HomeMy WebLinkAboutCT 77-03; TARA LA COSTA LOTS 187,188 & 189 OF LA COSTA VALLEY UNIT 4; REPORT OF SOIL CONDITION; 1977-06-100,
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PHILIP HENKING I!IENTON
I'RESIDENT • CIVIL ENGINIEER
Mr.' Mike O'Hara
P. O. Box 1009
Del Mar, Cal ifornia 92014
BENTON ENGINEERING. lNC.
APPLIED SOIL MECHANICS -FOUNDATIONS
6717 CONVOY COURT
SAN DIEGO. CALIFORNIA 92111
June 10, 197Z.
Subject: Project No. 77-4-150
Report of Soil Conditions
Tara La Costa -Carlsbad Tract No. 77-3 '"
Lots 187, 188, 189, 191 and 192
Carlsbad, California
Dear Mr. O'Hara:
TELEI'HONE (714) S6S·UU5S
RECEIVED
JUN 1 5 1977
CITY Ur CHIiL::>8AD
-:-,')oineering Department
This is to present the results of a soils investigation conducted on the subject lots in La
Cost,a Valley Unit No.4 in Carlsbad, Cal ifornia. The objectives of the i'nvestigation were
priniarily to determine the existing soil conditions, particularly with regard to the expansive
characteristics of the soils that might affect buildings constructed on these lots.
The investigation consisted of excavating thirteen exploration pits using a backhOe, logging
the soils encountered in the pits, and obtaining both undisturbed and loose bag samples for
laboratory testing. The approximate locations at which the pits were ~xcavated are shown
on the attached Drawing No. 1 The soils were classified using the field identification
procedures of the Unified Soil Classification Chart and the log of the soil conditions is presented
on the attached pages 5 and 9, ea,ch entitled "Log of Exploration Pits. II
Laboratory Tests
Exp<;.nsion tests were performed on representative samples of the soils encountered in the explora-
tion pits to determine their volumetric change characteristics with change in moisture content.
The-recorded eXJXlnsion of the samples are presented as follows:
,Depth of Sample Below
Pit Existing Ground
No. Surface in Feet
2
2
3
3
5
13
1.3-2.3
2.3-3.5*
0-2.3
2.3-3.5
2.0-3.0
4.0-6.0
Soil Description
Percent Expansion Under Unit
Load of 500 Pounds per Square
Foot from Air Dry to SQturation
,Brown fine sandy clay
Light brCM'nish gray fine sandy clay
BrCM'n and red brCM'n fine sandy clay
Light brCM'nish gray fine sandy clay
Brown and red brown fine sandy clay
Brown clayey fine sand
5.77
2.87
4.87
6.50
4.,67
1.22
* Indicates test was performed on a sample molded to 90 percent of maximum dry density.
Proiect No. 77-4-15D
Mr. Mike O' Hara
-2-June 10, 1977
Canpaction tests were performed on representative samples of certain soils to establish canpac-
tioncriteria. The soils were tested according. to the A.S. T.M. D 1557-70 method of compaction
which uses 25 blows of a 10 pound rammer dropping 18 inches on each of 5 layers in a 4 inch
diameter 1/30 cubic foot mold. The results of the tests are presented as foil ows:
Pit No.
2
13 '
Depth
of Sanple
in Feet
2.3-3.5 Light brownish gray fine
sandy clay
0-4.0 Light ,gray brown silty fine
to medium sand
Maximum
Dry Density
Ib/cw ft
125.7
123.7
Optimum mois-
ture Content
% dry wt
9.8
10.3
C,onc\usions and Recommendations
A. It is concluded from the results of the field investigation and laboratory tests that
certain of the soils encountered on the subject lots would be classified as Hexpansive lt with respect
to volumetric change with change in moisture content. Based on the results of the expansion tests.
and our visual and textural classification, the soils hove been grouped into three catagories des-
cribed as follOVls:
Type A -Critically expansive (Greater than 5.C1% expansion)
Type B -Marginally expansive (Between 2.5 and 5.0% expansion)
Type C -LO¥I expansion (Less than 2.5% expansion)
The soil conditions in.each building area should be classified after the canpletion of
gra~ing. _In order to minimize possible detrimental effects due to expansion in the potentially
expansive soil areas, the following special design and precautions are recommended:
TYPE itA /I (Critically expansive)
1. Use continuous interconnected reinforced concrete footings, wherever
possible, and place these at a minimum depth of 2.0 feet below the
lowest adjacent exterior final ground surface. If isolated interiOr
column footings are required, these should be placed at a depth of 2.5
feet below the lowest adjacent ground surface.
