HomeMy WebLinkAboutCDP 01-11; Frye Residence; Compilation of Prior Reports and Updates; 2001-05-21Geotechnical Report Update -
Compilation of Prior Reports and
Updates Addressing:
Design Criteria
Geotechnical Requirements
Soil Parameters
CDP 01-11 "Frye Residence"
5327 Carlsbad Boulevard
The Ash Company
OWEN ENGINEERING GROUP
Civil, Geotechnical and Structural Engineering
May 21,2001
City of Carlsbad
Engineering Department
2075 Las Palmas Drive
Carlsbad, CA 92009
Subject: Clarification, Engineering Reports Parcel's Numbers 2 and 3, PM
18236, Carlsbad Blvd
re: Geotechnical Requirements, Soil Parameters, Design Criteria for
Development. Copies at the City of Carlsbad, Engineering
Department
Mr. Clyde Wickham:
Attached are copies of previous reports which were written and addresses the
approval for the Parcel Map 18236 for Mr. Jon Jensen.
Parcel 818236 reflects a split to three parcels within this Parcel Map (18236).
The applicable Assessors Parcel Map Numbers are 210-120-33 for the Goetz
Family at 5323 Carlsbad Blvd, Parcel Number 2. Parcel Number 3 is Assessors
Parcel Map Number 210-120-34 for the Ash Group with the address of 5327
Carlsbad Blvd.
The information which is attached herein is applicable for the development of all
sites which are apart of the original parcel which has been subdivided by Mr. Jon
Jensen.
Included in the attachments are design criteria for the development of each site.
Note: these criteria remain unchanged from the original soil investigation, a copy
of which is attached.
Additional, we have included information relative to the pertinent parts of
numerous reports which have become a part of this geotechnical evaluation.
These portions are included as "References" which are on Page 1 of the report
dated March 16, 1998 report to Mr. Jon Jensen for Assessors Parcel Number
210-120-30.
1525 Grand Ave, San Marcos, California 92069 Telephone (760) 471 - 6000 Fax (760) 471-6096
14661 Myford Road, Suite C, TUstin, California 92806 Telephone (714) 734 - 7993 Fax (714) 734-9732
This information is complete and addresses the proposed development of these
projects.
Sincerely,
Owen Engineering Group
Charles J. Randle, P.E.
RCE 22096 CA
cc: Mr. Steve Ash S
Mr. Dean Goetz
Owen Engineering Group
Page 3
May 21,2001
Attachments:
1. March 6, 2001, letter to Mr. Steve Ash; June 14, 2000, letter to Mr. Jon
Jensen.
2. March 16,1998, Updated Geotechnical Report to Mr. Jon Jensen.
Excerpts from:
>
3. March 28,1991, Geotechnical Investigation and Bluff Retreat Study
prepared for M.B. Shores Corporation, Leucadia, California, "Geotechnical
Evaluation and Recommendations", Pages 14 and 15.
4. March 28,1991, Geotechnical Investigation and Bluff Retreat Study
prepared for M.B. Shores Corporation, Leucadia, California, Pages 15,16
17,18 and 19.
5. November 6,1989, Geotechnical Investigation and Bluff Retreat Study
prepared for Julie Krommenhoek/McKeown, Carlsbad, California, Pages
10,11,12 and Figures 2 and 3.
6. Jon Jensen Tentative Parcel Map.
OWEN ENGINEERING GROUP
Civil, Geotechnical and Structural Engineering
March 6, 2001
Attention: Steve Ash
14 Cameo Crest
Laguna Miguel, Ca 92679
Subject:
Geotechnical Review and Update of Applicable Geology and Geotechnical Reports for
Parcel No. 3 P.M., 18236, Carlsbad California,
Dear Mr. Ash:
This geotechnical update letter is presented in a format which updates all of the
referenced reports relative to the development of your site.
Prior to this report, these reports addressed bluff stability and recommended setbacks
relative to the construction of the proposed dwelling at this site.
Applicable criteria for this development are summarized as followed. Where these
values may differ in the original reports, the design parameters are updated herein and are
applicable to your proposed residence.
As noted in previous reports by this office, the recommended setback from the bluff is 40
feet from the top of the existing bluff.
Design criteria are as follows:
Item 1. Lateral pressure evaluation based on the angle of internal friction at 32
degrees and cohesion of 100 pounds psf
Item 2. Unit soil bearing for continuous foundations located a minimum of 18
inches below lowest adjacent grade shall not exceed 2500 psf. This is a
conservative value based on the Terzagbi Unit Bearing Value Formula for
this type soil. The unit soil bearing value may be increased 500 pounds
psf for each additional 12 inches of embedment of the footing relative to
the lowest adjacent grade to a maximmn of 4000 psf.
