HomeMy WebLinkAboutCT 75-09B; La Costa Lots 45-58, 139; Soils Report; 1986-07-11-
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EBERHART IL STONE, INC. DAN R. EBERHART, CEG
GEOTECHNICALCONSULTANTS GERALD L. STONE, RCE
2211 E. WlNSTONROAD.SUITEF*ANAHEIM.CA92606*1714~991-0163
6205AVENlDA ENCINAS. SUITE C*CARLSEAD.CA92009.~619)439-9416
The Anden Grouo
6544 Corte Montecito
Carlsbad, California 92008
Attention: Mr. Bob Fish
W.O. 1343
July 11, 1986
Received
JUL18 1986
CITY OF %ARLSBAD
DEVELOP, PRDCS SERV. DIV.
Subject: Completion of Rough Grading, Lots 45-58 and 139,
C.T. 75-9(B), Carlsbad, California.
Gentlemen:
Rough grading has recently been completed on the subject lots by Barry
Blanchard, Inc. Upon completion of grading for the remainder of the subject
tract, a mass grading geotechnical report will be prepared which will include a
review of the testing and observations provided by this firm during mass
grading. For the interim, opinions and recommendations relative to development
of the subject lots are presented herein.
OPINIONS AND RECOMMENDATIONS
Recommendations in this report are opinions based upon this firm's testing and
observations performed during rough grading, previous geotechnical studies, and
professional judgment. Opinions and recommendations are applicable to the
grading performed, and development proposed, under the purview of this report,
and should be incorporated into project design and construction practice.
GEGLOGY
Ground Water
No adverse effects from ground water are anticipated.
Landslidinq
No landsliding was observed within the limits of the subject lots. Suspected
landslides within other portions of the tract, or within adjacent properties,
are not expected to have an effect on the subject lots.
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Seismic Statement
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No active faults are present at the subject site;
not anticipated. Because of the proximity of the
Southern California area, moderate ground shaking
earthquake. Liquefaction is not anticipated.
W.O. 1343
therefore, ground rupture is
site to active faults in the
could occur during an
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Proposed structures should be designed to resist seismic forces in accordance
with criteria contained in the 1985 Uniform Building Code for seismic zone 4.
GRADING
The geotechnical aspects of rough grading under the purview of this report are
in compliance with this firm's reconnnendations and the various codes and/or
regulations established by the governinq authorities, as well as the Uniform
Building Code, Chapter 70. The subject lots, as graded, are considered
suitable for the proposed development.
Natural Ground
Topsoil, colluvium, and alluvium encountered within the subject lots were
removed to expose competent bedrock. Both cut and prepared natural ground are
considered suitable for support of the compacted fill and the proposed struc-
tures.
Slope Stability
Slopes, as-graded, are considered grossly and surficially stable.
CONVENTIOWAL FOUNDATIOWS
The following recommendations have been developed for the proposed one- and/or
two-story single-family residences. Wood-framed, slab-on-grade construction is
proposed, and is anticipated to yield light structural loading.
Based upon the proposed construction and anticipated light structural loading,
post-construction settlement should be within generally accepted tolerable
limits.
Foundations for an individual structure should be embedded entirely within com-
pacted fill.
Based on soluble sulfate content of the onsite materials, Type V cement should
be utilized in concrete for foundations. Concrete utilized for foundations
should contain at least 660 pounds of cement per cubic yard, with the
water/cement ratio no greater than 0.45.
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Bearinq Value
For design purposes, an allowable bearinq value of 1500 pounds per square foot,
based on an embedment of 12 inches into compacted fill, may be used for con-
tinuous footings or square pad foundations. This value is for dead load plus
live load conditions and may be increased by one-third in consideration of wind
or seismic loadings of short duration.
In designing to resist horizontal soil loadings, a lateral bearing resistance
of 150 pounds per square foot, per foot of embedment, and a friction factor of
0.2 may be utilized for foundations embedded in compacted fill.
Expansive Soil Guidelines
The potential expansion of the near-surface materials at rough grade on the sub-
ject lots ranges from High to Very High. Guidelines for residential foun-
dations, based on soil expansion, are presented in Table I.
Foundations Adjacent a Top-of-Slope
The bottom outer edge of foundations adjacent a top-of-slope should be set back
from the slope surface a horizontal distance of one-half the slope height under
consideration. The horizontal distance should not be less than five feet and
may be limited to ten feet.
