HomeMy WebLinkAboutCT 76-15; PALISADES POINT; PRELIMINARY SOILS INVESTIGATION; 1983-06-30,,-"
PRELIMINARY SOILS
ENGINEERING INVESTIGATION
TRACT No. 76-15
PALISADES POINT
CARLSBAD, CALIFORNIA
CONDUCTED FOR:
MOLA DEVELOPMENT
RECEIVED
~lAR 22 1985
CITY OF CARLSBAD
ENG1NE~RING DEPARTMENT
808 ADAMS AVENUE
HUNTINGTON-BEACH, CALIFORNIA 92648
w.O. 386901
JUNE 30, 1983
1630-G South Sunkist Street Anaheim,. California 92806 (714) 634-2092 (213) 852-4710.
,--~ACTION
~ ENGINEERING
'-------------<GEOTECHNIC:AL CONSULTANTS
June 30, 1983
Mola Development
808 Adams Avenue
Huntington Beach, California 92648
W.O. 386901
Subject: Preliminary Soils
Engineering Investigation
Tract No. 76-15
Palisades Point
Carlsbad, California
Gentlemen:
Pursuant to your request, a Preliminary Soils Engineering Investigation.
was performed at the subject site. The purpose of the investigation
was to determine the general engineering characteristics of the soils
and bedrock materials on and underlying the site and to provide
specific recommendations for the design of foundations and under-
ground improvements.
It is proposed to develop the site with 139 residential lots t,obe
occupied by one and two-story wood frame structures construc,ted over
slab on grade.
The structural loads are not known at this time, but for the purpose
of this report, they are assumed at the twenty (20) kip range for
column loads and wall loads in the range of three' (3) kips per lineal
foot.
Grading will be comprised. of a cut and fill operation. Maximum
thickness of fill will be on the order of fifty (50') feet. Cut
slopes will be up to sixty-five (65±') feet high at a ratio of
1.5:1 (horizontal:vertical) and fifty (50±') feet high at 2:1.
slopes will be up to forty-seven (47±') feet high at a ratio of
and sixty (60') feet high at 2:1.
J630-G South Sunkist St.. Anaheim. Ca_ 92806 (213) 852-4710 (714) 634-2092
Fill
1.5:1
Mo la Deve.lopment
P-e.ge 3
(.~
W.O. 386901
(. borings by backhoe and bucket auger drilling equipment at locations
shown on the attached plan. As the :test borings were advanced, the
soils were visually classified by the Field Engineer. A summary of
the borings is attached.
Undisturbed samples for detailed testing in our laboratory were
obtained by pushing or driving a sampling spoon into the material.
A solid barrel-type spoon was used having an inside diameter of
2.50 inches with a tapered cutting tip at the lower end and a ball
valve at the upper end. The barrel is lined with thin brass rings~
each one (1") inch in length. The spoon penetrated into the soil
below the depth of boring approximately twelve (12") inches. The
central portion of this sample was retained for testing. All samples
in their natural field condition were sealed in air-tight containers
and transported to the laboratory.
LABORATORY TESTING
Shear tests were made with a direct shear machine of the strain control
type in which the rate of strain is 0.05 inches per minute. The machine
is so designed that tests may be performed ensuring ~ minimum of distur-
bance from the field conditions. Saturated specimens were subjected
to shear under various normal loads. The results of tests, based on
ultimate residual values, are tabulated below:
Boring Depth in Cohesion Angle of Internal
No. Feet Material Lbs./Sq. Ft. Frictipn (Degrees)
B-1 44.5 Sandstone 300 35
B-3 26.5 Sandstone 1100 35*
TP:-3 11. 0 Claystone** 150 10 (initial shear) 150 20
TP-2 2.0 Silty Sandstone 250 26
TP-4 2.0 Sandstone . O' 39 .-.
TP-6 3.0 Terrace Deposit 150 33 .
TP-7 4.0 Clayey Sand***' :: 22 400
TP-9 5.0 Sandy Clay 27 250
1630-6 South Sunkist Street Anaheim, California 92806 (714) 634-2092 (213) 852~4 710 A
w.o. 386901 Mola Development
• P~~e 2
/.
SITE CONDITIONS
The subject site is a vacant forty-eight (48) acre parcel of gently
rolling terrain forming the east flank of a northwest trending ridge-
line. It is bound on the east by El Camino Real and existing condo-
minium units, and on the north, west and south by vacant land and
existing residences.
Elevations within the site range from a high of 330± feet along the
southwest property line to a low of 120± feet along El Camino Real
producing a relief of some 210 feet.
Vegetation consists of dry grass and brush and scattered small trees.