1800 Thibodo Road, Suite 320 Vista, California 92083 Telephone (760) 599 - 6767 Fax (760) 599-6070
14661 Myford Road, Suite C, lustin, California 92806 Telephone (714) 734 - 7993 Fax (714) 734-9732'
Grade measurements, in the event of a basement-type structure, relate to
the measurement of the inside or lowest adjacent grade. This is not a
reference to the finished exterior pad grade.
Item 3. The soil, as tested, is non-expansive and no special provisions for slab-on-
grade or similar considerations are required.
Item 4. The foundation system along the westerly perimeter of the dwelling may
include end bearing caissons placed on formation material, located
approximately 5 to 8 feet below grade. Unit soil bearing on formation
material shall not exceed 6000 psf.
The caisson system is an option. The proposed perimeter grade
beam/foundation will adequately support the proposed structure.
Caisson distribution and spacing shall be a part of the structural evaluation
and the dwelling and its foundation system. Note: this is only a
recommendation and is not a requirement for the dwelling "bluff setback"
as 40 feet.
Item 5. All slab on grade systems will require a sub-base material to consist of
compact dense free draining soil and/or gravel. Sub-slab materials, within
the living areas, will require the placement of at least 6 mil visqueen and 2
inches of sand as a leveling course. Concrete slab-on-grades are
recommended to be a minimum of 4 inches of thickness and contain
reinforcing steel as win be directed by the structural engineer. A
minimum would be a 6 gauge welded wire mat or as directed by the
structural engineer.
The above hems are specifically directed to the criteria necessary to design of this
building. The construction procedures shall be observed during embankment
construction, or prior to foundation concrete placement. This inspection will be to insure
mat the foundation dimensions, locations are per this report and the associated
restrictions imposed by these referenced reports which are considered a part of this
document and per project plans and specifications.
Site drainage must conform to criteria established to address bluff protection. All
drainage shall be directed away from the dwelling foundations. All drainage to the public
right-of-way (roadway) shall be hi conformance with applicable standards (City of
Carlsbad, California).
This report is an update to the attached report dated March 16,1998.
Limitations
Professional judgements presented herein are based partly on our evaluation of the
available technical information that was reviewed, partly on our understanding of the
proposed construction, and partly on our general experience in the civil and geotechnical
field.
The recommendations and civil engineering basis of design were based on the
assumption that the soil conditions present at the site do not deviate considerably from
those presented in the referenced reports and investigations performed by others (see
references). If variations or undesirable geotechnical or soil conditions are encountered
during construction, the engineering geologist and civil engineer should be notified
immediately and consulted for further recommendations. We do not guarantee the
performance of the project in any respect.
This firm does not practice or consult in the field of safety engineering. We do not direct
the contractor's operations, and cannot be responsible for the safety of other than our own
personnel on the subject site; therefore, the safety of others is the responsibility of the
contractor. The contractor should notify the owner if he considers any of the
recommended actions presented herein to be safe.
Sincerely,
Owen Engineerintt Group
C. J. Randle, P.E.
Principal Engineer
RCE 22096 CA
NO.C22086
Eqx Dot* 08001
Ash Letter
3-6-01
Jensen Letter
6-14-00
OWEN ENGINEERING GROUP
Civil, Geotechnical and Structural Engineering
June 14,2000
Mr. Jon Jensen
Jon A Jensen and Associates
451 South Escondido Blvd
Escondido.CA 92025
Subject: Review and Update of Applicable Geology and Geotechnical Reports
re: Parcel No. 210-120-30, Carlsbad, California
Dear Mr. Jensen:'•
This information is presented in a format which updates all of the referenced reports relative to the
development of your site.
Prior to this report, these reports addressed bluff stability and recommended setbacks relative to the
construction of the proposed dwelling at this site.
Applicable criteria for this development are summarized as followed. Where these values may
differ in the original reports, the design parameters are updated herein and are applicable to your
proposed residence.
As noted in previous reports by this office, me recommended setback from the bluff is 40 feet from
the top of the existing bluff
Design criteria are as follows:
Item 1. Lateral pressure evaluation based on the angle of internal friction at 32 degrees and
cohesion of 100 pounds psf.
Item 2. Unit soil bearing for continuous foundations located a minimum of 18 inches below
lowest adjacent grade shall not exceed 2500 psf. This is a conservative value based
on the Terzaghi Unit Bearing Value Formula for this type soil The unit soil bearing
value maybe increased 500 pounds psf for each additional 12 inches of embedment
of the footing relative to the lowest adjacent grade to a maximum of 4000 psf.
