HomeMy WebLinkAboutCT 82-23; Mass Grading for CT 82-23; Soils Report; 1984-05-21zRc761 301-2
SERVICES DURING MASS GRADING OPERATIONS
REPORT OF TESTING AND OBSERVATION
FOR
CARLSBN TRACT NO. 82-23
CARLSBAD , CALIFORNIA
For
MOLA DEVELOPMENT CORPORATION
Huntington Beach, Californla
GEOCON, INCORPORATED
San Diego. Callfornla
May, 1981
GEOCON
INCORPORATED ENGINEERS AND GEOLOGISTS CONSULTANTS M THE APS" EARTH SCIENCES
May 21, 1984
File No. D-2904-502
Mola Development Corporation
808 Adams Avenue
Huntington Beach, California 92648
Attention: Mr. Chris, Christie
Subject : CARLSBAD TRACT NO. 82-23
CARLSBAD, CALIFORNIA
REPORT OF TESTING AND OBSERVATION
SERVICES DURING MASS GRADING OPERATIONS
Gentlemen:
In accor$ance wlth your request, we are provldlng testing and observation services durlng the mass gradlng of the, subject subdlvlgion. Our services
to date were performed during the period of 'September 26, 1983 through
April 19, 1984. The scope of our servlces included the following:
a. Observing the gradlng operatlon. lncludlnn the installatlon -
of subdralns and the removal -and/or processing of loose
topsoll and alluvlal soll.
~ ~ ~.
e Perfonnlng In-place densicy tests in the placed and compacted
fill. .
Performing laboratory tests on samples of the prevailing soil
COndltiOn6 Used for fill.
e Preparing an As-Graded Geologic Map.
0 Providlng professional opinions as to the grading contrac- tor's general adherence to the geocechnical aspects of the
plans and specifications.
e Preparing this final report of grading.
- ,. File No. D-2904-502
May 21, 1984
General
The project plans were prepared by Soward Engineering, Incorporated and are
entitled Grading Plans for S.D.P. 82-4 and C.T. 82-23 dated August 1, 1983.
The project soils report is entitled "Geotechnical Investigation for
Tentative Planned Development, Map 82-23" prepared by Geocon, Incorporated
- dated May 25, 1983.
References to elevations and locations herein were based on surveyor's or
grade checker's stakes in the field and/or interpolation from the
referenced Grading Plans. -
Grading - Grading began with the removal of brush and vegetatlon from the area to be
graded and the material was then exported from the site. Loose topsoils
and loose alluvial soils in areas to receive fill were removed to firm
natural ground.
Prlor to placlng fill, the exposed natural ground surface was scarified,
until the design elevations were attained.
operations and imported soils were then placed and compacted in layers
-
- moisture conditioned and compacted. Fill solls derived from onsite cutring
Also, a canyon subdrain including a blanket drain was installed in the
presence of expansive topsoils at or near finish grade In some of the cut
seepage areas at the bottom of the canyon fill. In addltlon, due to the
feet and the depression vas replaced with compacted low expansive soil.
areas, it was necessary to overexcavate such areas approximately 2 to 3
place density tests (UTM D1556) were performed to evaluate the relative
During the gradlng operatlon, compaction procedures were observed and in-
compaction of the placed fill. Field observations and the results of the
in-place density tests lndicate that the fill has generally been compacted
to at least 90 percent relative compaction. The results of the in-place density tests are summarized in Table 11. The approximate locations of the
in-place density tests have been recorded on the enclosed Geologic As-Built
Map.
Laboratory tests were performed on samples of materlal used for fill to
evaluate moisture-density relationships, optlmum moisture content and
maximum dry density (ASTM D15S7-70, Method C) and expanslon
characteristics. The results of the laboratory tests are summarized in
Tables I and 111.
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File No. D-2904-502
May 21, 1984
Slopes
Both cut and fill slopes have inclinations of 2 to 1 (horizontal to
vertical) with maximum helghts on the order of 26 feet and 24 feet,
respectively. The fill slopes were periodically backrolled with a sheeps-
upon completion. All slopes should be planted, drained and maintained to
foot compactor during construction and were track-walked with a bulldozer
mixture of natlve plants and trees having a variable root depth. Iceplant
reduce erosion. Slope planting should consist of a drought-tolerant
should not be used on slopes. Slope watering should be kept to a mininum
to just support the vegetative cover.
