HomeMy WebLinkAboutParcel Map 9095 Parcel 3 Geotechnical Study
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COrPoration
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-lnspections-Construc\ionMalerialsTesling-LaboratoryTestinll-PercolalionTeslin!)
-Geology-Water Resource Studies . Phase I & II Environmental Site Assessments
ENVIRONMENTAL & GEOTECHNICAL ENGINEERING NETWORK
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LIMITED GEOTECHNICAL STUDY
Proposed Single Family Residence, Parcel 3 of Parcel Map 9095
East Vallejo Road, City of Temecula, County of Riverside, California
Project Number: T1666-LGS
March 26, 1999
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Prepared for:
Mr. Nathan Teng
32217 Carte Tomatan
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c:c":~Temecula, California 92592
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Mr. Nathan Ten9
Project No: T1666-LGS
TABLE OF CONTENTS
Section Numberiand Title
Paae
1.0 SITE DESCRIPTION ....................................................................................................... 1
1.1 Location ............................................................................................................... 1
1.2 Site Review .......................................................................................................... 1
2.0 EARTHWORK RECOMMENDATIONS ..........................................................................2
2.1 Structure Area......................................................................................................2
2.2 Structural Fill........................................................................................................3
3.0 FOUNDATION DESIGN RECOMMENDATIONS ........................................................... 3
3.1 General ............................................................................................................... 3
4.0 RETAINING WALL RECOMMENDATIONS................................................................... 4
4.1 Earth Pressures ...................................................................................................4
4.2 Foundation Design...............................................................................................4
4.3 Subdrain........ ... ...... ................ ....... ..... ................... ..... ... ...... ....... ..... ... ......... ..... .... 4
4.4 Backfill............... ....................... ........ ....... ....... .............. ................. .................... 5
5.0 RECOMMENDATIONS ................................................................................................... 6
5.1 Utility Trench ........................................................................................................6
5.2 Finish Lot Drainage Recommendations............................................................... 6
5.3 Planter Recommendations..................... ........................... ........ ................. .......... 7
5.4 Supplemental Construction Observations and Testing........................................ 7
5.5 Plan Review ......................................................................................................... 7
5.6 Pre-Bid Conference .............................................................................................8
5.7 Pre-Grading Conference. ....................... ........................ ................ ...................... 8
6.0 CLOSURE ..................................................................................................................... 8
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EnGEN Corporation
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COfl~oration
-Soil Engineering and ConsultingSel'lices e Engineering GlXllogy-CompactionTesting
-lnspec\ionseConslruclionMalerialsTestingelaboraloryTesling.Percolalion Tesling
. Geology. Water Resource Studies . Phase I & II Environmental Site Assessments
ENVIRONMENTAL & GEOTECHNICAL ENGINEERING NETWORK
March 26,1999
Mr. Nathan Teng
32217 Carte Tomatan
Temecula, California 92592
(619) 298-6303
LIMITED GEOTECHNICAL STUDY
Proposed Single Family Residence, Parcel 3 of Parcel Map 9095
East Vallejo Road, City of Temecula, County of Riverside, California
Project Number: T1666-LGS
Regarding:
Reference:
1.
Manning Engineering, Grading Plan, Parcel 3 of Parcel Map 9095, 40 scale
grading plan, plans undated.
lilearMr. Teng:
Fi'er your request and signed authorization, a representative of this firm has visited the subject site on
March 23, 1999, to visually observe the subject site.
1.0
1.1
1.2
SITE I PROJECT DESCRIPTION
Location I Proiect Description: The subject property is comprised of approximately six (6)
acres located near the terminus of East Vallejo Road in the City of Temecula. The proposed
development is a one or two story slab-an-grade residential structure, with access driveway
and associated hardscape and landscape improvements.
Site Review: Based on the site visit and literature research, it appears that Pauba Formation
bedrock and shallow depths of slopewash underlie the site and surrounding area. Based on
the density of the underlying earth material type (Pauba Formation) the potential for hazards
associated with liquefaction is considered low. Based on favorable geology and topography,
the potential for hazards associated with rockfalls or landslides is considered low.
The site is partially located within an Alquist-Priolo Earthquake Fault Zone. Although the
proposed pad area is IOg~~1~ outside of the earthquake fault zone, all of the property south of
where the proposed ....cr(~eway connects to the proposed pad area is located
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2.0
2.1
Mr. Nathan Teng
Project No: T1666-LGS
March 1999
Page 2
within the zone. Additional studies should be performed before any human habitable
structures are constructed in the earthquake fault zone. Based on the Referenced No. 1
undated plans, no human occupied structures are planned within the earthquake fault zone.
If plans should change, this office should be notified before construction so that additional
studies can be made (if necessary).
