HomeMy WebLinkAboutPD 2021-0045; 3880 WESTHAVEN DR; EVALUATION OF ALLOWABLE BEARING VALUE, ACTIVE, PASSIVE PRESSURES, LATERAL PRESSURES, AND SEISMIC AND RETAINING WALL DESIGN PARAMETERS; 2020-06-08Geotechnical C Geologic C Coastal C Environmental
5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com
June 8, 2020
W.O. 7861-A-SC
Mr. Danny Caldwell
3880 Westhaven Drive
Carlsbad, California 92008
Subject: Evaluation of Allowable Bearing Value, Active, Passive Pressures, Lateral
Pressures, and Seismic and Retaining Wall Design Parameters, Proposed
Additional Dwelling Unit (ADU)at 3880 Westhaven Drive, Carlsbad, San
Diego County, California 92008, APN 207-053-29-00
Dear Mr. Caldwell:
In accordance with your request, GeoSoils, Inc. (GSI) has obtained a representative
sample of site soil for laboratory testing. The purpose of our testing was to evaluate soil
parameters for proposed improvements during construction of the additional dwelling unit
(ADU) at the rear of the existing single-family residential home. The scope of our services
includes a site reconnaissance, soil sampling, a review of documents presented in
Appendix (References), laboratory testing, engineering analyses, and preparation of this
report. This summary report has been prepared for the sole purpose of simply providing
a limited description of soil conditions onsite and laboratory testing, and does not
constitute a geotechnical evaluation of the overall stability, or suitability of the site for
additional development.
FIELD STUDIES
Site-specific field studies were conducted by GSI on May 20, 2020, and consisted of the
excavation of three (3) exploratory excavations with a hand auger, for an evaluation of
near-surface soil and geologic conditions onsite. The auger excavations HA-1 and HA-2
were performed in the rear yard, in the vicinity of the proposed improvements and toe of
rear slope, respectively. HA-3 was excavated at the southeast corner of the existing
residence. All excavations were logged by a representative of this office who collected
representative bulk soil samples for appropriate laboratory testing. A description of the
soils encountered are described below.
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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SOIL CONDITIONS
General
The earth material units that were observed and/or encountered at the subject site consist
of surficial deposits of artificial fill overlying Tertiary-age Santiago Formation deposits at
shallow depth. A general description of each material type is presented as follows, from
youngest to oldest.
Quaternary-age Artificial Fill
As observed, engineered fill occurs at the surface and generally consists of dark brown,
moist to wet, loose to medium dense, silty sands with clay. Where encountered in our
excavations (HA-1 through HA-3), the thickness of the non-uniform artificial fill materials
was on the order of about ±1½ feet, ±½ foot, ±½ foot respectively. In the vicinity of the
rear yard house addition, the artificial fill is considered subject to settlement under loading,
and therefore should be removed and reused as properly engineered fill, in areas
proposed for settlement-sensitive improvements.
Tertiary-age Santiago Formation Deposits
Tertiary-age Santiago Formation deposits (bedrock at this site) were observed underlying
artificial fill in HA-1 through HA-3, on the subject site. These deposits generally consisted
of pale yellow silty sand, fine to coarse-grained sand, damp to moist, and dense in
consistency. Unweathered paralic deposits encountered were competent at
approximately ±2 to ±3 feet in the rear yard improvement area and are considered
suitable for support of settlement-sensitive improvements and/or planned fills in their
existing state, at that depth.
LABORATORY TESTING
Laboratory tests were performed on representative samples of site earth materials in order
to evaluate their physical characteristics. The results of our evaluation are summarized as
follows:
Classification
Soils were classified with respect to the Unified Soil Classification System (USCS) in
general accordance with ASTM D 2487 and ASTM D 2488.
Particle-Size Analysis
A particle-size evaluation was performed on a representative, soil sample (HA-1 @ 0'-1½')
in general accordance with ASTM D 422-63. The testing was utilized to evaluate the soil
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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classification in accordance with the Unified Soil Classification System (USCS). The results
of the particle-size evaluation indicate that the tested soil is a Silty Sand
(2.1% Gravel, 77.9% sand, 20% fines) (USCS Symbol-SM).
Expansion Index
A representative sample of near-surface site soils was evaluated for expansion potential.
Expansion Index (E.I.) testing and expansion potential classification was performed in
general accordance with ASTM Standard D 4829, the results of the expansion testing are
presented in the following table.
SAMPLE LOCATION
AND DEPTH (ft)EXPANSION INDEX EXPANSION POTENTIAL
HA-1 @ 0-1.5 <20 Very Low
Direct Shear Tests
Strain-controlled direct shear test (displacement #0.005 inches per minute), was performed
on a remolded sample of the foundational soils, in general accordance with the
ASTM D 3080 test method. The results of shear testing are summarized in the following
table.
The shear testing results are shown below.
SAMPLE LOCATION
AND DEPTH (ft)
WET
UNIT
WEIGHT
(PCF)
PRIMARY RESIDUAL
COHESION
(PSF)
FRICTION
ANGLE
(DEGREES)
COHESION
(PSF)
FRICTION
ANGLE
(DEGREES)
HA-2 @ 1-2 (remolded) 123.5 162 30.8 48 31.9
BEARING VALUE
Based on a review of Table 1806.2 of the 2019 California Building Code ([2019 CBC],
California Building Standards Commission [CBSC], 2019a), an allowable bearing value
of 2,000 pounds per square foot (psf) may be assumed for continuous footings, a
minimum 12 inches wide and 12 inches deep (below lowest adjacent grade [excluding soft
soils, landscape zones, slab and underlayment thickness, etc.]), bearing on
suitable, approved bedrock. It is anticipated that actual footing depths will be deeper than
those indicated above, in order to penetrate any loose, near surface soils. Actual footing
1::===1 =======:=======:~=======:11
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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depths would be based on conditions exposed within the footing excavation. The
allowable bearing value may be increased by 20 percent for each additional twelve
(12) inches in depth of embedment, into approved suitable bearing soil, to a maximum
value of 2,500 psf. The above values may be increased by one-third when considering
short duration seismic or wind loads. Differential settlement may be minimally assumed
as 1 inch in a 40-foot span, provided the footing bears on suitable, competent and similar
earth materials, approved by GSI. Foundations should be designed for all applicable
surcharge loads and should consider the inherent corrosive coastal environment.
LATERAL PRESSURE
Total Lateral Resistance (TLR) for shallow foundations is provided by the friction along the
footing bottoms and the passive pressure across footing faces in contact with either fill or
natural soil deposits. The TLR is influenced by the depth of the footing and the cohesion
(or apparent cohesion) of the soil material. The normal force or dead load on the footing
from the overlying structure will influence the amount of frictional resistance. For sands or
predominantly sandy soils, this friction is higher than clay or clayey/silty soils. The TLR and
vertical bearing of the soil were derived from soil(s) descriptions, multiple laboratory tests,
and the use of Table 1806.2 of the 2019 CBC (CBC, 2019a).
The TLR for the silty sands onsite may be taken as an equivalent fluid of 150 pcf (150 psf/ft
of depth) per foot of depth. This may be added to the frictional resistance of the sandy
earth material using a coefficient of 0.25 when combined with the normal (dead load) force.
When combining the frictional and passive components of the TLR, the passive value
should be reduced by one-third (a). The total maximum lateral bearing pressure
of 2,250 psf may be used for this site, unless further testing and analysis is performed. GSI
believes this to be a reasonably conservative value, considering the limited scope of work.
Please note that if foundations for either the main or appurtenant structures are pile or pier
supported, the frictional value noted above should be neglected.
SEISMIC DESIGN
General
It is important to keep in perspective that in the event of an upper bound (maximum
probable) or credible earthquake occurring on any of the nearby major faults, strong
ground shaking would occur in the subject site's general area. Potential damage to any
structure(s) would likely be greatest from the vibrations and impelling force caused by the
inertia of a structure's mass than from those induced by the hazards listed above. This
potential would be no greater than that for other existing structures and improvements in
the immediate vicinity.
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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Seismic Shaking Parameters
The following table summarizes the reevaluated site-specific design criteria obtained from
the 2019 CBC, Chapter 16 Structural Design, Section 1613, Earthquake Loads. The
computer program Seismic Design Maps, provided by the California Office of Statewide
Health Planning and Development (OSHPD, 2020) has now been utilized to aid in design
(https://seismicmaps.org). The short spectral response utilizes a period of 0.2 seconds.