FILL CONDITIONS
Fill materials were encountered as described in the attached Geological
Report and illustrated on the Geological Map. These materials are
considered to be moderately compact at best.
NATURAL CONDITIONS
Natural earth materials present consist of residual soils, alluvium,.
terrace deposits and sedimentary bedrock.
Residual soils and alluvium consist of clayey SANDS and sandy CLAYS.
Terrace deposits are composed of firm, RED/BROWN, silty SANDS with
occasional lenses of GRAVEL and CLAY SAND.
The sedimentary bedrock is made up of two (2) units: (1) a firm,
GREY/WHITE, silty and clayey SANDSTONE with (2) interbeds and lenses
of GREY/GREEN silty CLAY.
Additional details concerning the natural earth materials are presented
in the accompanying Geological Report.
FIELD INVESTIGATION
A field investigation was performed from May 25, 1983 through June
7, 1983, consisting of th~ excavation of fifteen (15) test pits and
t630-G South Sunkist Street Anaheim, California 92806 (714) 634-2092 (213) 852-4710
,.
{
Mola Development
" PaO'e 4
:rlP
W.O. 386901
Test results by Woodward-Gizienski & Associates (1973):
Sandstone
Claystone
Compacted Fill
.300
600
450
*Test performed at field moisture
35
25
27
**Re-molded to field density and re-sheared three times
***Re-molded to approximately 90% of maximum density
Consolidation tests were performed on in-situ moisture and saturated
specimens of typical soils. The consolidometer, like the direct shear
machine, is designed to receive the specimens in the field condition.
Porous stones, placed at the top of the specimens, permit the free
flow of water into or from the specimens during the test. Successive
load increments were applied to the top of the specimen and progressive
and final load settlements under each increment were recorded to an
accuracy of 0.0001 inch. The final settlements so obtained are plotted
to determine the curves shown in Appendix C.
Expansion tests were performed on typical specimens of natural soils.
These tests were performed in accordance with the procedures outlined
in U.B.C. Standard 29-2. Results of these tests are presented in
T~ble II and indicate ,the soil and bedrock materials exhibit expansion
potentials ranging from very high to low, with higher values corres-
ponding to claystone bedrock and lower values to sandstone bedrock.
CONCLusrONS AND RECOMMENDATIONS
On the basis of our investigation, development of the site as proposed
is considered feasible from a soils engineering s.tandpoint provided
that the recommendations,stated herein are incorpo~ated into the
design of the grading plan and foundation systems and are implementeq.
in the field.
Existing trees, low vegetation and old irrigation systems shall be
stripped and removed from the site.
1630-G South Sunkist Street' Anaheim, California 92806 (714) 634-2092 (213) 852-4710
Mqla Development
P~:~e 5
w.o. 386901
The entire grading operation shall be done in accordance with the
attached "Specifications for Grading."
All loose alluvial and fill material shall be removed from the proposed
fill areas. The bottoms of all excavations shall be inspected by the
Project Soil Engineer and Geologist prior to the placement of any fill.
Any import fill material to the site shall not have an expansion index
greater than twenty (20), and shall be tested by our laboratory~
All grading and/or foundation plans shall be reviewed by the Soil
Engineer.
SLOPE STABILITY
Based on the stability analyses contained i~ App.endix A, the following
maximum slope heights are recolllJllended:
Slope Maximum Surficial
Material Ratio Height Stability
Fill Slope 1.5:1 .35 ok
, -, 2:1 60 ok
Cut Slopes
Terrace 1. 5: 1 30 Low
Deposits
2:1 65 Low
Sandstone 1.5:1 65 ok
2:1 65 ok
Claystone 1.5:1 10 Low
2:1 15 Low
Surficial stability conditions should be re-evaluated at the time of
grading, since loose sands or clay in cut slopes could degrade stability,
and fill slopes composed primarily of sand will likely be subject to
surficial erosion.
Slopes exhibiting low surficial stability should be planted as soon
as grading is completed, and it may be prudent to consider the use of
1630-G South Sunkist Street Anaheim, California 92806 (714) ·634-2092 (213) 852-4710
Mola Development
P"~ge 6
w.o. 386901
hydromulch or"other means to encourage plant growth and retard slope
erosion.
The above s lope heights have been determined for the maximum he"ights
propo.sed by the current grading plan, .and where. these slopes exceed
a factor of safety of 1.5 and 1.1 for static and pseudostatic cases,
respectively", lower slope heights are indicated. Local geologic
structtlre, and the presence of claystone bodies in cuts, may require
~tabilization; such measures shall be evaluated at the time o.f
grading.
On the basis of the Geologist's report and stability calculations,
it has been determined that the proposed 1.5:1 sixty-five (65±') foot
high buttress/cut slope at the rear of Lots 100 through 109 does not
exhibit a suitable factor of safety again$t deep seated failure.
