HomeMy WebLinkAboutGeotechnicalInvestigation(Dec.16,1988)
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Converse Consultants Inland Empire
Consulting Engineers
and Geologists
630 East Brier Drive, Suite 100
San Bernardino, California 9240B
Telephone 714/889.8004
FAX 714 889.4830
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GEOTECHNICAL INVESTIGATION
TENTATIVE TRACT 24136
PLANNING AREA 8
PORTION OF THE MEADOWS
RANCHO CALIFORNIA, CALIFORNIA
PREPARED FOR
Rancho California Development Company
Post Office Box 755
28250 Ynez Road
Rancho California, California 92390
CCIE Project No. 88-81-148-01-B
December 16, 1988
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A Wholly Owned Subsidiary of
The Converse Professional Group
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Converse Consultants Inland Empire
Consulting Engineers
and Geologists
630 East Brier Drive, Suite 100
San Bernardino, California 92408
Telephone 714/8898004
FAX 714 889.4830
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December 16, 1988
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Rancho California Development Company
Post Office Box 755
28250 Ynez Road
Rancho California, California 92390
Attention: Mr. Csaba F. Ko
Subject: GEOTECHNICAL INVESTIGATION
Tentative Tract 24136
Planning Area 8
Western Portion of "The Meadows"
Rancho California, California
CCIE Project No. 88-81-148-01-B
Gentlemen:
Enclosed are the findings of our geotechnical investigation
performed for Planning Area 8 which is a portion of The Meadows
Master Planned Community in Rancho California, California. A
preliminary "Slope Stability Analysis" letter dated December 5,
1988 was written for this tract to expedite the County submittal
process.
Subsurface materi a 1 s encountered in the exploratory excavati ons
generally consisted of loose to medium dense granular sediments
and soft sandstone bedrock of the Pauba Formation. Groundwater
was not encountered in the exploratory borings.
Results of our investigation indicate that the site is suitable
for the proposed residential development, provided that the
recommendations contained herein are incorporated into final
development plans. Development of th,e' tract will involve
conventional mass grading. Anticipated'depths of overexcavation
in proposed fill areas are indicated on the enclosed maps and
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A Wholly Owned Subsidiary of
The Converse Professional Group
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Rancho California Development Company
CCIE Project No. 88-81-148-01-B
December 16, 1988
Page 2
discussed in the appropriate sections of this report. Con-
ventional 2:1 (horizontal to vertical) cut and fill fill slopes'
are proposed, with structure setbacks as recommended herein.
Spread footi ngs may be used to support the proposed res i denti a 1
structures.
We appreciate this opportunity to be of service. If you have any
questi ons, please feel free to contact the undersi gned or Mr.
David Simon.
Very truly yours,
CONVERSE CONSULTANTS INLAND EMPIRE
&:W~:e~
President
RMP/DBS/TCB:88aa
Dist: 5/Addressee
l/Robert Bein, William Frost and Associates
l/Dr. Roy J. Shlemon
Converse Consultants Inland Empire
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Converse Consultants Inland Empire
PROFESSIONAL REGISTRATION
For: CCIE Project No. 88-81-148-01-B
Dated: December '16, 1988
Thi s report has been prepared by the
staff of Converse Consultants Inland
Empire under the professional direction
of the Senior Geologist and Project
Engineer whose seals and signatures
appear hereon.
The findings, recommendationsj speci-
fications or professional oplnlons are
presented, within the limits prescribed
by the client, after being prepared in
accordance wi th generally accepted
professional engineering and geologic
practice. There is no other warranty,
either express or implied.
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TABLE OF CONTENTS
GEOTECHNICAL INVESTIGATION
PORTION OF THE MEADOWS
RANCHO CALIFORNIA, CALIFORNIA
CCIE PROJECT No. 88-81-148-01-B
Page
1.0 INTRODUCTION. . . .
2.0 PROJECT DESCRIPTION
2.1 Existing Site Conditions
2.2 Proposed Development
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4.0 SITE GEOLOGY. . . . .. ....
4.1 Earth Materials.. . . . . . .
4.1.1 Pauba Formation (Map Symbol
4.1.2 Colluvium (Map Symbol Qcol)
4.1.3 Recent Alluvium (Map Symbol
4.1.4 Topsoil. . . . .
4.2 Groundwater. . . . . .. . . .
4.3 Faulting and Seismicity. . . . . .
4.4 Subsurface Variations. . . . . . .
Qp)
. . .
Qal) .
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3.0 SCOPE OF INVESTIGATION. .
3.1 Site Reconnaissance.
3.2 Field Exploration.
3.3 Laboratory Testing. .
3.4 Research, Analyses and Report.
5.0 CONCLUSIONS AND TRACT DEVELOPMENT CONSIDERATIONS.
6.0 EARTHWORK/SITE GRADING RECOMMENDATIONS.
6.1 General. . . . . . . . .
6.2 Removals/Overexcavation.
6.3 Subdrains. . . . . . . .
6.4 Permanent Cut Slopes . .
6.5 Permanent Fill Slopes. . . .
6.6 Temporary Sloped Excavations
6.7 Utility Trench Backfill. . .
6.8 Shrinkage and Subsidence . .
6.9 Site Drainage. . . . . . . . . .
6.10 Slope Protection and Maintenance
6.11 Asphalt Pavements. . . . . .
7.0 STRUCTURAL DESIGN RECOMMENDATIONS
7.1 Residential Foundation Design Criteria
7.2 Slabs-on-Grade. . . .
7.3 Appurtenant Facilities
7.4 Corrosivity. . . . . .
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Table of Contents
CCIE Project No. 88-81-148-01-B
Continued
Page
8.0 GEOTECHNICAL SERVICES DURING CONSTRUCTION
9.0 CLOSURE
. . . . . . . . . . . . . . . . .
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REFERENCES
Drawing 1 "Geologic Map"
Drawing 2 "Tentative Tract Geologic Map"
Appendix A - Field Exploration
Appendix B - Laboratory Test Program
Appendix C - Recommended Earthwork Specifications
Appendix D - Stability Analyses
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1.0 INTRODUCTION
This report presents the findings of our geotechnical investigation applicable
to tentative tract 24136 which is a portion of the western 707 acres that
comprise The Meadows Master Planned Community at Rancho California. The 707
acres are located south of Pauba Road, north of California State Highway 79,
east of Margarita Road and west of proposed Buecking Parkway. Tentative Tract
24136 encompasses approximately 99.8 acres of The Meadows project as shown on
the site Location Map, Figure 1.
