HomeMy WebLinkAbout; Vacant Parcel S/O 5305 Carlsbad Blvd; Geotechnical Evaluation; 2007-02-14Southland Geotechnical Consu/tani
GEOTECHNICAL EVALUATION
OF COASTAL BLUFF PROPERTY
VACANT PARCEL SOUTH OF
5305 CARLSBAD BOULEVARD
CARLSBAD, CALIFORNIA
Project No. 126G21
March 10, 1997
Prepared for:
L.D. RICHARDS CO., BUILDER
1830 Oxford Avenue
Cardiff, California 92007
1238 GREENFIELD DRIVE, SUITE A EL CAJQN, CALIFORNIA 92021»
(619)442-8022 • FAX (619)442-7859
Southland Geotechnical Consultants
March 10, 1997 Project No. 126G21
To: L.D. Richards Co., Builder
1830 Oxford Avenue
Cardiff, California 92007
Attention: Mr. Larry Richards
Subject: Geotechnical Evaluation of Coastal Bluff Property, Vacant Parcel South
of 5305 Carlsbad Boulevard, Carlsbad, California
Introduction
In accordance with your request, Southland Geotechnicai Consultants has performed
a geotechnical evaluation of the subject coastal bluff property. We understand that
a single-family residence is proposed on the property. This report presents a
summary of our field and research studies and our conclusions and recommendations
relative to the proposed development. We understand that soils engineering services
for foundation design for the proposed residence are being performed by others.
Purpose and Scope
This report presents the results of our geotechnical evaluation of the coastal bluff
property located south of 5305 Carlsbad Boulevard in Carlsbad. The purpose of our
study was to evaluate the geotechnical conditions at the coastal bluff property and
provide recommendations relative to the proposed construction. The scope of our
geotechnical evaluation included the following:
Review of aerial photographs, geologic/topographic maps, and geologic
literature pertaining to the site and vicinity. A list of the items reviewed is
presented in Appendix A.
Geologic reconnaissance to observe the existing site conditions including the
coastal bluff and general vicinity.
Preparation of a tape and compass profile of the bluff face.
Geotechnical analysis of the data obtained including a computer-generated
slope stability analysis of the coastal bluff.
Preparation of this report summarizing the results of our geotechnical
evaluation of the coastal bluff property.
• 1238 GREENFIELD DRIVE, SUITE A EL CAJQN, CALIFORNIA 92021 •
(619)442-8022 • FAX (619)442-7859
Project No. 126G21
Site Description
The subject coastal bluff property is known as San Diego County Assessor's Parcel
Number 210-120-31. The roughly rectangular property is located south of the
existing residential development located at 5305 Carlsbad Boulevard in the City of
Carlsbad (see Figure 1). The parcel to the south of the subject lot is currently
undeveloped. The eastern property line at the site is located along the westerly side
of Carlsbad Boulevard (formerly Highway 101) and is approximately 60 feet long. The
relatively level bluff-top area of the property extends, from Carlsbad Boulevard to the
top of the coastal bluff, approximately 230 feet along the northerly property line and
approximately 200 feet along the southerly property line. An approximately 40-foot
high coastal bluff with an overall gradient of approximately 45 degrees is located in
the western portion of the property (see Photos 1 and 2). The approximate elevation
of the bluff edge is about 40 feet above sea level based on the City of Carlsbad 1991
orthophoto map (Appendix A).
In general, the bluff-top area at the site slopes gently towards the west and is mostly
vegetated with iceptant, weeds and scattered brush. On February 12, 1997, SGC
representatives made approximate measurements of the western portion of the bluff-
top area at the site. The resultant site plan (with the approximate location of the bluff
edge) is included as Figure 2. Please note that the bluff edge on the site is somewhat
obscured by vegetative growth and rodent burrowing activities (see Photos 3 and 4).
We emphasize that our measurements are approximate. Figure 2 is not a surveyed
map.
Bluff Description
During our site visit on February 12, 1997, a tape and compass profile of the coastal
bluff on the property was prepared. The results of our approximate measurements
are presented on Figure 3 (Coastal Bluff Profile). Following is a summary of the onsite
bluff conditions.
The approximately 40-foot high coastal bluff slopes at an overall gradient of
approximately 45 degrees (from the base of the seacliff to the upper bluff edge).
There is an approximately 10-foot high, irregular but overall, near-vertical seacliff at
the base of the coastal bluff (see Photos 1 and 2). This seacliff is not vegetated.
Portions of the seacliff are slightly undercut apparently by wave action. Indications
of minor sea cave development in the seacliff were observed at the site (see
Photos 1, 2 and 5). A relatively level "bench" area, approximately 5 to 15 feet wide,
has developed at the contact between the more resistant Santiago Formation
sandstone that comprises the seacliff and the overlying, less resistant terrace deposits
that comprise the upper portion of the bluff (see Photos 1 and 2). The upper
approximately 30 vertical feet of the coastal bluff generally is sparsely vegetated with
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iceplant and weeds. However, the uppermost portion of the bluff and the bluff edge
are generally moderately to well vegetated with iceplant. Gunite covers the bluff face
on the properties to the north and extends approximately 15 feet onto the subject
coastal bluff (see Photos 1, 2 and 6).
Proposed Development
Project plans have not yet been finalized. However, based on our conversations with
you, it is our understanding that a one- to two-story residence is proposed at the site.
We understand that the residence will be set back a minimum of 25 feet from the
bluff edge. We also understand that the residence will consist of typical, relatively
light, residential construction.
Geologic Units
Based on our review of a geologic map (Appendix A, Reference 13) and our onsite
observations, the property appears to be underlain by Eocene-aged Santiago
Formation sandstone overlain by Quaternary-aged terrace deposits. Surficial deposits
consisting of beach deposits along the toe of the seacliff were observed during our
site visit and fill soils were observed on the bluff face and bluff-top area. The
approximate limits of these units, as observed in our onsite studies, are shown on
Figure 3 and are described below:
Santiago Formation - The Eocene-aged Santiago Formation is exposed in the
approximately 10-foot high, irregular but near-vertical seacliff located just
easterly of the beach in the western portion of the site. The Santiago
Formation sandstone generally consists of a light gray-brown, well-cemented,
silty, fine-grained sandstone. The Santiago Formation is finer grained near its
contact with the overlying terrace deposits. Localized concretions and cross-
bedding were observed in the seacliff face.
Terrace Deposits- Quaternary-aged terrace deposits unconformably overlie the
Santiago Formation and comprise the majority of the bluff face. The terrace
deposits consist of orange-brown to light brown, dense but friable, slightly silty
fine- to medium-grained sand. Near the base of the terrace deposits, talus (or
slopewash) derived from the terrace deposits has accumulated by the
downslope actions of surface waters and gravity.
Beach Deposits - A variable thickness of unconsolidated beach deposits occur
on the beach at the base of the seacliff. During our site visits, the beach
deposits consisted of sand. This material is subject to addition and removal in
response to storm waves and currents.
