HomeMy WebLinkAboutMS 2021-0004; ACACIA BEACH HOMES; GEOTECHNICAL INVESTIGATION; 2021-06-21
GEOTECHNICAL INVESTIGATION
Proposed Residential Development
245 Acacia Avenue
Carlsbad, California
HETHERINGTON ENGINEERING, INC.
June 21, 2021
Project No. 9324.1
Log No. 21510
Rincon Homes/Rincon Real Estate Group
3005 S. El Camino Real
San Clemente, California 92672
Attention: Mr. Tom St. Clair
Subject: GEOTECHNICAL INVESTIGATION
Proposed Residential Development
245 Acacia Avenue
Carlsbad, California
References: Attached
Dear Mr. St. Clair:
In accordance with your request, we have performed a geotechnical investigation for the
proposed three, three-story detached single-family residences at the subject site. Our
work was performed during May through July 2021. The purpose of the investigation was
to evaluate the geologic and soil conditions at the site in order to provide grading and
foundation recommendations for the proposed construction.
Our scope of work included the following:
Research and review of readily available geologic literature, geotechnical reports and
plans pertinent to the site (see References).
Subsurface exploration consisting of test pits to depths of 5.5 and 6.0-feet for the
purpose of soil/bedrock sampling and geologic observation.
Laboratory testing of soil/bedrock samples obtained during the subsurface
exploration.
Engineering and geologic analysis.
Preparation of a report providing the results of our field and laboratory work, analysis
and our conclusions and recommendations.
SOIL & FOUNDATION ENGINEERING ENGINEERING GEOLOGY HYDROGEOLOGY
(760) 931-1917 Fax (760) 931-0545
333 Third Stree Laguna Beach, CA 9265 (949) 715-5440 Fax (949) 715-5442
Carlsbad, CA 92008-43695365 Avenida Encinas, Suite A
HETHERINGTON ENGINEERING, INC.
www.hetheringtonengineering.com
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 2
SITE DESCRIPTION
The subject property is located at 245 Acacia Avenue, Carlsbad, California (see Location
Map, Figure 1). The site consists of a relatively flat rectangular shaped parcel. The site
presently supports two, single-story single-family structures. The property is bounded by
Acacia Avenue to the north, and by similarly developed residential properties to the
south, west and east
PROPOSED DEVELOPMENT
Proposed development consists of three, three-story detached single-family residences.
We anticipate wood-frame construction founded on conventional continuous/spread
footings with slab-on-grade floors. Building loads are expected to be typical for this type
of relatively light construction. Grading is expected to consist of cut and fill on the order
of approximately 1 to 3-feet.
SUBSURFACE EXPLORATION
Subsurface exploration consisted of two hand excavated test pits to maximum depths of
5.5 and 6.0-feet below existing grades. The approximate locations of the test pits are
shown on the attached Plot Plan, Figure 2.
The subsurface exploration was supervised by an engineer from this office, who visually
classified the soil, and obtained bulk and relatively undisturbed samples for laboratory
testing. The soils were visually classified according to the Unified Soil Classification
System. Classifications are shown on the attached Logs of Test Pits, Figures 3 and 4.
LABORATORY TESTING
Laboratory testing was performed on samples obtained during the subsurface exploration.
Tests performed consisted of the following:
Dry Density/Moisture Content (ASTM: D 2216)
Maximum Dry Density/Optimum Moisture Content (ASTM: D 1557)
Direct Shear (ASTM: D 3080)
HETHERINGTON ENGINEERING, INC.
PROJECT NO. FIGURE NO.
GEOTECHNICAL CONSULTANTS
HETHERINGTON ENGINEERING,INC.
ADAPTED FROM: The Thomas Guide, San Diego County, 57th Edition, Page 1106
SCALE: 1" - 2000'
(1 Grid Equals: 0.5 x 0.5 miles)
LOCATION MAP
1
245 Acacia Avenue
Carlsbad, California
9324.1
N
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 3
Soluble Sulfate (Cal Test 417)
Results of the dry density and moisture content determinations are presented on the Logs
of Test Pits, Figures 3 and 4. The remaining laboratory test results are presented on the
attached Laboratory Test Results, Figure 5.
SOIL AND GEOLOGIC CONDITIONS
1. Geologic Setting
The subject site lies within a relatively level marine terrace that is contained within
the coastal plain region of northern San Diego County, California. The coastal plain
region is characterized by numerous regressive marine terraces of Pleistocene age that
have been established above wave-cut platforms of underlying middle Eocene
bedrock and were formed during glacio-eustatic changes in sea level. The terraces
extend from areas of higher elevation east of the site and descend generally west-
southwest in a “stair-step” fashion down to the present day coastline. These marine
terraces increase in age eastward. The site area is contained within the southwest
portion of the California Department of Conservation San Luis Rey 7-1/2 minute
quadrangle (Reference 10).
