HomeMy WebLinkAboutCDP 00-65; Clements Residence; Preliminary Investigation - 5021 Tierra Del Sol; 2001-03-07Efifjificcriiiij, Inc.
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CLIENT: SOTO
PROJECT: SOT 201 A
DATE: 7 MAR. 2001
MR. WILLIAM CLEMENTS
C/O S & S GENERAL CONTRACTOR
1611-AS. Melrose Drive
Vista, CA. 92083
Attention: Mr. Robert Soto
Subject: Preliminary Geotechnical Soil Investigation for the Proposed Residential
Construction for the Lot located at 5021 Tierra Del Sol, Carlsbad, CA.
(APN: 210-020-13)
Gentlemen:
Pursuant to your request, we have completed our Preliminary Soils
Investigation for the subject site. The purpose of the Investigation was to determine
the general engineering characteristics of the soils on and underlying the site and to
provide specific recommendations for the design parameters for foundations and
retaining structures, slab-on-grade floors and site earthwork.
The proposed development consists of the construction of a second story
addition to an existing single story residential structure.
SITE CONDITIONS
The subject site consists of a rectangular shaped lot located approximately
0.5 mile west of the 1-5 Freeway on the westerly side of Tierra Del Sol Street in the
City of Carlsbad. The property is bounded on the east by Tierra Del Sol Street, on
the north and south by existing single family residences, on the west by the Pacific
Ocean. The site topography consists of a level pad on the easterly side of the lot
with an existing single structure. On the westerly portion of the lot there is an
existing terraced slope at an approximate inclination of 1.5 : 1 horizontal to vertical.
At the time of this investigation, the slope was covered with ice plant and some low
lying shrubs. Along the toe of the westerly facing slope as well as along the toe of
the adjacent slopes extending to the north and south of the subject site is an existing
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erosion control device consisting of large boulders stacked at approximately 30 feet
wide by 10 feet high. The purpose of this jetty is for the protection of the westerly
facing slopes on this lot and adjacent properties against erosion caused by ocean
wave action.
FIELD AND LABORATORY TESTING
On 15 February 2001, a Field Investigation was performed at the subject site.
This investigation consisted of the excavation of two test pits dug with a hand drill
auger. Locations of these test holes are shown on the Plot Plan, Enclosure (1) and
the detailed Logs of these Test Pits are presented on Enclosure (2).
As the test pits were advanced, the soils were visually classified by the Field
Engineer. Undisturbed and bulk samples, as well as in-place density tests, were
obtained at various depths representative of the different soils horizons. All
samples were returned to our laboratory for detailed testing.
Results of the in-place compaction tests, the Maximum Dry Density Test
values for the various soils sampled and the Expansion Potential Test results are
presented on Enclosure (3). These materials were also tested for Shearing Strength,
Enclosure (4).
Shear tests were made with a direct shear machine of the strain control type
in which the rate of strain is 0.05 inches perminute. The machine is so designed
that tests may be performed ensuring a minimum of disturbance from the field
conditions. Saturated, remolded specimens were subjected to shear under various
normal loads. Expansion tests were performed on typical specimens of natural
soils. These tests were performed in accordance with the procedures outlined in the
Uniform Building Code.
SOIL CONDITIONS
As indicated by our Test Pit Logs, Enclosure (2), the westerly side of the
house pad is underlain with approximately 4 feet of fill materials consisting of dry
to damp, loose to dense, brown silty sands. Underlying the fill materials and
exposed on the westerly slope face are Terrace Deposit materials consisting of
damp, moderately well cemented, massively bedded, silty fine to medium sands.
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GEOLOGIC HAZARDS
According to published information, there are no known active or potentially
active faults on or in the immediate vicinity of the subject site. Therefore, the
potential for ground rupture at this site is considered low. There are, however,
several faults located within a close proximity to this site that the movement
associated with them could cause significant ground motion. The following table
presents the distance of major faults from the site, the assumed maximum credible
earthquake magnitudes and estimated peak accelerations anticipated at the site. The
probability of such an earthquake occurring during the lifetime of this project is
considered low. The severity of ground motion is not anticipated to be any greater
at this site than in other areas of San Diego County.
