HomeMy WebLinkAboutX2021-3462 - Soils (2)ENGINEERS + GEOLOGISTS + ENVIRONMENTAL SCIENTISTS
December 5, 2022
J.N. 21-422
NICHOLSON CONSTRUCTION
1 Corporate Plaza, Suite 110
Newport Beach, California 92660
Attention: Ms. Nanci Glass
Subject: Geotechnical Report of Rough Grading, Proposed Single -Family Residence,
225 Jasmine Avenue, Corona Del Mar Area, City of Newport Beach, California
Reference: Geotechnical Investigation, Proposed Single Family Residence, 225 Jasmine Avenue,
Corona Del Mar Area, City of Newport Beach, California; report by Petra Geosciences,
Inc., Q.N. 21-422), dated November 10, 2021.
Dear Ms. Glass:
Petra Geosciences, Inc. (Petra) is submitting herewith a summary of the observation and testing services
provided by this firm during rough grading operations within the subject site. Conclusions relative to the
suitability of the grading for the planned structures, and foundation design recommendations for the
proposed residences and other site improvements, are included herein.
The purpose of the grading was to develop an engineered fill pad for the construction of a single-family
residence and associated hadscape features. Grading began on November 15, 2022 and was completed on
November 16, 2022.
SUMMARY OF OBSERVATIONS AND TESTING
Site Clearin¢
Structural materials associated with the previous residential structure was removed from the site. Clearing
operations also included the removal of previous structural features, such as concrete walkways and patios
as well as landscape vegetation. Trees and large shrubs, where removed, were grubbed out to include their
stumps and major root systems. Side yard masonry block property line walls were protected in place.
Ground Preparation
Existing undocumented fill materials and near surface native terrace deposits to a depth of 3 feet were
slightly moist to moist and loose to medium dense. The terrace deposits underlying these surficial soil
materials remained moist and medium dense to dense. Therefore, in order to provide suitable and relatively
uniform support for the proposed structural foundations and exterior site improvements, the existing fill
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NICHOLSON CONSTRUCTION December 5, 2022
225 Jasmine Avenue / Corona Del Mar J.N. 21-422
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and unsuitable terrace deposits were over -excavated to competent terrace deposits at a minimum 2 feet
below the bottoms of the proposed structural footings. A brick septic tank was encountered during remedial
grading and was removed in its entirety to approximately 7 '/a feet below finish pad grade.
Prior to replacing the overexcavated soils as engineered fill, the exposed bottom surfaces were first scarified
to a depth of 6 inches, moisture conditioned to achieve a uniform moisture content that was greater than
optimum, and then recompacted in place to a minimum relative compaction of 90 percent of the applicable
laboratory maximum dry density in accordance with ASTM Test Method D 1557. Horizontal limits of
overexcavation and recompaction extended from approximately property line to property line; however,
consideration was given to the protection of adjacent property line structures. Existing side yard property
line block walls were protected in place.
Fill Placement and Testing
1. The fill materials placed within the subject site consisted of on -site soils.
2. The soils were placed in approximately 4- to 6-inch-thick lifts, moisture conditioned as necessary to
achieve at or above optimum moisture contents and compacted to a minimum relative compaction of
90 percent of the applicable laboratory maximum dry density in accordance with ASTM Test Method
D 1557. The maximum depth of fill placed across the building pad is approximately 7.5 feet.
3. Observations and field density testing were performed during fill placement. Field density and moisture
content tests were performed by nuclear methods (ASTM D 6938). Test results are summarized in
Table A, and approximate locations of the field density tests are depicted on the enclosed site plan
Figure 1.
4. Field density tests were taken at vertical intervals of 1 to 2 feet.
5. Visual and tactile classification of earth materials in the field was the basis for determining if the
laboratory maximum density value presented in Table I was applicable for each density test.
6. Fill placement within the subject lot was performed in general compliance with the recommendations
of our referenced reports and the Grading Code of the City of Newport Beach.
Laboratory Testing
Several laboratory tests were previously performed on samples of onsite soil materials obtained near finish
pad grade in order to determine their engineering characteristics and chemical activity (Reference). The test
results are provided in Table B at the end of this report.
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CONCLUSIONS AND RECOMMENDATIONS
Regulatory Compliance
Removals, overexcavation, processing of exposed surfaces, and placement of engineered fill under the
purview of this report have been completed under the part-time observation of, and with selective testing
by Petra and are found to be in general compliance with the recommendations provided in the reference
report and the grading codes of the City of Newport Beach, California. The completed work within this
firm's purview has been reviewed and is considered to be in compliance with project specifications. It is
our opinion that the as -graded condition of the subject lot and the proposed building construction will not
have an adverse effect on the geologic stability of adjacent properties.
Post -Grading Considerations
Site Drainage
Positive drainage devices such as sloped concrete flatwork, graded swales and area drains should be
provided around the new construction to collect and direct all water to a suitable discharge area. Neither
rain nor excess irrigation water should be allowed to collect or pond against building foundations. The
owner is advised that the drainage system should be properly maintained throughout the life of the proposed
development. The purpose of this drainage system will be to reduce water infiltration into the subgrade
soils and to direct surface water away from building foundations, and walls. The following
recommendations should be implemented during construction.
Area drains should be installed within all planter and landscape areas that are located within 10 feet
of building foundations to reduce excessive infiltration of water into the foundation soils. Per the
2019 CBC, the ground surfaces of planter and landscape areas that are located within 10 feet of
building foundations should be sloped at a minimum gradient of 5 percent away from the
foundations and towards the nearest area drains. The ground surfaces of planter and landscape areas
that are located more than 10 feet away from building foundations may be sloped at a minimum
gradient of 2 percent away from the foundations and towards the nearest area drains.
2. Per the 2019 CBC, concrete flatwork surfaces that are located within 10 feet of building foundations
should be inclined at a minimum gradient of 2 percent away from the building foundations and
towards the nearest area drains. Concrete flatwork surfaces that are located more than 10 feet away
from building foundations may be sloped at a minimum gradient of 1 percent away from the
foundations and towards the nearest area drains.
3. A watering program should be implemented for the landscape areas that maintain a uniform, near
optimum moisture condition in the soils. Overwatering and subsequent saturation of the soils will
cause excessive soil expansion and heave and, therefore, should be avoided. On the other hand,
allowing the soils to dry out will cause excessive soil shrinkage. As an alternative to a conventional
irrigation system, drip irrigation is strongly recommended for all planter areas. The owner is
advised that all drainage devices should be properly maintained throughout the lifetime of the
development.
