HomeMy WebLinkAbout3417; LA COSTA DOWNS; PRELIMINARY GEOTECHNICAL INVESTIGATION; 1993-08-03CARDIFF GEOTECHNICAL
CONSULTING ENGINEERS AND GEOLOGISTS
August 3, 1993
Martell B. Montgomery
La Costa Engineering
1967 North Hwy 101 Suite B
Encinitas, CA .92024
Subject: PRELIMINARY GEOTECHNICAL INVESTIGATION
Proposed Street Development
La Costa Downs
SP-201
Carlsbad, California
Dear Mr. Montgomery:
In response to your request, we have performed a preliminary
geotechnical investigation at the subject site for the propàsed
street development.
The findings of the investigation, laboratory test results and
recommendations for grading and pavement sections are presented
in this report.
From a geotechnical point of view, it is our opinion that the
site is suitable for the proposed development, provided the
recommendations in this report are implemented during the design
and construction phases.
If you have any questions, please do not hesitate to contact us
at 753-3697.
This opportunity to be of service is appreciated.
Respectfully submitted,
CARDIFF GEOTECHNICAL
AhlZei~
Mark Burwell
Geologist
Reviewed by:
Richard Merriam
C.E.G. 850
*
Vithaya S ingha net,P.E.
Geotechnical Engineer
S IV IN
782 M
Cr.P. 1231-93 io
CALIF OF
135 LIVERPOOL D E • SUITE A • CARDIFF
~t~'~eof
4
(6 1;9) 753-3697 • FAX (619) 753-4158
PRELIMINARY GEOTECHNICAL INVESTIGATION
Proposed Street Development
La Costa Downs
SP-201
Carlsbad, California
Prepared For:
Mr. Martell Montgomery
1967 North Hwy. 101 Suite B
Encinitas., California
August.3, 1993 W.O. 1/P-108073
Prepared By:
CARDIFF GEOTECHNICAL
135 Liverpool Drive
Suite A
Cardiff, California 92007
TABLE OF CONTENTS
INTRODUCTION . . . . . . . . . . . . . . . . . . . .•. . . . . . . . . . . . . . . . . . . . . . . . . . . I
SITE CONDITIONS . .... ...... •... •.......... •.. Is...... .•.. I.. ••I
PROPOSED DEVELOPMENT ........................................ 1
SITE INVESTIGATION ................................. 1l••Sl ... .2
LABORATORY TESTING ..1.... . . . . . . .. • .........• • • • I.e...... S I .3
GEOTEcI-INICAL CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .4
PAVEMENT DESIGN. . . . . . . . . •. . •. .............
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.
..6
CONCLUSIONS AND RECOMMENDATIONS ...........
.
................... 7
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
GRADING ..................................... ... ...7
ADDI TIONAL TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
OBSERVATION AND DENSITY TESTING. .......... ........8
DRAINAGE. ............. . II...... I.e...... ..8
ADDITIONAL GEOTECHNICAL STUDIES. ..... .... ..... ....9
LIMITATIONS... ......... ......... ........ .9.
APPENDICES
APPENDIXA ............................ LABORATORY TEST RESULTS
VICINITY MAP
TABLE S-I
PLATE S-I
TRENCH LOGS
GRAD I NG PLAN
August 3, 1993
W.O. 1/P-108073
Page 1
INTRODUCTION
This report presents the results of our preliminary geotechnical
investigation on the subject property. The purpose of this study
is to evaluate the nature and characteristics of the earth
materials underlying the site and their influence on the
construction of the proposed streets.
SITE CONDITIONS
The subject property is located south of Palomar Airport Road and
just east of Carlsbad Boulevard, in the city of Carlsbad. The
site includes approximately 5.0 acres of very gently sloping
terrain which descends to the east at a grade of about 5.0
percent. From the eastern property line, the slope continues to
descend gently to the top of a 12+ foot high, 1:1 slope which
facilitates the Atchison Topeka and Santa Fe Railroad line. The
western extent of the site is bounded by Carlsbad Boulevard. A
mobile home park bounds the property on the south. Relief on the
site is approximately 17 vertical feet.
