HomeMy WebLinkAboutTract Map 37341-6 Geotechnical Report
UPDATE GEOTECHNICAL REPORT
RORIPAUGH RANCH RESIDENTIAL
DEVELOPMENT
PLANNING AREAS 14 THROUGH 24
27 THROUGH 31 & 33B
TEMECULA, CALIFORNIA
Prepared for
WOODSIDE HOMES
11870 Pierce Street, #250
Riverside, CA 92505
Project No. 11835.002
June 28, 2018
CLEARED BY
CITY OF TEMECULA
PUBLIC WORKS
tricia.ortega
02/16/2023 02/16/2023
02/16/20
01/06/2021
June 28, 2018
Project No. 11835.002
Woodside Homes
11870 Pierce Street, #250
Riverside, CA 92505
Attention: Mr. Trent Heiner
Subject: Update Geotechnical Report
Roripaugh Ranch Residential Development
Planning Areas 14 through 24, 27 through 31 & 33B
Temecula, California
In accordance with your request, we are pleased to provide this update geotechnical
report for the subject residential development located in the City of Temecula, California
(see Figure 1). This report summarizes our geotechnical findings, conclusions and
recommendations regarding the design and construction of the proposed residential
development and associated improvements. Based on the results of our review, it is
our opinion that the site is suitable for the intended use provided the recommendations
included in this report are implemented during design and construction phases of
development. Although the previous site-specific geotechnical reports (Leighton, 2001
and Byerly, 2012) are included herein by reference, this report is a stand-alone
document and can be used for design and construction of the proposed development.
Other specific reports for Park and Ride (PA33B), Park Site (PA27) and Loop Road are
also included by reference.
If you have any questions regarding this report, please do not hesitate to contact the
undersigned. We appreciate this opportunity to be of service on this project.
Respectfully submitted,
LEIGHTON AND ASSOCIATES, INC.
Simon I. Saiid, GE 2641
Principal Engineer
Robert F. Riha, CEG 1921
Senior Principal Geologist
Distribution: (1) Addressee (PDF copy)
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TABLE OF CONTENTS
Section Page
1.0 INTRODUCTION .................................................................................................. 1
1.1 Purpose and Scope................................................................................................. 1
1.2 Project and Site Description .................................................................................... 1
1.3 Background ........................................................................................................... 2
2.0 GEOTECHNICAL AND GEOLOGIC FINDINGS ....................................................... 3
2.1 Regional Geology ................................................................................................... 3
2.2 Site Specific Geology .............................................................................................. 3
2.2.1 Earth Materials .......................................................................................................... 3
2.3 Groundwater and Surface Water ............................................................................. 4
2.4 Landslides/Debris Flow and Rockfalls ....................................................................... 4
2.5 Regional Faulting and Local Fault Activity ................................................................ 4
2.6 Seismic Coefficients per 2016 CBC ........................................................................... 5
2.7 Secondary Seismic Hazards ..................................................................................... 5
2.7.1 Dynamic Settlement (Liquefaction and/or Dry Settlement) .......................................... 6
2.7.2 Ground Rupture ........................................................................................................ 6
3.0 CONCLUSIONS AND RECOMMENDATIONS ......................................................... 7
3.1 General ................................................................................................................. 7
3.2 Earthwork .............................................................................................................. 7
3.2.1 Site Preparation and Remedial Grading ...................................................................... 7
3.2.2 Suitability of Site Soils for Fills .................................................................................... 8
3.2.3 Rippability ................................................................................................................. 8
3.2.4 Slope Construction .................................................................................................... 9
3.2.5 Canyon Subdrains ..................................................................................................... 9
3.2.6 Import Soils ............................................................................................................ 10
3.2.7 Utility Trenches ....................................................................................................... 10
3.2.8 Shrinkage ............................................................................................................... 11
3.2.9 Drainage ................................................................................................................. 11
3.3 Foundation Design ............................................................................................... 11
3.3.1 Bearing and Lateral Pressures .................................................................................. 11
3.3.2 Post Tension Design Parameters .............................................................................. 12
3.4 Foundation Setback from Slopes ........................................................................... 12
3.5 Vapor Retarder .................................................................................................... 13
3.6 Retaining Walls .................................................................................................... 14
3.7 Sulfate Attack ...................................................................................................... 15
3.8 Concrete Flatwork ................................................................................................ 15
3.9 Preliminary Pavement Design ................................................................................ 16
4.0 GEOTECHNICAL CONSTRUCTION SERVICES ..................................................... 18
5.0 LIMITATIONS ................................................................................................... 19
REFERENCES ............................................................................................................. 20
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Accompanying Tables, Figures, Plates and Appendices
Tables
Table 1. 2016 CBC Seismic Coefficients per USGS General Procedure ....................... 5
Table 2. PTI Method Design Parameters (3rd Edition) ................................................. 12
Table 3. Footing Setbacks ............................................................................................ 13
Table 4. Retaining Wall Design Earth Pressures (Static, Drained) ............................... 14
Table 5. Asphalt Pavement Sections............................................................................ 16
Figures (end of text)
Figure 1 – Site Location Map
Figure 2 – Site Plan
Appendices
Appendix A – Earthwork and Grading Specifications
Appendix B – GBA - Important Information About This Geotechnical-Engineering Report
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1.0 INTRODUCTION
1.1 Purpose and Scope
This geotechnical update is for the proposed Roripaugh Ranch Residential
Development (PA-14 through 24 and 27 through 31, and 33B) located in the City of
Temecula, California. Our scope of services for this update report included the
following:
Review of previous geotechnical reports, available site-specific geologic
information and provided site plans.
A cursory site reconnaissance.
Preparation of this report which presents our geotechnical conclusions and
recommendations regarding future grading and building construction.
This report is not intended to be used as an environmental assessment (Phase I or
other), or foundation/precise grade plan review.
1.2 Project and Site Description
The Roripaugh Ranch development is located north and northeast of the intersection
of Butterfield Stage Road (BSR) and Calle Chapos in the City of Temecula,
California (see Figure 1). The site is generally bounded by Santa Gertrudis Creek
on the north, Butterfield Stage Road on the west, and by large single family
residential properties on the south and east. Planning AREA PA 33B is located west
of Butterfield Stage Road and north of future Nicolas Road extension (see Figure 2).
The site is currently vacant and easily accessible from BSR. Previous site grading
has created building pads, sheet graded areas, roadways and detention basins.
The site was previously mass graded as part of the overall Roripaugh Ranch
residential development (Byerly, 2012). The site is currently traversed by “dirt”
access roads and has a moderate growth of weeds/grasses and local dense shrubs.
Erosion protection features (sand bags, plastic liners, etc.) were noted throughout
the site.
We understand the residential development portion will consist of 939 residential lots
with associated HOA and Open space lots, roadways, slopes, basins and landscape
areas (Rick, 2018a). Site grading to the current rough grade plan (Rick, 2018b) is
expected to have cuts up to approximately 15 feet and fills of up to approximately 10
feet, not including remedial grading, where applicable. Based on current rough
grade plan, portions of the site will be sheet graded (no lots) for future site lot
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specific grading plans. If site development significantly differs from the assumptions
made and the plans referenced herein, the recommendations included in this report
should be subject to further evaluation.
1.3 Background
Based on our review of referenced reports, we understand that the existing site was
graded to its current configuration during the period between 2003 and 2007.
Although no documentation is available for the original site grading work prior to
2005, previous reports provided field density testing until 2007 (Byerly, 2012a).
Based on our review of recent geotechnical borings performed for this site (Byerly,
2012), natural alluvium was removed to expose underlying dense Pauba formation
and compacted fill was then placed to achieve current site grades. Additional
borings were advanced by Leighton (Leighton 2017b, 2017d) to evaluate existing fill
in PA27 (Sports Park) and PA 33B (Park and Ride). Compacted fill extends to
depths of 60± feet along the boundary of Long Valley Wash channel and several
deep canyon fill areas (PA’s 18, 19, 22, 23, 24 and 31). Fill is expected to be
shallower in the northern and southern reaches of the site as well the Pauba
formation is expected to be locally encountered at the surface.
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2.0 GEOTECHNICAL AND GEOLOGIC FINDINGS
2.1 Regional Geology
The site is located within a prominent natural geomorphic province in southwestern
California known as the Peninsular Ranges. It is characterized by steep, elongated
ranges and valleys that trend northwestward. More specifically, the site is situated
within the Perris Block, an eroded mass of Cretaceous and older crystalline rock.
