HomeMy WebLinkAboutAppendix F - Geotechnical Investigation
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June 22, 2021
J.N. 21-177
NEWBRIDGE HOMES
500 Newport Center Drive, Suite 570
Newport Beach, California 92660
Attention: Mr. J. Rob Meserve
Subject: Feasibility/Due Diligence-Level Geotechnical Assessment, Live Oak Project,
Undeveloped Land Southeast of Live Oak Drive and Village Drive, Assessor’s Parcel
Number (APN) 0237-411-14, City of Fontana, San Bernardino County, California
References: See Attached List
Dear Mr. Meserve:
In accordance with your request, Petra Geosciences, Inc. (Petra) is providing this geotechnical due-
diligence review of the subject tract for undeveloped property in the city of Fontana, San Bernardino
County, California (Figure 1). This report presents our findings and professional opinions with respect to
the geotechnical feasibility of the proposed development, geotechnical constraints that should be taken into
consideration during design and development of the site, and potential mitigation measures to bring the site
to compliance from a geotechnical engineering viewpoint.
It must be emphasized that this report is intended as a feasibility-level geotechnical assessment only
and is based solely on a review of the referenced geotechnical reports, background geologic
literature and our limited subsurface exploration and soil test data. As such, the contents of this
report are not suitable for submittal to regulatory agencies, nor should the findings or conclusions
provided herein be relied upon for earthwork, quantity calculation or procedure, or structural
engineering design. It should be further noted that this geotechnical evaluation does not address
soil contamination or other environmental issues potentially affecting the property which was
provided under separate cover.
SITE GENERAL OVERVIEW
The irregular-shaped undeveloped property is comprised of approximately 27 acres of land in the city of
Fontana, identified as San Bernardino County Assessor’s Parcel Number (APN) 0237-411-14
(San Bernardino County, 2021). The site is bounded to the north by Village Drive, to the east by an
abandoned rock quarry and granitic hillside (Jurupa Mountains), to the west by an existing park (Southridge
Park), and to the south by existing residential tracts. The proposed residential development is a part of the
Southridge Village Specific Plan.
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A conceptual development plan provided by the client, dated March 28, 2021, indicated 96 single-family
residential lots are proposed, with interior streets, underground utilities, and other associated improvements.
Topographically, the subject property slopes from south to north with a component sloping east to west.
Elevations range from approximately 995 feet above mean sea level (msl) to 925 feet above msl.
Multiple dirt roads are located within the subject site. Native vegetation cover is well established within the
subject property. From a surface perspective, multiple areas of irregular slopes, depressions, dumped soils,
and boulders suggest portions of the subject site may have been previously graded. For example, the slope
along the southwest edge of the subject site, fronting Southridge Park, is a fill slope with large rock
fragments exposed in the slope face. Considering the proximity of the subject property to the abandoned
rock quarry, and the irregular cut face to the hillside along the east edge of the subject site, suggests
overburden materials may have been placed onsite; however, mining records for the quarry could not be
readily found.
DUE DILIGENCE ASSESSMENT
Literature Review
Petra has reviewed a geotechnical investigation report by GeoBoden, Inc. (GeoBoden, 2019) on the subject
property. In addition, we reviewed available online aerial imagery, historical aerials photographs by EDR,
and background geologic maps and literature in the vicinity of the project site (see References).
Site Reconnaissance and Subsurface Assessment
A representative of Petra conducted an initial site reconnaissance on May 7, 2021 to mark-out for DigAlert
clearance. Petra returned to the site on May 17, 2021 to conduct limited field exploration with a truck-
mounted hollow-stem drill rig to evaluate the natural subsurface soils. The initial field work included the
drilling and sampling of eight borings (B-1 through B-8) to depths of 2.5 to 45 feet below the ground surface
(bgs). All borings were advanced to practical refusal, including five borings achieving practical refusal at
depths of 2.5 to 5 feet bgs on over-size rock fragments. Relatively undisturbed ring and disturbed,
representative bulk samples of soil were collected from the borings for laboratory testing. Following
sampling, the borings were backfilled with spoils. Locations of the borings are depicted on Figure 2.
Subsequently, Petra returned to the subject site to excavate and log nine track hoe test pits (T-1 through
T-9) on May 25, 2021. A Caterpillar 325 excavator was used to excavate the test pits to depths between 6
and 14 feet bgs. Test pits were backfilled with spoils. Locations of the borings are depicted on Figure 2.
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Laboratory Testing
The laboratory program consisted of testing select undisturbed ring specimens and/or bulk samples of onsite
soil materials collected from the borings for in-situ dry density and moisture content, expansion index, and
general corrosion potential (sulfate and chloride content, pH, and resistivity). Results are provided in
Appendix B.