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Fill Soils - Fill soils exist locally on the bluff face and bluff-top area (not shown
on Figure 3). It appears that minor amounts of fill soils may have been used
to infill two relatively small gullies at the site (see Photos 1 and 2). In addition,
fill soils were apparently pushed over the bluff edge onto the bluff face. The
fill soils generally consist of locally-derived terrace deposit materials and
chunks of concrete and asphalt.
Geologic Structure
The Santiago Formation is well exposed in the seacliff at the property and to the
south. The Santiago Formation at and near the subject property is nearly flat-lying.
Bedding in the Quaternary terrace deposits can be observed as alternating more
resistant and less resistant beds. Where observed on site and in the general site
vicinity, the terrace deposits appear to be horizontally bedded with localized cross
bedding.
Fractures were observed in the sea cliff and a dominant near-vertical joint orientation
of N50W was measured. However, no major out-of-slope bedding components were
observed that would be adverse to slope stability. Indications of deep-seated
landslide features were not observed during our research studies or site visits.
Review of Geotechnical Hazards/Constraint Map
Our review of Geotechnical Hazards/Constraint Map page 14 of the City of Carlsbad
Geotechnical Hazards Analysis and Mapping Study (Appendix A) indicates that the
site is located in Hazard Categories 41 and 53. Category 41 pertains to "coastal
stability: moderately stable: high steep bluffs, unfavorable structure, moderate to
rapid erosion." Category 53 pertains to areas with "other terrain conditions:
generally stable: relatively level mesa areas underlain by terrace deposits, sandstone
or granitic/metavolcanic bedrock." Please note that the Geotechnical Hazards
Analysis and Mapping Study is primarily intended for planning purposes and should
not be construed as definitive data for a specific site.
Faulting
Our review of geologic literature (Appendix A) pertaining to the general site area
indicates that there are no known "active" faults on or in the immediate vicinity of the
site. An "active" fault is defined by the California Division of Mines and Geology as
one which has "had surface displacement within Holocene time (about the last
11,000 years)" (Appendix A, Reference 4). Indications of active faulting were not
observed in the subject coastal bluff. The nearest known active faults are the Rose
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Canyon fault located offshore approximately 4 miles west of the site, the Coronado
Bank fault located offshore approximately 19.5 miles west, and the Elsinore fault
located approximately 25 miles northeast of the site. The San Andreas fault is
located approximately 62 miles northeast of the site.
Our review of the City of Carlsbad Geotechnical Hazards Analysis and Mapping Study
(Appendix A) indicates that a relatively short, northerly-trending fault trace has been
mapped on and near the site. It appears to coincide with the gully located off site to
the south of the subject property (see Figure 1}. We did not observe direct, definitive
evidence for the presence of this fault during our site visits, however, it may be
obscured by fill soils present in the offsite gully. The City of Carlsbad study states
that "all faults that have been mapped within the City limits based on current
knowledge are all considered inactive". Based on its relatively short length and
northerly trend, it is our opinion that this mapped fault does not present a seismic-
source hazard to the subject project.
Tsunami and Storm Waves
Tsunami are sea waves generated by submarine earthquakes, landslides or volcanic
action. Submarine earthquakes are common along the edge of the Pacific Ocean and
coastal areas are subject to potential inundation by tsunami. Most of the 19 tsunami
recorded on the San Diego tidal gauge (between 1854 to 1872 and 1906 to 1977)
have only been a few tenths of a meter in height (Appendix A, Reference 1). The
largest San Diego area tidal gauge excursion (1 meter) was associated with the
tsunami of May 22, 1960 and was recorded at La Jolla (Scripps Pier) (Appendix A,
Reference 12). The tsunami was generated by a Richter magnitude 8.5 earthquake
in Chile. For comparison, the diurnal range of tides at San Diego Bay is 1.7 meters.
The possibility of a destructive tsunami along the San Diego coastline is considered
low (Appendix A, Reference 5). However, tsunami or storm waves (associated with
winter storms), in conjunction with high tides, may erode the coastal bluff face
(especially the friable terrace deposits) but generally are not anticipated to have the
potential for inundation of the bluff-top building site.
Groundwater and Surface Water
During our site visits, groundwater seepage was observed in the coastal bluff near the
southern edge of the gunite coating on the northern portion of the site (see Photo 6).
Based on our experience and observations, our estimation to the depth of
groundwater is that it is at or near sea level and may also be perched locally on the
Santiago Formation at its contact with the overlying terrace deposits. Groundwater
levels can be expected to fluctuate with the tides, seasonal precipitation and
irrigation. Groundwater is not expected to be a constraint to construction of the
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proposed residence. However, our experience indicates that near-surface
groundwater conditions can develop in areas where no such groundwater conditions
previously existed, especially in areas where a substantial increase in surface water
infiltration results from landscape irrigation or unusually heavy precipitation.
The bluff-top surface waters appear to primarily drain towards the west as sheet flow.
As they approach the bluff edge on the site, the surface waters are concentrated into
generally shallow gullies that have been eroded into the bluff edge and discharge
down the bluff face.
Historic Research Summary
We have reviewed the literature, maps and aerial photographs of the site and general
vicinity listed in Appendix A. Following is a limited outline summary of our review
observations:
The oldest map we found on file at the County of San Diego is an 1898 survey
for the Fifth Road District (Appendix A). The bluff along the coastline is
sketched on the map and the railway line is shown.
The oldest photograph we reviewed was one from the 1928-29 aerial
photograph set on file at the County of San Diego. The railroad and coastal
highway (approximately the current Carlsbad Boulevard) are shown on this
photo. A dirt road west of the coastal highway, roughly parallel to the
coastline, and along the bluff top in the general site vicinity is shown. A wider,
cleared spot on this dirt road (a turn-out or viewpoint?) is located in the vicinity
of the subject coastal bluff property. The offsite gully to the south is apparent.
The subdivision roadway (Shore Drive) and some of the subdivision homes to
the north of the subject property are shown on the 1953 aerial photographs.
The single-family residence that currently exists adjacent to and north of the
subject lot is not shown. A dirt road exists along the bluff edge in the site
vicinity. The subject property appears it may have been cleared and used for
agricultural purposes. A relatively small gully perpendicular to the bluff edge
is apparent near the southern boundary of the subject property. The larger
offsite gully (approximately 25 feet to the south of the site) is also apparent on
the photos.
The existing residence to the north of the subject property is shown on the
April 9, 1964 photograph and subsequent photos. On the 1964 photo and
photos from the late 1960's, 1970's and early 1980's and on the County's
1975 orthophoto topographic map, the subject coastal bluff face appears to be
generally moderately vegetated. The bluff face appears generally smooth and
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uniform as it extends from the bluff edge to the westward edge of the near-
vertical seacliff at its base. The currently existing "bench" on the resistant
Santiago Formation is not apparent.
Based on our review of a 1978 photo looking north towards the site
(Appendix A, Reference 11), gunite appears to cover the lower part of the
coastal bluff at the site and on the properties to the north and south of the site.
