HomeMy WebLinkAboutTract Map 9833-2 Lot 29 Soil Report
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RECEIVED
APR 7 1999
CITY OF TEMECULA
ENGINEERING DEPARTMENT
SOIL AND FOUNDATION INVESTIGATION REPORT
LOT 29 OF TRACT NO. 9833-2
A.P.N. 945-030-007
31422 JEDEDIAH SMITH ROAD
CITY OF TEMECULA
CALIFORNIA
FOR
MER CONSTRUCTION C/O MR. MIKE REGUS
PROJECT NO. 99-006.PI
DATED APRIL 5. 1999
Lakeshore Engineering
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LAKESHORE
Engineering
Consulting Civil Engineering and Geologists
April 5, 1999
Project No: 99-006.PI
Client:
Mr. Mike Regus C/O MER Construction
21841 Kiowe Lane
Huntington Beach, CA 9646
(714) 963-0338
Subject:
Soil and Foundation (Geotechnical) Report
Proposed New Single Family Residence
Lot 29 of Tract No. 9833-2
City of Temecula, CA.
A.P.N. 945-030-007
INTRODUCTION
This report presents our findings and conclusions of a soil and
foundation investigation for the proposed development of a new single
family residence to be located at the subject site. The purpose of
this investigation was to 1) evaluate the foundation and subsurface
soil conditions at the site, and 2) provide pertinent foundation
recommendations for proposed development.
This investigation included the following scope of work:
1) Performed four exploratory trenches within the proposed
building pad and driveway areas to determine subsurface
conditions and recover soil samples for laboratory testing
(Appendix A).
2) Laboratory testing of a representative soil sample to
determine the soil properties (Appendix B).
3) Engineering analyses for foundation and necessary
earthwork preparation.
4) The preparation of this report.
PROPOSED DEVELOPMENT
The proposed building area is situated on the nose of a broad ridge,
therefore grading is anticipated to truncate the ridge top to
construct a level building pad.
The proposed development will consist of a one and/or story, custom
built, upper scaled, single family residence in the order of 3000
square of living space, founded on a level graded pad. Construction
is expected to be of woodframed and stucco walls with tile roofing,
supported on conventional spread footings.
31740-2 Railroad Canyon Road. Canyon Lake, CA 92587 . (909) 244-2913 . FAX: (909) 244-2987
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IN: 0990011.01
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INDEX MAP
OF
MIKE REGUS PROPERTY
LOT 29, TRACT 9833-2
31422 JEDEDfAH SMITH ROAD
CITY OF TEMECULA
RIVERSIDE COUNTY
CALIFORNIA
:?
BASE MAP:
State of Califomia, Speclal Studies Zone Official Map 1980
on Base Map of USGS 7.5 min. Peachanga Quadrangle. 1973
FIGURE 1
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April 5, 1999
Project No: 99-006.PI
Page Two
SITE DESCRIPTION
The subject property is a flag lot, consisting of approximately 2.88
gross acres of undulating rolling hill country. Natural slopes on the
site average about 4:1 (H:V), with 3:1 maximum pitch. Maximum relief
between valley and ridge top onsite is about 50 feet.
The property is at present unimproved, and supports annual local
grass and scattered cacti clusters. No fills and/or debris were
observed on the property. The surface contours in general is smooth
and uniform with no boulder or rock outcrop noted.
A drainage course, crosses the property along the easterly side, in a
north-southerly direction. The general drainage appears to be by
natural sheetflow towards the seasonal watercourse with exit at the
southeasterly corner of the property.
SUBSURFACE CONDITIONS
Four exploratory backhoe pits were excavated on the site to determine
the subsurface soil profile. Based on our exploratory efforts, the
upper ridge areas are mantle with a thin layer of topsoil underlain
by Pauba Formation of Sandstone and Siltstone seams. The topsoil
consist of a thin layer of approximately 2 1/2 feet of a lighter
brown, Silty SAND/Sandy SILT with trace of clay.
In the low wash areas (proposed driveway crossing) the loose
topsoil/colluvial soil section is thicker, at about 5 to 6 feet,
consisting of grey-brown Sandy Silt and fine sand. Below 5 feet, the
soil becomes dense and slightly cemented. pauba Sandstone is
suspected to underlie this alluvial soil at lower depths (about 10
feet) .
Generally, the upper topsoil is considered LOW in expansion
potential. No water seepage, rocks and/or boulders were exposed in
our exploratory trenches.
REGIONAL GEOLOGY SETTING
For regional geologic conditions, groundwater, faulting and
seismicity and secondary effects, please refer to geology report
prepared by Mr. JOhnathan L. Rossi, report dated March 29, 1999 (P.N.
09900ll.0l) attached in the appendix as part of this report.
Lakeshore Engineering ~
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April 5, 1999
Project No: 99-006.PI
Page Three
CONCLUSION AND RECOMMENDATIONS
GENERAL
From a soil and foundation engineering standpoint, the site will be
suitable for the proposed new single family residential construction,
provided all conclusions and recommendations presented in this report
are incorporated in the design considerations, project plans and
specifications.
GRADING AND EARTHWORK
Based upon our review of grading plan already prepared for subject
property (please see grading plan in pocket), it is our understanding
that site grading will be required to provide: 1) a single level
building pad; 2) suitable foundation conditions to support the
proposed building structure; 3) adequate surface gradients for
control of water runoff; and 4) excavation into native soils and/or
compacted fills to accommodate the installation of foundation and
utility systems.
