HomeMy WebLinkAboutTract Map 3883 Lot 387 Preliminary Geotechnical Evaluation
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W. C. HOBBS, CONSULTING ENGINEER
22800 COVE VIEW STREET
CANYON LAKE, CALIFORNIA 92587
(909) 244-5177
Date: April 16, 1993
Project No: 93017-1
Windsor Homes
31477 Corte Sonora
Temecula, Califomla, 92590
Attention: Mr..Dennis McKee
Subject: Preliminary Geotechnical Evaluation,
Lot~7, Tract 3883, Felicita Dr
Meadow View, City of Temecula, Califomia
Dear Mr. McKee
Pursuant to yourauthorization, a preliminary geotedmical evaluation was conducted at the subject
site in order to determine the distribution and engineering characteristics of the near surface soils.
Particular attention was placed on soil strength relative to slope stability, lateral earth forces and
foundation design parameters. This information should be useful for the design of retaining walls,
foundations of structures and construction of the slopes proposed for the site.
In addition to this evaluation, a cursory review of the grading plan has also been performed to
determine if any geotechnical constraints exist for the earlhwor1< construction and if so,
recommendations provided for mitigating measures.
SCOPE OF WORK
The scope of wor1< for this evaluation indudes the following:
Site reconnaissance, induding nearby areas for correlation of soil types and
formational materials;
Obtaining representative samples for physical testing;
Laboratory testing of recovered samples to determine the engineering
characteristics;
Engineering analysis of the data obtained;
Preparation of this report induding results of analyses, condusions and
recommendations pertinent to the proposed construction.
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Mr. Dennis McKee, Lot 387, Tract 3883, Felicila Rd.
project No: 93017-1
Page: 2
ACCOMPANYING ILLUSTRATIONS AND APPENDICES
Site Vidnity Map, Page 2
Location Map ofTest Trenches, Plate 1
Appendix A, Summary ofTrench Logs
Appendix 8, Summary of Laboratory Test Data and Analysis
Appendix C, Standard Specifications For Earthwor1< Construction
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VICINITY MAP
NOT TO SCAlE
W. C. HOBBS, CONSULTING ENGINEER
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Mr. Dennis McKee, Lot 387, Tract 3883, Felicila Rd.
Project No: 93017"1
Page: 3
SITE DESCRIPTION
The site is located at the eastem end of the cul-de-sac of Felidta Road. It is roughly rectangular
in shape with the north west comer fronting the street The site is currently graded with a building
pad and drive access. Review of the site conditions and proposed grading plan reveals that the
l,igreement of the represented site configuration on the plan is good. The site is currently covered
with grasses and weeds and shows minor signs of erosion from recent rains.
FIELD WORK
Field wor1< on the site consisted of observation of three backhoe excavations and existing cuts on
the site. Samples of representative earth materials were recovered for laboratory testing from
various depths in the excavations. The results of these tests are contained in the attached
appendix. Additionally, a reconnaissance of the nearby area was conducted in order to obtain
additional information pertinent to the site.
0bservation of the walls of the excavations and cuts existing on the property indicated that the fill
and native materials are dense in place. The observed fill on the site is dense, moist, free of voids
and deleterious mate,rials. The contact between the bottom of the fill and native materials was
observed to be 6to 7 feet below the ground surface, roughly where the topographic representation
of the plans would place it The contact was observed to be dean and no evidence of topsoil or
loose materials were ,observed below the contact.
LABORATORY TESTING
A moisture density determination of a representative sample recovered from the field excavation
was conducted in the laboratory in order to evaluate the relative compaction potential of the fill
soils proposed on the site. The maximum dry density and optimum moisture content of the soil
was determined in accordance with ASTM test designation D 1557-82. A representative sample
was remolded to 90 percent relative compaction and a shear test was conducted to determine the
strength characteristics of a fill blend. This representative set of parameters was then used to
determine fill slope stability for the proposed grading.
W. C. HOBBS, CONSULTING ENGINEER
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Mr. Dennis McKee, Lot 387, Tract 3883, Felicila Rd.