Grade measurements, in the event of a basement-type structure, relate to the
measurement of the inside or lowest adjacent grade. This is not a reference to the
finished exterior pad grade.
1525 Grand Ave, San Marcos, California 92069 . Telephone (760) 471 - 6000 Fax (760) 471-6096
14661 Myford Road, Suite C, TUstin, California 92806 Telephone (714) 734 - 7993 Fax (714) 734-9732
Item 3. The soil, as tested, is nonexpansive and no special provisions for slab-on-grade or
similar considerations are required.
Item 4. The foundation system along the westerly perimeter of the dwelling may include end
bearing caissons placed on formation material, located approximately 5 to 8 feet
below grade. Unit soil bearing on formation material shall not exceed 6000 psf.
The caisson system is an option. The proposed perimeter grade beam/foundation
will adequately support the proposed structure
Caisson distribution and spacing shall be a part of the structural evaluation and the
dwelling and its foundation system. Note: this is only a recommendation and is not
a requirement for the dwelling "bluff setback" as 40 feet.
Item 5. All slab on grade systems will require a sub-base material to consist of compact
dense free draining soil and/or gravel. Sub-slab materials, within the living areas,
will require the placement of at least 6 mil visqueen and 2 inches of sand as a
leveling course. Concrete slab-on-grades are recommended to be a minimum of 4
inches of thickness and contain reinforcing steel as will be directed by the structural
engineer. A minimum would be a 6 gauge welded wire mat or as directed by the
structural engineer.
The above items are specifically directed to the criteria necessary to design of this building. The
construction procedures shall be observed during embankment construction, or prior to foundation
concrete placement This inspection will be to insure that the foundation dimensions, locations are
per this report and the associated restrictions imposed by these referenced reports which are
considered a part of this document and per project plans and specifications.
Site drainage must conform to criteria established to address bluff protection. All drainage shall be
directed away from the dwelling foundations. All drainage to the public right-of-way (roadway)
shall be in conformance with applicable standards (City of Carlsbad, California).
This report is an update to the attached report dated March 16,1998.
Limitations
Professional judgements presented herein are based partly on our evaluation of the available
technical information that was reviewed, partly on our understanding of the proposed construction,
and partly on our general experience in the civil and geotechnical field.
The recommendations and civil engineering basis of design were based on the assumption that the
soil conditions present at the site do not deviate considerably from those presented in the referenced
reports and investigations performed by others (see references). If variations or undesirable
geotechnical or soil conditions are encountered during construction, the engineering geologist and
civil engineer should be notified immediately and consulted for further recommendations. We do
not guarantee the performance of the project in any respect.
This firm does not practice or consult in the field of safety engineering. We do not direct the
contractor's operations, and cannot be responsible for the safety of other than our own personnel
on the subject site; therefore, the safety of others is the responsibility of the contractor. The
contactor should notify the owner if he considers any of the recommended actions presented herein
to be safe.
Sincerely,
Owen Engineering Group
C. J. Randle, P.E.
RCE 22096 CA
TERZAGHI'S BEARING CAPACITY EQUATION
CONDITIONS
Friction Angle (ji:=32.deg
Cohesion c:=100-psf
Maximum Density y := 120-pcf
Footing Width B:=l-ft z:=l-ft.l.5-ft..B
Footing Depth D :=66-in
Effective Overburden Pressure q :=y'D q = 660-psf
TERZAGHI VARIABLES
(see table 4-1 of Foundation Analysis and Design, Joseph E.
Bowles)
For strip round square
Sr 1.0 1.3 1.3 Se:=lc c
Sy 1.0 0.6 0.8 Sy:=l
N Factors
(For the following values, see Terzaghi bearing-capacity values)
Nc:=44.90 Nq:=29.5 Ny:=27.8
Bearing Capacity Allowable Bearing Capacity
qult(z):=c.Nc.S0-Hq-Nq-t-0.5.y.z.Ny.Sy SF:=4 qa(z):=-SF
£.1 1^=25628 .1^=6407
ft psf psf
APPENDIX A
UNIT SOIL BEARING VALUES
References
1. Geotechnical Update, Carlsbad Beach Lot, APN 210-120-30, Carlsbad Drive,
Carlsbad, California; 1966, by Geotechnics, Inc., Project No. 0319-001-00, dated
Septembers, 1996.