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Bottomless Trench Drains
When gravel filled bottomless infiltration systems are constructed near foundations, a potential exists for
oversaturation of the foundation soils which conflicts with the intended purpose of onsite drainage facilities.
In addition, it has been our experience that a leading cause of distress to buildings and foundations is due
to poor management of water next to building foundations. Petra recommends a setback of at least 15 feet
between any infiltration system and building foundations. If this setback distance cannot be maintained,
then a modified foundation system may be required to alleviate any distress that could be caused by
infiltration of water near the footing. A modified foundation system could consist of constructing deepened
footings within 15 feet of the infiltration system and installing extra reinforcement. Design of a modified
foundation system is referred to the project structural engineer.
Utility Trench Backfill
All utility trench backfill should be compacted to a minimum relative compaction of 90 percent. Onsite
soils cannot be densifred adequately by flooding and jetting techniques; therefore, trench backfill materials
should be placed in lifts no greater than approximately 6 inches in thickness, watered or air dried as
necessary to achieve a uniform moisture content that is equal to or slightly above optimum moisture, and
then mechanically compacted in -place to a minimum relative compaction of 90 percent. A representative
of the project geotechnical consultant should probe and test the backfills to document that adequate
compaction has been achieved.
For shallow trenches where pipe may be damaged by mechanical compaction equipment, such as under the
building floor slab, imported clean sand exhibiting a sand equivalent value (SE) of 30 or greater may be
utilized. The sand backfill materials should be watered to achieve near optimum moisture conditions and
then tamped in place. No specific relative compaction will be required; however, observation, probing, and,
if deemed necessary, testing should be performed by a representative of the project geotechnical consultant
to document that the sand backfill is adequately compacted and will not be subject to excessive settlement.
Where utility trenches enter the footprint of the building, they should be backfrlled through their entire
depths with on -site fill materials, sand -cement slurry or concrete rather than with any sand or gravel
shading. This "plug" of less- or non -permeable materials will mitigate the potential for water to migrate
through the backfilled trenches from outside of the building to the areas beneath the foundations and floor
slabs.
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If clean, imported sand is to be used for backfill of exterior utility trenches, it is recommended that the
upper 12 inches of trench backfill materials consist of property compacted on -site soil materials. This is to
reduce infiltration of irrigation and rainwater into granular trench backfill materials
Where an interior or exterior utility trench is proposed parallel to a building footing, the bottom of the
trench should not be located below a 1:1 plane projected downward from the outside bottom edge of the
adjacent footing. Where this condition exists, the adjacent footing should be deepened such that the bottom
of the utility trench is located above the 1:1 projection.
FOUNDATION DESIGN CONSIDERATIONS
Near -Fault Site Determination
Based on our review of the referenced geologic maps and literature, no active faults are known to project
through the property. Furthermore, the site does not lie within the boundaries of an "Earthquake Fault Zone"
as defined by the State of California in the Alquist-Priolo Earthquake Fault Zoning Act (CGS, 2018). The
Alquist-Priolo Earthquake Fault Zoning Act (AP Act) defines an active fault as one that "has had surface
displacement within Holocene time (about the last 11,000 years)" The main objective of the AP Act is to
prevent the construction of dwellings on top of active faults that could displace the ground surface resulting
in loss of life and property.
However, it should be noted that according to the USGS Unified Hazard Tool website and/or 2010 CGS
Fault Activity Map of California, the Newport -Inglewood fault, located approximately 3 miles southwest
of the site, would probably generate the most severe site ground motions and, therefore, is the majority
contributor to the deterministic minimum component of the ground motion models. The subject site is
located at a distance of less than 9.5 miles (15 km) from the surface projection of this fault system, which
is capable of producing a magnitude 7 or larger events with a slip rate along the fault greater than 0.04 inch
per year. As such, the site should be considered as a Near -Fault Site in accordance with ASCE 7-16,
Section 11.4.1.
Seismic Design Parameters
Earthquake loads on earthen structures and buildings are a function of ground acceleration which may be
determined from the site -specific ground motion analysis. Alternatively, a design response spectrum can be
developed for certain sites based on the code guidelines. To provide the design team with the parameters
necessary to construct the design acceleration response spectrum for this project, we used two computer
applications. Specifically, the first computer application, which was jointly developed by Structural
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Engineering Association of California (SEAOC) and California's Office of Statewide Health Planning and
Development (OSHPD), the SEA/OSHPD Seismic Design Maps Tool website, hltps://seismicmus.org, is
used to calculate the ground motion parameters. The second computer application, the United Stated
Geological Survey (USGS) Unified Hazard Tool website, httns:Hearthguake.usgs.gov/hazards/interactive/,
is used to estimate the earthquake magnitude and the distance to surface projection of the fault.
To run the above computer applications, site latitude and longitude, seismic risk category and knowledge
of site class are required. The site class definition depends on the direct measurement and the ASCE 7-16
recommended procedure for calculating average small -strain shear wave velocity, Vs30, within the upper
30 meters (approximately 100 feet) of site soils.
A seismic risk category of II was assigned to the proposed building in accordance with 2019 CBC, Table
1604.5. No shear wave velocity measurement was performed at the site, however, the subsurface materials
at the site appears to exhibit the characteristics of stiff soils condition for Site Class D designation.
Therefore, an average shear wave velocity of 600 to 1,200 feet per second for the upper 100 feet was
assigned to the site based on engineering judgment and geophysical experience. As such, in accordance
with ASCE 7-16, Table 20.3-1, Site Class D (D- Default as per SEA/OSHPD software) has been assigned
to the subject site.
The following table, Table 1, provides parameters required to construct the seismic response coefficient,
Cs, curve based on ASCE 7-16, Article 12.8 guidelines.