2. Geologic Units
a. Weathered Paralic Deposits: Weathered paralic deposits were observed to
immediately underlie the property to a depth of approximately 1 to 3-feet below
existing site grades. The weathered paralic deposits consist generally of dry to
damp, medium dense to dense, brown silty sand. The existing weathered paralic
deposits are not considered suitable for support of proposed improvements or
compacted fill in their existing condition.
b. Paralic Deposits: Underlying the weathered paralic deposits are sediments
classified as Pleistocene paralic deposits. These sediments consist generally of
damp, dense to very dense, orange brown silty sand.
3. Groundwater
Groundwater or seepage was not encountered in the test pits to the maximum
explored depths. It should be noted, however, that fluctuations in the amount and
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 4
level of groundwater may occur due to variations in rainfall, irrigation, and other
factors that might not have been evident at the time of our field investigation.
SEISMICITY
Based on our review of the available geologic maps/literature, there are no active or
potentially active faults that traverse the subject site, and the property is not located
within the currently mapped limits of an Alquist-Priolo Earthquake Fault Zone. The
following table lists the known active faults that would have the most significant impact
on the site:
Fault
Maximum Probable
Earthquake
(Moment Magnitude)
Slip Rate
(mm/year)
Rose Canyon
(4.8-miles/7.7 kilometers southwest)6.9 1.5
Palos Verdes/Coronado Bank
(20.5-miles/33.0-kilometers
southwest)
7.7 3.0
SEISMIC EFFECTS
1. Ground Accelerations
The most significant probable earthquake to affect the property would be a 7.7
magnitude earthquake on the Palos Verdes/Coronado Bank fault. Based on Section
1803.5.12 of the 2016 California Building Code and Section 11.8.3 of ASCE 7-10,
peak ground accelerations (PGAM) of 0.540g are possible for the design earthquake.
2. Landsliding
Review of the referenced geologic maps/literature indicates that the subject property
is not included within the limits of any previously mapped landsliding. The risk of
seismically induced landsliding affecting the proposed structures is considered low
due to the relatively level topography.
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 5
3. Ground Cracks
The risk of fault surface rupture due to active faulting is considered low due to the
absence of a known active fault on site. Ground cracks due to shaking from seismic
events in the region are possible, as with all of southern California.
4. Liquefaction
The risk of seismically induced liquefaction within the site is considered low due to
the dense nature of the terrace deposits and lack of shallow groundwater.
5. Tsunamis
The site is not located within a mapped tsunami inundation area. The risk of a
tsunami adversely impacting the site is considered low due to the elevation of the
property above sea level.
CONCLUSIONS AND RECOMMENDATIONS
1. General
The proposed development is considered feasible from a geotechnical standpoint.
Grading and foundation plans should take into account the appropriate geotechnical
features of the site. Provided that the recommendations presented in this report and
good construction practices are utilized during design and construction, the proposed
construction is not anticipated to adversely impact the adjacent properties from a
geotechnical standpoint.
2. Seismic Parameters for Structural Design
Seismic considerations that may be used for structural design at the site include the
following:
a. Ground Motion - The proposed improvements should be designed and constructed
to resist the effects of seismic ground motions as provided in Section 1613 of the
2019 California Building Code and ASCE 7-16.
Site Address: 245 Acacia Avenue, Carlsbad, CA 92008
Latitude: 33.1519582 N
Longitude: 117.3462458 W
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 6
b. Spectral Response Accelerations - Using the location of the property and data
obtained from the SEAOC/OSHPD Seismic Design Maps Program, short period
Spectral Response Accelerations Ss (0.2 second period) and S1 (1.0 second
period) are:
Ss = 1.094g
S1 = 0.395g
c. Site Class - In accordance with Chapter 20 of ASCE 7, and the underlying
geologic conditions, a Site Class D is considered appropriate for the subject
property.
d. Site Coefficients Fa and Fv - In accordance with Table 1613.3.3 and considering
the values of Ss and S1, Site Coefficients for a Class D site are:
Fa = 1.062
Fv = null
e. Spectral Response Acceleration Parameters Sms and Sm1 - In accordance with
Section 1613.3.3 and considering the values of Ss and S1, and Fa and Fv, Spectral
Response Acceleration Parameters for Maximum Considered Earthquake are:
Sms = 1.162g
Sm1 = null
f. Design Spectral Response Acceleration Parameters Sds and Sd1 - 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 = 0.775g
Sd1 = 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 - In accordance with Tables 1604.5, 1613.3.5(1) and
1613.3.5(2), and ASCE 7, a Risk Category II and a Seismic Design Category D
are considered appropriate for the subject property.
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 7
3. Site Grading
Prior to grading, areas of proposed improvements should be cleared of existing
surface improvements, obstructions, vegetation and debris. Materials generated
during clearing should be disposed of at an approved location off-site. Holes resulting
from the removal of buried obstructions should be filled with compacted fill or lean
concrete. Seepage pits and/or septic systems, if encountered during site development,
should be abandoned in accordance with local guidelines.