Our review of the Army Corps of Engineers' report, "Coastal Cliff Sediments,
San Diego Region" (Appendix A, Reference 11), indicates that an episode of
erosion occurred between August 7 and 9, 1983, "as a result of waves from
a southern hemisphere storm." In the 'cove' area, approximately 100 feet
south of the site, the report states that "the cliff retreated 28 to 35 feet" and
"this was more erosion at the site than had occurred during the previous
40-year period." The photos show that, at the subject property, a "bench"
developed on the resistant Santiago Formation as a result of landward retreat
(approximately 1 5 to 20 feet) of the toe of the terrace deposits at the site.
However, even though the toe of the terrace deposits retreated, the upper
portion of the bluff and bluff edge do not appear to have eroded, based on our
review of the photos.
The "bench" on the resistant Santiago Formation is shown on the 1984 and
more recent photos and was observed during our site visits.
On the 1991 orthophoto mapping sheet and 1992 photographs, the bluff-top
area is vegetated generally similarly to what we observed during our recent site
visits. However, the bluff edge and bluff face were less vegetated in the early
1990's than observed during our 1997 site visits.
Coastal Bluff Retreat
The Carlsbad coastline in the vicinity of the subject property consists of a slight
headland to the north of the site and is indented (into a 'cove') to the south of the
subject property (see Figure 1). The site is located on the northern edge of the
indentation in the coast (concave to the ocean). Mechanisms for seacliff retreat at
the site include slow abrasion and undercutting by marine erosion (wave action) of
the hard, erosion-resistant Santiago Formation sandstone bedrock exposed in the
near-vertical seacliff. Storm surf and higher high tides contribute to the natural
process of marine erosion. Other factors affecting the rate of retreat of a near-vertical
seacliff at the toe of a coastal bluff include degree of fracturing, jointing,
consolidation of sediments, steepness of slope, groundwater and surface water
conditions, vegetation or lack of, and intensity of pedestrian and animal traffic.
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In response to the landward retreat of the seacliff, the overlying coastal bluff becomes
undermined and also retreats landward. During storm surf and higher tides, the base
of the terrace deposits at the site are also subject to marine erosion. Other
mechanisms contributing to bluff retreat include failure of overhanging bedrock
projections, shallow failure of oversteepened portions of the bluff-face terrace
deposits, and rilling and ravelling of the terrace deposits. Portions of coastal bluffs
are also exposed to precipitation, wind, pedestrian/animal erosion (including foot
traffic and burrowing rodents), variations in landscape, landscape maintenance, and
other activities by humans.
During our studies, we did not observe indications of deep-seated instability, such as
ancient or active landslides, on the site, and the Santiago Formation sandstone that
comprises the seacliff at the site is not known to be prone to large, deep-seated
failures. The terrace deposits are friable and commonly rill and ravel in oversteepened
slopes, however, they are not known to be prone to large, deep-seated failures.
Coastal Bluff-Edae Retreat Rates
The rate and magnitude of coastal bluff retreat at a specific site are dependent on a
variety of factors, both natural and manmade. Many of these factors are ongoing
processes and historic documentation can be helpful in estimating general bluff-edge
retreat rates. However, there are other factors affecting coastal bluff retreat that
cannot be estimated from historic documentation. Such factors include future human
activities or possible extreme variations in regional weather patterns.
Detrimental changes in factors affecting bluff-edge retreat, such as misdirected
drainage, water line breaks, very heavy storm surf and/or precipitation, could increase
the rate of future erosion. However, favorable changes in the factors affecting bluff-
edge retreat could decrease the rate of future erosion. Some of these include
eliminating detrimental human activities on the bluff, proper maintenance of a bluff-
stabilizing vegetative cover, enhanced site drainage provisions and beach sand
replenishment currently proposed by San Diego County coastal communities.
Research studies along the San Diego coast and historic photograph and map review
are components in providing an estimation of the rate of bluff-edge retreat. We
assume that the historic retreat rate may give an indication of the future retreat rate
at a particular site. However, accurate and clear photographic and map
documentation for measuring retreat is not always available or is of fairly short time
intervals so changes may not be noticeable.
Lee and others (Appendix A, Reference 6) performed research studies of regional
historic seacliff retreat and provide a maximum annual rate of seacliff recession of 0.7
inch. The research studies also estimated a maximum annual bluff-edge retreat rate
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of 0.22 to 0.33 feet per year. Over a 75-year period (assumed to be the economic
lifetime of the new construction), this equates to a conservative estimate of bluff-
edge retreat of a maximum of 16.5 to 24.8 feet. This maximum is based on research
studies of regional historic bluff retreat that includes coastal bluffs with generally
favorable conditions, as well as coastal bluffs that are affected by more adverse
conditions (fracturing, sea caves, groundwater, human activities, etc.). The estimated
values of maximum retreat are very conservative, and the actual rate of bluff retreat
at the subject property is expected to be less considering the site conditions and
historic bluff-edge retreat at the site.
Documentation of a two-day erosion period at and near the site in August 1983
(discussed above) is included in the U.S. Army Corps of Engineers' report, "Coastal
Cliff Sediments, San Diego Region" (Appendix A, Reference 11). This report indicates
that an episode of erosion occurred between August 7 and 9, 1983, "as a result of
waves from a southern hemisphere storm." In the 'cove' area, approximately 100
feet south of the site, the report states that "the cliff retreated 28 to 35 feet" and
"this was more erosion at the site than had occurred during the previous 40-year
period." The photos show that at the subject property, a "bench" developed on the
resistant Santiago Formation as a result of landward retreat (approximately 1 5 to
20 feet) of the toe of the terrace deposits at the site. However, even though the toe
of the terrace deposits retreated landward, the upper portion of the bluff and bluff
edge did not appear to have retreated landward at the site.
Our historic photograph review (Appendix A) indicates that the coastal bluff at the
subject property is generally similar in configuration in the 1929, 1953, and 1964
through early 1983 photos. The location of the onsite bluff edge is generally similar
on the vertical aerial photographs (1929 through 1989) listed in Appendix A and also
on the 1975 and 1991 orthophoto topographic maps. However, in early
August 1983, the base of the onsite terrace deposits eroded inland up to
approximately 15 to 20 feet and resulted in the onsite "bench" on the resistant
Santiago Formation sandstone.
If we assume that there were no definitive points of reference (such as the existing
home to the north) to accurately measure prior to the 1964 aerial photographs
(although the bluff appears to be similar in configuration), the resolution and scale of
the photographs are such that if bluff-edge retreat were in excess of approximately
5 to 6 feet, it would likely be apparent. No apparent retreat of the bluff edge was
seen on the photos, however, we could assume, as a "worst-case" scenario, that the
bluff edge had retreated 6 feet over the 25-year time interval viewed (from 1964 to
1989), and a historic maximum bluff-edge retreat rate of approximately 0.24 feet per
year may then be estimated from the photographs. Over a 75-year period, this
equates to a "worst-case" or maximum of bluff-edge retreat of 18 feet.