2. Geotechnical Investigation and Bluff Retreat Study. Parcel No 210-120-39,
Carlsbad, California; 1991, by ICG, Inc., Job No. 04-8529-001-00-00, dated March
28,1991.
3. Geotechnical Investigation and Bluff Retreat Study, Parcel No. 210-120-31,
Carlsbad, California; 1989, by ICG, Inc., Job No. 05-8109-001-00-00, dated
November 6,1989.
4. California's Battered Coast; 1985, California Coastal Commission Meeting,
Professional Papers and Publication, San Diego, California, September, 1985 San
Diego Association of Geologists.
5. Supplemental Geotechnical Investigation, Proposed Coastal Protection Measures for
the 2+1- acre coastal site, Carlsbad, California; 1984, by Converse Consultants,
Project No. 83-2299-02, dated September 20,1984.
6. Geotechnical Investigation, Proposed Coastal Protection Measures for Ecke Site,
Carls bad, California; 1984, by Converse Consultants, Project No. 83-02299-01,
dated February 1,1984.
Wickham Letter
4-2-98
JON A. JENSEN & ASSOCIATES
-ATTORNEYS AT LAW
451 SOUTH ESCONDIDO BOULEVARD
ESCONDIDQ. CALIFORNIA 92025
TELEPHONE (760) 743-7966
FACSIMILE (760) 743-3793
RECEIVED
April 2,1998 APR 02 1998
ENGINEERING
Clyde Wickham DEPARTMENT
Associate Engineer
City of Carlsbad
207 Las Palmas Drive
Carlsbad, CA 92009-1576
Re: Tentative Parcel Map 98-1 and GDP 98-057 Jensen Tentative Parcel Map
Dear Mr. Wickham:
Enclosed please find all of the information which was requested to complete the application
as above described. Please note that I have also included for your further information and
review complete copies of the prior geological reports for the site.
In this regard, please note that these copies were also provided and approved in the prior
project which involved the construction of the stairs to the beach. At that time, Mr. John
R. Theissen, GE825 reviewed the documents and provided a written report to you and the
City regarding the sufficiency of the reports, and regarding the stairway project and
construction of the stairway project.
Please also note that the stairs have now been completed, and the site has also been
sandbagged and provides for surface water to be moved away from the bluff and to the
drainage areas provided in the stairway construction. As a result of the elimination of the
foot traffic near any bluff area, and as a further result of the diversion of the surface water
away from the bluff edge, and the construction of the stairs, the bluff retreat has
dramatically decreased. In addition, further development of the property will also reduce
bluff retreat. In order to deal with these issues, C.J. Randle, P.E. Civil Engineer, conducted
and drafted an additional geotechnical report dated March 16,1998. This report took into
consideration the improvement of the hydrology issues on the site as well as the reduction
and elimination of foot traffic along the bluff. In addition, C.J. Randle, P.E. Civil Engineer
also was the site engineer for the construction of the stairs and developed additional
geotechnical data during the caisson drilling and inspection of soil and soil conditions at
JON A. JENSEN & ASSOCIATES
ATTORNEYS AT LAW
Clyde Wickham
Associate Engineer
April 2, 1998
Page 2
the time of the construction of the stairway. This data and information further allowed Mr.
Randle to not only update, but create specificity and certainty to his findings and
conclusions as opposed to the more general observations and estimates that were made
without the benefit or basis of construction and drillings.
At any rate, the conclusions of C.J. Randle, P.E. Civil Engineer, are consistent with all prior
engineering, and are also consistent with the engineering and geology work done on the
adjacent Richards property, all of which concluded that the property is buildable.
In addition, the findings of C.J. Randle, P.E. Civil Engineer, and the geotechnical engineers
that conducted site evaluations on the Richards property pursuant to their prior approval,
are both consistent with the 25' setback. In fact, the only differentiation between these two
reports is that Mr. Richards' 25' setback is and has been approved for slab-on grade
construction, and the recommendations of C.J. Randle, P.E. Civil Engineer is that the 25'
setback should be utilized for caisson foundation systems only with additional setback
requirements for post and beam and slab-on grade. Therefore, it appears that the Randle
engineering conclusions are far more conservative than the geotechnical studies previously
approved on the Richards project. Because such findings and conclusions are more
conservative than the prior approvals conducted on the Richards' contiguous property,
further review may not be required. However, and should you desire further review, please
have such review completed as soon as possible. In addition, and in this regard, and since
all of the technical reports have previously been read, reviewed, and approved by Mr.