The property has recently been plowed and only sparse pockets of
brush were observed. Drainage is generally by sheet flow to the
east, however, considerable infiltration occurs prior to runoff.
PROPOSED DEVELOPMENT
Grading plans for development of the proposed roads were prepared
by La Costa Engineering. The project includes the construction
August 3, 1993
W.O. #P-108073
Page 2
of two, 600 to 650 foot long, parallel roads (Franciscan and
Anacapa) which terminate along the southern property line. A 2
8
0
foot section of road (Descanso Boulevard) will connect t
h
e
I proposed streets along the northern end of the site. The
I
proposed U-shaped road development will include approxima
t
e
l
y
1527 total lateral feet of paved surface. The proposed western
I road (Anacapa) is part of Ponto Road which is presently
p
a
v
e
d
.
This section of asphaltic concrete will be removed. Minima
l
I grading is anticipated for Street development. Most of the
c
u
t
s
l
and fills will be approximately 2.0 feet. A maximum 3.0 fe
e
t
o
f
fill will be placed along the terminus of Franciscan Road.
SITE INVESTIGATION
Five test trenches were excavated •on the site with a tractor-
mounted backhoe to a maximum depth of 6.0 feet. However, f
i
v
e
additional shallow trenches were excavated in the northeastern
I
portion of the site, in order to isolate a clay lens encou
n
t
e
r
e
d
in Trench No. 3. Earth materials encountered were visually
I classified and logged by our field geologist.. Undisturbed,
representative samples of the earth materials were obtai
n
e
d
a
t
I selected intervals. Samples were obtained by driving a thin
walled steel sampler into the desired strata. The samples are
retained in brass rings of 2.5 inches inside diameter and 1.0
I
inches in height. The central portion of the sample is reta
i
n
e
d
in close fitting, waterproof containers and transported to our
I laboratory for testing and analysis.
August 3, 1993
W.O. 1/P-108073
Page 3
LABORATORY TESTING
I Classification
The field classification was verified through laboratory
I examination, in accordance with the Unified Soil Classification
System. The final classification is shown on the enclosed
I exploratory Logs.
Moi sture/Density
The field moisture content and dry unit weight were determined
for each of the undisturbed soil samples. This information is
useful in providing a gross picture of the soil consistency or
variation among exploratory excavations. The dry unit weight was
determined in pounds per cubic foot. The field moisture content
was determined as a percentage of the dry unit weight. Both are
shown on the enclosed Appendix A.
I
Maximum Dry Density/Optimum Moisture Content
The maximum dry density and optimum moisture content were
I determined for selected samples of earth materials taken from the
site. The laboratory standard tests were in accordance with ASTM
I D-1557-78. The results of the tests are presented in Appendix
HI
I
August 3, 1993
W.O. /fP-108073
Page 4
GEOTECHNICAL CONDI TIONS
The subject property is underlain' by nearly flat-lying, friable
Pleistocene sands mantled by thin soil deposits. At depth, the
Pleistocene terrace deposits are underlain by sedimentary units
which have corrinonly been designated as the Santiago Formation on
published geologic maps. A brief description of the earth
materials is discussed below.
- Soil
u Approximately 12 to 18 inches of soil mantles the subject
property. The soil is composed of brown silty sand with minor
amounts of clay. Due to the recent plowing of the site, the soil
is dry and loose. U
U Terrace Deposits
Late Pleistocene terrace deposits underlie the surficial
materials. These deposits consist of poorly consolidated silty
and fine-grained sands. However, a large clay lens was
encountered in the northeastern portion of the site. The 1.0 to
P 2.0 foot thick lens is composed of silty and sandy clay with
gradational contacts above and below. The contacts grade from
I sandy clay to clayey sand with abundant caliche. The lens
extends laterally for at least 300 feet and was encountered
approximately 2.0 to 3.5 feet below the existing grade.