2. Reinforce and interconnect continuously with steel bars all interior and
exterior footings with a minimum of one #5 bar at 3 inches above the'
bottom of all footings and one #5 bar placed 1 1/2 inches below the top
of the stems of the footings.
3. Reinforce all concrete slabs with a minimum of 6 x 6 -10/10 welded
wire fabric and provide a base layer of at least 4 inches of 3/4 to 1 inch
size crushed rock beneath all concrete slabs. A moisture barrier should
BENTON ENGINEERING. INC.
Project No. 77-4-15D
Mr. Mike O'Hara
-3-June 10, 1977
be provided above the crushed rock and then 2 inches of sand
should be placed over the moisture barrier and below the bottan
of the slab.
4. Separate garage slabs fran perimeter footings by a 1/2 inch
thickness of construction felt or equivalent, to allow independent
movement of garage slabs relative to perimeter footings. Assure
canplete separation by extending the felt over the full depth of the
front thickened edge of the garage slab. Also, cut off the garage door
stops at least V2 inch above the slab.
5. Provide positive drainage away fran all perimeter footings with a
vertical fall of at least 5 inches in a horizontal distance of 5 feet
outside the perimeter of the house.-
6. Exercise every effort to assure that the soil under the foundations and'
slabs has a uniform moisture content of at least 3 percent greater
than optimum throughout the top 3 feet below finished grade at the
time of placing foundations and slabs.
TYPE IIBII (Marginally expansive)
Use the same design as recanmended for Type IIAII condition except items 1 and 2
should be modified as follows:
1. The continuous footings may be placed at a minimum depth of 1.5 feet
below the lowest adjacent exterior final ground surface.
2. Single #4 bars, placed as directed above, may be substituted for the
#5 bars recanmended for the Type IIAII condition.
TYPE lIe ll (Low expansion)
1. Special design for expansive soil conditions will not be required for this
condition.
Economic considerations may indicate that it would be desirable to provide either
marginal or nonexpansive soil conditions in certain areas. In order to provide a nonexpansive
soil condition a thickness of 3.0 feet of nonexpansive soil would be required over the Type HAil
soils and 2.0 feet of nonexpansive soil should be placed over the Type IIBII soils.
B. Shallow depths of filled ground have been placed on the southwesterly portion of
the site in the vicinity of Pit Nos. 1, 2, 4 and 5. This fill was not inspected or tested by
BENTON ENGINEERING. INC.
Project No. 77-4-15D
Mr. Mike O'Hara
-4-June 10, 1977
Benton Engineering, hic. Therefore, if this fill has not been tested and approved for
structural support, it is recommended that the fill should be removed to suitable firm natural
soils and be replaced with filled ground uniformly compactea to at least 90 percent of
maximum dry density. .
The compacted filled ground encountered on all other portions of the site was'
inspected and tested by Benton Engineering, Inc. The results of tests taken in these
existing compacted fill soils were presented in our report on Project No. 66-3-31 D,
dated December 16, 1966.
C. All filled ground placed during the final site grading should be placed under
engineering inspection and should be uniformly compacted to at least 90 percent of maxi-
mum dry density. It has been determined that the fill materials, compacted to 90 percent of
the maximum dry density, have a safe bearing value of 1500 pounds per square"foof for one
foot wide continuous footings founded at the minimum required depth and placed five feet
or more inside the top of compacted filled ground slopes. If foqti ngs are placed closer to
the exposed slopes than 5 feet inside the top of compacted filled ground slopes, these should
be deepened one foot below a 1 1/2 horizontal to 1 vertical I ine projected outward and
downward from a point 5 feet horizontally inside the top of compacted filled grrund slopes.
D. All buried exterior utility I ines should be City of Carlsbad approved plastic
lines due to the corrosive characteristics of the soils, unless sufficient field tests are taken
to establ ish that only noncorrosive soils exist in the uti! ity trench areas.
Respectfu II y subm i tted I
BENTON ENGINEERING, INC.
By Rc:::~
R. C. Remer
D i str: (3) Addressee
(2) Duca -McCoy
Consulting Civil Engineers
RCR/PHB/sm
BENTON ENGINEERING, INC.
Project No. 77-4-150 e
Mr. Mike O'Hara
Depth
Below
Existing
Pit Grade
No. in Feet
1 0.-3.7
(G;t 1.5*)
2 0.-1.3
(Fill 0..2')
1.3-2.3
2.3-3.5
3 0.-2.3
(Fill 0..2')
2.3-3.5
4 0.-1.0.