2019 CBC SEISMIC DESIGN PARAMETERS
PARAMETER VALUE VALUE PER ASCE 7-16 2019 CBC OR REFERENCE
Risk Category II -Table 1604.5
Site Class D (default)-Section 1613.2.2/Chap. 20
ASCE 7-16 (p. 203-204)
Spectral Response - (0.2 sec),
sS 1.018 g -Section 1613.2.1
Figure 1613.2.1(1)
1Spectral Response - (1 sec), S 0.371 g -Section 1613.2.1
Figure 1613.2.1(2)
aSite Coefficient, F 1.2 -Table 1613.2.3(1)
vSite Coefficient, F null - see Section
11.48 ASCE 7-16 2.5 (Section 21.3)Table 1613.2.3(2)
Maximum Considered
Earthquake Spectral
Response Acceleration
MS(0.2 sec), S
1.222 g -Section 1613.2.3
(Eqn 16-36)
Maximum Considered
Earthquake Spectral
Response Acceleration
M1(1 sec), S
null - see Section
11.48 ASCE 7-16 1.367 (Section 21.4)Section 1613.2.3
(Eqn 16-37)
5% Damped Design Spectral
Response Acceleration
DS(0.2 sec), S
0.815 g -Section 1613.2.4
(Eqn 16-38)
5% Damped Design Spectral
Response Acceleration
D1(1 sec), S
null - see
Section 11.48
ASCE 7-16
0.911
(Section 21.4)
Section 1613.2.4
(Eqn 16-39)
MPGA - Probabilistic Vertical
Ground Acceleration may be
assumed as about 50% of
these values.
0.535 g -ASCE 7-16 (Eqn 11.8.1)
Seismic Design Category
null - see
Section 11.48
ASCE 7-16
D
(Section 11.6)
Section 1613.2.5/ASCE 7-16
(p. 85: Table 11.6-1 or 11.6-2)
1. FV = 2.5 S1>0.2 per Section 21.3,
2. SM1= (1.5)SD1 =(1.5)(0.595)=0.8928 per Section 21.4
3. SD1 $ 0.2 => 0.8928 $ 0.2 , per Section 11.6 site is in Risk Category D
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GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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GENERAL SEISMIC PARAMETERS
PARAMETER VALUE
Distance to Seismic Source (A fault)6.3 mi (10.1 km)(1)(2)
WUpper Bound Earthquake (Rose Canyon)M = 7.2 (1)
- Cao, et al. (2003)(1)
- Blake (2000)(2)
Conformance to the criteria above for seismic design does not constitute any kind of
guarantee or assurance that significant structural damage or ground failure will not occur
in the event of a large earthquake. The primary goal of seismic design is to protect life, not
to eliminate all damage, since such design may be economically prohibitive. Cumulative
effects of seismic events are not addressed in the 2019 CBC (CBSC, 2019a) and regular
wmaintenance and repair following locally significant seismic events (i.e., M 5.5) will likely
be necessary, as is the case in all of southern California.
DEVELOPMENT CRITERIA
General
All earthwork should conform to the guidelines presented in the 2019 CBC (CBSC, 2019a)
and the requirements of the City, except where specifically superceded in the text of this
report. Prior to earthwork, a GSI representative should be present at the preconstruction
meeting to provide additional earthwork guidelines, if needed, and review the earthwork
schedule. This office should be notified in advance of any fill placement, supplemental
regrading of the site, or backfilling underground utility trenches and retaining walls after
rough earthwork has been completed. This includes grading for pools, driveway
approaches, driveways, and exterior hardscape.
During earthwork construction, all site preparation and the general grading procedures of
the contractor should be observed and the fill selectively tested by a representative(s) of
GSI. If unusual or unexpected conditions are exposed in the field, they should be reviewed
by this office and, if warranted, modified and/or additional recommendations will be
offered. All applicable requirements of local and national construction and general industry
safety orders, the Occupational Safety and Health Act (OSHA), and the Construction Safety
Act should be met. It is the onsite general contractor and individual subcontractors
responsibility to provide a save working environment for our field staff who are onsite. GSI
does not consult in the area of safety engineering.
Demolition/Grubbing
1. Vegetation and any miscellaneous debris should be removed from the areas of
proposed grading.
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Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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2. Any existing subsurface structures uncovered during the recommended removal
should be observed by GSI so that appropriate remedial recommendations can be
provided.
3. Cavities or loose soils remaining after demolition and site clearance should be
cleaned out and observed by the soil engineer. The cavities should be replaced
with fill materials that have been moisture conditioned to at least optimum moisture
content and compacted to at least 90 percent of the laboratory standard.
4. Onsite septic systems (if encountered) should be removed in accordance with
San Diego County Department of Environmental Health (DEH)
standards/guidelines.
Treatment of Existing Ground
1. Removals should consist of all surficial deposits of artificial fill within the
upper ±2 to ±3.0 feet, or alternatively, any slab should be designed as a structural
slab, spanning between deepened footings, and not relying on the soil for support.
Removed fill soils may be reused as fill, provided that the soil is cleaned of any
deleterious material, moisture conditioned, and compacted to a minimum 90 percent
relative compaction per ASTM D 1557. Removals should be completed throughout
the site, and minimally at least five (5) feet beyond the limits of any
settlement-sensitive improvement, or to a lateral distance equal to the depth of the
removal beneath the improvement, whichever is greater. Should the removal and
recompaction of existing artificial fill not be performed, a structural slab, spanning
between footings, and not relying on soil for support, will be required. In that case,
the minimum footing depths would be ±3 to ±4 feet deep.
2. In addition to removals within the building envelope, overexcavation of the
underlying formational/bedrock soil should be performed in order to provide for at
least four (4) feet of compacted fill below finish grade, or two (2) feet below the
bottom of the deepest foundation, whichever is greater.
3. Subsequent to the above removals/overexcavation, the exposed bottom should be
scarified to a depth of at least eight (8) inches, brought to at least optimum moisture
content, and recompacted to a minimum relative compaction of 90 percent of the
laboratory standard, prior to any fill placement.
4. Localized deeper removals may be necessary due to buried drainage channel
meanders or dry porous materials, septic systems, etc., or deeper sections of the
former reservoir that may be present. The project soils engineer/geologist should
observe all removal areas during the grading.
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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5. Removed natural ground materials may be reused as compacted fill provided that
major concentrations of vegetation and miscellaneous debris are removed from the
site, prior to or during fill placement. See subsequent sections for a discussion of
select grading.
Fill Suitability
Surficial onsite soils (artificial fill) generally appear to consist of silty sands with lesser
quantities of gravels locally. Oversize material (12-inch plus) is not anticipated. Existing fill
soils are very low expansive. Any soil import should be evaluated by this office prior to
importing in order to assure compatibility with the onsite site soils and the
recommendations presented in this report. Import soils, if used, should be relatively sandy
and very low expansive (i.e., E.I. less than 20).
Shrinkage/Bulking
Based on our experience, a preliminary value of 8 to 15 percent shrinkage for
topsoil/colluvium, and highly weathered formation may be considered. Cuts in formation
may result in nominal shrinkage (ranging to ±5 percent).
Fill Placement
1. Subsequent to ground preparation, fill materials should be brought to at least
optimum moisture content, placed in thin 6- to 8-inch lifts, and
mechanically compacted to obtain a minimum relative compaction of 90 percent of
the laboratory standard.
2. Fill materials should be cleansed of major vegetation and debris prior to placement.
Perimeter Conditions
It should be noted, that the 2019 CBC (CBSC, 2019) indicates that removals of unsuitable
soils be performed across all areas under the purview of the grading permit, not just within
the influence of the proposed buildings. Relatively deep removals may also necessitate a
special zone of consideration, on perimeter/confining areas.
Any proposed improvement or future homeowner improvements such as walls, swimming
pools, house additions, etc. that are located above a 1:1 (h:v) projection up from the
outermost limit of the remedial grading excavations will require deepened foundations that
extend below this plane. Other site improvements, such as pavements, constructed above
the aforementioned plane would retain some potential for settlement and associated
distress, which may require increased maintenance/repair or replacement. This potential
should be disclosed to all interested/affected parties should remedial grading excavations
be constrained by property lines.
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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Graded Slope Construction
Based on site grades and the planned construction, graded fill and cut slope construction
is not anticipated, or considered feasible.
Fill Drainage
Based on site grades and the planned construction, subdrainage is not anticipated, or
considered feasible.
Temporary Slopes
Temporary slopes for excavations greater than 4 feet, but less than 20 feet in overall height
should conform to CAL-OSHA and/or OSHA requirements for Type “B” soils. Temporary
slopes, up to a maximum height of ±20 feet, may be excavated at a 1:1 (h:v) gradient, or
flatter, provided groundwater and/or running sands are not exposed. Construction
materials or soil stockpiles should not be placed within ‘H’ of any temporary slope where
‘H’ equals the height of the temporary slope. All temporary slopes should be observed by
a licensed engineering geologist and/or geotechnical engineer prior to worker entry into the
excavation.
Groundwater
The site lies approximately ±1.6 miles east of the Pacific Ocean, which would be
considered the regional water table. Within the regional water table, groundwater is subject
to tidal fluctuations when near the coast. Based on our review of site conditions, the
regional groundwater table is anticipated to be at depths of greater than 50 feet below
grade, and should not be of significant concern during site design/construction.
Flooding/Inundation
Based on our review of the Federal Emergency Management Agency (FEMA) website
(https://msc.fema.gov), the site is located within a “minimal flood hazard area.” This should
be further evaluated by the project design civil engineer.
New Foundations
Current laboratory testing indicates that the onsite soils exhibit expansion index values of
less than 20. As such, site soils do not appear to meet the criteria of detrimentally
expansive soils as defined in Section 1803.5.2 of the 2019 CBC (CBSC, 2019a).
Concrete mix design should be designed to comply. Exposure classes S0 and C1, per
ACI 318-14, should be followed. GSI does not practice in the field of corrosion engineering.