August 3, 1993
W.O. //P-108073
Page 5
Santiago Formation
Although not encountered in the exploratory trenches, the terrace
deposits are underlain by sedimentary units of the Santiago
Formation. Exposures along the coastal bluff, northwest of the
site, consist of 3.0 to 4.0 foot thick beds of massive sandstone
with thin interbeds of clayey siltstone. The sedimentary units
of the Santiago Formation are nearly flat-lying with dips ranging
up to 4 degrees to the northwest.
Expansive Soils
The majority of the terrace deposits are composed of granular
deposits which have a potential expansion in the low range.
However, the silty clay deposits encountered in the clay lens
have a potential expansion in the high range.
Groundwater
No evidence of perched groundwater was observed in the terrace
deposits on the subject property. This sedimentary unit is
relatively pervious and infiltrated water typically percolates
down to the relatively impervious Santiago Formation.
Se 1 smi city
Based on a review of pertinent geological maps, no active faults
- have been recognized on the subject property. The nearest active
fault is the Rose Canyon Fault located about three miles west of
U...
I .
August 3, 1993
I . W.O. //P-I08073
Page 6
I the site. Other active faults which could affect the site are
listed on the enclosed Table S-I.
I Although the likelihood of ground rupture on the site is remote,
I it is almost a certainty the property will be exposed to ground
[notion resulting from the release of energy along the numerous
I
known and unknown faults in Southern California. Table S-I
indicates seismic parameters for active faults which could affect
I the site. The enclosed Seismic Map (Plate S-I) shows the general
proximity of active faults.
I
PAVEMENT DESIGN
R-value tests were performed on a representative mixture of soil
I and terrace deposits. The results of testing indicate an R-value
I of 70 for on-site granular deposits. Previous studies in the
area indicate R-values range from a minimum of 34 to a maximum of
70 for the Pleistocene sands depending upo.n silt and clay
content. Therefore, the minimum pavement section, as per the
I city of Carlsbad standards, should be utilized.
Recommended Pavement Section
I Franciscan Road, Anacapa Road and Descanso Boulevard (Traffic
Index of 4.5)
I
3.0 inches of asphaltic paving on
6.0 inches of select base (Class 11) on
I 12 inches of recompacted granular native soil
August 3, 1993
W.O. 1/P-108073
Page 7
Subgrade soils should be compacted to the thickness indicated in
the structural section and left in a condition to receive base
materials. Class II base should have a minimum R-.value of 78 and
a minimum sand equivalent of 30. Subgrade soils and base
materials, should be compacted to a minimum of 95 percent of their
laboratory maximum dry density.
CNCLUS IONS AND RECCMMENDAT IONS
General
The soil and weathered terrace deposits are in a loose condition
and compressible within the upper 2.5 feet of the existing grade.
Loose and weathered deposits should be removed and replaced as
properly compacted fill during mass grading. However, select
grading will be necessary where clay lenses are encountered at a
shallow depth. The clay deposits should be removed to a minirnuz'n
depth of 3.0 feet below the proposed rough grade and replaced
with on-site granular deposits.
Grading
Loose soil and weathered terrace deposits should be removed to a
minimum depth of 2.5 feet below existing grade. The granular
earth deposits are generally suitable for reuse, provided they
are cleaned of all vegetation and thoroughly mixed. The exposed
bottom should be scarified to •a minimum depth of 9.0 inches,
moistened as required and compacted to a minimum of 90 percent of
the laboratory maximum dry density. Fill should be placed in 6.0
I
August 3, 1993
W.O. /fP-108073
Page 8
to 8.0 inch lifts, moistened as required and compacted to a
minimum of 90 percent of the laboratory maximum dry density. As
previously indicated, clay deposits should be removed to a
minimum depth of 3.0 feet below the proposed rough grade. The
excavated clayey deposits are not suitable.for reuse. Additional
recommendations will be presented should any septic tanks,
cisterns, seepage pits or other unforeseen geotechnical
conditions be encountered during grading.