Project No: 93017"1
Page: 4
GEOTECHNICAL ENGINEERING
Analyses were conducted to determine the appropriate vertical and horizontal earth contact
pressures and forces for foundation design. These determinations are presented in the
condusions and recommendations section of this reports following.
CONCLUSIONS AND RECOMMENDATIONS
€ondusions and recommendations contained herein are based upon W. C. Hobbs, Consulting
Engineer, being retained for the follow up services as set forth in sections to follow. This provides
an ability to confirm design assumptions and verify conditions as representative. If during the
construction phase of this project, materials and conditions are observed to be substantially
different than those stated herein, they should be evaluated and if necessary, recommendations
modified to reflect those conditions.
CONCLUSIONS
The project is safe and feasible from a geotechnical stand point provided that the
recommendations contained herein are observed and adhered to during construction. The grading
as proposed on the plan reviewed is safe and feasible from a geotechnical standpoint.
This evaluation'condudes the following:
1. Earth materials encountered in this evaluation consist of silty to slightly silty fine to medium
sand. The materials exist in both there native condition and embankment. 80th are dense and
free of voids as observed in the excavations.
2. Laboratory testing and observation indicate an expansion potential of fill blend materials to be
low to very low, and for cuts the expansion potential of soils in the vidnity of foundations is
antidpated to be very low.
3. Ground water was not observed on the site or in any of the ravines located so as to "leave" the
site.
4. Slope stability for ,surfidal and gross underlying conditions for the proposed cut slopes is
determined to be adequate by analysis. The safety factors of these conditions exceed 1.5 and
results of analysis are contained in a separate report.
W. C. HOBBS, CONSULTING ENGINEER
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Mr. Dennis McKee, Lot 387, Tract 3883, Felicila Rd.
Project No: 9301H
Page: 5
Conclusions, continued
5.. Standard "type" foundations proposed for cut or fill materials will be acceptable. No spedal
design features are anticipated at this time and standard design will be adequate.
6. The granular nature of the materials encountered on the site indicate that the potential for
erosion of graded and unplanted surfaces is high.
RECOMMENDATIONS
The recommendations contained herein are contingent upon W. C. Hobbs being retained to
provide the following services in order to confirm design assumptions and review the field
conditions of any excavations.
Site Grading
In order to provide proper support for foundations and performance of slopes and fills, site grading
should be conducted in accordance with the appropriate sections of the Uniform Building Code,
, chapter 70, the :County of Riverside Ordinance 457 (modified), and the Standard Specifications
'for Earlhwor1< Construction, contained herein as Appendix C. The most stringent of any
, combination of the above mentioned specifications shall apply to the grading of this project.
It is understood !that the site exists in a graded configuration. The proposed grading for the site
I does not need to indude the removal of any existing fills encountered in this evaluation and those
I fills may be incorporated into the proposed fills.
W. C. HOBBS, CONSULTING ENGINEER
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Mr. Dennis McKee, Lot 387, Tract 3883, Felicila Rd.
Project No: 93017"1
Page: 6
Recommendations, continued
Bearing Value and Footing Geometry
A safe allowable bearing value for foundations embedded a minimum of 12 inches below lowest
adjacent grade 'into observed competent native ground and compacted fill ground is 2500 pst and
1800 pst, respectively. These values may be increased by 100 pst per foot of width or depth, not
exceeding an additional 500 pst. Continuous footings should have a minimum width of 12 inches.
The use of isolated .column footings is not discouraged and where utilized, should have a
minimum embedment of 24 inches below lowest soil grade. Interior column footings need not be
tied to perimeterfootiAgs, but should meet a minimum embedment criteria of 18". Exteriorcolumn
footings should be tied to the building perimeter by grade beams if located out on slopes.
Settlement
The bearing values recommended above reflects a total settlement of 0.5" and a differential
settlement of 0.25". This settlement is expected to oo::ur during construction and as the loads are
being applied. INhere foundations are embedded into competent native soil, settlements are
expected to be'negligible.