The Perris Block, approximately 20 miles by 50 miles in extent, is bounded by the
San Jacinto Fault Zone to the northeast, the Elsinore Fault Zone to the southwest,
the Cucamonga Fault Zone to the northwest, and the Temecula Basin to the
southeast. The southeast boundary of the Perris block is poorly defined. The Perris
Block has had a complex tectonic history, apparently undergoing relative vertical
land movements of several thousand feet in response to movement on the Elsinore
and San Jacinto Fault Zones. Thin sedimentary materials locally mantle the
crystalline bedrock and alluvial and colluvial deposits fill the lower valley areas.
2.2 Site Specific Geology
2.2.1 Earth Materials
Based on our field explorations and review of previous site-specific
geotechnical reports, the site is covered by artificial fill underlain by
Pleistocene-aged Pauba Formation. These units are discussed in the
following sections in order of increasing age.
Artificial Fill: As indicated above, the artificial fill on this site extends up
to an estimated depth of 60±-feet in some areas of the site. The fill
appears to vary in density and composition and generally consist of
medium dense to dense, silty to clayey sand (SM/SC) with layers of
sandy silt (ML), sandy clay (CL) and well-graded sand (SM-SW). Based
on the results of the laboratory testing, these materials appear to
possess adequate relative density and generally possess very low to
medium expansion potential (0<EI<91). Some low density fill (upper 9
feet) was reported in the eastern portion of PA 20B (Byerly, 2012).
Pauba Formation: Where encountered, Pleistocene-aged Pauba
Formation was encountered (Leighton, 2017) or reported (Byerly, 2012)
at the surface to below the artificial fill at depths ranging from 2 to 60
feet. These materials generally consist of medium-dense to very dense
poorly and well-graded sands (SP/SW), silty sand (SM), and medium
stiff to hard sandy/clayey silts (ML). Some low density silty sand was
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encountered in the planned Park and ride area (PA33B) (Leighton,
2017d).
Granitic Bedrock: Cretaceous age granitic rock is exposed along the
northerly natural slopes within PA-17. The rock consists of dense to
very dense, white to light-brown coarse-grained granodiorite.
2.3 Groundwater and Surface Water
Surface water as not observed during our recent site visit. Groundwater was not
encountered during our previous explorations (Leighton, 2017). The Department of
Water Resource data for Well 335412N1170712W001 indicates a depth to
groundwater on the order of 339 feet in September 2017. The well is located along
Vino W ay, approximately 1 mile east of the site. Fluctuations in ground water should
be expected due to site irrigation and infiltration of storm water.
2.4 Landslides/Debris Flow and Rockfalls
No evidence of on-site landslides/debris flow or rock fall was observed during our
field review or previous investigation (Leighton, 2001). Due to the dense underlying
nature of the Pauba formation and lack of previous landslides, landslides are not
considered a hazard on this site. Due to the planned grading/development, the
distance of planned residences from rock out crop and the elevated topography of
the site, the hazard for debris flow and rock fall is considered nil.
2.5 Regional Faulting and Local Fault Activity
The subject site, like the rest of Southern California, is located within a seismically
active region as a result of being located near the active margin between the North
American and Pacific tectonic plates.
The principal source of seismic activity to affect the Roripaugh Ranch site is
movement along the northwest-trending regional fault systems such as the San
Andreas, San Jacinto, and Elsinore Fault Zones. Based on published geologic
maps, this site is not located within a currently designated Alquist-Priolo
Earthquake Fault Zone (CGS, 2018) or Riverside County Fault Hazard Zone
(Riverside, 2018). Several lineaments suggestive of possible faulting were
mapped within or trending into the site in a CDMG Special Report 131 (Kennedy,
1997). Those lineaments are shown on current County Fault Hazard Maps
(Riverside, 2018). However, these lineaments are not part of a County Fault
Hazard zone. The lineaments were investigated by Leighton (Leighton,1990) and
concluded no active faulting was present.
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The nearest active State Zoned fault is the Elsinore Fault Zone located
approximately 3.6 miles southwest of the site. The nearest County Fault Zone is
the Murrieta Hot Springs Fault Zone located approximately 0.45 miles (2,400 feet)
northwest of the site. The nearest known active strand of the Murrieta Hot Springs
fault is approximately 1.5 Miles (7,800 feet) northwest of the site (Leighton, 1999).
No active fault traces are known to traverse the project site (CGS, 2018, County of
Riverside, 2018 and Leighton, 1990, 1999, 2001).
2.6 Seismic Coefficients per 2016 CBC
Strong ground shaking can be expected at the site during moderate to severe
earthquakes in this general region. This is common to virtually all of Southern
California. Intensity of ground shaking at a given location depends primarily upon
earthquake magnitude, site distance from the source, and site response (soil type)
characteristics. The site-specific seismic coefficients provided in this section are
based on an interactive tool/program currently available on USGS website. Based
on ASCE 7-10 as the Design Code Reference Document and site Class D, the
seismic coefficients for this site are as listed in the following table:
Table 1. 2016 CBC Seismic Coefficients per USGS General Procedure
CBC Categorization/Coefficient Design Value (g)
Site Longitude (-117.09209) Site Latitude (33.54439)
Site Class Definition D
Mapped Spectral Response Acceleration at 0.2s Period, Ss 1.72
Mapped Spectral Response Acceleration at 1s Period, S1 0.67
Short Period Site Coefficient at 0.2s Period, Fa 1.00
Long Period Site Coefficient at 1s Period, Fv 1.50
Adjusted Spectral Response Acceleration at 0.2s Period, SMS 1.72
Adjusted Spectral Response Acceleration at 1s Period, SM1 1.01
Design Spectral Response Acceleration at 0.2s Period, SDS 1.15
Design Spectral Response Acceleration at 1s Period, SD1 0.67
* g- Gravity acceleration
2.7 Secondary Seismic Hazards
Ground shaking can induce “secondary” seismic hazards such as liquefaction,
dynamic densification, and ground rupture, as discussed in the following
subsections:
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2.7.1 Dynamic Settlement (Liquefaction and/or Dry Settlement)
Due to the lack of shallow groundwater and relatively dense nature of
underlying materials, the potential for dynamic-induced settlement is
considered very low on this site or not expected to exceed one inch. This
settlement is expected to be generally global and over a large area with
differential settlement less than ½ inch over a horizontal distance of 40 feet.
2.7.2 Ground Rupture
Since this site is not located within a State mapped Fault Zone and no faults
are known to exist onsite or trend into this site; the possibility of ground
surface-fault-rupture is very low.
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3.0 CONCLUSIONS AND RECOMMENDATIONS
3.1 General
The proposed site development appears feasible from a geotechnical viewpoint
provided that the following recommendations are incorporated into the design and
construction phases of the proposed development. Specific design and grading
recommendations for the planned Community Sports Park (PA 27) and Park-and-
Ride (PA33B) are presented in separate reports (Leighton, 2017b and 2017d).
3.2 Earthwork
Earthwork should be performed in accordance with the following recommendations
and the Earthwork and Grading Specifications included in Appendix A of this
report. In case of conflict, the following recommendations should supersede those
in Appendix A. The contract between the Owner and the earthwork contractor
should be worded such that it is the responsibility of the contractor to place fill
properly and in accordance with recommendations presented in this report,
including the guide specifications in Appendix A, notwithstanding the testing and
observation of the geotechnical consultant.
3.2.1 Site Preparation and Remedial Grading
Prior to grading, the proposed structural improvement areas (i.e. all-
structural fill areas, pavement areas, buildings, etc.) should be cleared of
surface and subsurface pipes, obstructions and erosion control materials.
Heavy vegetation, roots, sand bags, straw waddles and debris should be
disposed of offsite. Voids created by removal of buried/unsuitable materials
should be backfilled with properly compacted soil in general accordance
with the recommendations of this report. Area specific remedial grading
recommendations are provided as follows:
Fill Areas: In all areas requiring additional fill greater than 2 feet, the
upper 12 inches of soils should be removed/over-excavated and
recompacted. Localized areas of deeper removals/ over-excavation
may be required in existing site basins depending on the actual
conditions encountered and pending verification by our field
representative during grading. Deeper removal (up to 9 feet) should be
anticipated in the vicinity of Lots 9 and 10 (PA 20/Tract 37341-12).
