HomeMy WebLinkAboutX2019-3127 - Soils (2)X 2otci �I Z"I
ENGINEERS + GEOLOGISTS + ENVIRONMENTAL SCIENTISTS
March 4, 2022
J.N. 19-265
NICHOLSON CONSTRUCTION
1 Corporate Plaza, Suite 110
Newport Beach, California 92660
Attention: Ms. Nanci Glass
Subject: Final Soils Report, Geotechnical Observations and Testing, Foundation Excavations,
Slab Subgrades and Utility Trench Backfill, 304 Goldenrod Avenue, Corona Del Mar
Area, City of Newport Beach, California
References: 1) Geotechnical Investigation, Proposed Two -Unit Condominium Building, 304
Goldenrod Avenue, Corona Del Mar Area, City of Newport Beach, California; report by
Petra Geosciences, Inc., dated July 31, 2019 (J.N. 19-265).
2) Geotechnical Report of Rough Grading, Proposed Two -Unit Condominium Building,
304 Goldenrod Avenue, Corona Del Mar Area, City of Newport Beach, California; report
by Petra Geosciences, hie., dated August 27, 2020 (J.N. 19-265).
Dear Ms. Glass:
Petra Geosciences, Inc. (Petra) is submitting herewith a summary of our observations of foundation
excavations for the site structures, and our observations and test results pertaining to slab subgrade soils,
and placement and compaction of backfill within utility trenches located in landscape areas, and under slabs
within the subject site.
Representatives from our firm performed on -call field density testing and field observations at the request
of the project superintendent during post -grade operations.
SUMMARY
Foundation Excavation Observations
Excavations of footing trenches for the residence and site structures were observed and found to be
excavated into engineered fill per the foundation plans and the recommendations presented in our reference
reports.
Utilitv Trench Backfill
1. Backfill of interior and exterior trenches consisted of onsite soils placed above select sand bedding.
The sand bedding placed above utility lines was jetted and varied from approximately 6 inches to 2 feet
in depth. Backfill materials were moisture conditioned, as necessary, to achieve optimum or above
optimum moisture conditions prior to and/or during placement, and then compacted in 6- to 8-inch lifts
with a pneumatic tamper to a minimum relative compaction of 90 percent (based on ASTM D 1557).
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NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
March 4, 2022
J.N.19-265
Page 2
2. Exterior trench backfill under the observation and testing of Petra consisted of sewer, water, area
drain, and a common (joint) trench containing electric, gas, telephone and data lines. The
approximate maximum depth of soil backfill placed over bedding sand for the various trenches was
approximately 3 feet in the sewer trench excavation.
3. Utility trench backfills, where probed and/or tested, are considered to have been placed in
accordance with the recommendations presented in the referenced reports.
Slab Subgrades
Due to the amount of time that had elapsed since the completion of rough grading, and due to disturbance
during construction activities, the surficial subgrade soils of the slabs were moisture conditioned to achieve
optimum or above optimum moisture content and then compacted in -place to a minimum relative
compaction of 90 percent of the applicable laboratory maximum dry density in general accordance with
ASTM Test Method D 1557. These subgrade soils were tested prior to concrete placement and are
considered acceptable from a geotechnical point of view. The subgrade soils were also presaturated as per
our recommendations.
Field and Laboratory Testing
1. Field density tests results for the trench backfills and slab subgrades are summarized in Table I, and
approximate test locations are shown on the accompanying Density Test Location Map (Figure 1). Field
density tests were taken with a Nuclear Gauge (ASTM D 6938).
2. Field density tests were taken at vertical intervals of 1 to 2 feet.
3. The laboratory maximum dry density and optimum moisture values for the most prominent onsite soils
(Soil Type A) were determined according to Test Method ASTM D 1557 and are listed in Table II.
Footing trench excavations for the residence and site structures were observed to have been founded into
engineered fill. In addition, where observed and tested, utility trench backfill and slab subgrade soils as
discussed in this report were found to be in general compliance with our recommendations and the grading
codes of the City of Newport Beach, California. The completed work within this firm's purview to the
extent observed, as discussed herein, has been reviewed and is considered adequate from a geotechnical
perspective.