After the areas to be graded have been stripped and cleared of
vegetation, the on-site soils will be considered satisfactory for
reuse in the construction of on-site fills. Per review of grading
plan prepared for the site, the nose of ridge top will be
truncated/lowered an average of 10 feet, with proposed building
footprint to be situated on the cut portion of the constructed pad.
Sliver perimeter fill slopes are proposed to enlarge the cut pad.
Manufactured fill slopes will be in the order of about 20 feet high
with 8 to 10 feet of vertical fill and cut slope is also in the order
of 20 high. All slopes will be pitched at 2:1 (H:V).
The exposed cut building pad (after removal of 10+ feet of hill top)
will likely expose competent, very dense to hard surface subgrade,
considered suitable for support of proposed structure. Determination
to overexcavate building pad to provide for a uniform foundation fill
cushion blanket will be made by consultant based on field inspections
at time of grading operation.
In the area of the driveway wash crossing, the upper surface soils
are loose and considered in its present condition, unsuitable for
support of vehicle traffic. The upper 5 to 6 feet of topsoil or
slopewash should be removed and reworked (moisture conditioned and
recompacted) prior to concrete driveway paving. Actual depths of
overexcavation should be field determined by geologist or engineer at
the time of grading operations. In addition, Lakeshore Engineering
recommends that the upper 18 inches of driveway subgrade in the
watercourse crossing section be underlain by a rockbed (1 1/2 +
inches diameter) to provide for an unyielding base layer.
Lakeshore Engineering ~
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April 5, 1999
Project No: 99-006.PI
Page Four
All exposed bottom of grading excavation should first be scarified
another 12 inches, moisture conditioned to near optimum and densified
to at least 90 percent of the maximum laboratory dry density as
determined by the A.S.T.M. D1557-78 compaction method. Boulders
encountered during grading that are 6 inches in diameter or larger,
should not be used in structural fills.
If overexcavation of building pad is required, the limits of rework
should extend at least 5 feet beyond the building footprints.
Any surface or subsurface obstructions encountered during grading
such as rocks, utility/irrigation lines should be removed .from any
areas to receive fill. No underground obstructions nor facilities
should remain in any structural areas which receive compacted fills,
building foundations, concrete slabs and/or pavements.
Depression and/or cavities (including exploratory trenches) created
as a result of the grading obstruction removal, should be properly
backfilled with suitable fill materials and compacted under
engineering observation and testing. All fills should be densified in
conformance with the appropriate grading code but shall be less than
90 percent relative compaction by mechanical means only.
EXCAVATING AND RIPPABILITY
Rework of on-site soils should not be difficult to accomplish with
standard earthmoving equipment such as a D-6 or larger. The walls of
temporary construction excavations should stand nearly vertical,
provided the total depth does not exceed 5 feet and surficial
stability is verified. Shoring of excavation walls or flattening may
be required if greater excavation depths are necessary. For deeper
cuts, slopes should not be made steeper than 1:1 (H:V).
All work associated with trench shoring must conform to the State of
California Safety Codes. Native organic free soils may be permitted
provided both the backfill and the native materials have a m~n~mum
sand equivalent of 30 and the required relative compaction can be
achieved.
GRADING CONTROL
All grading and earthwork including trench backfill should be
performed under the observation and testing of the soils consultant
or their representative. Sufficient notification prior to stripping
and earthwork construction is essential in order that the work be
adequately observed and tested. In order for us to provide a written
opinion as to the adequacy of the soil compaction and trench
backfill, the entire operation, most importantly at the time of
trench backfill, should be performed under our observation and
testing.
Lakeshore Engineering (p
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April 5, 1999
Project No: 99-006.PI
Page Five
FOUNDATION DESIGN
FOOTING
The proposed single family residential development may be supported
on conventional spread footings established in competent native
subgrade or entirely on engineered (compacted) fills. These spread
footings may be designed for an allowable bearing value of 1500
pounds per square foot. This deSign value may be increase by one
third, if the Structural Engineer takes into consideration short
duration structural loading conditions, such as induced by wind
and/or seismic forces.
Footings should be founded at least 18 inches below the lowest
adjacent ground surface, for one and/or two story structures. All
continuous foundations should be reinforced with at least two no. 4
rebars at top and two rebars at bottom (total of 4 rebars) and
consistent with the recommendations of the Structural Engineer or
Architect and the guidelines in the U.B.C. Reinforcement should also
be placed across garage grade beam at door opening.
SETTLEMENT
Total settlement due to structural loads should not be a design
factor as they should be less than 3/4 inch. Differential settlement
should be within tolerable limits.
LATERAL CAPACITY
For design, resistance to lateral loads can be assumed to be provided
by friction acting at the based of the foundations and by passive
earth pressure and may be combine without reduction. If passive earth
pressure is used, it is important that backfill should be placed
under engineering observation and testing.
A coefficient of friction of 0.30 may be used with the dead load
forces. An allowable lateral passive earth pressure of 200 pounds per
square foot per foot of depth may be used for the sides of footings
poured against undisturbed and/or recompacted soils.
The lateral bearing values indicated above are for the total of dead
and frequently applied live loads. If the normal code requirements
are used for seismic design, the values may be increased by 1/3 for
short durations of the loading which include the effect of wind or
seismic forces.
RETAINING WALLS Per review of grading plan, no retaining walls are
proposed at this time.