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From our site visits and photograph review, we observed, for the recent past, no
indications that the current rate of retreat for the bluff edge is greater than this
estimated "worst-case" historic rate of 0.24 feet per year and it apparently is
significantly less. However, it is very difficult to predict the future and the magnitude
of bluff-edge retreat that may occur in one year, during one storm event or over the
75-year assumed economic lifetime of the new construction. The rate of coastal bluff
retreat over a particular interval of time {day, year, decade, etc.) may vary from very
little to several tenths of a foot. However, severe erosion is generally episodic in
nature and is dependent on the intensity of storms and combined high tides (or man's
detrimental actions). It is probable that several feet of coastal bluff-edge retreat could
occur at one time or over a short period of time. However, it is also likely that there
will be periods in the future when erosion along the coast and bluff edge is rather
insignificant and undetectable. Erosion is a naturally-occurring process that is
affected by human actions. With time, the bluff edge will retreat landward.
If we assume a future retreat rate based on the "worst-case" site-specific historic
aerial photograph evaluation, the maximum amount the bluff edge may retreat
landward over the next 75 years would be approximately 18 feet. If a future retreat
rate based on the regional study of bluff-top retreat rates (Appendix A, Reference 6)
is assumed, the maximum amount the bluff edge may retreat over the next 75 years
would range from 16.5 to 24.8 feet. However, as stated above, this maximum
retreat rate is based on a research study of regional historic bluff-edge retreat which
also included coastal bluffs that are more adversely affected by conditions that
contribute to higher rates of erosion (fracturing, sea caves, groundwater, human
activities, etc.) than those known at the subject property. We may speculate that the
actual maximum value of future bluff-edge retreat at the site over the next 75 years
will range somewhere from 18 (the site-specific, historic "worst-case") to 24.8 feet
(the regional study "worst-case") and that the actual bluff-edge retreat is likely to be
less.
It is our opinion that the residence, proposed to be set back a minimum of 25 feet
from the bluff edge, will not be endangered by coastal bluff retreat over the next
75 years. However, improvements, such as patios, fences, etc., that are within this
setback zone may become endangered (undermined) by bluff-edge retreat during the
next 75 years and may need to be removed from the site.
Sea Cave Influence - Sea cave formation and subsequent collapse are localized
factors in the bluff retreat process. Indications of sea cave development in the
seacliff were observed at the subject property during our site visits. Photos 1
and 2 are views of the subject coastal seacliff/bluff and Photo 5 is a closer
view of a sea cave on site. Figure 1 shows the property, nearby vicinity and
locations of the onsite and nearby known area of sea cave development. Our
approximate measurements made on February 12, 1997, indicate that the
onsite sea cave extends a maximum of approximately 5 feet obliquely into the
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seacliff with a trend of roughly N75W. The sea cave is about 1 foot in height.
The nearest offsite sea cave to the site is located approximately 3 feet
southerly of the southern property boundary (see Photo 2). This sea cave
extends approximately 2 feet into the seacliff with a maximum height of 1.5
feet. Fractures and bedding planes apparently control the development of
these two caves. Due to their relatively small sizes, it is our opinion that if
either (or both) of these sea cave areas enlarged and failed within the next
75 years, their collapse would not impact the proposed residence (which will
be set back a minimum of 25 feet from the bluff edge).
Seismic Shaking Influence - In general, the role seismic shaking plays in bluff
retreat is dependent on bluff conditions at the moment of shaking. Failure of
bedrock projections on seacliffs, failure of marginally stable blocks of bedrock,
collapse of sea caves, and failures of undercut bluffs may be common
occurrences along the San Diego coastline during strong ground shaking. The
Shoreline Erosion Assessment and Atlas of the San Diego Region (Appendix A,
Reference 3} states that the "potential for cliff failure due to earthquake activity
in San Diego is probably small, but since San Diego has not experienced strong
motion in such a long time, the cliffs here may be more susceptible to sliding
than those in areas with shorter quake-return intervals."
Slope Stability Calculations
A computer-generated slope stability analysis was performed on the coastal bluff at
the site. The slope stability was analyzed using 'Janbu's Simplified Method of Slices'
with the PCSTABL 5M computer program. Groundwater was included in our slope
stability analyses. The slope stability calculations are included in Appendix B. The
soil strength parameters used in our analysis are presented below. These values are
based on laboratory test results, back-calculation, our past experience in this area,
and our professional judgement.
Soil Type Unit Weight Friction Angle Cohesion
Terrace Deposits 120.0 pcf 40 degrees 500 psf
Santiago Fm Sandstone 120.0 pcf 35 degrees 200 psf
The results of the analyses (Appendix B) indicate that for the existing configuration,
the calculated factor of safety against deep-seated failure is in excess of 1.5 (the
generally accepted standard for the geotechnical industry). In addition, there are no
indications of large ancient landslides in the site vicinity.
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CONCLUSIONS AND RECOMMENDATIONS
Based on our geotechnical evaluation of the coastal bluff at the site, it is our opinion
that the proposed residence (and the loading from this relatively light bluff-top
construction) will not adversely impact the existing coastal bluff. In addition, if the
residence is set back a minimum of 25 feet from the bluff edge as planned, it is our
opinion that the proposed construction should not be affected by the maximum
estimated coastal bluff retreat during its economic lifetime (assumed to be 75 years).
Slope Stability and Erosion
Our geotechnical evaluation of the present overall static stability on the subject
property indicates that the bluff is grossly stable. In its present state, the slope is
moderately to highly erodible and has a low to moderate potential for future surficial
instability. We provide the following recommendations to help reduce erosion of the
bluff and to reduce potential for future instability of the bluff face.
Irrigation of the landscape areas on the property should be limited to the
minimum amount required to establish vegetation and maintain plant vigor.
The upper portion of the subject coastal bluff and the bluff edge are currently
moderately to well vegetated with iceplant. At this time, it is our opinion that
modifications to the vegetation in these areas should not be considered.
However, if landscape planting and/or plant removal on the westerly bluff-top
area is performed, it should be done without significantly disturbing the bluff-
top soils. The surficial stability of those portions of the bluff that are not well
vegetated may be increased by planting in accordance with the
recommendations of a professional landscape company experienced with
coastal bluffs. Terracing or excavation of the bluff-face soils should be
avoided.
Drainage at the site should be directed such that surface waters discharge into
non-erosive drainage provisions. Runoff at the site should not be directed over
the bluff edge. Eave gutters should be considered for the residence and should
be properly maintained. Pedestrian and animal traffic (and burrowing, etc.) on
the bluff face and bluff edge should be curtailed.
Bluff-Too Setback
As previously stated, we speculate that the maximum value of future bluff-edge
retreat at the site over the next 75 years may range somewhere from 18 to 24.8 feet,
and the actual value of bluff-edge retreat is likely to be less. The proposed residence
will be set back a minimum of 25 feet from the bluff edge. It is our opinion that the
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proposed setback will safeguard the proposed residence from bluff retreat during the
economic lifetime of the residence.