Accordingly, consultation from a qualified corrosion engineer may obtained based on the
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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level of corrosion protection requirements by the project architect and structural engineer.
From a geotechnical viewpoint, foundation construction should minimally conform to the
following:
1. Exterior and interior footings should be founded at a minimum depth of 12 inches
below the lowest adjacent grade, or embedded at least 12 inches into suitable GSI
approved bearing material, whichever is deeper. If removal and recompaction is not
performed, the depth would be about 3 to 4 feet (with a structural slab). Footing
widths should be per Code. Isolated pad footings should be 24 inches square,
by 24 inches deep, and minimally embedded at least 24 inches into suitable bearing
soil, whichever is deeper. Isolated pad footings would need to be deepened
similarly, if removal and recompaction is not performed.
2. All footings should be minimally reinforced with four No. 4 reinforcing bars, two
placed near the top and two placed near the bottom of the footing. Isolated pad
footing reinforcement should be per the structural engineer.
3. Interior and exterior column footings should be tied together via grade beams in at
least one direction to the main foundation. The grade beam should be at
least 12 inches square in cross section, and should be provided with a minimum of
two No. 4 reinforcing bars at the top, and two No. 4 reinforcing bars at the bottom
of the grade beam. The base of the reinforced grade beam should be at the same
elevation as the adjoining footings.
4. A minimum concrete slab-on-grade thickness of 5 inches is recommended.
5. Concrete slabs should be reinforced with a minimum of No. 3 reinforcement bars
placed at 18 inches on-center, in two horizontally perpendicular directions (i.e., long
axis and short axis). Should removal and recompaction not be performed, the slab
should be designed as a structural slab, spanning between footings, and not relying
on the soil for support.
6. All slab reinforcement should be supported to ensure proper mid-slab height
positioning during placement of the concrete. "Hooking" of reinforcement is not an
acceptable method of positioning.
7. Slab subgrade pre-soaking is recommended for these soil conditions. Slab
subgrade should be pre-wetted to at least the soils optimum moisture content, to a
depth of 12 inches, prior to the placement of the underlayment sand and vapor
retarder.
8. Loose and/or compressible materials likely occur at the surface, overlying suitable
bearing material. As such, a deeper footing will likely be recommended, and should
be anticipated. The depth of the deepened footing should be evaluated prior to the
placement of reinforcing steel and foundational concrete.
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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9. Foundations should maintain a minimum 7-foot horizontal distance between the
base of the footing and any adjacent descending slope, and minimally comply with
the guidelines per the 2019 CBC (CBSC, 2019a). This may also result in a deeper
footing than per plan.
Floor Slabs
GSI has evaluated the potential for vapor or water transmission through the concrete floor
slabs, in light of typical floor coverings, improvements, and use. Please note that slab
moisture emission rates range from about 2 to 27 lbs/24 hours/1,000 square feet from a
typical slab (Kanare, 2005), while floor covering manufacturers generally recommend
about 3 lbs/24 hours as an upper limit. The recommendations in this section are not
intended to preclude the transmission of water or vapor through the foundation or slabs.
Foundation systems and slabs shall not allow water or water vapor to enter into the
structure so as to cause damage to another building component or to limit the installation
of the type of flooring materials typically used for the particular application (State of
California, 2020). These recommendations may be exceeded or supplemented by a water
“proofing” specialist, project architect, or structural consultant. Thus, the client will need
to evaluate the following in light of a cost vs. benefit analysis (owner expectations and
repairs/replacement), along with disclosure to all interested/affected parties. It should also
be noted that vapor transmission will occur in new slab-on-grade floors as a result of
chemical reactions taking place within the curing concrete. Vapor transmission through
concrete floor slabs as a result of concrete curing has the potential to adversely affect
sensitive floor coverings depending on the thickness of the concrete floor slab and the
duration of time between the placement of concrete, and the floor covering. It is possible
that a slab moisture sealant may be needed prior to the placement of sensitive floor
coverings if a thick slab-on-grade floor is used and the time frame between concrete and
floor covering placement is relatively short.
Considering the E.I. test results presented herein, and known soil conditions in the region,
the anticipated typical water vapor transmission rates, floor coverings, and improvements
(to be chosen by the Client and/or project architect) that can tolerate vapor transmission
rates without significant distress, the following alternatives are provided:
• Non-vehicular concrete slab-on-grade floors should be thicker than 5 inches.
• Concrete slab underlayment should consist of a 15-mil vapor retarder, or equivalent,
with all laps sealed per the 2019 CBC and the manufacturer’s recommendation. The
vapor retarder should comply with the ASTM E 1745 - Class A criteria, and be
installed in accordance with American Concrete Institute (ACI) 302.1R-04 and
ASTM E 1643. An example of a vapor retarder product that complies with
ASTM E 1745 - Class A criteria is Stego Industries, LLC’s Stego Wrap.
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Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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• The 15-mil vapor retarder (ASTM E 1745 - Class A) shall be installed per the
recommendations of the manufacturer, including all penetrations (i.e., pipe, ducting,
rebar, etc.).
• Concrete slabs, shall be underlain by 2 inches of clean, washed sand (SE > 30)
above a 15-mil vapor retarder (ASTM E-1745 - Class A, per Engineering
Bulletin 119 [Kanare, 2005]) installed per the recommendations of the manufacturer,
including all penetrations (i.e., pipe, ducting, rebar, etc.). The manufacturer shall
provide instructions for lap sealing, including minimum width of lap, method of
sealing, and either supply or specify suitable products for lap sealing (ASTM E 1745),
and per code.
ACI 302.1R-04 (2004) states “If a cushion or sand layer is desired between the vapor
retarder and the slab, care must be taken to protect the sand layer from taking on
additional water from a source such as rain, curing, cutting, or cleaning. Wet
cushion or sand layer has been directly linked in the past to significant lengthening
of time required for a slab to reach an acceptable level of dryness for floor covering
applications.” Therefore, additional observation and/or testing will be necessary for
the cushion or sand layer for moisture content, and relatively uniform thicknesses,
prior to the placement of concrete.
• The vapor retarder should be underlain by a capillary break consisting of at
least 2 inches of clean sand (SE 30, or greater). The vapor retarder should be
sealed to provide a continuous retarder under the entire slab, as discussed above.
• Concrete should have a maximum water/cement ratio of 0.50. This does not
supercede Table 19.3.1.1 of the ACI (2019) for corrosion or other corrosive
requirements (such as coastal, location, etc.). Additional concrete mix design
recommendations should be provided by the structural consultant and/or
waterproofing specialist. Concrete finishing and workablity should be addressed by
the structural consultant and a waterproofing specialist.
• Where slab water/cement ratios are as indicated herein, and/or admixtures used, the
structural consultant should also make changes to the concrete in the grade beams
and footings in kind, so that the concrete used in the foundation and slabs are
designed and/or treated for more uniform moisture protection.
• The owner(s) should be specifically advised which areas are suitable for tile flooring,
vinyl flooring, or other types of water/vapor-sensitive flooring and which are not
suitable. In all planned floor areas, flooring shall be installed per the manufactures
recommendations.
• Additional recommendations regarding water or vapor transmission should be
provided by the architect/structural engineer/slab or foundation designer and should
be consistent with the specified floor coverings indicated by the architect.
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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Regardless of the mitigation, some limited moisture/moisture vapor transmission through
the slab should be anticipated. Construction crews may require special training for
installation of certain product(s), as well as concrete finishing techniques. The use of
specialized product(s) should be approved by the slab designer and water-proofing
consultant. A technical representative of the flooring contractor should review the slab and
moisture retarder plans and provide comment prior to the construction of the foundations
or improvements. The vapor retarder contractor should have representatives onsite during
the initial installation.
The above assumes that the surficial fill/colluvium has been removed and recompacted
beneath the slab. If this is not the case, a structural slab is recommended. The structural
slab should be designed to span between the footings, and not rely on the soil for support.
RETAINING WALLS
Conventional Retaining Walls
The design parameters provided below assume that either very low expansive soils
(typically Class 2 permeable filter material or Class 3 aggregate base) or native onsite
materials with an expansion index less than 21 and a plasticity index less than 15 are used
to backfill any retaining wall. The type of backfill (i.e., select or native), should be specified
by the wall designer, and clearly shown on the plans. Building walls, below grade, should
be water-proofed. The foundation system for the proposed retaining walls should be
designed in accordance with the recommendations presented in this and preceding
sections of this report, as appropriate. Footings should be embedded a minimum
of 18 inches below the lowest adjacent grade (excluding landscape layer, 6 inches) and
should be 24 inches in width. Planned retaining wall footings may need to be deepened
where loose surficial soils are present, or to provide for the recommended setback to the
slope face. Recommendations for specialty walls (i.e., crib, earthstone, geogrid, etc.) can
be provided upon request, and would be based on site specific conditions.
Retaining Wall Foundation Design
The foundation design for retaining walls should incorporate the following
recommendations:
Minimum Footing Embedment - 18 inches below the lowest adjacent grade
(excluding landscape layer [upper 6 inches]).
