTIONS, INC.
Comment 4: The Consultant should provide geologic cross-sections utilizing the current grading plan to
clearly show (at minimum): a) existing topography, b) proposed structures/improvements, c) proposed
finish grades, d) geologic contacts, e) geologic structure, f) locations of the subsurface exploration, g)
temporary construction slopes, and h) remedial grading, etc.
AGS Response - AGS has prepared the attached geologic cross-section A-A in Plate 1 presenting
the requested information.
Comment 5: The Consultant should address the gross and surficial stability of the proposed slopes.
AGS Response - Fill slopes on the project are designed at 2:1 ratio (H:V). The highest proposed
2:1 fill slope is approximately fourteen (14) feet. Shear strength testing was conducted by AGS
(2021). Revised shear strength parameters used by AGS for slope stability analysis are presented
in Table 2.
TABLE 2
SHEAR STRENGTH PARAMETERS
Material Cohesion
(psf)
Friction Angle
(degrees)
Moist Density
(pcf)
Compacted Fill – afc 200 30 130
Old Paralic Deposits – Qop 200 32 125
Gross stability calculations for 2:1 fill slopes are presented in Figures 1 and 2. Surficial stability
calculations for a 2:1 fill slope are presented in Figure 3. Fill slopes constructed at 2:1 ratios or
flatter can be expected to perform satisfactorily when properly constructed with onsite materials
and maintained. Marginal surficial stability may exist if slopes are not properly maintained or are
subjected to inappropriate irrigation practices. Slope protection and appropriate landscaping will
improve surficial stability and should be considered.
Keyways should be constructed at the toe of all fill slopes toeing on existing or cut grade. Fill keys
should have a minimum width equal to fifteen (15) feet or one-half (1/2) the height of ascending
slope, whichever is greater. Where possible, unsuitable soil removals below the toe of proposed fill
slopes should extend outward from the catch point of the design toe at a minimum 1:1 projection
to an approved cleanout. Backcuts should be cut no steeper than 1:1 (H:V) or as recommended by
the geotechnical engineer.
Where possible, skin fills or thin fill sections against natural slopes should be avoided. If skin fill
conditions are identified in the field or are created by remedial grading, it is recommended that a
backcut and keyway be established such that a minimum fill thickness equal to one-half (1/2) the
remaining slope height [not less than fifteen (15) feet] is provided for all skin fill conditions. This
criterion should be implemented for the entire slope height. Drains are required at the heel of
keyways and will be designed based upon exposed conditions.
December 17, 2021 Page 4
P/W 1901-03 Report No. 1901-03-B-3
ADVANCED GEOTECHNICAL SOLUTIONS, INC.
Comment 6: The Consultant should address impacts to adjacent property and improvements as a result of
site grading and construction.
AGS Response – Based on AGS’ review, site grading and construction will not impact the adjacent
properties or improvements. Permission for offsite grading into Adams Street right-of-way and the
adjacent vacant lot to the east may be necessary to complete the keyway construction on the
southern limits of the project.
Comment 7: The Consultant should provide recommendations for fill keys, benching and subdrainage
(widths, depths, etc.).
AGS Response – Recommendations for fill keyways are provided above in AGS’ response to
Comment 5 and are presented in the attached geologic cross-section A-A.
Comment 8: The Consultant should provide a list of recommended testing and observation during grading
and construction.
AGS Response - Recommendations for testing and observation during grading and construction
remedial grading were provided by AGS (2020) in Section 8.2 - Observation During Construction
of the geotechnical report.
Conditions of the referenced report remain applicable unless specifically superseded herein.
Advanced Geotechnical Solutions, Inc., appreciates the opportunity to provide you with geotechnical
consulting services and professional opinions. If you have any questions, please contact the undersigned
at (619) 867-0487.
Respectfully Submitted,
Advanced Geotechnical Solutions, Inc.
___________________________________ ________________________________
ANDRES BERNAL, Sr. Geotechnical Engineer PAUL J. DERISI, Vice President
RCE 62366/GE 2715, Reg. Exp. 9-30-23 CEG 2536, Reg. Exp. 5-31-23
Distribution: (1) Addressee
Attachments: Plate 1 - Geologic Map and Exploration Location Plan
Figures 1 through 3 - Slope Stability Analyses
Third-Party Geotechnical Review Comments
EI. 82.5'
0-5' Afu
5'-21.5' Qop
No GW
EI. 81.8'
0-2.5' Afu
2.5'-21.5' Qop
T.D.=21.5'
No GW
EI. 94'
0-2.5' Afu
2.5'-21.5' Qop
AAA
Keyway
15x2x3
4
4
4
4
AAA
Tie-In 4" Heel Drain to 8" Storm Drain
Proposed Keyway
Location of Heel Drain
with size in inches4
z:
0
f----<( > LLI _J
LLI
A
100
90
Ir.