FINDINGS
Proposed Development
Based on a conceptual development plan provided by the client (dated March 28, 2021), the Live Oak
Project in Fontana, California would consist of 96 building pads for single-family residences along with
associated low-height slopes and with various roadway improvements. Based upon information provided
by the client, a trailhead park is proposed at the southeast corner of Live Oak Avenue and Village Drive.
A recent topographic map provided by the client (undated) depicts topography in proximity to the subject
property. Generally, the eastern subject property boundary does not encroach into the abandoned quarry
slopes, which ascend at a steep gradient above the subject property. The fractured and disturbed quarry
slopes will require a rockfall hazard assessment prior to development of the site.
Site Reconnaissance
During our limited field exploration, a representative of Petra conducted a site reconnaissance to observe the
current surface conditions at subject site. Dumped stockpiles of earth materials are common along the east
and central portions of the subject site. The larger stockpiles throughout the property, including boulder
piles, are likely remnants of the abandoned quarry operations. Dirt roads and trails exist throughout the
subject site, including access to Southridge Park to the west and Southridge Village Open Space Preserve
to the east. An abandoned motorcycle track was observed in the northwesterly portion of the property. A
small, square concrete slab was observed on a knoll in the west central portion of the property. Natural
vegetation is well established within the subject property. Rockfall debris (talus) exists along the easterly
edge of the subject property. Overall, minimal trash/debris was observed within the subject property.
Offsite Quarry Slope
Abutting the eastern property boundary are disturbed bedrock slopes of the abandoned Declez/Declezville
Quarry (Anicic Jr., 2005). Explosives were used to fracture and loosen the stone from the hillside, and the
large irregular blocks were loaded into railroad cars at the quarry and taken offsite. Drilling was done with
steam drills. Large steam-powered derricks were used to handle the stone.
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Remnants of the quarry excavation consist of large, angular granitic outcrops that exhibit varying degrees
of fracturing. Open fractures are visible indicating disturbance by blasting. One of the dominant fracture
patterns is orientated out-of-slope. Weed-covered talus slopes are common between bedrock outcrops.
Although thick vegetation is common along the toe-of-slope, there does not appear to be a large
accumulation of boulders near the base. Rockfall hazards associated with the offsite bedrock slopes should
be assessed by an experienced rockfall hazard engineer.
Based upon information provided from historical aerial photographs from 1938 to 2016, the subject
property was used during quarry operations, including a railroad spur along the northwest edge of the
subject property. Small rail spurs were also observed within the site. Overburden or spoils from the quarry
were placed as fill within the subject property, typically identified by irregular slopes, or mounds.
Literature Review
As previously noted, Petra has reviewed the ‘Geotechnical Investigation Report” on the subject property
by GeoBoden, Inc., dated August 2, 2019 (see References). Noteworthy findings and conclusions gleaned
from the report are summarized below as paraphrased excerpts.
Purpose
The purposes of this investigation were to determine the geotechnical properties of subsurface soil
conditions, to evaluate their in-place characteristics, evaluate site seismicity, and to provide geotechnical
recommendations with respect to site grading and for design and construction of buildings foundations and
other site improvements.
Field Exploration
The current field exploration program was initiated under the technical supervision of the undersigned
geotechnical engineer. A total of 10 exploratory borings were drilled using a truck-mounted drilling rig
equipped with 8-inch diameter hollow stem augers. The borings were advanced to depths ranging from 16.5
to 21.5 feet (below ground surface). Logs of subsurface conditions encountered in the borings were prepared
in the field by a representative of our firm. Soil samples consisting of relatively undisturbed brass ring
samples and Standard Penetration Tests (SPT) samples were collected at approximately 5-foot depth
intervals and were returned to the laboratory for testing.
Selected samples collected during drilling activities were tested in the laboratory to assist in evaluating
controlling engineering properties of subsurface materials at the site. Physical tests performed included
moisture and density determination, consolidation (Collapse), No. 200 sieve wash, direct shear, expansion
index, and corrosion.
Site and Subsurface Conditions
The site is underlain by native soils consisting of sandy silt, sand with silt and silty sand with gravel.
Construction debris were limited to the near surface. No rubble fill was encountered during our exploration.
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Based on blow counts recorded during sampling, the native soils encountered within borings were found to
be predominately medium dense to very dense.
Groundwater was not encountered within our exploratory borings to the maximum depth of exploration
(21.5 feet below ground surface). Groundwater is expected to be present at depths as shallow as 50 feet or
greater below the ground surface. A log of their borings are provided in Appendix B.
Laboratory Test Results
Consolidation test was performed on sample of the existing native overburden soils recovered from the
boring. Results of the consolidation test indicate that the overburden material will have low compressibility
under the anticipated loads.
Results of consolidation test on a sample of native soil indicate that the native soil will have low collapse
potential. The potential for hydro-collapse, in general, decreases with depth for the site materials. Removal
and recompaction of the surficial soils are expected to reduce the anticipated amount of total differential
settlement within the site.