Goncrete Slabs
All concrete slabs on grade should be 4 inches thick. They should be underlain by 3 inches of
sand or gravel. Areas that are to be carpeted or tiled, or where the intrusion of moisture is
objectionable, should be underlain by 6 mil visqueen properly protected from puncture with an
additional 1 inch of sand over it This arrangement of materials would result in a profile downward
of concrete, 1 inch of sand, 6 mil visqueen, 3 inches of sand and subgrade soil. Contractors
should be advise thatwhen pouring during hot or windy weather conditions, they should provide
large slabs with sufficiently deep weakened plane joints to help direct cracking and inhibit the
, development of unsightly and irregular cracks.
Reinforcement
i Continuous footings should be reinforced with a minimum of one number 4 steel bar placed at the
I top and one at the bo.ttom. Slabs should be reinforced with a minimum of number 3 steel bars
I placed at the center of thickness at 18-inch centers both ways or welded wire fabric equivalent
I to 10x10, 10/10 maybe used. These recommendations are very differen~ however, it is the
I experience of this engineer that the placement of number 3 bars has a better performance history
I than the WNF. The selection is left to the dient and or structural engineer.
W. C. HOBBS. CONSULTING ENGINEER
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Mr. Dennis McKee, Lot 387, Tract 3883, Felicila Rd.
project No: 93017"1
Page: 7
Recommendations, continued
lateral Loads
The bearing value of the soil may be increased by one third for short duration loading (wind,
seismic). Lateral loads may be resisted by passive forces developed along the sides of concrete
footings or by friction along the bottom of concrete footings. The value of the passive resistance
may be computed using an equivalent fluid density of 450 pd. This force reflects the condition
of a level ground surface adjacent to the footings evaluated. The total force should not exceed
3000 pst. A coeffident of friction of .35 may be used for the horizontal soiVconcrete interface for
resistance of lateral forces. If friction and passive forces are combined, then the passive values
should be reduced by one third. A safety factor of 1.5 should be used for design.
Retaining Walls
Retaining walls'should be designed to resist the active pressures summarized in the following
table. The active pressure is normally calculated from the lowermost portion of the footing to the
highest ground : surface at the back of the wall. The active pressures indicated in the table are
equivalent fluid densities. Walls that are not free to rotate or that are braced at the top should use
active pressures that are 50% greater than those indicated in the table.
. RETAINING WALL DESIGN PRESSURES
Slooe of
adiacentoround
Active Pressure
Passive Pressure
LEVEL
2:1
30 per
43 per
450 pd
200 pd
, These pressures are for retaining walls backfilled with non- cohesive, granular materials and
provided with drainage devices such as weep holes or subdrains to prevent the build-up of
hydrostatic pressures beyond the design values.
. Additional information relative to the obtaining and establishment of active and passive forces is
contained in calculations in Appendix B.
W. C. HOBBS, CONSULTING ENGINEER
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Mr. Dennis McKee, Lot 387, Tract 3883, Felicila Rd.
Project No: 93017"1
Page: 8
Recommendations, continued
Fine Grading
Fine grading of areas outside of the residence or buildings should be accomplished such that
positive drainage exists away from all footings. Run-off should be conducted off the property in
a non-erosive manner toward approved drainage devices. Water should not be allowed to pond
adjacent to footings or be allowed to flow directly over the tops of slopes. Berms should be
constructed at :the tops of all slopes and brow ditches provided at the tops of cut slopes in
accordance with appropriate agency ordinances.
Foundation Plan Review
In order to curtail any potential misunderstandings of this report or ifs applicability, the foundation
plans for any proposed residence should be reviewed by this firm. The purpose of this review
would be to confirm design conformance with specifications contained herein and to modify these
recommendations by additional investigations should that be deemed necessary by the soil
engineer. For,example, unusual foundations or a bearing capacity higher than that recommended
in this report could warrant additional investigation and/or testing.
Construction
A soil engineer should be present during earthwor1< construction, to test and or confirm the
conditions encountered during this study. A report of earthwor1< construction should be prepared
documenting the procedures used, test results, and final recommendations for construction at the
completion of grading.
W. C. HOBBS, CONSULTING ENGINEER
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Mr. Dennis McKee, Lot 387, Tract 3883, Felicila Rd.
