HomeMy WebLinkAboutCT 75-08; 22 UNIT CONDOMINIUM PROJECT; GEOTECHNICAL INVESTIGATION; 1975-11-10~
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GEOTECHNICAL INVESTIGATION
Tentative Map CT75-8
22 unit Condominium Project
Pine Avenue and Washington Street
Carlsbad, California
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Client:
Tony Regan
Job No. 75-1452-1
November 10, 1975
KENNETH G. OSBORNE & ASSOCIATES
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TABLE OF CONTENTS
INTRODUCTION-----------------------------------1
FIELD INVES'l'IGATION--------------------·,..---.,..-·--1
LABORATORY TESTING-----------------------------2
CONCLUSIONS AND RECOMMENDATIONS
Site Conditions---------------------------.2
Subsurface Conditions---------------------2
Soil Bearing------------------------------3
Settlement----------------~---------------3
Lateral Soil Pressure-----------~---------3 .
Retaining Wall Design----------'-----------4
~xpansive Soi1s---------------------------4 .
Concrete Slab Construction-----~---------
Shrinkage and Subsidence---------------.,..--
Stability of Excavations------------------
Grading-----------:------------------------
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5
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General--~------------------------~-------·6
APPENDIX
Laboratory Testing Procedures----~--------,A-C
Grading Specifications-General Provisions-D-E
Boring Logs-------------------------------F-H
Direct Shear Summary---------------------~ I
Boring Locations--------------------------J
@ KENNETH G. OSBORNE & ASSOCIATES
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I~ ·' Jop No. 75-1452-1 Page 1
IN'l'RODUCTION
This report presents, the results of a Geotechnical
Investigation performed on the property located on the
southwest corner of Pine Avenue and Washington S,treet in
the City of Carlsbad, California. This property, 'vlhich covers
an area of one acre, has been designated as Tentative Map
CT75-8.
Planneu for construction is a 22 unit condominium pro-,
j ect. It is expected that the three-story 'VlOod-frame structures
will be constructed on both continuous and pad footings with
slab-on-grade concrete floors.
The exact structural loads for the building are unkhmffi
at this time. However, for the purpose of analysis, it ha$ been
assumed that exterior footings will carry 1500. pounds per lineal
foot of which 90 percent is dead load and that pad footing's \';rill
carry 15 kips each of which 90 percent is dead load. If'it is
found that the actual loads are substantiablydifferent from
those assumed, this office should be notified for reevaluation.
FIELD INVESTIGATION
The field investigation consisted of excavating three
exploratory borings ,to depths of 16 feet. The borings were
drilled using an 18 inch bucket auger drilling rig. Selected
specimens of the in situ soils were obtained by using a 2.5 inch
I.D. drive tube sampler equipped with brass liner rings. In
addition to these relatively undisturbed specimens, bulk sample's
of the soils were obtained for additional laboratory analysis.
These soil samples served as the basis for 'the laboratory testing
and the engineering conclusions contained in this report.
The logs of the borings and a plot plan showing approximate
boring locations are included with .this report.
@ KENNETH G. OSBORNE & ASSOCIATES
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Job No. 75-1452-1 Page ,2
The elevations shown on the boring logs were determined by
interpolating from contaurs shown on the topographic ~apof the
property as prepared by Environmental Design, Planning and
Graphics dated August 22, 1975.
The locations of the borings were determined in the field
by measuring from property lines.
LABORATORY TESTING
The laboratory testing consisted of performing classi-
fication and strength tests, determining in situ dry density
and moisture content, and determining. the moisture-density
relationship of major soils.
Descriptions of test standards' used in this investigation
in addition to other tests not used in this investigation are
included in the Appendix of this report.
CONCLUSIONS AND RECOMMENDATIONS
Site Conditions
The site is situated on the ,flank of a small hiil, the
slope of which drops to the northeast toward Washington Street.
" An elevation difference across the site is approximately 10 feet.
The surface contains minor weeds and the sparse vines of
watermelon~ and squash. The surface is loose due to tilling the
soil for gardening.
One house and garage was observed on the southwest side.
Subsurface Conditions
Slightly silty sands form the predominate soil encountered
in the borings. These fine to coarse materials are generally
loose within the upper 18 inches but become dense with depth.
-No ground water was encountered during the subsurface in-
vestigation.
@ KENNETH G. OSBo.RNE & ASSOCIATES
Job No. 75-1452-1
Soil Bearing
The proposed structures may be supported on both con-·
tinuous and pad footings.
