HomeMy WebLinkAbout; La Costa Estates North Lot 23; Soils Report Preliminary; 1980-10-22John B. Fox P.E.
Stephen D. D~llemuth P.E.
SAN DIEGUITO ENGINEERING,INC.
AVENKJA DE ACACIAS
P.O. BOX 2OO+ RANCH0 SANTA FE, CA 92067
756-1861 756-3064
C,V,L ENGINEERING
SURVEYING
SOIL TESTING
SDE 2082
October 22, 1980
T.L. Construction Mr. Tom Elliott 124 Cliff Street Solana Beach, CA 92075
SUBJECT: Preliminary Soil Investigation at Lot 23 La Costa Estates
North, Located on Managua Court, La Costa.
Dear Mr. Elliott:
In accordance with your request, this office performed a Preliminary
Soil Investigation at the subject site to provide recommendations
pertinent,to the proposed development. The scope of our work
included:
1. Reconnaissance of the site and adjoining areas,
2. Review of pertinent, published and unpublished soil
information.
3. Limited subsurface exploration.
4. Limited laboratory testing.
5. Engineering analysis.
6. Preparation of this report.
PROPOSED DEL'ELOPMENT
The proposed development is understood to comprise of cut-fill
operations to create a building pad for construction of a single
family residence. It is understood that cut slopes of maximum
anticipated height of 2 30' are also planned for the site.
ENGINEERING DEPT. LIBRARY City of Carlsbad 2075 Las Palmas Drive Carlsbad CA 92009-4859
SDE 2082 October 22, 1980 Page Two
SITE DESCRIPTION
The site is comprised of an irregular parcel located northwest of
Managua Court in La Costa, California. The site slopes gently
towards southeast. An existing approximately l/2:1 cut slope
descends from the southeast portion of the site to Managua Court.
The site is bounded by existing residential lots, Vegetation at
the site consists of weeds and some small shrubs native to the area.
SUBSURFACE EXPLORATION
Subsurface exploration consisted of examination of soils in 2 trenches
excavated with a tractor mounted backhoe to refusal at a maximum depth
of 4 feet.
Soils were visually classified in accordance with unified soil class-
ification system, detailed logs of the trenches were recorded and are
presented as Plates 2 and 3.
LABORATORY ?&JD FIELD TESTING
Laboratory and 'field testing consisted of:
1. Determination of field dry densities and moisture contents
2. Direct shear tests
3. Expansion potential
4. Maximum density and optimum moisture content
,
SDE 2082 October 22, 1980 Page Three
1) Field dry density determinations were made on representative
foundation soils using chunk samples. The results of the tests
performed in accordance with accepted engineering practice are as
follows:
SAMPLE LOCATION
T-l @ 1' - 2'
T-l @ 2' - 3'
FIELD DRY FIELD MOISTURE
DENSITY (pcf) CONTENT (%)
80.7 3.7
96.6 12.5
2) A direct shear test was performed on representative samples
of the proposed foundation soils, remolded to the natural conditions.
The results of the test performed in general accordance with accepted
engineering practice are as follows:
DENSITY CONDITION ANGLE OF INTERNAL APPARENT FRICTION g COHESION C (psf)
Remolded to 90% of max density at optimum moisture content 290 450
3) The expansion potential of representative soils from the site
was determined by allowing the material, remolded to field conditions
to swell against a surcharge of 150 psf when brought into contact
with water. The results of the expansion test performed in accordance
with accepted engineering practice are summarized below: '
SAMPLE CONDITION
Remolded to 90% of maximum density and optimum moisture content
% SWELL
2.8%
SDE 2082 October 22, 1980 Page Four
4) Maximum density and optimum moisture content of representative
samples of on-site soils was determined in accordnace with A.S.T.M.
D-1557-70 test standard, the results are summarised below:
SOIL DESCRIPTION
Dark brown slightly clayey silty sand
MAXIMUM DENSITY (pcf)
125.0
OP?IMUM MOISTURE
11.5%
SOIL CONDITIONS
The site is mantled by slightly sandy, silt to silty clayey sand
topsoil, to depths of approximately 2 to 4 feet.