Within the limits of proposed improvements and to 3-feet beyond, any existing
fill/weathered paralic deposits should be removed down to approved undisturbed
paralic deposits. We anticipate removal depths on the order of 1 to 3-feet below
existing site grades. Actual removal depths should be determined in the field by the
Geotechnical Consultant based on conditions exposed during grading.
Following removals, the exposed surface soils should be scarified to a depth of 6 to 8-
inches, moisture conditioned to about optimum moisture content and compacted to at
least 90-percent relative compaction (ASTM: D 1557).
Fill should be moisture conditioned to about optimum moisture content and
compacted by mechanical means in uniform horizontal lifts of 6 to 8-inches in
thickness. All fill should be compacted to a minimum relative compaction of 90-
percent based upon ASTM: D 1557. The on-site materials are suitable for use as
compacted fill provided all vegetation and debris are removed. Rock fragments over
6-inches in dimension and other perishable or unsuitable materials should be
excluded from the fill.
All grading and compaction should be observed and tested as necessary by the
Geotechnical Consultant.
4. Foundation and Slab Recommendations
The proposed improvements should be supported on conventional continuous/spread
footings founded at least 18-inches into compacted fill and/or approved paralic
deposits. Continuous footings should be at least 12-inches wide, and reinforced with
a minimum of four #4 bars, two top and two bottom. Foundations located adjacent to
utility trenches should extend below a 1:1 (horizontal to vertical) plane projected
upward from the bottom of the trench.
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 8
Foundations bearing as recommended may be designed for a dead plus live load
bearing value of 2000-pounds-per-square-foot. This value may be increased by one-
third for loads including wind and seismic forces. A lateral bearing value of 250-
pounds-per-square-foot per foot of depth and a coefficient of friction between
foundation soil and concrete of 0.35 may be assumed. These values assume that
footings will be poured neat against the foundation soils. Footing excavations should
be observed by the Geotechnical Consultant prior to the placement of reinforcing
steel in order to verify that they are founded in suitable bearing materials.
Total and differential settlement due to foundation loads is considered to be less than
3/4 and 3/8-inch, respectively, for foundations founded as recommended.
Slab-on-grade floors should have a minimum thickness of 5-inches and should be
reinforced with #4 bars spaced at 18-inches, center-to-center, in two directions, and
supported on chairs so that the reinforcement is at mid-height in the slab. Floor slabs
should be underlain with a moisture vapor retarder consisting of a minimum 15-mil
membrane. At least 2-inches of sand should be placed over the vapor retarder to
assist in concrete curing and at least 2-inches of sand should be placed below the
vapor retarder. The vapor retarder should be placed in accordance with ASTM: E
1643. Prior to placing concrete, the slab subgrade soils should be thoroughly
moistened.
Vapor retarders are not intended to provide a waterproofing function. Should
moisture vapor sensitive floor coverings be planned, a qualified consultant/contractor
should be consulted to evaluate moisture vapor transmission rates and to provide
recommendations to mitigate potential adverse impacts of moisture vapor
transmissions on the proposed flooring.
5. Sulfate Content
A representative sample of the on-site soil was submitted for sulfate testing. The
results of the sulfate content test are summarized on the Laboratory Test Results,
Figure 5. The sulfate content is consistent with a not applicable (S0) sulfate exposure
classification per Table 4.2.1 of the American Concrete Institute Publication 318,
consequently, no special provisions for sulfate resistant concrete are considered
necessary. Other corrosivity testing has not been performed, consequently, on-site
soils should be assumed to be severely corrosive to buried metals unless testing is
performed to indicate otherwise.
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 9
6. Retaining Walls
Retaining wall foundations should be designed in accordance with the foundation
recommendations provided previously in this report. Retaining walls free to rotate
(cantilevered walls) should be designed for an active pressure of 35-pounds-per-
cubic-foot (equivalent fluid pressure). Walls restrained from movement at the top
should be designed for an at-rest pressure of 55-pounds-per-cubic-foot (equivalent
fluid pressure). These values are based on level backfill consisting of onsite granular
soils. Any additional surcharge pressures behind 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 walls should consist at a minimum of 4-inch diameter Schedule 40
(or equivalent) 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 an approved
filter fabric. The subdrain system should be connected to a solid outlet pipe with a
minimum of 1-percent fall that discharges to a suitable drainage device.
Recommendations for wall waterproofing should be provided by the Project Architect
and/or Structural Engineer.
The lateral pressure on retaining walls due to earthquake motions (dynamic lateral
force) should be calculated as PA = 3/8 γ H2kh where
PA = dynamic lateral force (pounds/foot)
γ = unit weight = 110-pounds-per-cubic-foot
H = height of wall (feet)
kh = seismic coefficient = 0.18
The dynamic lateral force may also be expressed as 15-pounds-per-cubic-foot
(equivalent fluid pressure).