Theissen, G.E., with the exception of the updated Randle Engineering Report dated March
16,1998, perhaps only the updated report needs to be further reviewed. Whether or not
any further review is required, I leave to the discretion of the engineering department. If
any type of further review is necessary, or if there is any charge for either any prior reviews
or future reviews, please allow this correspondence to confirm that I will pay for such
reviews or prior reviews.
JON A. JENSEN & ASSOCIATES
ATTORNEYS AT LAW
Clyde Wickham
Associate Engineer
April 2, 1998
PageS
In addition to the above, and should you be in need of any further information, please do
not hesitate to contact me at your most earliest convenience. I would like to take this
opportunity to thank you for your time and cooperation.
Very truly yours,
JON A. JENSEN & ASSOCIATES
.Attorneys atLaw ; .f.,-
JAJ/nb
jaj\wickham.1
Enclosure
K>n A. Jensen
Geotechnical Update
3-16-98
March 16,1998
C. J. Handle, P.E., Civil Engineer
5858 Mt AHfan Drive, Suite 235
San Diego, CA 92111
Telephone (619) 571-6271
Fai (619) 571-3943
Mr. Jon Jensen
Jon A. Jensen and Associates
451 South Escondido Blvd.
Escondido, CA 92025
Subject: Assumption of Geotechnical Responsibility
Updated Geotechnical Report
Assessor Parcel Number 210-120-30
Carlsbad, California
References:
1. Geotechnical Update, Carlsbad Beach Lot, APN 210-120-30, Carlsbad Drive, Carlsbad,
California; 1996* by Geotechnics, Inc., Project No. 0319-001-00, dated Septembers, 1996.
2. Geotechnical Investigation and BluffRetreat Study, Parcel No. 210-120-30, Carlsbad,
California; 1991, by ICG, Inc., Job No. 04-8529-001-00-00, dated March 28,1991.
3. Geotechnical Investigation and Bluff Retreat Study, Parcel No. 210-120-31, Carlsbad,
California; 1989, by ICG, Inc., Job No. 05-8109-001-00-00, dated November 6,1989.
4. California's Battered Coast; 1985, California Coastal Commission Meeting, Professional
Papers and Publication, San Diego, California, September, 1985 - San Diego Association
of Geologists.
5. Supplemental Geotechnical Investigation, Proposed Coastal Protection Measures for the 2+1-
acre coastal site, Carlsbad, California; 19S4, by Converse Consultants, Project No. 83-2299-
02, dated September 20,1984.
6. Geotechnical Investigation, Proposed Coastal Protection Measures for the Ecke Site,
Carlsbad, California; 1984, by Converse Consultants, Project No. 83-02299-01, dated
. February 1,1984.
Page 2
APN 210-120-30
March 16,1998
INTRODUCTION
In accordance with your request, we have completed an updated geotechnical study of the subject
site, APN 210-120-30, in the City of Carlsbad, California. The purpose of this study was to review
geologic and soils engineering data as they relate to future site development, evaluate sea bluff rate
of retreat, and establish building and construction set-backs relative to the top of the sea bluff.
SCOPE OF WORK "
The scope of our work has included the following tasks:
Review available geological reports and data pertinent to the subject site. The list of
referenced and/or review data is included on page 1 of this report.
Field review of the site and adjacent areas including an assessment of the nearby geological
units and conditions, to include existing sea bluff conditions.
Preparation and processing of this report.
In addition, our study is supplemented by our engineering services, subsurface work and
observation services during-construction of a stairway access to the beach along the south
property boundary of the subject site placed into the bedrock and constructed on caissons.
PROPOSED DEVELOPMENT
The actual plans for future development at the property are not yet complete, but include provisions
that will preclude any excess drainage from within the site to be channeled over the sea bluff face.
This is proposed to be accomplished through landscaping controls, graded earthen swales and other
devices to collect and divert water away from the sea bluff. Additionally, the surface drainage of
the property is enhanced by the surface drainage provisions, which have been developed in and
around the concrete beach access stairway along the south boundary of the property.
Page 3
APN 210-120-30
March 16, 1998
SUMMARY OF REVIEW
Based on our study, references 1,2, 5 and 6 adequately describe the property soil and geological
conditions and the report conclusions and recommendations are still appropriate and applicable to
development of the property except for those items described within the discussion section of this
report.
DISCUSSION "
Previous reports based sea cliff retreat and construction setbacks upon an "empirical" figure of 25
feet extrapolated over 62 years (ref. 2). However, the same report indicates "relatively little
. changes" to the bluff top. Reference S.indicates "There has been little retreat of the bluff top in the
•vicinity... " of the site based on a study interval from 1929 through 1984.