Seismic Considerations
The principal considerations for most structures in southern California are surface
rupturing of fault traces and damage caused by ground shaking or seismically-induced
ground settlement or liquefaction. The possibility of damage due to ground rupture
is considered minimal since no active faults are known to cross the site. It is our
opinion that the potential for liquefaction or seismically-induced ground settlement at
the site due to an earthquake is very low because of the dense nature of the
underlying terrace deposits and Santiago Formation sandstone.
The seismic hazard most likely to impact the site is ground shaking resulting from an
earthquake on one of the major active regional faults. The nearest known active fault
is the Rose Canyon fault located offshore approximately 4 miles west of the site. It
is estimated that a maximum earthquake on this portion of the Rose Canyon fault
(magnitude 6.5) could produce moderate to severe ground shaking at the site.
As previously indicated, in general, the role seismic shaking plays in bluff retreat is
dependent on bluff conditions at the moment of shaking. The seacliff at the subject
property is near-vertical and locally portions are slightly overhanging. It is possible
that some of the bedrock projections may fail as the result of severe ground shaking
at the site. Oversteepened portions of the terrace deposits may undergo shallow
failure and some ravelling of the poorly indurated bluff-face terrace deposits may also
occur during ground shaking, especially on the unvegetated portions of the bluff face.
However, it is our opinion that the potential for deep-seated or severe, catastrophic
failure of the bluff due to expected seismic ground shaking is low at the site.
Other Considerations
The recommendations provided in this report are based on our understanding that a
single-family residence (with its relatively light loading) is planned at the site and will
be set back a minimum of 25 feet from the bluff edge. The site conditions and bluff
edge indicated on Figures 2 and 3 have been compiled from approximate
measurements made during our site visits. They should not be relied on for site
development. If needed, we suggest that a licensed land surveyor be retained to
prepare a site topographic plan that accurately delineates the property boundaries and
bluff edge. In addition, a comprehensive site drainage study may be conducted to
develop a site-specific drainage plan for the proposed development. Please note that
the recommendations contained herein may be revised based on modified and/or
additional information regarding the structure and improvements planned at the site.
13
SGC
Project No. 126G21
A qualified consultant should be retained to review site conditions and assess
potential site impacts following significant erosion events in the future or if major
changes in the bluff configuration are noticed.
Limitations and Uniformity of Conditions
This geotechnical evaluation report addresses the coastal bluff conditions at the
property and is based on our understanding that the proposed development consists
of design and construction of a new single-family residence set back a minimum of
25 feet from the bluff edge. We understand that soils engineering services for design
and construction of this proposed residential development are being performed by
others. In addition, we have not performed an evaluation of the presence of
hazardous materials/contamination at the site.
This report is based on our document/photograph review, surficial observations of the
geologic conditions exposed at the site and vicinity. This report assumes that the
geologic/soils conditions do not deviate appreciably from those observed during our
site visits. The recommendations of this report pertain only to the coastal bluff
property evaluated.
The findings of this report are valid as of this date. Changes in conditions of a
property can, however, occur with the passage of time, whether they be due to
natural processes or the work of man on this or adjacent properties. In addition,
changes in applicable or appropriate standards may occur, from legislation or the
broadening of knowledge in the fields of geotechnical engineering or geology. Hence,
the findings of this report may be invalidated wholly or in part by changes beyond our
control. Therefore, this report should not be relied upon after a period of two years
without a review by us.
If there are questions regarding the information contained herein, we should be
contacted. We will not be responsible for the interpretation by others of the
information herein. Our services consist of professional consultation and no warranty
of any kind whatsoever, express or implied, is made or intended in connection with
the work performed by us.
14
SGC
Project No. 126G21
If you have any questions regarding our report, please call. We appreciate this
opportunity to be of service.
Sincerely,
SOUTHLAND GEOTECHNICAL CONSULTANTS
0 S,
Susan E. Tanges, CEG 1
Managing Principal/Engj^H&^ig Geologist' ,
Attachments:
Project Engineer
r
Figure 1 - Site Location Map
Figure 2 - Site Plan
Figure 3 - Coastal Bluff Profile
Photographs 1 through 6
Appendix A - References
Appendix B - Slope Stability Calculations
Distribution:(3) Addressee
15
SGC
SITE LOCATION MAP
Project No. 126G21
Vacant Parcel South of 5305 Carlsbad Boulevard, Carlsbad
Scale (approximate): 1 inch = 100 feet
Base Map:
City of Carlsbad
Orthophoto Topographic Map 93
dated 1991 FIGURE 1
SGC
X
Property extends
easterly to
Carlsbad Boulevard
,-chain link fence —vJL— x X"
APPROX. NORTH
Scale (approximate):
1 inch = 10 feet
Site plan compiled from
approximate measurements
made by SGC representatives
on 02-12-97
THIS IS NOT A SURVEYED MAP
SITE PLAN
Vacant Parcel South of
5305 Carlsbad Blvd, Carlsbad
Project No. 126G21 FIGURE 2
SGC
Scale (approximate):
1 inch = 10 feet
Approximate location of
25-foot setback line for
new residence
bluff edge
seacliff
BEACH SAND
TERRACE DEPOSITS
- . ' SANTIAGO FORMATION N60E
:'&iz&'"'
Coastal bluff profile compiled
from approximate measurements
made by SGC representatives on 02-12-97
(see FIGURE 2 for profile location)
COASTAL BLUFF PROFILE
Vacant Parcel South of
5305 Carlsbad Blvd. Carlsbad
Project No, 126G21 FIGURE 3
SGC
Project No. 126G21
OFFSITE
SEA CAVE
PHOTO 1 Coastal bluff, view southerly from near northern property boundary 1-31-97
"BENCH"
PHOTO 2 Coastal bluff, view northerly from near southern property boundary 2-12-97
SGC
Project No. 126G21
<-PHOT03 1-31-97
Bluff edge, view northerly
from south of site
PHOTO 4-* 2-12-97
Bluff edge, view northerly from fence
inside southerly property boundary
SGC
Project No. 126G21
PHOTO 5 Onsite sea cave in sea cliff (see Figure 1 for location}2-12-97
PHOTO 6 Onsite gunite and groundwater seep near northerly property boundary 2-12-97
SGC
APPENDIX A
Project No. 126G21
APPENDIX A
REFERENCES
1. Agnew, D.C., 1979, Tsunami history of San Diego, jn Abbott, P.L., and Elliott,
W.J., eds.. Earthquakes and Other Perils: Geological Society of America field
trip guidebook.
2. California Division of Mines and Geology, 1994, Fault activity map of California
and adjacent areas: CDMG Geologic Data Map No. 6.
3. Flick, R.E., ed., 1994, Shoreline erosion assessment and atlas of the San Diego
region: California Department of Boating and Waterways and the San Diego
Association of Governments publication, dated December (two volumes).
4. Hart, E.W., 1994, Fault-rupture hazard zones in California: California Division
of Mines and Geology, Special Publication 42, revised.