The dynamic lateral force is in addition to the static force and should be applied as a
triangular distribution at 1/3H above the base of the wall. The dynamic lateral force
need not be applied to retaining walls 6-feet or less in height.
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 10
7. Temporary Slopes
Temporary slopes necessary to facilitate construction may be cut vertically in terrace
deposits up to 5-feet where the cuts are not influenced by existing property line
constraints or structures/improvements. Temporary slopes near existing
structures/improvements/property lines, over 5-feet in height, and/or cuts exposing
fill should be inclined at a slope ratio no steeper than 1:1 (horizontal to vertical) or
shored. Field observations by the Engineering Geologist during grading of temporary
slopes are recommended and considered necessary to confirm anticipated conditions
and provide revised recommendations if warranted. Shoring recommendations can be
provided on request.
8. Retaining Wall and Utility Trench Backfill
All retaining wall and utility trench backfill should be compacted to at least 90-
percent relative compaction (ASTM: D 1557). Backfill should be tested and observed
by the Geotechnical Consultant.
9. Site Drainage
The following recommendations are intended to minimize the potential adverse
effects of water on the structures and appurtenances.
a. Consideration should be given to providing the structures with roof gutters and
downspouts that discharge to an area drain system and/or to suitable locations
away from the structure.
b. All site drainage should be directed away from the structures.
c. No landscaping should be allowed against buildings. Moisture accumulation or
watering adjacent to foundations can result in deterioration of building materials
and may effect foundation performance.
d. Irrigated areas should not be over-watered. Irrigation should be limited to that
required to maintain the vegetation. Additionally, automatic systems must be
seasonally adjusted to minimize over-saturation potential particularly in the
winter (rainy) season.
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 11
e. All yard and roof drains should be periodically checked to verify they are not
blocked and flow properly. This may be accomplished either visually or, in the
case of subsurface drains, by placing a hose at the inlet and checking the outlet for
flow.
10. Recommended Observation and Testing During Construction
The following tests and/or observations by the Geotechnical Consultant are
recommended:
a. Observation and testing of grading.
b. Foundation excavations prior to placement of forms and reinforcement.
c. Utility trench backfill.
d. Retaining wall backdrains and backfill.
11. Grading and Foundation Plan Review
Grading and foundation plans should be reviewed by the Geotechnical Consultant to
confirm conformance with the recommendations presented herein or to modify the
recommendations as necessary.
LIMITATIONS
The analyses, conclusions and recommendations contained in this report are based on site
conditions as they existed at the time of our investigation 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 during construction, the Geotechnical
Consultant should be promptly notified for review and reconsideration of
recommendations.
Our investigation was performed using the degree of care and skill ordinarily exercised,
under similar circumstances, by reputable Geotechnical Consultants practicing in this or
similar localities. No other warranty, express or implied, is made as to the conclusions
and professional advice included in this report.
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL INVESTIGATION
Project No. 9324.1
Log No. 21510
June 21, 2021
Page 12
This opportunity to be of service is sincerely appreciated. If you have any questions,
please call this office.
Sincerely,
HETHERINGTON ENGINEERING, INC.
Mark D. Hetherington Edwin R. Cunningham
Civil Engineer 30488 Civil Engineer 81687
Geotechnical Engineer 397 (expires 3/31/22)
(expires 3/31/22)
Jose Pimentel
Engineer-in-Training
Attachments: Location Map Figure 1
Plot Plan Figure 2
Logs of Test Pits Figures 3 and 4
Laboratory Test Results Figure 5
Distribution: 1-via e-mail Tom St. Clair (tstclair@rincongrp.com)
4-Addressee
HETHERINGTON ENGINEERING, INC.
REFERENCES
Project No. 9324.1
Log No.
1) American Society of Civil Engineers/Structural Engineers Institute, "Minimum
Design Loads for Buildings and Other Structures,” ASCE 7-10, dated May 2010.
2) California Geological Survey, "Tsunami Inundation Map for Emergency Planning-
San Luis Rey Quadrangle," dated June 1, 2009.
3) ICBO, California Building Code, 2016 Edition.
4) Stephen Dalton Architects, Floor Plans, dated May 24, 2021 (Sheets A2-1, A2-2, A2-
3).
5) Peterson, Mark P., et al, “Documentation for the 2008 Update of the United States
National Seismic Hazards Maps,” USGS Open File Report 2008-1128, dated 2008.
6) SEAOC/OSHPD Seismic Design Maps Website.
7) Tan, Siang S. and Kennedy, Michael P., "Geologic Maps of the Northwestern Part of
San Diego County, California," California Division of Mines and Geology, Open-File
Report 96-02, dated 1996.
8) Tan, Siang S. and Giffen, Desmond G., "Landslide Hazards in the Northern Part of
the San Diego Metropolitan Area, San Diego, California," California Division of
Mines and Geology, Open File Report 95-04, dated 1995.