Project No: 93017"1
Page: 9
CLOSURE
This evaluation,was performed in accordance with generally accepted engineering practices. The
condusions and recommendations contained in this report were based on the data available and
the interpretation of ,such data as dictated by our experience and background. Hence, our
condusions and recommendations are professional opinions; therefor, no other warranty is offered
or implied.
The opportunity to be of service is appreciated. Should questions or comments arise pertaining
to this documen~ or if we may be of further service, please do not hesitate to call our office.
Respectfully submitted,
W. C. HOBBS, CONSULTING ENGINEER
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Bill Hobbs, ROE 42265
Civil Engineer
Distribution: Addressee (5)
W. C. HOBBS, CONSULTING ENGINEER
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APPENDIX A
W. C. HOBBS, CONSULTING ENGINEER
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APPENDIX B
W. C. HOBBS, CONSULTING ENGINEER \5"'
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I SOFTWARE:
I SHEAR TEST DIAGRAM
I J.D. 93017-1 DATE 4/16/93
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COHESION 267 PSF
PHI = 38 EGREES
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APPENDIX B
SUMMARY OF MAXIMUM DENSITY TEST RESULTS
Cur;ve
Letter
Soil
DescriDtion
Maximum Optimum
Densitv Dct Moisture %
A
Silty SAND
Tan-Brown (SM)
128.5
11.5
Maximum density and optimum moisture determined in accordance with
test method ASTM D 1557-78.
SUMMARY OF EXPANSION INDEX TEST
Test
Location
Expansion
Index
Expansion
Classification
Trench 1
9
VERY LOW
Expansion index test conducted in accordance with UBC 29-2.
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Ka, active pressure coefficient
+= 38. deg angle of internal friction of soil
o := 17. deg angle of friction between soil and wall, (concrete or masonry)
a := 90. deg angle of the wall plane to the horizontal
~= 0.. 34 slope angle range, degrees
"(= 125 unit weight of soil (pet)
Kall= sin(a + +)2 2
. ( ):2 . ( <) (1 sin(+ + o).sin(+ - ~'deg))
sin a . sin a - U' +
sin(a - o).sin(a + ~.deg)
0.45
0.4
/
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----- -----
-
--
0.35
Kall
0.3
0.25
0.2
o
5
10
15
20
25
30
35
II
slope angle
RELATION BETWEEN SLOPE ANGLE AND Ka
"(ll= "(. Kall 'equivalent fluid density
Coefficient
SIODe of Backfill Behind Wall
Eauivalent fluid (oct)
Kao = 0.218
Ka18 = 0.269
KB:26 = 0.311
Ka31 = 0.357
LEVEL BACKFILL BEHIND WALL
3:1 BACKFILL BEHIND WALL
2:1 BACKFILL BEHIND WALL
1.6:1 BACKFILL BEHIND WALL
"(0 = 27.239
"(18 = 33.567
"(26 = 38.865
"(31 = 44.603
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~" 38. deg
0, 17- deg
a= 90. deg
~= 330..360
Y= 125
Kp, passive pressure coefficient
angle of internal friction of soil
angle of friction between soil and wall, (concrete or masonry)
angle of the wall plane to the horizontal
slope angle range from horizontal
unit weight of soil (pet)
sin(a _ +)2
2 1 _ ( sin (+ + 0)' sin (+ + ~. deg) ) ]2
sin(a) .sin(a + 0)'
sin(a + o).sin(a + ~.deg)
KpJl=
KpJl
YJl= y. KpJl
Gaefficient
Kp360 = 8.662
Kp342 = 3.279
Kp334 = 2.109
10
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----- ------
r-
8
6
4
2
o
330 335 340 345 350 355 360
Jl
Slope angle
RELATION BETWEEN SLOPE ANGLE AND Kp
iequivalent fluid density
Backfill slaDe
LEVEL GRADE IN FRONT OF WALL
3:1 SLOPE DOWN AWAY FROM FRONT OF WALL
2:1 SLOPE DOWN AWAY FROM FRONT OF WALL
Eauivalent fluid (Dcf)
Y360 = 1.083.103
Y342 = 409.914
Y334 = 263.637
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APPENDIX C
W. C. HOBBS, CONSULTING ENGINEER
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GENERAL EARTHWORK AND GRADING SPECIFICATIONS
1.0 GENERAL INTENT
These specifications present general procedures and requirements for grading and earthwork as shown on the
approved grading p1ans,including preparation of areas to be filled, placement of fill, installation of subdrains, and
excavations. The recommendations contained in the geotechnical report are a part ofthe earthwork and grading
specifications and shall, supersede the provisions contained hereinafter in the case of conflict. Evaluations
performed by the consultant during the course of grading may result in new recommendations of the geotechnical
report.