The topsoil layer is underlain by native bedrock of probable Santiago
Peak Formation. The bedrock appears slightly fractured. The observa-
tions are based on examination of soil conditions explored. Although
conditions are not anticipated to vary significantly, soil and/or
geologic conditions should be verified by the soil engineer during
construction.
CONCLUSIONS AND RECOMMENDATIONS
Based on the laboratory testing and evaluation of site conditions from
a soils engineering standpoint, the site is considered suitable for the prOpOSed development provided the following recommendations are incorp-
orated in the design and construction of the project.
The on-site loose top soils are considered to be relatively compressible
and are considered unsuitable for support of any structures. It is
therefore recommended that all loose soils be removed till firm formational
soils or bedrock is exposed, and replaced with fill compacted to minimum
90% of the maximum density at optimum moisture content as per A.S.T.M.
D-1557-70.
SDE 2082 October 22, 1980 page Five
1. PLACEMENT AND COMPACTION OF FILL
All fill materials placed at the site shall be in accordance with
recommended grading specifications included with this report and
in compliance with the City of Carlsbad Grading Ordinance.
All imported soils (if any) for construction of fill shall be
inspected and tested by the soil engineer prior to being placed as'
compacted fill.
Fill slopes should be provided with toe keys and benching as per
recommendations contained in grading specifications included herein,
2. FOUNDATIONS
The proposed structures may be supported on conventional continuous
or isolated spread footings, founded minimum 18" below lowest adjacent
grade into compacted fill or competent bedrock. The footings shall be
al least 12" wide.
Footings placed as recommended may be designed for an allowable soil
bearing pressure of 2000 psf.
An allowable lateral bearing pressure of 300 psf per foot of depth
may be assumed provided footings are poured tight surround$ng firm
soils or competent bedrock. A coefficient of friction of 0.25 may be
assumed for sliding between concrete and underlying soils.
Lateral bearing may be increased by l/3 for short durations of wind
and seismic forces.
Minimum foundation reinforcement shall consist of 1 #4 bar placed at top
and 1 #4 bar placed at bottom of continuous footings. In order to span
local soil irregularities.
SDE 2082 October 22, 1980 Page Six
3. SLABS
Slabs on grade supported on non-expansive or slightly expansive soils
may be reinforced with 6 x 6 - lO/lO welded wire mesh, slabs shall be
minimum 4" thick. Slabs should be underlain by a minimum 4 inch layer
of l/4" crushed rock or gravel base. A 6 mil thick plastic or vinyl .
moisture barrier, overlian by 2 inches of clean sand should be-provided
over the base material to prevent upward capillary movement of soil
moisture. Pad soils should be premoistened prior to placement of
moisture barrier or concrete.
The above recommended foundation and slab designs should be considered
preliminary and revised recommendations (if necessary) regarding allowable
soil bearing pressures, lateral resistance, expansion etc.,-should be
presented by the soil engineer after testing of soils at finish grade.
In order to minimise the likelihood of differential settlements, it
is recommended that footings should not straddle a cut-fill interface.
Cut areas should be over excavated to minimum depth of 4 l/2 feet and
replaced with compacted fill.
4. SLOPE STABILITY
Stability of proposed cut slopes to anticipated maximum heights of
30: feet were analysed by using Singh's charts, (Journal of Soil
Mechanics and Foundation Engineering, ASCE No. SM5, Nov., 1970, pp 1879-
1892).
The results are summarized below and are also included as Plates 5 and 6.
1:5:1 Slopes
+ - 30 feet Static F.S. = 2.1
2:l Slopes
+ - 30 feet Static F.S. = 2.4
SDE 2082 October 22, 1980 Page Seven
Based on the analysis, the proposed 2:l fill slopes and 1 l/2:1 cut
slopes are considered grossly stable for the intended use. However,
it should be noted that the basis forming the present design are
preliminary. Stability of all fill and cut slopes shall be re-
evaluated during construction.
All cuts shall be inspected by the soil engineer and/or a certified
engineering geologist. If any adverse soil or geologic conditions
are observed supplemental or revised reccrmw dations should be presented at that time.
Due to the fractured nature of the bedrock generally underlying the
site some localized sloughing may be anticipated, it is recommended
that a slough wall should be provided at the toe of the cut slopes.
However, the need for the slough wall should be verified by a soil
engineer after inspection of cut slopes at completion of grading
operations.