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TABLE I
Seismic Design Parameters
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Ground Motion Parameters
Specific Reference
Parameter
Value
Unit
Site Latitude (North)
-
33.5957
°
Site Longitude (West)
-
-117. 8743
°
Site Class Definition
Section 1613.2.2 (I), Chapter 20 (1)
D-Default (4)
-
Assumed Seismic Risk Category
Table 1604.5 (1)
II
-
Mw - Earthquake Magnitude
USGS Unified Hazard Tool (3)
7.5 (3)
-
R— Distance to Surface Projection of Fault
USGS Unified Hazard Tool (3)
5.0 (3)
km
S, - Mapped Spectral Response Acceleration
Figure1613.2.1(1) 0)
1.358 (4)
g
Short Period (0.2 second)
St -Mapped Spectral Response Acceleration
Figure 1613.2.1(2) 0)
0.482(4)
g
Long Period 1.0 second
Fs — Short Period (0.2 second) Site Coefficient
Table 1613.2.3(1) (1)
1.2(4)
-
F,— Long Period (1.0 second) Site Coefficient
Table 1613.2.3(2) (1)
Null (4)
-
Sms— MCER Spectral Response Acceleration Parameter
Equation 16-36 (1)
1.63(4)
g
Adjusted for Site Class Effect 0.2 second
Sm, - MCER Spectral Response Acceleration Parameter
Equation I6-37 0)
Null (4)
g
Adjusted for Site Class Effect (1.0 second)
SDs - Design Spectral Response Acceleration at 0.2-s
Equation 16-38 0)
1.087(4)
g
SDI -Design Spectral Response Acceleration at 1-s
Equation 16-39 (I)
Null (4)
g
T. = 0.2 SDI/ SDs
Section 11.4.6 (z)
Null
s
Ts= SDI/ SDs
Section 11.4.6 of
Null
s
TI, - Long Period Transition Period
Figure 22-14 (2)
8 (4)
s
PGA - Peak Ground Acceleration at MCEG (`)
Figure 22-9 (r)
0.594
g
FPGA - Site Coefficient Adjusted for Site Class Effect (2)
Table 11.8-1 (2)
1.2 (4)
-
PGAM —Peak Ground Acceleration (z)
Equation 11.8-1 (1)
0.712(4)
g
Adjusted for Site Class Effect
Design PGA = (% PGAM) - Slope Stability (r)
Similar to Eqs. 16-38 & 16-39 (2)
0.475
g
Design PGA z (0.4 SDs) — Short Retaining Walls (t)
Equation 11.4-5 (z)
0.435
g
CRs - Short Period Risk Coefficient
Figure 22-18A (2)
0.909 (4)
-
CRt - Long Period Risk Coefficient
Figure 22-19A (2)
0.921 (4)
-
SDC - Seismic Design Category W
Section 1613.2.5 (1)
1 Null (4)
-
References:
111 California Building Code (CBC), 2019, California Code of Regulations, Title 24, Part 2, Volume I and H.
(2) American Society of Civil Engineers/Structural Engineering Institute (ASCE/SEI), 2016, Minimum Design Loads and Associated Criteria
for Buildings and Other Structures, Standards 7-16.
(3) USGS Unified Hazard Tool - hnpsl/eartliquake.usgs.gov/hazards/interactive/
(') SEI/OSHPD Seismic Design Map Application—hltps://Seisn icmaps.org
Related References:
Federal Emergency Management Agency (FEMA), 2015, NEHERP (National Earthquake Hazards Reduction Program)
Recommended Seismic Provision for New Building and Other Structures FEMA P-1050).
Notes:
Calculated at the MCE return period o£2475 years (2 percent chance of exceedance in 50 years).
t PGA Calculated at Design Level of/3o£MCE; appreximately equivalent to a reurn period of475 yens(10 percent chance ofexceedance
in 50 years).
PGA Calculated for short, stubby retaining walls with an infinitesimal (zero) fundamental period.
The desi ation provided herein maybe superseded by the structural engineer in accordance with Section 1613.2.5.1, if applicable.
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Discussion - General
Owing to the characteristics of the subsurface soils, as defined by Site Class D-Default designation, and
proximity of the site to the sources of major ground shaking, the site is expected to experience strong ground
shaking during its anticipated life span. Under these circumstances, where the code -specified design
response spectrum may not adequately characterize site response, the 2019 CBC typically requires a site -
specific seismic response analysis to be performed. This requirement is signified/identified by the "null"
values that are output using SEA/OSHPD software in determination of short period, but mostly, in
determination of long period seismic parameters, see Table 1.
For conditions where a "null" value is reported for the site, a variety of design approaches are permitted by
2019 CBC and ASCE 7-16 in lieu of a site -specific seismic hazard analysis. For any specific site, these
alternative design approaches, which include Equivalent Lateral Force (ELF) procedure, Modal Response
Spectrum Analysis (MRSA) procedure, Linear Response History Analysis (LRHA) procedure and
Simplified Design procedure, among other methods, are expected to provide results that may or may not be
more economical than those that are obtained if a site -specific seismic hazards analysis is performed. These
design approaches and their limitations should be evaluated by the project structural engineer.
Discussion — Seismic Design Category
Please note that the Seismic Design Category, SDC, is also designated as "null" in Table 1. For conditions
where the mapped spectral response acceleration parameter at I — second period, SI, is less than 0.75, the
2019 CBC, Section 1613.2.5.1 allows that seismic design category to be determined from Table 1613.2.5(1)
alone provided that all 4 requirements concerning fundamental period of structure, story drift, seismic
response coefficient, and relative rigidity of the diaphragms are met. Our interpretation of ASCE 7-16 is
that for conditions where one or more of these 4 conditions are not met, seismic design category should be
assigned based on: 1) 2019 CBC, Table 1613.2.5(1), 2) structure's risk category and 3) the value Of SDS, at
the discretion of the project structural engineer.
Discussion — Equivalent Lateral Force Method
Should the Equivalent Lateral Force (ELF) method be used for seismic design of structural elements, the
value of Constant Velocity Domain Transition Period, Ts, is estimated to 0.537 seconds and the value of
Long Period Transition Period, TL, is provided in Table I for construction of Seismic Response Coefficient
— Period (Cs -T) curve that is used in the ELF procedure.
As stated herein, the subject site is considered to be within a Site Class D-Default. A site -specific ground
motion hazard analysis is not required for structures on Site Class D-Default with Si > 0.2 provided that
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the Seismic Response Coefficient, Cs, is determined in accordance with ASCE 7-16, Article 12.8 and
structural design is performed in accordance with Equivalent Lateral Force (ELF) procedure.
Allowable Bearing Capacity, Estimated Settlement and Lateral Resistance
Allowable Soil Bearing Capacities
Pad Footings
An allowable soil bearing capacity of 1,500 pounds per square foot may be utilized for design of isolated
24-inch-square footings founded at a minimum depth of 12 inches below the lowest adjacent final grade
for pad footings that are not a part of the slab system and are used for support of such features as roof
overhang, second -story decks, patio covers, etc. This value may be increased by 20 percent for each
additional foot of depth and by 10 percent for each additional foot of width, to a maximum value of 2,500
pounds per square foot. The recommended allowable bearing value includes both dead and live loads, and
may be increased by one-third for short duration wind and seismic forces.
