HomeMy WebLinkAboutSDP 02-19; LA COSTA CANYON HOMES; LIMITED SITE INVESTIGATION; 2001-06-09•
EAST COUNTY SOIL CONSULTATION
AND ENGINEERING, INC.
c;..t>Po2.,-rq
RECEIVED
June 9, 2001
10925 HARTLEY ROAD, SUITE "I"
SANTEE, CALIFORN_IA 92071
(619) 258-7901
Fax 258-7902
Legacy Development, LLC
6965 El Camino Real, Suite 105-451
Carlsbad, California 92009
Subject: Project No. 01-1147Hl(l)
Limited~~igation
DEC 3 1 2002
CITY OF CARLSBAD
PLANNING DEPT.
Propos~ 26-Unit _bpartment Complex
4 Vacan~rth Side of La Costa Avenue
West of Romeria Street
City of Carlsbad, California.
Ladies/ Gentlemen:
In accordance with your request, we have performed a limited
investigation of the soil conditions at the subject site. The
investigation was undertaken to provide the soil engineering
criteria for site grading and to recommend an appropriate
foundation system for the proposed apartment complex.
Our investigation found that the proposed building pads are
primarily underlain by undocumented fill soils to a maximum depth
of approximately 15 feet below existing grade. Mudstone and
sandstone of the Santiago Formation were underlying the
undocumented fill.
The fill soils generally consist of soft to medium stiff sandy
clay exhibiting a moderate expansion potential and a moderate
compressibility.
It is our opinion that the
provided the recommendations
c;::onstruction.
Respectfully submitted,
~c£.L~ ~>\1
Mamadou Saliou Diallo, P.E
RCE 54071
proposed
herein
development is feasible
are implemented during
LEGACY !vELOP MENT, LLC PROJECT NO. o'8147 HJ (1)
INTRODUCTION
This is to present the findings and conclusions of a soils
investigation for a proposed 26-unit apartment complex to be
located on the north side of La Costa Avenue, west of Romeria
Street, in the City of Carlsbad, California.
The objectives of the investigation were to determine the existing
soils conditions and provide recommendations for site development.
In order to accomplish these objectives, five (5) exploratory
borings were drilled to a maximum depth of 31.0 feet; undisturbed
and loose bag samples were obtained, and laboratory tests were
performed.
SITE DESCRIPTION AND PROPOSED CONSTRUCTION
The subject site is located on the north side of La Costa Avenue,
west of Romeria Street, in the City of Carlsbad, California. The
site was previously graded into 4 relatively level building pads.
Prior to the grading operation, the site sloped moderately to the
north. Vegetation consists of grass. The proposed development
includes the construction of a 26-unit, two-story over garage
apartment complex to be founded on caisson footings with a slab-
on-grade floor system.
FIELD INVESTIGATION
Five exploratory borings were drilled with a gas-powered auger to
a maximum depth of 31 feet on April 12, 2001 at the approximate
locations shown on the attached Plate No. 1, entitled "Location of
Exploratory Borings". A continuous log of the soils encountered
was recorded at the time of excavation and is shown on Plates No.
2 & 6 entitled "Summary Sheet".
The soils were visually and texturally classified according to the
filed identification procedures set forth on the attached Plate
No. 7 entitled "Uniform Soil Classification Chart.
2
LEGACY.VELOPMENT, LLC PROJECT NO .147Hl (])
SURFACE CONDITIONS
The surface soils encountered during the course of our
investigation were fill soils consisting of tan sandy clay, moist
to wet, loose to medium dense to a maximum depth of fifteen (15)
feet. These soils were underlain by mudstone and sandstone of the
Santiago Formation (Tsa).
EXPANSIVE SOILS
An expansion test was performed on representative samples of the
fill soils encountered to determine volumetric change
characteristics with change in moisture content. An Expansion index
of 61 indicates a moderate potential for expansion.
GROUNDWATER
Groundwater was not encountered during the course of our
investigation. Groundwater is anticipated at a depth greater than
100 feet. We do not expect ground water to affect the proposed
development.