Cut and Transition Cut/Fill Lots in Pauba formation: In cut areas or
cut/fill transition lots exposing Pauba formation, the cut portion should be
over-excavated to a minimum of 2 feet below pad grade or 1 foot below
footing bottom (whichever is deeper). Over-excavation and
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recompaction should extend a minimum horizontal distance of 5 feet
from perimeter edges of proposed buildings/ foundations. Localized
areas of deeper over-excavation may be required in fill/cut transition lots
so the maximum differential depth of fill within a horizontal distance of 30
feet does not exceed 10 feet vertical.
Cut Areas/Lots in Previously Placed Fill (cut> 2 feet): In such areas,
the subgrade soils should be scarified to a minimum depth of 12-inches,
moisture conditioned and compacted to minimum 90 percent
compaction.
Pavement Areas: Whether exposing fill or Pauba formation, the
cleared and exposed surface should be scarified to a minimum depth of
12 inches, moisture conditioned and compacted to minimum 90 percent
compaction or to an unyielding condition.
Geotechnical observation of removal or over-excavation bottoms should be
performed during grading to confirm the competency of the materials being
left in place. After completion of the recommended removal of unsuitable or
surficial soils and prior to fill placement, or in areas of greater than 2 feet of
cut in fill, the exposed surface should be scarified to a minimum depth of 8-
inches, moisture conditioned and compacted using heavy pneumatic
compaction equipment to minimum 90 percent compaction of the laboratory
maximum dry density (ASTM D1557) and to an unyielding condition. In
general, all structural fill should be compacted throughout to 90 percent.
3.2.2 Suitability of Site Soils for Fills
Topsoil and vegetation layers, root zones, and similar surface materials
should be striped and stockpiled or removed from the site. Existing fill
should be considered suitable for re-use as compacted fills provided the
recommendations contained herein are followed. Fill materials with
expansion index greater than 51 should not be used in subgrade soils below
building pad and/or footings or construction of new slopes. If cobbles and
boulders larger than 6-inches in largest diameter are encountered or
produced during grading, these oversized cobbles and boulders should be
reduced to less than 6 inches or placed in structural fill as outlined in
Appendix A.
3.2.3 Rippability
The onsite Pauba formation and existing fill soils are considered rippable
with typical conventional grading equipment. Isolated lenses of dense or
gravelly or well cemented Pauba can be expected but are anticipated to be
rippable with typical heavy duty earth moving equipment. The granitic rock
exposed along the northerly natural slopes within PA-17 may be difficult to
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excavate and require special excavating equipment if cuts are to extend
more than 5 feet below natural ground surface.
3.2.4 Slope Construction
The existing and proposed 2:1 slopes especially those along the Long
Valley Wash (Leighton, 2017a) are considered grossly stable. Any new 2:1
slopes using the onsite soils compacted to minimum 90 percent should also
be stable under short and long term conditions. The outer portion of fill
slopes should be either overbuilt by 2 feet (minimum) and trimmed back to
the finished slope configuration or compacted in vertical increments of 5 feet
(maximum) by a weighted sheeps foot roller as the fill is placed. The slope
face should then be track-walked by dozers of appropriate weight to achieve
the final slope configuration and compaction to the slope face.
New fill slopes should be provided a toe of slope keyways as depicted in
Appendix A. Any new fill slopes placed along existing fill slope, the
minimum new fill width should be 8 feet. No stab fills allowed. If fill is
placed against existing cut slope (exposing Pauba formation), the minimum
fill width should be 15 feet per Appendix A. All cut slopes should be
observed and mapped by a Leighton geologist to confirm the exposed
conditions are stable and no minor fill width is left in place. In this case
when cutting an existing fill slope back into the fill core, a minimum
remaining fill width of 15 feet is recommended. Any existing cut or fill slopes
to remain in the current condition should be minimally scarified to remove
minor erosion rills or vermin burrow, moisture conditioned thoroughly and
compacted by track walking large dozer to achieve a compacted slope face.
The slope below Lot 114 in Planning Area PA-17 (Tract 37341-5) will
require re-construction due to past erosion. Due to the steepness of the
adjacent natural slopes and limited slope area/access, a geogrid reinforced
slope or a geogrid reinforced retaining wall or other re-construction/
supporting methods may be needed.
Slope faces are inherently subject to erosion, particularly if exposed to
rainfall and irrigation. Landscaping and slope maintenance should be
conducted as soon as possible in order to increase long-term surficial
stability. Berms should be provided at the top of fill slopes and drainage
should be directed such that surface runoff over slopes is prevented.
3.2.5 Canyon Subdrains
Canyon subdrains were reported to have been installed in major canyon
areas during original mass grading. These subdrains were to outlet into
long Valley Wash. However, the documentation of their locations have not
been recorded or verified (Byerly, 2012a). In the event the presence of
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these canyon drains cannot be located or verified, long-term settlement
should be re-evaluated for the overlying lots. This should be determined on
a lot-by-lot basis; however, the increased settlement is not expected to
exceed 1-inch total and ½-inch differential due to the dense nature and
similarity of the underlying fill and Pauba formation.
3.2.6 Import Soils
Import soils and/or borrow sites, if needed, should be evaluated by us prior
to import. Import soils should be uncontaminated, granular in nature, free of
organic material (loss on ignition less-than 2 percent), have low expansion
potential (E<51) and have a low corrosion impact to the proposed
improvements and R-value greater than 30 if to be used in upper 12 inches
of street subgrade.
3.2.7 Utility Trenches
Utility trenches should be backfilled with compacted fill in accordance with
the Standard Specifications for Public Works Construction, (“Greenbook”),
2018 Edition. Fill material above the pipe zone should be placed in lifts not
exceeding 8 inches in uncompacted thickness and should be compacted to
at least 90 percent relative compaction (ASTM D 1557) by mechanical
means only. Site soils may generally be suitable as trench backfill provided
these soils are screened of rocks over 1½ inches in diameter and organic
matter. If imported sand is used as backfill, the upper 3 feet in building and
pavement areas should be compacted to 95 percent. The upper 6 inches of
backfill in all pavement areas should be compacted to at least 95 percent
relative compaction.
Where granular backfill is used in utility trenches adjacent moisture sensitive
subgrades and foundation soils, we recommend that a cut-off “plug” of
impermeable material be placed in these trenches at the perimeter of
buildings, and at pavement edges adjacent to irrigated landscaped areas. A
“plug” can consist of a 5-foot long section of clayey soils with more than 35-
percent passing the No. 200 sieve, or a Controlled Low Strength Material
(CLSM) consisting of one sack of Portland-cement plus one sack of
bentonite per cubic-yard of sand. CLSM should generally conform to
requirements of the “Greenbook”. This is intended to reduce the likelihood
of water permeating trenches from landscaped areas, then seeping along
permeable trench backfill into the building and pavement subgrades,
resulting in wetting of moisture sensitive subgrade earth materials under
buildings and pavements.
Excavation of utility trenches should be performed in accordance with the
project plans, specifications and the California Construction Safety Orders
(latest Edition). The contractor should be responsible for providing a
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"competent person" as defined in Article 6 of the California Construction
Safety Orders. Contractors should be advised that sandy soils (such as fills
generated from the onsite alluvium) could make excavations particularly
unsafe if all safety precautions are not properly implemented. In addition,
excavations at or near the toe of slopes and/or parallel to slopes may be
highly unstable due to the increased driving force and load on the trench
wall. Spoil piles from the excavation(s) and construction equipment should
be kept away from the sides of the trenches.
3.2.8 Shrinkage
The volume change of excavated onsite soils upon recompaction is
expected to vary with materials, density, insitu moisture content, and
location and compaction effort. The in-place and compacted densities of
soil materials vary and accurate overall determination of shrinkage and
bulking cannot be made. Therefore, we recommend site grading include, if
possible, a balance area or ability to adjust grades slightly to accommodate
some variation. Based on our geotechnical laboratory results, we expect
recompaction shrinkage (when recompacted to an average 93 percent of
ASTM D1557) of 3- to 10-percent by volume for the existing fill. The Pauba
formation can experience 10 percent shrink for highly weathered materials
to 5 percent bulk for excavations deep than 10 to 15 feet.