80 Adams
Street
70J-.--Y
Existing
Grade
J
206-180-38
Proposed
Wall Retaining Existing
Wall Residence Projected 23'
Proposed \:=:....::==--==j'.:'.t--===--==::....:====::-':::-i;::--:::::. Grode / -, _ -?--
L --/ ?-----
/ ,,-------------=-=-=-=-~==-=-=-=-=--===~i=-=-=-=-=___,,,,,;;::JBT-12 _____ ~-~--?-----.
afu ?--
Qop
a IJ..--
:-=:L----~?"---?-- --?-- - -
---
Qop T.D.=21.5'
Qop
r---PVC ~------/ 4" Drain Pipe
15x2x3
Keyway
60 T.D.=21.5'
CROSS-SECTION A-A'
SCALE: 1"=10'
11,-1
EXISTING l D" ACP WATER ~
MAIN P[R DWG 149-8
Highland A'
Drive
?/ .,,_
100
90
z:
0
f----
80 ;!
70
60
LLI _J
Lu
I
206-192-07
LEGEND:
A
B-3+
afu
Qop
Tsa
A'
Approximate Location of Boring
(AGS, 2017)
Artificial Fill -Undocumented
Old Paralic Deposits
(Bracketed where buried)
Santiago Formation
(Bracketed where buried)
Approximate Location of
Geologic Cross Section
-----?-'
Existing Grade/Structures
Proposed Grade/Structures
Approximate Location of Geologic
Contact (Queried were uncertain)
0--
10
PLATE 1
Geologic Map and Exploration Location Plan
ADVANCED GEOTECHNICAL SOLUTIONS, INC
Project:
P/W 1901-03
Report:
1901-03-B-3
a 10 20
SCALE 1 •-1 O'
FUSION ENG TECH
1810 GILLESPIE WAY #207
EL CAJON, CA 92020
(619) 736-2800
Date:
Dec. 2021
30
rfESS10
x-" s.Riv,: e ,
1'_,. ,ts
C 73878 ~
xp. os/30/23 SI •
CIVIL
C,-c;J>I..I<
"AS BUILT"
RCE EXP. DATE
REVIEWED BY:
INSPECTOR DATE
I SHEET I CITY OF CARLSBAD I SgETS I
ENGINEERING DEPARTMENT
FORESTER RESIDENCE
4464 ADAMS STREET
APPROVED: JASON S. GELDERT
CITY ENGINEER RCE 63912 EXPIRES 9/30/22 DATE
OWN BY:
I
PROJECT NO. I DRAWING NO. CHKD BY:
RVWD BY:
0 20 40 60 80 100
40
60
80
100
1901-03 Forester Residence 2:1 Fill Slope (Static)
k:\1901-03 forester residence\slope stability\highest fill - static.pl2 Run By: AGS 12/17/2021 04:55PM
1
2
3 4
5
6
7
2
1
12
2
2
2
bcdefghija
#FSa 2.469b 2.469c 2.469
d 2.472
e 2.472
f 2.485g 2.485h 2.487i 2.487
j 2.487
SoilDesc.
afc
Qop
SoilTypeNo.1
2
TotalUnit Wt.(pcf)130.0
125.0
SaturatedUnit Wt.(pcf)
130.0
125.0
CohesionIntercept(psf)
200.0
200.0
FrictionAngle(deg)
30.0
32.0
PorePressureParam.
0.00
0.00
PressureConstant(psf)
0.0
0.0
Piez.SurfaceNo.
0
0
GSTABL7 v.2 FSmin=2.469
Safety Factors Are Calculated By The Modified Bishop Method
FIGURE 1
0 20 40 60 80 100
40
60
80
100
1901-03 Forester Residence 2:1 Fill Slope (Pseudo-static)
k:\1901-03 forester residence\slope stability\highest fill - pseudo static.pl2 Run By: AGS 12/17/2021 04:54PM
1
2
3 4
5
6
7
2
1
12
2
2
2
bcdefg hija
#FSa 1.823b 1.823c 1.825
d 1.825
e 1.825
f 1.827g 1.827h 1.828i 1.828
j 1.832
SoilDesc.
afc
Qop
SoilTypeNo.1
2
TotalUnit Wt.(pcf)130.0
125.0
SaturatedUnit Wt.(pcf)
130.0
125.0
CohesionIntercept(psf)
200.0
200.0
FrictionAngle(deg)
30.0
32.0
PorePressureParam.
0.00
0.00
PressureConstant(psf)
0.0
0.0
Piez.SurfaceNo.