REPORT LIMITATIONS
Representatives of Petra were present on -site on an on -call basis during post -grading operations for the
purpose of providing the owner's representative with professional opinions and recommendations. These
PETRA SOLID AS A ROCK
GEOSCIENCES"°
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
March 4, 2022
J.N. 19-265
Page 3
opinions and recommendations were developed based on field observation 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.
As documented in this report, our observations and testing did not reveal any obvious deviations from the
recommendations provided in the referenced geotechnical reports; however, Petra does not in any way
guarantee the contractor's work, nor do our services relieve the contractor (or any subcontractors) of their
liability should any defects subsequently be discovered in their work product.
Based on our findings, this report was prepared in conformance with generally accepted professional
engineering practices, and no warranty is implied nor made.
This report is subject to review by the controlling authorities for the project. Please call if you have any
questions pertaining to this report.
Respectfully submitted,
INC.
Don Obert NO, MDarrel Roberts
Associate Engineer z Principal Geologist
RGE 2872 % ; o CEG 1972
SM/DO/DR/ly
Attachments: Table I — Field Density Test Summary
Table II — Laboratory Optimum Moisture and Maximum Dry Density Tes
Figure 1 — Density Test Location Map
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PETRA
SOLO ASA ROCK
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
TABLE
FIELD DENSITY TEST SUMMARY
March 4, 2022
J.N.19-265
Date of
Test
Test No.
Location
Depth*
ft.
Moist:.
%
Unit Wt:
bs./co.ft.
%° Ref.
Comp.
Soil
T e
11/02/2020
1-SG
Building Pad
0.0
11.7
111.8
93
A
11/22/2020
1-IT
Building Pad
0.5
11.2
111.3
93
A
10/18/2021
1-S
Exterior
1.0
10.8
110.6
92
A
10/18/2021
1-W
Exterior
0.5
11.4
110.8
92
A
10/18/2021
1-1
Exterior
0.5
10.2
111.7
93
A
10/18/2021
I -AD
Side Yard
0.0
11.9
109.7
91
A
10/18/2021
2-SG
Drive Approach
0.0
11.6
110.5
92
A
10/18/2021
3-SG
Entry
0.0
11.8
110.9
92
A
SG - SUBGRADE
IT - INTERIOR TRENCH
S - SEWER
W - WATER
J - JOINT (ELECTRIC, TELEPHONE, TV, GAS)
AD - AREA DRAIN
* . DEPTH BELOW FINISH GRADE
It
PETNCRA SOLID ASA ROCK
NICHOLSON CONSTRUCTION March 4, 2022
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
TABLE I1
LABORATORY OPTIMUM MOISTURE AND MAXIMUM DRY DENSITY TEST DATA
Soil Type
Optimum Moisture
Maximum Dry Density
c
A —Brown Silty Sand (SM)
9.0
120.0
PETRA SOLID ASA ROCK
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ENGINEERS + GEOLOGISTS + ENVIRONMENTAL SCIENTISTS
August 27, 2020
J.N.19-265
NICHOLSON CONSTRUCTION
1 Corporate Plaza, Suite 110
Newport Beach, California 92660
Attention: Ms. Nanci Glass
Subject: Geotechnical Report of Rough Grading, Proposed Two -Unit Condominium Building,
304 Goldenrod Avenue, Corona Del Mar Area, City of Newport Beach, California
Reference: Geotechnical Investigation, Proposed Two -Unit Condominium Building, 304 Goldenrod
Avenue, Corona Del Mar Area, City of Newport Beach, California; report by Petra
Geosciences, Inc., dated July 31, 2019 (J.N. 19-265)
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 residential building and other site improvements, are included herein.
The purpose of the grading was to develop an engineered fill pad for the construction of a two unit
condominium building and associated hardscape features. Grading began on August 6, 2020 and was
completed on August 11, 2020.
SUMMARY OF OBSERVATIONS AND TESTING
Site Clearine
Structural materials associated with the previous residential structures were removed from the site. This
included previous structural features, such as concrete walkways, patios and block walls. Clearing
operations also included the removal of landscape vegetation. Trees and large shrubs, when removed, were
grubbed out to include their stumps and major root systems.