Minimum Footing Width - 24 inches
Allowable Bearing Pressure - An allowable bearing pressure of 2,500 pcf may be
used in the preliminary design of retaining wall foundations provided that the footing
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maintains a minimum width of 24 inches and extends at least 18 inches into
approved engineered fill overlying dense formational materials. This pressure may
be increased by one-third for short-term wind and/or seismic loads. The allowable
bearing value may be increased by no more than 100 psf for each additional foot of
width to a maximum allowable bearing of 3,000 psf, on a preliminary basis.
Passive Earth Pressure - A passive earth pressure of 250 pcf with a maximum earth
pressure of 2,500 psf may be used in the preliminary design of retaining wall
foundations provided the foundation is embedded into suitable formation.
Lateral Sliding Resistance - A 0.30 coefficient of friction may be utilized for a
concrete to soil contact when multiplied by the dead load. When combining passive
pressure and frictional resistance, the passive pressure component should be
reduced by one-third.
Backfill Soil Density - Soil densities ranging between 110 pcf and 120 pcf may be
used in the design of retaining wall foundations. This assumes an average
engineered fill compaction of at least 90 percent of the laboratory standard
(ASTM D 1557).
Footing depths may need to be deepened in order to penetrate any unsuitable, surficial soil,
for adequate vertical and lateral bearing support. All retaining wall footing setbacks from
slopes should comply with Figure 1808.7.1 of the 2019 CBC. GSI recommends a minimum
horizontal setback distance of 7 feet as measured from the bottom, outboard edge of the
footing to the slope face.
Restrained Walls
Any retaining walls that will be restrained prior to placing and compacting backfill material
or that have re-entrant or male corners, should be designed for an at-rest equivalent fluid
pressure (EFP) of 55 pounds per cubic foot (pcf) and 65 pcf for select and very low
expansive native backfill, respectively. The design should include any applicable surcharge
loading. For areas of male or re-entrant corners, the restrained wall design should extend
a minimum distance of twice the height of the wall (2H) laterally from the corner.
Cantilevered Walls
The recommendations presented below are for cantilevered retaining walls up to 10 feet
high. Design parameters for walls less than 3 feet in height may be superceded by City of
Carlsbad and/or County of San Diego standard design. Active earth pressure may be used
for retaining wall design, provided the top of the wall is not restrained from minor
deflections. An equivalent fluid pressure approach may be used to compute the horizontal
pressure against the wall. Appropriate fluid unit weights are given below for specific slope
gradients of the retained material. These do not include other superimposed loading
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conditions due to traffic, structures, seismic events or adverse geologic conditions. When
wall configurations are finalized, the appropriate loading conditions for superimposed loads
can be provided upon request.
For preliminary planning purposes, the structural consultant should incorporate the
surcharge of traffic on the back of retaining walls. The traffic surcharge may be taken
as 100 psf/ft in the upper 5 feet of backfill for light truck and cars traffic within “H” feet from
the back of the wall, where “H” equals the wall height. This does not include the surcharge
of parked vehicles which should be evaluated at a higher surcharge to account for the
effects of seismic loading.
SURFACE SLOPE OF
RETAINED MATERIAL
(HORIZONTAL:VERTICAL)
EQUIVALENT
FLUID WEIGHT P.C.F.
(SELECT BACKFILL)(2)
EQUIVALENT
FLUID WEIGHT P.C.F.
(NATIVE BACKFILL)(3)
Level(1)
2 to 1
38
55
50
605
Level backfill behind a retaining wall is defined as compacted earth materials, properly drained, without(1)
a slope for a distance of 2H behind the wall, where H is the height of the wall.
SE > 30, P.I. < 15, E.I. < 21, and < 10% passing No. 200 sieve.(2)
E.I. = 0 to 50, SE > 30, P.I. < 15, E.I. < 21, and < 15% passing No. 200 sieve.(3)
Seismic Surcharge
For engineered retaining walls, and if required, GSI recommends that the walls be evaluated
for a seismic surcharge (in general accordance with 2019 CBC requirements). The site
walls in this category should maintain an overturning Factor-of-Safety (FOS) of
approximately 1.25 when the seismic surcharge (increment), is applied. For restrained
walls, the seismic surcharge should be applied as a uniform surcharge load from the
bottom of the footing (excluding shear keys) to the top of the backfill at the heel of the wall
footing. This seismic surcharge pressure (seismic increment) may be taken as 14H where
"H" for retained walls is the dimension previously noted as the height of the backfill
measured from the bottom of the footing to daylight above the heel of the wall footing. The
resultant force should be applied at a distance 0.6 H up from the bottom of the footing. For
the evaluation of the seismic surcharge, the bearing pressure may exceed the static value
by one-third, considering the transient nature of this surcharge. For cantilevered walls the
pressure should be an inverted triangular distribution using 14H. Reference for the seismic
surcharge for Seismic Design Category “D” is Section 1803.5 of the 2019 CBC. Please note
this is for local wall stability only.
I I I I
I --I
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Mr. Danny Caldwell W.O. 7861-A-SC
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Retaining Wall Construction
Wall foundation and wall construction shall be per the appropriate San Diego Regional
Standard Drawing (SDRSD), or as indicated by the project engineer, for engineered walls.
Any plans for engineered walls shall be reviewed by this office prior to construction.
The foundation depths presented in this report should be considered minimums. Footing
depths may need to be deepened in order to penetrate any unsuitable, surficial soil, or to
maintain a minimum setback of 7 feet from the outside bottom edge of the footing to the
face of slope.
Retaining Wall Backfill and Drainage
Positive drainage must be provided behind all retaining walls in the form of gravel wrapped
in geofabric and outlets. A backdrain system is considered necessary for retaining walls
that are 2 feet or greater in height. Details 1, 2, and 3, present the backdrainage options
discussed below. Backdrains should consist of a 4-inch diameter perforated PVC or ABS
pipe encased in either Class 2 permeable filter material or ¾-inch to 1½-inch gravel
wrapped in approved filter fabric (Mirafi 140 or equivalent). For select backfill, the filter
material should extend a minimum of 1 horizontal foot behind the base of the walls and
upward at least 1 foot. For native backfill that has up to E.I. = 20, continuous
Class 2 permeable drain materials should be used behind the wall. This material should
be continuous (i.e., full height) behind the wall, and it should be constructed in accordance
with the enclosed Detail 1 (Typical Retaining Wall Backfill and Drainage Detail). For limited
access and confined areas, (panel) drainage behind the wall may be constructed in
accordance with Detail 2 (Retaining Wall Backfill and Subdrain Detail Geotextile Drain).
Materials with an expansion index (E.I.) potential of greater than 50 should not be used as
backfill for retaining walls. For more onerous expansive situations, backfill and drainage
behind the retaining wall should conform with Detail 3 (Retaining Wall And Subdrain Detail
Clean Sand Backfill). Outlets should consist of a 4-inch diameter solid PVC or ABS pipe
spaced no greater than ±100 feet apart, with a minimum of two outlets, one on each end.
The use of weep holes, only, in walls higher than 2 feet, is not recommended. The surface
of the backfill should be sealed by pavement or the top 18 inches compacted with native
soil (E.I. # 50). Proper surface drainage should also be provided. For additional mitigation,
consideration should be given to applying a water-proof membrane to the back of all
retaining structures. The use of a waterstop should be considered for all concrete and
masonry joints.
Wall/Retaining Wall Footing Transitions
Site walls are anticipated to be founded on footings designed in accordance with the
recommendations in this report. Should wall footings transition from cut to fill, the civil
designer may specify either:
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3880 Westhaven Drive, Carlsbad June 8, 2020
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a) A minimum of a 2-foot overexcavation and recompaction of cut materials for a
distance of 2H, from the point of transition.
b) Increase of the amount of reinforcing steel and wall detailing (i.e., expansion joints
or crack control joints) such that a angular distortion of 1/360 for a distance of 2H on
either side of the transition may be accommodated. Expansion joints should be
placed no greater than 20 feet on-center, in accordance with the structural
engineer’s/wall designer’s recommendations, regardless of whether or not transition
conditions exist. Expansion joints should be sealed with a flexible, non-shrink grout.
c) Embed the footings entirely into native formational material (i.e., deepened footings).
If transitions from cut to fill transect the wall footing alignment at an angle of less
than 45 degrees (plan view), then the designer should follow recommendation "a" (above)
and until such transition is between 45 and 90 degrees to the wall alignment.
Planting
Water has been shown to weaken the inherent strength of all earth materials. Only the
amount of irrigation necessary to sustain plant life should be provided. Over-watering
should be avoided as it can adversely affect site improvements, and cause perched
groundwater conditions. Plants selected for landscaping should be light weight, deep
rooted types that require little water and are capable of surviving the prevailing climate.
Utilizing plants other than those recommended above will increase the potential for perched
water, staining, mold, etc., to develop. A rodent control program to prevent burrowing
should be implemented. These recommendations regarding plant type, irrigation practices,
and rodent control should be provided to all interested/affected parties.
Drainage
Adequate lot surface drainage is a very important factor in reducing the likelihood of
adverse performance of foundations and hardscape. Surface drainage should be sufficient
to prevent ponding of water anywhere on the property, and especially near structures. Lot
surface drainage should be carefully taken into consideration during landscaping.