·5-"
Footings may be designed for an allowal;>le bearing value
of 1680 pounds per square foot for footings placed to a
minimum width of 12 inches and depth of 18 in~hes. ~his value
may be increased by 400 p~unds per square foot for each ad-
ditional foot in width to a maximum value o.f 2480 pounds per
square foot. An increase of 1/3 of the above bearing value
for short duration loading is permissible.
The above bearing values have been based on footings
placed into approved natural ground or certified cO~p'acted
fill.
Settlement
Estimates of settlement have been made based on the
anticipated loading and the settlement characteristics of
the in situ soils. These estimates ind~cate that footings
will settle less than 1/2 inch.
Differential settlement is expected to be 1/2 of the
total settlement. It is anticipated that t~e majority of
settlement will occur during construction •.
The above settlement estimates are based on the assumption \ .
that the grading will be performed in accordance with the
Grading Specifications •.
Lateral Soil Pressure
For purposes of designing the structures for l~teral
forces, an allowable lateral soil pressure of 400 pounds
per square foot per foot may be used for the building design.
A coefficient of friction of 0.43 m~ybe used for concrete
placed directly on the natural soils.
(§ KENNETH G. OSBORNE & ASSOCIATES
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Job No. 75-1452-1 Page 4
Retaining Wall Design
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Retaining ,,;aIls may be designed using ,the following
parameters:
Bearing -2000 psf
Active earth piessure, level backfill
Sliding coefficient -0.43
Passive earth pressure -400 psf/ft
30 psf/ft
The natural soils are considered ad~quate for badkfill
of retaining walls. "
Retaining walls should be provided with adequate drainage
to prevent hydrostatic pressures.
Expansive Soils
The results of tests indicate that the soils existing
on the site are nonexpansive. The test resuits are as fpllows:
J.Jocation
B-1 surface
Maximum
Densitl
131.0
Optimum
Moisture
8.7
% Relative
.Compaction
90.0
% Expans~on
144#/ft ,
0.0
No special construction is considered necessary for expansive'
soils on this project.
Concrete Slab Construction
It is recommended that concrete floor slabs in are~s
to be covered with moisture sensitive coverings be ,con-
structed over a 6 mil plastic membrane. The plastic
membrane should be properly lapped, sealed, and protected
with sand.
Shrinkage and Subsidence
Based on the in situ densities of the natural soil and
assuming an average fill 'density of 92 percent ~elative com-
paction, calculations indicate that there will be a 7
KENNETH G. OSBORNE & ASSOCIATES'
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Job No. 75-1452-1 Page 5
percent decrease in volume between the cut and fill operations.
In addition, it is estimated that there will be a 0.2 of a
foot of subsidence due to reworking the surface soils. These
values are estimated only and should be verified durin~ the
grading if earthwork quantities are critical.'
Stability of Excavations
Even though no caving was experienced during the sub-
surface exploration, it can be expected that' instability
of utility treriches may be expeiie~ced and; as a cons~quence,
shoring or sloping excavations may be required to protect
workers. The contractor should refer to the State of
California, Division of Industrial Safety for minimum safety
standards.
Grading
It was found that the upper 18 inches of the surface 'VIas
in a loose condition. It is felt that this zone should be
densified prior t6 placing footings oi fill to minimize settle-
ment. The following specifications have been made, assuming
that the upper 18 inches will need reworking. If it is found
that these soils are more dense, the amount of recompaction
can be reduced.
1. The natural soils in areas to receive fill shall be
scarified and compacted to a depth of 18 inches below the
existing surface.
2. Soil utilized for other filling shall consist of ap-
proved on-site materials or imported soil.
3. All imported soil shall be approved by the Soils Engineer
for both expansive and strength qualities.
4. All fill shall be. compacted to at least 90 percent of
maximum density as determined in accordance with A.S •. T.M. Test
Method D-1557-70.
@ . KENNETH G. OSBORNE & ASSOCIATES.
Job No. 75-1452-1 Pag.e 6
5. All fill shall be placed at or above the optimum
moisture content.
6. Areas to receive pavement shall be compacted to a
minimum depth of 6 inches below finished subgrade.
General
It ha~ been assumed, and it is expected, that the soil
conditions between the borings are similar to that 'encountered
in the borings. However, no warrani:y of such is implied in
this report.
The recommendations contained in this report are based
on the results of field investigation and laboratory testing
and represent our best engineering judgment. If soil conditions
encountered during the gradi!ig, or at· any other time, differ
substantially from those described in this report, this of-fiee
should be notified immediately so that appropriate recommenda-
tions can be made.
This report is issued with the understanding that it is
the responsibility of the owner or his representative to
ensure that the information and reqommendations contained
herein are called to the attention of the Project Architect
and Engineer and are incorporated into the plans and specifica-, .
tions and that necessary steps are taken to' see that the Con-
tractors and Subcontractors carry out such recommendations.
