HomeMy WebLinkAboutCitrus Continuation High School HYDROLOGY STUDY
FOR
Citrus Continuation High School
Prepared for:
FONTANA UNIFIED SCHOOL DISTRICT
9680 Citrus Avenue
Fontana, CA 92334
Prepared by:
Carolina Gonzalez
FUSCOE ENGINEERING, INC.
2850 Inland Empire Blvd., Ste B
Ontario, CA 91764
.-- Phone: (909) 581 -0676 Fax: (909) 581 -0696
Reviewed by:
mando J. Garcia - Baldizzone P.E.
FUSCOE ENGINEERING, INC.
2850 Inland Empire Blvd., Ste B
Ontario, CA 91764
Ph • ne: (909) 581 -0676 Fax: (909) 581 -0696
Date Prepared: October 6, 2009
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INDEX MAP
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SCALE: 1"=150'
2.5 Secondary Sejsmic Hazards 602562 -001
In general, secondary seismic hazards for sites in the region could include soil
liquefaction, earthquake - induced settlement, lateral displacement, landsliding, seiches,
and tsunamis. The potential for secondary seismic hazards at the site is discussed below.
2.5.1 Lique Potential
Liquefaction is the loss of soil strength or stiffness due to a buildup of excess
pore -water pressure during strong ground shaking. Liquefaction is associated
primarily with loose (low density), granular, saturated soil. Effects of severe
liquefaction can include sand boils, excessive settlement, bearing capacity
failures, and lateral spreading.
The site is mapped in an area designated as having a low liquefaction potential in
the San Bernardino County Official Land Use Plan for the Fontana Quadrangle
(San Bernardino County, 2007). In addition, regional groundwater maps and
groundwater data indicate that shallow groundwater conditions do not exist
locally, nor have they existed historically (see Section 2.3, Groundwater). Based
on these findings, the potential for liquefaction onsite is considered very low.
2.5.2 Seismically Induced Settlement
Seismically induced settlement consists of dry dynamic settlement (above
groundwater) and liquefaction - induced settlement (below groundwater). During a
strong seismic event, seismically induced settlement can occur within loose to
moderately dense sandy soil due to reduction in volume during, and shortly after, an
earthquake event. Settlement caused by ground shaking is often nonuniformly
distributed, which can result in differential settlement.
We have performed analyses to estimate the seismically induced settlement using
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the methods set forth by Tokimatsu and Seed (1987). The results of our analyses
indicate that there are thin silt and sand layers at depths which have relatively low
density based on the low blow counts. However, these layers are not anticipated to
develop more than 1 inch of dry seismic settlement based on the analysis.
Differential settlement due to seismic loading is expected to be half of the total
settlement over a horizontal distance of 40 feet. Seismic settlement is not
considered a geotechnical constraint to the project. Seismically induced settlement
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1 slump concrete can reduce the potential for shrinkage cracking. Additionally, our
experience indicates that reinforcement in slabs and foundations can generally reduce the
potential for concrete cracking.
Moisture retarders can reduce, but not eliminate moisture vapor rise from the underlying
soils up through the slab. Floor covering manufacturers should be consulted for specific
recommendations.
Leighton does not practice in the field of moisture vapor transmission evaluation.
Therefore, we recommend that a qualified person be consulted to evaluate the general and
specific moisture vapor transmission paths and any impact on the proposed construction.
That person should provide recommendations for mitigation of potential adverse impact of
moisture vapor transmission on various components of the structures as deemed
appropriate.
3.5 Retaining Walls
If planned, we recommend that retaining walls be backfilled with very low expansive
soil, and constructed with a backdrain in accordance with the recommendations provided
on Figure 8, Retaining Wall Backfll and Subdrain Detail. Using expansive soil as
retaining wall backfill will result in higher lateral earth pressures exerted on the wall.
Based on these recommendations, the following parameters may be used for the design of
conventional retaining walls up to 6 feet tall, with a level backfill:
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Table 2. Retaining Walls with Level Backfill
t nnoLli „n. r, yui+,:lc nr 1:110:1I
ponud.. Ater -i a hir -r,nq
Active (cantilever) 35
At -Rest (braced) 55
Passive 350 (allowable)
(Maximum of 3.500 psf)
Cantilever walls that are designed to yield at least 0.001H, where H is equal to the wall
1 height, may be designed using the active condition. Rigid walls and walls braced at the
top should be designed using the at -rest condition. Passive pressure is used to compute
I soil resistance to lateral structural movement. In addition, for sliding resistance, a
frictional resistance coefficient of 0.35 may be used at the concrete and soil interface.
The lateral passive resistance should be taken into account only if it is ensured that soil
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40 .
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t: 602562 -001
Based on our laboratory testing, the onsite soil is considered mildly corrosive to ferrous
metals. Corrosion information presented in this report should he provided to your
underground utility subcontractors.