Therefore, care should be taken that future landscaping or construction activities do not
create adverse drainage conditions. Positive site drainage within the property should be
provided and maintained at all times. Water should be directed away from foundations and
not allowed to pond and/or seep into the ground. In general, the area within 5 feet around
a structure should slope away from the structure. We recommend that unpaved lawn and
landscape areas have a minimum gradient of 1 percent sloping away from structures, and
whenever possible, should be above adjacent paved areas. Consideration should be given
to avoiding construction of planters adjacent to structures. Site drainage should be directed
toward the street or other approved area(s). Although not a geotechnical requirement, roof
gutters, downspouts, or other appropriate means may be utilized to control roof drainage.
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Downspouts, or drainage devices should outlet a minimum of 5 feet from structures or into
a subsurface drainage system. Areas of seepage may develop due to irrigation or heavy
rainfall, and should be anticipated. Minimizing irrigation will lessen this potential. If areas
of seepage develop, recommendations for minimizing this effect could be provided upon
request.
Landscape Maintenance
Only the amount of irrigation necessary to sustain plant life should be provided.
Over-watering the landscape areas will adversely affect existing and proposed site
improvements. We would recommend that any proposed open-bottom planters adjacent
to proposed structures be eliminated for a minimum distance of 10 feet. As an alternative,
closed-bottom type planters could be utilized. An outlet placed in the bottom of the planter,
could be installed to direct drainage away from structures or any exterior concrete flatwork.
If planters are constructed adjacent to structures, the sides and bottom of the planter should
be provided with a moisture retarder to prevent penetration of irrigation water into the
subgrade. Provisions should be made to drain the excess irrigation water from the planters
without saturating the subgrade below or adjacent to the planters. Consideration should
be given to the type of vegetation chosen and their potential effect upon surface
improvements (i.e., some trees will have an effect on concrete flatwork with their extensive
root systems). From a geotechnical standpoint leaching is not recommended for
establishing landscaping. If the surface soils are processed for the purpose of adding
amendments, they should be recompacted to 90 percent minimum relative compaction.
Gutters and Downspouts
As previously discussed in the drainage section, the installation of gutters and downspouts
should be considered to collect roof water that may otherwise infiltrate the soils adjacent
to the structures. If utilized, the downspouts should be drained into PVC collector pipes or
non-erosive devices that will carry the water away from the house. Downspouts and gutters
are not a geotechnical requirement provided that positive drainage is incorporated into
project design (as discussed previously).
Tile Flooring
Tile flooring can crack, reflecting cracks in the concrete slab below the tile, although small
cracks in a conventional slab may not be significant. Therefore, the designer should
consider additional steel reinforcement for concrete slabs-on-grade where tile will be
placed. The tile installer should consider installation methods that reduce possible cracking
of the tile such as slipsheets. Slipsheets or a vinyl crack isolation membrane (approved by
the Tile Council of America/Ceramic Tile Institute) are recommended between tile and
concrete slabs on grade.
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
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Subsurface and Surface Water
Subsurface and surface water are generally anticipated to not significantly affect site
development, provided that the recommendations contained in this report are properly
incorporated into final design and construction and that prudent surface and subsurface
drainage practices are incorporated into the construction plans. Perched groundwater
conditions along zones of contrasting permeabilities may not be precluded from occurring
in the future due to site irrigation, poor drainage conditions, or damaged utilities, and should
be anticipated. Should perched groundwater conditions develop, this office could assess
the affected area(s) and provide the appropriate recommendations to mitigate the observed
groundwater conditions. Groundwater conditions may change with the introduction of
irrigation, rainfall, or other factors.
Site Improvements
Recommendations for exterior concrete flatwork design and construction can be provided
upon request. If in the future, any additional improvements (e.g., pools, spas, etc.) are
planned for the site, recommendations concerning the geological or geotechnical aspects
of design and construction of said improvements are recommended to be provided at that
time. This office should be notified in advance of any fill placement, grading of the site, or
trench backfilling after rough grading has been completed. This includes any grading,
utility trench, and retaining wall backfills.
Footing Trench Excavation
All footing excavations should be observed by a representative of this firm subsequent to
trenching and prior to concrete form and reinforcement placement. The purpose of the
observations is to verify that the excavations are made into the recommended bearing
material and to the minimum widths and depths recommended for construction. If loose
or compressible materials are exposed within the footing excavation, a deeper footing or
removal and recompaction of the subgrade materials would be recommended at that time.
In general, deepened footings beyond the minimum depths indicated herein will likely be
recommended, and should be anticipated. A preliminary test hole indicated relatively dense
native soil at a depth of approximately 24 to 36 inches below existing grade. Based on this
depth, without upper soil mitigation, footings should minimally be 36 to 48 inches deep.
The Client may want to consider having a representative of GSI onsite at the start of
foundation trenching to evaluate the depth to competent bearing soils and provide
recommendations for footing embedment to the contractor performing the work. Footing
trench spoil and any excess soils generated from utility trench excavations should be
compacted to a minimum relative compaction of 90 percent, if not removed from the site.
Trenching
Considering the nature of the onsite soils, it should be anticipated that caving or sloughing
could be a factor in subsurface excavations and trenching. Shoring or excavating the
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Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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trench walls at the angle of repose (typically 25 to 45 degrees) may be necessary and
should be anticipated. All excavations should be observed by one of our representatives
and minimally conform to Cal-OSHA and local safety codes.
Utility Trench Backfill
1. All interior utility trench backfill should be brought to at least optimum moisture
content and then compacted to obtain a minimum relative compaction of 90 percent
of the laboratory standard. As an alternative for shallow (12-inch to 18-inch)
under-slab trenches, sand having a sand equivalent value of 30, or greater, may be
utilized and jetted or flooded into place. Observation, probing, and testing should
be provided to verify the desired results.
2. Exterior trenches adjacent to, and within, areas extending below a 1:1 plane
projected from the outside bottom edge of the footing, and all trenches beneath
hardscape features and in slopes, should be compacted to at least 90 percent of the
laboratory standard. Sand backfill, unless excavated from the trench, should not be
used in these backfill areas. Compaction testing and observations, along with
probing, should be accomplished to verify the desired results.
3. All trench excavations should conform to Cal-OSHA and local safety codes.
4. Utilities crossing grade beams, perimeter beams, or footings should either pass
below the footing or grade beam utilizing a hardened collar or foam spacer, or pass
through the footing or grade beam in accordance with the recommendations of the
structural engineer.
SUMMARY OF RECOMMENDATIONS REGARDING
GEOTECHNICAL OBSERVATION AND TESTING
We recommend that observation and/or testing be performed by GSI at each of the
following construction stages:
• During grading/recertification.
• During significant excavation (i.e., higher than 4 feet).
• During placement of subdrains or other subdrainage devices, prior to placing fill
and/or backfill.
• After excavation of building footings, retaining wall footings, and free standing walls
footings, prior to the placement of reinforcing steel or concrete.
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Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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• Prior to pouring any slabs or flatwork, after presoaking/presaturation of building pads
and other flatwork subgrade, before the placement of concrete, reinforcing steel,
capillary break (i.e., sand, pea-gravel, etc.), or vapor retarders (i.e., visqueen, etc.).
• During retaining wall subdrain installation, prior to backfill placement.
• During placement of backfill for area drain, interior plumbing, utility line trenches, and
retaining wall backfill.
• During slope construction/repair.
• When any unusual soil conditions are encountered during any construction
operations, subsequent to the issuance of this report.
• When any improvements, such as flatwork, spas, pools, walls, etc., are constructed.
• A report of geotechnical observation and testing should be provided at the
conclusion of each of the above stages, in order to provide concise and clear
documentation of site work, and/or to comply with code requirements.
OTHER DESIGN PROFESSIONALS/CONSULTANTS
The design civil engineer, structural engineer, architect, landscape architect, wall designer,
etc., should review the recommendations provided herein, incorporate those
recommendations into all their respective plans, and by explicit reference, make this report
part of their project plans. This report presents minimum design criteria for the design of
slabs, foundations and other elements possibly applicable to the project. These criteria
should not be considered as substitutes for actual designs by the structural
engineer/designer. The structural engineer/designer should analyze actual soil-structure
interaction and consider, as needed, bearing, expansive soil influence, and strength,
stiffness and deflections in the various slab, foundation, and other elements in order to
develop appropriate, design-specific details. As conditions dictate, it is possible that other
influences will also have to be considered. The structural engineer/designer should
consider all applicable codes and authoritative sources where needed. If analyses by the
structural engineer/designer result in less critical details than are provided herein as
minimums, the minimums presented herein should be adopted. It is considered likely that
some, more restrictive details will be required. If the structural engineer/designer has any
questions or requires further assistance, they should not hesitate to call or otherwise
transmit their requests to GSI. In order to mitigate potential distress, the foundation and/or
improvement’s designer should confirm to GSI and the governing agency, in writing, that
the proposed foundations and/or improvements can tolerate the amount of differential
settlement and/or expansion characteristics and design criteria specified herein.
GeoSoils, Inc.