Continuous Footings
An allowable soil bearing capacity of 1,500 pounds per square foot may be utilized for design of continuous
footings founded at a minimum depth of 12 inches below the lowest adjacent final grade. This value may
be increased by 20 percent for each additional foot of depth and by 10 percent for each additional foot of
width, to a maximum value of 2,500 pounds per square foot. The recommended allowable bearing value
includes both dead and live loads, and may be increased by one-third for short duration wind and seismic
forces.
Estimated Footing Settlement
Based on the allowable bearing values provided above, total static settlement of the footings under the
anticipated loads is expected to be on the order of Y: inch. Differential settlement is estimated to be on the
order of 1/4 inch over a horizontal span of 40 feet. The majority of settlement is likely to take place as
footing loads are applied or shortly thereafter.
Lateral Resistance
A passive earth pressure of 210 pounds per square foot per foot of depth, to a maximum value of 2,100
pounds per square foot, may be used to determine lateral bearing resistance for footings. In addition, a
coefficient of friction of 0.35 times the dead load forces may be used between concrete and the supporting
soils to determine lateral sliding resistance. The above values may be increased by one-third when designing
for transient wind or seismic forces. It should be noted that the above values are based on the condition
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where footings are cast in direct contact with engineered fill or competent native soils. In cases where the
footing sides are formed, all backfill placed against the footings upon removal of forms should be
compacted to at least 90 percent of the applicable maximum dry density.
Guidelines for Footings and Slabs on -Grade Design and Construction
The results of our laboratory tests performed on representative samples of near -surface soils within the site
during our -investigation indicate that these material predominantly exhibit expansion indices that are less
than 20. As indicated in Section 1803.5.3 of 2019 California Building Code (2019 CBC), these soils are
considered non -expansive and, as such, the design of slabs on -grade is considered to be exempt from the
procedures outlined in Sections 1808.6.2 of the 2019 CBC and may be performed using any method deemed
rational and appropriate by the project structural engineer. However, the following minimum
recommendations are presented herein for conditions where the project design team may require
geotechnical engineering guidelines for design and construction of footings and slabs on -grade the project
site.
The design and construction guidelines that follow are based on the above soil conditions and may
be considered for reducing the effects of variability in fabric, composition and, therefore, the
detrimental behavior of the site soils such as excessive short- and long-term total and differential
heave or settlement. These guidelines have been developed on the basis of the previous experience
ofthis firm on projects with similarsoil conditions. Although construction performed in accordance
with these guidelines has been found to reduce post -construction movement and/or distress, they
generally do not positively eliminate all potential effects of variability in soils characteristics and
future heave or settlement.
It should also be noted that the suggestions for dimension and reinforcement provided herein are
performance -based and intended only as preliminary guidelines to achieve adequate performance
tinder the anticipated soil conditions. However, they should not be construed as replacement for
structural engineering analyses, experience and judgment. The project structural engineer,
architect and/or civil engineer should make appropriate adjustments to slab and footing
dimensions, and reinforcement type, size and spacing to accountfor internal concrete forces (e.g.,
thermal, shrinkage and expansion), as well as external forces (e.g., applied loads) as deemed
necessary. Consideration should also be given to minimum design criteria as dictated by local
building code requirements.
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Conventional Slabs on -Grade System
Given the expansion index of less than 20, as generally exhibited by onsite soils, we recommend that
footings and floor slabs be designed and constructed in accordance with the following minimum criteria.
Footings
1. Exterior continuous footings supporting three- and four-story structures should be founded at a
minimum depth of 18 inches below the lowest adjacent final grade, respectively. Interior continuous
footings may be founded at a minimum depth of 10 inches below the top of the adjacent finish floor
slabs.
2. In accordance with Table 1809.7 of 2019 CBC for light -frame construction, all continuous footings
should have minimum widths of 15 inches for three-story construction. We recommend all continuous
footings should be reinforced with a minimum of two No. 4 bars, one top and one bottom.
3. A minimum 12-inch-wide grade beam founded at the same depth as adjacent footings should be
provided across garage entrances or similar openings (such as large doors or bay windows). The grade
beam should be reinforced with a similar manner as provided above.
4. Interior isolated pad footings, if required, should be a minimum of 24 inches square and founded at a
minimum depth of 15 inches below the bottoms of the adjacent floor slabs. Pad footings should be
reinforced with No. 4 bars spaced a maximum of 18 inches on centers, both ways, placed near the
bottoms of the footings.
5. Exterior isolated pad footings intended for support of roof overhangs such as second -story decks, patio
covers and similar construction should be a minimum of 24 inches square and founded at a minimum
depth of 24 inches below the lowest adjacent final grade. The pad footings should be reinforced with
No. 4 bars spaced a maximum of 18 inches on centers, both ways, placed near the bottoms of the
footings. Exterior isolated pad footings may need to be connected to adjacent pad and/or continuous
footings via tic beams at the discretion of the project structural engineer.
6. The minimum footing dimensions and reinforcement recommended herein may be modified (increased
or decreased subject to the constraints of Chapter 18 of the 2019 CBC) by the structural engineer
responsible for foundation design based on his/her calculations, engineering experience and judgment.
Building Floor Slabs
1. Concrete floor slabs should be a minimum 4 inches thick and reinforced with No. 3 bars spaced a
maximum of 24 inches on centers, both ways. All slab reinforcement should be supported on concrete
chairs or brick to ensure the desired placement near mid -depth.
Slab dimension, reinforcement type, size and spacing need to account for internal concrete forces (e.g.,
thermal, shrinkage and expansion) as well as external forces (e.g., applied loads), as deemed necessary.
2. Living area concrete floor slabs and areas to receive moisture sensitive floor covering should be
underlain with a moisture vapor retarder consisting of a minimum 10-mil-thick polyethylene or
polyolefin membrane that meets the minimum requirements of ASTM E96 and ASTM E1745 for vapor
retarders (such as Husky Yellow Guard®, Stego® Wrap, or equivalent). All laps within the membrane
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should be sealed, and at least 2 inches of clean sand should be placed over the membrane to promote
uniform curing of the concrete. To reduce the potential for punctures, the membrane should be placed
on a pad surface that has been graded smooth without any sharp protrusions. If a smooth surface cannot
be achieved by grading, consideration should be given to lowering the pad finished grade an additional
inch and then placing a 1-inch-thick leveling course of sand across the pad surface prior to the
placement of the membrane. To comply with Section 1907.1.1 of the 2019 CBC, the living area
concrete floor slab should also be underlain with capillary break consisting of a minimum of 4 inches
of gravel or crushed stone containing not more than 10 percent of material that passes through a No. 4
sieve. The capillary break should be placed below the 10-mil moisture vapor retarder.