GEOLOGIC HAZARDS
A review of the available geological literature pertaining to the
site indicates the existence of the Rose Canyon Fault Zone
approximately 10.5 Km to the west. Ground shaking from this fault
or one of the major active faults in the region is the most likely
happening to affect the site. With respect to this hazard, the
site is comparable to others in the general area.
The proposed
accordance with
Building Code
California using
residential structures should be designed in
seismic design requirements of the 1997 Uniform
or • the Structural Engineers Association of
the following seismic design criteria:
PARAMETER VALUE UBC REFERENCE
Seismic Zone Factor, Z 0.40 Table 16-1
Soil Profile Type So Table 16-J
Seismic Coefficient, Ca 0.44 Table 16-Q
Seismic Coefficient, Cv 0.64 Table 16-R
Near-Source Factor, Na 1.0 Table 16-S
Near-Source Factor, Nv 1.0 Table 16-T
Seismic Source B Table 16-U
3
.;J>
LEGACY.VELOPMENT, LLC PROJECT NO .• 147Hl(l)
Based on the absence of shallow ground water, type and consistency
of the underlying soils, it is our opinion that the potential for
liquefaction is very low. •
CONC~USIONS AND RECOMMENDATIONS
The following conclusions and recommendations are based upon the
analysis of the data and information obtained from our soil
investigation. This include-s visual inspection; field
investigation; laboratory testing and our general knowledge of the
soils native to the site. The site is suitable for the proposed
development provided the recommendations set forth are implemented
during construction.
GRADING AND EARTHWORK
Site grading should begin with clearing and grubbing, e.g. the
removal of vegetation and deleterious materials. It is our
understanding that the four previously graded pads will be graded
into two level building pads. Therefore, we recommend that the
existing fill soils to a minimum depth of five (5) feet be
overexcavated, moisture conditioned 2 to 4 percent over optimum
and compacted to a minimum of 90 percent relative density. The
compacted fill mat will provide support for the garage slabs,
underground utilities, driveway .and parking areas. Prior to the
fill placement, the lower building pads should be overexcavated to
a minimum depth of 2 feet, and recompacted as recommended above.
The actual depth apd extent of removal should be evaluated in the
field at the time of excavation by a representative of this firm.
Grading should be done in accordance with the attached appendix A.
IMPORTED SOILS
If imported soils are required to achieve proposed grades, they
should be non-expansive, i.e. an expansion index of 20 or less and
approved by the soils engineer prior to site delivery.
4
LEGAcAl:vELOPMENT, LLCPROJECTNO. l1147HI(IJ
Where moisture sensitive floor coverings are anticipated over the
slab, the 10-mil plastic moisture barrier should be underlain by a
capiilary break at ,least 4 inches thick, consisting of 3/ 4 inch
crushed rock.
SLOPE SETBACK
Proposed structures and other improvements that are located within
8 feet of the face of existing slope could suffer differential
movement as a result of the poor lateral stability of these soils.
Therefore, caisson footings for the proposed residential
development should be placed at least 8 feet back from the top of
these slopes.
ALTERNATIVE TO CAISSON FOUNDATIONS
GRADING AND EARTHWORK
Site grading should begin with clearing and grubbing, e.g. the
removal of vegetation and deleterious materials. The undocumented
fill and mudstone layer should be overexcavated, moisture
conditioned 2 to 4 percent over optimum and compacted to a minimum
of 90 percent rel~tive density. The maximum depth of
.overexcavation is anticipated to be_ approximately 15. The actual
depth and extent of removal should be evaluated in the field at
the time of excavation by a representative of this firm. Grading
should be done in accordance with the attached appendix A.
FOUNDATION AND SLAB
a. Continuous footings and/or spread footings are suitable for use
and shall extend a minimum of 24 inches for the two story
residential family dwellings into the compacted fill soils.