3.2.9 Drainage
All drainage should be directed away from structures, slopes and
pavements by means of approved permanent/temporary drainage devices.
Adequate storm drainage of any proposed pad should be provided to avoid
wetting of foundation soils or slopes. Irrigation adjacent to buildings should
be avoided when possible. As an option, sealed-bottom planter boxes
and/or drought resistant vegetation should be used within 5-feet of
buildings.
3.3 Foundation Design
3.3.1 Bearing and Lateral Pressures
Based on our analysis, the proposed single-family residential structures may
be founded on conventional or Post-tensioned slab on-grade foundation
systems based on a Plasticity Index of 15 and the design parameters
provided below. The proposed foundations and slabs should be designed in
accordance with the structural consultants’ design, the minimum
geotechnical recommendations presented herein, and the applicable CBC.
In utilizing the minimum geotechnical foundation recommendations, the
structural consultant should design the foundation system to acceptable
deflection criteria as determined by the architect. Foundation footings may
be designed with the following geotechnical design parameters:
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- Allowable Bearing Capacity: 2,000 psf at a minimum depth of embedment of 12
inches (minimum width of 12 inches). This bearing
capacity may be increased by ⅓ for short-term
loading conditions (e.g., wind, seismic).
- Sliding Coefficient: 0.35
- Differential Settlement: 1-inch in 40 feet horizontal distance
The footing width, depth, reinforcement, slab reinforcement, and the slab-
on-grade thickness should be designed by the structural consultant based
on recommendations and soil characteristics indicated herein. If exterior
footings are within 5 feet horizontally of side yard swales, the footing should
be embedded sufficiently to ensure embedment below the swale bottom is
maintained.
3.3.2 Post Tension Design Parameters
If needed for settlement considerations, the following post-tensioned design
parameters are provided in accordance with the Post-Tensioning Institute
(PTI) Method (3rd Edition).
Table 2. PTI Method Design Parameters (3rd Edition)
Design Parameters PI≤15 or EI≤51
Thornthwaite Moisture Index -20
Clay Content (% of total sample) ≤15
Depth to Constant Soil Suction 9.0 ft.
Constant Soil Suction 3.9 ft.
Edge Moisture Variation Distance, em
- Edge Lift
- Center Lift
4.9 ft
9.0 ft
Soil Differential Movement, ym
- Edge Lift - Swell
- Center Lift - Shrink
1.0 inches
0.7 inches
3.4 Foundation Setback from Slopes
We recommend a minimum horizontal setback distance from the face of slopes for
all structural footings (retaining and decorative walls, flatwork, building footings,
pools, etc.). This distance is measured from the outside bottom edge of the footing
horizontally to the slope face (or the face of a retaining wall) and should be a
minimum of H/2, where H is the slope height (in feet).
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Table 3. Footing Setbacks
Slope Height Recommended Footing Setback
<5 feet 5 feet minimum
5 to 15 feet 7 feet minimum
>15 feet H/2, where H is the slope height, not to exceed 10
feet to 2:1 slope face
The soils within the structural setback area generally possess poor lateral stability
and improvements (such as retaining walls, pools, sidewalks, fences, pavements,
decorative flatwork, etc.) constructed within this setback area will be subject to
lateral movement and/or differential settlement. Potential distress to such
improvements may be mitigated by providing a deepened footing or a pier and
grade-beam foundation system to support the improvement. The deepened footing
should meet the setback described above. Modifications of slope inclinations near
foundations may increase the setback and should be reviewed by the design team
prior to completion of design or implementation.
3.5 Vapor Retarder
It has been a standard of care to install a moisture-vapor retarder underneath all
slabs where moisture condensation is undesirable. Moisture vapor retarders may
retard but not totally eliminate moisture vapor movement from the underlying soils up
through the slabs. Moisture vapor transmission may be additionally reduced by use
of concrete additives. Leighton and Associates, Inc. does not practice in the field of
moisture vapor transmission evaluation/mitigation. Therefore, we recommend that a
qualified person/firm be engaged/consulted with to evaluate the general and specific
moisture vapor transmission paths and any impact on the proposed construction.
This person/firm should provide recommendations for mitigation of potential adverse
impact of moisture vapor transmission on various components of the structure as
deemed appropriate.
However, based on our experience, the standard of practice in Southern California
has evolved over the last 15 to 20 years into a construction of a vapor retarder
system that generally consisted of a membrane (such as 10-mil thick or greater),
underlain by a capillary break consisting of 4 inches of clean ½-inch-minimum gravel
or 2-inch sand layer (SE>30). The structural engineer/architect or concrete contractor
often require a sand layer be placed over the membrane (typically 2-inch thick layer)
to help in curing and reduction of curling of concrete. If such sand layer is placed on
top of the membrane, the contractor should not allow the sand to become wet prior to
concrete placement (e.g., sand should not be placed if rain is expected).
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In conclusion, the construction of the vapor barrier/retarder system is dependent
on several variables which cannot be all geotechnically evaluated and/or tested.
As such, the design of this system should be a design team/owner decision taking
into consideration finish flooring materials and manufacture’s installation
requirements of proposed membrane. Moreover, we recommend that the design
team also follow ACI Committee 302 publication for “Guide for Concrete Slabs that
Receive Moisture-Sensitive Flooring Materials” (ACI 302.2R-06) which includes a
flow chart that assists in determining if a vapor barrier /retarder is required and
where it is to be placed.
3.6 Retaining Walls
Retaining wall earth pressures are a function of the amount of wall yielding
horizontally under load. If the wall can yield enough to mobilize full shear strength
of backfill soils, then the wall can be designed for "active" pressure. If the wall
cannot yield under the applied load, the shear strength of the soil cannot be
mobilized and the earth pressure will be higher. Such walls should be designed for
"at rest" conditions. If a structure moves toward the soils, the resulting resistance
developed by the soil is the "passive" resistance. Retaining walls backfilled with
non-expansive soils can be designed using the following equivalent fluid
pressures:
Table 4. Retaining Wall Design Earth Pressures (Static, Drained)
Loading
Conditions
Equivalent Fluid Density (pcf)
Level Backfill 2:1 Backfill
Active 36 55
At-Rest 55 85
Passive* 350 125 (2:1, sloping down)
* This assumes level condition in front of the wall will remain for the
duration of the project, not to exceed 2,000 psf at depth.
Unrestrained (yielding) cantilever walls should be designed for the active
equivalent-fluid weight value provided above for very low to low expansive soils
that are free draining. In the design of walls restrained from movement at the top
(non-yielding) such as basement or elevator pit/utility vaults, the at-rest equivalent
fluid weight value should be used. Total depth of retained earth for design of
cantilever walls should be measured as the vertical distance below the ground
surface measured at the wall face for stem design, or measured at the heel of the
footing for overturning and sliding calculations. Should a sloping backfill other than
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a 2:1 (horizontal:vertical) be constructed above the wall (or a backfill is loaded by
an adjacent surcharge load), the equivalent fluid weight values provided above
should be re-evaluated on an individual case basis by us. Non-standard wall
designs should also be reviewed by us prior to construction to check that the
proper soil parameters have been incorporated into the wall design.
All retaining walls should be provided with appropriate drainage. The outlet pipe
should be sloped to drain to a suitable outlet. Wall backfill should be non-
expansive (EI ≤ 21) sands compacted by mechanical methods to a minimum of 90
percent relative compaction (ASTM D 1557). Clayey site soils should not be used
as wall backfill. Walls should not be backfilled until wall concrete attains the 28-
day compressive strength and/or as determined by the Structural Engineer that the
wall is structurally capable of supporting backfill. Lightweight compaction
equipment should be used, unless otherwise approved by the Structural Engineer.
3.7 Sulfate Attack
The results of the laboratory testing on representative soils samples indicate
negligible exposure to concrete per ACI 318. Further testing should be performed at
the completion of site grading to confirm soluble-sulfate content of finish subgrade
soils.
3.8 Concrete Flatwork
Sidewalk/Flatwork should conform to City of Temecula standards. A representative
of Leighton should verify subgrade soil expansion, moisture conditions and
compaction prior to formwork and reinforcement placement. If subgrade soils
possess expansion index greater than 21, we recommend a minimum 8-inch
deepened edge be constructed for all flatwork to reduce moisture variation in
subgrade soils along concrete edges adjacent to open (unfinished) or irrigated
landscape areas.