At the present time, some slab designers, geotechnical professionals and concrete experts view
the sand layer below the slab (blotting sand) as a place for entrapment of excess moisture that
could adversely impact moisture -sensitive floor coverings. As a preventive measure, the
potential for moisture intrusion into the concrete slab could be reduced ifthe concrete is placed
directly on the vapor retarder. However, if this sand layer is omitted, appropriate curing
methods must be implemented to ensure that the concrete slab cures uniformly. A qualified
materials engineer with experience in slab design and construction should provide
recommendations for alternative methods of curing and supervise the construction process to
ensure uniform slab curing. Additional steps would also need to be taken to prevent puncturing
of the vapor retarder during concrete placement.
Garage floor slabs should be a minimum 4 inches thick and reinforced in a similar manner as living
area floor slabs. Garage slabs should also be poured separately from adjacent wall footings with a
positive separation maintained using'/4-inch-minimum felt expansion joint material. To control the
propagation of shrinkage cracks, garage floor slabs should be quartered with weakened plane joints.
Consideration should be given to placement of a moisture vapor retarder below the garage slab, similar
to that provided in Item 2 above, should the garage slab be overlain with moisture sensitive floor
covering.
4. Presaturation of the subgrade below floor slabs will not be required; however, prior to placing concrete,
the subgrade below all dwelling and garage floor slab areas should be thoroughly moistened to achieve
a moisture content that is at least equal to or slightly greater than optimum moisture content. This
moisture content should penetrate to a minimum depth of 12 inches below the bottoms of the slabs.
5. The minimum dimensions and reinforcement recommended herein for building floor slabs may be
modified (increased or decreased subject to the constraints of Chapter 18 of the 2019 CBC) by the
structural engineer responsible for foundation design based on his/her calculations, engineering
experience and judgment.
Foundation Observations
All foundation excavations should be observed by a representative of the project geotechnical consultant to
verify that they have been excavated into competent fill materials. These observations should be performed
prior to the placement of forms or reinforcement. The excavations should be trimmed neat, level and square.
All loose, sloughed or moisture -softened materials and/or any construction debris should be removed prior
IFPETFM SOLID AS A ROCK
NICHOLSON CONSTRUCTION December 5, 2022
225 Jasmine Avenue / Corona Del Mar J.N. 21422
Page 13
to the placement of concrete. Excavated soils derived from footing and utility trenches should not be placed
in slab -on -grade areas unless they are compacted to at least 90 percent of maximum dry density.
General Corrosivity Screening
As a screening level study, limited chemical and electrical tests were performed on samples considered
representative of the onsite soils to identify potential corrosive characteristics of these soils. The common
indicators associated with soil corrosivity include water-soluble sulfate and chloride levels, pH (a measure
of acidity), and minimum electrical resistivity.
It should be noted that Petra does not practice corrosion engineering; therefore, the test results,
opinion and engineering judgment provided herein should be considered as general guidelines
only. Additional analyses would be warranted, especially, for cases where buried metallic building
materials (such as copper and cast or ductile iron pipes) in contact with site soils are planned for
the project. In many cases, the project geotechnical engineer may not be informed of these choices.
Therefore, for conditions where such elements are considered, we recommend that other, relevant
project design professionals (e.g., the architect, landscape architect, civil and/or structural
engineer) also consider recommending a qualified corrosion engineer to conduct additional
sampling and testing of near -surface soils during the final stages of site grading to provide a
complete assessment of soil corrosivity. Recommendations to mitigate the detrimental effects of
corrosive soils on buried metallic and other building materials that may be exposed to corrosive
soils should be provided by the corrosion engineer as deemed appropriate.
In general, a soil's water-soluble sulfate levels and pH relate to the potential for concrete degradation;
water-soluble chlorides in soils impact ferrous metals embedded or encased in concrete, e.g., reinforcing
steel; and electrical resistivity is a measure of a soil's corrosion potential to a variety of buried metals used
in the building industry, such as copper tubing and cast or ductile iron pipes. Table 2, below, presents a
single value of individual test results with an interpretation of current code indicators and guidelines that
are commonly used in this industry. The table includes the code -related classifications of the soils as they
relate to the various tests, as well as a general recommendation for possible mitigation measures in view of
the potential adverse impact on various components of the proposed structures in direct contact with site
soils. The guidelines provided herein should be evaluated and confirmed, or modified, in their entirety by
the project structural engineer, corrosion engineer and/or the contractor responsible for concrete placement
for structural concrete used in exterior and interior footings, interior slabs on -ground, garage slabs, wall
foundations and concrete exposed to weather such as driveways, patios, porches, walkways, ramps, steps,
curbs, etc.
PETRASOr117 AS A ROCK
GEOSCIENCES"°
NICHOLSON CONSTRUCTION
225 Jasmine Avenue / Corona Del Mar
TABLE 2
Soil Corrosivity Screening Results
December 5, 2022
J.N. 21-422
Page 14
Test
Test Results
Classification
General Recommendations
Soluble Sulfates
0.0087 %
SO'
Min. f c= 2,500 psi
Cal 417
pH
7.72
Type I-P (MS) Modified or Type II Modified cement
Cal 643
Allkal' e
Soluble Chloride
C12
Residence: No max water/cement ratio, f e = 2,500 psi
Cal 422
300 ppm
C2
Spas/Decking: water/cement ratio 0.40, f c = 5,000 si
Resistivity
8,100
Moderately
Consult a Corrosion Engineer
Cal 643)
ohm -cm
Corrosives
Notes:
1. ACI 318-14, Section 19.3
2. ACI 318-14, Section 19.3
3. Pierre R. Roberge, "Handbook of Corrosion Engineering"
4. Exposure classification C2 applies specifically to swimming pools/spas and appurtenant concrete elements
Retaining Wall Design and Construction Considerations
Provided herein are geotechnical design and construction recommendations for exterior retaining walls,
should they be proposed for construction onsite.