Finish Grade Soil Conditions
During the grading operation, building pads which encountered clayey soils
at grade were undercut at least 2.5 feet and capped:wlth granular soils.
Slmllarly, our observatlons and test results indicate that granular soils
were placed within at least the upper 3 feet of flnish grade'on flll lots.
.The laboratory test results lndlcate that the prevalling soll conditions
withln 3 feet of finished grade on each building 'pad have an Expansion
Index of' less than 20 and are classlfled as having a "very low" expanslon
potential as deflned by UBC Standard Table 29-C. Table I11 presents a
summary of the indicated Expansion Index of the prevailing soll condition
of each unit.
In addition to capplng building pads as descrlbed above, the cut portlon of
those pads whlch contalned a cut-fill transition wlthln the building area
was undercut at least 2.5 feet and replaced with compacted flll soll.
Subdrains
Subdrains were installed at the general locations shown on the approved
Grading Plans. In additlon, a blanket draln was installed in the seepage
areas at the bottom of the canyon fill. The subdralns were "as-built" for
locatlon and elevation by the project Clvil Engineer.
Soil and Geologic Condltions
The soil and geologlc conditlons encountered durlng gradlng were found to
be similar to those described in the project geotechnical report. The
enclosed reductlons of the approved Grading Plans depict the as-graded
geologlc condltlons observed. The approximate locations of subdrains and
the blanket draln are also Indicated. No soll or geologic conditions were
continued development of the property as planned.
observed during the gradlng which, In our opinlon, would preclude the
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Flle No. E-2904-502
May 21, 1984
CONCLUSIONS AND RECOMMeNDATIONS
Based upon laboratory test results and field observations, it is our
opinion that the prevailing soll conditions wlthln 3 feet of finish pad
grade consist of “very low“ expansive soils as classified by UBC Table 29C.
We recommend the following foundation and slab design criteria for the
proposed residential structures.
Foundations
1. Conventlonal. spread andlor continuous footlngs founded at least 12
undisturbed “low” expansive soll may be designed for an allowable soll
lnches below lowest adjacent grade in properly compacted or dense
bearing pressure of 2,000 psf (dead plus live loads). Footings should have
a.mlnlmum wldth of 12 lnches. Thls bearing pressure may be.lncreased by up
to one-thlrd for transient loads such as wind or selsmic forces.
2. All continuous footlngs should be relnforced wlth at least two No. 4
reinforcing bars, one placed near the top of the footlng and one near the
bottom. . The above minLmum reinforcement is based on soil characterlstlcs
and 1s not lntended to be In lieu of relnforcement necessary for structural
conslderatlons.
3. Concrete slabs-on-grade should have a nomlnal thlckness of 4 lnches and
should be relnforced wlth 6x6-10/10 welded wire mesh. The slabs should be
underlaln wlth 4 lnches of clean sand and, where moisture sensitive floor
coverings are planned, a vlsqueen moisture barrler protecced by a 2-lnch
sand cushion should be provided. Great care should be taken durlng the
placement and curlng of concrete flatwork to reduce the potentlal for
shrlnkage cracking.
4. Footings should not be placed wlthin 8 feet of the top of slopes.
Footlngs that must be located In thls zone should be extended In depth such
from the face of the slope.
that the outer bottom edge of the footlng 1s at least 8 feet horizontally
5. No special subgrade presaturatlon Ls deemed necessary prior to placing
concrete, however, the exposed foundatlon and slab subgrade solls should be
sprlnkled as necessary to maintain a molst condltlon as would be expected
in any such concrete placement.
Lateral Loads
6. The pressure exerted by an equlvalent fluld welght of 300 pcf should be
used to provide resistance to design lateral loads. Thls deslgn value
assumes that fOOtlngS or shear keys are poured neat against properly
..
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INCQIPOIA~=D
-.
May 21, 1984
File No. E-2904-502
compacted granular fill soils or undisturbed formational soils and that the
soil mass extends at least 5 feet horizontally from the face of the footing
whichever is greater. The upper 12 inches of material not protected by
or three rimes the height of the surface generating passive pressure,
floor slabs or pavement should not be included in design for passive
resistance.
7. If friction is to be used to resist lateral loads, a coefficient of - friction between soil and concrete of 0.40 may be utilized.