Lakeshore Engineering \
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April 5, 1999
Project No: 99-006.PI
Page Six
SLOPE STABILITY
Proposed cut and fill slopes are less than 30 feet in overall height
and pitched at 2:1 (H:V). Slopes to be constructed as proposed
considered grossly stable from deep seated failure.
CONCRETE SLAB - ON - GRADE
The onsite native and stockpile soils are granular in nature and
considered to be low in expansion potential. Expansive soil potential
should be reviewed at completion of rough grading operation.
Concrete floor slabs may be supported directly on properly prepared
subgrade. Presaturation of subgrade is not required. If a floor
covering that could be critically affected by moisture, such as vinyl
tile, slabs should be protected by a plastic vapor barrier of six-mil
thickness. The sheet should be covered by at least two-inches of sand
cushion to prevent punctures and aid in concrete cure.
The concrete floor slabs should be reinforced with at least 6" x
6"-#10/#10 welded wire mesh or equivalent bar reinforcing ( no. 4
rebars at 24 inches on center) and installed at mid-height (using
chair support). Concrete floor slabs should be at least 4 inches
thick nominal.
SITE DRAINAGE
Positive drainage should be provided around the perimeter of all
structures to minimize water infiltrating into the underlying soils.
Finish subgrade adjacent to exterior footings should be sloped down
and away to facilitate surface drainage. All drainage should be
directed off-site via non-erosive devices (swales and ditches).
The homeowner should be made aware of the potential problems which
may develop when drainage is altered through construction of
retaining walls, patios and pools. Ponding water, leaking irrigation
systems, overwatering or other conditions which could lead to ground
saturation must be avoided.
FOOTING TRENCH EXCAVATION INSPECTION
All footing excavations should be inspected and approved by the Soils
Consultant prior to placement of footing forms, reinforcement, or
concrete. Materials generated from excavations should not be spread
on slab-on-grade areas, provided they are compacted and tested.
Lakeshore Engineering ~
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April 5, 1999
Project No: 99-006.PI
Page Seven
GENERAL INFORMATION AND LIMITATIONS
This report presents recommendations pertaining to the subject site
based on the assumption that the subsurface conditions do not deviate
appreciably from those disclosed by our exploratory trenches. In view
of the general conditions of the area, the possibility of different
local soil conditions cannot be discounted.
It is the responsibility of the owner to bring any deviations or
unexpected conditions observed during construction to the attention
of the consulting engineer. In this way, any required supplemental
recommendations can be made with a minimum of delay to the project.
Prior to initiation of grading, a meeting should be arranged by the
developer and should be attended by representatives of the
governmental agencies, contractors, consultants and the developer.
Construction should be inspected at the following stages by the
Geotechnical Consultant.
o Upon completion of demolition and clearing.
o During all rough grading operations including removal
of unstable materials, precompaction and filling
operations.
o During trench backfilling but prior to paving or
other construction over backfill.
o When any unusual conditions are encountered.
The findings and recommendations of this report were prepared in
accordance with generally accepted professional principles and
practice in the field of geotechnical engineering. This warranty is
in lieu of all other warranties, either express or implied.
to be of service. If you have
A - EXPLORATORY LOGS
B - LAB. RESULTS
GEOLOGIC REPORT BY JOHN L. ROSSI
IN POCKET
Lakeshore Engineering l2\
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APPENDIX t.
FIELD EXPLORATION
Field exploration was performed on the morning of April 5, 1999 using
a backhoe (Jack Curtis Backhoe 909-674-6156). The soils were
continuously logged by our field personnel and classified by visual
examination in accordance with the Unified Soil Classification
System. Our trench logs are attached for review.
To evaluate the compaction characteristics of the fill material,
field density tests were performed. Also, representative bulk samples
were recovered and shipped to the laboratory in polythelene bags for
laboratory testing.
MER Construction/Mike Regus
Lot 29 Tract 9833-2
Jedediah Smith
Project No. 99-014.PI
Dated April 5, 1999
Lakeshore Engineering
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PLOT PLAN
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LAKESHORE
Engineering
SINGLE FAMILY RESIDENCE
LOT 29 TRACT 9833-2
31422 JEDEDlAH SMITH RD.
TEMECULA . CA.
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CONSULTING CIVIL ENGINEERS
Project No:
99-06.PI
Dote
3/11/1999
Agure No:
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TRENCH
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Logged By: f' '/0 N (" .
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Groundwater Depth: ~~.
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LAKESHORE
Engineering
CONSULTING ENGINEERS AND GEOLOGIST
SINGLE FAMILY RESIDENCE
LOT 29 TRACT 9833-2
31422 JEDEDIAH SMITH RD.
TEMECULA , CA.
Fig. No. 3
~
PROJ. NO.
99-06.PI
I
I Surface Elevation: Logged By: F,.:::jl)l'qC:,.
Trench Orientatio~ \)llST V'LAN. Date.:::! I'S 1'11- .
Trench Dimensions24'ltA (,'''X "." Equipment: ClAl2.."T~ ~HoE-.
x 'U..J '- L . Thlllog II I r.pttlerCation olwb5urtiCI, ICIR andgtOuna<<iiler conditio,. It the time and place 01 exeiViItion.
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TRENCH
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Surface Elevation:
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Trench Dimensions2l!h<::ixE'-D)( \2Yz.