Ground Preparation
Existing fill materials and terrace deposits to depths of approximately 4 feet were found to have low in -
place densities and were considered subject to compression under the anticipated footing loads. Therefore,
in order to provide support of the proposed residential structure and exterior hardscape features, existing
ground surfaces in shallow cut areas and in areas to receive fill were overexcavated to a depth of at least 4
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NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 2
feet and the excavated materials then replaced as engineered fill. 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 to approximately property line to property line; however, consideration was given to the protection
of adjacent property line structures.
Fill Placement and Testing
1. The fill materials placed within the building area consisted of onsite 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 within the building pad is approximately 4 feet.
3. Field density tests results are summarized in Table A, and approximate test locations are shown on the
accompanying Figure 1. Field density tests were taken with a Nuclear Gauge in accordance with ASTM
D 6938.
4. Field density tests were taken at vertical intervals of 1 to 2 feet.
5. The maximum dry density and optimum moisture values for the onsite soils were determined
according to Test Method ASTM D 1557 and are listed in Table B.
6. Visual and tactile classification of earth materials in the field was the basis for determining -if the
laboratory maximum density value presented in Table B was applicable for each density test.
7. Fill placement within the subject lot was performed in general compliance with the recommendations
of our referenced report and the Grading Code of the City of Newport Beach.
Laboratory Testing
Several laboratory tests were previously performed on onsite soil materials obtained near finish pad grade
in order to evaluate their engineering characteristics and chemical activity (Reference). These test results
are provided in Table B at the end of this report.
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
PETRASOLID AS A ROCK
GEOSCIENCES'
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 3
by, Petra and are found to be in general compliance with our recommendations and of the Grading Code of
the City of Newport Beach. The completed work has been reviewed and is considered adequate for the
construction now planned.
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.
1. Area drains should be extended into all planters and landscape areas that are located within 10 feet
of building foundations and masonry block walls to mitigate excessive infiltration of water into the
foundation soils. Per the 2016 CBC, the ground surfaces within all landscape areas located within
10 feet of building foundations should be sloped at a minimum gradient of 5 percent away from the
walls and foundations and to the area drains. Landscape areas located more than 10 feet from
building foundations may be sloped at a minimum gradient of 2 percent.
2. Per the 2016 CBC, concrete flatwork surfaces located within 10 feet of building foundations should
be inclined at a minimum gradient of 2 percent away from building foundations. Concrete flatwork
surfaces located more than 10 feet from building foundations may be sloped at a minimum gradient
of 1 percent.
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.
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,
10PETRA SOLID ASAROCK
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 4
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 BackIIII
All utility trench backfill should be compacted to a minimum relative compaction of 90 percent of the
applicable laboratory maximum dry density in accordance with ASTM Test Method D-1557. Onsite soils
cannot be densified 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 backfilled 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.
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
PETRASOLID ASA ROCK
GEOSCIENCE15-
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
August 27, 2020
J.N. 19-265
Page 5
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 Recommendations
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 the site 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 the computer
application that is available at the Structural Engineers Association of California (SEAOC) and California's
Office of Statewide Health Planning and Development (OSHPD) Seismic Design Maps web site -
https://seismicmaps.org/ which was used to calculate the ground motion parameters.
To run the above computer applications, site latitude, longitude, risk category and knowledge of "Site
Class" are required. The site class definition depends on the average shear wave velocity, Vs3o, within the
upper 30 meters (approximately 100 feet) of site soils. A shear wave velocity of 600 to 1,200 feet per second
for the upper 30 meters was used for the site based on engineering experience and judgment.
The following table, Table 1, provides parameters required to construct the site -specific acceleration
response spectrum based 2016 CBC guidelines.
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NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
TABLE I
Seismic Design Parameters
August 27, 2020
J.N. 19-265
Page 6
Ground Motion Parameters
Specific Reference
Parameter
Unit
Value
Site Latitude (North)
33.5976
°
Site Longitude (West)
-
-117.8757
°
Site Class Definition'''
Section 1613.3.2
D
-
Assumed Risk Category t"
Table 1604.5
I/11/111
-
S,- Mapped Spectral Response Acceleration 'r.21
Figurel613.3.1(I)
1.702
g
Si - Mapped Spectral Response Acceleration
Figure 1613.3.1(2)
0.623
g
Fs- Site CoefficienttI.tl
Table 1613.3.3(1)
1.0
-
F, - Site Coefficient i1.'-1
Table 1613.3.3(2)
1.5
-
S,ms- Adjusted Maximum Considered Earthquake
Spectral Response Acceleration (1.21 .