SEISMICITY OF MAJOR FAULTS
MAXIMUM CREDIBLE ESTIMATED
FAULT DISTANCE MAGNITUDE(RICHTER) ACCELERATION(g)
Rose Canyon 4 mi. 7.0 0.25
Elsinore 29 mi. 7.5 0.35
SanJacinto 52 mi. 7.8 0.17
San Andreas 76 mi. 8.3 0.12
The following information is presented relative to the subject site and
Seismic Zone 4 per the U.B.C.:
SEISMIC PROFILE UBC TABLE
(z) Seismic zone factor = 0.4 16 A-I
(Na) Near-source factor = 1.0 16A-S
(A) Seismic source type = A 16A-U
(Sd) Soil profile type = Sd 16A-J
(Ca) Seismic coefficient = 0.44 Na 16A-Q
(Cv) Seismic coefficient = 0.64 Nv 16A-R
(Nv) Near-source factor =1.2 16 A-T
3
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LIQUEFACTION POTENTIAL
Liquefaction analysis of the soils underlying the site was based on the
consideration of various factors which include the water level, soil type gradation,
relative density, intensity of ground shaking and duration of shaking. Liquefaction
potential has been found to be the greatest where the ground water level is shallow
and loose fine sands occur within a depth of 50 feet or less. These conditions are
not present within the site area and, therefore, the potential for generalized
liquefaction in the event of a strong to moderate earthquake on nearby faults is
considered to be low.
STABILITY
The relatively dense nature of the slopes within the site and the nature of the
material underlying the site generally preclude the occurrence of major landslide
conditions. The area surrounding the site is not known to be within an area of
ground subsidence. The potential for deep seated slope failure at the subject site is
considered low.
The site surface materials consist of silty sands that are relatively dense in
their dry state. These materials are susceptible to erosion. Drainage control is
essential to maintain the stability of any planned slopes or slope areas.
FLOODING
Flooding is not expected to present a hazard to the existing or proposed
development, assuming that structures are constructed above the design historical
flood elevations.
TSUNAMIS
Tsunamis are large sea waves generated by a submarine earthquake or
volcanic eruption. The highest waves historically to affect the San Diego coastal
area has been slightly in excess of 6 feet. There is a possibility that the site could be
subject to tsunami related hazards in an offshore seismic event.
4
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CONCLUSIONS AND RECOMMENDATIONS
Based on field data and our laboratory tests results, the following
Conclusions and Recommendations are presented and are to be utilized in
conjunction with the Building Plans.
Based on the present site conditions, it is concluded that the long term
recession of the westerly slope has been significantly reduced by the installation of
the sea-wall jetty. It is further concluded that if the sea-wall jetty is properly
maintained throughout the life of the project, the residence should have a usable life
span of at least 75 years.
On the basis of our investigation, development of the site as proposed is
considered feasible from a soils engineering standpoint provided that the
recommendations stated herein are incorporated in the design of foundation systems
and are implemented in the field.
The main consideration in developing the subject site is the presence of loose
to dense fill materials subject to possible creep. The thickness of these materials is
approximately 2 to 4 feet below the existing surface. These materials are
considered unsuitable in their present condition for the support of the proposed
second story addition to the existing structure. In order to help mitigate this
potentially adverse condition we recommend that the proposed foundation system
shall be embedded into the underlying terrace deposit soils.
Foundations shall be sized and constructed in accordance with the Structural
Engineer's design, based on the earth pressures and the allowable bearing values
listed below, along with the expected live and dead loads, and the projected wind
and seismic loads.
All structural fill shall be compacted to at least 90% of the maximum dry
density at near optimum moisture content as determined in accordance with ASTM
Test Procedure D 1557-91 or equivalent.
Site drainage should be dispersed by non-erodible devices in a manner to
preclude concentrated runoff over graded and natural areas in accordance with the
City of Carlsbad requirements.
5
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FOUNDATIONS
For foundation design purposes, the following earth pressures were
calculated based on our Shear Test Results (Enclosure 4) and based on a foundation
depth and width of 12 inches:
Shear Test: Cohesion =180 psf; Angle of Friction = 35° .
Allowable Bearing Value = 2050 psf
Equivalent Fluid Pressure = 35 psf
Passive Lateral Resistance = 475 psf
Active Pressure = 35 psf
Coefficient of Friction = 0.35
Expansion Index = 0 (NON EXPANSIVE)
These values are for dead plus live loads and may be increased by one-third
(1/3) for seismic and wind loads where allowed by code. These design bearing
values are in accordance with the Uniform Building Code and were calculated
based on Terzaghis1 Formula.