The purpose of thi s i nvesti gati on was to evaluate subsurface conditi ons and
pertinent engineering properties of the encountered materials such that
recommendations regarding general site grading, slope stability and pre-
1 iminary foundation design criteria can be provided for submittal of eight
Tentative Tract Maps to the County of Riverside. Converse Consultants Inland
Empire (CCIE) performed a concurrent investigation to evaluate the lique-
faction potential at the southerly portion of the tract (Converse, 1988).
It is our understanding that the subject tract will be developed according to
Specific Plan 219, The Meadows at Rancho California, dated September 6, 1988.
We understand that the proposed development of "The Meadows" will consist of a
combination of residential, commercial, schools, a neighborhood park, Day Care
Center, greenbelt areas and an extensive circulation road network within the
comprehensive plan. Vesting Tentative Tract Map 24136, addressed herein will
be developed exclusively for residential use.
Pertinent geologic and geotechnical data generated from this investigation of
the 707 acre western portion of The Meadows project together with the location
of explorations are shown on Drawing 1, titled "Geologic Map" (pocket).
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REFERENCE:
Alquist-Priolo Special Studies Zon~ Mop
Pechanga Quadrangle, Colifornia Division
of Mine ond Geology, Jonuory 1, 1980
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SCALE IN FEET
SITE LOCATION MAP
WESTERN PORTION OF "THE MEADOWS"
Roncho California, Californici
for: Rancho California Development Company
@ 'CoQye!:.se...,9ons~ltali!; Inliinct' Empire
Project No.
88-81-148-01
Figure No.
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2.0 PROJECT DESCRIPTION
2.1 Existing Site Conditions
Tentative Tract 24136 is located within the west-central region of The Meadows'
Development. The approximately 99.8-acre...site is bounded on the north by the
undeveloped Tentative Tract Nos. 24131, 24133, and 24135; on the east by an
undeveloped hilly region scheduled to become Tentative Tract No. 24184; on the
south by a south sloping region which is scheduled to become Tentative Tracts
24130, and 24137; and on the west by an existing residence and the proposed
Joan F. Sparkman Elementary School, both of which are fronted on Margarita
Road. Currently, the site is characterized by several hills, with a drainage
running along the northwestern boundary of the tract draining southwest, and a
minor "Y" shaped drainage draining south in the south-central region of the
tract. In general, the site topography slopes down from the northeast to the
southwest with as much as 170 feet of relief across the site. Site elevations
range from approximately 1,237 feet (lot 33), to elevation 1,067 feet (lot
149). The site has a moderate growth of weeds, shrubs, and grasses, with
occasional barbed wire fences traversing the site. In general, the site has
not been previously developed.
2.2 Proposed Development
Based upon Tentative Tract Map 24136, provided by Robert Bein, William Frost
and Associates, dated December 4, 1988, (scale I" = 200'), site earthwork,
exclusive of any potential overexcavations, is anticipated to consist of cuts
on the order of 70 feet (Lot 33) and fills on the order of 32 feet in
thickness (Lot 237). This map was used as the base map for Drawing 2,
Tentative Tract Geologic Map (pocket).
As depicted on Drawing 2, 400 residential lots are proposed. Slopes on the
order of 30 feet in height are proposed. No retairing walls are anticipated.
For the purposes of this report, it is assumed that the residential structures
will consist of one to two story wood frame single family homes. All of the
proposed homes are assumed to have concrete slabs-on-grade, without basements.
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3.0 SCOPE OF INVESTIGATION
3.1 Site Reconnaissance
Our geologist performed a site reconnaissance of the property for mapping of
geologic units and pertinent surficial features (Drawings 1 and 2). Aerial
photographs of the site vicinity were examined stereoscopically to assist the
geologic reconnaissance. A set of aerial photographs was obtained from
Riverside County Flood Control District taken in 1983 (see references).
3.2 Field Exploration
A total of 23 exploratory bori ng and 55 exploratory trenches were excavated
within the 707 acres that comprise the western portion of The Meadows
investigated. Borings were drilled using a bucket auger drill rig and the
trenches were excavated using a rubber-tired backhoe. All excavations were
visually logged by our field personnel who carefully described the materials
encountered. Selected borings were entered by a CCIE geologist who carefully
observed and documented the exposed materials.
Relatively undisturbed and bulk samples of representative materials
encountered were obta i ned from the borings. A descri pti on of the fi el d
exploration and sampling program are presented in Appendix A.
Approximate locations of the exploratory borings and trenches excavated
for the 707-acre portion of The Meadows project are shown on Drawing 1.
Approximate locations of the exploratory borings and trenches within Tentative
Tract 24136, as well as exploratory excavations within immediately adjacent
tracts utilized for this analysis of Tentative Tract 24136. are shown on
Drawi ng 2.
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3.3 Laboratory Testing
Samples were tested in the laboratory to aid in the classification and to
determine certain engineering properties of the site soils and bedrock. These
tests include:
. in-situ dry unit weight and moisture content;
. maximum density and optimum moisture curves;
. direct shear tests; ,
. moisture sensitivity (collapse) tests;
. consolidation tests;
. R-value test; and
. pH, resistivity, and soluble sulfate and chloride testing.
A description of the laboratory test methods and test results are presented in
Appendix B. Moisture and density data are presented on the boring summary
sheets of Appendix A.
3.4 Research, Analyses and Report
In addition to pertinent published geologic literature concerning rock units
of the area, unpublished geotechnical reports were also reviewed, particularly
those of Paci fi c Soil sEngi neeri ng, Inc. (1987a, 1987b, 1987c). Perti nent
publications reviewed for this investigation are included in the list of
references.
This report was written to present the findings of this geotechnical investi-
gation for the tentative tract, and to provide recommendations for the
proposed development. Based upon the field and laboratory findings, slope
stability analyses were performed, as presented in Appendix D.
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4.0 SITE GEOLOGY
A general descri phon of the subsurface conditi ons and vari ous materi a 1 s
encountered at the site during field exploration is presented in this section.