EARTHWORK RECOMMENDATIONS
Structure;Area
. All vegetation should be removed from areas to be graded and should not used in fills.
. It appears that a cuVfill transition traverses the proposed residential structure.
Therefore the cut portion (and shallow fill portion) will need to be overexcavated so
that all footings will be embedded into competent engineered fill. The depth of
overexcavation is expected to be a minimum of three (3) feet below proposed finish
grades and may be deeper depending on exposed conditions encountered during
grading. Overexcavation should extend a minimum of five (5) feet beyond the
perimeter footings.
. An ,alternative to overexcavation would be to deepen all footings into competent native
Pauba Formation bedrock. Footing depths would depend upon the depth of
competent bedrock. Footings should be founded into a minimum of 12-inches of
competent bedrock. Footing depths are expected to be up to one (1) to three (3) feet
below pad grades but may be deeper depending on exposed conditions encountered.
Recompaction of the slab subgrade will be required to mitigate the effects of any
cuVfill transition, by removing 12-inches of soil, scarifying a minimum of 6 inches and
re-compacting a uniform support mat to at least 90 percent of maximum density.
. If the house can be positioned so that the entire footprint is in competent cut, then no
overexcavation or other earthwork will be required within the footprint area. However,
earthwork will be required for yard fills outside the footprint area.
. All areas to receive fill will require removals of loose, incompetent fill slopewash or
weathered bedrock. Depths of removals are expected to be two (2) to three (3) feet
below existing grades but may be deeper depending on exposed conditions
encountered.
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EnGEN Corporation
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3.0
3.1
Mr. Nathan Teng
Project No: T1666-LGS
March 1999
Page 3
. All removal and overexcavation bottoms should be inspected by the Soil Engineer's
representative prior to placing fill. After bottom approval, all bottoms should be
scarified 12-inches, moisture conditioned to near optimum moisture and then
recompacted to a minimum of 90 percent relative compaction.
. A keyway excavated into competent native earth materials should be constructed at
the toe of all proposed fill slopes that are proposed on natural grades of 5: 1
(horizontal to vertical) or steeper. Keyways should be a minimum of 15 feet wide
(equipment width) and tilted a minimum of 2 percent into the hillside. A series of level
benches should be constructed into native competent earth materials on natural
grades of 5: 1 (horizontal to vertical) or steeper prior to placing fill.
. An expansion test should be performed on a representative soil sample retrieved from
the finished pad area subgrade so that foundation recommendations can be verified.
Structural Fill: All fill material, whether on-site material or import, should be approved by the
Project Geotechnical Engineer and/or his representative before placement. All fill should be
free from vegetation, organic material, and other debris. Import fill should be no more
expansive than the existing on-site material. Approved fill material should be placed in
horizontal lifts not exceeding 6.0 to 8.0-inches in thickness and watered or aerated to obtain
near-optimum moisture content (2.0 percent of optimum). Each lift should be spread evenly
and should be thoroughly mixed to ensure uniformity of soil moisture. Structural fill should
meet a minimum relative compaction of 90 percent of maximum dry density based upon
ASTM 01557-78 (90) procedures. Moisture content of fill materials should not vary more
than 2.0 percent of optimum, unless approved by the Project Geotechnical Engineer.
FOUNDATION DESIGN RECOMMENDATIONS
General: Foundations for the proposed structure may consist of conventional column
footings and continuous wall footings founded in competent engineered fill. Minimum footing
depth should be 12-inches below lowest adjacent grade. Recommendations for foundation
design and construction should be provided by the Structural Engineer in accordance with the
latest edition of the UBC and should be based on geotechnical characteristics for a silty sand
(SM) and a low expansion potential for the supporting soils and should not preclude more
restrictive structural requirements.
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EnGEN Corporation
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4.0
4.1
Mr. Nathan T eng
Project No: T1666-LGS
March 1999
Page 4
RETAINING WALL RECOMMENDATIONS:
Earth Pressures: Retaining walls backfilled with non-expansive granular soil (EI=O) or very
low expansive potential materials (Expansion Index of 20 or less) within a zone extending
upward and away from the heel of the footing at a slope of 0.5: 1 (horizontal to vertical) or
flatter can 'be designed to resist the following static lateral soil pressures:
Condition
Level Backfill
2:1 Slope
Active
30 pet
60 pet
45 pet
At Rest
4.2
The on-site materials may be used as backfill within the active I at-rest pressure zone as
defined above. Walls that are free to deflect 0.001 radian at the top should be designed for
the above-recommended active condition. Walls that are not capable of this movement
should be assumed rigid and designed for the at-rest condition. The above values assume
well-drained backfill and no buildup of hydrostatic pressure. Surcharge loads, dead and/or
live, acting on the backfill within a horizontal distance behind the wall should also be should
considered in the design. Uniform surcharge pressures should be applied as an additional
uniform (rectangular) pressure distribution. ,The lateral earth pressure coefficient for a
uniform vertical surcharge load behind the wall is 0.50.