(Fill·1.6')
1.0.-1.8
1.8-3.0.
3.0.-3.8
5 0.-1.3
(Fill 5.51)
1.3-2.0.
2.0.-3.0.
3.0.-3.7
6 0.-1.0.
(Fill 4~31)
1.0.-2.0.
2.0.-3.5
7 0.-3.0.
(Fill 1.6')
3.0.-4.0.
Expansion
Classifi-
cation
C
C
A
B
B
A
C
C
A
B
C
A
B
C
C'
C
A
C
A
-5-e June 10., 1977
LOG OF EXPLORATION PITS
Soil Description
. FILL ** -Red brown and gray clayey fine to medium
sand with scattered gravel end cobbles to 8 inches
(moist I compact)
FILL -Red brown and gray clayey fine to medium
sand with scattered gravel (moist, compact)
Brown fine sandy clay (moist I very firm)
Light brownish gray fine sandy clay (moist I very firm)
Brown and red brown fine sandy clay (moist, very
firm)
Light brownish gray fine sandy clay (moist, very firm)
FILL -Red brown and gray clayey fine sand with
scattered gravel (moist I compact)
Brown silty fine sand (sl ightly moist, compact)
Brown fine sandy clay (moist I very firm)
Light brownish gray fine sandy clay (moist, very firm)
FILL-Brown, red brownr and gray clayey fine to
meduim sand with scattered gravel (moist, compact)
Brown silty fine sand (moist I compact)
Brown and red brown fine sandy clay (moist I very firm)
Brown clayey fine to medium sand (moist I very frim)
Compacted Fill***-Brown silty fine to medium sand
with scattered gravel and cobbles to 8 inches (moist I
compact) .
Compacted Fill -Light gray silty fine to medium sand
tn orst I compact)
Brown and red brown fine sandy clay (moist I very firm)
Compacted Fill -Light gray brown slightly clayey fine
to medium sand (moist, compact)
Compacted Fill-Brown fine sandy .clay (moist I very firm)
* Indicates proposed cut or fill
** Indicates filled ground not tested by Benton Engineering, Inc.
*** Indicates compacted filled ground tested by Benton Engineering, Inc.
BENTON ENGINEERING. INC.
•
Project No. 77-4-150
Mr. Mike 01Hara
Depth
Below
Existing
Pit Grade
No. in Feet
8 0-4.0
(Cut 0.81)
9 0-4.0
·(Fill 1.01)
10 0-0.3
0.3-2.5
2.5-3.2
3.2-4.2
11 0-4.0
(Fill 1.21)
12 0-3.0
(Fill 0.5:)
13 0-4.0
(Cut 3.91)
4.0-6.0
6.0-7.0
• -6-e June 10, 1977
LOG OF E~LORATION PITS, CONT.
Expansion
Classifi-
cation
C
C
C
B
C
C
C
C
C
C
C
Soil Description
Compacted Fill -Light brown and gray silty fine to
. to meduim sand with sl ight clay binder (moist, compact)
Compacted Fill -Light brown and gray silty fine to
medium sand with sl ight clay binder (moist, compact)
cted Fill-Light gray brown silty fine sand
moist, medium compact)
Com cted Fill -Brown to red brown fine sandy clay
moist I medium firm)
Light gray brown silty fine sand (moist, compact)
Brown to red brown gravelly clayey fine to medium
sand (moist, compact! 20010 gravel)
Compacted Fill -Light gray brown silty fine to medium
sand with sl ight clay binder (moist, compact)
Compacted Fill -Light fray brown silty fine sand
Compacted Fill -Light gray brown silty fine to medium
sand (moist, compact)
Compacted Fill -Brown clayey fine sand (moist, firm)
Brown dayey fine to medium sand (moist, compact)
BENTON ENGINEERING. INC.
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LE:GEND
~. IMdicof.es Appr-o"';lmo+e Location Of Exp\orahon Pit.
BENTON ENGINEERING, INC .•
SAN DI EGO, CALIFORNIA
LOCATION OF EXPLORA.TION P\TS
TARA LA C05TA
CARLSBAD TRACT NO. 77-5
LOTS 187, t88, 18~, t~1 ~ t~Z OF
LA COSTA VALLE'? UN1T NQ 4
CAI<LSIOAD, CALIFORNIA
PRonCT NO. f DRAWING NO
77-4-15D. 1
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