0
0
Load ValuePeak(A) 0.528(g)kh Coef. 0.150(g)<
GSTABL7 v.2 FSmin=1.823
Safety Factors Are Calculated By The Modified Bishop Method
FIGURE 2
FORESTER RESIDENCE
SURFICIAL SLOPE STABILITY
Assume: (1) Saturation To Slope Surface
(2) Sufficient Permeability To Establish Water Flow
Pw = Water Pressure Head=(z)(cos^2(a))
Ws = Saturated Soil Unit Weight
Ww = Unit Weight of Water (62.4 lb/cu.ft.)
u = Pore Water Pressure=(Ww)(z)(cos^2(a))
z = Layer Thickness
a = Angle of Slope
phi = Angle of Friction
c = Cohesion
Fd = (0.5)(z)(Ws)(sin(2a))
Fr = (z)(Ws-Ww)(cos^2(a))(tan(phi)) + c
Factor of Safety (FS) = Fr/Fd
2:1 SLOPE - ARTIFICIAL FILL
Given:Ws z a phi c
(pcf)(ft) (degrees)(radians)(degrees)(radians)(psf)
130 4 26.565 0.464 30 0.5236 200
Calculations:
Pw u Fd Fr FS
3.20 199.68 208.00 324.89 1.56
ADVANCED GEOTECHNICAL SOLUTIONS, INC.FIGURE 3
SLOPE SURFACE
--------::--------J a
Fd< l 1 l
Ws-Ww I --------------~ --------------:,-----Fr-----' -------------------
FAILURE PATH
FLOW LINES
I •
HETHERINGTON ENGINEERING, INC.
SOIL & FOUNDATION ENGINEERING • ENGINEERING GEOLOGY • HYDROGEOLOGY
November 11, 2021
Project No. 9541.1
Log No. 21675
City of Carlsbad
Land Development Engineering
1635 Faraday Avenue
Carlsbad, California 92008-7314
Attention:
Subject:
Ms. Nichole Fine
THIRD-PARTY GEOTECHNICAL REVIEW (FIRST)
4464 Adams Street
Carlsbad, California
GR2021-0037/CDP2021-0037
References: 1) "Geotechnical Investigation and Preliminary Design Recommendations
Dear Ms. Fine:
for Proposed Single-Family Residence, 4464 Adams Street, Carlsbad,
California", by Advanced Geotechnical Solutions, Inc., dated December
31 , 2019.
2) "Grading and Improvement Plans for: Forester Residence, 4464 Adams
Street", by Fusion Eng Tech, undated (9-sheets).
In accordance with your request, Hetherington Engineering, Inc. has provided third-party
geotechnical review of Reference 1. The following comments are provided for analyses
and/or response by the Geotechnical Consultant.
1. Due to the age of the geotechnical investigation, the Consultant should update the
project seismic, grading and foundation recommendations to comply with requirements
of the 2019 California Building Code and ASCE 7-16.
2. The Consultant should review the project grading and improvement plans (Reference
2), and foundation plans, provide any additional geotechnical
analyses/recommendations considered necessary, and confirm that the plans have been
prepared in accordance with the geotechnical recommendations.
3. The Consultant should provide an updated geoteclmical map utilizing the current
grading plan for the project to clearly show (at minimwn): 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.
5365 Avenida Encinas, Suite A • Carlsbad, CA 92008-4369 • (760) 931-1917 • Fax (760) 931-0545
333 Third Street • Laguna Beach, CA 92651 • (949) 715-5440 • Fax (949) 715-5442
www.hetheringtonengineering.com
THIRD-PARTY GEOTECHNICAL REVIEW (FIRST)
Project No 9541.1
Log No. 21675
November 11, 2021
Page2
4. The Consultant should provide geologic cross-sections utilizing the Cll!Tent grading
plan to clearly show (at minimum): a) existing topography, b) proposed
strnctures/improvements, c) proposed finish grades, d) geologic contacts, e) geologic
strncture, f) locations of the subsurface exploration, g) temporary construction slopes,
and h) remedial grading, etc.
5. The Consultant should address the gross and surficial stability of the proposed slopes.
6. The Consultant should address impacts to adjacent property and improvements as a
result of site grading and construction.
7. The Consultant should provide recommendations for fill keys, benching and
subdrainage (widths, depths, etc).
8. The Consultant should provide a list of recommended testing and observation during
grading and construction.
\
Please call ifthere are any questions.
Sincerely,
HETHERING
Paul A. Bogs
Professio Geol gist
Certified ngineering Geologist 1153
Certified Hydrogeologist 591
( expires 3/31/22)
Mark D. etherington
Civil Engineer 30488
Geotechnical Engineer 397
( expires 3/31/22)
Distiibution: 1-via e-mail (Nichole.Fine@carlsbadca.gov)
I-via e-mail (ldetrackingdesk@carlsbadca.gov)
I-via e-mail (Tim.Carroll@carlsbadca.gov)
HETHERINGTON ENGINEERING, INC.