9) California Department of Conservation- Division of Mines and Geology, "Geologic
Maps of the Northwestern Part of San Diego County, California- Plate 1," dated
1996.
10) United States Geological Survey, "San Luis Rey Quadrangle- San Diego County 7.5-
Minute Series,” dated 2015.
HETHERINGTON ENGINEERING, INC.
2
LEGEND
APPROXIMATE LOCATION OF TEST PITAC
A
C
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A
A
V
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N
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AVENUE245 ACACIA
TP-1
TP-2
TP-1
GEOTECHNICAL CONSULTANTS
HETHERINGTON ENGINEERING,INC.
PROJECT NO. FIGURE NO.
PLOT PLAN
012
5 1015200
245 Acacia Avenue
Carlsbad, California
9324.1
N
SCALE: 1" = 10'
99
103
109
3.0
3.3
4.2
SM
WEATHERED PARALIC DEPOSITS: Brown silty sand, dry to damp,
dense
PARALIC DEPOSITS: Orange brown silty sand, damp, dense to very
dense
Total Depth: 5.5-feet
No Groundwater
No Caving
GEOTECHNICAL CONSULTANTS PROJECT NO.FIGURE NO.
HETHERINGTON ENGINEERING,INC.
06/17/21
9324.1 3
Mansolf Excavation
Carlsbad, California245 Acacia Avenue
TEST PIT NO.ELEVATION:TP-1DR
Y
DE
N
S
I
T
Y
(p
c
f
)
MO
I
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T
U
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(%
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SO
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A
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S
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(U
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S
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C
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S
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)
BACKHOE COMPANY:BUCKET SIZE:DATE:
SOIL DESCRIPTION
LOG OF TEST PITS
+-DE
P
T
H
(F
E
E
T
)
'BU
L
K
SA
M
P
L
E
DE
N
S
I
T
Y
TE
S
T
0.0
5.0
10.0
15.0
20.0
105
108
3.0
5.6
SM
WEATHERED TERRACE DEPOSITS: Brown silty sand, dry to
damp, dense to very dense
PARALIC DEPOSITS: Orange brown silty sand, damp, dense to very
dense
@ 3': No recovery of Drive Sample
Total Depth: 6-feet
No Groundwater
No Caving
GEOTECHNICAL CONSULTANTS PROJECT NO.FIGURE NO.
HETHERINGTON ENGINEERING,INC.
06/17/21
9324.1 4
Mansolf Excavation
Carlsbad, California245 Acacia Avenue
TEST PIT NO.ELEVATION:TP-2DR
Y
DE
N
S
I
T
Y
(p
c
f
)
MO
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SO
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(U
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)
BACKHOE COMPANY:BUCKET SIZE:DATE:
SOIL DESCRIPTION
LOG OF TEST PITS
+-DE
P
T
H
(F
E
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T
)
'BU
L
K
SA
M
P
L
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DE
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S
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0.0
5.0
10.0
15.0
20.0
LABORATORY TEST RESULTS
Figure 5
Project No. 9324.1
Log No.
DIRECT SHEAR
(ASTM: D 3080)
Sample Location Angle of Internal
Friction (º)
Cohesion (psf) Remarks
TP-1 @ 0’-1’ 34 50 2.5 – in. ring, remolded to 90%, soaked,
consolidated, drained
SULFATE TEST RESULTS
(CAL 417)
Sample Location Soluble Sulfate in Soil (%)
TP-1@ 0’ to 1’ 0.045
MAXIMUM DRY DENSITY/OPTIMUM MOISTURE CONTENT
(ASTM: D 1557A)
Sample Location Description Maximum Dry
Density (pcf)
Optimum Moisture
Content (%)
TP-1 @ 0’ to 1’ Brown silty sand 125.0 9.5
HETHERINGTON ENGINEERING, INC.
ADDENDUM LETTERS
September 28, 2021
Project No. 9324.1
Log No. 21614
Rincon Homes/Rincon Real Estate Group
3005 S. El Camino Real
San Clemente, California 92672
Attention: Mr. Tom St. Clair
Subject: RESPONSE TO LDE REVIEW #1, CITY OF CARLSBAD
Proposed Residential Development
245 Acacia Avenue
Carlsbad, California
References: 1. “LDE Review #1,” by City of Carlsbad, dated August 5, 2021.
2. “Geotechnical Investigation, Proposed Residential Development, 245
Acacia Avenue, Carlsbad, California,” by Hetherington Engineering,
Inc., dated June 21, 2021
Dear Mr. St. Clair:
In accordance to the request by Brian Knapp, Pasco Laret Suiter & Associates, we are
providing the following responses to the City of Carlsbad review comments included in
the “LDR Review #1…” (Reference 1).
1. Pervious pavers are not being considered for the site at this time.
2. The proposed landscape areas are not anticipated to adversely impact the adjacent
structure from a geotechnical standpoint as long as the landscape areas drain away
from the structure at a minimum of 5% for 10-feet in accordance with the 2019
California Building Code Section 1804.4.