Laboratory testing of representative samples of onsite soils indicate that these materials exhibit VERY
LOW to LOW expansion potentials. An Expansion Index (EI) of 15 was reported.
Corrosion testing was performed on a selected soil sample in the near surface to determine the corrosivity
of the site soil to steel and concrete. The soil sample was tested for soluble sulfate (Caltrans 417), soluble
chloride (Caltrans 422), and pH and minimum resistivity (Caltrans 643). A soluble sulfate concentration of
0.0143 percent by weight was reported. Chloride content was listed as 43 parts per million (ppm). A pH
of 7.2 and a resistivity of 1,876-ohm cm was reported. Based upon these results the following
recommendations are provided:
• Below grade ferrous metals should be given a high-quality protective coating, such as an 18-mil
plastic tape, extruded polyethylene, coal tar enamel, or Portland cement mortar.
• Below grade ferrous metals should be electrically insulated (isolated) from above grade ferrous
metals and other dissimilar metals, by means of dielectric fittings in utilities and exposed metal
structures breaking grade.
• Steel and wire reinforcement within concrete in contact with the site soils should have at least two
inches of concrete cover.
• If ferrous building materials are expected to be placed in contact with site soils, it may be desirable
to consult a corrosion specialist regarding chosen construction materials, and/or protection design
for the proposed facility.
Corrosion test results also indicate that the surficial soils at the site have negligible sulfate attack potential
on concrete, according to the Uniform Building Code (UBC) Table 19-A-4. No special sulfate-resistant
cement will be necessary for concrete placed in contact with the on-site soils.
Grading Recommendations
In general, all fill soils within the proposed buildings footprints should be over-excavated and replaced with
engineered fill. As a minimum, removals should extend to competent native soils. At least 2 feet of
compacted fill should be provided underneath all spread footings and floor slabs. The compacted fill should
extend laterally a minimum of 5 feet beyond the foundation footprints, where possible. All existing low-
density, near-surface soils will require removal to competent material from areas to receive newly
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compacted fill. The basis for establishing a competent exposed surface on which to place fill should consist
of competent materials exhibiting an in-place relative compaction of at least 85 percent. Prior to placing
structural fill, exposed bottom surfaces in each removal area approved for fill should first be scarified to a
depth of at least 6 inches, water or air dried as necessary to achieve near optimum moisture conditions, and
then recompacted in place to a minimum relative compaction of 90 percent.
Based on the observations made in our borings and the results of pertinent laboratory tests, anticipated
depths of removal of unsuitable soils will vary from 3 to 4 feet. However, actual removal depths will have
to be determined during grading based on in-grading observations and testing performed by a representative
of geotechnical consultants.
Field Assessment
Boring Data
Nine exploratory borings were drilled within the subject property (designated B-1 through B-8) to a
maximum depth of 45 feet bgs. Independent of the surface stockpiles and dumped fill materials on site,
near-surface fills were encountered in all of our recent borings. Based on our observations and sampling
conducted from the exploratory hollow-stem auger borings, undocumented fill materials underlain by
residual surficial soils exist within the subject property. Based upon historical aerial photographic
assessment, it is likely that these fills represent a disposal area during the former quarry operations. In
addition to low sample blow counts, a distinct characteristic of the existing fill materials is sub-angular to
angular rock fragments in contrast with the subrounded rock fragments of the underlying residual soils or
alluvium. In four borings, where drilling was able to penetrate the undocumented fill materials, depths
ranged from 2 to 15 feet bgs.
Where encountered underlying the undocumented fill materials, residual soils and alluvium were
encountered at thicknesses of approximately 5 to 20 feet. Where encountered in four of the recent borings,
weathered granitic bedrock was found at depths of 2 to 28 feet bgs. The locations of our borings are shown
on Figure 2. Logs of the borings are provided in Appendix A.
Test Pits
To further asses the characteristics of the undocumented fill materials on-site, nine exploratory test pits
(designated T-1 through T-9) were excavated within the subject property to a maximum depth of 14.5 feet
bgs. Where encountered, fill materials consisted of a dry, loose, sandy matrix with angular gravels, cobbles,
and boulders up to 7 feet in one dimension. In some cases, buried debris was encountered such as plastic
sandbags, metal cables and metal pipe (T-3), construction debris and roots (T-8), and PVC piping and string
(T-9). Heavy sidewall caving commonly hindered continuing excavation. Granitic bedrock was
encountered at a depth of 10 feet in T-1; 13 feet in T-3; 3 feet in T-5; and 7 feet in T-8. The locations of
our test pits are shown on Figure 2. Logs of the test pits are provided in Appendix A.
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Laboratory Testing
Limited laboratory testing of various representative samples collected from the drill rig locations for
classification and engineering analysis purposes. Testing included in-situ density and moisture content,
maximum density and optimum moisture content, expansion potential, and soil corrosivity. Results of in
situ density and moisture content are provided on the boring logs, Appendix A. Results of limited in-house
testing of representative samples indicate that the expansion index (EI) of the soils are in the Very Low EI
range (0-20).