I Additional Testing
If the earth materials used as compacted fill differ
significantly from those anticipated in this study, additional R-
value testing and revised pavement sections will be necessary.
I
Observation and Density Testing
Fill should be placed while a representative of this firm is
present to observe and test. Additional recommendations may be
necessary during the grading phase.
I
Dr a in age
I Paved areas should be protected from moisture migrating under the
I pavement from adjacent water sources, such as planted or grass
areas. Pad water should not be allowed to pond.
I
August 3,• 1993
W.O. I/P-108073
Page 9
Additional Geotechnical Studies
This report is limited to the proposed Street development. Prior
to construction of residential lots, additional geotechnical
studies for foundation design and individual site grading may be
necessary.
LIMITATIONS
This report is presented with the provision that it is the
responsibility of the owner or the owner's representative to
bring the information and recommendations given herein to the
attention of the project's architects and/or engineers so that
they may be incorporated into plans.
If conditions encountered during grading appear to differ from
those described in this report, our office should be notified so
that we may consider whether modifications are needed. No
responsibility for construction compliance with design concepts,
specifications or recommendations given in this report is assumed
unless on-site review is performed during the course of
construction.
The subsurface conditions, excavation characteristics and
geologic.structure described herein are based on individual
exploratory excavations made on the subject property. The
subsurface conditions, excavation characteristics and geologic
structure discussed should in no way be construed to reflect any
variations which may occur among the exploratory excavations.
August 3, 1993
W.O. //P-108073
Page 10
Please note that fluctuations in the level of groundwater may
occur due to variations in rainfall, temperature and other
factors not evident at the time measurements were made and
reported herein. Cardiff Geotechnical assumes no responsibility
for variations which may occur across the site.
The conclusions and recorrinendations of this report apply as of
the current date. In time, however, changes can occur on a
p property whether caused by acts of man or nature on this or
adjoining properties. Additionally, changes in professional
standards may be brought about by legislation or the expansion of
knowledge. Consequently, the conclusions and recommendations of
this report may be rendered wholly or partially invalid by events
beyond our control. This report is therefore subject to review
and should not be relied upon after the passage of three years.
The professional judgments presented herein are founded partly
on our assessment of the technicaldata gathered, partly on our
understanding of the proposed construction and partly on our
general experience in the geotechnical field. Our engineering
work and the judgments given meet present professional standards.
However, in no respect do we guarantee the outcome of the
project.
If you have any questions, please do not hesitate to contact our
office at 753-3697.
'a
The opportunity to be of service is greatly appreciated.
APPENDIX "A"
LABORATORY TEST RESULTS
TABLE I
Maximum Dry Density and Optimum Moisture Content
(Laboratory Standard ASTM D-1557-78)
Sample Max. Dry Optimum
Location Density (pcf) Moisture Content
T-2 @ 1 1 -3' 126.2 9.2
TABLE II
Field Dry Density and Moisture Content
Sample Field Dry Field Moisture
Location Density (pcf) Content (%)
T-1 @ 2.25' 99.2 4.0
1-1 @ 3.25' 106.6 5.5
1-i @ 5.5' 08.7 8.0
T-2 @ 4.5' 116.7 8.2
1-3 @ 3.5' 106.6 19.9
T-3 @ 4.0' 108.2 16.7
T-3 @ 6.0' 112.2 7.8
T-4 @ 1.0' 101.0 4.7
T-4 @ 2.5' 109.2 7.6
T-5 @ 1.0' 100.2 4.2
J
j us
SCALE 1:24000 0 IMLL
10 0 1000 2000 3000 4000 5000 (000 7000 FEET
I 5 0 1 KILOMETER
TABLE S-i
SEISMIC PARAMETERS FOR ACTIVE AND POTENTIALLY ACTIVE FAULTS
Max. Max.