This slope should be constructed at a ratio of 2:1 or flatter. A
retaining or crib wall may be used at the toe of the' slope, in order
to prevent reduction in lot sizes. Plans for any such retaining
structures should be reviewed by this office prior to construction.
Proposed fill slopes over thirty-five (35') feet in height should be
flattened from 1.5:1 to 2:1.
Additional recommendations regarding slope stability are contained
in the attached Geological Report.
FOUNDATIONS
The proposed structures shall be supported by isolated and continuous
spread footings placed a minimum depth of twelve (12") inches below
lowest adjacent finish grade utilizing a recommended safe bearing-value
of 2600 pounds per square foot and 2100 pounds per square foot, respect-
ively. This value is for dead plus live load and may be increased by
one-third (1/3) for total including seismic and wind loads. where allowed
by code. Increases in bearing capacity for increases in footing
dimensions are tabulated below:
1630-G South Sunkist Street Anaheim, California 92806 (714) 634-2092 (213) 852-4710
Mola Development
Page 7
Continuous
Isolated
Minimum
Depth
(inches)
12
12
Minimum
Width
(inches)
12
12
Bearing
Value
(psf)
2100
2600
W.O. 386901
Depth Width
(psf/ft) (psf/ft)
314
314
109
105
Maximum
4100
4100
Due to varying expansive conditions, minimum embedments will vary in
accordance with the attached "Expansive Soil Recommendations."
Footings which span from native material to compacted fill shall be
reinfor.ced.: with' a minimum of one (1) 115 bar top and bottom to control
potential differential movement. Reinforcing bars shall extend a
minimum of ten (10') feet on either side of transition line.
Footings placed on or adjacent to slopes shall have a minimum horizontal
distance of five (5') feet from .the edge of the footings to the face
of the slope.
LATERAL DESIGN
Lateral restraint at the base of footings and on slabs may be assumed
to be the product of the dead load and a coefficient of friction of
0.35. Passive pressure on the face of footings may als·o be used to
resist lateral forces. A passive pressure of zero at the surface of
finished grade, increasing at the rate of 240 pounds per square foot
of depth to a maximum value of 2400 pounds per square foot may be used
for natural soil and compacted fill at this site. If passive pressure
and friction are combined when evaluating the lateral resistance, the
value of the passive pressure should be limited to two-thirds (2/3)
of the values given above.
EXPANSIVE SOILS
Results of expansion tests indicate that the near surface soils have
a very low to very high expansion potential (refer to Table I).
Expansive soil recommendations in Ap.pendix C shall -be considered in
design of foundations and slabs for puildings lying within the
respective soil types. A lot by lot testing at the completion of
grading will be made to determine the expansion potential.
1630-G South Sunkist Street Anaheim, California 92806 (714) 634-2092 (213)B5N710 . A
Mola Development
I>age 8
w.o. 386901
Positive drainage away from the foundations shall be maintained.
CDT/FILL LOTS
On pads where a transition from cut to fill occurs within the planned
building area, the natural material should be undercut toa depth
of thirty (30") inches below finished grade and replaced as compacted
fill to develop a more uniform condition of support for the buildings
affected. This requirement may be waived at the discretion of the
Soil Engineer if field tests show the natural material. to be satis-
factorily compacted -(85% minimum relative compaction) within the
specified depth.
After completing the undercut,. the exposed surface material should be
scarified to a minimum depth of six (6") inches, brought_ to approximate
optimum moisture content and compacted to at least ninety (90%) percent
of maximum density in preparation to receive fill. As an alternative
to undercutting transition pads, it would be acceptable. to deepen
footings in shallow fill areas so that the ent-i,re foundation system
would rest on natural material.
GRADING REQUIREMENTS
It is recommended that site grading be carried out in accordance with
the "Specifications for Grading" in Appendex B. Additional requirements
may be recorrnnended by the Soil Engineer in the course of work, depending
upon conditions exposed during grading.
SETTLEMENT
The maximum anticipated total settlement is on the order of ·one-half
(1/2") inch. Differential settlements are expected to be less than
one-fourth (1/4) inch, measured between adjacent structural elements.
SUBSIDENCE AND SHRINKAGE
Subsidence over the site is anticipated to be on the order of 0.20
feet. Shrinkage of reworked materials should be in the range of
fifteen (15%) percent.
1630-G South Sunkist Street Anaheim, California 92806 (714) 634-2092 (213) 852-4710
Mola Development
.Page 9 ,
PAVEMENT STRUCTURAL SECTIONS
W.O. 386901
Representative samples of subgrade materials should be obtained after
the roadways have been rough-graded and tested to establish R~values
for use in calculating suitable pavement structural sections for the
various areas.