Respectfully submitted,
KENNETH G. OSBORNE & ASSOCIATES
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Kenneth G. Osborne
KGO:dhc R .• C.E. 14340
KENNETH G, OSBORNE. & ASSOCIATES
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APPENDIX
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LABORATORY TESTING PROCEDURES
SIIBAR STRBNGTII
The shear strength of the soil is d~termined by per-
forming direct shear tests and u~confined compression tests.
The direct shear tests nre performed on both undisturbed,
specimens and on samples remolded to 90 percent of A.S.~.M.
Test Hethod D-1557-70T, either unmodified or· modified to use
three layers in lieu of five. The samples are eithe'r tested
at in situ moisture or are saturated to simulate the worst
field condition and sheared at a constant rate of 0.1 inches
per minute. The relationship between normal stress and sheal;
stress is shown on t-he attached Direct Shear Summary!
The unconfined shear strength of s~lected undistu~bed
specimens is determined in accordance with A.S.T.M. Test,
Method D-2l66-66T. !hese tests are performed at the, existing
moisture content. The results of these tests are shbwn on
the Boring Logs.
E~~PANSION
Tests for volume change with moisture ~re performed on
compacted soil in accordnnce with either of thefollowing·two
methods:
a. The American Society of Civil r:ngineers'
Bxpansion Index Test, or
b. The Orange Empire Chapter o.f ICBO Soil
r:xpansion Test.
The samples are either undisturbed or are remOlded to 90·
percent of A.S.T.M. Test !1ethod D-1557-70T, eit~er unmodified
or modified to use three layers in lieu of five. The spec.imens
are dried, as required, and ~he percentage of 'expansion is
measured after saturation under surcharge lOads'of 60, 144, or
650 pounds per square foot.
Job No. 75-1452-1
11/73 -lab testing
Page'A
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SE'r'l'LEMEt1'l'
The settlement characteristics of the in situ soii
are determined by performing standard consolidation tests
on undisturbed specimens. The samples are tested in the
original sample liner ring and the increment loads for con~
solidation are applied for periods of 24 hours by means ot
a single counterbalnnced lever system. The p~essure settle-
ment curves arc shown on the attached plates.
MOISTURE DENSI'fY
The moisture-density relationship of. the-major soil
is determined in accordance with A.S.T.M. Te~t Method
D-1557-70T. This test may be modified to use three layers --
in lieu of five. The test results are shown on the Boring
Logs.
CLASSIFICATION
The following test methods are used to aid in the
classification of soils in accordance with the Unifie~ Soil
Classification system:
1. A.S.T.M. Test Method D-422-63
2. A.S.T.M. Test Method D-423-66
3. A.S.T.M. Test Method D-424-59
The results of grain size tests are shown on the Grading
. Analysis sheets. The results of consistency tests are shown
on the Boring Logs.
RESISTANCE "R" VALUE
The resistance IIR" Value of soils to support: paveme,nt
is determined by means of California Test Method NO.301.,..G.
Representative curves for the soils are obtained by remolding
three briquette specimens.
Job No. 75-1452-1
11/73 -lab testing
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SAND EQUIVl\LEtJ'r
The sand equivalent of granular soils and fine
'aggregates is determined in accordance ~ith A.S.T.M.
T~st Method D-24l9-69. T~ree representative samples
of. the soils are tested and the final sand equivalent
is computed as the average of the three individual
sand equivalents.
SOLUBLE SULFATE CONTENT
The concentration of soluble sulfates in the soLIs
is determined by measuring the optical density o,f a barium
sulfate precipitate. The precipitate results from a reaction
of barium chloride with water extractions from the soil
samples. 'rhe measured optical density is correlated with
a calibration curve obtained from readings on precipitates
of known sulfate concentrations.
Job No. 75-1452-1
11/73 -lab testing
Page C
RESPONSIDILI'J'Y
GRADING SPECIFICATIONS
GENEML PROVISIONS
1. The Soil Engineer and Bngineering Geoiogist are'
the Owner's or Builder's representative on the project.
For the purpose of these specifications, ~upervision by
the Soil Engineer includes that inspection performed by
any person or persons employed by, and responsible to,
the licensed Civil Engineer sighing the soil report.
2. All clearing, site preparation, or earthwork per-
formed on the project shall be conducted by the Con:tractor
under the supeivision"of a qualifi~d Soil Engineer.
3. It is the Contractor's responsibility to conform
to the Grading Specifications.
CLEARING
1. The site shall be cleared Of all vegetable growth
including but not limited to trees, stumps, logs, trash,
heavy weed growth, and organic deposits.