Equation I6-37
1.702
g
Svu - Adjusted Maximum Considered Earthquake
Equation I (i-38
0.935
g
Spectral Response Acceleration
Sos - Design Spectral Response Acceleration t"t
Equation I6-39
1.134
g
Sm - Design Spectral Response Acceleration
Equation 16-40
0.623
e
T„=0 _ Sin/ Sus" p
Section 11.3
0A 10
s
T,= Sm" Sus f'
Section 11.3
0.549
s
Tr - Long Period Transition Period °p
Figure 22-12
8
s
Fran - Site Coefficient("
Figure 22-7
1.000
-
PGAsi - Peak Ground Acceleration at MCE O
Equation 1 1.8-1
0.701
g
Design PGA = ('.3 PGAm) - Slope Stability
Similar to Equations 16-39 & 16-40
0.467
g
Design PGA - (0.4 Sos) -- Short Retaining Walls
Equation 11.4-5
0.454
e
Can - Short Period Risk Coeftcient
Figure 22-17
0.898
-
CzI - Long Period Risk Coefficient f'
Figure 22-18
0.916
-
Seismic Desien Category n.47
Section 1613.3.5
D
-
References:
1n California Building Code (CBC), 2016, California Code of Regulations, Title 24, Part 2, Volume I and II.
('-) SEAOC & OSHPD Seismic Design Maps Web Application— haos'//seismimnans orJ
(4) American Society of Civil Engineers (ASCE/SEL, 2010, Minimum Design Load for Buildings and Other Structures, Standards 7-10.
Related References:
Federal Emergency Management Agency (FEMA), 2009, NEHERP (National Earthquake Hazards Reduction Program) Recommended
Seismic Provision for New Building and Other Structures FEMA P-750 .
Notes:
PGA Calculated at the NICE return period or2475 years (2 percent chance ofexceedanee in 50 )ears).
PGA Calculated at the Design Level of?. of MCE; appro.xintately equivalent to a return period 0f475 years (10 percent
chance ofexeeedauce in s0 vears).
PGA Calculated fur shw't, stubby retaining walls with an infinitesimal (zero) fundamental period.
The designation provided herein may be superseded by the structural engineer in accordance with Section 1613.3.5.1. if
applicable.
V PET OM SOLID ASA ROCK
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 7
FOUNDATION DESIGN GUIDELINES
Allowable Bearing Capacity, Estimated Settlement and Lateral Resistance
Allowable Soil Bearine 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 Y2 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 240 pounds per square foot per foot of depth, to a maximum value of 2,400
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
where footings are cast in direct contact with compacted fill or competent native soils. In cases where the
PETNeRA SOLID ASA RUCK
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
August 27, 2020
J.N. 19-265
Page 8
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 2016 California Building Code (2016 CBQ, 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 2016 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 similar soil 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
under 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 account for 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.
PETRA SOLID AS AROCK
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 9
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.
Footines
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 12 inches below the top of the adjacent finish floor
slabs.
2. In accordance with Table 1809.7 of 2016 CBC for light -frame construction, all continuous footings
should have minimum widths of 15 inches for three- and four-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 for three- and four-story
buildings. 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 tie 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 2016 CBC) by the structural engineer
responsible for foundation design based on his/her calculations, engineering experience andjudgment.
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 E 1745 for vapor
PETRASOLID ASA BOCK
GEOSCIENCES-
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
August 27, 2020
J.N. 19-265
Page 10
retarders (such as Husky Yellow Guard®, Stego® Wrap, or equivalent). All laps within the membrane
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 2016 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 ofexcess 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 if the 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 preventpuncturing
of the vapor retarder during concrete placement.
3. 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 3/4-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 2016 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
PETRA$0119 ASA ROCK
GEOSCIENCES-
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 11
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 Screenin¢
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 (Reference
No. 1). 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.