Mr. Danny Caldwell W.O. 7861-A-SC
3880 Westhaven Drive, Carlsbad June 8, 2020
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LIMITATIONS
The materials encountered on the project site and utilized for our analysis are believed
representative of the area; however, soil and bedrock materials vary in character between
excavations and natural outcrops or conditions exposed during mass grading. Site
conditions may vary due to seasonal changes or other factors.
Inasmuch as our study is based upon our review, engineering analyses, and laboratory
data, the conclusions and recommendations presented herein are professional opinions.
These opinions have been derived in accordance with current standards of practice, and
no warranty is express or implied. Standards of practice are subject to change with time.
This report has been prepared for the purpose of providing soil design parameters derived
from testing of a soil sample received at our laboratory, and does not represent an
evaluation of the overall stability, suitability, or performance of the property for the proposed
development. GSI assumes no responsibility or liability for work or testing performed by
others, or their inaction; or work performed when GSI is not requested to be onsite, to
evaluate if our recommendations have been properly implemented. Use of this report
constitutes an agreement and consent by the user to all the limitations outlined above,
notwithstanding any other agreements that may be in place. In addition, this report may be
subject to review by the controlling authorities. Thus, this report brings to completion our
scope of services for this portion of the project.
The opportunity to be of service is sincerely appreciated. If you should have any questions,
please do not hesitate to contact our office.
Respectfully submitted,
GeoSoils, Inc.
Todd M. Page David W. Skelly
Engineering Geologist, CEG 2083 Civil Engineer, RCE 47857
TMP/DWS/JPF/mn
Attachments: Appendix - References
Distribution: (2) Addressee (2 wet signed)
GeoSoils, Inc.
APPENDIX
REFERENCES
American Concrete Institute, 2014a, Building code requirements for structural concrete (ACI
318-14), and commentary (ACI 318R-14): reported by ACI Committee 318, dated
September.
_____, 2014b, Building code requirements for concrete thin shells (ACI 318.2-14), and
commentary (ACI 318.2R-14), dated September.
_____, 2004, Guide for concrete floor and slab construction: reported by ACI Committee
302; Designation ACI 302.1R-04, dated March 23.
American Society for Testing and Materials (ASTM), 1998, Standard practice for installation
of water vapor retarder used in contact with earth or granular fill under concrete
slabs, Designation: E 1643-98 (Reapproved 2005).
_____, 1997, Standard specification for plastic water vapor retarders used in contact with
soil or granular fill under concrete slabs, Designation: E 1745-97 (Reapproved 2004).
American Society of Civil Engineers, 2018a, Supplement 1 to Minimum Design Loads and
Associated Criteria for Buildings and Other Structures (ASCE/SEI 7-16), first printing,
dated December 13.
_____, 2018b, Errata for Minimum Design Loads and Associated Criteria for Buildings and
Other Structures (ASCE/SEI 7-16), by ASCE, dated July 9.
_____, 2017, Minimum design loads and associated criteria and other structures, ASCE
Standard ASCE/SEI 7-16, published online June 19.
_____, 2010, Minimum design loads for buildings and other structures, ASCE Standard
ASCE/SEI 7-10.
Blake, Thomas F., 2000, EQFAULT, A computer program for the estimation of peak
horizontal acceleration from 3-D fault sources; Windows 95/98 version.
Building News, 1995, CAL-OSHA, State of California, Construction Safety Orders, Title 8,
Chapter 4, Subchapter 4, amended October 1.
California Building Standards Commission, 2019a, California Building Code, California
Code of Regulations, Title 24, Part 2, Volume 2 of 2, based on the 2018 International
Building Code, effective January 1, 2020.
_____, 2019b, California Building Code, California Code of Regulations, Title 24, Part 2,
Volume 1 of 2, Based on the 2018 International Building Code, effective
January 1, 2020.
GeoSoils, Inc.Mr. Danny Caldwell Appendix A
File:e:\wp9\7800\7861a.eoa Page 2
California Code Of Regulations, 2011, CAL-OSHA State of California Construction and
Safety Orders, dated February.
California Department of Conservation, California Geological Survey (CGS), 2018,
Earthquake fault zones, a guide for government agencies, property
owners/developers, and geoscience practitioners for assessing fault rupture hazards
in California: California Geological Survey Special Publication 42 (revised 2018), 93
p.
California Office of Statewide Health Planning and Development (OSHPD), 2020, Seismic
design maps, https://seismicmaps.org/.
Cao, T., Bryant, W.A., Rowshandel, B., Branum, D., and Willis, C.J., 2003, The revised 2002
California probalistic seismic hazard maps, dated June,
http://www.conversation.ca.gov/cgs/rghm/psha/fault_parameters/pdf/documents/
2002_ca_hazardmaps.pdf.
Cascade Stream Solutions, Caldwell Residential Improvements - Existing Topography, 1
sheet, scale:1"=20', undated.
Kanare, H.M., 2005, Concrete floors and moisture, Engineering Bulletin 119, Portland
Cement Association.
Kennedy, M.P., and Tan, S.S., 2008, Geologic map of the San Diego 30' x 60' quadrangle,
California:California Geological Survey, Regional Map No. 3, scale:1:100,000, Plate
1 of 2.
Post-Tensioning Institute, 2014, Errata to standard requirements for design and analysis of
shallow post-tensioned concrete foundations on expansive soils, PTI DC10.5-12,
dated April 16.
_____, 2013, Errata to standard requirements for design and analysis of shallow
post-tensioned concrete foundations on expansive soils, PTI DC10.5-12, dated
November 12.
_____, 2012, Standard requirements for design and analysis of shallow post-tensioned
concrete foundations on expansive soils, PTI DC10.5-12, dated December.
_____, 2004, Design of post-tensioned slabs-on-ground, 3 edition.rd
Sowers and Sowers, 1979, Unified soil classification system (After U. S. Waterways
Experiment Station and ASTM 02487-667) in Introductory soil mechanics, New York.
State of California, 2020, Civil Code, Sections 895 et. seq.
Geotechnical C Geologic C Coastal C Environmental
5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com
February 25, 2022
Revised March 9, 2022
W.O. 7861-A1-SC
Mr. Danny Caldwell
3880 Westhaven Drive
Carlsbad, California 92008
Subject: Response to Third-Party Review (First) and Plan Review, Proposed
Improvements Revision, 3880 Westhaven Drive, Carlsbad, San Diego
County, California APN 207-053-29-00
Dear Mr. Caldwell:
In accordance with your request and authorization, GeoSoils, Inc. (GSI) has prepared the
following response to third-party review and plan review for the subject site. The purpose
of this response and review is to: 1) provide responses to the third-party review and plan
review of the grading plan and 2) to clarify the previous geotechnical recommendations
in regards to the newly proposed site improvements. Our geotechnical recommendations
were first presented in the GeoSoils, Inc. report (GSI, 2020 ) dated June 4, 2020, and
remain pertinent and valid, unless superceded herein.
Foundation recommendations presented in our previous report (GSI, 2020) are still valid
and applicable to the newly revised improvements (addition to front and rear of existing
residence and 1 new ADU and 1 accessory structure in the rear yard) and should be
implemented for the duration of the project.
RESPONSE TO THIRD-PARTY REVIEW
For convenience, the reviewers comments are listed below in italics, followed by GSI’s
response.
Review Comment No. 1
“The geotechnical letter submitted is for a proposed ADU. The grading plans submitted
indicate the site is to be re-graded with a new single-family residence, two additional
unidentified structures, retaining walls, graded slopes, and appurtenant improvements. The
Consultant should provide a preliminary geotechnical investigation addressing site grading
and construction, and the project seismic, grading and foundation recommendations
consistent with requirements of the City of Carlsbad Technical Guidelines for Geotechnical
Reports, the 2019 California Building Code and ASCE 7-16.”
GeoSoils, Inc.
Response to Review Comment No. 1
The reviewer appears to have misinterpreted the project plans. The two (2) unidentified
structures are 1 ADU and 1 accessory structure. The existing single-family residence is to
remain and additions to the front and rear of the existing residence are planned. The front
addition will be a raised-wood type foundation to marry to the existing raised wood
foundation (existing residence). A 2:1 fill slope will be constructed in the front yard to raise
grade slightly to facilitate the proposed front yard patio addition. The rear addition and rear
yard ADU and additional accessory structure will be slab-on-grade with perimeter footings
type foundation systems. The grading will only be performed in the front and rear existing
residence improvement areas, driveway expansion, and the proposed new ADU and
accessory structure. The remainder of the site will remain untouched. Deepened footings
will be used for the proposed perimeter walls and the raised wood front patio. Remedial
grading should be performed at least 5 feet beyond the proposed foundation footprint for
the slab on grade with perimeter footing foundations (i.e., ADU and accessory structure
and rear addition). Where removals are constrained by the existing footing, a stem wall or
retaining wall should be constructed in accordance with the recommendations of the
structural engineer, considering the planned fill will be juxtaposed against the stem
wall/retaining wall. The soils report for this project is a bearing value report (GSI, 2020)
applicable to this type of site improvements, as per code.
Review Comment No. 2
“The Consultant should review the project 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.”
Response to Review Comment No. 2
Comment Acknowledged. GeoSoils, Inc. has reviewed the grading plan by Van Ryn
Engineering (VRE, 2022), and foundation plan and structural details by Paul Christenson
San Diego Engineering (PCSD, 2021) were found to be general conformance with the GSI
soils report (GSI, 2020).