2. All houses, barns or other buildings shall be
removed.
3. The foundations and slabs left from the demolition
of structures shall be removed. Included with the removal
of foundations and slabs shall be the removal of basements,
cellars, cisterns, septic tanks, paving, curbs, pipes or
other deleterious materials.
4. Unless otherwise specified, al~ cleared materials
shall be removed from the site.
Job No. 75-1452-1
11/73 -grading specifications
Page D
SITE PREPl\.Hl\TION
1. Loose soils within. areas of fill shall be processed
by either excavating and stockpiling the loose soil or by
scarifying~ adjusting the coil moisture content to approxi-
.mately optimum, and compacting to the recommended relative
compaction.
2. The soils within areas of fill shall be processed
to a depth adequate to insure the removal of major tree roots
and pipe lines and the compaction of cavities left from tree
removal.
3. Excavations for the removal of subsurface structures
shall be cleared of loose soil and filied with compacted soil.
The'backfill of such excavations shall be compacted to the'
recommended relative compaction.
4. Cesspools shall be pumped out and backfilled with
clean sand. The sand backfill shall be flooded and jett~d
for obtaining compaction. Any unsuitable backfill of
cesspools shall be removed. The preparation of cesspools
shall be supervised by the Soil Eng.ineer.
5. Abandonment of oil wells shall be in accordance with
California State Law.
6. Unless otherwise specified, the tops of any abandoned
subsurface structure shall be removed to a depth 6f 5 feet
below the finished grade in building areas and to' a depth 6f
10 feet below 'finished grade in all other area.s.·
FILL PLACEHENT
1. No cobbles over 4 inches in diameter shall be accepted
in any fill, unless otherwise approved.
2. All on-site and imported soils shall be approved by
the Soil Engineer for use in an engine~red fi~l.
3. The placement of fill shall conform to the Special
Grading Provisions.
Job No. 75-1452-1
11/73 -grading specifications Page E
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surFACE ELEV~TION -I I
'105 131 80 I 3.1.
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: 4.01 11.0 130 , 85 -
108 5.2
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Sl\ND, iine, silty, dry, I f--reddish brown
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' ' . , fine to medium, slight to
4 .' moderate cemented, damp,
reddif.ih brown-brown-yellow ' ,
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14 -. i I 16 -~~ · Bottom of 130ring I No Ground
-No Caving
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(1, ~4 1:'1; r.'·1 ~ ~ I rrES'r BOLE vl ('t·1 > .. NO. 1
,~ :r,,: l" ~. u..U'J ~t~ (1) I H (,1) r---;-:r--' H .-J S ~~ ~r0n NO. DNfE I ~; ~ 5-14 ~) 2R Q.(2l L2i!j s: n '.!~'1' 1. (,'J;: 1 ,,'It.
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• SURFhCE ELEVATION
1 _ ... , . · SAND, fi~;-t·~ m~~i~n\', ~l'i;h;' 1
131 \ 8514.2 · . to moderate cemented, m01st,
112 2 · reddish brQwn, occasional u -.. thin clayey 1ayers . .
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120 131 92 5.9 4 --r ••• I
I • .. 'red bro\l/n..,.ycllow Ii) 115 131 88 · · . 6 --· SW ·
8 -yellow
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10 -l-i . light yellow, no ·fines l no, · cementation 12 -...
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14 -. -slight cemented · . brown, . . '
, Bottom of Boring -16 -No Ground Wa,ter
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ell t> [) U E" U :.) r~ ~ .. "4 ~ iil ~ f~ I , TEST HOl.E NO. 2 0 ........... ....... .. ~ ,-:,: r .... (-I :z ' .. l W ... ,.f ... · . • I-~ (\, (fl ~'J ) (..') Z l-t !~'i r ... (I) j >, til x til f~ ,. H ~l: H ~(/) H ~. , -.
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--------t I---·-t-'. : SAND, finc to In(~dium, slight
IlJ_-.Lll_1 fjS 13.:->1_ 2 __ .. .... to moderate cementC.!d,
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114 131! 87 3.0 .,
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~ light yellow, no fines, no
cementation
Bottom of Boring
No Ground Water
No Caving
r,ORI:-JG LOG
TEST HOLE NO. 3
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JOB NUMBER 75-1-'152
BORING NUMBER A::r 'Show,n
DEPTH A" :Show n
MOISTURE .:;sC(f.ur-a-l-a:.d
UNDIS'rURBED -~-
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800 1200
NOR"'1AL LOAD, P. S. F.
REHOLDED ---o-@ 90% MJ'I.XH1UM DENSITY
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1600 , 0 2000 .
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