Continuous footings should be 15 inches wide and reinforced with
four #5 steel bars; two bars placed near the top of the footings
and the other two bars placed near the bottom of the footings.
b. Concrete floor slabs should be a minimum 4 inches thick.
Reinforcement should consist of #3 bars placed at 12 inches on
center each way. Slab reinforcement should be placed within the
middle third of the slab by supporting the steel on chairs or
concrete blocks "dobies''. The slab should be underlain by 2 inches
of clean sand over a 10-mil visqueen moisture barrier and another
2 inche$ of clean sand or gravel not exceeding 3/ 4 inch in size
with no more than 5 percent passing the #200 sieve. The effect of
concrete shrinkage will result in cracks in virtually all concrete
slabs. To reduce the extent of shrinkage, the concrete should be
7
LEGACY,VELOPMENT, LLC PROJECT NO. O'J J 47HI (I)
slabs. To reduce the extent of shrinkage, the concrete should be
placed at a maximum of 4-inch slump. The minimum steel recommended
is not intended to prevent shrinkage cracks.
SOIL BEARING VALUE (COMPACTED FILL SOILS)
An allowable soil bearing value of 1500 pounds per square foot may
be used for the design of continuous foundations and spread
footings founded a minimum of 12 inches into the compacted fill
soils. This value may be increased by 300 psf for each additional
foot of depth to a maximum value of 3000 lb/ft2.
LATERAL SOIL PRESSURE
Lateral resistance to horizontal movement may be provided by the
soil passive pressure and the friction of concrete to soil. An
allowable passive pressure of 1;30 pounds per square foot per foot
of depth may be used. A coefficient of friction of 0. 25 is
recommended. The soils passive pressure as well as the bearing
value may be increased by 1/3 for wind and seismic loading.
SETTLEMENT
Settlement of compacted fill soils is normal and should be
anticipated. Based on the consolidation test results, a total
settlement ·up to 0. 7 5 inches acr.oss the structural span and a
corresponding differential settlement up to 0.50 inches need to be
considered in the structural design.
UTILITY TRENCH EXCAVATIONS
Excavations for on-site utility trenches may be made vertically
for shallow depths and must be either shored or sloped at lH: lV
for depths greater than 4 feet. Utilities should be bedded and
backfilled with clean sand or approved granular soil to a depth of
at lea-st one foot over the pipe.
This backfill shall be uniformly watered and compacted to a firm
condition for pipe support. The remainder of the backfill shall be
on-site soils or non-expansive imported soils, which shall be