UTILITY LINE BACKFILLS
It is recommended that backfills placed below and within five (5') feet
of buildings, below asphalt concrete pavement and portland cement
concrete flatwork, and within ten (10') feet of any slope, be compacted
to at least ninety (90%) percent of maximum density. Backfills placed
in other areas to be landscaped need only to be compacted to eighty-five
(85%) percent of maximum density. All backfills require:~ testing at
two (2') foot vertical intervals during placement.
On-site sandy materials are considered excellent for use in utility
line backfills; however, finer-grained materials may be difficult
to compact. As an alternative to compacting the backfills, trenches
could be backfilled with a sand-cement slurry containing at least five
(5%) percent cement per cubic yard. In this case, field density testing
will be waived by this office; however, batch plant tickets and perio.ciic
inspection during placement may be required.
If the slurry method is selected, eighteen (18") inche.s of compacted,.
fine-grained site material should be provided in areas to be landscaped
to minimize water infiltration and to promote plant growth.
CAVING
Caving did not occur in any of the bo:rings drilled for this investigation
and is not expected to be of significant concern during grading and
construction operations. The regulations of Cal/OSHA should be observed
during pe.rformance of all work.
FLOQR SLABS
Slabs on grade should be designed according to recommendations for
medium expansive conditions, as shown in A.ppendix. C. -Care should .. be
1630-G South Sunkist Street Anaheim, California 92806 . (714) 634-2092 (213) 852-4710
MoJa Deve lopment
i Page 10
W.O. 386-901
exercised to ensure that reinforcing mesh is placed in the center of
the slab.
The soil should be kept moist prior to casting the slab. However, if
the soils at grade become disturbed during construction, they should
be brought to approximately optimum moisture content and be rolled
to a firm, unyielding condition prior t·o placing concrete.
In areas where a moisture sensitive floor covering will be used, a.
vapor barrier consisting of a plastic film (6 mil polyvinyl chloride
or equivalent) should be used. Since the vapor barrier will prevent
moisture from draining from fresh concrete, a better concrete finish
can usually be obtained if at least two (2") inches of sand is spread
over the vapor barrier prior to placement of concrete.
IN-GRADING TESTING AND INSPECTION
Periodic site inspections by our Soil Engineer and/or Qeologist
during grading and foundation construction will be necessary to
verify the soil and geological conditions encountered during the
course of this investigation. Further recommendations may be required
if conditions other than anticipated are encountered.
In addition, continuous testing during placement of fill will be
necessary in order to verify that adequate compaction is being achieved.
GENERAL INFORMATION
This re.port presents recommendations pertaining' to the subject site
based on the assumption that the subsurface conditions do not deviate
appreciably from those disclosed by our exploratory excavations. Our
recommendations are based on the technical information gathered, our
understanding of the proposed construction, and our experience in the
geotechnical field. We do not guarantee the performance of the project,
only that our engineering work and judgements meet the standard of care
of our profession at this time.
In view of the general conditions in the area, the possibility of
different local .soil conditions cannot be discounted. Any deviations
1630-G South Sunkist Street Anaheim, California 92806 (714) 634-2092 (213) 852-4710
Mola Development
Page 11
w.o. 386901
or unexpected conditions observed during construction should be brought
to the attention of the Geotechnical Engineer. In this way, any
required supplemental recommendations can be made with a minimum of
delay to the project.
If the proposed construction will differ from our present. understanding
of the proj ect, the existing information and pos.sibly new factors may
have to be evaluated. Any design changes and the finished plans should
be reviewed by the Geotechnical Consultant. Of particular importance
would be ext~nding development to new areas, changes in structural
loading conditions, postponed development for more than a year, or
changes in ownership.
This report is issued with the understanding that it is the respon-
sibility of the owner, or of his representative, to ensure that the
information and recommendations contained here are called to the
attention of the Architects and Engineers for the project and incor-
porated into the plans and that the necessary steps are taken to see
that the Contractors and Subcontractors carry out such recotmnendations
in the field.
This report is subject to review by the controlling authorities for
this project.
We appreciate this opportunity to be of service to you.
Respectfully submitted:
ACTION ENGINEERING CONSULTANTS
~t?~
BRUCE A. PACKARD RCE 13801
VICE PRESIDENT -ENGINEERING
GW:RA:ss
#a~ «WaKV-GARY ALLACE
STA GEOLOGIST
0J~
ROLAND ACUNA
STAFF ENGINEER
1630-G South Sunkist Street Anaheim, California 92806 (714) 634-2092 (213) 852-4710