Footings for retaining walls proposed on level ground may be designed in accordance with the bearing and
lateral resistance values provided previously for building footings; however, when calculating passive
resistance, the resistance of the upper 6 inches of the soils should be ignored in areas where the footings
will not be covered with concrete flatwork, or where the thickness of soil cover over the top of the footing
is less than 12 inches.
Active and At -Rest Earth Pressures
Active and at -rest earth pressures to be utilized for design of any retaining walls to be constructed within
the site will be dependent on whether on -site soils or imported granular materials are used for backfill. For
this reason, active and at -rest earth pressures are provided below for both conditions.
1. On -Site Soils Used for Backfill
If on -site soils are used as backfill, active earth pressures equivalent to fluids having densities of
35 and 51 pounds per cubic foot should be used for design of cantilevered walls retaining a level
backfill and ascending 2:1 backfill, respectively. For walls that are restrained at the top, at -rest earth
pressures of 53 and 78 pounds per cubic foot (equivalent fluid pressures) should be used. The above
values are for retaining walls that have been supplied with a proper subdrain system (see Figure
RW-1). All walls should be designed to support any adjacent structural surcharge loads imposed
by other nearby walls or footings in addition to the above recommended active and at -rest earth
pressures.
PETRASOLID ASA ROCK
GEOSCIENCE13—
NICHOLSON CONSTRUCTION December 5, 2022
225 Jasmine Avenue / Corona Del Mar J.N. 21-422
Page 15
2. Imported Sand, Pea Gravel or Rock Used for Wall Backfill
Where imported clean sand exhibiting a sand equivalent value (SE) of 30 or greater, or pea gravel
or crushed rock are be used for wall backfill, the lateral earth pressures may be reduced provided
these granular backfill materials extend behind the walls to a minimum horizontal distance equal
to one-half the wall height. In addition, the sand, pea gravel or rock backfill materials should extend
behind the walls to a minimum horizontal distance of 2 feet at the base of the wall or to a horizontal
distance equal to the heel width of the footing, whichever is greater (see Figures RW-2 and RW-
3). For the above conditions, cantilevered walls retaining a level backfill and ascending 2:1 backfill
may be designed to resist active earth pressures equivalent to fluids having densities of 30 and 41
pounds per cubic foot, respectively. For walls that are restrained at the top, at -rest earth pressures
equivalent to fluids having densities of 45 and 62 pounds per cubic foot are recommended for
design of restrained walls supporting a level backfill and ascending 2:1 backfill, respectively. These
values are also for retaining walls supplied with a proper subdrain system. Furthermore, as with
native soil backfill, the walls should be designed to support any adjacent structural surcharge loads
imposed by other nearby walls or footings in addition to the recommended active and at -rest earth
pressures.
Earthquake Loads Retaining Walls
Note 1 of Section 1803.5.12 of the 2019 CBC indicates that the dynamic seismic lateral earth pressures on
foundation walls and retaining walls supporting more than 6 feet of backfill height due to design earthquake
ground motions be determined. It is unlikely that any wall retaining 6 or more feet of backfill will be
constructed onsite. Accordingly, dynamic seismic lateral earth pressures are not considered necessary for
this project.
Subdrainage
Perforated pipe and gravel subdrains should be installed behind all basement and retaining walls to prevent
entrapment of water in the backfill (see Figures RW-1 through RW-3). Perforated pipe should consist of 4-
inch-minimum diameter PVC Schedule 40, or SDR-35, with the perforations laid down. The pipe should
be encased in a 1-foot-wide column of %-inch to 1'/z-inch open -graded gravel. I£ on -site soils are used as
backfill, the open -graded gravel should extend above the wall footings to a minimum height equal to one-
third the wall height or to a minimum height of 1.5 feet above the footing, whichever is greater. If imported
sand, pea gravel, or crushed rock is used as backfill, subdrain details shown on Figures RW-2 and RW-3
should be utilized. The open -graded gravel should be completely wrapped in filter fabric consisting of
Mirafi 140N or equivalent. Solid outlet pipes should be connected to the subdrains and then routed to a
suitable area for discharge of accumulated water.
If a limited area exists behind the walls for installation of a pipe and gravel subdrain, a geotextile drain mat
such as Mirafi Miradrain, or equivalent, can be used in lieu of drainage gravel. The drain mat should extend
the full height and lengths of the walls and the filter fabric side of the drain mat should be placed up against
It PETRA SOLID ASA ROCK
NICHOLSON CONSTRUCTION December 5, 2022
225 Jasmine Avenue / Corona Del Mar J.N. 21-422
Page 16
the backcut. The perforated pipe drain line placed at the bottom of the drain mat should consist of 4-inch
minimum diameter PVC Schedule 40 or SDR-35. The filter fabric on the drain mat should be peeled back
and then wrapped around the drain line.
Wateraroofine
The portions of retaining walls supporting backfill should be coated with an approved waterproofing
compound or covered with a similar material to inhibit infiltration of moisture through the walls.
Wall Backfill
Recommended active and at -rest earth pressures for design of retaining walls are based on the physical and
mechanical properties of the on -site soil materials. On -site soil materials may be difficult to compact when
placed in the relatively confined areas located between the walls and temporary backcut slopes. Therefore,
to facilitate compaction of the backfill, consideration should be given to using pea gravel or crushed rock
behind the proposed retaining walls. For this condition, the reduced active and at -rest pressures provided
previously for sand, pea gravel, or crushed rock backfill may be considered in wall design provided they
are installed as shown on Figures RW-2 and RW-3.
Where the onsite soils materials or imported sand (with a Sand Equivalent of 30 or greater) are used as
backfill behind the proposed retaining walls, the backfill materials should be placed in approximately 6- to
8-inch-thick maximum lifts, watered as necessary to achieve near optimum moisture conditions, and then
mechanically compacted in place to a minimum relative compaction of 90 percent. Flooding or jetting of
the backfill materials should be avoided. A representative of the project geotechnical consultant should
observe the backfill procedures and test the wall backfill to verify adequate compaction.
If imported pea gravel or rock is used for backfill, the gravel should be placed in approximately 2- to 3-
foot-thick lifts, thoroughly wetted but not flooded, and then mechanically tamped or vibrated into place. A
representative of the project geotechnical consultant should observe the backfill procedures and probe the
backfill to determine that an adequate degree of compaction is achieved.