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 that are generally associated with soil corrosivity, among other indicators, include water-soluble
sulfate (a measure of soil corrosivity on concrete), water-soluble chloride (a measure of soil corrosivity on
metals embedded in concrete), pH (a measure of soil acidity), and minimum electrical resistivity (a measure
of corrosivity on metals embedded in soils). Test methodology and results are presented in Table 1.
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, and/or determination of other indicators, 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, etc.) to be involved. We also
recommend considering 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 chloride 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 1, below, presents test
results with an interpretation of current code approach and guidelines that are commonly used in building
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construction 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 of corrosive soils 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.
TABLE 1
Soil Corrosivity Screening Results
Sample ID
Test
(Test Method
Designation)
Test Results Classification General Recommendations
B-1` @ 0-5’
B-5 @ 3-6’
Soluble Sulfate
(Cal 417)
SO42- < 0.10 %
by weight
S0(1) - Not
Applicable
Type II cement; minimum fc’(2) = 2,500
psi; no water/cement ratio restrictions.
B-5 @ 3-6’ pH
(Cal 643) 8.5 – 9.0 Strongly
Alkaline(3) No special recommendations
B-1` @ 0-5’ pH
(Cal 643) > 9.0 Very Strongly
Alkaline(3) No special recommendations
B-1` @ 0-5’
B-5 @ 3-6’
Soluble Chloride
(Cal 422) < 500 ppm C1(1) -
Moderate
Residence: No special
recommendations; fc’(2) should not be
less than 2,500 psi.
B-5 @ 3-6’ Resistivity
(Cal 643)
10,000 – 20,000
ohm-cm
Mildly
Corrosive(5)
Protective wrapping/coating of buried
pipes; corrosion resistant materials
B-1` @ 0-5’ Resistivity
(Cal 643)
5,000 – 10,000
ohm-cm
Moderately
Corrosive(5)
Protective wrapping/coating of buried
pipes; corrosion resistant materials
Notes:
1. ACI 318-14, Section 19.3
2. fc’, 28-day unconfined compressive strength of concrete
3. The United States Department of Agriculture Natural Resources Conservation Service, formerly Soil Conservation Service
4. Exposure classification C2 applies specifically to swimming pools and appurtenant concrete elements
5. Pierre R. Roberge, “Handbook of Corrosion Engineering”
Groundwater
Borings drilled by GeoBoden, Inc. (GeoBoden, 2019) reported that no groundwater was encountered to a
maximum depth of 21 feet below the ground surface. Historical data from a State well northwest of the
subject property, near the corner of Cherry Avenue and Jurupa Avenue, reported groundwater at depth of
approximately 225 to 250 feet below the ground surface between 2000 and 2020 (MWD, 2021).
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Groundwater was not encountered in our recent borings to a maximum depth of 45 feet below grade.
General area groundwater is not anticipated to affect the proposed remedial grading operations; however,
contingencies should be planned for cases where localized areas of saturated soils requiring stabilization
are encountered perched along the upper bedrock contact.
Undocumented Fill
Much of the subject property is either mantled by stockpiled fill or underlain by undocumented fill. Fills
were more than likely placed during historic quarry operations within to the subject property to create a
level working area for equipment and rail spurs. Where encountered and the depth of fill observed in borings
onsite, the thickness of this material was found to be: 2 feet in B-5; 5 feet in B-1; 25 feet in B-2; and 28 feet
in B-8. The absence of residual soil and/or young alluvial soils found between the fill and the underlying
bedrock suggests that portion of the site may have been lowered to create a level working surface. Borings
within the remainder of the site encountered practical refusal on coarse gravel, cobbles, or boulders at depths
of 2 to 3.5 feet bgs, thereby preventing the determination of total fill thickness.
Where encountered in test pits, undocumented fill materials consisted of dry, loose silty sand with angular
rock fragments up to 7 feet in one dimension. Fill material thicknesses were found to be: 7 feet in T-9; and
11 feet in T-3. In addition, depth to bedrock was found to be: 7 feet in T-1 and T-8; 13 feet in T-3; and 3
feet in T-5. In the remainder of the test pits, caving of the excavation sidewalls hindered continued depth,
indicating undocumented fill soils exceeded 9 to 14 feet in thickness. Visual observation of the fill slopes
along the western site boundary indicates undocumented fill thicknesses equal to at least the height of the
slope.
Over-Size Rock
Large angular boulders are commonly scattered throughout the subject property, typically exceeding 4 feet
in one dimension. Boulders up to 7 feet in one dimension were encountered in test pits excavated within
the subject site. Boulders exceeding 3 feet in one dimension will require special handling, consisting of
breaking, isolated burial in fills, or offsite disposal.