placed in thin lifts, moisture-conditioned and compacted to at
least 90 % relative compaction.
8
LEGAC~VELOPMENT, LLC PROJECT NO. ~ 147Hl (1)
I R
s BORINGN0.1 N E
0 M L
I p 0 A
s L EQUIPMENT: GAS-POWERED AUGER L I T
0 A s I
I C C T V
D L L SAMPLING METHOD: E u E
E A R
p s s C= CHUNK SAMPLE D E C
T A s B= BULK SAMPLE, R 0
H M I y C M
p F U= UNDISTURBED DRIVE 0 p
I L I D N A
N E C E T C
A N E T
F T T s N I
E y I I T 0
E p 0 SOIL DESCRIPTION T N
T E N y % %
0 SC FILL (Qat) -TAN BROWN, MOIST, LOOSE TO MEDIUM DENSE, CLAYEY SAND
I ...... -.. -B 100.l 21.5 88
2 -
3 -" " " " WET, MEDIUM DENSE
4 -
5 ............ -
6 -
7 -
8 -
9 -
10 -
II SC SANTIAGO FORMATION (Tsa) -BLUEISH GRAY, MOIST TO WET, CLAYEY SAND
12 . 100.3 23.6 88
-
13 ........... CL. BROWN, MOIST, SOFT TO MEDIUM STIFF CLAY 13. 0'-13. S'= 8 BLOWS (SPT)
-u 13. S'-14. 0'= 14BLOWS (SPT)
14 . 14. 0'-14. 5'=25 BLOWS (SPT)
-14. S'-15. 0'=13 BLOWS (SPT)
15 15. 0'-15. 5'=13 BLOWS (SPT) 105.7 19.6
-SM TAN, MOIST, DENSE, FINE GRAINED SILTY SAND IS. S'-16. 0'=41 BLOWS (SPT)
16 ------103.7 19.3 -17 BOTTOM OF BORING -18
PLATENO.-2 I D~TE LOGGED: APRIL 12, 2001
LOGGED BY: M. DUNCAN
LEGAcAl:vELOPMENT, LLCPROJECTNO. l1147HJ(JJ
I R
s BORJNGNO. 2 N E
0 M L
I p 0 A
s L EQUIPMENT: GAS-POWERED AUGER
L I T
0 A s I
I C C T V
D L L SAMPLING METHOD: E u E
E A R
p s s C= CHUNK SAMPLE D E C
T A s B= BULK SAMPLE, R 0
H M I y C M
p F U= UNDISTURBED DRIVE 0 p
I L I D N A
N E C E T C
A N E T
F T T s N I
E y I I T 0
E p 0 SOIL DESCRIPTION T N
T E N y % %
0 FILL (Qat)
-TAN BROWN, MOIST TO WET, LOOSE TO MEDIUM DENSE, CLAYEY SAND
1 -
2 -
3 -
4 -
5 -
6 -
7 -
8 -
9 -
10 -
11 -
12 -
13 SM SANTIAGO FORMATION (Tsa)
-........... LIGHT TAN, MOIST, DENSE, FINE GRAINED SILTY SAND
14 -B -..........
15 -BOTTOM OF BORING
16.
-
17 -
18
PLATE NO. 3 I I DATE LOGGED: APRIL 12, 2001
LOGGEDBY:M.DUNCAN
11
LEGACY.VELOPMENT, LLC PROJECT NO .• 147Hl (1)
I R
s BORING NO. 3 N E
0 M L
I p 0 A
s L EQUIPMENT: GAS-POWERED AUGER L I T
0 A s I
I C C T V
D L L SAMPLING METHOD: E u E
E A R
p s s C= CHUNK SAMPLE D E C
T A s B= BULK SAMPLE, R 0
H M I y C M
p F U= UNDISTURBED DRIVE 0 p
I L I D N A
N E C -E T C
A N E T
F T T s N I
E y I I T 0
E p 0 SOIL DESCRIPTION T N
T E N y % %
I,
FILL (Qaf)
0 SC TAN BROWN, MOIST, LOOSE TO MEDIUM DENSE, CLAYEY SAND ----
5 ----.......... 9. 0'-9. 5'=8BLOWS(SPT)
IO -U 9. 5'-IO. 0'= 13 BLOWS (SPT)
-.......... IO. 0'-IO. 5'=40BLOWS (SPT) 107.0 20.7 94
---
15 SANTIAGO FORMATION (Tsa) -CL · DARK GRAYISH BROWN, MOIST, MEDIUM STIFF CLAY ---
20 ---SC-TAN MOIST, MOIST, DENSE, CLAYEY SAND -SM
25 . SM TAN, MOIST, DENSE, FINE GRAINE:D SILTY SAND -BOTTOM -OF BORING . .