Also, a discussion of site specific geologic hazards is presented below.
4.1 Earth Materials
The site is underlain by bedrock materials of the Pauba Formation, colluvium,
and alluvium. These, in turn, are locally mantled by a thin veneer of
topsoil. Areal distribution of the earth materials is shown on the geologic
maps (Drawings 1 and 2), and these materials are described below from
geologically oldest to youngest.
4.1.1 Pauba Formation (Map Symbol Qp): The Pauba Formation of late-
Pleistocene age (Kennedy, 1977) underlies the site. In general, the
formation consists of distal alluvial fan and braided channel deposits,
with numerous intra-formation unconformities. Sedimentary features
characteristic of the depositional environment such as channel lag, scour
and fill and cross-bedding were observed in trench and boring exposures.
Within the subject site, lithology of the Pauba Formation is highly
variable, consisting of poorly interbedded to massive, moderately to well
con sol idated, fine to coarse sandstones. The sandstones are alluvial
channe l-type depos i ts with 1 enses of gravelly sandstone, siltstone and
silty claystone.
Bedrock structures within the Pauba Formation can vary over a relatively
short distance. Bedding attitudes recorded at the site indicate strikes
being roughly east-west, with dips to the south at 50 to 100. Numerous
horizontal and gradational bedding boundaries ~ere also observed.
4.1.2 Colluvium (Map Symbol Qcol): Colluvial materials were encountered
withi n the northeastern regi on of the tract, as shown on Drawi ng 2.
These materials were classified as silty sand with minor amounts of sandy
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silt. The colluvium was dry to slightly moist, loose to medium dense or
firm, and contained numerous rootcasts and pinhole voids.
4.1:3 Recent Alluvium (Map Symbol Qal): Recent alluvium was encountered
within the drainage channels as shown on Drawings 1 and 2. These
materials were classified as silty sand, sand, and sandy silt. The
alluvium was dry to moist, loose to medium dense, and contained numerous
root casts and pinhole voids.
4.1.4 Topsoil: Topsoil materials mantled the majority of the site and
ranged in thickness, where observed, from 1 to 1 1/2 feet. These soils,
not differenti ated on the geo 1 ogi c maps, cons i st of silty sands, are
generally loose to medium dense and contain numerous root casts and
pinhole voids.
4.2 Groundwater
Groundwater was not encountered in the exploratory borings drilled within
Tentative Tract 24136.
4.3 Faulting and Seismicity
A site-specific fault investigation (which included 4,000 feet of fault
trenching) was performed for the 1,377 acres that comprise The Meadows project
by Pacific Soils Engineering (1987b). Other faults or possible fault-related
features in addition to those documented in the Pacific Soils Engineering
Investigation (1987b) were not observed during field exploration,
reconnaissance or analysis of aerial photographs.
The findings of the Pacific Soils Engineering study (1987b) indicate that the
faults within The Meadows project do not displace Holocene-age (about 11,000
years before present) sediments. As such, according to the California
Division of Mines and Geology (CDMG), these faults, are not considered active,
and building restrictions are not mandated.
In summary, there are no known active faults trending towards or through the
site. Also, the subject tract is not situated within a currently designated
State of California Alquist-Priolo Special Studies Zone (see Figure 1 for
regional active fault).
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During our concurrent liquefaction investigation (Converse, 1988), major
faults within a 100-km (62-mile) radius of the site were considered in regard
to generating significant ground shaking at The Meadows project. The faults
in Table 4-2 are those most likely to cause ground shaking at the site in case
of a major earthquake [Richter magnitude (M) greater than 6.0]. Table 4-2
also summarizes important seismic characteristics for each causative fault.
TABLE 4-2
SEISMIC CHARACTERISTICS OF REGIONAL FAULTS
HORIZONTAL GROUND MOTION
PARAMETERS
MINIMUM MAX I MUM* MAXIMUM PEAK** DURATIONt
SITE CREDIBLE GROUNO OF STRONG
OISTANCE MAGNITUDE ACCELERATION SHAKING
FAULT (mil EARTHQUAKE (g) (seconds)
Elsinore 1 1/2 7.5 0.63 25 - 3S
(Wildomar Branch)
San Jacinto 20 7.5 0.30 23 - 32
Whittier 33 7.5 0.10 21 - 30
San Andreas (South) 36 7.5 0.17 20 - 25
El Modena 43 6.S 0.07 5 - 10
San Andreas (Central) 43 8.25 0.21 18 - 2S
Peralta Hills 46 6.S 0.07 4 - 8
Sierra Madre (Cucamonga) 59 7.0 O.OB 7 - 11
Norwalk 55 6.5 O.OS <5
* From Greensfelder (1974).
** From Seed and Idr;ss (1982).
t From Bolt (1973).
As is the case for most regions of Southern California, groundshaking
resulting from earthquakes along nearby and di stant faults wi 11 occur. Duri ng
the life of the project, seismic activity associated with active faults in the
region (particularly the Elsinore, San Jacinto and San Andreas Fault Systems)
may generate moderate to strong ground shaking at the site.
The occurrences of ground acceleration during
period were calculated for the site area
an average 100-year and 50-year
as part of the liquefaction
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investigation (Converse, 1988). Probable maximum horizontal ground accelera-
ti ons are O. 29g once on the average every 100 years and O. 23g once on the
average every 50 years.
4.4 Subsurface Variations
Based on the results of our subsurface exploration and experience, variations
in the continuity and depth of subsoil and bedrock deposits should be
anticipated. Due to the nature and depositional characteristics of the
natural soils at the site, care should be exercised in interpolating or
extrapolating subsurface conditions between or beyond test borings and
trenches. Vari ati ons in groundwater 1 eve 1 s can be expected due to seasonal
changes, or artificial changes such as variable regional irrigation, changes
in groundwater pumping, and/or variations in the Vail Lake Reservoir
downstream discharge.
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5.0 CONCLUSIONS AND TRACT DEVELOPMENT CONSIDERATIONS
The results of this investigation indicate that Tentative Tract 24136 is
suitable for its intended usage and may be developed as planned.