5. Lee, L.J., 1977, Potential foundation problems associated with earthquakes in
San Diego, in Abbott, P.L., and Victoria, J.K., eds.. Geologic Hazards in San
Diego, Earthquakes, Landslides, and Floods: San Diego Society of Natural
History John Porter Dexter Memorial Publication.
6. Lee, L., Pinckney, C., and Bemis, C., 1976, Sea bluff erosion: American
Society of Civil Engineers, National Water Resources and Ocean Engineering
Convention Preprint No. 2708.
7. Legg, M.R., Agnew, D.C., and Simons, R.S., 1978, Earthquake history and
seismicity of coastal San Diego County, California, 1800-1976 (unpublished).
8. Southland Geotechnical Consultants, in-house geologic information.
9. Tan, S.S., and Giffen, D.G., 1995, Landslide hazards in the northern part of the
San Diego metropolitan area: California Division of Mines and Geology, Open-
file Report 95-04.
10. U.S. Army Corps of Engineers, 1985, Coast of California Storm and Tidal
Waves Study, Shoreline Movement Data Report, Portuguese Point to Mexican
Border (1852-1982) (CCSTWS 85-10), dated December.
11. U.S. Army Corps of Engineers, 1985, Coast of California Storm and Tidal
Waves Study, Coastal Cliff Sediments, San Diego Region (CCSTWS 87-2),
dated June.
SGC
Project No. 126G21
APPENDIX A
REFERENCES
(continued)
12. Van Dorn, W.G., 1979, Theoretical aspects of tsunamis along the San Diego
coastline, ]n Abbott, P.L., and Elliott, W.J., eds.. Earthquakes and Other Perils:
Geological Society of America field trip guidebook.
13. Weber, F.H., Jr., 1982, Recent slope failures, ancient landslides and related
geology of the north-central coastal area, San Diego County, California:
California Division of Mines and Geology, Open-File Report 82-12.
AERIAL PHOTOGRAPHS
Aerial Fotobank, Book 8 (vertical, not stereoscopic):
Frame 1528, dated March 29, 1965.
Frame 2252, dated August 12, 1965.
Frame 8-4531, dated November 21, 1966.
Aerial Fotobank, Book 8A (vertical, not stereoscopic):
Frame 10,602, dated November 8, 1968.
Frame 12,972, dated July 8, 1969.
Frame 15,073, dated November 2, 1969.
Aerial Fotobank, Book 8C (vertical, not stereoscopic):
Frame 51-356, dated September 27, 1971.
Aerial Fotobank, Book 8D (vertical, not stereoscopic):
Frame 25,039, dated December 16, 1980.
Frame 25,818, dated February 11, 1983.
Aerial Fotobank, Book 8E (vertical, not stereoscopic):
Frame 26,376, dated October 13, 1984.
Aerial Fotobank, 1990's and Carlsbad books:
Frame 0082 (3-7D), dated January 1, 1983.
Frame 1663 (4-8D), dated January 28, 1984.
Frame SD87-8D, dated January 21, 1987.
Frame CV90-5, dated January 18, 1990.
County of San Diego, 1929, Photo 30D1 (vertical, not stereoscopic).
SGC
Project No. 126G21
APPENDIX A
AERIAL PHOTOGRAPHS
(continued)
County of San Diego, 1967, Series GS-VBTA, Flight Line 1, Photos 1-142 and 1-143,
dated May 8 (vertical, stereoscopic).
County of San Diego, 1970, Series SDCO, Flight Line 2, Photos 2-1 (015) and 2-2
(014), dated October 9 (vertical, stereoscopic), scale 1:24,000.
County of San Diego, 1975, Flight SDPD, Flight Line 36, Photos 36-2 (129) and 36-3
(128), dated January 20 (vertical, stereoscopic), scale 1 inch = 1,000 feet.
County of San Diego, 1983, Flight C11109 83059, Photos 256 (023) and 257 (024),
dated November 22 (vertical, stereoscopic), scale 1 inch = 2,000 feet.
County of San Diego, 1989, Series WAC-89A, Photo 3-7, dated April 7 (vertical, not
stereoscopic).
Geo-Tech Imagery Intl., 1992, Carlsbad Frames 6 and 7, dated November 1 (infrared,
oblique, stereoscopic).
U.S. Department of Agriculture, 1953, Series AXN, Flight Line 14M, Photos 17
and 18, dated May 2 (vertical, stereoscopic), scale 1:20,000.
U.S. Department of Agriculture, 1964, Series AXN, Flight Line 4DD, Photo 97, dated
April 9 (vertical, not stereoscopic).
MAPS
City of Carlsbad, 1992, Geotechnical Hazards Analysis and Mapping Study, dated
November.
City of Carlsbad, 1991, Orthophoto Mapping, Sheet 93, scale 1" = 100' (aerial
photography dated September-October 1988).
County of San Diego, 1975, Orthophoto Topographic Map 350-1665, dated
September 17, scale 1" = 200'.
County of San Diego, Assessor's Map Book, page 210-12.
County of San Diego, 1898, Survey Number 148, Fifth Road District, Oceanside to
Encinitas, two parts, dated October.
SGC
Project No. 126G21
APPENDIX A
MAPS
(continued)
County of San Diego, 1915, Map of Partition of a Portion of the Land Owned by the
Undersigned in the Rancho Agua Hedionda, Map No. 823, dated May 1.
County of San Diego, 1958, Poinsettia Beach Unit No.1, Map No. 3897, dated
May 21.
County of San Diego, 1984, Record of Survey, Map No. 9595, dated February 29.
County of San Diego, 1987, Record of Survey, Map No. 11280, dated October 22.
SGC
-.
APPENDIX B
** PCSTABL5M **
by
Purdue University
—Slope Stability Analysis—
Simplified Janbu, Simplified Bishop
or Spencer's Method of Slices
Run Date:
Time of Run:
Input Data Filename:
Output Filename:
Plotted Output Filename:
March 4, 1996
5:00 pm
Carlsbad.in
Carlsbad.out
Carlsbad.pit
PROBLEM DESCRIPTION STABILITY ANALYSYS - Carlsbad bluff
BOUNDARY COORDINATES
10 Top Boundaries
11 Total Boundaries
Boundary
No.
1
2
3
4
5
6
7
8
9
10
11
X-Left
(ft)
20.00
33.00
34.00
37.70
39.00
46.70
65.00
70.00
79.50
114.80
39.00
Y-Left
(ft)
20.00
25.00
30.50
31.00
39.00
41.00
56.80
67.30
69.00
70.00
39.00
X-Right
(ft)
33.00
34.00
37.70
39.00
46.70
65.00
70.00
79.50
114.80
220.00
220.00
Y-Right
(ft)
25.00
30.50
31.00
39.00
41.00
56.80
67.30
69.00
70.00
70.00
39.00
Soil Type
Below Bnd
1
1
1
1
2
2
2
2
2
2
1
ISOTROPIC SOIL PARAMETERS
2 Type(s) of Soil
Soil Total Saturated Cohesion Friction Pore Pressure Piez.