30
PLATENO.4 · . I DATE LOGGED: APRIL 12, 2001
LOGGED BY:,M. DUNCAN
12
LEGAC~VELOPMENT, LLCPROJECTNO. l1147Hl(l)
I R
s BORINGN0.4
N E
0 M L
I p 0 A
s L EQUIPMENT: GAS-POWERED AUGER
L I T
0 A s I
I C C T V
D L L SAMPLING METHOD: E u E
E A R
p s s C= CHUNK SAMPLE D E C
T A s B= BULK SAMPLE, R 0
H M I y C M
p F U= UNDISTURBED DRIVE 0 p
I L I D N A
N E C E T C
A N E T
F T T s N I
E y I I T 0
E p 0 SOIL DESCRIPTION T N
T E N y % %
FILL (Qat)
0 SC TAN BROWN, MOIST, LOOSE TO MEDIUM DENSE, CLAYEY SAND ---
-5 ---SANTIAG,0 FORMATION (Tsa) -CL DARK GRAYISH BROWN, MOIST, MEDIUM STIFF CLAY
10 --BROWN, MOIST, MEDIUM_STIFF SANDY CLAY
--
15 ----
20 --SC-TAN MOIST, MOIST, DENSE, CLAYEY SAND -SM -
25
-SM TAN MOIST, DENSE, FINE GRAINE SILTY SAND ---30 BOTTOM OF BORING ----35
PLATE NO. 5 I DATE LOGGED: APRIL 12, 2001
LOGGED BY: M. DUNCAN
13
LEGAc.AlvELOPMENT, LLCPROJECTNO. '1147Hl(l)
I R
s BORING NO. 5 N E
0 M L
I p 0 A
s L EQUIPMENT: GAS-POWERED AUGER L I T
0 A s I
I C C T V
D L L SAMPLING METHOD: E u E
E A R
p s s C= CHUNK SAMPLE D E C
T A s B= BULK SAMPLE, R 0
H M I y C M
p F U= UNDISTURBED DRIVE 0 p
I L I D N A
N E C E T C
A N E T
F T T s N I
E y I I T 0
E p 0 SOIL DESCRlPTION T N
T E N y % %
0 SC FILL(Qat) -TAN BROWN, MOIST TO WET, LOOSE TO MEDIUM DENSE, CLAYEY SAND
1 -
2 -
3 -
4 -
5 -
6 -
7 -
8 -
9 -
10 -
11 -
12 CL SANTIAGO FORMATION (Tsa) -BLUEISH GRAY, MOIST, SOFT ro MEDIUM STIFF CLA y
13 -
14 SM TAN MOIST, DENSE, FINE GRAINED SILTY SAND -15 -
16 -
17 17 0'-17. 5'=28 BLOWS (SPT)
-17 5'-18. 0'=70 BLOWS (SPT)
18 BOTTOM OF BORING
PLATE NO. 6 I DATE LOGGED: APRIL 12, 2001
LOGGED BY: M. DUNCAN
14
·•
LEGAcYlvELOPMENT, LLC PROJECT NO. ol147HI (JJ
LABORATORY T~ST RESULTS
PAGE L-1
The maximum dry densities and optimllhl moisture contents of the fill materials as determined by
ASTM D1557-91, Procedure A and B which uses 25 blows of a 10 pound slide hammer falling
from a height of 18 inches on each of 5 equal layers in a 4 inch diameter 1/30 cubic foot
compaction cylinder and Procedure C which uses 56 blows of a 10 pound slide hammer falling
from a height of 18 inches on each of 5 equal layers in a 6 inch diameter 1/13 .3 cubic foot
compaction cylinder are presented as follows:
SOIL TYPE/PROCEDURE
BORING NO. 1 @ 1.0' TO 11.0'
1/A TAN BROWN SILTY CLAYEY
SAND
MAXIMUM
DRY DENSITY
LB/CU. FT.
114.0
OPTIMUM
MOISTURE
CONTENT
%DRYWT.
14.8
An expansion test in conformance with UBC 18-2 was performed on representative samples of on-
site soils to determine volumetric change characteristics with change in moisture content. The
recorded expansion of the sample is presented as follows:
INITIAL SATURATED INITIAL DRY
MOISTURE MOISTURE DENSITY EXPANSION
CONTENT% CONTENT% LB.ICU. FT. INDEX
BORING NO. 2@ 1.0' TO 3.5'
13.6 29.7 97.5 61
15
..
, LEGACY D'ELOPMENT, LLC PROJECT NO. 01,47HJ(l)
REFERENCES
1: "1997 Edition, Uniform · Building Code, Volume 2, Structural
Engineering and Design Provisions".