As depicted on Figure 2, lots with fill thickness of 32 feet are proposed, and,
lots which transition from cut to fill are also proposed. Of geotechnical
concern for this project is the potential for differential settlement due to
the variable fill thicknesses proposed to underly the various pads. Much of
the residential distress which occurs in hillside graded lots is due to
changes in moisture in the fill mass. Therefore subdrains should be installed
as depicted on Figure 2. Also landscape irrigation and surface drainage
should be controlled and provided such that the fill mass does not become
excessively moist or wet. Any appurtenant structures such as swimming pools,
retaining walls, grade changes and/or landscaping irrigation systems should be
designed such that these changes do not adversely affect the graded lot
stability or drainage. Therefore, it is strongly recommended that these
changes be reviewed by CCIE or an experienced Geotechnical Engineer and/or
Certified Engineering Geologist. These tract development considerations are
described further in the following sections.
Design recommendations are presented
structural design, for the development
for additional geotechnical services,
been approved by appropriate governing
below for earthwork/site grading and
proposed on Drawing 2. Recommendations
to be performed after thi s report has
agencies, are also provided.
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6.0 EARTHWORK/SITE GRADING RECOMMENDATIONS
6.1 General
Site grading is expected to consist of cuts, removals and fill operations to
prepare building pad areas. Cuts on the order of 70 feet (lot 33) are
proposed. Maximum fills are expected to be on the order of about 32 feet (lot
237), based on site grade information as depicted on Drawing 2. Grading is
also expected to include backfill for utility trenches. Loose backfill
exp 1 oratory trenches located throughout the site wi 11 requi re overexcavati on
and recompaction prior to the placement of structural fills. See Drawing 1
for approximate locations of trenches. All fill should be placed in
accordance with the recommendati ons presented in Appendi xC, ti tl ed
"Recommended Earthwork Specifications". All structural fill should be
compacted to at least 90% relative compaction (ASTM D1557-78).
To reduce the potential for differential settlement across cut/fill transition
lots, the cut portion of the lot should be overexcavated 3 feet below final
grade. A fill zone "buffer" should then be backfilled to finish grade. All
fi 11 shoul d be properly benched into fi rm and unyi el di ng nati ve bedrock
materials, which are expected to consist solely of the Pauba Formation. In
areas where fill is to be placed above cut slopes, the fill slope should be
keyed into the firm and undisturbed bedrock, as discussed in Appendix C, and
depicted on Drawing C-2, titled "Typical Fill Above Cut Slope".
Grading recommendati ons for removals, subdrai ns, permanent slopes, temporary
sloped excavations, utility trench backfill, and site drainage are presented
below. Stability calculations for the anticipated slopes are presented in
Appendix D, "Stabil ity Analyses".
6.2 Removals/Overexcavation
All surface trash and vegetati on (i nc 1 udi ng, but not 1 imi ted to, heavy weed '
growth, trees, stumps, logs, and roots) should be removed from the areas to be
graded. Organic materials resulting from the clearing and grubbing operations
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should be hauled off the site.
hauled off site or stockpiled
methods in deeper fill areas.
Non-organic debris from site clearing may be
for crushing and/or placement by approved
Removal of all topsoil, and loose shallow alluvium and/or disturbed bedrock
(such as the shallow collapsible silty sands in ravines) will be necessary
pri or to placement of structural fi 11 s . Although not encountered in CCIE
explorations, any existing fill should be excavated. Recommended removal
depths are depicted on Drawing 2 in triangles adjacent to the explorations,
and discussed below:
. Ravine Areas: Removal depths will vary from 2 to 10 feet, with possible
localized areas of deeper removals.
. Areas to Receive Fill Outside of Ravine Areas: Removal depths will
generally vary from 3 to 5 feet, with possible localized areas of deeper
co 11 uvi a 1 removals. The topsoi 1 /s 1 opewash may be removed by stri ppi ng,
heavh benching during grading, or a combination of both stripping and
benc ing.
. Exp 1 orati on Trenches: All exploratory trenches were loosely backfi 11 ed
and will requi re overexcavati on and recompacti on for new improvements
support. Approximate locations of the trenches are shown on Drawing 1.
The bottom of the excavated areas must be observed by a CCIE representative
prior to placement of new fill. Soils' removed during the overexcavation
procedures may be utilized as compacted fill, provided they have been stripped
of organics and other deleterious materials. All proposed fills should be
placed on competent native materials as determined in the field by a CCIE
representative and in accordance with the specifications presented in Appendix
C, titled "Recommended Earthwork Specifications".
6.3 Subdrains
A subdrain should be installed within the northwesterly ravine area, sub-
sequent to alluvial removals and prior to fill pla~ement. Discharge from this
subdrain should be directed to the existing storm. drain located along
proposed Pio Pi co Road. A typical subdrain detail is provided in Appendix C.
Subdrains should generally be installed where shown on Drawing 2, but may be
modified by the Certified Engineering Geologist and project Civil Engineer,
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based upon post removal observations. All subdrain devices should be
accurately located by the project Land Surveyor.
6.4 Permanent Cut Slopes
Permanent cut slopes up to 35 feet are anticipated (lot 277). As shown in
Appendix D, cut slopes in the encountered materials not exceeding 35 feet in
height and cut no steeper than 2:1 (horizontal :vertical) have a calculated
factor-of-safety (FS) greater than 1.5. Cut slope ratios should not be
steeper than 2:1 (horizontal:vertical). A primary concern for cut slopes on
this site is the high potential for erosion of the sandy material, and the
resultant surficial instability. Structures should be set back from slopes as
shown on Figure 29-1 of the 1988 Edition of the Uniform Building Code (UBC).
Cut slopes should be observed during grading by a Certified Engineering
Geol ogi st (CEG) to determi ne if any adversely ori ented planes of weakness
(i .e., claystone or siltstone beds) are exposed. If these materials are
exposed in a proposed cut slope during grading and are found to be adversely
oriented, a buttress or stabilization fill may be required.
6.5 Permanent Fill Slopes
Proposed fill slopes should be constructed with slope ratios no steeper than
2:1 (horizontal:vertical). Fill slopes in excess of 35 feet in height are not
anticipated. Fill slopes should be properly compacted out to the slope face.
This may be achieved by either overbuilding and cutting back to the compacted
core, or other methods which meet the intent of the project specifications.