PETRASOaO AS A ROCK
GEOSCIENCES'"`
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
TABLE 2
Soil Corrosivity Screening Results
August 27, 2020
J.N. 19-265
Page 12
Test
Test Results
Classification
General Recommendations
Soluble Sulfates
0.0036 %
so'
Min. fc=2,500 psi
Cal 417
pH
Cal 643
6.5
Slightly Acid
Type I-P (MS) Modified or Type II Modified cement
Soluble Chloride
54 ppm
C lz
Residence: No max water/cement ratio, f c = 2,500 psi
Cal 422
C24
Pools/Decking: water/cement ratio 0.40, t c = 5,000 si
Resistivity
I
11,000
Mildly
Protective wrapping/coating of buried pipes; corrosion
Cal
ohm -cm
Conosive3
resistant materials; or cathodic protection
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 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.
Allowable Bearing Values
An allowable soil bearing capacity of 1,500 pounds per square foot, including dead and live loads, may be
utilized for design of 24-inch square pad footing and 12-inch-wide continuous footings founded at a
minimum depth of 12 inches below the lowest adjacent final grade. Recommended allowable bearing values
include both dead and live loads, and may be increased by one-third for short duration wind and seismic
forces.
Lateral Resistance
A passive earth pressure of 240 pounds per square foot per foot of depth 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. However, when
calculating passive resistance, the resistance of the upper 6 inches of the soil cover in front of the wall
should be ignored in areas where the front of the wall will not be covered with concrete.
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 where footings are cast in direct contact
with compacted fill or competent native soils. In cases where the footing sides are formed, all backfill
RVP PETRA SOLID AS A RUCK
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
August 27, 2020
J.N. 19-265
Page 13
placed against the footings upon removal of forms should be compacted to at least 90 percent of the
applicable maximum dry density.
Reinforcement
All continuous footings should be reinforced with a minimum of two No. 4 bars, one top, and one bottom.
Pad footings should be a minimum 24 inches square and be reinforced at a minimum with No. 4 bars spaced
a maximum of 18 inches on centers, both ways, near the bottom of the footings.
Footing Embedment
The base of retaining -wall footings constructed on level ground may be founded at a depth of 12 inches or
more below the lowest adjacent final grade.
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-I). 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.
2. Imoorted 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.
PETFM SOaO AS A ROCK
NATIVE SOIL BACKFILL
Sloped or level ground surface
)mpacted on -site soil
imende'd backout*
ng compound
12-inch-wide column of 3/4" - 1 1/2"
open graded gravel wrapped in filter fabric.
""'Filter fabric (should consist of
140N or equivalent)
p6ft6rated pipe. Perforated pipe should
-consist of 4" diameter ABS SDR-35 or PVC
Schedule 40 or approved equivalent with the
,`,;perforations laid down. Pipe should be laid on
at least 2 inches of open -graded gravel.
Vertical height (h) and slope angle
of backout per soils report. Based
on geologic; conditions, configuration
of backcut may require revisions
(i.e. reduced vertical height,
revised slope angle, etc.)
100 PETRA RETAINING WALL BACKFILL FIGURE RW-1
AND SUBDRAIN DETAILS I
IMPORTED SAND BACKFILL
Sloped or level ground surface
`:'•. On -site native soil cap
.;?'•.. (12"thick)
.Non -expansive imported
compound
nstall subdraln system
I cubic foot per foot min. of 3/4" -1 1 /2"
)pen graded gravel wrapped in filter
abric.
:liter fabric (should consist of
vlirafi 140N or equivalent).
I inch perforated pipe. Perforated pipe should
:onsist of 4" diameter ABS SDR-35 or PVC
ichedule 40 or approved equivalent with the
ierforations laid down. Pipe should be laid on
it least 2 inches of open -graded 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.