Concrete flatwork should be constructed of uniformly cured, low-slump concrete and
should contain sufficient control/contraction joints. Additional provisions such as
ascending/descending slope conditions, perched (irrigation) water, special surcharge
loading conditions, potential expansive soil pressure and differential settlement/heave
should be incorporated into the design of exterior improvements. Additional exterior
slab details are suggested in the American Concrete Institute (ACI) guidelines.
Homeowners (HOA) should be advised of their maintenance responsibilities as well
as geotechnical issues that could affect performance of site improvements.
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3.9 Preliminary Pavement Design
The preliminary pavement design provided below is based on the locally accepted
Caltrans Highway Design Manual and a preliminary R-value of 25 based on our
laboratory testing for the proposed parking area. For planning and estimating
purposes, the pavement sections are calculated based on assumed Traffic Indexes
(TI) indicated in Table below
Table 5. Asphalt Pavement Sections
General Traffic
Condition*
Traffic Index
(TI)**
Asphalt Concrete
(inches)
Aggregate Base*
(inches)
Access Road 5.0 4.0 4.0
Local Street 6.0 4.0 6.0
*Per City of Temecula Standards
**Per city of Temecula Standard 115
Actual R-value of the subgrade soils will need to be verified after completion of site
grading to finalize the pavement design. Pavement design and minimum sections
should also conform to applicable City standards, where applicable.
For rigid pavement design, we recommend that a minimum of 6 inches of PCC
pavement be used, in high impact load areas or if to be subjected to truck traffic.
The PCC pavement should be placed on a minimum 4-inch aggregate base. The
PCC pavement may be placed directly on a compacted subgrade with an R-Value
of 40 or higher. The PCC pavement should have a minimum of 28-day
compressive strength of 3250 psi. Aggregate base should conform to the Standard
Specifications for Public Works Construction (Green Book), 2015 Edition.
Placement of concrete materials should follow applicable ACI and County standards.
The upper 6 inches of the subgrade soils should be moisture-conditioned to near
optimum moisture content, compacted to at least 95 percent relative compaction
(ASTM D1557) and kept in this condition until the pavement section is constructed.
Minimum relative compaction requirements for aggregate base should be 95
percent of the maximum laboratory density as determined by ASTM D1557. If
applicable, aggregate base should conform to the “Standard Specifications for
Public Works Construction” (Greenbook) current edition or Caltrans Class 2
aggregate base and applicable City standards
If pavement areas are adjacent to watered landscape areas, some deterioration of
the subgrade load bearing capacity may result. Moisture control measures such as
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deepened curbs or other moisture barrier materials may be used to prevent the
subgrade soils from becoming saturated. The use of concrete cutoff or edge
barriers should be considered when pavement is planned adjacent to either open
(unfinished) or irrigated landscaped areas.
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4.0 GEOTECHNICAL CONSTRUCTION SERVICES
Geotechnical review is of paramount importance in engineering practice. Poor
performances of many foundation and earthwork projects have been attributed to
inadequate construction review. We recommend that Leighton and Associates, Inc. be
provided the opportunity to review the grading plan and foundation plan(s) prior to bid.
Reasonably-continuous construction observation and review during site grading and
foundation installation allows for evaluation of the actual soil conditions and the ability to
provide appropriate revisions where required during construction. Geotechnical
conclusions and preliminary recommendations should be reviewed and verified by
Leighton and Associates, Inc. during construction, and revised accordingly if geotechnical
conditions encountered vary from our findings and interpretations. Geotechnical
observation and testing should be provided:
After completion of site demolition and clearing,
During over-excavation of compressible soil,
During compaction of all fill materials,
After excavation of all footings and prior to placement of concrete,
During utility trench backfilling and compaction, and
When any unusual conditions are encountered.
Additional geotechnical exploration and analysis may be required based on final
development plans, for reasons such as significant changes in slopes locations, heights
or proposed structure locations/footprints. We should review grading (civil) and
foundation (structural) plans, and comment further on geotechnical aspects of this project.
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5.0 LIMITATIONS
This report was based in part on data obtained from a limited number of observations,
site visits, soil excavations, samples and tests. Such information is, by necessity,
incomplete. The nature of many sites is such that differing soil or geologic conditions
can be present within small distances and under varying climatic conditions. Changes
in subsurface conditions can and do occur over time. Therefore, our findings,
conclusions and recommendations presented in this report are based on the
assumption that we (Leighton and Associates, Inc.) will provide geotechnical
observation and testing during construction as the Geotechnical Engineer of Record for
this project. Please refer to Appendix B, GBA’s Important Information About This
Geotechnical-Engineering Report, prepared by the Geoprofessional Business
Association (GBA) presenting additional information and limitations regarding
geotechnical engineering studies and reports.
This report was prepared for the sole use of Client and their design team, for application
to design of the proposed development, in accordance with generally accepted
geotechnical engineering practices at this time in California. Any unauthorized use of or
reliance on this report constitutes an agreement to defend and indemnify Leighton and
Associates, Inc. from and against any liability which may arise as a result of such use or
reliance, regardless of any fault, negligence, or strict liability of Leighton and Associates,
Inc.
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REFERENCES
Army Corps of Engineers, Evaluation of Settlement for Dynamic and Transient Loads,
Technical Engineering and Design Guides as Adapted from the US Army Corps
of Engineers, No. 9, American Society of Civil Engineers Press.
American Society of Civil Engineers, 2010, Minimum Design Loads for Buildings and
Other Structures, ASCE/SEI 7-10 Publication.
Byerly, John R., Inc., 2012, Interim Grading and Fill Evaluation Report - Planning Areas
(PAs) 14-24 and 27-31, Roripaugh Ranch, Butterfield Stage Road and Murrieta
Hot Springs Road, Temecula, California, Report No. 9794, File No. S-13141,
dated November 27, 2012.
Byerly, John R., Inc., 2012a, Report of Existing Grading and Fill; Roripaugh Ranch,
Phase II, Report No. 9794, File No. S-13141, dated December 10, 2012.
California Building Code, 2016, California Code of Regulations Title 24, Part 2, Volume
2 of 2.
California Geologic Survey (CGS), 2018, Earthquake Fault Zones, A guide for
Government Agencies, Property Owners / Developers, And Geoscience
Practitioners for Assessing Fault Rupture Hazards in California, Department of
Conservation, Division of Mines and Geology, Special Publication 42. Revised
2018.
California Geologic Survey (CGS), 2003. The Revised 2002 California Probabilistic
Seismic Hazard Maps, June 2003. By Tianquing Cao, William A. Bryant, Badie
Rowshandel, David Branum and Christopher J. Wills.
Kennedy, M.P., 1977, Recency and Character of Faulting Along the Elsinore Fault Zone
in Southern Riverside County, California, CDMG Special Report 131.
Leighton and Associates, Inc., 1999, Supplemental Fault Investigation, Winchester
Properties, planning Areas 6, 7 and 8, Murrieta Hot Springs Area, Riverside
County, California, Project No. 11861432.072, dated March 23.
Leighton and Associates, Inc., 2001, Preliminary Geotechnical Evaluation, Portion of
Roripaugh Ranch, Tentative Tract No. 29661, City of Temecula, Riverside
Country, California, Project No. 11990013-001, dated May 22.
Leighton Consulting, Inc., 2013, Geotechnical Exploration, Eastern Municipal Water
District’s (EMWD’s), Wine Country Infrastructure Project – Gravity Sewers and
Force Mains, Riverside County, California, PN. 603350002, dated January 31.
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Leighton Consulting, Inc., 2015, Geotechnical Observations and Compaction Testing
Report, Wine Country Infrastructure Project Sewer - Phase I Pipelines, Sta.~
10+00 to 72+76 (Butterfield Stage Rd to Roripaugh Ranch East), Wine Country
Area, Riverside County, California, Project No. 10504.001, dated March 12.
Leighton and Associates Inc., 2017a, Geotechnical Review, Long Valley Wash Channel
Improvements, Roripaugh Ranch Phase 2 – PN 4001, Temecula California, dated
April 19, 2017, Project No. 10967.108.
Leighton and Associates Inc., 2017b, Geotechnical Exploration Report, Roripaugh Ranch
Community Sports Park (PA 27) – PN 3008, Roripaugh Ranch, Temecula
California, dated October 9, 2017, Project No. 10967.106.