Assuming that fill slopes are properly compacted to the slope face, are graded
no steeper than 2:1 (horizontal:vertical) and are no taller than 35 feet in
height, the calculated factor-of-safety for compacted fill slopes is greater
than 1.5.
Fill slopes higher,than 30 feet should be terrace~ as recommended in Section
7012 of the Uniform Building Code '(1988 Edition). Structures should be set
back from graded slopes in accordance with Chapter 29 (UBC Figure 29-1) of the
Uniform Buil di ng Code (UCB). Where fill is proposed over cut slopes, fi 11
should be benched into the bedrock as shown on Drawing C-2, in Appendix C.
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6.6 Temporary Sloped Excavations
The use of sloped excavations may be applicable where plan dimensions for
excavation are not constrained by property lines, existing streets, or other
structures. Where constraints exist, temporary. shoring or a combination of
slopes and shoring will be required. Recommendations for shoring design will
be presented separately from this report, if requested. Excavations adjacent
to existing roadways should not undercut the existing embankments.
Based upon soils encountered in the test borings, it is our Op1nlOn that
sloped temporary excavations may be made according to the slope ratios
presented in the following table.
TEMPORARY EXCAVATION SLOPES
MAXIMUM
DEPTH OF CUT
(ft)
o - 5
5 - 15
1S - SO
MAXIMUM SLOPE RATIO*
(horizontal:vertical)
vertical to 1/2:1
3/4:1 to 1 1/4:1
1.5:1 to 2:1
* Selection of temporary slope ratios
shaul d be made by the gradi 09
contractor based on actual materials
encountered during excavation.
Slope ratios given above are assumed to be uniform from top to toe of slope.
Sandy surfaces exposed in sloped excava ti ons shoul d be kept moi st but not
saturated to retard ravelling and sloughing during construction. Adequate
provisions should be made to protect the slopes from erosion during periods of
rainfall. Surcharge loads should not be permitted within 10 feet of the top
of slope, or at least one-third the slope height.
6.7 Utility Trench Backfill
Buried utility conduits should be bedded and backfilled around the conduit in
accordance with the project specifications. Materials may be flooded/jetted
around large-diameter pipelines, below the spring line. Care should be taken
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not to move or damage utilities during compaction operations. Where conduit
underl ies concrete slabs-on-grade and pavement or is adjacent to proposed
structures, the remaining trench backfill above the conduit should be placed
and compacted in accordance with Appendix C.
6.8 Shrinkage and Subsidence
Based on our test results, an average shrinkage value of 8% is considered
appropriate to estimate the loss in volume during recompaction of existing
loose shallow soils. However, shrinkage due to recompaction may vary from
negligible to 17% by volume. Volume losses due to stripping of organics
should be included during the calculations of earthwork quantities. Sub-
sidence due to construction equipment activity will range from about 0.1 to
0.3 foot. These estimates are based upon the assumption that all removals and
compaction is performed as recommended herein.
6.9 Site Drainage
Adequate positive drainage should be provided away from structures to prevent
ponding and to reduce percolation of water into the foundation soils. A
desirable slope for surface drainage is 2% to 4% in landscaped areas and 1% to
2% in paved areas. Pl anters and 1 andscaped areas adjacent to the buil di ng
perimeter should be designed to minimize water infiltration into the subgrade
soils. Gutters and downspouts should be installed on the roof, and runoff
should be directed to the street through non-erosive devices. Surface
drainage should be directed to suitable non-erosive devices. Slope drainage
devices should be constructed in accordance with Chapter 70 of the Uniform
Building Code (1988 Edition). Lot drainage should preclude the possibility of
flow over slope faces, wi th the use of brow di tches, earth berms and other
methods.
6.10 Slope Protection and Maintenance
Proposed slopes should be planted as soon as possible after construction.
Slopes wi 11 requi re maintenance through time to perform in a sati sfactory
manner. In most cases, lot and site maintenance can be provided along with
normal care of the grounds and landscaping. Costs of maintenance is less
expensive than repair resulting from neglect.
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Most hillside lot problems are associated with water. Uncontrolled water from
a broken pipe, excess landscape watering, or exceptionally wet weather causes
most damage. Drainage and erosion control are important aspects of slope
stability and the provisions incorporated into the graded site must not be
altered without competent professional advice.
Terrace drains
ma i nta i ned and
caus i ng eros i on.
soil which could
and brow ditches on the slopes should be periodically
kept clear so that water will not overflow onto the slope,
All subdrains should be kept open and clear of debris and
block them.
Landscaping on the slopes should disturb the soil as little as possible and
utilize drought resistant plants that require a minimum amount of landscape
irrigation. Wet spots on or around the site should be noted and brought to
the attention of the soils engineer. These may be natural seeps or an
indication of broken water or sewer lines.
Watering should be limited or stopped altogether during the rainy season when
little irrigation is required. Over-saturation of the ground can cause
subsidence within subsurface soils. Slopes should not be over-irrigated.
Ground cover and other vegetation will require moisture during the hot summer
months; but, during the wet season, irrigation can cause ground cover to pull
loose. This not only destroys the cover, but also starts serious erosion. It
is suggested to consult a profess i ona 1 1 andscape architect for p 1 anti ng and
irrigation recommendations.
6.11 Asphalt Pavements ~~
Asphalt pavement sections have been designed based on an~R-value of 25:..1 Final
street structural sect10ns should be provided by CCIE ba~~~al soil
conditi ons after gradi ng. Based upon the CAL TRANS Traffi c Indexes (TI' s)
provided below, either full depth or composite ,asphalt and base pavement
sections may be used as tabulated below:
CALTRANS
TRAFFIC INDEX
4
5
6
7
ASPHALT PAVEMENT SECTIONS
ASPHALT OVER BASE
BASE (,n) ASPHALT (in)
4 2 1/2
6 3
7 4
11 4
FULL DEPTH
ASPHALT (in)
5
6 1/2
7 1/2
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In areas to support asphaltic pavement, the subgrade should be recompacted to
a depth of at least one foot below the final subgrade as recommended in
Appendix C. At the time of placing pavements, the subgrade should be firm and
unyielding during proof rolling, and be within 2% to 3% of optimum moisture.