5. RETAINING WALLS
Retaining walls, (unrestrained) at the top, may be designed for an
equivalent fluid pressure of 35 pcf.
Restrained retaining walls may be designed for an EFP of 60 pcf.
The above values assume compacted, level backfill, comprising free
draining sandy soils. If conditions are otherwise, this office
should be notified as to present revised recommendations.
Temporary cut for retaining walls should not be made steeper than
1:l (horizontal to vertical ratio).
Any surcharge loads affecting the walls should also be added to the
above values. Adequate drainage should be provided behind the
retaining walls.
SDE 2082 October 22, 1980 Page Eight
6. DRAINAGE
The site should be provided with positive drainage. The surrounding
topography should slope away from the building areas at a minimum
gradient of 3% to a suitable point of discharge.
In no case should water be allowed to pond at or near the building
areas or be allowed to drain over the slopes in an uncontrolled
manner. Drainage swales having a minimum gradient of 2% should be
provided at the site wherever required and should be designed by a
registered civil engineer.
I. INSPECTION
All footing excavations should be inspected by the soil engineer
prior to placement of steel or pouring of concrete.
It is suggested that a joint meeting between the owner/developer,
contractor and the soil engineer, be set up prior to commencement
of grading operations, to discuss construction schedules and other
related aspects.
SDE 2082 October 22, 1980 Page Nine
LIMITATIONS AND UNIFORMITY OF COhiDITIONS
The recommendations of this report pertain only to the site
investigated and are based upon the assumption that the soil
conditions do not deviate from those observed in the test pits.
If any variations or undesirable conditions are encountered
during construction, or if the proposed construction will differ . ,
from that planned at the present time, San Dieguito Engineering.
Incorporated should be notified so that supplemental recommenda-
tions can be given. .
This report is issued with the understanding that it is the
responsibility of the owner, or of his representative, to ensure
that the information and recommendations contained herein are
brought to the attention of the architect and engineer for the
project and incorporated into the plans, and that the necessary
steps are taken to see that the contractor and subcontractors
carry out such recommendations in the field.
The findings of this report are valid as of the present date.
However, changes in the conditions of a property can occur with
the passage of time, whether they be due to natural processes
or the works of man on this or adjacent properties. In addition,
changes in applicable or appropriate standards may occur, whether
they result from legislation or the broadening of knowledtge.
Accordingly, the findings of this report may be invalidated
wholly or partially by changes outside our control. Therefore,
this report is subject to review and should not be relied upon
after a period of three years.
SDE 2082 October 22, 1980
If you have any questions regarding this report, please do not
hesitate to contact this office.
This opportunity to be of service is greatly appreciated.
Respectfully submitted, SAN DIEGUITO ENGINEERING, INC.,
RCE 26525
JBF/ZA/cs
Page Ten
cc: (4) submitted
.
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PROJEC’l- ELL, /oT-
NO. 2082
- -.- - DATE /o-2/- &~~---
PLATE Q __
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ND #J OF SOIL iN0 7 6ND Ii
LOPE PLOT POINT c/yH,.+
1 FIACTORIOF SATETY., .
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<,h y DEGREES ,I*-
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+, DEGREES
~COMTWJRS FOR SLOPE 29.
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L’.,’ PL ATE 6
RECOMENDED GRADING SPECIFICATION - GENERAL PROVISIONS
GENERAL INTENT:
The intent of these specifications is to establish pro-
cedures for clearing, compacting natural ground, preparing
areas to be filled and placing and compacting fill soil to
the lines and grades shown on the accepted plans. The
recommendations contained in the preliminary soil invest- .
igation report and/or the attached special provisions are a
part of the recommended grading specifications and shall
supersede the provisions contained hereinafter in the case
of conflict.
INSPECTION AND TESTING
A qualified soil engineer shall be employed to observe and
test the earthwork in accordance with these specifications.
It will be necessary that the soil engineer or his repre-
sentative provide adequate observations so that he may
provide a memorandum that the work was or was not accom-
plished as specified. It shall be the responsibility of the
contractor to assist the soil engineer and to keep him
appraised of work schedules, changes and new information and
data so that he may provide the memorandum to the owner and
proper county authorities, as required.