The reports also indicate a concern relative to the cove area of the site. The cove area is reported
to have undergone a short tern) interval of episodic and relative rapid erosion. Cove areas are not
uncommon along the coastal area of San Diego County, and even if underlain by more credible or
"softer" material once the weaker or more credible material forms the cove feature, that natural set
back is sufficient to create a buffer from the brunt of direct wave attack. Thus, once formed, the top
of bluff retreat rate for the cove area becomes similar to 'that of adjacent tops of bluff to both sides
of the cove.
Reference 4 (a compilation of professional studies), the. 1985 California Coastal Commission
Meeting Publication at San Diego provides documented studies for sea bluff retreat and erosion of
the San Diego County Coastal area. These documents include both short term and long term
studies, as well as work comparison of similar rates for the base and tops of bluffs.
These studies confirmed an overall rate of retreat for both the upper and lower parts of the bluffs
at 1 to 3 inches per year. The studies also confirmed that rates tended to decrease slightly in areas
after episodic rapid erosion and/or retreat had occurred in any given area. These studies were based
on the time interval of about 50 to 75 years.
For the property, we can assume for the 75 year design period that a rate of retreat of about 6 to 19
feet might occur. Because there was a period of relatively rapid episodic erosion for the site area
in about 1977 through 1983, we can assume that the longer terra overall rate will be less and more
likely on the order of about 6 to 12 feet, or less. These'rates will be significantly affected and
reduced in the event that longer'term sea cliff erosion control devices are constructed at the site.
Page 4
APN 210-120-30
March 16, 1998
Based on our study, the previous soil and geologic findings for the site are still appropriate and
applicable for the site, except for those items outlined in the Discussion section of this report and
updated in the following paragraphs. We assume soil and geologic responsibility for the previous
reports, findings, conclusions and recommendations of the previous reports.
Based on the site conditions and our study, the rate of retreat for the top of bluff at the project site
is established to be on the order of 1 to 2 inches per yearfor the 75 year planned life of the proposed
development of the property.
»
The bluff retreat may be addressed with the following dimensions and criteria:
1. A 25 foot set back from the face of the bluff with all foundations to be placed on deep
caissons founded in firm dense to very dense, formational sandstone (bedrock). The bedrock
appears to be at maximum depths of elevations of -4 to -6 feet (msl) at elevation +8 and
increases easterly.
2. Bluff setbacks will be established at 30 feet from the face of the bluff for all foundation
systems which conform to the current Uniform Building Code criteria. However,
conventional foundation systems will require development of a deepened grade beam
foundation system which will be a minimum of 36 inches below lowest adjacent grade.
3. Typical slab on grade construction with minimal footing depths may be constructed with a
set back of 40 feet established from the face of the bluff.
Based on our elevation of the recommended setbacks (with relation to the proposed 3 lot Parcel
Map) each lot will easily provide for the necessary building area, without encroaching into the
proposed setback. Similarly, the remaining land area will easily accommodate this proposed
development.
The option of set backs is prudent and will easily address coastal retreat, which essentially will be
mitigated by the restrictions placed on the site drainage controls. The 30 and 40 foot options are
for all intents and purposes a conservative response to the bluff top setbacks. When compared to
the proposery 25 foot setback for the northerly and adjacent vacant parcel.
Page 5
APN210-120-30
March 16, 1998
Actual foundation recommendations for future proposed site development and construction will
require a specific analysis study which should address the type of foundations outlined above and
other factors unique to each structure.
LIMITATIONS
Soil and bedrock conditions may vary in character and soil moisture content from those disclosed
during the previous site subsurface studies. We assume no responsibility or liability for work,
testing, or recommendations performed or provided by others.
»
The conclusions and recommedations contained herein are professional opinions. These opinions
. have been derived in accordance with current standards of practice and no warranty is expressed or
implied.
Should you have any questions, or require additional service please do not hesitate to contract us.
Very truly yours,
c;
Ernest R. Artim •"-i~c::J1-
CEG 1084
Distribution: (3) client
Charles J. Ran
RCE 22096
ICG for MB Shores
3-28-91
M.B. Shores Corporation Job No. 04-8529-001-00-00
March28,1991 . Log No. 1-1418
Page 14
8.0 GEOTECHNICAL EVALUATION AND RECOMMENDATIONS
8.1 General Discussion
No geotechnical conditions were apparent during our investigation which would
preclude the site development as planned. The site condition which should most
severely impact the development is the potential for future erosion and slope stability
of the bluff area. The on-site soils are considered non-expansive and should be
suitable to support the proposed structure once the existing fills and loose soils have
been removed or recompacted.