I �` PETRA I RETAINING WALL BACKFILL I FIGURE RW-2 I
AND SUBDRAIN DETAILS
IMPORTED GRAVEL OR CRUSHED ROCK BACKFILL
/
/ Sloped or level ground surface
on -site native soil cap
(12" thick)
{pensive imported
or crushed rock
MINi3 q s� o; ��"tiy ° f ::^Instalifilterfabric(Mirafi 140N
H `bnap a e s� °d® �� •. equal)or of fies ito bto t migration
Is
r, ackflll
compound
Inch perforated pipe. Perforated pipe should
Q4 ffi o� ?consist of 4"diameter ABS SDR-35 or PVC
�1 : ,.,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
in filter fabric (Mirafi 140N or equal)
Pipe should b laid n e d o at least 2 inches of
`2 min.
ravel.
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.
0 PETRA
RETAINING WALL BACKFILL
FIGURE RW-3
AND SUBDRAIN DETAILS
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 14
Earthquake Loads Retaining Walls
Note 1 of Section 1803.5.12 of the 2016 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 1/4-inch to 1 %z-inch open -graded gravel. If 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
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.
Waterproofing
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.
PETRA SOLID ASA ROCK
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 15
Wall Backfrll
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 Mirafi
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.
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.
10
PETRA SOLID AS AAOCK
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 16
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.
EXTERIOR CONCRETE FLATWORK
General
Near -surface compacted 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. If sufficient time
will be allowed in the project schedule for verification sampling and testing prior to the concrete pour, the
test results generated may dictate that a somewhat less conservative design could be used.
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
Q�� PETRA SOLID ASA ROCK
GEOSCIENCES-
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
August 27, 2020
J.N. 19-265
Page 17
the use of passenger cars for access to private garages should also be at least 5 inches thick and provided
with construction j oints or expansion j oints 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 andlor 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.
Pre-Moistenine
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
PETRASOLID AS A DOCK
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
August 27, 2020
J.N. 19-265
Page 18
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.
FUTUREIMPROVEMENTS
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
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:
10 PETN A SOLID ASA ROCK
NICHOLSON CONSTRUCTION August 27, 2020
304 Goldenrod Avenue / Corona Del Mar J.N. 19-265
Page 19
1. Building Construction
• Observe all footing trenches when first excavated to verify competent soil bearing conditions.
• Re -observe all 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 all slab areas to verify adequate moisture content and
penetration.
2. Masonry Block Walls and Retaining Walls
• Observe all footing trenches when first excavated to verify competent soil bearing conditions.
• Re -observe all 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 concrete flatwork areas to document field densities, moisture
content, and moisture penetration.
5. Re-Grading/Additional Grading
• Observe and perform field density testing of 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.
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,
10
PETRA SOLID AS A HOCK
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
August 27, 2020
J.N. 19-265
Page 20
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.
This opportunity to be of service is sincerely appreciated. Please call if you have any questions pertaining
to this report.
Respectfully submitted,
f�T
INC.
Don Obert I, J n,t Darrel Roberts 5g\O GF
Associate Engineer i 1 Principal Geologist
RGE 2872 CEG 1972 O
a OAiQ�LR[]BFA
SM DOlDR kg NO. Iffm
0 CEFMFI®
_— Bi61NEMIN3
Attachments: Table A — Field Density Test Results Nj GEOIAGN
Table B — Laboratory Data Summary 9 t
Figures RW-1 through RW-3 — Retaining Wall Details �OF CAl-\F
Figure 1— Density Test Location Plan
W:@0142019\2 M00\19-265 Nicholson Conshuelion(3M Goldenrod Ave., Corona del Mar)\Rcport\19-265200 Rough Grade Re,uMdocx
�°6°
•
NICHOLSON CONSTRUCTION
304 Goldenrod Avenue / Corona Del Mar
TABLE A
Field Density Test Results
August 27, 2020
J.N. 19-265
Date of
Test
Test
No.
Location
*Depth
ft.
Moisture
%
Unit Wt.
lbs./cu.ft.
% Rel.
Comp.
Soil
Type
8/6/20
1
Building Pad
2.0
11.3
111.7
93
A
8/7/20
2
Building Pad
1.0
12.1
112.9
94
A
8/7/20
3
Building Pad
3.0
11.8
111.4
93
A
8/7/20
4
Building Pad
1.0
12.7
111.9
93
A
8/10/20
5
Building Pad
2.0
12.2
110.6
92
A
8/10/20
6
Building Pad
0.0
11.7
111.2
93
A
8/11/20
7
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A
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FP — Finish Pad
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