If, in the opinion of the soil engineer, substandard con-
ditions are encountered, such as questionable soil,' poor
moisture control, inadequate compaction, adverse weather,
etc., he will be empowered to either stop construction until
the conditions are remedied or corrected or recommend rejection
of the work.
Soil tests used to determine the degree of compaction will
be performed in accordance with the following American
Society for Testing and Materials test methods:
Maximum Dry Density and Optimum Content.
A.S.T.M. D-1557-70
Density of Soil In-Place
A.S.T.M. D-1556-64
PREPARATION OF AREAS TO RECEIVE FILL: -
All vegetation, brush and debris shall be removed, piled and
burned or otherwise disposed of. After clearing, the natural
ground shall be scarified to a depth of 6 inches, brought to
the proper moisture content, compacted and tested for the
minimum density specified in the special provisions or the
recommendations contained in the preliminary soil investi-
gation report.
When the slope of the natural ground receiving fill exceeds
20% (5 horizontal to 1 vertical), the original ground shall
be stepped or benched as shown on the attached Plate A.
Benches shall be cut to a firm competent soil condition. The
lower bench shall be at least 10 feet wide and all other
benches at least 6 feet wide. Ground slopes flatter than
20% shall be benched when considered necessary by the soil
engineer.
FILL MATERIAL:
Materials placed in the fill shall be approved by ;he soil
engineer and shall be free of vegetable matter and other
deleterious substances. Granular soil shall contain suffic-
ient fine material to fill the voids. The difinition and
disposition of oversized rocks, expansive and/or detrimental
soils are covered in the special provisions. Expansive
soils, soils of poor graduation or strength characteristics
may be thoroughly mixed with other soils to provide satis-
factory fill material, but only with the explicit consent of
the soil engineer.
PLACING AND COMPACTION OF FILL:
Approved material shall be placed in areas prepared to
receive fill in layers not to exceed six inches in compacted
thickness. Each layer shall have a uniform moisture content
in the range that will allow the compaction effort to be
efficiently applied to achieve the specified degree of'
compaction to a minimum specified density with adequately
sized equipment, either specifically designed for soil
compaction or of proven reliability. The minimum degree of
compaction to be achieved is specified in either the special
provisions or the recommendations contained in the prelimin-
ary soil investigation report.
Field tests and inspection to check'the degree of compaction
of the fill will be taken by the soil engineer or his
representative. The location and frequency of the tests
shall be at the soil engineer's discretion. In general, the
density tests will 3e made at an interval not exceeding two
feet in vertical rise and/or 500 cubic yards of embankment.
SEASON LIMITS: -
Fill shall not be placed during unfavorable weather con-
ditions. When work is interrupted by heavy rain, filling
operations shall not be resumed until the proper moisture
content and density of the fill has been achieved. Damage
resul.ting from weather shall be repaired before acceptance
of work.
UNFORSEEN CONDITION:
In the event that conditions are encountered during the site
preparation and construction that were not encountered
during the preliminary soil investigation, San Dieguito
Engineering, Inc., assumes no responsibility for conditions
encountered which differ from those conditions found and ~
described in the prelinimary soil investigation report.
SPECIAL PROVISIONS
The minimum degree of compaction of compaction to be ob-
tained in compacting natural ground and in the compacted
fill shall be 90 percent of the maximum dry density obtained
in the laboratory, A.S.T.M. D-1557-70.
Detrimentally expansive soil is defined as soil which will
swell more than 3 percent of the original sample thickness.
The expansive potential is determined by allowing the mat-
erial, remolded to 90% of its maximum dry density, to swell
against a surcharge of 150 psf when brought into contact
with water. the expansion of the sample is determined by
measuring the swell from air-dry to saturated conditions.
Oversized fill material is defined as rocks or lumps over
six inches in diameter. At least 40 percent of the fill
soil shall pass through a No. 4 U.S. Standard Sieve.
RECOMMENDAT IONS FOR I= ILLING
ON SLOPING GROUND
Existing Ground Surface
Zone of Loose Surface Soil
Compacted Fill
Firm Ground, 6 Feet
Toe Key - Width To Be Determined By Soil Engineer, But Not Less Than 10 Feet
SCHEMATIC ONLY
NOT TO SCALE
SAN DIEGUlTO ENGR. INC. PLATE A