It is recommended that the continuous perimeter foundations and concrete
slabs for a light weight wood-framed structure shall be reinforced in accordance
with the following minimum designs:
a. Foundation dimensions: it is recommended that the continuous perimeter
foundations for support of the proposed two story structure shall extend to a
minimum depth of 24 inches and a minimum width of 18 inches into the firm native
terrace deposit soils. Due to the thickness of the upper fill soils, it anticipated that
the depth of proposed footings may be 6 foot below the existing surface. Footings
placed adjacent to the existing house foundations shall be doweled with No. 4 bars
at 12 inches on center with an minimum embedment of 6 inches into both footings.
b. All perimeter foundations shall be reinforced with at least four No.4 steel
bars horizontally, two bars shall be placed 3 inches from the top of the foundation
and the other bars shall be placed 3 inches from the bottom. Interim horizontal steel
bars, ie: two No. 4 steel rebars, shall be placed at 12 inches on center vertically in
the deepened foundations.
6
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c. All interior concrete slabs shall be a minimum of four inches in thickness
and reinforced with a minimum of No. 3 rebar at 24 inches on center both ways
placed in the center of the slab. The slab steel reinforcement shall be bent
downward into the perimeter footings and connected to the foundation steel at 24
inches on center. In order to minimize vapor transmission, an impermeable
membrane (ie: 10 mil visqueen) shall be placed over 2 inches of clean, poorly
graded, coarse sand, decomposed granite, or crushed rock. The membrane shall be
covered with 2 inches of sand to protect it during construction and the sand should
be lightly moistened just prior to placing concrete. All concrete used on this project
shall have a minimum compressive strength of 2500 psi unless otherwise stated on
the Building Plans.
If imported soil materials are used during grading to bring the building pad to
the design elevations, or if variations of soils or building locations are encountered,
foundation and slab designs shall be reevaluated by our firm upon the completion of
foundation excavations.
Footings located on or adjacent to the top of slopes shall be extended to a
sufficient depth to provide a minimum horizontal distance of 7 feet between the
bottom edge of the footing and the face of the slope.
These foundation recommendations are minimum design requirements for the
soils encountered during this investigation; however, actual foundations shall be
designed by the Structural Engineer for the expected live and dead loads, and for
wind and seismic loads.
Findings of this Report are valid as of this date; however, changes in
conditions of a property can occur with passage of time, whether they be due to
natural process or works of man on this or adjacent properties. In addition, changes
in applicable or appropriate standards occur whether they result from legislation or
broadening of knowledge. Accordingly, 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 one year.
In the event that any changes in the nature, design, or location of buildings
are planned, the conclusions and recommendations contained in this Report shall
not be considered valid unless the changes are reviewed and the conclusions of this
Report are modified or verified in writing.
7
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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 called to the attention of the project Architect and Engineer
and are incorporated into the plans. Further, the necessary steps shall be taken to
ensure that the contractor and subcontractors carry out such recommendations in the
field.
It is recommended that the Soil Engineer be provided the opportunity for a
general review of the final design plans and specifications for this project in order
that the recommendations of this report may be properly interpreted and
implemented in the design. It is also recommended that the Soil Engineer be
provided the opportunity to verify the foundation and slab construction in the field
prior to placing concrete. (If the Soil Engineer is not accorded the privilege of
making these reviews, he can assume no responsibility for misinterpretation of his
recommendations) .
The Soil Engineer has prepared this Report for the exclusive use of the client
and authorized agents. This Report has been prepared in accordance with generally
accepted soil and foundation engineering practices. No other warranties, either
expressed or implied, are made as to the professional advice provided under the
terms of this agreement, and included in the Report.
B & B Engineering Inc. and Associates appreciate this opportunity to be of
service. Should you have any questions regarding this project, please do not
hesitate to contact us.
Sincerely,
Arthur C. Beard RCE RGE
Chief Engineer
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APPROXIMATE LOCATION OF FIELD EXPLORATORY TEST PIT
PLOT PLAN
OWNER ;WILLIAM
LOCAT I ON ; 5O 2 1 PEL
PROJECT; 50T 2O)A DATE:
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ENCLOSURE (1)
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20t A
LOG OF TEST PITS
EXCAVATED.
PIT DIMENSIONS IN FEET W
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SHEARING STRENGTH TEST