Review Comment No. 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.”
Mr. Danny Caldwell W.O. 7861-A1-SC
3880 Westhaven Drive, Carlsbad Revised March 9, 2022
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GeoSoils, Inc.
Response to Review Comment No. 3
An updated geotechnical map has been generated and is included at the rear of the text.
Review Comment No. 4
“The consultant should address the gross and surficial stability of the proposed slopes.”
Response to Review Comment No. 4
A slope stability analysis was performed on the proposed construction. The location of
cross-sections A-A’ and B-B’ are shown on the revised geotechnical map located at the
rear of the text. The site meets the minimum city requirements of 1.5 factor of safety (FOS)
for proposed static condition (A-A’), and seismic condition (A-A’); and seismic and
temporary slope conditions along B-B’ (ADU) were also analyzed for slope stability. Slope
stability analysis methodology is described in Appendix B. Slope stability results are
included in Appendix B.
Review Comment No. 5
“The Consultant should address the feasibility of the proposed grading and construction
from a geotechnical perspective.”
Response to Review Comment No. 5
According to review of the grading plan by Van Ryn Engineering (VRE, 2022) and
foundation/structural details by Paul Christenson San Diego (PCSD, 2021), the proposed
grading and construction appear to be feasible, provided the project is completed with the
recommendations contained within our soils report (GSI, 2020), for the duration of the
project. The extent of grading will be limited to the main residence front yard area where
a small 2:1 slope approximately 3 feet high is planned and rear of the existing residence
where an addition is planned, east side of driveway, and lower rear slope areas where
1 ADU and 1 accessory structure are planned. Some fine grading will be performed to
widen the driveway and construct infiltration structures. The front patio addition will be
raised wood type foundation construction. The remaining new foundations, consisting of
slab-on-grade with perimeter footings, will require remedial grading to at least 5 feet
outside the proposed foundation footprint (rear addition, and 1 ADU and 1 accessory
structure), as discussed previously. Some confining conditions will be encountered
adjacent the existing residence. As such, alternating A-B-C slot cuts, not to exceed 5 feet
in width should be employed to facilitate removals adjacent the existing residence.
The foundation of the existing residence is raised wood with perimeter footings and interior
isolated piers. The proposed rear addition is to be slab on grade with perimeter footings.
The joining of these two different foundation types may lead to differential settlement
Mr. Danny Caldwell W.O. 7861-A1-SC
3880 Westhaven Drive, Carlsbad Revised March 9, 2022
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GeoSoils, Inc.
issues. The structural engineer should address this condition and provide
recommendations for mitigation.
Review Comment No. 6
“The Consultant should address impacts to adjacent property and improvements as a result
of site grading and construction.”
Response to Review Comment No. 6
Site perimeter condition recommendations are discussed on page 8 of the GeoSoils report
(GSI, 2020). Since the graded fill slope proposed in the center of the rear yard will only be
5 feet high, minimal grading is anticipated. Footings for the planned perimeter walls will
be deepened into formational soils, approximately 2½ to 3 feet below the ground surface.
No permanent adjacent structures should be affected by perimeter wall construction
consisting of deepened footings.
BACKGROUND AND NEWLY PROPOSED IMPROVEMENTS
Our previous geotechnical evaluation was performed on May 20, 2020 and consisted of
the excavation of three (3) shallow hand-auger borings in the front and rear of the existing
residence, and in the vicinity of the previously proposed accessory dwelling unit (ADU).
A bearing value report was issued by GSI for the subject site on June 4, 2020.
After the initially proposed improvements consisting of one rear yard ADU near the center
of the rear base of slope and additions to the front and rear of the existing residence, the
site improvements were expanded to include an accessory structure at the south portion
of the base of the rear yard slope and the original ADU was moved to the north side of the
base of slope.
LIMITATIONS
The conclusions and recommendations presented herein are professional opinions. These
opinions have been derived in accordance with current standards of practice, and no
warranty is express or implied. Standards of practice are subject to change with time. GSI
assumes no responsibility or liability for work or testing performed by others, or their
inaction; or work performed when GSI is not requested to be onsite, to evaluate if our
recommendations have been properly implemented. Use of this report constitutes an
agreement and consent by the user to all the limitations outlined above, notwithstanding
any other agreements that may be in place. In addition, this report may be subject to
review by the controlling authorities. Thus, this report brings to completion our scope of
services for this portion of the project.
Mr. Danny Caldwell W.O. 7861-A1-SC
3880 Westhaven Drive, Carlsbad Revised March 9, 2022
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GeoSoils, Inc.
The opportunity to be of service is sincerely appreciated. If you should have any
questions, please do not hesitate to contact our office.
Respectfully submitted,
GeoSoils, Inc.
Todd M. Page Stephen J. Coover
Engineering Geologist, CEG 2083 Geotechnical Engineer, GE 2057
TMP/JPF/SJC/sh
Attachments: Appendix A - References
Appendix B - Slope Stability Analysis
Plate 1 - Geotechnical Map
Distribution: Addressee (PDF via email)
Mr. Danny Caldwell W.O. 7861-A1-SC
3880 Westhaven Drive, Carlsbad Revised March 9, 2022
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GeoSoils, Inc.
APPENDIX A
REFERENCES
GeoSoils, Inc.
APPENDIX A
REFERENCES
Das, B. M., 1993, Principals of soil dynamics, Southern Illinois University at Carbondale,
PWS-Kent Publishing Company, Boston.
GeoSoils, Inc., 2020, Evaluation of allowable bearing value, active, passive pressures,
lateral pressures, and seismic and retaining wall design parameters, proposed
additional dwelling unit (ADU) at 3880 Westhaven Drive, Carlsbad, California,
W.O. 7861-A-SC, dated June 5.
Griffiths, D. H. and King, R. F., 1965, Applied Geophysics for engineers and geologists,
Pergamon Press, reprinted 1976.
Heatherington Engineering, Inc., 2021, Third-party geotechnical review (first), 3880
Westhaven Drive, Carlsbad, California, GR2021-0046/PD2021-0045
Hunt, R. E., 1986, Geotechnical Engineering analysis and evaluation, McGraw-Hill Book
Company.
Paul Christenson San Diego Engineering, 2021a, Structural design calculations, PCSD
File #: 21-195, sheets S2 and SD1, dated April 20, 2021, sheets S1, S3, SD2, SD3, SN1,
dated May 12, 2021, and sheets WSW1 and WSW2, dated July 1, 2016.
_____, 2021b, Foundation Plans and structural details, sheets, job # 21-195, scale:1/4"=1',
dated May 12.
Van Ryn Civil Engineering/Land Surveying, 2022, Grading plans for 3880 Westhaven Drive,
Carlsbad, California, 5 sheets, scale:1"=10', undated.
GeoSoils, Inc.
APPENDIX B
SLOPE STABILITY ANALYSIS
GeoSoils, Inc.
APPENDIX B
SLOPE STABILITY ANALYSIS
INTRODUCTION OF GSTABL7 v.2 COMPUTER PROGRAM
Introduction
GSTABL7 v.2 is a fully integrated slope stability analysis program. It permits the engineer
to develop the slope geometry interactively and perform slope analysis from within a single
program. The slope analysis portion of GSTABL7 v.2 uses a modified version of the
popular STABL program, originally developed at Purdue University.
GSTABL7 v.2 performs a two dimensional limit equilibrium analysis to compute the factor
of safety (FOS) for a layered slope using the Modified Bishop or Simplified Janbu methods.
This program can be used to search for the most critical surface or the FOS may be
determined for specific surfaces. GSTABL7, Version 2, is programmed to handle:
1. Heterogenous soil systems
2. Anisotropic soil strength properties
3. Reinforced slopes
4. Nonlinear Mohr-Coulomb strength envelope
5. Pore water pressures for effective stress analysis using:
a. Phreatic and piezometric surfaces
b. Pore pressure grid
c. R factor
d. Constant pore water pressure
6. Pseudo-static earthquake loading
7. Surcharge boundary loads
8. Automatic generation and analysis of an unlimited number of circular, noncircular,
and block-shaped failure surfaces
9. Analysis of right-facing slopes
10. Both SI and Imperial units
General Information
If the reviewer wishes to obtain more information concerning slope stability analysis, the
following publications may be consulted initially:
1. The Stability of Slopes, by E.N. Bromhead, Surrey University Press, Chapman and
Hall, N.Y., 411 pages, ISBN 412 01061 5, 1992.
2. Rock Slope Engineering, by E. Hoek and J.W. Bray, Inst. of Mining and Metallurgy,
London, England, Third Edition, 358 pages, ISNB 0 900488 573, 1981.
GeoSoils, Inc.
3. Landslides: Analysis and Control, by R.L. Schuster and R.J. Krizek (editors), Special
Report 176, Transportation Research Board, National Academy of Sciences,
234 pages, ISBN 0 309 02804 3, 1978.
4. Landslides: Investigation and Mitigation, by A.K. Turner and R.J. Krizek (editors),
Special Report 247, Transportation Research Board, National Research Board,
675 pages, ISBN 0 309 06208-X, 1996.