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LAKESHORE
Engineering
CONSULTING ENGINEERS AND GEOLOGIST
SINGLE FAMILY RESIDENCE
LOT 29 TRACT 9833-2
31422 JEDEDIAH SMITH RD.
TEMECULA , CA.
Fig. No. 3A.
~
PROJ. NO.
99-06.PI
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APPENDIX B
LABORATORY TESTING
EXPANSION INDEX TEST
A representative soil sample was collected in the field and tested in
the laboratory in accordance with the A.S.C.E. Expansion Index Test
Method as specified by U.B.C. The degree of expansion potential was
evaluated from.measured soil volume changes obtained during soil
moisture alterations. The results of the test are presented below:
Trench Depth Soil Expansion Expansion
No. (Ft. ) Description Index Potential
------ ----- ----------- --------- ---------
T-l 0-2 Silty SAND < 20 LOW
(SM/SP)
MER Construction/Mike Regus
Lot 29 Tract 9833-2
Jedediah Smith
Project No. 99-0l4.PI
Dated April 5, 1999
\Lit
Lakeshore Engineering
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JONATHAN L. ROSSI
CONSULTING GEOLOGIST
REGIONAL
GEOLOGIC CONDITIONS
AT THE
REGUS PROPERTY
31422 JEDEDIAH SMITH ROAD
TEMECULAlRANCHO CALIFORNIA AREA
RIVERSIDE COUNTY
CALIFORNIA
PROJECT NO. 0990011.01
PREPARED FOR:
LAKESHORE ENGINEERING
31606 Railroad Canyon Road #101
Canyon Lakes, California
92587
PREPARED BY:
JONATHAN L. ROSSI, CONSULTING GEOLOGIST
P.O. Box 4018, Big Bear Lake
California 92315
March 29, 1999
\-6
P.O. BOX 4018, BIG BEAR LAKE, CALIFORNIA 92315.
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IN: 0990011.01
TABLE OF CONTENTS
Page
1.0 INTRODUCTION
1.0
2.0 SUMMARY OF FINDINGS
2.1 Geologic Setting
2.2 On-Site Geology - Earth Materials -
2.2.1 Topsoil
2.2.2 Quaternary Alluvium
2.2.3 Bedrock - Pauba Formation
3.0
3.0
5.0
5.0
5.0
5.0
3.0 GROUNDWATER
6.0
4.0 FAULTING AND SEISMICITY
4.1 Faulting
4.2 Seismicity
4.3 Secondary Seismic Effects
6.0
6.0
8.0
10.0
5.0 CONCLUSIONS & RECOMMENDATIONS
5.1 Conclusions
5.2 Recommendations
10.0
10.0
11.0
6.0 LIMITATIONS STATEMENT
12.0
ACCOMPANYING MAPS. TABLES. PLATES AND APPENDICES
Fiaures -
Figure 1 - Index Map (EQ Fault Map; 2000 sc.)------------------------------------------------------ 2.0
Figure 2 -- Site Plan & Geologic Map (photoreduction) ------------------------------------------- 4.0
Figure 3 - Regional Fault & Seismicity Map ------------------------------------------------------------ 7.0
Tables -
Table I - Regional Active Faulting ____________m___________________________________________--------------- 8.0
Table 11- Maximum Credible EQ., Maximum Ground Acceleration _____________________m_______ 9.0
ADDendices -
Appendix - References
ii
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IJONATHAN L. ROSSI,CONSULTING GEOLOGIST. P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315.
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JONATHAN L. ROSSI
CONSULTING GEOLOGIST
March 29, 1999
IN: 0990011.01
TO: Lakeshore Engineering
31740-2 Railroad Canyon Rd.
Canyon Lakes, Ca. 92587
SUBJECT: REPORT - Geologic Conditions at the Site of Proposed Residential Structure,
Regus Property, Located on the North Side of Jedediah Smith Rd., East of
Pescado Dr., in the Rancho CaliforniafTemecula Area, Riverside County,
California.(E 1/2. NW1/4, Sec 17, TBS, R2W, SBB&M).
ATTENTION: Fen Yong, RCE - Principal, Lakeshore Engineering
Mike Regus - Owner
1.0 INTRODUCTION-
We are pleased to present this letter report of findings for the existing geologic conditions at
the proposed residential development located on the north side of Jedediah Smith Road, East
Temecula/Rancho California area, Riverside County, California. The proposed site consists of
a graded cut/fill lot facing Jedediah Smith Road. A small south facing cut slope is located at
the north side of the lot. A graded driveway provides access to the site. Roads are paved with
curb and gutter in places.
Our scope of work is limited to providing a description of the geologic conditions present at the
subject site including general geology, faulting and seismicity, groundwater description, and
presentation in this letter report. Seismic conditions were evaluated based on published
earthquake and seismic information. Our scope of work does not address or consider any
aspects of a Phase I Site Assessment for Hazardous Materials or Asbestos containing building
materials, and is not a soils & foundation investigation, but provides geologic interpretation of
site conditions for the soils engineer and the geotechnical report.
This letter report presents our findings, conclusions, and recommendations concerning the
existing geologic and earthquake/seismic conditions present at the subject site. Our work is
provided to the soils engineer for further geotechnical evaluation. A Precise Grading Plan
prepared by Lakeshore Engineering dated February 5, 1999 was used to review the proposed
grading, and topography. The site was visited on Monday, March 29. 1999.
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P.O. BOX 4018, BIG BEAR LAKE, CALIFORNIA 92315.