Foundation Desian: Retaining wall footings should be founded to the same depths into
properly compacted fill or competent native earth materials as standard foundations and may
be designed for the same average allowable bearing value across the footing (as long as the
resultant force is located in the middle one-third of the footing), and with the same allowable
static lateral bearing pressure and allowable sliding resistance as developed for conventional
footings.
4.3
Subdrain: A subdrain system should be constructed behind and at the base of all retaining
walls to allow drainage and to prevent the buildup of excessive hydrostatic pressures. Typical
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EnGEN Corporation
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Mr. Nathan Teng
Project No: T1666-LGS
March 1999
Page 5
subdrains 'may include weep holes with a continuous gravel gallery, perforated pipe
surrounded by filter rock, or some other approved system. Gravel galleries and/or filter rock, if
not properly designed and graded for the on-site and/or import materials, should be enclosed
in a geotextile fabric such as Mirafi 140N, Supac 4NP, or a suitable substitute in order to
prevent infiltration of fines and clogging of the system. The perforated pipes should be at least
4.0 inches in diameter. Pipe perforations should be places downward. Gravel filters should
have volume of at least 1.0 cubic foot per lineal foot of pipe. Subdrains should maintain a
positive flow gradient and have outlets that drain in a non-erosive manner. In the case of
Subdrains for basement walls, they need to empty into a sump provided with a submersible
pump activated by a change in the water level.
4.4 Backfill: Backfill directly behind retaining walls (if bac;kfill width is less than 3 feet) may
consist of 0.5 - to 0.75-inch diameter, rounded to subrounded gravel enclosed in a geotextile
fabric such as Mirafi 140N, Supac 4NP, or a suitable substitute or a clean sand (Sand
Equivalent Value greater than 50) water jetted into place to obtain proper compaction. If water
jetting is used, the subdrain system should be in place. Even if water jetting is used, the sand
should be densified to a minimum of 90 percent relative compaction. If the specified density is
not obtained by water jetting, mechanical methods will be required. If other types of soil or
gravel are used for backfill, mechanical compaction methods will be required to obtain a
relative compaction of at least 90 percent of maximum dry density. Backfill directly behind
retaining walls should not be compacted by wheel, track or other rolling by heavy construction
equipment unless the wall is designed for the surcharge loading. If gravel, clean sand or other
imported backfill is used behind retaining walls, the upper 18-inches of backfill in unpaved
areas should consist of typical on-site material compacted to a minimum of 90 percent relative
compaction in order to prevent the influx of surface runoff into the granular backfill and into the
subdrain system. Maximum dry density and optimum moisture content for backfill materials
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EnGEN Corporation
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5.2
Mr. Nathan Teng
Project No: T1666-LGS
March 1999
Page 6
should be determined in accordance with ASTM 01557-78(90) procedures.
5.0
5.1
RECOMMENDATIONS
Utility Trench Recommendations: Utility trenches within the zone of influence of
foundations or under building floor slabs, hardscape, and/or pavement areas should be
backfilled with properly compacted soil. It is recommended that all utility trenches excavated
to depths of 5.0 feet or deeper be cut back to an inclination not steeper than 1: 1 (horizontal to
vertical) or be adequately shored during construction. Where interior or exterior utility
trenches are proposed parallel and/or perpendicular to any building footing, the bottom of the
trench should not be located below a 1:1 plane projected downward from the outside bottom
edge of the adjacent footing unless the utility lines are designed for the footing surcharge
loads. Backfill material should be placed in a lift thickness appropriate for the type of backfill
material and compaction equipment used. Backfill material should be compacted to a
minimum :of 90 percent relative compaction by mechanical means. Jetting of the backfill
material will not be considered a satisfactory method for compaction. Maximum dry density
and optimum moisture content for backfill material should be determined according to ASTM
01557-78(90) procedures.
Finish Lot Drainaqe Recommendations: Finish lot surface gradients in unpaved areas
should be provided next to tops of slopes and buildings to direct surface water away from
foundations and slabs and from flowing over the tops of slopes. The surface water should be
directed toward suitable drainage facilities. Ponding of surface water should not be allowed
next to structures or on pavements. In unpaved areas, a minimum positive gradient of 2.0
percent away from the structures and tops of slopes for a minimum distance of 5.0 feet and a
minimum of 1.0 percent pad drainage off the properly in a non-erosive manner should be
provided.