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3.7 Pavement Design
II A representative soil sample tested during this investigation had an R -value of 76. Based
on the design procedures outlined in the current Caltrans Ilighway Design Manual. our
11 geotechnical experience in the site vicinity, and selecting a design R -value of 60,
preliminary flexible pavement sections may consist of the following for the Traffic
Indices (Ti) indicated. Final pavement design should he based on the Traffic Index
determined by the project civil engineer and R -value testing provided near the end of
grading of the new parking lots.
Table 3. Preliminary Asphalt Pavement Sections
1 Traffic index Asphalt Concrete (1(') Class :ARgregate Base (.\B) Thickness
r hirkness (foot) (Coot)
6 or less (Auto Parking) 0 25 0.31
1 7(nustane) 011! 015
If the pavement is to he constructed prior to construction of the structures. we
recommend that the full depth of the pavement section he placed in order to support
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heavy construction traffic.
All pavement construction should be performed in accordance with the Standard
Specifications for Public Works Construction. Field inspection and periodic testing, as
needed during placement of the base course materials, should he undertaken to ensure
that the requirements of the standard specifications are fulfilled. Prior to placement of
aggregate base, the suhgrade soil should he processed to a minimum depth of 6 inches,
moisture- conditioned, as necessary, and recomputed to a minimum of 90 percent relative
compaction as determined by AS'i'M Test Method D1557 (95 percent for full depth
asphalt, such as for playground areas). Aggregate base should be moisture conditioned,
as necessary, and compacted to a minimum of 95 percent relative compaction.
3.8 Temporary Excavations
I 1 All temporary excavations, including utility trenches, retaining wall excavations and
other excavations should be performed in accordance with project plans, specifications
and all OSIIA requirements.
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602562 -001
No surcharge loads should be permitted within a horizontal distance equal to the height of
cut or 5 feet, whichever is greater from the top of the slope, unless the cut is shored
appropriately. Excavations that extend below an imaginary plane inclined at 45 degrees
below the edge of any adjacent existing site foundation should be properly shored to
maintain support of the adjacent structures.
Cantilever shoring should be designed based on an active fluid pressure of 35. If
excavations are braced at the top and at specific design intervals, the active pressure may
then be approximated by a rectangular soil pressure distribution with the pressure per foot
of width equal to 25H, where H is equal to the depth of the excavation being shored.
During construction, the soil conditions should be regularly evaluated to verify that
conditions are as anticipated. The contractor should be responsible for providing the
"competent person" required by OSHA, standards to evaluate soil conditions. Close
coordination between the competent person and the geotechnical engineer should be
maintained to facilitate construction while providing safe excavations.
3.9 Trench Backfill
Utility -type trenches onsite can be backfilled with the onsite material, provided it is free
1 of debris, significant organic material and oversized material. Prior to backfilling the
trench, pipes should be bedded and shaded in a granular material that has a sand
equivalent of 30 or greater. The sand should extend 12 inches above the top of the pipe.
The bedding/shading sand should be densified in- place. The native backfiil should be
placed in loose layers, moisture conditioned, as necessary, and mechanically compacted
using a minimum standard of 90 percent relative compaction. The thickness of layers
should be based on the compaction equipment used in accordance with the Standard
Specifications for Public Works Construction (Greenbook).
3.10 Surface Drainage
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Positive surface drainage should be provided to direct surface water away from structures
an d ave drainage facilities. Surface drainage should be provided
to prevent towards pondsuiting ble of collecti water adjacent to the structures. In general, the area around the
buildings should slope away from the buildings. Care should be taken to avoid heavy
irrigation, and under- irrigation should also be avoided.
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3.11 Additional Geotechnigal Investigation and Services 602562 - 001
The geotechnical recommendations presented in this report are based on subsurface
conditions as interpreted from limited subsurface explorations and limited laboratory
testing. Our geotechnical recommendations provided in this report are based on
information available at the time the report was prepared and may change as plans are
developed. Leighton should review the site and grading plans when available and
comment further on the geotechnical aspects of the project. Our conclusions and
recommendations should be reviewed and verified by Leighton during construction and
revised accordingly if geotechnical conditions encountered vary from our findings and
interpretations. Geotechnical observation and testing should be provided:
• During overexcavation 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.
• During pavement subgrade and base preparation.
• When any unusual conditions are encountered.
3.12 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 Leighton
Consulting, Inc. will provide geotechnical observation and testing during construction.
Environmental services were not included as part of this study. This report was prepared
for the sole use of Fontana Unified School District for application to the design of the
proposed Fontana USD Citrus Continuation High School project in accordance with
generally accepted geotechnical engineering practices at this time in California.
3.13 ASFE Important Information about this Geotechnical Engineering Report
9 9 p
See ASFE insert on the following page.
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