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IN: 0990011.0l
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INDEX MAP
OF
MIKE REGUS PROPERTY
LOT 29, TRACT 9833-2
31422 JEDEDIAH SMITH ROAD
CITY OF TEMECULA
RIVERSIDE COUNTY
CALIFORNIA
'vro
BASE MAP:
State of California, Special Studies Zone Official Map 1980
nn R.......l..........I 11~"'~"7 It!. _,_ "'__~L ___ __ -. . . . ~__
FIGURE 1
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-3-
March 29, 1999
IN: 0990011.01
2.0 SUMMARY of FINDINGS -
2.1 GEOLOGIC SETTING -
The subject site is situated at the southwestern margin of an elevated older alluvial plain
forming a pediment surface of rolling foothills north and east of the Temecula Valley, and north
of the Pauba Valley. The older alluvium in this area consists primarily of a massive, partially
cemented, well-indurated Pleistocene sandstone (Pabua Formation-Sandstone unit) exposed
across most of the region. The Pauba Formation contains a massive to poorly bedded, reddish
brown, coarse to graded sandstone unit, in places containing thin (6" to 12") interbeds of grey
green to grey brown micaceous siltstone. Siltstone can be predominant in a portion of the
section with minor sandstone. In the south Temecula Valley and Pauba Valley the older
Pleistocene/Pliocene Temecula Arkose underlies the Pauba Sandstone. The Temecula Arkose
consists of a thick section of layered very fine sandstone to siltstone. Narrow, thin deposits of
younger alluvium are present within the erosional canyons developed within the pediment
surface. The older alluvial pediment surface is bordered on the north and east by intrusive
granitic and older marine metasediments of Bachelor Mtn. and Black Hills. Traces of the Agua
Caliente Fault zone are mapped (CDMG Santa Ana Sheet-1965) at the contact of the Pauba
sandstone with these hard rock units. The Wildomar Fault on the northeast, and the Willard
Fault on the southwest border the TemeculalElsinore Graben. Both of these fault segments
are considered part of greater Whittier/Elsinore Fault Zone. The Pabua sandstone pediment
surface is located within the boundaries of the Perris structural block.
The Perris Block is a northwest-southeast trending structural block bordered on the northeast
by the San Jacinto fault, on the southwest by the Whittier/Elsinore Fault System (Wildomar
Fault), on the northwest by the Chino Basin, and on the southeast by the Agua Calenti fault
Zone and Boreggo Valley. The Santa Ana Mountains Block lies to the southwest of the Perris
Block.
The closest active or potentially actiye faults capable of effecting the subject site (if an
earthquake event were to occur on one of these faults near the site) are the Wildomar Fault
approximately 1/2 mile to the southwest, and the San Jacinto Fault approximately 21.0 miles to
the northeast. Both of these faults are considered active, and are Earthquake Fault Zones.
The recently zoned Wolf Valley fault located some 1.75 miles to the south-southwest. This is
on the southwest side of the Temecula Graben. The Wolf Valley Fault is considered a portion
of the Elsinore Fault Zone, and possibly an extension of the Willard Fault further to the
northeast, on the southwest side of the Temecula Valley. No active or potentially active faults
were observed on the subject property, or were present on the site in the literature reviewed.
The site is not included within the Wildomar Fault Earthquake Fault Zone. Other fault features
or linear fault like features are reported on M.P. Kennedy's Map (CDMG Sp.Rpt. 131, Plate 1)
within the Pauba Plain to the north and east of the site. These features are not Earthquake
Fault Zones, and are not well defined in the literature. The original and the second MWD San
Diego Aqueducts (oriented N-S) are located 1/4 mile to the west.
\l\
IJONATHAN L. ROSSI,CONSULTING GEOLOGIST. P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315 .
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-5-
March 29, 1999
IN: 0990011.01
2.2 ON-SITE GEOLOGY - EARTH MATERIALS-
2.2.1 TODsoil-
A thin layer of poorly developed topsoil is usually present over native subsoil and bedrock.
Topsoil in the area consist of loose, brown to reddish brown, porous, well graded silty sands
and clayey sands where shallow bedrock is present (Pauba Fm. sandstone). There were no.
exploratory trenches excavated during the course of this study. Natural soil profiles are
exposed in existing cut slopes in the surrounding area, and in nearby road cuts.
2.2.2 Alluvium 10all-
A thick (several feet), porous, topsoil section is typical over sandy alluvial and colluvial soil
deposits seen in the central stream channel shown on Figure 2. Unconsolidated soils are
typically loose to medium dense, easily excavated, poorly graded fine to medium sand, sandy
silts, and gravelly sands. Pauba Sandstone bedrock is suspected to underlie the alluyial soils.
Pauba Sandstone is mapped across the local area (CDMG SpRpt. 131), and is mapped at the
site.