The following recommendations are intended to provide a suitable bearing pad for
foundations. We recommend that all loose soils or undocumented fill soils within the
building area be removed and replaced as compacted fill. Once these soils have been
prepared, the structure can be supported on a conventional shallow foundation system
bearing entirely on bedrock or compacted fill.
The remainder of Section 8.0 presents our recommendations for foundation design and
construction in detail. These recommendations are based on empirical and analytical
methods typical of the standard of practice in southern California. If these
recommendations appear not to cover any specific feature of the project, please
contact our office for additions or revisions to our recommendations.
•»
8.2 Structural Setback and Slope Stability
A structural setback from the bluff rim is recommended to protect dwellings from
collapse within the economic life of the residence. The setback depicted on the
t
Geotechnical Maps (Plates 1 and 3) is based on slope stability analysis along two cross
sections through the site (Plate 2). Engineering practice uses a factor of safety of 1.5
as the minimum criteria for a stable slope (a factor of safety of less than 1.0 indicates
that a slope should fail). Slope stability calculations indicate that the trial failure
surfaces behind the setback line exhibit a factor of safety greater than 1.5. Trial
MB. Shores Corporation Job No. 04-8529-001-00-00
March 28, 1991 . Log No. 1-1418
Page 15
failure surfaces west of the setback line had factors of safety less than 1.5. Our
analysis was conducted using the STABL5 computer program. Failure surfaces were
generated for circular type failures. Circular failures were used in the analysis
because of the absence of continuous places of weakness which are used in block glide
type failures. Soil strengths parameters used in our calculations were based on the
residual strength of the soil as calculated from direct shear tests in our laboratory. It
is our understanding that no new slopes are currently planned for the site. If future
plans include slopes or the placement of fill beyond the setback line, ICG Inc. should
be contacted to analyze the slope stability.
The major factor affecting the future stability of the existing bluff is the erosion
s* '—~"potential of the bluff soils. As discussed in Section 6.4, theQ>luff retreat rate is
estimated tp_beJX4"Tefe per year. A factor of safety of 1.5 is applied, and the result
is multiplied by 75 years,E^aw*v»^t^ft^^jma^p^|^£l|g^bluff retreat over a 75
year economic life for the proposed residence. The loss of 45 feet of bluff, back from
the existing rim, would still fall well short of the structural setback establish through
slope stability calculations and the 1.5 factor of safety. Appurtenant structures,
temporary structures, decks and landscaping constructed fee^aad^gg^g^^^f^l^ujE:
a^igJ^iyjIfe^aM^^^llll^^B^BMBSS^iy ^ne r'sk ^or damage increases as the bluff
top is approached. It is recommended that measures be taken to prevent the erosion
of the bluff face. Such measures could include the channeling of surface drainage
away from the bluff face, construction of a sea wall and/or covering the bluff face
with an erosion resistant material, ie. rip rap, or gunite.\ *
8.3 Grading and Earthwork
8.3.1 Geotechnical Observation
During grading, ICG Inc. should provide observation and testing services
continuously. Such observations are considered essential to'identify field
conditions that differ from those anticipated by the preliminary investigations,
to adjust designs to actual field conditions, and to determine that the grading
M.B. Shores Corporation Job No. 04-8529-001-00-00
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• ' Page 16
is in general accordance with the recommendations of this report. Our
personnel should perform sufficient testing of any fill placed to support our
opinion as to whether compaction recommendations have been complied with.
8.3.2 Site Preparation
i
Site preparation should begin with the removal of all vegetation and
deleterious materials within the area to be graded. In addition all loose soils
and undocumented fill should be completely removed down to firm bedrock
»
materials. The exposed bedrock should be scarified to a depth of 8 to 12
inches and recompacted to 90 percent of maximum density, ASTM D-1557.
Native on-site soils can be used as fill material, provided all deleterious
materials have been completely removed.
If during grading a cut/fill transition is created, and deep foundations are not
used in the fill portion, the following recommendation should be implemented.
The cut portion of the pad should be overexcavated to a depth of 5 feet below
finish grade and replaced as a compacted fill. The lateral extent of the
excavation should be 5 feet out side of the building perimeter. Alt fill soils
. should be compacted as recommended in Section 8.3.3 Fill Compaction.
8.3.3 Fill Compaction
\ •
All fill and backfill to be placed in association with site development should
be accomplished at slightly over optimum moisture conditions and using
equipment that is capable of producing a uniformly compacted product. The
minimum relative compaction recommended for fill is 90 percent of maximum
density based on ASTM Dl 557 (modified Proctor). Sufficient observation and
testing should be performed by the geotechnical consultant so that an opinion
can be rendered as to the degree of compaction achieved.