3. See attached complete plot plan.
SOIL & FOUNDATION ENGINEERING ENGINEERING GEOLOGY HYDROGEOLOGY
(760) 931-1917 Fax (760) 931-0545
333 Third Street Laguna Beach, CA 92651 (949) 715-5440 Fax (949) 715-5442
Carlsbad, CA 92008-43695365 Avenida Encinas, Suite A
HETHERINGTON ENGINEERING, INC.
www.hetheringtonengineering.com
PROPOSAL FOR GEOTECHNICAL SERVICES
Project No. 9324.1
Log No. 21614
September 28, 2021
Page 2
This opportunity to be of service is appreciated. If you have any questions, please contact
our Carlsbad office.
Sincerely,
HETHERINGTON ENGINEERING, INC.
Mark D. Hetherington Edwin R. Cunningham
Civil Engineer 30488 Civil Engineer 81687
Geotechnical Engineer 397 (expires 3/31/22)
(expires 3/31/22)
Attachments: Plot Plan Figure 2
Distribution: 1-via e-mail (tstclair@rincongrp.com)
1-via e-mail (bknapp@plsaengineering.com)
3- Addressee
HETHERINGTON ENGINEERING, INC.
2
LEGEND
APPROXIMATE LOCATION OF TEST PITAC
A
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AVENUE245 ACACIA
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GEOTECHNICAL CONSULTANTS
HETHERINGTON ENGINEERING,INC.
PROJECT NO. FIGURE NO.
PLOT PLAN
012
5 1015200
245 Acacia Avenue
Carlsbad, California
9324.1
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SCALE: 1" = 10'
GEOTECHNICAL | ENVIRONMENTAL | MATERIALS
August 16, 2022
Project No. 3819-SD
Rincon Homes
5315 Avenida Encinas, Suite 200
Carlsbad, CA 92008
Attention: Mr. Stuart Hatch
Subject: Intelocking Concrete Pavement
Acacia Beach Homes Project
245 Acacia Ave
Carlsbad, California, 92008
APN: 204-240-08-00
Dear Mr. Hatch,
As requested, by Bryan Knapp, Pasco Laret Suiter & Associates (PLSA), GeoTek, Inc. (GeoTek)
is providing Interlocking Concrete Pavement (ICP) recommendations for onsite driveways at the
subject site. Based on review of the “Geotechnical Investigation, 245 Acacia Avenue, Carlsbad,
California,” by Hetherington Engineering, Inc. (HEI) the following ICP recommendations are
provided.
The onsite subgrade soils consist of weathered paralic deposits, classified as silty sands (SM)
according to the boring logs in the above referenced report. A Traffic Index of 5 and an assumed
R-Value of 10 were used for design of the preliminary pavement section.
The final ICP section for the driveways should be based on R-Value testing of the finished
subgrade soils.
Impermeable interlocking concrete pavement should consist of 3 1/8-inch thick (minimum)
concrete pavers (with edge restraints and sand filled joints) underlain by bedding sand layer (for
leveling) and compacted base.
Materials for use as bedding sand and aggregate base should meet the following specifications in
Table - I:
Rincon Homes Project No. 3819-SD
Interlocking Concrete Pavement August 16, 2022
245 Acacia Ave Page 2
Carlsbad, California
Table - I
Material Layer Thickness Specification
Bedding Sand 1-inch ASTM No. 8 Stone
Aggregate Base 8-inches Caltrans Class 2
The aggregate base should be compacted to a minimum of 95-pecent of the maximum dry density
as determined by ASTM: D 1557. Prior to placement of aggregate base, the underlying subgrade
soils should be scarified to a depth of 12-inches and compacted to 95-percent relative
compaction.
The opportunity to be of service is sincerely appreciated. If you should have any questions, please
do not hesitate to call GeoTek
Respectfully submitted,
GeoTek, Inc.
Christopher D. Livesey
CEG 2733, Exp. 05/31/23
Associate Vice President
Edwin R. Cunningham
RCE 81687, Exp. 03/31/24
Project Engineer
Distribution: (1) Addressee via email
Rincon Homes Project No. 3819-SD
Interlocking Concrete Pavement August 16, 2022
245 Acacia Ave Page 3
Carlsbad, California
REFERENCES
Hetherington Engineering, Inc., 2021, “Geotechnical Investigation,245 Acacia Avenue, Carlsbad,
California,” dated June21, 2021.
Interlocking Concrete Pavement Institute, 2014, “Tech Spec 4: Structural Design of Intelocking
Concrete Pavement for Roads and Parking Lots,” revised September 2014.