To reduce the potential for the direct infiltration of surface water into the backfill, imported sand, gravel,
or rock backfill should be capped with at least 12 to 18 inches of on -site soil. Filter fabric such as MirafL
140N or equivalent, should be placed between the soil and the imported gravel or rock to prevent fines from
penetrating into the backfill. If a thicker cap is desired (for planting or other reasons), consultation with the
project structural engineer may be required to ascertain if the wall design is appropriate for the additional
lateral pressure that a thicker cap of native material may impose.
PETRASOLID ASAROCK
GEOSCIENCES"°
NICHOLSON CONSTRUCTION December 5, 2022
225 Jasmine Avenue / Corona Del Mar J.N. 21-422
Page 17
Geotechnical Observation and Testing
All grading and construction phases associated with retaining wall construction, including backcut
excavations, observation of the footing and pier excavations, installation of the subdrainage systems, and
placement of backfill should be provided by a representative of the project geotechnical consultant.
Masonry Block Walls (Non -Retaining)
Footings for free-standing (non -retaining) masonry block walls may be designed in accordance with the
bearing and lateral resistance values provided previously for building footings. However, as a minimum,
the wall footings should be embedded at a minimum depth of 12 inches below the lowest adjacent final
grade. The footings should also be reinforced with a minimum of two No. 4 bars, one top and one bottom.
In order to reduce the potential for unsightly cracking related to the possible effects of differential settlement
and/or expansion, positive separations (construction joints) should also be provided in the block walls at
each corner and at horizontal intervals of approximately 20 to 25 feet. The separations should be provided
in the blocks and not extend through the footings. The footings should be poured monolithically with
continuous rebars to serve as effective "grade beams" below the walls.
Planter Walls
Low -height planter walls should be supported by continuous concrete footings constructed in accordance
with the recommendations presented previously for masonry block wall footings.
General
Near -surface engineered fill soils within the site are variable in expansion behavior and are expected to
exhibit very low to low expansion potential. For this reason, we recommend that all exterior concrete
flatwork such as sidewalks, patio slabs, large decorative slabs, concrete subslabs that will be covered with
decorative pavers, private vehicular driveways and/or access roads within the site be designed by the project
architect and/or structural engineer with consideration given to mitigating the potential cracking and uplift
that can develop in soils exhibiting expansion index values that fall in the low category.
The guidelines that follow should be considered as minimums and are subject to review and revision by the
project architect, structural engineer and/or landscape consultant as deemed appropriate
PETRA SOLID AS A ROCK
NICHOLSON CONSTRUCTION December 5, 2022
225 Jasmine Avenue / Corona Del Mar J.N. 21-422
Page 18
Thickness and Joint Spacing
To reduce the potential of unsightly cracking, concrete walkways, patio -type slabs, large decorative slabs
and concrete subslabs to be covered with decorative pavers should be at least 4 inches thick and provided
with construction joints or expansion joints every 6 feet or less. Private driveways that will be designed for
the use of passenger cars for access to private garages should also be at least 5 inches thick and provided
with construction joints or expansion joints every 10 feet or less.
Reinforcement
All concrete flatwork having their largest plan -view panel dimension exceeding 5 feet should be reinforced
with a minimum of No. 3 bars spaced 24 inches on centers, both ways. The reinforcement should be
properly positioned near the middle of the slabs.
The reinforcement recommendations provided herein are intended as guidelines to achieve
adequate performance for anticipated soil conditions. The project architect, civil and/or structural
engineer should make appropriate adjustments in reinforcement type, size and spacing to account
for concrete internal (e.g., shrinkage and thermal) and external (e.g., applied loads) forces as
deemed necessary.
Edge Beams (Optional)
Where the outer edges of concrete flatwork are to be bordered by landscaping, it is recommended that
consideration be given to the use of edge beams (thickened edges) to prevent excessive infiltration and
accumulation of water under the slabs. Edge beams, if used, should be 6 to 8 inches wide, extend 8 inches
below the tops of the finish slab surfaces. Edge beams are not mandatory; however, their inclusion in
flatwork construction adjacent to landscaped areas is intended to reduce the potential for vertical and
horizontal movement and subsequent cracking of the flatwork related to uplift forces that can develop in
expansive soils.
Subgrade Preparation
Compaction
To reduce the potential for distress to concrete flatwork, the subgrade soils below concrete flatwork areas
to a minimum depth of 12 inches (or deeper, as either prescribed elsewhere in this report or determined in
the field) should be moisture conditioned to at least equal to, or slightly greater than, the optimum moisture
content and then compacted to a minimum relative compaction of 90 percent.
- PETRA SOLID ASA HOCK
NICHOLSON CONSTRUCTION December 5, 2022
225 Jasmine Avenue / Corona Del Mar J.N. 21-422
Page 19
Pre-Moistenin¢
As a further measure to reduce the potential for concrete flatwork cracking, subgrade soils should be
thoroughly moistened prior to placing concrete. The moisture content of the soils should be at least 1.2
times the optimum moisture content and penetrate to a minimum depth of 12 inches into the subgrade.
Therefore, moisture conditioning should be achieved with sprinklers or a light spray applied to the subgrade
over a period of few to several days just prior to pouring concrete. Pre -watering of the soils is intended to
promote uniform curing of the concrete, reduce the development of shrinkage cracks and reduce the
potential for differential expansion pressure on freshly poured flatwork. A representative of the project
geotechnical consultant should observe and verify the density and moisture content of the soils, and the
depth of moisture penetration prior to pouring concrete.
Drainage
Drainage from patios and other flatwork areas should be directed to local area drains and/or graded earth
swales designed to carry runoff water to the adjacent streets or other approved drainage structures. The
concrete flatwork should be sloped at a minimum gradient as discussed earlier in the Site Drainage section
of this report, or as prescribed by project civil engineer or local codes, away from building foundations,
retaining walls, masonry garden walls and slope areas.
Tree Wells
Tree wells are not recommended in concrete flatwork areas since they introduce excessive water into the
subgrade soils and allow root invasion, both of which can cause heaving and cracking of the flatwork.
FUTURE IMPROVEMENTS
Should any new structures or improvements be proposed at any time in the future other than those shown
on the enclosed grading plan and discussed herein, our firm should be notified so that we may provide
design recommendations. Design recommendations are particularly critical for any new improvements that
may be proposed on or near descending slopes, and in areas where they may interfere with the proposed
permanent drainage facilities.
Potential problems can develop when drainage on the pad is altered in any way (i.e., excavations or
placement of fills associated with construction of new walkways, patios, block walls and planters).