2.2.3 Bedrock 10Dssl-
Bedrock was not exposed on the site, but is seen on the adjacent property to the east, and is
mapped (CDMG 131) underlying the property. Bedrock consists of the Quaternary Pauba
Formation Sandstone, a regionally distributed poorly cemented (CaC03 & salts), friable well
graded sandstone with limited poorly defined bedding, and containing interbeds of grey to
brown siltstone. The Pauba is a young continental deposit containing a large number of
sedimentary depositional structures: coarse channel fills, cross-bedding and graded bedding,
and alluvial fan structures. Pauba sandstone at the subject site consists of reddish brown to
brown well graded sandstone with a moderately high silt and clay content. In addition to salt
cementation clay acts to bind the sand grains of the arkosic sediment into poorly consolidated
continental sandstone. Excayation is relatively easy with standard backhoe, and the Pauba
stands up well in cut slopes up to 30 feet. However, the Pauba is easily eroded, and can be
cut with water where run-off is not controlled. Erosional gullying and animal burrowing in the
slope face is considered a problem with existing slopes in the area. Bedrock is not exposed at
the surface at the subject site, however is present some 3 to 5 feet below the existing grade.
The Temecula Arkose is thought to underlie the Pauba Sandstone at the subject site, howeyer
the Temecula Arkose is not exposed in the site vicinity.
7,.\
I JONATHAN L. ROSSI,CONSULTING GEOLOGIST. P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315 .
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March 29, 1999
IN: 0990011.01
3.0 GROUNDWATER-
Groundwater is present throughout the region as an unconfined alluvial aquifer within the
Younger and Older AlluYium underlying the site, and in the underlying Pauba sandstone. The
bedrock is considered as moderately good water bearing aquifer, and can yield limited
amounts of groundwater to domestic water wells from primary and secondary porosity.
Regional groundwater within the graben basin occurs oyer a thick section of several hundred.
feet, and is utilized by numerous domestic, municipal, and irrigation water wells. Localized
perched groundwater may be present at the site and typically occurs at the base of the
bedrock-weathered zone. Perched groundwater is the result of local winter season percolating
surface waters collecting over low permeability silt layers within the upper weathered Pauba
sandstone. No springs or seeps were reported on the subject site. Additional information
concerning the on-site hydrogeologic conditions may be obtained, if required, through the
review of available water well driller logs, and by additional on-site hydrogeologic investigation
under separate study.
4.0 FAULTING & SEISMICITY -
4.1 Faultina-
No surficial or other evidence of active or potentially active faulting was observed at the
subject site during our field investigation. The subject site is not included in any Earthquake
Study Zone for fault hazard. The Wildomar Fault Zone located approximately 1/2 miles to the
northeast, the Wolf Valley Fault 1.75 miles to the southwest, and the San Jacinto Fault Zone
located approximately 21.0 miles to the northeast are the closest Special Study Zone faults to
the site. The Wildomar Fault Zone is considered to be a high angle and strike slip fault,
strongly developed and clearly visible from aerial photographs. The Wolf Valley Fault is
described as a high angle fault possibly induced due to groundwater withdrawal in the Wolf
Valley (1988)(Iower Temecula Valley). The San Jacinto Fault Zone extends along the foothills
of the San Timoteo Badlands, and at the base of the south San Jacinto Mountains. The fault
zone is considered to be a complex zone of high angle normal and strike slip faults with
multiple and discontinuous fault strands as wide as 2 to 3 miles (San Jacinto & Casa Loma
Faults San Jacinto Graben Valley). There are several other faults within the greater Southern
California area, which could effect the site in terms of ground shaking in the event of an
earthquake. The following list includes some of these faults and their maximum probable
earthquake magnitude (Richter):
Z.V
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March 29, 1999
IN: 0990011.01
TABLE I
REGIONAL ACTIVE OR POTENTIALLY ACTIVE
CAUSATIVE FAULTS
FAULT DISTANCE FROM SITE MAXIMUM CREDIBLE
APPROXIMATE EARTHQUAKE
(RICHTER MAGNITUDE)
San Andreas Fault 41.0 mi. NNE 8.0 M
San Jacinto Fault 21.0 mi. NE 7.5M
Elsinore (Wildomar) Fault Y:. mi.SW 7.5M
Banning Fault 37.0 mi. ENE 7.5M
Whittier 50.0 mi. NNW 7.5M
Sierra Madre/Cucamonga 53.0 mi. NW 7.5M
4.2 Seismicitv-
Based on information provided by CDMG Map Sheet 23 - Greensfelder; CDMG OF 92-1,
'Peak Accelerations from Maximum Credible Earthquakes in California - Caltrans 1992'; and
Seed & Idriss . Ground Motion and Soil Liquefaction During Earthquakes' (Earthquake
Engineering Research Institute), the following conditions were determined for ground
accelerations for specific earthquake events at or near the subject site. Maximum credible
earthquake magnitudes listed in CDMG OF-92-1 and associated bedrock accelerations are
presented in TABLE II below.
The subject site should perform essentially as a bedrock or stiff soil site because of the nature
of the bedrock at the proposed graded pad site. Groundshaking and ground surface
deformation will occur to a greater extent at an alluvial site than at a bedrock site. The Pauba
sandstone can be considered stiff alluvial soil or soft bedrock.
Review of CDMG Map Sheet 54, which is presented in CDMG OF-92-1 as a peak ground
acceleration contour map includes the area of the subject site within the .6 g acceleration
contour, one of the highest ground accelerations for southern California.
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I JONATHA.N L. ROSSI,CONSULTING GEOLOGIST. P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315.