2. "Maps of Known Active Fault Near-Source Zones in California and
Adjacent Portions of. Nevada", Page 0-38, used with the 1997
Edition of the Uniform Building Code, Published by International
Conf·erence of Building Officials.
3. "Geologic Maps of th~ Northwestern Part of San Diego County,
California. Plate No. 2, Geologic Maps of the Encinitas and Rancho
Santa Fe 7.5' Quadrangles", by Siang s. Tan and Michael P.
Kennedy, 1996.
4: "Soii Mechanics in Engineering Practice, 3rd Edition", by K.
Tetzaghi, R. B. Peck and G. Mesri, Dated 1996
5: "Drilled Piers and Caissons II", New York, NY, American Society
of Civil Engineers, 153 p., Baker, C.M., Jr., -Oated 1985.
16 •
. )
LEGACY.VELOPMENT, LLC PROJECT NO. ol147HI(IJ
LABORATORY TEST RESULTS
PAGE L-1
The maximum dry densities and optimum moisture contents of the fill materials as determined by
ASTM D1557-91, Procedure A and B which uses 25 blows of a 10 pound slide hammer falling
from a height of 18 inches on each of 5 equal layers in a 4 inch diameter 1/30 cubic foot
compacfam cylinder and Procedure C which uses 56 blows of a 10 pound slide hammer falling
from a height of 18 inches on each of 5 equal layers in a 6 inch diameter 1/13.3 cubic foot
compaction cylinder are presented as follows:
SOIL TYPE/PROCEDURE
BORING NO. 1 @ 1.0' TO 11.0'
1/A TAN BROWN SILTY CLAYEY
SAND
MAXIMUM
DRY DENSITY
LB/CU. FT.
114.0
OPTIMUM
MOISTURE
CONTENT
%DRY WT.
14.8
An expansion test in conformance with UBC 18-2 was performed on representative samples of on-
site soils to determine volumetric change characteristics with change in moisture content. The
recorded expansion of the sample is presented as follows:
INITIAL SATURATED INITIAL DRY
MOISTURE MOISTURE DENSITY EXPANSION
CONTENT% CONTENT%. _LB.ICU. FT. INDEX
BORING NO. 2@ 1.0' TO 3.5'
13.6 29.7 97.5 61
15
. , •
DIRECT SHEAR SUMMARY
5000
4500
4000
3500
Ci:' f 3000 ....
Cf)
Cf) w ~ 2500 :
Cf) v· 0:: ~ 2000 ./
V
,,,,---
Cf)
,/ 1500 V I I l
1000 /
500
0
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
NORMAL STRESS [PSF] (2 13/32" SAMPLE) I l
2M (0.545) 1L (1.093) 2L (2.185)
ANGLE OF COHESION
INTERNAL INTERCEPT
SAMPLE DESCRIPTION FRICTION (PSF)
H3@9'-10 Undisturbed 22 ° 1000
~ SOUTHERN CALIFORNIA _LEGACY D~VELOPMENT, LLC PROJECT
SOIL & TESTING, INC. BY: OBA/SD IDATE: 04-27-01 ~~ JOB NUMBER: Ol-11li.7Hl Ci) I 'pA,~'R T-2
•
DIRECT SHEAR SUMMARY
5000
4500
4000 I
3500 -LL. f 3000 -U)
U) w 1: 2500 I
U) ! a:: i ~ 2000
i
i
V ti)
/ 1500 Y ~
1000 I .
V l ~v i ' I I l
500 ' V i I
! i I
0 ;
0 500 1000 1500 -2000 2500 3000 3500 4000 4500 5000
NORMAL STRESS [PSF] (213/32" SAMPLE)
2M (0.545) 1L (1.093) 2L (2.185)
ANGLE OF COHESION
INTERNAL INTERCEPT
SAMPLE DESCRIPTION FRICTION (PSF)
H5@ 17' Undisturbed 30 ° 300
~~· SOUTHERN CALIFORNIA LEGACY DEVELOPMENT, LLC PROJECT
\,~~ SOIL & TESTING, INC. BY: OBA/SD !DATE: 04-27-01 -
.. JOB NUMBER: 01-U47Hi°(l) I. 'PA(!H' T-~
• EAST COUNTY SOIL CONSULTATION
AND ENGINEERING, INC.