Retaining Walls
8. Unrestrained retaining walls should be designed to resist the exerted.
onsite material will be used for backfill, that the backfill surface will
by an equivalent fluid weight of 30 pcf. This value assumes that granular
walls with backfill surfaces inclined at no steeper than 2.0 to 1.0, an
be level, and that no surcharge loads will be acting on the wall. For
active pressure exerted by an equivalent fluid weight of 45 pcf should be
used.
9. For 'walls restrained from'movement at the top, such as basement walls,
an additional uniform horizontal pressure of (7H) psf (A equals the height
pressures given above.
10. All retaining walls should be provlded with a backfill dralnage system
adequate to prevent the buildup of hydrostaeic forces.
-
-
-
- of 'the wall in feet) should be applled in addltion to the active lateral
Drainage
should .water be. allowed tq pond adjacene to footings. The lots and
11. Adequate drainage provlslons are imperative. Under no circumstances
building pads should be properly finish graded after buildings and other
improvements are in place so that drainage water 1s dlrected away from
foundations, concrete slabs and slope tops to controlled drainage devices.
Any additional gradlng performed at the site should be done under our
observation and testing. All trench backfill material in excess of 12
inches in depth should be compacted to at least 90 percent relative compac-
tion. This office should be notified at least 48 hours prior to commencing
additional grading or backfill testing.
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File No. D-2904-302
May 21, 1984
LIMITATIONS
The conclusions and recommendatlons contained herein apply only to our work
with respect to grading, and represent conditlons at the date this report.
Any subsequent grading should be done under our observation and testing. AS
used herein, the term "observation" implies only thac we observed the
progress of the work with which we agreed to be involved. Our conclusions
and opinions as to whether the work essentially complies with the job
specifications are based on our observations, experience and testing.
Subsurface conditions, and the accuracy of tests used to measure such
or implied, except that our services were performed in accordance with
conditions, can vary greatly at any time. We make no warranty, expressed
engineering principles generally accepted at thls tlme and location.
We will 'accept no responsibility for any subsequent changes made to the
site by others, by the uncontrolled action of water, or by the failure of
water.
others to properly repalr damages caused by the uncontrolled action of
further service, please contact the undersigned.
If there-are any questions regardlng'our recommendations or if we may be of
Very truly yours,
GEgCON. INCORPORATED
RRG:JEL:lm
(2) addressee
(4) Job Site
-6- GEOCON
INCOI~OIATID
File No. D-2904-502
May 21, 1984
Sample
No.
1
2
3
4
5
6
7
'8
9
10
11
12
13
TABLE I
Summary of Laboratory Compaction Test Results
ASTM D1557-70
Maximum Dry
Density
Description pcf
Brown-tan, fine to medium,
slightly Clayey SAND
Brown, Clayey, Silty, fine
SAND
Green-tan, Silty Sandy CLAY
Brown, flne to medlum, Silty
Clayey SAND
Tan, fine to medium, Silty
SAND
Brown, very flne to fine,
Silty SAND
Tan, very fine to flne, Silty
SAND
Reddish-brown. very flne to
fine, Silty SAND
White to gray, very fine to
fine, Silty SAND
Red-brown, very fine to fine
SAND
Tan, medium-grained, Clayey
SAND
Dark brown, flne SAND
Light green, Silty Sandy CLAY
123.1
120.2
111.1
122.1
117.4
119.2
118.0
117.8
112.9
127.2
125.2
124.9
124.0
Optimum
Moisture
% Dry ut.
11.1
12.5
16.6
11.6
12.9
11.8
12.8
12.1
15.0
10.1
10.6
10.7
11.5
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File No. D-2904-502
May 21, 1984
"7 '\
TABLE I11
Summary of Expansion Index Test Results
Unit Nos.
1, 2, 3
7, 8, 9, 10
Expansion Index
14
I
- File No. D-2904-302
Subject\. CARLSBAD
RECOMMENDED PAVEMENT '~ECTI
Gentlemen:
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.. rock. Locay'interi'or st of base rock. Asp'ndt,a
the. City-of Carlsbad." T "minimum relative
.' f.
#. - File No. D-2904-502
June 7, 1984
compaction of 952 based upon ASTM compaction test D-1557-70, Method C.
minimum relative compaction of 90% based on the aforementioned ASTM
Subgrade preparation should consist of compacting subgrade soils to a
standard to a minimum depth of 12 inches below subgrade elevations.
Please contact us if you have questions or if we can be of further service.
- Very truly yours,
GEO,C?N, INCORPORATED
JEL:mr
(4) addressee