Leighton and Associates Inc., 2017c, Geotechnical Exploration / Pavement Design
Report, Roripaugh Ranch Loop Road, Roripaugh Ranch Phase 2 – PN 3004,
Temecula California, dated October 30, 2017, Project No. 10967.107.
Leighton and Associates Inc., 2017d, Geotechnical Exploration Report, Proposed
Roripaugh Ranch Park and Ride (PA 33B) (PN 4002), Roripaugh Ranch,
Temecula California, dated October November 27, 2017, Project No. 10967.109.
Public Works Standard, Inc., 2018, Greenbook, Standard Specifications for Public
Works Construction: 2018 Edition, BNI Building News, Anaheim, California.
Rick Engineering Company, 2018a, Roripaugh Ranch Tentative Tract Map 37341, a
subdivision of TTM 37368, 60 scale, 37 sheets, plot date April 25, 2018.
Rick Engineering Company, 2018b, Rough Grading Plan TM 37368, 40 scale, 46
sheets, plot date May 11, 2018.
Riverside County, 2018, Map My County, Riverside County Integrated Project Website,
https://gis.countyofriverside.us/Html5Viewer/?viewer=MMC_Public.
Tokimatsu, K., and Seed, H.B., 1987, Evaluation of Settlements in Sands Due to
Earthquake Shaking, ASCE Journal of Geotechnical Engineering, Vol. 113, No.
8, dated August.
USGS, 2018, A Web Based Computer Program Published by USGS to calculate
Seismic Hazard Curves and Response and Design Parameters based on ASCE
7-10 seismic procedures.
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Date: June 2018
Legend
Parcel Boundary
Project Boundary
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APPENDIX A
EARTHWORK AND GRADING SPECIFICATIONS
-i-
LEIGHTON AND ASSOCIATES, INC.
GENERAL EARTHWORK AND GRADING SPECIFICATIONS FOR ROUGH GRADING
TABLE OF CONTENTS
Section Page
1.0 GENERAL 1
1.1 Intent 1
1.2 The Geotechnical Consultant of Record 1
1.3 The Earthwork Contractor 2
2.0 PREPARATION OF AREAS TO BE FILLED 2
2.1 Clearing and Grubbing 2
2.2 Processing 3
2.3 Overexcavation 3
2.4 Benching 3
2.5 Evaluation/Acceptance of Fill Areas 3
3.0 FILL MATERIAL 4
3.1 General 4
3.2 Oversize 4
3.3 Import 4
4.0 FILL PLACEMENT AND COMPACTION 4
4.1 Fill Layers 4
4.2 Fill Moisture Conditioning 5
4.3 Compaction of Fill 5
4.4 Compaction of Fill Slopes 5
4.5 Compaction Testing 5
4.6 Frequency of Compaction Testing 5
4.7 Compaction Test Locations 6
5.0 SUBDRAIN INSTALLATION 6
6.0 EXCAVATION 6
7.0 TRENCH BACKFILLS 6
7.1 Safety 6
7.2 Bedding & Backfill 7
7.3 Lift Thickness 7
7.4 Observation and Testing 7
Standard Details
A - Keying and Benching Rear of Text
B - Oversize Rock Disposal Rear of Text
C - Canyon Subdrains Rear of Text
D - Buttress or Replacement Fill Subdrains Rear of Text
E - Transition Lot Fills and Side Hill Fills Rear of Text
Retaining Wall Rear of Text
LEIGHTON AND ASSOCIATES, INC.
General Earthwork and Grading Specifications
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1.0 General
1.1 Intent
These General Earthwork and Grading Specifications are for the grading and
earthwork shown on the approved grading plan(s) and/or indicated in the
geotechnical report(s). These Specifications are a part of the recommendations
contained in the geotechnical report(s). In case of conflict, the specific
recommendations in the geotechnical report shall supersede these more general
Specifications. Observations of the earthwork by the project Geotechnical
Consultant during the course of grading may result in new or revised
recommendations that could supersede these specifications or the
recommendations in the geotechnical report(s).
1.2 The Geotechnical Consultant of Record
Prior to commencement of work, the owner shall employ the Geotechnical
Consultant of Record (Geotechnical Consultant). The Geotechnical Consultants
shall be responsible for reviewing the approved geotechnical report(s) and
accepting the adequacy of the preliminary geotechnical findings, conclusions, and
recommendations prior to the commencement of the grading.
Prior to commencement of grading, the Geotechnical Consultant shall review the
"work plan" prepared by the Earthwork Contractor (Contractor) and schedule
sufficient personnel to perform the appropriate level of observation, mapping, and
compaction testing.
During the grading and earthwork operations, the Geotechnical Consultant shall
observe, map, and document the subsurface exposures to verify the geotechnical
design assumptions. If the observed conditions are found to be significantly
different than the interpreted assumptions during the design phase, the
Geotechnical Consultant shall inform the owner, recommend appropriate changes
in design to accommodate the observed conditions, and notify the review agency
where required. Subsurface areas to be geotechnically observed, mapped,
elevations recorded, and/or tested include natural ground after it has been cleared
for receiving fill but before fill is placed, bottoms of all "remedial removal" areas,
all key bottoms, and benches made on sloping ground to receive fill.
The Geotechnical Consultant shall observe the moisture-conditioning and
processing of the subgrade and fill materials and perform relative compaction
testing of fill to determine the attained level of compaction. The Geotechnical
Consultant shall provide the test results to the owner and the Contractor on a
routine and frequent basis.
LEIGHTON AND ASSOCIATES, INC.
General Earthwork and Grading Specifications
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1.3 The Earthwork Contractor
The Earthwork Contractor (Contractor) shall be qualified, experienced, and
knowledgeable in earthwork logistics, preparation and processing of ground to
receive fill, moisture-conditioning and processing of fill, and compacting fill. The
Contractor shall review and accept the plans, geotechnical report(s), and these
Specifications prior to commencement of grading. The Contractor shall be solely
responsible for performing the grading in accordance with the plans and
specifications.
The Contractor shall prepare and submit to the owner and the Geotechnical
Consultant a work plan that indicates the sequence of earthwork grading, the
number of "spreads" of work and the estimated quantities of daily earthwork
contemplated for the site prior to commencement of grading. The Contractor
shall inform the owner and the Geotechnical Consultant of changes in work
schedules and updates to the work plan at least 24 hours in advance of such
changes so that appropriate observations and tests can be planned and
accomplished. The Contractor shall not assume that the Geotechnical Consultant
is aware of all grading operations.
The Contractor shall have the sole responsibility to provide adequate equipment
and methods to accomplish the earthwork in accordance with the applicable
grading codes and agency ordinances, these Specifications, and the
recommendations in the approved geotechnical report(s) and grading plan(s). If,
in the opinion of the Geotechnical Consultant, unsatisfactory conditions, such as
unsuitable soil, improper moisture condition, inadequate compaction, insufficient
buttress key size, adverse weather, etc., are resulting in a quality of work less than
required in these specifications, the Geotechnical Consultant shall reject the work
and may recommend to the owner that construction be stopped until the
conditions are rectified.
2.0 Preparation of Areas to be Filled
2.1 Clearing and Grubbing
Vegetation, such as brush, grass, roots, and other deleterious material shall be
sufficiently removed and properly disposed of in a method acceptable to the
owner, governing agencies, and the Geotechnical Consultant.
The Geotechnical Consultant shall evaluate the extent of these removals
depending on specific site conditions. Earth fill material shall not contain more
than 1 percent of organic materials (by volume). No fill lift shall contain more
than 5 percent of organic matter. Nesting of the organic materials shall not be
allowed.
LEIGHTON AND ASSOCIATES, INC.
General Earthwork and Grading Specifications
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If potentially hazardous materials are encountered, the Contractor shall stop work
in the affected area, and a hazardous material specialist shall be informed
immediately for proper evaluation and handling of these materials prior to
continuing to work in that area.
As presently defined by the State of California, most refined petroleum products
(gasoline, diesel fuel, motor oil, grease, coolant, etc.) have chemical constituents
that are considered to be hazardous waste. As such, the indiscriminate dumping
or spillage of these fluids onto the ground may constitute a misdemeanor,
punishable by fines and/or imprisonment, and shall not be allowed.
2.2 Processing
Existing ground that has been declared satisfactory for support of fill by the
Geotechnical Consultant shall be scarified to a minimum depth of 6 inches.