Type Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface
No. (pcf) (pcf) (psf) (deg) Param. (psf) No.
120.0
120.0
135.0
135.0
500.0
200.0
40.0
35.0
.00
.00
.0
.0
1 PIEZOMETRIC SURFACE HAS BEEN SPECIFIED
Unit Weight of Water = 62.40
Piezometric Surface No. 1 Specified by 2 Coordinate Points
Point
No.
1
2
X-Water
(ft)
39.00
220.00
Y-Water
(ft)
39.00
40.00
BOUNDARY LOAD(S)
1 Load(s) Specified
Load
No.
X-Left
(ft)
X-Right
(ft)
Intensity
(Ib/sqft)
Deflection
(deg)
95.00 96.00 1000.0 .0
NOTE - Intensity Is Specified As A Uniformly Distributed
Force Acting On A Horizontally Projected Surface.
A Critical Failure Surface Searching Method, Using A Random
Technique For Generating Irregular Surfaces, Has Been Specified.
Janbus Empirical Coef. is being used for the case of c & phi both > 0
100 Trial Surfaces Have Been Generated.
10 Surfaces Initiate From Each Of 10 Points Equally Spaced
Along The Ground Surface Between X = 28.00 ft.
and X = 60.00 ft.
Each Surface Terminates Between X = 70.00 ft.
and X = 170.00 ft.
Unless Further Limitations Were Imposed, The Minimum Elevation
At Which A Surface Extends Is Y = .00 ft.
10.00 ft. Line Segments Define Each Trial Failure Surface.
Factor Of Safety Calculation Has Gone Through Ten Iterations
The Trial Failure Surface In Question Is Defined
By The Following 13 Coordinate Points
Point X-Surf Y-Surf
No. (ft) (ft)
1 28.00 23.08
2 35.39 16.34
3 43.45 10.42
4 52.02 5.27
5 61.99 6.12
6 71.97 6.62
7 79.76 12.90
8 81.00 22.82
9 81.08 32.82
10 81.51 42.81
11 82.27 52.78
12 .82.54 62.78
13 82.69 69.09
Factor Of Safety For The Preceding Specified Surface ~ 5.619
Factor Of Safety Calculation Has Gone Through Ten Iterations
The Trial Failure Surface In Question Is Defined
By The Following 10 Coordinate Points
Point X-Surf Y-Surf
No. (ft) (ft)
1 28.00 23.08
2 36.39 17.64
3 45.56 13.65
4 55.38 15.54
5 62.54 22.52
6 69.71 29.50
7 70.62 39.46
8 70.98 49.45
9 71.25 59.45
10 71.31 67.53
Factor Of Safety For The Preceding Specified Surface = 3.284
Factor Of Safety Calculation Has Gone Through Ten Iterations
The Trial Failure Surface In Question Is Defined
By The Following 10 Coordinate Points
Point X-Surf Y-Surf
No. (ft) (ft)
1 35.11 30.65
2 42.48 23.89
3 52.42 22.79
4 62.00 25.66
5 71.41 29.06
6 79.02 35.55
7 79.87 45.51
8 79.96 55.51
9 79.97 65.51
10 79.99 69.01
Factor Of Safety For The Preceding Specified Surface = 3.715
Factor Of Safety Calculation Has Gone Through Ten Iterations
The Trial Failure Surface In Question Is Defined
By The Following 18 Coordinate Points
Point X-Surf Y-Surf
No. (ft) (ft)
1 52.89 46.34
2 60.06 39.37
3 67.18 32.35
4 75.06 26.19
5 83.94 21.59
6 92.11 15.83
7 100.39 10.22
8 108.62 4.54
9 118.12 1.42
10 128.07 2.41
11 135.69 8.88
12 136.54 18.85
13 136.97 28.84
14 137.00 38.84
15 137.82 48.81
16 139.57 58.65
17 142.13 68.32
18 142.14 70.00
Factor Of Safety For The Preceding Specified Surface = 83.3O3
Following Are Displayed The Ten Most Critical Of The Trial
Failure Surfaces Examined. They Are Ordered - Most Critical
First.
* * Safety Factors Are Calculated By The Modified Janbu Method * *
Failure Surface Specified By 6 Coordinate Points
Point
No.
1
2
3
4
5
6
X-Surf
(ft)
52.89
62.50
71.06
79.20
84.98
85.34
Y-Surf
(ft)
46.34
49.12
54.28
60.09
68.26
69.17
1.648
Individual data on the 8 slices
Slice
No.
1
2
3
4
5
6
7
8
Width
Ft(m)
9.6
2.5
5.0
1.1
8.1
.3
5.5
.4
Weight
Lbs(kg)
3178.3
1755.6
5947.5
1711.0
10770.4
312.8
3082.1
19.4
Water Water Tie Tie Earthquake
Force Force Force Force Force Surcharge
Top Bot Norm Tan Hor Ver Load
Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg)
.0 .0 .0 .0 .0 .0 .0
.0 .0 .0 .0 .0 .0 .0
.0 .0 .0 .0 .0 .0 .0
.0 .0 .0 .0 .0 .0 .0
.0 .0 .0 .0 .0 .0 .0
.0 .0 .0 .0 .0 .0 .0
.0 .0 .0 .0 .0 .0 .0
.0 .0 .0 .0 .0
Failure Surface Specified By 6 Coordinate Points
.0 .0
Point
No.
1
2
3
4
5
6
X-Surf
(ft)
45.78
55.78
65.14
71.69
73.64
74.11
Y-Surf
(ft)
40.76
40.75
44.27
51.82
61.63
68.04
1.735
Failure Surface Specified By 8 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
X-Surf
(ft)
45.78
55.38
64.82
73.73
79.59
87.03
94.65
97.67
Y-Surf
(ft)
40.76
37.96
41.24
45.79
53.90
60.57
67.05
69.51
1.766
Failure Surface Specified By 7 Coordinate Points
Point
No.
1
2
3
4
5
6
7
X-Surf
(ft)
38.67
48.58
56.43
65.18
71.14
75.42
75.94
Y-Surf
(ft)
36.95
38.29
44.49
49.33
57.36
66.39
68.36
1.807
Failure Surface Specified By 11 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
9
10
11
X-Surf
(ft)
Y-Surf
(ft)
28.00
35.31
45.31
53.93
62.10
68.33
73.13
78.92
83.46
88.95
88.98
23.08
16.25
16.17
21.23
27.00
34.83
43.60
51.75
60.66
69.02
69.27
1.821
Failure Surface Specified By 9 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
9
X-Surf
(ft)
Y-Surf
(ft)
31.56
40.27
49.97
56.30
62.86
67.84
71.81
75.64
76.18
24.44
19.53
21.96
29.70
37.24
45.91
55.09
64.33
68.41
1.875
Failure Surface Specified By 5 Coordinate Points
Point
No.
1
2
3
4
5
X-Surf
(ft)
56.44
66.39
75.08
78.63
80.92
Y-Surf
(ft)
49.41
48.41
53.36
62.71
69.04
1.895
Failure Surface Specified By 7 Coordinate Points
Point
No.