Compressible Soils
In the two borings drilled to a depth of 40 feet bgs (B-8) and 45 feet bgs (B-2), loose and dry residual soils
and/or young alluvial soils were encountered at depths of 15 to 25 feet bgs. These soils, underlying
undocumented fills within the subject property, are deemed to be compressible. In addition, localized soil
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piles have been dumped on the subject property. Buried compressible soils will require removal and
recompaction. Soil piles will require reprocessing prior to placement s fill as needed.
Faulting and Nearby Seismic Sources
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. No evidence of faulting was reported on the subject property by the former
consultant GeoBoden (2019) or was observed within the subject site during our recent field work.
According to the USGS Unified Hazard Tool website and/or 2010 CGS Fault Activity Map of California,
the San Bernardino segment of the San Jacinto Fault zone, located approximately 15.9 kilometers east 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. This fault system is
capable of producing a magnitude 8.06 or larger event.
Strong Ground Motions
The site is in a seismically active area of Southern California and will likely be subjected to very strong
seismically related ground shaking during the anticipated life span of the project. Structures within the site
should therefore be designed and constructed to resist the effects of strong ground motion in accordance
with the 2019 California Building Code (2019 CBC).
Secondary Seismic Effects
The site exhibits gentle-sloping land that is not typically prone to landsliding; however, the offsite quarry
slopes and the Jurupa Mountains as a whole, are mapped by San Bernardino County as moderately to highly
susceptible to landslides (San Bernardino County, 2007).
Secondary effects of seismic activity normally considered as possible hazards to a site include several types
of ground failure. Various general types of ground failures, which might occur because of severe ground
shaking at the site include ground subsidence, ground lurching and lateral spreading. The probability of
occurrence of each type of ground failure depends on the severity of the earthquake, distance from faults,
topography, subsoil, and groundwater conditions, in addition to other factors. Based on existing site
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conditions, lateral spreading is consisted unlikely; however, landsliding and ground lurching are considered
likely at the site. Removal and recompaction of undocumented fills and protection of the site from rockfall
and talus slope hazards would decrease impacts to the proposed subject development.
Seismically induced flooding that might be considered a potential hazard to a site normally includes
flooding due to tsunami or seiche (i.e., a wave-like oscillation of the surface of water in an enclosed basin)
that may be initiated by a strong earthquake or failure of a major reservoir or retention structure upstream
of the site. No major reservoirs are located up-gradient within the near vicinity of the site. The potential for
seiche is considered very low.
Seismically Induced Settlement
Assessment of liquefaction potential for a particular site requires knowledge of several regional as well as
site-specific parameters, including the estimated design earthquake magnitude, the distance to the assumed
causative fault and the associated probable peak horizontal ground acceleration at the site, subsurface
stratigraphy and soil characteristics and groundwater elevation. Parameters such as distance to causative
faults and estimated probable peak horizontal ground acceleration can readily be determined using
published references, or by utilizing a commercially available computer program specifically designed to
perform a probabilistic analysis. Stratigraphy and soil characteristics can only be accurately determined by
means of a site-specific subsurface evaluation combined with appropriate laboratory analysis of
representative samples of onsite soils.
Liquefaction occurs when dynamic loading of a saturated sand or silt causes pore-water pressures to
increase to levels where grain-to-grain contact is lost, and material temporarily behaves as a viscous fluid.
Liquefaction can cause settlement of the ground surface, settlement and tilting of engineered structures,
flotation of buoyant buried structures and fissuring of the ground surface. A common manifestation of
liquefaction is the formation of sand boils – short-lived fountains of soil and water that emerge from fissures
or vents and leave freshly deposited conical mounds of sand or silt on the ground surface.
San Bernardino County does not identify the subject property within a zone of liquefaction potential (San
Bernardino County, 2007). Although deep groundwater may not contribute to liquefaction-induced
settlement, dry and unconsolidated undocumented fill materials encountered during our field exploration
suggests the potential for seismically induced dynamic settlement is anticipated to be high.
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CONCLUSIONS AND RECOMMENDATIONS
Based on our site reconnaissance, limited subsurface exploration/laboratory testing and literature review of
readily available data, development of the proposed project within this subject site is feasible from a
geotechnical standpoint, provided rockfall hazards associated with the offsite rock quarry can be mitigated,
and that the following geotechnical issues be considered by the Client during this due diligence period.
Primary Geotechnical Issues
Our professional opinion, from a geotechnical engineering viewpoint, regarding various aspects of site
condition and/or proposed development is presented herein. The following presents the salient points of our
due diligence assessment that we recommend be considered for future site development.