POST-TENSIONED STRUCTURAL SLABS
As an alternative to conventional concrete foundations, post-tensioned struc-
tural slab systems may be utilized.
Post-tensioned structural slab foundation systems should be designed by a struc-
tural engineer to resist expansive soil and provide relatively uniform bearing
over the slab area. Allowable bearing should be limited to a value of about
1000 pounds per square foot. A cut-off footing should be provided along the
perimeter of post-tensioned slabs, with an embedment of about I2 inches below
lowest adjacent grade.
Though presaturation of slab subgrade is not a requirement, the subgrade area
should be moistened just prior to the placement of slab concrete.
A visqueen-type moisture barrier should be placed at grade below concrete slabs,
in areas to be tiled or carpeted, and be overlain by one inch of protective sand
cover. This moisture barrier should be heavily overlapped or sealed at splices.
A concrete footing should separate areas requiring a moisture barrier from those
that do not.
EBERHART 8 STONE. INC.
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SITE DEVELOPMENT
Should future property owners desire to construct additional structures, such
as pools, walls, patios, etc., plans for such improvements should be provided to
the geotechnical consultant for review and comment.
Prior to the commencement of additional grading and/or site development, including subgrade preparation of pavement areas, backfilling of trenches and
walls, etc., the geotechnical consultant should be notified two working days in
advance in order to schedule testing and observations as needed.
Foundation Excavations
Foundation excavations should be observed by the geotechnical consultant so that
foundation bearing materials may be compared with those upon which the guidelines
in Table I are based. This should be accomplished prior to the placement of
forms, reinforcement, and concrete. Excavations should be level, square, and
free of loose material and debris prior to the placement of concrete.
Slab Subgrade
For conventional foundations, presaturation is recommended beneath interior
slabs. The recommended moisture (see Table I) should penetrate to the depth of
the perimeter footings. The moisture content should be tested by the geotech-
nical consultant within 24 hours prior to the placement of concrete.
Trench Backfill
Trench backfill consisting of onsite materials should be placed in horizontal
lifts and mechanically compacted to 90% of the laboratory maximum density.
For shallow trenches below slab areas, an alternative to backfilling with onsite
materials would be to jet, in place, imported granular material having a sand
equivalent of 30 or more.
Wall Backfill
Materials to be placed as wall backfill should be tested by the geotechnical
consultant so that retaining wall design parameters may be formulated.
Wall backfill should be placed in horizontal lifts and mechanically compacted to
90% of the laboratory maximum density.
The use of heavy compaction equipment adjacent a retaining wall may produce
strains greater than those normally associated with the development of active
earth pressures, and/or lateral soil loading exceeding design parameters,
resulting in excessive wall movement. Therefore, caution should be used during
backfill placement and compaction.
Pavement Areas
Prior to the placement of aggregate base or asphaltic concrete pavement, the
exposed subgrade surface should be scarified, moisture-conditioned as needed to
obtain near-optimum conditions, and recompacted in place. Isolated overex-
cavations may also be required, as field conditions dictate, to eliminate any
dry, wet, loose, or soft areas that may exist at the time of subgrade
preparation.
EBERHART P STONE,INC.
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Slope Maintenance
Vegetation planted on slopes should be native to the area, deep rooting, and
drought resistant. A landscape architect should be consulted for recommen-
dations on types of plants and planting configuration.
Surficial slope instability can be mitigated by minimizing moisture variations
near the slope surface. Overwatering of slope surfaces, alteration of drainage
patterns and slope configurations, obstruction of drainage devices, and
burrowing rodents can be detrimental to slope stability. Provisions should be
made to interrupt automatic timing devices of irrigation systems during rainy
seasons.
Pad Drainage Maintenance
Roof and pad drainage should be collected and directed away from proposed struc-
tures. As-graded drainage patterns and devices created during fine grading of
the lots should be maintained to provide positive drainage. Alteration and/or
obstruction of these may cause foundation distress.