1
2
3
4
5
6
7
X-Surf
(ft)
38.67
48.66
58.63
67.09
72.78
75.99
77.39
Y-Surf
(ft)
36.95
36.55
37.26
42.60
50.82
60.29
68.62
1.897
Failure Surface Specified By 6 Coordinate Points
Point
No.
1
2
3
4
5
6
X-Surf
(ft)
52.89
62.16
71.29
80.24
86.78
87.67
Y-Surf
(ft)
46.34
50.08
54.18
58.63
66.19
69.23
1.907
Failure Surface Specified By 8 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
X-Surf
(ft)
42.22
52.15
62.13
71.65
77.50
81.46
84.37
84.40
Y-Surf
(ft)
39.84
38.60
39.08
42.16
50.27
59.45
69.02
69.14
*** 1.916
.00 27.50 55.00 82.50 110.00 137.50
X /\f\ j .^_.^^_^A j _ .1— * i-. UU +————————-1—————————t-—————————-r—————————t——————— ——-r
27.50 + 5
* *5... * 4
. 6.. *
..5 *
—.. ...6 .84..
A 55.00 + 5..6..32417
- 8. ...
- 5. ..632.1..*
~ ... .......5*8.6*.* .*.
- 05382142 42
- 053 16.*
X 82.50 + 95. 7
- 3.91
S 137.50 +
165.00 +
F 192.50 +
- 331/1
I 110.00 + .
*
220.00 + *W
125 •
iee •
75
58 •
25 •
8
u
B 25 50 75 108 125 150
X - AXIS
175 200 225
Project No. 126G21
125
108
75
50
25
0
u
8 25 50 75 100 125
X - AXIS
150 175 200 225
Project No. 126G21
A Critical Failure Surface Searching Method, Using A Random
Technique For Generating Circular Surfaces, Has Been Specified,
100 Trial Surfaces Have Been Generated.
10 Surfaces Initiate From Each Of 10 Points Equally Spaced
Along The Ground Surface Between X = 20.00 ft.
and X = 60.00 ft.
Each Surface Terminates Between X = 70.00 ft.
and X = 170.00 ft.
Unless Further Limitations Were Imposed, The Minimum Elevation
At Which A Surface Extends Is Y = .00 ft.
10.00 ft. Line Segments Define Each Trial Failure Surface.
Following Are Displayed The Ten Most Critical Of The Trial
Failure Surfaces Examined. They Are Ordered - Most Critical
First.
* * Safety Factors Are Calculated By The Modified Janbu Method * *
Failure Surface Specified By 5 Coordinate Points
Point
No.
1
2
3
4
5
X-Surf
(ft)
51.11
60.52
68.57
74.59
76.99
Y-Surf
(ft)
44.81
48.20
54.13
62.11
68.55
1.518
Individual data on the 6 slices
Slice
No.
1
2
3
4
5
6
Width
Ft(m)
9.4
4.5
3.6
1.4
4.6
2.4
Water Water Tie Tie Earthquake
Force Force Force Force Force Surcharge
Weight Top Bot Norm Tan Hor Ver Load
Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg)
2674.6 .0 .0 .0 .0 .0 .0 .0
2698.8 .0 .0 .0 .0 .0 .0 .0
3316.5 .0 .0 .0 .0 ,0 .O .0
1838.8 .0 .0 .0 .0 .0 .0 .0
4764.5 .0 .0 .0 .0 .0 .0 .0
865.3 .0 .0 .0 .0 .0 .0 .0
Failure Surface Specified By 8 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
X-Surf
(ft)
37.78
47.44
56.66
65.27
73.11
80.02
85.88
88.38
Y-Surf
(ft)
31.48
34.05
37.92
43.01
49.23
56.45
64.56
69.25
1.584
Failure Surface Specified By 10 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
9
10
X-Surf
(ft)
Y-Surf
(ft)
20.00
29.92
39.57
48.77
57.34
65.11
71.95
77.72
82.30
84.24
20.00
21.27
23.89
27.81
32.97
39.26
46.55
54.72
63.61
69.13
1.598
Failure Surface Specified By 6 Coordinate Points
Point
No.
1
2
3
4
5
6
X-Surf
(ft)
42.22
52.22
61.49
68.66
72.65
72.84
Y-Surf
(ft)
39.84
39.80
43.55
50.52
59.69
67.81
1.646
Failure Surface Specified By 10 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
9
10
X-Surf
(ft)
Y-Surf
(ft)
20.00
30.00
39.82
49.11
57.54
64.80
70.65
74.86
77.30
77.52
20.00
20.01
21.90
25.61
30.99
37.86
45.98
55.05
64.74
68.65
1.650
Failure Surface Specified By 6 Coordinate Points
Point
No.
1
2
3
4
5
6
X-Surf
(ft)
51.11
61.04
70.35
78.48
84.90
87.81
Y-Surf
(ft)
44.81
46.02
49.66
55.49
63.16
69.24
1.651 ***
Failure Surface Specified By 10 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
9
10
X-Surf
(ft)
Y-Surf
(ft)
28.89
38.88
48.77
58.21
66.86
74.42
80.61
85.21
88.06
88.43
23.42
23.00
24.47
27.77
32.79
39.34
47.20
56.07
65.66
69.25
1.677
Failure Surface Specified By 4 Coordinate Points
Point X-Surf Y-Surf
No. (ft) (ft)
1 60.00 52.48
2 69.29 56.18
3 76.70 62.89
4 79.87 69.01
f 707
Failure Surface Specified By 11 Coordinate Points
Point
No.
1
2
3
4
5
6
7
8
9
10
11
X-Surf
(ft)
28.89
38.88
48.73
58.27
67.34
75.80
83.49
90.29
96.08
100.77
101.06
Y-Surf
(ft)
23.42
23.87
25.60
28.60
32.80
38.14
44.53
51.87
60.02
68.85
69.61
1.760
Failure Surface Specified By 6 Coordinate Points
Point
No.
1
2
3
4
5
6
X-Surf
(ft)
51.11
60.35
69.22
77.67
85.63
90.78
Y-Surf
(ft)
44.81
48.64
53.25
58.60
64.66
69.32
1.779
.00 27.50 55.00 82.50 110.00 137.50
X . 00 + + + + + +
*
27.50 + ..7
.53*.*
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53. . *
- 2 .*
™ *******O<J * » *f J.
A 55.00 + 2 . .
- 753 ..4618
3.2... *
- 7. . 5401. *
7. 32.5 41.4
- 9 32.85*
X 82.50 97. ..3 3
- 7. 272
9 . .0
- 9 ..1/1
- 9
I 110.00 +- *
S 137.50 +
165.00 +
F 192.50 +
T 220.00 + *W
125
iae
75 -
58 •
25
e
u
e 25 75 109 125
X - AXIS
159 175 200 225
Project No. 126G21
125
188
75
58
25 ••u u
B 25 75
—i 1—
188 125
X - AXIS
158 175 288 225
Project No. 126G21