Existing ground that is not satisfactory shall be overexcavated as specified in the
following section. Scarification shall continue until soils are broken down and
free of large clay lumps or clods and the working surface is reasonably uniform,
flat, and free of uneven features that would inhibit uniform compaction.
2.3 Overexcavation
In addition to removals and overexcavations recommended in the approved
geotechnical report(s) and the grading plan, soft, loose, dry, saturated, spongy,
organic-rich, highly fractured or otherwise unsuitable ground shall be
overexcavated to competent ground as evaluated by the Geotechnical Consultant
during grading.
2.4 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 or key
shall be a minimum of 15 feet wide and at least 2 feet deep, into competent
material as evaluated by the Geotechnical Consultant. Other benches shall be
excavated a minimum height of 4 feet into competent material or as otherwise
recommended by the Geotechnical Consultant. Fill placed on ground sloping
flatter than 5:1 shall also be benched or otherwise overexcavated to provide a flat
subgrade for the fill.
2.5 Evaluation/Acceptance of Fill Areas
All areas to receive fill, including removal and processed areas, key bottoms, and
benches, shall be observed, mapped, elevations recorded, and/or tested prior to
being accepted by the Geotechnical Consultant as suitable to receive fill. The
Contractor shall obtain a written acceptance from the Geotechnical Consultant
LEIGHTON AND ASSOCIATES, INC.
General Earthwork and Grading Specifications
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prior to fill placement. A licensed surveyor shall provide the survey control for
determining elevations of processed areas, keys, and benches.
3.0 Fill Material
3.1 General
Material to be used as fill shall be essentially free of organic matter and other
deleterious substances evaluated and accepted by the Geotechnical Consultant
prior to placement. Soils of poor quality, such as those with unacceptable
gradation, high expansion potential, or low strength shall be placed in areas
acceptable to the Geotechnical Consultant or mixed with other soils to achieve
satisfactory fill material.
3.2 Oversize
Oversize material defined as rock, or other irreducible material with a maximum
dimension greater than 8 inches, shall not be buried or placed in fill unless
location, materials, and placement methods are specifically accepted by the
Geotechnical Consultant. Placement operations shall be such that nesting of
oversized material does not occur and such that oversize material is completely
surrounded by compacted or densified fill. Oversize material shall not be placed
within 10 vertical feet of finish grade or within 2 feet of future utilities or
underground construction.
3.3 Import
If importing of fill material is required for grading, proposed import material shall
meet the requirements of Section 3.1. The potential import source shall be given
to the Geotechnical Consultant at least 48 hours (2 working days) before
importing begins so that its suitability can be determined and appropriate tests
performed.
4.0 Fill Placement and Compaction
4.1 Fill Layers
Approved fill material shall be placed in areas prepared to receive fill (per
Section 3.0) in near-horizontal layers not exceeding 8 inches in loose thickness.
The Geotechnical Consultant may accept thicker layers if testing indicates the
grading procedures can adequately compact the thicker layers. Each layer shall be
spread evenly and mixed thoroughly to attain relative uniformity of material and
moisture throughout.
LEIGHTON AND ASSOCIATES, INC.
General Earthwork and Grading Specifications
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4.2 Fill Moisture Conditioning
Fill soils shall be watered, dried back, blended, and/or mixed, as necessary to
attain a relatively uniform moisture content at or slightly over optimum.
Maximum density and optimum soil moisture content tests shall be performed in
accordance with the American Society of Testing and Materials (ASTM Test
Method D1557).
4.3 Compaction of Fill
After each layer has been moisture-conditioned, mixed, and evenly spread, it shall
be uniformly compacted to not less than 90 percent of maximum dry density
(ASTM Test Method D1557). Compaction equipment shall be adequately sized
and be either specifically designed for soil compaction or of proven reliability to
efficiently achieve the specified level of compaction with uniformity.
4.4 Compaction of Fill Slopes
In addition to normal compaction procedures specified above, compaction of
slopes shall be accomplished by backrolling of slopes with sheepsfoot rollers at
increments of 3 to 4 feet in fill elevation, or by other methods producing
satisfactory results acceptable to the Geotechnical Consultant. Upon completion
of grading, relative compaction of the fill, out to the slope face, shall be at least
90 percent of maximum density per ASTM Test Method D1557.
4.5 Compaction Testing
Field-tests for moisture content and relative compaction of the fill soils shall be
performed by the Geotechnical Consultant. Location and frequency of tests shall
be at the Consultant's discretion based on field conditions encountered.
Compaction test locations will not necessarily be selected on a random basis. Test
locations shall be selected to verify adequacy of compaction levels in areas that
are judged to be prone to inadequate compaction (such as close to slope faces and
at the fill/bedrock benches).
4.6 Frequency of Compaction Testing
Tests shall be taken at intervals not exceeding 2 feet in vertical rise and/or
1,000 cubic yards of compacted fill soils embankment. In addition, as a guideline,
at least one test shall be taken on slope faces for each 5,000 square feet of slope
face and/or each 10 feet of vertical height of slope. The Contractor shall assure
that fill construction is such that the testing schedule can be accomplished by the
Geotechnical Consultant. The Contractor shall stop or slow down the earthwork
construction if these minimum standards are not met.
LEIGHTON AND ASSOCIATES, INC.
General Earthwork and Grading Specifications
-6-
4.7 Compaction Test Locations
The Geotechnical Consultant shall document the approximate elevation and
horizontal coordinates of each test location. The Contractor shall coordinate with
the project surveyor to assure that sufficient grade stakes are established so that
the Geotechnical Consultant can determine the test locations with sufficient
accuracy. At a minimum, two grade stakes within a horizontal distance of 100
feet and vertically less than 5 feet apart from potential test locations shall be
provided.
5.0 Subdrain Installation
Subdrain systems shall be installed in accordance with the approved geotechnical
report(s), the grading plan. The Geotechnical Consultant may recommend additional
subdrains and/or changes in subdrain extent, location, grade, or material depending on
conditions encountered during grading. All subdrains shall be surveyed by a land
surveyor/civil engineer for line and grade after installation and prior to burial. Sufficient
time should be allowed by the Contractor for these surveys.
6.0 Excavation
Excavations, as well as over-excavation for remedial purposes, shall be evaluated by the
Geotechnical Consultant during grading. Remedial removal depths shown on
geotechnical plans are estimates only. The actual extent of removal shall be determined
by the Geotechnical Consultant based on the field evaluation of exposed conditions
during grading. Where fill-over-cut slopes are to be graded, the cut portion of the slope
shall be made, evaluated, and accepted by the Geotechnical Consultant prior to placement
of materials for construction of the fill portion of the slope, unless otherwise
recommended by the Geotechnical Consultant.
7.0 Trench Backfills
7.1 Safety
The Contractor shall follow all OSHA and Cal/OSHA requirements for safety of
trench excavations.
LEIGHTON AND ASSOCIATES, INC.
General Earthwork and Grading Specifications
-7-
7.2 Bedding and Backfill
All bedding and backfill of utility trenches shall be performed in accordance with
the applicable provisions of Standard Specifications of Public Works
Construction. Bedding material shall have a Sand Equivalent greater than 30
(SE>30). The bedding shall be placed to 1 foot over the top of the conduit and
densified by jetting. Backfill shall be placed and densified to a minimum of
90 percent of relative compaction from 1 foot above the top of the conduit to the
surface.
The Geotechnical Consultant shall test the trench backfill for relative compaction.
At least one test should be made for every 300 feet of trench and 2 feet of fill.
7.3 Lift Thickness
Lift thickness of trench backfill shall not exceed those allowed in the Standard
Specifications of Public Works Construction unless the Contractor can
demonstrate to the Geotechnical Consultant that the fill lift can be compacted to
the minimum relative compaction by his alternative equipment and method.
7.4 Observation and Testing
The jetting of the bedding around the conduits shall be observed by the
Geotechnical Consultant.
Update Geotechnical Report 11835.002
Roripaugh Ranch Residential Development, Planning Areas 14 through 24, 27 through 31 & 33B June 28, 2018
APPENDIX B
GBA - IMPORTANT INFORMATION ABOUT THIS GEOTECHNICAL-ENGINEERING
REPORT
Geotechnical-Engineering Report
Important Information about This
Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.
While you cannot eliminate all such risks, you can manage them. The following information is provided to help.