2.0 EARTHWORK OBSERVATION AND TESTING
Prior to the commencement of grading, a quaDfied geotechnical consultant (soils engineer and engineering
geologist, and their representatives) shall be employed for the purpose of observing earthwork and testing the
fills for confonnance with the recommendations of the geotechnical report and these specifications.
It will be necessary that the consultant provide adequate testing and observation so that he may detennine that
the work was accomplished as specified. It shall be the responsibility of the contractor to assist the consultant
and keep him apprised of work schedules and changes so that he may schedule his personnel accordingly.
It shall be the sole responsibility of the contractor to provide adequate equipment and methods to accompDsh the
work in accordance with ,applicable grading codes or agency ordinances,these specifications and the approved
grading plans. If in the opinion of the consultant, unsatisfactory conditions, such as questionable soil, poor
moisture condition, inadequate compaction, adverse weather, etc., are resulting in a quality of work less than
required in these specifications, the consultant will be empowered to reject the work and recommend that
construction be topped until the conditions are rectified.
Maximum dry density tests used to detennine the degree of compaction will be performed in accordance with the
American Society: of Testing and Materials tests method ASTM 0 1557-78.
3.0 PREP.4iRATION OF AREAS TO BE FILLED
3.1 Clearing and Grubbing: All brush, vegetation and debris shall be removed or piled and otherwise disposed
of.
3.2 Processing: The existing ground which is detennined to be satisfactory for support of fill shall be scarified
to a minimum depth of 6 inches. Existing ground which is not satisfactory shall be overexcavated as specified
in the following section.
Scarification shall continue until the soils are broken down and free of large clay lumps or clods and until the
, working surface is reasonably uniform and free of uneven features which would inhibit uniform compaction.
3,3 Overexcavalion: Soft, dry, spongy, highly fractured or otherwise unsuitable ground, extending to such a depth
. that the surface processing cannot adequately improve the condition, shall be overexcavated down to firm ground,
, approved by the consultant.
3.4 Moisture Conditioning: Overexcavated and processed soils shall be watered, dried-back, blended, and/or
I mixed, as required to attain a uniform moisture content near optimum.
W. C. HOBBS, CONSULTING ENGINEER
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3.5 Recompaction: Overexcavated and processed soils which have been properly mixed and moisture-
conditioned shall be recompacted to a minimum relative compaction of 90 percent.
3.6 Benching: Where fills are to be placed on ground with slopes steeper than 5: 1 (horizontal to vertical units),
the ground shall be stepped or benched. The lowest bench shall be a minimum of 15 feet wide, shall be at least
2 feet deep, shall expose finn material, and shall be approved by the consultant. Other benches shall be
excavated in finn material for a minimum width of 4 feet. Ground sloping flatter than 5 : 1 shall be benched or
otherwise overexcavated when considered necessary by the consultant.
3.7 Approval: All areas to receive ill, including processed areas, removal areas and toe-of-fill benches shall be
approved by the consuftant prior to fill placement.
4.0 FILL MATERIAL
4.1 General: Material to be placed as fill shall be free of organic matter and other deleterious substances, and
shall be approved: by the consuftant. Soils of poor gradation, expansion, or strength characteristics shall be placed
in areas designated by consultant or shall be mixed with other soils to serve as satisfactory fill material.
4.2 Oversize: Oversize material defined as rock, or other irreducible material with a maximum dimension greater
than 12 inches, shall not be buried or placed in fills, unless the location, materials, and disposal methods are
specifically approved by the consultant. Oversize disposal operations shall be such that nesting of oversize
material does not occur, and such that the oversize material is completely surrounded by compacted or densified
fill. Oversize material shall not be placed within 10 feet vertically of finish grade or within the range of Mure
utilities or underground construction, unless specifically approved by the consultant.