SUf@iARY
Testing and observations were provided, and opinions and recommendations were
developed, in accordance with generally accepted engineering and geologic prin-
ciples and practices. No warranty is expressed nor implied. Upon completion of
rough grading for the remainder of the subject tract, a mass grading geotech-
nical report will be prepared. This report will include a review of the testing
and observations provided by this firm during mass grading operations, opinions
and recommendations relative to foundations and site development, a sumnary of
field and laboratory test results, and plans depicting the approximate loca-
tions of field tests and geologic data.
This report is subject to review by the governing agencies.
Respectfully submitted,
EBERHART & STONE, INC.
t? R. Eberhart and
President
CEG 965
Vice President
RCE 32233
MWM:DRE:GLS:ke (33)
Enclosure: Table I - Guidelines for Residential Foundations
Based on Soil Expansion
Distribution: (6) Addressee
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EBERHARTP STONE,INC.
/&den ’ ’ i / I I I TABLE ‘I I I I I I.- I w.io. 134; I .
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POTENTIAL FOOTINGS SLABS
EXPANSION
(UBC 29-2) EMBEDMENT REINFORCEMENT THICK. REINFORCEMENT PRESAT. BASE
1 STORY 2 STORY COURSE
Very Low
(O-20)
12” perimeter 18“ perimeter 12” Interior 18” Interior
12” perimeter 18” perimeter 2 No. 4 bars: 12” Interior 18” Interior 1 top, 1 bottom
Medium
(51-90)
18” perimeter 18” perimeter 2 No. 4 .bars: 4” net 6”x6”; #6x#6 120% of 4” 12” interior 18” interior 1 top, 1 bottom W.W.F. optimum
or moisture -
No. 3 bars 8 24”
O.C. .each way
50-58
‘*
High
(91-130)
24” perimeter 24” perimeter 4 No. 4 bars: 4” net 6”x6”, #6x#6 120% of 4”
12” interior 18“ interior 2 top, 2 bottom W.W.F. optimum
or or moisture - - 2 No, 6 bars: No. 3 bars @ 18” -:.b
1 top, 1 bottom O.C. each way
45-49,
139
Very High 24” perimeter 24” perimeter 4 No. 5 bars: 6” net No. 4 bars 8 18” 120% of 6” (7130) 12” interior 18” interior 2 top, 2 bottom O.C. each way optimum
or or moisture - -
2 No. 8 bars: No. 3 bars’@ 12”
1 top. 1 bottom O.C. each way
Notes on the following page are considered part of this table.
I I 1 1 I I I , I I I I I I I I I
Anden NOTES TO TABLE I W.O. 1343
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These guidelines are based on site soil expansion and should not preclude more restrictive structural
or agency requirements. As an alternative to conventionally reinforced concrete foundations, post-
tensioned structural slab systems, designed by a structural engineer, may be utilized.
Footing embedments should be measured below lowest adjacent grade. At the time of concrete placement,
footing excavations should be moist and free of desiccation cracks.
A reinforced concrete grade beam should be. constructed across garage entrances, with similar depth
and reinforcement as adjacent perimeter footings.
For soil with a potential expansion greater than “Low”, interior isolated spread footings and/or partial
length footings are not recommended.
Where presaturation is recommended beneath interior slabs, the recommended moisture should penetrate
to the depth of the perimeter footings. The moisture content should be tested by the geotechnical
consultant 24 hours prior to the placement of concrete. Though presaturation of slab subgrade is not
a requirement for Very Low and Low expansion potentials, optimum moisture conditions should be maintained
or reestablished just prior to the placement of slab concrete.
Below proposed slabs-on-grade in areas to be tiled or carpeted, a visqueen-type moisture barrier should
be placed at grade and be overlain by one inch of protective sand cover. This moisture barrier should
be heavily overlapped or sealed at splices.
Where a base course is recommended beneath interior slabs, it should consist of pea gravel, clean sand,
or other granular material acceptable to the geotechnical consultant. The above moisture barrier/sand
cover requirement may be included as part of the recommended base course thickness.
Slab reinforcement should be supported at mid-slab height.
Garage slabs should be placed separate from footings, Garage slab reinforcement may be omitted if slab
cracking can be tolerated, provided that the slabs are saw cut or jointed for crack control.
For soil with a potential expansion greater than “Low”. slabs should be free-floated or structurally tied
to perimeter footings, Structural ties could be provided by the placement of No. 3 bars @ 24” O.C.,
bent from perimeter footings about three feet into the slab.