Credible Probable Bedrock Design Earth- Earth' Accel- Accel- Fault Distance Quake Quake eration eration
--Magnitude--
Rose Canyon 4 mi. S.W. 7.1 6.2 0.319 0.20g
Coronado Banks 19.mi. S.W. 6.5 6.0 0.15g 0.10g
Elisnore 25 mi. N.E. 7.5 7.3 0.19g 0.12g
San Jacinto 50 mi. N.E. 7.5 7.3 0.19g 0.06g
San Andreas 71.mi. N.E. 8.2 8.0 0.08g 0.05g
The Rose Canyon fault has recently been designated as active (C.D.M.G.)
Design acceleration is commonly considered to be about 65 percent of
the maximum (peak) acceleration for the site within approximately 20
miles of the epicenter.
.84R WN SEISMIC MAP Il '\ • *
•- Total length of fault Zone that breaks 11010€ R
deposits or that has had seismic activity j
Fault segment with surface rupture during a %\
historic earthquake, or with asejic z \k\ 7fl\
. jz.% '\.
Approximate epicentrol area of earthquakes I
.
. that occurred 1769 - 1933 .
1899 C, \
1NGS p
0
Earthquake epicenters since 1933
Ref: AEG Special Publication, Oct-1973 (by Richard J. Procte: AP
1948
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EXPLORATORY TRENCHES LOG
Depth Description
Trench No.1 0-1' SOIL: Sand, silty and .fine-grained,
brown, dry, dense
1 1 -5.5' TERRACE DEPOSITS: Sandstone, fine and
medium-grained slightly silty, reddish
brown, weakly cemented, moderately dense,
slightly moist to 5.01 , moist below
Trench No.2 0-1' SOIL: Sand, silty and fine-grained,
brown, dry, loose
1 1 -4.5' TERRACE DEPOSITS: Sandstone, fine and
medium-grained, slightly silty, reddish
brown, weakly cemented, moist @ 4.0 1 ,
grades to slightly clayey sand @ 4.5'
Trench No.3 0-1.5' SOIL: Sand, silty and fine-grained,
brown, dry, loose, slightly clayey
1.5 1 -2.0' TERRACE DEPOSITS: Sandstone, fine and
medium-grained, reddish brown, moderately
dense, slightly moist
2.0 1 -4.0' Clay lens, pale grey silty clay with
discontinuous striations, soft, very
damp, expansive, upper contact grades
from clayey sand to sandy clay from
2.0'-3.0'
4.0'-5.5' Gradational lower contact: sandy clay
grades to clayey sand with irregular
stringer and pockets of caliche
5.5 1 -6.0' Clay lens underlain by loose, grey
medium-grained sand, moist
Trench 3A 2.3' Depth to clay lens
3B 2.5' Depth to clay lens
3C 3.0' Depth to clay lens
3D 3.5' Depth to clay lens
Trench 3E 0-I' SOIL: Sand, silty and fine-grained,
brown, dry, loose
I 1 -4.0' TERRACE DEPOSITS: Sandstone, fine and
medium-grained, slightly silty, reddish
brown, moderately dense, slightly moist
4.0'-5.5' Sand, slightly clayey, reddish brown,
moist, moderately dense clay lens not
encountered
Trench No.4 0.-I' SOIL: Sand, silty and fine-grained,
brown, dry, loose
1 1 -5.0' TERRACE DEPOSITS: Sandstone, fine and
medium-grained, slightly silty, reddish
brown, slightly moist, moderately dense
5.0 1 -6.5' Sand, medium-grained, grey, slightly
moist, moderately dense, weakly cemented
Trench No.5 0-1.5' SOIL: Sand, silty and fine-grained,
brown, dry, loose, slightly clayey
1.5 1 -5.5' TERRACE DEPOSITS: Sandstone, fine and
medium-grained, slightly silty, reddish
brown, slightly moist, moderately dense
I--
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TERRACE DEPOSITS
Ti TRENCH LOCATION (approx.)