GEOTECHNICAL | ENVIRONMENTAL | MATERIAL
September 22, 2022
Project No. 3819-SD
Rincon Homes
5315 Avenida Encinas, Suite 200
Carlsbad, California 92008
Attention: Mr. Tom St. Clair
Subject: Response to Third-Party Geotechnical Review Comments
Proposed Residential Development
245 Acacia Avenue
Carlsbad, California
Reference: See Page 6
Dear Mr. St. Clair:
As requested, by Bryan Knapp, Pasco Lauret Suiter & Associates (PLSA), GeoTek, Inc., (GeoTek)
has prepared this letter to provide a supplemental responds to City of Carlsbad third-party
review comments of the “Geotechnical Investigation, Proposed Residential Development, 245
Acacia Avenue, Carlsbad, California, Project No. 9324.1” by Hetherington Engineering, Inc. (HEI),
dated June 21, 2021 and “Grading Plans For: Acacia Beach Homes, 245 Acacia Avenue, Project
No. MS 2021-0004” by Pasco Laret Suiter & Associates, dated 2022 (sheets 1 through 7). Our
numbering corresponds to that used by the reviewer.
Review Comment No. 1
The Geotechnical Consultant should review the project grading and foundation plans and provide any
additional geotechnical recommendations, as appropriate, and indicate if the plans have been prepared
in accordance with the geotechnical recommendations provided in the referenced geotechnical report
(Hetherington Engineering, Inc., 2021).
Response to Review Comment No. 1
We have reviewed the project grading and foundation plans. The grading and foundation plans
have incorporated the geotechnical recommendations provided in the referenced geotechnical
report (Hetherington Engineering, Inc., 2021) and are considered suitable from a geotechnical
standpoint. The conclusions and recommendations provided in the geotechnical report
(Hetherington Engineering, Inc., 2021) remain applicable to the referenced grading and foundation
plans.
RINCON HOMES Project No. 3819-SD
Acacia Beach Homes September 22, 2022
245 Acacia Avenue, Carlsbad, California Page 2
Review Comment No. 2
The Geotechnical Consultant should provide a geotechnical cross-section(s) of the site or discussion as to
why one is not presented. If a geologic cross section is prepared, an updated geotechnical map/plot plan
showing the location of the cross-section should be provided.
Response to Review Comment No. 2
We have provided an updated geotechnical map/plot plan as Figure 1and a geologic cross section
as Figure 2.
Review Comment No. 3
The Geotechnical Consultant should provide a geotechnical map/plot plan to clearly show the limits of the
proposed structures and the lateral limits of the recommended remedial grading.
Response to Review Comment No. 3
A geotechnical map/plot plan is provided as Figure 1.
Review Comment No. 4
The Geotechnical Consultant should provide recommendations for import materials to be used for general
fill, retaining wall backfill, and utility trench backfill.
Response to Review Comment No. 4
Import fill should consist of granular soil with a “very low” to “low” expansion potential (EI of 50
or less) and free of deleterious material or rock larger than 6-inches. Import fill used as select
backfill for retaining walls should consist of granular soil with a “very low” expansion potential
(EI of less than 20) and free of deleterious material or rock larger than 6-inches. GeoTek should
be notified of the imported soil source and should be authorized to perform laboratory testing
of import soil prior to its arrival at the site to evaluate its suitability as fill.
Review Comment No. 5
The Geotechnical Consultant should provide recommendations for vehicular pavements.
Response to Review Comment No. 5
Traffic indices have not been provided during this stage of site planning. In addition, site
conditions have not been graded to a final design to evaluate specific pavement subgrade
conditions. Therefore, the minimum structural sections provided below are based on an assumed
R-Value of 10 and assumed traffic indices.
RINCON HOMES Project No. 3819-SD
Acacia Beach Homes September 22, 2022
245 Acacia Avenue, Carlsbad, California Page 3
PRELIMINARY ASPHALT PAVEMENT STRUCTURAL SECTION
Design Criteria Traffic Index
(TI)
Pavement Thickness
(inches)
Aggregate Base (AB)
Thickness (inches)
Driveway 5.0 4 7
Parking Stalls 4.0 4 6
Actual structural pavement design is to be determined by the geotechnical engineer’s testing (R-
Value) of the exposed subgrade.
It is anticipated that Portland Cement Concrete (PCC) pavements will be utilized. Based on the
City of Carlsbad minimum design guidelines for driveways, the following recommended minimum
PCC pavement section is provided for these areas:
PRELIMINARY PCC PAVEMENT STRUCTURAL SECTION
Design Criteria Traffic Index
(TI)
Pavement Thickness
(inches)
Aggregate Base (AB)
Thickness (inches)
Driveway 5.0 7 6
Parking Stalls 4.0 6 0
Interlocking concrete paver (ICP) section has been addressed in a separate “Interlocking
Concrete Paver” letter attached as Appendix A.
Review Comment No. 6
The Geotechnical Consultant should provide recommendations for exterior concrete flatwork.