• Rockfall Hazard: The exposed quarry face is comprised of large, angular granitic bedrock outcrops
that are naturally and/or mechanically fractured. Open fractures are visible in some locations related
to near-vertical overhangs. One of the prominent fracture orientations is out-of-slope toward the
proposed development. Between the large angular outcrops are fan-shaped slopewash deposits that
are covered with dry vegetation. Slopewash deposits consist of variable mixtures of sand, gravel,
cobble, and boulders; however, high concentrations of boulders are not present along the toe-of-
slope. The blocky nature of exposed outcrops and existing loose boulders suggest that dislodged
rocks are not likely to bounce as compared to rounded boulders. Rockfall hazards are currently
being evaluated by an experienced professional.
• Undocumented Fill: Much of the subject property is either mantled by stockpiled fill or underlain
by undocumented fill placed during historic quarry operations within or adjacent to the subject
property. Where encountered in borings onsite, the thickness of this material was found as 5 feet
(B-1), 25 feet (B-2), and 28 feet bgs (B-8) within the northern portion of the subject property. The
fill thickness encountered in boring B-5 (2 feet), located in the southern portion of the site, suggests
thinning of the fill to the south. The absence of residual soil and/or young alluvial soils found
between the fill and the underlying bedrock suggests the southern portion of the site may have been
lowered to create a level working surface. Borings within the remainder of the site encountered
practical refusal on coarse gravel, cobbles, or boulders at depths of 2 to 3.5 feet bgs.
Where encountered in test pits, undocumented fill materials consisted of dry, loose silty sand with
angular rock fragments up to 7 feet in one dimension. Using the angular to subangular rock
fragment characteristic to differentiate fill from the underlying residual soil and young alluvial
materials, fill material thicknesses were found at 7 feet in T-9 and 11 feet in T-3. In addition, depth
to bedrock was found at 7 feet in T-1 and T-8; 13 feet in T-3; and 3 feet in T-5 suggesting localized
lowering of the former quarry work surface. In the remainder of the test pits, caving of the
excavation sidewalls hindered continued depth, indicating undocumented fill soils exceeded 9 to
14 feet in thickness. Visual observation of the fill slopes along the western site boundary indicates
undocumented fill thicknesses equal to at least the height of the slope.
NEWBRIDGE HOMES June 22, 2021
Live Oak Project / Fontana J.N. 21-177
Page 13
Based upon the dry and loose nature of the undocumented fill materials encountered onsite, these
materials are considered unsuitable to support settlement sensitive improvements in their present
condition and should be completely removed. Based upon the limited existing data, fill thicknesses
appear to be irregular but are anticipated to increase from east to west and to the north following
natural topography sloping away from the hillside. Additional subsurface exploration is
recommended to further characterize remedial earthwork limits.
• Over-Size Rock: Large boulders are commonly scattered throughout the subject property, typically
consisting of isolated clusters and large piles. Boulders up to 7 feet in one dimension were
encountered in test pits excavated within the subject site. Boulders exceeding 3 feet in one
dimension will require special handling, consisting of breaking, isolated burial in fills, or offsite
disposal. Over-size rock buried in engineering fills within the site shall be at least 10 feet below
finish pad grade and 15 feet from the face of finished slope grade. Additional recommendations
can be provided upon request.
• Settlement: Based upon the dry and loose nature of the undocumented fill materials encountered
onsite, as well as the likely presence of voids in buried rock clusters, these materials are susceptible
to piping and seismically induced settlement in their present condition and should be completely
removed and replaced as compacted (engineered) fill. Additional subsurface exploration is
recommended to further characterize remedial earthwork limits.
• Clearing and Grubbing: The building pads generally have a light to heavy amount of vegetation
growth and minimal scattered trash and debris. All vegetation, debris, trash etc. should be cleared
and hauled offsite. Voids created by removal of large bushes and trees shall be cleaned of loose
soil and the backfill compacted to at least 90 percent relative density per ASTM D 1557.
• Expansion Potential of Soils to Foundations: Limited testing by this office found soils within the
subject tract indicated a Very Low expansion potential. It is expected that graded lots will likely
exhibit Very Low expansion potential. Such expansion conditions typically are accommodated by
conventional slab-on-ground foundation systems. Additional laboratory testing would be required
at the completion of rough grading to confirm the as-built expansion conditions prior to finalizing
foundation recommendations.
• Corrosion Potential: Our limited corrosion testing indicates site soils have a negligible to moderate
exposure to soluble sulfates, moderate exposure to soluble chlorides and are extremely corrosive
to metallic elements. We recommend enlisting a corrosion engineer to provide corrosion protection
recommendations, in addition to sampling and testing of pad grade soils during future precise
grading.
• Building Foundation Design: Seismic and foundation design recommendations for the residential
buildings should be provided in accordance with the most recently approved California Building
Code (CBC), which is currently the 2019 CBC. Proposed structures should also be designed in
accordance with the most recently approved CBC.