Therefore, it is recommended that we be engaged to review the final design drawings, specifications and
grading plan prior to any new construction. If we are not given the opportunity to review these documents
PETRASOLID AS AROCK
GEOSCIENCES-
NICHOLSON CONSTRUCTION
225 Jasmine Avenue / Corona Del Mar
December 5, 2022
J.N. 21-422
Page 20
with respect to the geotechnical aspects of new construction and grading, it should not be assumed that the
recommendations provided herein are wholly or in part applicable to the new construction or grading.
POST -GRADING OBSERVATIONS AND TESTING
Our firm should be notified at the appropriate times in order that we may provide the following observation
and testing services during the various phases of post grading construction:
1. Building Construction
• Observe footing trenches when first excavated to verify competent soil bearing conditions.
• Re -observe footing trenches, if necessary, if trenches are found to contain a significant
accumulation of loose, saturated or otherwise compressible soils.
• Observe and test subgrade soils below slab areas to evaluate moisture content and penetration.
2. Masonry Block Walls and Retaining Walls
• Observe footing trenches when first excavated to verify competent soil bearing conditions.
• Re -observe footing trenches, if necessary, if trenches are found to contain significant slough,
saturated or compressible soils.
• Observe the subdrain systems installed behind the retaining walls.
• Observe and perform field density testing of retaining wall backfill.
3. Utility Trench Backfill
• Observe and perform field density testing of utility trench backfill.
4. Concrete Flatwork Construction
• Observe and test subgrade soils below spa and concrete flatwork areas to document field density,
moisture content, and moisture penetration.
5. Re-Grading/Additional Grading
• Observe and perform field density testing of fill placed to proposed grades and any fill to be placed
in temporary excavations, as well as above or beyond the grades shown on the accompanying
grading plan.
REPORT LIMITATIONS
A representative of Petra was present on -site during grading operations on an on -call, as -needed basis for
the purpose of providing the owner's representative with professional opinions and recommendations.
PETRASOLID AS A ROCK
GEOSCIENCES"`
NICHOLSON CONSTRUCTION
225 Jasmine Avenue / Corona Del Mar
December 5, 2022
J.N. 21-422
Page 21
These opinions and recommendations were developed based on field observations and selective testing of
the contractor's work. Our scope of services during this project did not include supervision or direction of
the contractor, his personnel or his subcontractors. Our observations and testing did not reveal any obvious
deviations from the recommendations provided in the referenced geotechnical report by our firm; however,
Petra does not in any way guarantee the contractor's work, nor do our services relieve the contractor (or any
sub -contractors) of their liability should any defects subsequently be discovered in their work product.
Based on our findings, the conclusions and recommendations presented herein and within the referenced
report by our firm were prepared in conformance with generally accepted professional engineering
practices. No warranty is expressed or implied.
As noted above, existing side yard property line block walls were protected in place. These walls were
designed and constructed by others; therefore, Petra assumes no responsibility for the long-term
performance of these walls.
This opportunity to be of service is sincerely appreciated. Please call if you have any questions pertaining
to this report.
Respectfully submitted,
PET E CIENCES, INC.
L
Don Obert
Associate Engineer
GE 2872
SNUDO/DR/ly
Darrel Roberts
Principal Geologist
CEG 1972
Attachments: Table A — Field Density Test Results
Table B — Laboratory Data Summary
Figures RW-1 through RW-3 — Retaining Wall Details
Figure 1 — Density Test Location Plan
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SOLID AS A ROCK
NICHOLSON CONSTRUCTION
225 Jasmine Avenue / Corona Del Mar
TABLE A
Field Density Test Results
December 5, 2022
J.N.21-422
Date of
Test
Test
No.
Location
Depth*
(ft.)
Moisture
(%)
Unit Wt.
(lbs./cu.ft.)
% Rel.
Com
Soil
T e
11/15/2022
1
Building Pad
6.0
12.7
111.2
93
A
11/15/2022
2
Building Pad
4.0
12.2
109.5
92
A
11/15/2022
3
Building Pad
2.0
11.6
110.4
92
A
11/15/2022
4
Building Pad
0.5
12.0
112.4
94
A
11/16/2022
5
Building Pad
2.5
12.9
111.6
93
A
11/16/2022
6
Building Pad
1.5
11.9
112.1
94
A
11/16/2022
7
Building Pad
0.5
12.3
111.3
93
A
11/16/2022
8
Building Pad
FP
11.1
112.6
94
A
* Depth below finish grade
FP — Finish Pad
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Recommended backcut*
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at least 2 inches of open -graded gravel.
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Vertical height (h) and slope angle
of backcut per soils report. Based
on geologic conditions, configuration
of backcut may require revisions
(i.e. reduced vertical height,
revised slope angle, etc.)
L PETRA I RETAINING WALL BACKFILL I FIGURE RW-1 I
AND SUBDRAIN DETAILS
IMPORTED SAND BACKFILL
Sloped or level ground surface
On -site native soil cap
(12"thick)
� Z� Non -expansive imported
sand, SE>30.
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1 cubic foot per foot min. of 3/4" - 1 1 /2"
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fabric.
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w ° .4 inch perforated pipe. Perforated pipe should
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' y - Schedule 40 or approved equivalent with the
perforations laid down. Pipe should be laid on
at least 2 inches of open -graded gravel.
2' mini
* At base of wall, the non -expansive
backfill materials should extend to a
min. distance of 2' or to a horizontal
distance equal to the heel width of
the footing, whichever is greater.
RETAINING WALL BACKFILL
PETRA I AND SUBDRAIN DETAILS FIGURE RW-2
IMPORTED GRAVEL OR CRUSHED ROCK BACKFILL
/
/
/ Sloped or level ground surface
On -site native soil cap
(.12" thick)
° Non -e expansive imported
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Waterproofing compound
4 inch perforated pipe. Perforated pipe should
consist of 4" diameter ABS SDR-35 or PVC
Schedule 40 or approved equivalent with the
;perforations laid down. If pea gravel used,
<;
pipe should be encased in 1 cubic foot per
foot min. of 3/4" - 1 1/2" open -graded gravel
wrapped in filter fabric (Mirafi 140N or equal)
2
Pipe should be laid on at least 2 inches of
min.*
gravel.
*At base of wall, the non -expansive
backfill materials should extend to a
min. distance of 2' or to a horizontal
distance equal to the heel width of
the footing, whichever is greater.
PETRA I RETAINING WALL BACKFILL I FIGURE RW-3 I
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