Response to Review Comment No. 6
Exterior concrete flatwork should be designed using a four-inch minimum thickness with 6”x6”
– WI.4/WI.4 welded wire fabric, placed in the middle of slab. It is recommended that control
joints be placed in two directions spaced the numeric equivalent roughly 24 times the thickness
of the slab in inches (e.g., a 4-inch slab would have control joints at 96-inch [8-feet] centers).
These joints are a widely accepted means to control cracks and should be reviewed by the project
structural engineer. Some shrinkage and cracking of the concrete should be anticipated as a
result of typical mix designs and curing practices typically utilized in construction.
Presaturation of flatwork subgrade should be verified to be a minimum of 100% of the soils
optimum moisture to a depth of 12-inches for soils having a “very low” expansive index potential.
RINCON HOMES Project No. 3819-SD
Acacia Beach Homes September 22, 2022
245 Acacia Avenue, Carlsbad, California Page 4
Review Comment No. 7
The referenced grading plans (Pasco Lauret Suiter & Associates, 2022) depict the use of permeable
pavers for vehicular pavements. The Geotechnical Consultant should provide conclusions regarding the
suitability of using permeable pavers for vehicular pavements and recommendations for their design and
construction.
Response to Review Comment No. 7
Permeable pavers are not being utilized for this project at this time. Decorative concrete pavers
are part of the proposed project and recommendations have been provided in the “Interlocking
Concrete Pavement…” letter by GeoTek, dated August 16, 2022 and attached as Appendix A.
Review Comment No. 8
The Geotechnical Consultant should provide conclusions regarding the suitability of using of infiltration
devices such as the permeable pavers onsite.
Response to Review Comment No. 8
Permeable pavers are not being proposed for the project.
Review Comment No. 9
The referenced grading plans (Pasco Lauret Suiter & Associates, 2022) depict the structures being placed
in both cut and fill areas of the site. The Geotechnical Consultant should review the plans for areas of
potential cut/fill transitions beneath the buildings and provide recommendations to mitigate these
conditions, as appropriate.
Response to Review Comment No. 9
Grading may result in a cut/fill transition at the proposed building pad finish grades. If a geologic
contact of Formational material against fills is encountered at finish pad grades, the cut portion
should be over-excavated a minimum of three feet below pad grades, or two feet below the base
of proposed footings, whichever is deeper, and be replaced with engineered fill.
Review Comment No. 10
On Page 4 under “Seismic Effects – Ground Accelerations” and on Page 9 under References” of the
referenced geotechnical report (Hetherington Engineering, Inc., 2021) there are typos as the reports
refers to the 2016 California Building Code (CBC) and American Society of Civil Engineers (ASCE)
Publication 7-10 rather than 2019 and 2017 versions, respectively.
RINCON HOMES Project No. 3819-SD
Acacia Beach Homes September 22, 2022
245 Acacia Avenue, Carlsbad, California Page 5
Response to Review Comment No. 10
We concur that the above referenced documents CBC 2016 and ASCE publication 7-10 are
typos, and the correct referenced documents are CBC 2019 and ASCE publication 7-16. The
above comment is noted.
Review Comment No. 11
There are more recent geology maps available for the project vicinity. The Geotechnical Consultant should
review those and may consider updating their references, as appropriate.
Response to Review Comment No. 11
The above comment is noted.
Closure
Should you have any questions after reviewing this addendum, please feel free to contact our
office at your convenience.
Respectfully submitted,
GeoTek, Inc.
ENCLOSURES
Figure 1 – Geotechnical Map
Figure 2 – Cross-Section
Appendix A – Interlocking Concrete Paver Recommendations
Distribution: (1) Addressee Via Email
(1) PLSA – Bryan Knapp
Christopher D. Livesey
CEG, 2733 Exp. 05/31/23
Associate Vice President
Edwin R. Cunningham
RCE, 81687 Exp. 03/31/24
Project Engineer
RINCON HOMES Project No. 3819-SD
Acacia Beach Homes September 22, 2022
245 Acacia Avenue, Carlsbad, California Page 6
References
Hetherington Engineering, Inc., 2021, “Geotechnical Investigation, Proposed Residential
Development, 245 Acacia Avenue, Carlsbad, California,” dated June 21, 2021.
Ninyo & Moore, 2022, “Third-Party Geotechnical Review, Proposed Residential Development,
245 Acacia Avenue, Carlsbad, California,” dated June 24, 2022.
Pasco Lauret Suiter & Associates, 2022, “Preliminary Grading Plans For: Acacia Beach Homes,
245 Acacia Avenue,) 3 sheets, undated.
HE TP-1
HE TP-2
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Approximate Location and Orientation of
Test Pit
HE TP-2
Approximate Limits of Recommended Remedial Grading
Cross Section
Old Paralic DepositsQop
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LEGEND
PN: 3819-SD
Figure 1
Geotechnical Map
1384 Poinsettia Avenue, Suite A
Vista, California 92081DATE: September 2022
Rincon Homes
245 Acacia Ave
Carlsbad, California
0 30 60
Scale: 1" = 30'
10