All base material should be compacted to a minimum of 95% of the ASTM D1557-78
laboratory maximum dry density. Base course should consist of CALTRANS Class
II aggregate base or equivalent. Placement of full depth asphalt will require
that the compacted subgrade soils provide competent support for paving
equipment. Clean cohesionless sands are subject to yielding under rubber tire
and track loads from paving equipment. The paving contractor should confirm
in writing the acceptability of the compacted subgrade prior to placement of
full depth asphalt pavement.
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7.0 STRUCTURAL DESIGN RECOMMENDATIONS
7.1 Residential Foundation Design Criteria
Conventional spread footings, founded in properly compacted structural fill
may be used to support the proposed residences. Footings should be set back
at least 5 feet or one-third the slope height, whichever is greater, from the
top-of-slope. Or footings may be embedded such that there is adequate setback
between footings and the face of slopes. In any case, footings should have a
minimum embedment of 12 and 18 inches below lowest adjacent grade for one and
two stories, respectively. Residential footings should have a minimum width
of 12 inches. Footings for one to two-story wood frame homes may be designed
for an allowable bearing pressure of 1,500 pounds-per-square foot (psf). All
continuous footings should be reinforced with at least #4 reinforcing bars top
and bottom, along the full width of the footings to mitigate the potential for
differential fill settlement. Additional reinforcement may be required by the
project Structural Engineer.
Structure settlement will be due to relatively light foundation loads, as well
as long-term consolidation of fill soils and compressible native materials
below the fill. Maximum anticipated structural load induced settlements of
continuous residential footings, designed as recommended "above, are 1/2 inch
or less. Compacted fills will settle depending on the fill thickness and
future changes in the "as-compacted" moisture conditions. For instance, 15
feet of properly compacted fill is expected to settle approximately an
additional one to two inches if the soils are allowed to become saturated.
These fill settlements should be considered in structural design.
Residential structures lateral load resistance should be designed using Table
29-B of the 1988 Edition of the UBC, where residences are setback as
recommended herein. Where reduced foundation set~ack is required, CCIE can
evaluate structure specific cases, and provide appropriate passive resistance
pressures for design.
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7.2 Slabs-on-Grade
Conventional 4-inch minimum thickness slabs-on-grade may be constructed for
support of nominal ground floor residential live loads. All slab subgrades
shoul d be moi sture conditi oned and compacted as recommended in Appendi xC.
Care should be taken to avoid slab curling if slabs are poured in hot weather.
A mix design should also be provided to reduce the potential for shrinkage
cracks. Slabs should be. designed and constructed as promulgated by the
Portland Cement Association (PCA). If non-expansive soils are imported
(Expansion Index less-than 30), then the Structural Engineer need not design
the slabs for expansive soils. Reinforcement should be provided as
recommended by the Structural Engineer, and may include conventional,
post-tensioned, or fiber reinforced slabs.
If a moisture-sensitive floor covering (such as vinyl tile) is used, slabs
should be protected by a 6-mil thick polyethylene vapor barrier. If the
barrier is used, it should be protected with 2 inches of sand placed above and
below to prevent punctures and to aid in the concrete cure. Vapor barrier
seams should be lapped a minimum 6 inches and sealed.
7.3 Appurtenant Facilities
It is anticipated that residential lots will be customized, including home
additions and construction of garden walls, pools, landscape ponds, retaining
wa 11 s, general regrading, and modi fi cati ons of 1 andscapi ng. Any of these
modifications may adversely change the foundation conditions, lot stability,
and/or adversely affect adjacent lots. It is therefore strongly recommended
that proposed lot modifications be reviewed by CCIE or an experienced
Geotechnical Engineer and/or Certified Engineering Geologist. All homeowners
should be made aware of the need for geotechnical evaluation of proposed
foundation, grading, irrigation, and/or landscaping modifications.
7.4 Corrosivity
A bulk sample obtained from the exploration was tested for resistivity, pH,
and soluble sulfate and chloride content. Relatively low sulfate con-
centrations were measured, and therefore conventional Type I and II portland
cements may be used. Relatively high resistivity and pH and low chloride
content were also measured, which would indicate low corrosivity. Some
variations over this large site should be anticipated.
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8.0 GEOTECHNICAL SERVICES DURING CONSTRUCTION
This report' has been prepared to aid in evaluation of the site, to prepare
site grading recommendations, and to assist the Structural Engineer in the
design of the proposed structures. As indicated above, additional studies may
be required for appurtenant structures. It is recommended that this office be
provided the opportunity to review the final design drawings and specifica-
tions to determine if the recommendations of this report have been properly
implemented.
Recommendations presented herein are predicated upon the assumption that
continuous earthwork monitoring will be provided by CCIE. Removal excavation
bottoms should be observed by a CCIE representative. Structural fill and
backfill should be placed and compacted during observation and testing by
this office. Footing excavations should be observed prior to placement of
steel and concrete to see that footings are founded on satisfactory soil and
that excavations are free of loose and disturbed materials.
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9.0 CLOSURE
The findings and recommendations of this report were prepared in accordance
with generally accepted professional engineering and engineering geologic
principles and practice. Our conclusions and recommendations are based on the
results of the field and laboratory investigations, combined with an
interpolation of subsurface conditions between and beyond exploration
locations.
Our continued consultation and construction monitoring will be necessary for
the success of the project as the project evolves. CCIE should review plans
and specifications to check if the recommendations presented herein have been
appropriately interpreted, and that the design assumptions used in this study
are valid. Where significant design changes occur, CCIE may be required to
augment or modify the recommendations presented herein. Conditions may differ
in some locations from those encountered in the explorations and may require
additional analyses and possibly modified recommendations. This report was
written for Rancho Ca 1 iforni a Development Company, for the proposed
development described herein, only.
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REFERENCES
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PARTIAL LIST OF REFERENCES
BOLT, B.A., 1973; "Duration of Strong Ground Motion," Proceedings on Fifth
World Conference on Earthquake Engineering, V. 2, No. 292, p.10
CALIFORNIA DIVISION ON MINES AND GEOLOGY, 1980; "Alquist-Priolo Special
Studies Zone Map, Pechanga 7 1/2' Quadrangle".
CONVERSE CONSULTANTS INLAND EMP IRE, December 9, 1988; "Li quefacti on
Investi gati on, The Meadows at Rancho Ca 1 iforni a APN Nos.