GSTABL7 v.2 Features
The present version of GSTABL7 v.2 contains the following features:
1. Allows user to calculate FOS for static stability and seismic stability evaluations.
2. Allows user to analyze stability situations with different failure modes.
3. Allows user to edit input for slope geometry and calculate corresponding FOS.
4. Allows user to readily review on-screen the input slope geometry.
5. Allows user to automatically generate and analyze defined numbers of circular,
non-circular and block-shaped failure surfaces (i.e., bedding plane, slide plane,
etc.).
Input Data
Input data includes the following items:
1. Unit weight, cohesion, and friction angle of earth materials and bedding planes.
2. Slope geometry and surcharge boundary loads.
3. Apparent dip of bedding planes can be specified in angular range (i.e., from 0 to
90 degrees).
4. Pseudo-static (seismic) earthquake loading. A seismic coefficient of 0.15i and a
peak horizontal ground acceleration PGAM of 0.535 g were used in the seismic
analyses.
5. Soil parameters used in the slope stability analyses are provided in Table B-2.
Mr. Danny Caldwell Appendix B
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GeoSoils, Inc.
TABLE B-1
SOIL MATERIALS
SOIL UNIT
WEIGHT (pcf)
STATIC SHEAR
STRENGTH PARAMETERS
Total Saturated C (psf)M (degrees)
Artificial Fill (Af)125 130 50 28
Tertiary Santiago Formation (Tsa)130 135 162 31
Seismic Discussion
Seismic stability analyses were approximated using a pseudo-static approach. The major
difficulty in the pseudo-static approach arises from the appropriate selection of the seismic
coefficient used in the analysis. The use of a static inertia force equal to this acceleration
during an earthquake (rigid-body response) would be extremely conservative for several
reasons including: (1) only low height, stiff/dense embankments or embankments in
confined areas may respond essentially as rigid structures; (2) an earthquake's inertia force
is enacted on a mass for a short time period. Therefore, replacing a transient force by a
pseudo-static force representing the maximum acceleration may be considered overly
conservative; (3) assuming that total pseudo-static loading is applied evenly throughout
the embankment for an extended period of time is an incorrect assumption, as the length
of the failure surface analyzed is usually much greater than the wave length of seismic
waves generated by earthquakes; and (4) the seismic waves would place portions of the
mass in compression and some in tension, resulting in only a limited portion of the failure
surface analyzed moving in a downslope direction, at any one instant of earthquake
loading.
The coefficients usually suggested by regulating agencies, counties and municipalities are
in the range of 0.05g to 0.25g. For example, past regulatory guidelines within the city and
county of Los Angeles indicated that the slope stability pseudostatic coefficient = 0.1 to
0.15i.
The method developed by Krinitzsky, Gould, and Edinger (1993) which was in turn based
on Taniguchi and Sasaki (1986), was referenced. This method is based on empirical data
and the performance of existing earth embankments during seismic loading. Our review
of “Guidelines for Evaluating and Mitigating Seismic Hazards in California” California
Department of Conservation, California Geological Survey ([CGS], 2008) indicates the
State of California recommends using pseudo-static coefficient of 0.15i for design
earthquakes of M 8.25 or greater and using 0.1 for earthquake parameter M 6.5.
Therefore, for reasonable conservatism, a seismic coefficient of 0.15i was used in our
analysis for a M7.2 event on the Rose Canyon fault. GSI also incorporated a peak
horizontal ground acceleration (PGAM) of 0.432 g into the seismic analysis.
Mr. Danny Caldwell Appendix B
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GeoSoils, Inc.
Output Information
Output information includes:
1. All input data.
2. FOS for the 10 most critical surfaces for static and pseudo-static stability situation.
3. High quality plots can be generated. The plots include the slope geometry, the
critical surfaces and the FOS.
4. Note, that in the analysis, 4,999 trial surfaces were analyzed for each section for
either static or pseudo-static analyses.
Results of Slope Stability Calculations
Table D-2 provides a summary of the results of our stability analyses. Computer printouts
from the GSTABL7 program are included as Plates D-1 through D-6.
TABLE B-2 - SUMMARY OF SLOPE STABILITY ANALYSES
ANALYSIS
FACTOR-OF-SAFETY (FOS)
EXISTING SLOPE CONDITION METHOD COMMENTS
STATIC SEISMIC
Section A-A’1.92 1.36 Modified Bishop Adequate Static & Seismic
FOS
Section B-B’1.64 1.22 Modified Bishop Adequate Static & Seismic
FOS
Mr. Danny Caldwell Appendix B
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I
I I I I I I
0204060801001201402402602803007861-A-SC CALDWELL A-A' SECTION - SEISMICx:\shared\word perfect data\carlsbad\7800\7861 danny caldwell\slope stability\7861-a x-x' section seismic.pl2 Run By: Username 2/11/2022 01:00PM1 2 3 4 5 6 7 1122222L1bcdefghijaInit Points: 30. to 50.Term Limits: 85. to 110.# FSa 1.360b 1.360c 1.360d 1.361e 1.361f 1.361g 1.361h 1.362i 1.362j 1.362SoilDesc.AfTsaSoilTypeNo.12TotalUnit Wt.(pcf)125.0130.0SaturatedUnit Wt.(pcf)130.0135.0CohesionIntercept(psf)50.0162.0FrictionAngle(deg)28.031.0PorePressureParam.0.150.10Piez.SurfaceNo.00Load ValueL1 1000 psfPeak(A) 0.535(g)kh Coef. 0.150(g)<kv Coef. 0.050(g)/\GSTABL7 v.2 FSmin=1.360Safety Factors Are Calculated By The Modified Bishop MethodW.O. 7861-A1-SC PLATE B-1
0204060801001201402402602803007861-A-SC CALDWELL A-A' SECTION - STATICx:\shared\word perfect data\carlsbad\7800\7861 danny caldwell\slope stability\7861-a x-x' section static.pl2 Run By: Username 2/11/2022 12:59PM1 2 3 4 5 6 7 1122222L1bcdefghijaInit Points: 30. to 50.Term Limits: 85. to 110.# FSa 1.924b 1.924c 1.924d 1.924e 1.924f 1.924g 1.925h 1.925i 1.927j 1.927SoilDesc.AfTsaSoilTypeNo.12TotalUnit Wt.(pcf)125.0130.0SaturatedUnit Wt.(pcf)130.0135.0CohesionIntercept(psf)50.0162.0FrictionAngle(deg)28.031.0PorePressureParam.0.150.10Piez.SurfaceNo.00Load ValueL1 1000 psfGSTABL7 v.2 FSmin=1.924Safety Factors Are Calculated By The Modified Bishop MethodW.O. 7861-A1-SC PLATE B-2
0204060801001201402402602803007861-A-SC CALDWELL B-B' SECTION TEMPORARY CUT - SEISMICx:\shared\word perfect data\carlsbad\7800\7861 danny caldwell\slope stability\7861-a b-b' section seismic.pl2 Run By: Username 2/11/2022 12:57PM1 2 3 4 5 6 7 8 9 111222222L1bcdefghijaInit Points: 55.9 to 56.Term Limits: 85. to 110.# FSa 1.222b 1.222c 1.222d 1.222e 1.223f 1.223g 1.223h 1.223i 1.223j 1.223SoilDesc.AfTsaSoilTypeNo.12TotalUnit Wt.(pcf)125.0130.0SaturatedUnit Wt.(pcf)130.0135.0CohesionIntercept(psf)50.0162.0FrictionAngle(deg)28.031.0PorePressureParam.0.150.08Piez.SurfaceNo.00Load ValueL1 1000 psfPeak(A) 0.535(g)kh Coef. 0.150(g)<kv Coef. 0.050(g)/\GSTABL7 v.2 FSmin=1.222Safety Factors Are Calculated By The Modified Bishop MethodW.O. 7861-A1-SC PLATE B-3
0204060801001201402402602803007861-A-SC CALDWELL B-B' SECTION TEMPORARY CUT - STATICx:\shared\word perfect data\carlsbad\7800\7861 danny caldwell\slope stability\7861-a b-b' section static.pl2 Run By: Username 2/11/2022 12:54PM1 2 3 4 5 6 7 8 9 111222222L1bcdefghijaInit Points: 55.9 to 56.Term Limits: 85. to 110.# FSa 1.648b 1.648c 1.648d 1.648e 1.648f 1.648g 1.649h 1.649i 1.649j 1.649SoilDesc.AfTsaSoilTypeNo.12TotalUnit Wt.(pcf)125.0130.0SaturatedUnit Wt.(pcf)130.0135.0CohesionIntercept(psf)50.0162.0FrictionAngle(deg)28.031.0PorePressureParam.0.150.08Piez.SurfaceNo.00Load ValueL1 1000 psfGSTABL7 v.2 FSmin=1.648Safety Factors Are Calculated By The Modified Bishop MethodW.O. 7861-A1-SC PLATE B-4
ALL LOCATIONS ARE APPROXIMATE
This document or efile is not a part of the Construction
Documents and should not be relied upon as being anaccurate depiction of design.
W.O.DATE:SCALE:7861-A-SC 02/22 1" = 20'
Plate 1
GEOTECHNICAL MAP
GSI LEGEND
Tsa
B-3
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