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TABLE II
MAXIMUM CREDIBLE EARTHQUAKE
PEAK GROUND ACCELERATION
REPEATABLE GROUND ACCELERATIONS
CAUSATIVE FAULTS
FAULT DISTANCE MAGNITUDE PEAK REPEATABLE
ACCELERATION ACCELERATION
WILDOMAR 1/2 mi. 7.5 M .73 9 .475 9
SAN JACINTO 21.0 mi. 7,5M .250 9 .165 9
SAN ANDREAS 41.0mi. 8.0 M .175 9 .113 9
BANNING 37.0 mi. 7.5M .155 9 .101 9
WHITTIER 50.0mi. 7.5 M .100 9 .065g
CUCAMONGA 53.0mi. 7.5M .080g .052g
. Repeatable ground acceleration =.85 of maximum 'g'.
Peak ground accelerations are provided for use by the soils engineer and the structural
engineer in foundation design where applicable. Repeatable ground accelerations are not
used by the engineering community at this time, but are provided here for the layman.
Repeatable ground accelerations are comparable to dampened groundshaking. These ground
acceleration values are for bedrock accelerations, and can be applied for any seismic condition
stability evaluation of the subject site. Earthquake design criteria presented in the current
adopted Uniform Building Code, or in the County of Riverside Building Code Seismic Design
Section, or design provided by the structural engineer and soils engineer in accordance with
these requirements, whichever takes precedence, should be applied to the proposed
development. Other active or potentially active faults in the region will probably prOduce less
sever effects on the site as a result of an earthquake event, and considering fault to site
distances will probably have a less sever to negligible effect on the site. (see Table II above).
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I JONATHA,N L. ROSSI,CONSULTING GEOLOGIST · P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315 .
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4.3 SecondarY Seismic Hazards -
The potential for secondary seismic effects such as liquefaction due to the presence of
granular sediments, shallow groundwater, and nearby active faulting capable of generating
large earthquake events should be evaluated by the soils engineer. Based on our geologic
observations at the site, and knowledge of the geology of the area, we do not consider the
bedrock (Pauba Sandstone) at the location of the proposed building pad (as shown on Figure
2), to be a high risk for liquefaction.
Other secondary seismic effects such as differential settlement/compaction, ground surface
rupture due to fault movement, or ground surface rupture due to lurching is not considered
likely, but cannot be ruled out due to the faulted nature of the region and the close proximity of
active faulting. Ground surface rupture is suspected to have occurred along the Wildomar
Fault in the past, at the fault location. Seismically induced land sliding is not common in the
Pauba sandstone, and is considered unlikely to effect the subject site.
Other potential secondary seismic hazards: tsunami, and seiches flooding due to reservoir
failure are considered nil due to the site location, and nature of the bedrock deposits.
5.0 CONCLUSIONS & RECOMMENDATIONS -
5.1 Conclusions -
o The subject site is suitable, in terms of the on site geologic conditions, for the proposed
residential construction. Topsoil and Pauba Fm. sandstone bedrock should not present
any significant geologic impediment to the excavation of the residential building pad
and foundation footings. Footings cannot be founded in porous, unsuitable soil
materials as per the soils engineer.
o The subject site is close (1/2 mile) to the Wildomar Fault Zone. There are no reported
or mapped traces of the fault close (adjacent) to, or on the subject site. Strong
groundshaking (secondary seismic hazard) is considered a possibility should a medium
to large earthquake event occur on the Wildomar Fault adjacent or close to the subject
site.
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IJONATHAN L. ROSSI,CONSULTING GEOLOGIST · P.O. BOX 4018.BIG BEARLAKE,CALlFORNIA 92315.
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5.2 Recommendations-
o Footina Insoection - The footing excavation should be inspected for competency by the
soils engineer or the engineering geologist prior to the setting of reinforcing steel bar, or
any imported sand or gravel base.
o Groundshakina - Due to close proximity of the active Wildomar Fault, the structural
engineer should consider seismic peak accelerations and groundshaking criteria in the
steel reinforcing design for the residential foundation.
o Drainaae Control - Any proposed cut slope exceeding 10 ft. in height should have a
drainage 'V' brow ditch (24" wide, 12" deep) cut across the top of the proposed cut
slope, set back 3 feet from the top of slope. The brow ditch should be lined with
concrete grout. Drainage from all sources should not be allowed to flow over any
proposed cut or fill slope faces.
o Landscaoe Veaetation - Any proposed cut slopes should be planted with standard
grasses and indigenous plants (hydroseed) possibly using a landscape stability growth
net on the slope face. Deep-rooted vegetation should be planted in order to increase
slope surficial stability over time. All landscaping design and plant type should conform
to Riverside County landscaping guidelines.
o Cut Slooe - Review of the Precise Grading Plan (Figure 2) indicates that a 2:1 (H:V) cut
slope is proposed for the north side of the graded pad. The slope is :t17.5 ft. in height,
:t150 ft. in length. The cut slope should be inspected by the geologist when
approximately one-half of the cut (8 ft.) is completed, and upon completion.
o Other Soils & Geoloaic Insoections - Any proposed vertical cut slope for retaining wall,
cut pad/foundation footing excavations, fill slope keys, or other graded exposures of
bedrock should be inspected by the engineering geologist upon excavation. Any
observed lineation, offset feature, fissure, slide feature, or other unusual geologic or
soils condition should be inspected by the soils engineer and/or the engineering
geologist prior to any further grading or construction.
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IJONATHAN L. ROSSI,CONSULTING GEOLOGIST · P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315.