4.3 Import: If importing of fill material is required for grading, the import material shall meet the requirements of
Section 4.1.
5.0 FILL PLACEMENT AND COMPACTION
5.1 Fill Lifts: Approved fill material shall be placed in areas prepared to receive fill in near-horizontallayers not
exceeding 6 inches in compacted thickness. The consuftant may approve thicker ills if testing indicates the
grading procedures are such that adequate compaction is being achieved with ills of greater thickness. Each
layer shall be spread evenly and shall be thoroughly mixed during spreading to attain uniformity of material and
moisture in each layer.
5,2 Fill Moisture: Fill layers at a moisture content less than optimum shall be watered and mixed, and wet fill
layers shall be aerated by scarification or shall be blended with drier material. MoisturlH:Onditioning and mixing
of fill layers shall continue until the fill material is at a unifonn moisture content or near optimum.
5.3 Compaction of Fill: Afler each layer has been evenly spread, moisture conditioned, and mixed, it shall be
unifonnly compacted to not less than 90 percent of maximum dry density. Compaction equipment shall be
adequately sized and shall be either specifically designed for soil compaction or of proven reDabilily, to efficiently
achieve the specified degree of compaction.
5.4 Fill Slopes: Compaction of slopes shall be accomp6shed, in addition to normal compacting procedures, by
backfilDng of slopes with sheepsfoot rollers at frequent increments of 2 to 3 feet in fill elevation gain,or by other
methods producing, satiSfactory results. At the completion of grading ,the relative compaction of the slope out to
the slope face shall be at least 90 percent.
W. C. HOBBS, CONSULTING ENGINEER
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5.5 Compaction' Testing: Field tests to check the ill moisture and degree of compaction will be performed by
the consuttant. The location and frequency of tests shall be at the consultanfs discretion. In general, the tests will
be taken at an interval not exceeding 2 feet in vertical rise and/or 1,000 cubic yards of embankment.
6.0 SUBDRAIN INSTALLATION
Subdrain systems, if required, shall be installed in approved ground to confonn to the approximate a6gnment and
details shown on the plans or herein. The subdrain location or materials shall not be changed or modified without
the approval of the consultant. The consultant, however, may recommend and upon approval, direct changes in
subdrain ine, grade or material. All subdrains should be surveyed for ine and grade after installation, and
sufficient time shall be allowed for the surveys, prior to commencement of fil6ng over the subdrains.
7.0 EXCAVATION
Excavation and cut slopes will be examined during grading. If directed by the consuttant, further excavation or
overexcavation and refil6ng of cut areas shall be performed, and/or remedial grading of cut slopes shall be
performed. Where fill-over-(;ut slopes are to be graded,
<R>unless otherwise approved, the cut portion of the slope shall made and approved by the consultant prior to
placement of materials for construction of the fill portion of the slope.
8.0 TRENCH BACKFILL
8.1 Supervision: Trench excavations for the utility pipes shall be backfilled under engineering supervision.
8.2 Pipe Zone: After the utility pipe has been laid, the space under and around the pipe shall be backfilled with
clean sand or approved granular soil to a depth of at least one foot over the top of the pipe. The sand backfill
shall be unifonnly jetted into place before the controlled backfill is placed over the sand.
8.3 Fill Placement: The onsite materials, or other soils approved by the engineer, shall be watered and mixed
as necessary prior to placement in ills over the sand backfill.
8.4 Compaction: The controlled backfill shall be compacted to at least 90 percent of the maximum laboratory
density as determined by the ASTM compaction method described above.
8.5 Observation and Testing: Field density tests and inspection of the backfill procedures shall be made by the
soil engineer during backfil6ng too see that the proper moisture content and unifonn compaction is being
maintained. The contractor shall provide test holes and exploratory pits as required by the soil engineer to enable
samp6ng and testing.
W. C. HOBBS, CONSULTING ENGINEER
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