NEWBRIDGE HOMES June 22, 2021
Live Oak Project / Fontana J.N. 21-177
Page 14
REPORT LIMITATIONS
This report is based on the existing conditions of the subject property and the geotechnical observations
made during our site reconnaissance, limited field exploration, limited laboratory testing and review the
previous consultant’s available reports and data. However, note that soil and groundwater/moisture
conditions can vary in characteristics between points of excavations, both laterally and vertically. The
conclusions and opinions contained in this report are based on the results of the described geotechnical
evaluations and represent our professional judgment.
This report has been prepared consistent with that level of care being provided by other professionals
providing similar services at the same locale and in the same time period. The contents of this report are
professional opinions and as such, are not to be considered a guaranty or warranty.
This report should be reviewed and updated after a period of one year or if the site ownership or project
concept changes from that described herein. This report has not been prepared for use by parties or projects
other than those named or described herein. This report may not contain sufficient information for other
parties or other purposes.
This opportunity to be of service is sincerely appreciated. If you have any additional questions or concerns,
please feel free contact this office.
Respectfully submitted,
PETRA GEOSCIENCES, INC.
6/22/21
Edward Lump Grayson R. Walker
Associate Geologist Principal Engineer
CEG 1924 GE 871
EL/GRW/lv
Attachments: References
Figure 1 – Site Location Map
Figure 2 – Exploration Location Map
Appendix A – Boring and Test Pit Logs
Appendix B – Boring Logs, GeoBoden, Inc., 2019
W:\2020-2025\2021\100\21-177 Newbridge Homes (Live Oak Project, Fontana)\Reports\21-177 100 Due Diligence Report.docx
NEW BRIDGE HOMES, LLC June 22, 2021
Live Oak Project / Fontana J.N. 21-177
Page 15
REFERENCES
American Concrete Institute, 2008, Building Code Requirements for Structural Concrete (ACI 318-08) and
Commentary.
American Society for Testing and Materials (ASTM) – Standard – Section Four – Construction, Volume 04.08 Soil
and Rock.
Anicic, John Charles, Jr., 2005, Images of America Series - Eight, Ailea, San Sevaine, Declez, Declezville, and South
Fontana, 1888 to Present, Arcadia Publishing.
Bryant, W.A., and Hart, E.W., 2007, Fault-Rupture Hazard Zones in California, Alquist-Priolo Earthquake Fault
Zoning Act with Index to Earthquake Fault Zones Maps, California Geological Survey, Special
Publication 42.
California Building Code (2019), California Code of Regulations, Title 24, Par 2, Volume 2 of 2, Based on the 2018
International Building Code, California Building Standards Commission.
California Department of Water Resources, 2004, California Groundwater - Bulletin 118.
, 2021, Water Data Library, accessed March, http://www.water.ca.gov/waterdatalibrary/groundwater/
County of San Bernardino, 2007, San Bernardino County Land Use Plan, General Plan, Geologic Hazards Overlay,
Sheet FH29 C, Fontana, accessed May 2021.
EDR, 2021, The EDR Aerial Photo Decade Package, Live Oak Ave. & Village Dr., Fontana, CA 92337, Inquiry
Number 6500241.1, dated May 20.
GeoBoden, Inc., 2019, Geotechnical Investigation Report, Proposed Residential Development, APN: 0237-411-14,
Fontana, California, Project No. GD-01-16, dated August 2.
Google Earth™ 2021, by Google Earth, Inc., http://www.google.com/earth/index.html, accessed March.
International Conference of Building Officials, 1998, “Maps of Known Active Fault Near-Source Zones in California
and Adjacent Portions of Nevada”, California Division of Mines and Geology.
Jennings, C.W. and Bryant, W.A., 2010, Fault Activity Map of California: California Geological Survey, Geologic
Data Map No. 6.
Morton, D.T., 2003, Preliminary Geologic Map of the Fontana 7.5’ Quadrangle, San Bernardino and Riverside
Counties, California, USGS Open-File Report 03-418.
Office of Statewide Health Planning and Development (OSHPD), 2021, Seismic Design Maps,
U.S. Seismic Design Maps (seismicmaps.org)
Petra Geotechnical, Inc., 2010, Feasibility-Level Geotechnical Review, Lots 1, 5-14, 20-47, 57-69, and 90-97 of Tract
30092, Piazza Serena Project, Northwest Corner of Monroe and Avenue 58, City of La Quinta, Riverside
County, California, for Capstone Advisors, J.N. 356-10, dated November 19.
Sladden Engineering (Sladden), 2001, Geotechnical Investigation, Tentative Tract 30092, Avenue 58 and Monroe
Street, La Quinta Area, Riverside County, California, for Barton Properties, Inc., Project No. 544-1029, 01-
02-070, dated February 9.
, 2004, Geotechnical Update, Residential Development, Avenue 58 and Monroe Street, La Quinta, California,
for Forecast Homes, Project No. 544-1029, 04-09-611, dated August 31.