The Geoprofessional Business Association (GBA)
has prepared this advisory to help you – assumedly
a client representative – interpret and apply this
geotechnical-engineering report as effectively
as possible. In that way, clients can benefit from
a lowered exposure to the subsurface problems
that, for decades, have been a principal cause of
construction delays, cost overruns, claims, and
disputes. If you have questions or want more
information about any of the issues discussed below,
contact your GBA-member geotechnical engineer.
Active involvement in the Geoprofessional Business
Association exposes geotechnical engineers to a
wide array of risk-confrontation techniques that can
be of genuine benefit for everyone involved with a
construction project.
Geotechnical-Engineering Services Are Performed for
Specific Purposes, Persons, and Projects
Geotechnical engineers structure their services to meet the specific
needs of their clients. A geotechnical-engineering study conducted
for a given civil engineer will not likely meet the needs of a civil-
works constructor or even a different civil engineer. Because each
geotechnical-engineering study is unique, each geotechnical-
engineering report is unique, prepared solely for the client. Those who
rely on a geotechnical-engineering report prepared for a different client
can be seriously misled. No one except authorized client representatives
should rely on this geotechnical-engineering report without first
conferring with the geotechnical engineer who prepared it. And no one
– not even you – should apply this report for any purpose or project except
the one originally contemplated.
Read this Report in Full
Costly problems have occurred because those relying on a geotechnical-
engineering report did not read it in its entirety. Do not rely on an
executive summary. Do not read selected elements only. Read this report
in full.
You Need to Inform Your Geotechnical Engineer
about Change
Your geotechnical engineer considered unique, project-specific factors
when designing the study behind this report and developing the
confirmation-dependent recommendations the report conveys. A few
typical factors include:
• the client’s goals, objectives, budget, schedule, and
risk-management preferences;
• the general nature of the structure involved, its size,
configuration, and performance criteria;
• the structure’s location and orientation on the site; and
• other planned or existing site improvements, such as
retaining walls, access roads, parking lots, and
underground utilities.
Typical changes that could erode the reliability of this report include
those that affect:
• the site’s size or shape;
• the function of the proposed structure, as when it’s
changed from a parking garage to an office building, or
from a light-industrial plant to a refrigerated warehouse;
• the elevation, configuration, location, orientation, or
weight of the proposed structure;
• the composition of the design team; or
• project ownership.
As a general rule, always inform your geotechnical engineer of project
changes – even minor ones – and request an assessment of their
impact. The geotechnical engineer who prepared this report cannot accept
responsibility or liability for problems that arise because the geotechnical
engineer was not informed about developments the engineer otherwise
would have considered.
This Report May Not Be Reliable
Do not rely on this report if your geotechnical engineer prepared it:
• for a different client;
• for a different project;
• for a different site (that may or may not include all or a
portion of the original site); or
• before important events occurred at the site or adjacent
to it; e.g., man-made events like construction or
environmental remediation, or natural events like floods,
droughts, earthquakes, or groundwater fluctuations.
Note, too, that it could be unwise to rely on a geotechnical-engineering
report whose reliability may have been affected by the passage of time,
because of factors like changed subsurface conditions; new or modified
codes, standards, or regulations; or new techniques or tools. If your
geotechnical engineer has not indicated an “apply-by” date on the report,
ask what it should be, and, in general, if you are the least bit uncertain
about the continued reliability of this report, contact your geotechnical
engineer before applying it. A minor amount of additional testing or
analysis – if any is required at all – could prevent major problems.
Most of the “Findings” Related in This Report Are
Professional Opinions
Before construction begins, geotechnical engineers explore a site’s
subsurface through various sampling and testing procedures.
Geotechnical engineers can observe actual subsurface conditions only at
those specific locations where sampling and testing were performed. The
data derived from that sampling and testing were reviewed by your
geotechnical engineer, who then applied professional judgment to
form opinions about subsurface conditions throughout the site. Actual
sitewide-subsurface conditions may differ – maybe significantly – from
those indicated in this report. Confront that risk by retaining your
geotechnical engineer to serve on the design team from project start to
project finish, so the individual can provide informed guidance quickly,
whenever needed.
This Report’s Recommendations Are
Confirmation-Dependent
The recommendations included in this report – including any options
or alternatives – are confirmation-dependent. In other words, they are
not final, because the geotechnical engineer who developed them relied
heavily on judgment and opinion to do so. Your geotechnical engineer
can finalize the recommendations only after observing actual subsurface
conditions revealed during construction. If through observation your
geotechnical engineer confirms that the conditions assumed to exist
actually do exist, the recommendations can be relied upon, assuming
no other changes have occurred. The geotechnical engineer who prepared
this report cannot assume responsibility or liability for confirmation-
dependent recommendations if you fail to retain that engineer to perform
construction observation.
This Report Could Be Misinterpreted
Other design professionals’ misinterpretation of geotechnical-
engineering reports has resulted in costly problems. Confront that risk
by having your geotechnical engineer serve as a full-time member of the
design team, to:
• confer with other design-team members,
• help develop specifications,
• review pertinent elements of other design professionals’
plans and specifications, and
• be on hand quickly whenever geotechnical-engineering
guidance is needed.
You should also confront the risk of constructors misinterpreting this
report. Do so by retaining your geotechnical engineer to participate in
prebid and preconstruction conferences and to perform construction
observation.
Give Constructors a Complete Report and Guidance
Some owners and design professionals mistakenly believe they can shift
unanticipated-subsurface-conditions liability to constructors by limiting
the information they provide for bid preparation. To help prevent
the costly, contentious problems this practice has caused, include the
complete geotechnical-engineering report, along with any attachments
or appendices, with your contract documents, but be certain to note
conspicuously that you’ve included the material for informational
purposes only. To avoid misunderstanding, you may also want to note
that “informational purposes” means constructors have no right to rely
on the interpretations, opinions, conclusions, or recommendations in
the report, but they may rely on the factual data relative to the specific
times, locations, and depths/elevations referenced. Be certain that
constructors know they may learn about specific project requirements,
including options selected from the report, only from the design
drawings and specifications. Remind constructors that they may
perform their own studies if they want to, and be sure to allow enough
time to permit them to do so. Only then might you be in a position
to give constructors the information available to you, while requiring
them to at least share some of the financial responsibilities stemming
from unanticipated conditions. Conducting prebid and preconstruction
conferences can also be valuable in this respect.
Read Responsibility Provisions Closely
Some client representatives, design professionals, and constructors do
not realize that geotechnical engineering is far less exact than other
engineering disciplines. That lack of understanding has nurtured
unrealistic expectations that have resulted in disappointments, delays,
cost overruns, claims, and disputes. To confront that risk, geotechnical
engineers commonly include explanatory provisions in their reports.
Sometimes labeled “limitations,” many of these provisions indicate
where geotechnical engineers’ responsibilities begin and end, to help
others recognize their own responsibilities and risks. Read these
provisions closely. Ask questions. Your geotechnical engineer should
respond fully and frankly.
Geoenvironmental Concerns Are Not Covered
The personnel, equipment, and techniques used to perform an
environmental study – e.g., a “phase-one” or “phase-two” environmental
site assessment – differ significantly from those used to perform
a geotechnical-engineering study. For that reason, a geotechnical-
engineering report does not usually relate any environmental findings,
conclusions, or recommendations; e.g., about the likelihood of
encountering underground storage tanks or regulated contaminants.
Unanticipated subsurface environmental problems have led to project
failures. If you have not yet obtained your own environmental
information, ask your geotechnical consultant for risk-management
guidance. As a general rule, do not rely on an environmental report
prepared for a different client, site, or project, or that is more than six
months old.
Obtain Professional Assistance to Deal with Moisture
Infiltration and Mold
While your geotechnical engineer may have addressed groundwater,
water infiltration, or similar issues in this report, none of the engineer’s
services were designed, conducted, or intended to prevent uncontrolled
migration of moisture – including water vapor – from the soil through
building slabs and walls and into the building interior, where it can
cause mold growth and material-performance deficiencies. Accordingly,
proper implementation of the geotechnical engineer’s recommendations
will not of itself be sufficient to prevent moisture infiltration. Confront
the risk of moisture infiltration by including building-envelope or mold
specialists on the design team. Geotechnical engineers are not building-
envelope or mold specialists.
Copyright 2016 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly
prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission
of GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any
kind. Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent
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