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6.0 L1MITATIONS-
This Engineering Geologic report section has been completed by Jonathan L. Rossi,
Consulting Geologist, Lakeshore Engineering, and licensed or certified subcontractors.
to Lakeshore Engineering. It should be noted that J.L. Rossi, Consulting Geologist has
been retained for the purposes of providing geologic interpretation of existing and
gathered data, to provide the geology portion of the Preliminary Geotechnical
Investigation. Our conclusions and recommendations are based solely on the data
made available to us from one site visit, and information made available by Lakeshore
Engineering. Our work has been performed in accordance with the professional
practices currently accepted in the Geotechnical Consulting Industry today. No warranty
is either expressed or implied.
Should you have any questions conceming this Letter Report of Existing Geologic
Conditions please do not hesitate to contact me at (909) 584-2084.
~~o'
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~ JONATHAN ~j
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SINCERELY YOURS; ROSSI
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ENGINEERING V
' \ Jl GEOLOGIST
~r. No. 1460 ~'(-
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IJONATHAN L. ROSSI,CONSULTING GEOLOGIST. P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315.
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APPENDIX
IJONATHAN L. ROSSI,CONSULTlNG GEOLOGIST · P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315.
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Page 1 of 2
REFERENCES
Association of Engineering Geologist, 1973 - Earthquake Recurrence Intervals on Major Faults
in Southern California, AEG Special Publication October 1973; D.L. Lamar, P.M. Merifield, RJ.
Proctor.
California Division of Mines & Geology - 1974; Map Sheet 23, Maximum Credible Rock
Accelerations; R Greensfelder.
- 1992; Peak Acceleration from Maximum Credible Earthquakes in Ca.; DMG Open-File
Report 92-1; L. Mualchin, & A.L. Jones.
----- 1990; CDMG Map Sheet 54; unpublished for CalTrans.
- 1954; CDMG SR 43; Geology of a Portion of the Elsinore fault Zone, California; John F.
Mann, Jr.
- 1977; CDMG SR 131; Recency & Character of faulting Along the Elsinore Fault Zone in
Southern California; M.P. Kennedy
--- 1988 - Summary Report: Fault Evaluation Program, 1986-1987, Mojaye Desert and Other
Areas - Open File Report 88-1 LA; E.W. Hart, W.A. Bryant, J.E. Kahle, M.W. Manson, &
E.J. Bortugno.
-- 1967 - Geologic Map of California, Map No.1, Santa Ana Sheet; Jennings, C.w.
- 1983 - The 1983 Coalinga, California Earthquakes, CDMG Special Publication 66,
J.H.Bennelt & RW.Sherburne, Editors.
Dudley, Paul H., 1935 - Geology of a Portion of the Perris Block, Southern California;
California Division of Mines, California Journal of Mines & Geology Vol. 31, No.4, October
1935.
Earthquake Engineering Research Institute, 1982 - Ground Motion and Soil Liquefaction
During Earthquakes; H.Bolton Seed & I.M. Idriss. Pub: EERI Berkley, California.; ISBN
0943198240
Earthquake Engineering, 1970 - Robert Wiegel, Coordinating Editor; Pub: Prentice-Hall, N.J.,
ISBN 132226464.
Earthquake Engineering, Damage Assessment and Structural Design, 1983 - S.F. Borg;
Pub:Wiely Heyden, Ltd.; ISBN 0471262617.
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I JONATHA.N L. ROSSI,CONSULTING GEOLOGIST. P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315 .
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REFERENCES
Geological Society of America, 1982 - Neotectonics in Southern California, Guidebook Field
Trip No.3, 4, 14.
1986 - Neotectonics and Faulting in Southem California, Guidebook Field Trips 10, 12,
18.
1987 - Paleoseismicity and Active Tectonics, The Structural Geology and Tectonics
Division, GSA.
Grey, Cliffton H.,Jr, 1961 - Geology of the Corona South Quadrangle and the Santa Ana
Narrows Area, Riverside, Orange & San Bernardino Counties, California., and Mines and
Mineral Deposits of the Corona South Quadrangle, Riverside and Orange Counties, California;
California Division of Mines and Geology Bulletin 178.
lnstution of Mining & Metallurgy, 1981 - Rock Slope Engineering, 3rd Edition; E. Hoek & J.w.
Bray; Pub: lnst. Mining & Metallurgy, London ISBN 0900488573
South Coast Geological Society, 1983 - Geology of the Northern Elsinore Trough, Annual Field
Trip - 1983.
United States Geologic Survey - 1985; PP 1306; 'Earthquake Hazards in the Los Angeles
Region'; J.1. Ziony.
Webber, Harold F.,1977 - Seismic Hazards Related to Geologic Factors, Elsinore and Chino
Fault Zones, Northwestern Riverside County, California.
MAPS UTILIZED
USGS 71/2' Temecula Quadrangle Topographic Map 1975 rev.
USGS 71/2' Bachlor Mtn. Quadrangle Topographic Map 1973 rev.
USGS 71/2' Peachanga Quadrangle Topographic Map 1988 rev.
CDMG Special Study Zone Map (Earthquake Fault Zone Map), Temecula Quadrangle 71/2'
Revised Official Map January 1, 1980.
CDMG Special Study Zone Map (Earthquake Fault Zone Map), Peachanga Quadrangle 71/2'
Revised Official Map January 1, 1980.
- 1967 - Geologic Map of California, Map No.1, Santa Ana Sheet; Jennings, C.W.
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IJONATHAN L. ROSSI,CONSULTlNG GEOLOGIST. P.O. BOX 4018,BIG BEARLAKE,CALlFORNIA 92315.