NEW BRIDGE HOMES, LLC June 22, 2021
Live Oak Project / Fontana J.N. 21-177
Page 16
REFERENCES
Sneed, M., Brandt, J.T., and Solt, M., 2014, Land Subsidence, Groundwater Levels, and Geology in the Coachella
Valley, California, 1993-2010, USGS Scientific Investigation Report 2014-5075.
Sneed, M. and Brandt, J.T., 2020, Detection and Measurement of Land Subsidence and Uplift Using Global
Positioning System Surveys and Interferometric Synthetic Aperture Radar, Coachella Valley, California,
2010 – 2017, USGS Scientific Investigations Report 2020-5093.
Southern California Earthquake Center (SCEC), 1999, Recommended Procedures for Implementation of DMG
Special Publication 117, Guidelines for Analyzing and Mitigating Liquefaction Hazards in California:
organized through the Southern California Earthquake Center, University of Southern California.
Southern California Earthquake Data Center (SCEDC), 2014, http://www.data.scec.org/significant/index.html.
Standard Specifications for Public Works Construction (Greenbook), 2009, BNI Publishers.
Tokimatsu, K.; Seed, H.B.; 1987; Evaluation of settlements in sands due to earthquake shaking; Journal of
Geotechnical Engineering: Vol. 113, No. 8, p. 861-879.
United States Geologic Survey (U.S.G.S.), 1996a, Probabilistic Seismic Hazard Assessment for the State of California,
Open-File Report 96-706.
, 1996b, National Seismic-Hazards Maps, Open-File Report 96-532.
, 2002, Documentations for the 2002 Update of the National Seismic Hazard Maps, Open-File Report 02-20.
, 2007, Preliminary Documentation for the 2007 Update of the United States National Seismic Hazard Maps,
Seismic Hazards Mapping Project, Open-File Report 2007-June Draft.
, 2011, Earthquake Ground Motion Parameters, Version 5.1.0, utilizing ASCE 7 Standard Analysis Option,
dated February 10.
, 2021, Unified Hazard Tool Calculator, Unified Hazard Tool (usgs.gov)
Site Location Map
PETRA GEOSCIENCES, INC.
COSTA MESA MURRIETA PALM DESERT SANTA CLARITA
Figure 1J.N.:
SCALE:
June 2021 21-177
epl NTS
DATE:
DWG BY:
40880 COUNTY CENTER DRIVE, SUITE M
TEMECULA, CALIFORNIA 92591
PHONE: (951) 600-9271
Live Oak Project
City of Fontana, San Bernardino County, California
- Approximate Site Location
LEGEND
N
N
TP-15
- Approximate location of exploratory test pit
- Approximate Location of Exploratory Boring
LEGEND
B-7
Af
Qal
- Artificial Fill
- Quaternary Young Alluvium
- Quaternary/Tertiary Sandstone
Qls - Quaternary Landslide Deposits
QTsw
GEOLOGIC UNITS
N
SITE
Scale
0 2 miles
- Reproduced from: USGS, 2021, The National Map Viewer
B-1
B-2 B-3
B-4
B-5
B-6
B-7
B-8
B-9
B-10
B-10
Approximate Location of Borings (by GeoBoden, 2019)
Approximate Location of Borings (by Petra, 2021)
Approximate Location of Test Pits (by Petra, 2021)
B-1
B-2
B-3
B-4
B-5
B-6
B-8
T-1
T-2
T-3
T-4
T-5
T-6
T-7
T-8T-9
T-9
B-8
B-7
Refusal on Shallow Cobbles/Boulders
Refusal Due to Heavy Caving and Boulders
Base Map Reference:
PETRA GEOSCIENCES, INC.
40880 County Center Drive, Suite M
Temecula, California 92591
PHONE: (714) 549-8921
COSTA MESA TEMECULA VALENCIA PALM DESERT CORONA
Exploration Location Map
Live Oak Project
Fontana, San Bernardino County, California
DATE: June 2021
J.N.: 21-177 Figure 2
N N
TP-15
- Approximate location of exploratory test pit
- Approximate Location of Exploratory Boring
LEGEND
B-7
Af
Qal
- Artificial Fill
- Quaternary Young Alluvium
- Quaternary/Tertiary Sandstone
Qls - Quaternary Landslide Deposits
QTsw
GEOLOGIC UNITS
GEOSCIENCES
LEGEND
N
APPENDIX A
BORING AND TEST PIT LOGS
1.8 107.0
Disturbed
1.0 91.2
1.1 74.7
Disturbed
Disturbed
1.1 79.9
0.8
0.6
0.6 Disturbed
No
Recovery
1.8 86.0
1.6 112.7
1.0 Disturbed
1.1 Disturbed
1.3 Disturbed
1.0 Disturbed
0.7 Disturbed
0.8 Disturbed
1.0
1.0 93.1
APPENDIX B
BORING LOGS, GEOBODEN, INC., 2019