10925 HARTLEY ROAD, SUITE I
SANTEE, CALIFORNIA 92071
(619) 258-7901
APPENDIX A
RECOMMENDED EARTHWORK SPECIFICATIONS
1. General Description·
The intent of these specifications is to obtain uniformity and adequate strength in filled ground so
that the proposed structures may be safely supported. The procedures include the clearing and
preparation of the land to be filled, processing the fill soils, the spreading, and compaction of the
filled areas to conform with the lines and grades as shown on the approved plans.
The owner shall retain a Civil Engineer qualified in soil mechanics (herein referred to as engineer)
to inspect and test earthwork in accordance with these specifications. The engineer shall advise the
owner and grading contractor immediately if any unsatisfactory conditions are observed to exist
and shall have the authority to reject the compacted filled ground until such time that corrective
measures are taken, necessary to comply with the specifications. It shall be the sole responsibility
of the grading contractor to achieve the specified degree of compaction.
2. Preparing Areas to be 'Filled
(a) All brush, vegetation and any biodegradable refuse shall be removed or otherwise
disposed of so as to leave the ,areas to be filled free of vegetation and debris. Any uncompacted
filled ground or loose compressible natural ground shall be removed unless the report recommends
otherwise. Any buried tanks or other structures shall be removed and the depression backfilled to
the satisfaction of the engineer.
(b) The natural ground which is determined to be satisfactory for the support of the filled
ground shall then be plowed or scarified to a depth of at least 12 inches (12").
( c) After the natural ground has been prepared, it shall then be brought to the proper
moisture content and compacted to not less than 90 percent of maximum dry density in accordance
with ASTM D1557-9'1.
( d) Where fills are made ort slopes greater than 20 percent, horizontal benches shall be cut
into the firm natural ground. The initial bench at the toe of the fill shall be at least 15 feet in width
on firm undisturbed natural ground. The width of all succeeding benches shall be at least 6 feet.
~
EAST COUNTY SOIL CONSULTATION
AND ENGINEERING, INC.
10925 HARTLEY ROAD, SUITE I
SANTEE, CALIFORNIA 92071
(619) 258-7901
APPENDIXC
RECOMMENDED PROCEDURES FOR SLAB FOUNDATIONS
BASED ON EXPANSION INDEX
For soils that are expansive with respect to change in volume with change in moisture content,
there is no economical way to absolutely prevent movement if there is a change in moisture
content. Therefore, insofar as it is feasible, stable soil moisture content should be established and
maintained throughout the life of the structures. Since it is usually not practical to maintain a
completely stable soil moisture content, in order to minimize the undesirable effects of the
expansive soils ort the structures if these soils are placed or allowed to remain within the upper
three feet below finish grade, it is recommended that the following special precautions be exercised
in desigri and construction of slabs and foundations.
a. Design of foundations and slabs on expansive soils are presented in Table 1 based on expansion
indices and there may be more stringent structural design or agency requirements. As an alternative
to conventionally reinforced concrete foundations, post-tensioned structural slab systems, designed
by a structural engineer, may be utilized.
b. Footing depth should be measured below lowest exterior finish grade.
c. A reinforced concrete grade beam should be constructed across garage entrances, with similar
depth and reinforcement as adjacent perimeter footings for all soils with expansion potential greater
than "very low".
d. For soil with a potential expansion greater than "low", interior isolated spread footings are not
recommended.
e. Where pre-saturation is recommended beneath interior slabs, the recommended moisture should
penetrate to one foot below the depth of the perimeter footings. Pre-saturation should be completed
at least 24 hours prior to concrete placement.
f. For soils with an expansive index greater than "low" slab reinforcement should be structurally
tied to the footings.