926-13-9, -10, -12, -13, and -14, Rancho California, California" (CCIE
No. 88-81-148-02".
DUNCAN, J.M., and Buchignani, A.L., March 1975; "An Engineering Manual for
Slope Stability Studies", University of California, Berkeley, Department
of Civil Engineering.
GREENSFELDER, R., 1974; "Maximum Credible Rock Accelerations from Earthquakes
in California", California Division of Mines and Geology, Map Sheet 23.
INTERNATIONAL CONFERENCE OF BUILDING OFFICIALS, 1988 Edition; lIUniform
Building Code (UBC)".
MARACHI, N.D., and DIXON, S.J., 1972; "A Method for Evaluation of Seismicity,"
Proceedings of the International Conference on Microzonation, Seattle,
Washington.
PACIFIC SOILS ENGINEERING, INC., May 5, 1987a; "Geotechnical Report for
Environmental Impact Purposes, Butterfield Hills, Rancho California,
County of Riverside, Cal ifornia" (WO #400082A).
PACIFIC SOILS ENGINEERING, INC., August 1987b; "Fault Study, 1,400 acre, The
Meadows at Rancho California, Rancho California" (WO #400082A).
PACIFIC SOILS ENGINEERING, INC., September 30, 1987c; "Evaluation of
Liquefaction Potential, A Portion of Vail Meadows Located North of
Highway 79 and South of De Portola Road, between Margarita Road and
future Butterfield Stage Road, Rancho California, California" (WO
#400082A) .
PLOESSEL, M.R., and SLOSSON, J.E., 1974; "Repeatable High Ground Accelerations
from Earthquakes," California Geology, September.
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DRAWINGS
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APPENDIX A
FIELD EXPLORATION
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APPENDIX A
FIELD EXPLORATION
Field exploration included a site reconnaissance and subsurface exploration
program. During the site r~connaissance, the surface conditions were noted,
and the locations of the test borings and trenches were determined. The
exp 1 oratory borings and trenches were approximately located us i ng ex i sti ng
boundary and other features as a gui de. El evati ons shown on the logs were
interpolated from the contours shown on the provided site topographic map.
Exploratory borings were advanced using 18, 24, and 26 inch diameter bucket
auger dri 11 i ng equ i pment. Exploratory trenches were excavated by a backhoe
equipped with a 24 inch width bucket. Soils were continuously logged by an
experienced geologist and classified in the field by visual examination in
accordance with the Unified Soil Classification system. Where deemed
appropriate, the exploratory borings and trenches were entered by an
engineering geologist who observed the exposed earth materials. Where appro-
priate, field descriptions and classifications have been modified to reflect
laboratory test results.
Ring samples of the subsurface materials were obtained at frequent intervals
in the exploratory borings and trenches using a drive sampler (2.4-inch inside
diameter, 3-inch outside diameter) lined with sample rings. The steel ring
sampler was driven into the bottom of the borehole or trench with successive
drops of a driving weight. Successive drops of telescoping kelly drove the
sampl es in the bucket auger bori ngs. The soil is retai ned in brass rings
(2.4 inches inside diameter, 1.0 inch in height). The central portion of the
sample was retained and carefully sealed in waterproof plastic containers for
shipment to the laboratory. Bulk samples of typical soil types were also
obtained. Calculated drive energies for each sample interval are presented on
the boring logs.
Logs of the exploratory borings and trenches are presented in the boring and
trench summary sheets A-I through A-87. Boring and trench summary sheets also
include descriptions of the materials, pertinent field data and supplementary
laboratory data. A key to soil symbols and terms is presented on the key
sheet which is the last page in Appendix A.
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APPENDIX B
LABORATORY TEST PROGRAM
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APPENDIX B
LABORATORY TEST PROGRAM
Laboratory tests were conducted in the Converse Consultants Pasadena (CCP)
laboratory on representative samples for the purpose of evaluating their
physical properties and engineering characteristics. Test results are
presented on the exploration logs and in this appendix. A summary of the
various laboratory tests conducted is presented below.
In-Situ Moisture Content and Dry Density
Data obtained from these tests, performed on relatively undisturbed ring
samples obtained from the field, were used to aid in the classification and
correlation of the earth materials and to provide qualitative information
regarding strength and compressibility. The percent of moisture as a function
of dry weight, and the encountered dry density in units of pounds-per-cubic-
foot (pcf) are provided in the right-hand columns on the exploration logs.
Laboratory Maximum Density and Optimum Moisture Tests
Laboratory maximum density and optimum moisture tests were performed on
representative bulk samples of the site materials. These tests were run in
accordance with the ASTM D1557-78 laboratory procedure. Laboratory maximum
density and optimum moisture curves are presented on Drawings B-1 and B-2.
Shear Tests
Direct shear tests were performed on both undisturbed ring and remolded
samples. Individual rings were prepared, soaked and vertical surcharge
applied. Each ring was then sheared at a constant rate of strain. A range of
norma 1 loads was app 1 i ed and the shear strength envelope was determi ned.
Results of the tests are presented on Drawings B-3 through B-8.
Collapse Tests
To evaluate the moisture sensitivity (collapsibility) of the encountered
soils, ri ng sampl es were loaded up to approximately 2 ki ps-per-square-foot
(ksf), allowed to stabil ize under load, and then submerged. The percent of
consolidated measured after the sample was submerged is reported on the logs
in the far right column as percent collapse.
Consolidation Tests
Data obtained from this test, performed on relatively undisturbed and remolded
soil samples, were used to evaluate the settlement characteristics of on site
soils ,and remolded soils under load. This test 'involved loading specimens
into the test apparatus which contained porous stones to accommodate vertical
drainage during testing. Normal vertical axial loads were applied to one end
of the sample through the porous stones, and the resulting vertical
defl ecti ons were recorded at vari ous time peri ods. The load was increased
after the sample reached a reasonable state of equilibrium.
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B-2
Samples were loaded at field moisture and submerged for additional loading.
Test results are shown on Drawings B-9 through B-19 entitled Consol idation
Test, including a time-rate of consolidation plot.