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EnGEN Corporation
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5.3
5.4
Mr. Nathan Tang
Project No: T1666-LGS
March 1999
Page 7
Planter Recommendations: Planters around the perimeter of the structure should be
designed with proper surface slope to ensure that adequate drainage is maintained and
minimal irrigation water is allowed to percolate into the soils underlying the building.
Supplemental Construction Observations and Testina: Any subsequent grading for
development of the subject property should be performed under engineering observation and
testing performed by EnGEN Corporation. Subsequent grading includes, but is not limited to,
any additional overexcavation of cut and/or cut/fill transitions, fill placement, and excavation of
temporary and permanent cut and fill slopes. In addition, EnGEN Corporation, should
observe all foundation excavations. Observations should be made prior to installation of
concrete forms and/or reinforcing steel so as to verify and/or modify, if necessary, the
conclusions and recommendations in this report. Observations of overexcavation cuts, fill
placement, finish grading, utility or other trench backfill, pavement subgrade and base course,
retaining wall backfill, slab presaturation, or other earthwork completed for the development
of subject property should be performed by EnGEN Corporation If any of the observations
and testil'1g to verify site geotechnical conditions are not performed by EnGEN Corporation,
liability for the safety and performance of the development is limited to the actual portions of
the project observed and/or tested by EnGEN Corporation.
5.5
Plan Review: Subsequent to formulation of final plans and specifications for the project but
before bids for construction are requested, grading and foundation plans for the proposed
development should be reviewed by EnGEN Corporation to verify compatibility with site
geotechnical conditions and conformance with the recommendations contained in this report.
If EnGEN Corporation is not accorded the opportunity to make the recommended review,
we will assume no responsibility for misinterpretation of the recommendations presented in
this report.
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EnGEN Corporation
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5.6
5.7
6.0
Mr. Nathan Teng
Project No: T1666-LGS
March 1999
Page 8
Pre-Bid Conference: It is recommended that a pre-bid conference be held with the owner or
an authorized representative, the Project Architect, the Project Civil Engineer, the Project
Geotechnical Engineer and the proposed contractors present. This conference will provide
continuity in the bidding process and clarify questions relative to the supplemental grading
and construction requirements of the project.
Pre-Grading Conference: Before the start of any grading, a conference should be held
with the owner or an authorized representative, the contractor, the Project Architect, the
Project Civil Engineer, and the Project Geotechnical Engineer present. The purpose of this
meeting should be to clarify questions relating to the intent of the supplemental grading
recommendations and to verify that the project specifications comply with the
recommendations of this geotechnical engineering report. Any special grading procedures
and/or difficulties proposed by the contractor can also be discussed at that time.
CLOSURE: This report has been prepared for use by the parties or project named or
described in this document. It mayor may not contain sufficient information for other parties
or purposes. In the event that changes in the assumed nature, design, or location of the
proposed ,structure and/or project as described in this report, are planned, the conclusions
and recommendations contained in this report will not be considered valid unless the changes
are reviewed and the conclusions and recommendations of this report modified or verified in
writing. This study was conducted in general accordance with the applicable standards of our
profession and the accepted soil and foundation engineering principles and practices at the
time this report was prepared. No other warranty, implied or expressed beyond the
representations of this report, is made. Although every effort has been made to obtain
information regarding the geotechnical and subsurface conditions of the site, limitations exist
with respect to the knowledge of unknown regional or localized off-site conditions that may
have an impact at the site. The recommendations presented in this report are valid as of the
EnGEN Corporation
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Mr. Nathan Teng
Project No: T1666-LGS
March 1999
Page 9
date of the report. However, changes in the conditions of a property can occur with the
passage of time, whether they are due to natural processes or to the works of man on this
and/or adjacent properties. If conditions are observed or information becomes available
during the design and construction process that are not reflected in this report, EnGEN
Corporation should be notified so that supplemental evaluations can be performed and the
conclusions and recommendations presented in this report can be modified or verified in
writing. Changes in applicable or appropriate standards of care or practice occur, whether
they result from legislation or the broadening of knowledge and experience. Accordingly, the
conclusions and recommendations presented in this report may be invalidated, wholly or in
part, by changes outside of the control of EnGEN Corporation which occur in the future.
Thank you for the opportunity to provide our services. Often, because of design and construction
details which occur on a project, questions arise concerning the geotechnical conditions on the site.
If we can be of further service or you should have questions regarding this report, please do not
tnesitate to contact this office at your convenience. Because of our involvement in the project to date,
we would be pleased to discuss engineering testing and observation services that may be applicable
on!the project.
TD/OB:aa
Distribution: (4) Addressee
F;ILE: EnGENIReportingIGSIT1666LGS Nathan Teng. Umited Geotechnical Study
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EnGEN Corporation