Resistance R-Value Test
A selected bulk soil sample was tested in a Converse Consultants laboratory to
determine the "R" value using the California "R" Value Test Method No. 301
(ASTM D 2844-69). Results of the "R" value test is presented below:
SAMPLE
BORING SAMPLE DEPTH
No. No. -11!l-
BH-2 B-2 10-11
SOIL DESCRIPTION
SILTY SAND (SM), fine
RESISTANCE
"R"
VALUE*
26
* By exudation.
Corrosivity and Chemical Attack
A bulk sample was sent to an analytical laboratory to test the soil pH,
resistivity, and soluble sulfate and chloride content. These tests were
performed to evaluate the corros i vi ty and chemi ca 1 attack potenti a 1 for the
site soils. The results are as follows:
SAMPLE
BORING DEPTH
~ -11!l-
DESCR I PTI ON
RESISTIVITY SOLUBLE (ppm)
2!!... (ohm - em) SULFATE CHLORIDE
BH-3
30-31 CLAYEY SILT (CL/ML) 7.9
4,290
242
1S8
Sample Storage
Soil samples presently stored in our 1 aboratory wi 11 be di scarded 30 days
after the date of this report unless this office receives a specific request
to retain the samples for a longer period.
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APPENDIX C
RECOMMENDED EARTHWORK SPECIFICATIONS
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APPENDIX C
RECOMMENDED EARTHWORK SPECIFICATIONS
Grading
1. Areas to recei ve compacted fi 11 shall be stri pped of all vegetati on,
organics, debris and existing structure remnants. Any existing fill
materials shall be excavated. Any other unsuitable soils shall be
excavated as recommended by Converse Consultants Inland Empire (CCIE).
All areas that are to receive compacted fill shall be observed by CCIE
prior to placement of fill.
2. Subsequent to the removal of unsuitable materials, subgrade soil surfaces
that wi 11 receive compacted fi 11 shall be scarifi ed to a depth of at
least 6 inches. The scarified soil shall be moisture-conditioned to at
or slightly above optimum moisture content. Scarified soil shall be
compacted to at least a relative compaction of 90%. Relative compaction
is defined as the ratio of the inplace soil density to the laboratory
maximum dry density as determined by the ASTM D1557-78 test procedure.
3. Subdrains shall be installed in canyons and ravines as indicated by the
project Certified Engineering Geologist (CEG). Subdrains shall be
installed as depicted on the attached Drawings C-1a and C-1b.
4. Fill shall be placed in suitable lifts, with lift thickness modified as
necessary to achieve adequate compaction. All fill soils shall be
compacted mechani ca lly throughout to the spec i fi ed dens i ty. Each 1 ayer
shall be compacted to at least a minimum relative compaction of 90%.
However, pavement base material shall be compacted to at least 95% of,the
ASTM D1557-78 laboratory maximum density. Fills shall be benched into
unyi e 1 di ng bedrock on slopes steeper than 4: 1 (hori zonta 1: verti ca 1).
Where fill is to be placed above cut slopes, fill shall be benched into
bedrock as shown on Drawing C-2. The field density of the compacted soil
shall be measured by the ASTM D1556-82 or D2922-81 test methods or
equivalent.
5. Fill soils shall consist of excavated on site non-expansive soils
essentially cleaned of organic and deleterious material or imported soils
approved by CCIE. All imported fill shall be granular and non-expansive
with an Expansion Index (EI) less than 30, as defined by the Uniform
Building Code (UBC) Standard 29-2. Rocks larger than 6 inches in
diameter shall not be used unless they are sufficiently broken down.
CCIE shall evaluate and/or test import mate,ri a 1 s for conformance wi th
specifications prior to delivery to the site. The contractor shall
notify CCIE at least two normal working days prior to importing'fill to
the site.
6. CCIE shall observe the placement of compacted fill and conduct inplace
field density tests on the compacted fill to check for adequate moisture
content and the required relative compaction. Where less than the
specified relative compaction is indicated, additional compactive effort
88-81-148-01-B
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Converse Consultants Inland Empire
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shall be applied and the soil moisture-conditioned as necessary until the
specified relative compaction is attained. The contractor shall provide
level testing pads for the soils engineer to conduct field density tests
on. The contractor shall provide safe and timely access for CCIE
personnel throughout the grading site, to allow continued monitoring and
testing.
7. Wherever, in the opinion of the Owner's or CCIE's Representatives, an
unstable condition is being created, either by cutting or filling, the
work shall not proceed in that area until an investigation has been made~
and the grading plan revised if found necessary.
Erosion Control
1.
Fi 11 and cut slopes shall be graded
water-induced surficial erosion/sloughing.
measures shall be initiated immediately
construction.
and 1 andscaped to reduce
Permanent erosion control
after completion of slope
2. All interceptor ditches, drai nage terraces, down-dra ins and any other
drainage devices shall be maintained and kept clear of debris. Runoff
shall be directed to a suitable non-erosive drainage device, and shall
not flow uncontrolled offsite.
3. A suitable proportion of slope plantings shall have root systems which
will develop well below 3 feet, such as drought-resistant shrubs and low
trees, or equivalent. Intervening areas shall be planted with
lightweight surface plantings with shallower root systems. In any event,-
lightweight, low-moisture planting shall be used.
4. Construction delays, climate/weather conditions, and plant grow~h rates
may be such that additional short-term, nonplant erosion control measures
may be needed; including matting, netting, sprayed compounds, deep
(5 feet) staking, etc. These measures shall be reviewed by CCIE.
5. Rodent burrowi ng, human trespass (footpri nts), sma 11 concentrati ons or
uncontrolled surface/subsurface water, or poor compaction of util ity
trench backfill on slopes shall be repaired and controlled as soon as
possible.
6. All possible precautions shall be taken to maintain moderate, uniform
soil moisture. Slope irrigation systems shall be properly operated and
ma i nta i ned., and system controls shall be placed under conti nued control
by a landscape architect or similar qualified person.
7. If completion of new slopes occurs during the rainy season, contingency
plans shall be developed to provide prompt temporary protection against
major eros i on/sl oughi ng. Offs ite improvement shall be protected from
site ru noff.
8. Any erosion damage which occurs prior to the completion of the project
shall be repaired by the Contractor.
88-81-148-01-B
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Converse Consultants Inland Empire