M.B. Shores Corporation Job No. 04-8529-001-00-00
March 28, 1991 Log No. 1-1418
Page 17
Representative samples of imported materials and on site soils should be tested
by the geotechnical consultant in order to evaluate the maximum density,
*-x
optimum moisture content, and where appropriate, shear strength,
consolidation, and expansion characteristics of the soil.
During grading operations, soil types other than those analyzed in the
geotechnical reports may be encountered by the contractor. The geotechnical
consultant should be notified to evaluate the suitability of these soils for use
as fill and as finish grade soils.
»
8.3.4 Trench Backfill
All trench backfill should be compacted by mechanical means in uniform lifts
of 8 to 12 inches. The backfill should be uniformly compacted to at least 90
percent of ASTM D1557.
8.4 Site Drainage
Foundation and slab performance depends greatly on how well the runoff waters drain
from the site. This is true both during construction and over the entire life of the
structure. The ground surface around structures should be graded so that water flows
rapidly away from the structures without ponding. The surface gradient needed to
achieve this depends on the prevailing landscape. In general, we recommend that
pavement and lawn areas within five feet of buildings slope away at gradients of at
least two percent. Densely vegetated areas should have minimum gradients of at least
five percent away from buildings in the first five feet. Densely vegetated areas are
considered those in which the planting type and spacing is such that the flow of water
is impeded.
Planters should be built so that water from them will not seep into the foundation,
slab, or pavement areas. Site irrigation should be limited to the minimum necessary
to sustain landscaping plants. Should excessive irrigation, water line breaks, or
M.B. Shores Corporation Job No. 04-8529-001-00-00
March 28, 1991 - Log No. 1-1418
Page 18
unusually high rainfall occur, saturated zones or "perched" groundwater may develop
in fill soils.
Because of the highly erosion prone nature of the on-site soils additional care should
be taken to direct runoff water away from the top of the bluff. Drainage channels
and swales should be constructed to help channel water away from erosion prone
areas. We recommend that drainage water be carried in a pipe or conduit to the base
of the bedrock bench in the lower portion of the bluff, rather than be allowed to flow
freely over the bluff face.
»
8.5 Foundation Recommendations
8.5.1 General
Special design considerations for soil expansion are not considered necessary.
All foundations should bear entirely on either uniformly compacted fill or on
bedrock. The following paragraphs in Section 8.6 will present our
recommendations for foundation design. Our recommendations are considered
to be generally consistent with the standards of practice. They are based on
both analytical methods and empirical methods derived from experience with
similar geotechnical conditions. Reinforcement recommendations are
considered the minimum necessary for the likely soil conditions and are not
intended to supersede the design of the Structural Engineer or criteria of
governing agencies.
8.5.2 Foundations on Bedrock
If the building area is prepared such that all footings will bear entirely on
bedrock the following foundation design parameters should be applicable.
M.B. Shores Corporation
March 28, 1991
Job No.04-8529-001-00-00
Log No. 1-1418
Page 19
Allowable Soil Bearing:3000 psf (allow a one-third increase for short-
term wind or seismic loads)
Minimum Footing Width: 12 inches
Minimum Footing Depth: 18 inches
Minimum Reinforcement:1 no. 4 bar at both top and bottom in continuous
footings, or design as simply supported beam capable
of supporting the applied loads over a span of 4 feet,
whichever is greater. Equal resistance to positive and
negative moments should be provided.
8.5.3 Foundations on Fill
If all footings will bear entirely on compacted fill soils, the following
foundation design parameters should be applicable.
Allowable Soil Bearing:2000 psf (allow a one-third increase for short-
term wind or seismic loads)
Minimum Footing Width: 12 inches
Minimum Footing Depth: 18 inches
Minimum Reinforcement:1 no. 5 bar at both top and bottom in continuous
footings, or design as simply supported beam capable
of supporting the applied loads over a span of 6 feet,
whichever is greater. Equal resistance to positive and
negative moments should be provided.
8.5.4 Settlement
The anticipated total and differential settlement for the proposed structure
should be within tolerable limits provided that the recommendations of this
report are followed. In general, total settlements are estimated to be less than
1 inch, and differential settlement is expected to be less than I inch. It is
recommended that we review the actual foundation plans to evaluate the
footing configurations and loading conditions.
ICG-McKeown
11-6-89
Julie Hampton Job No. 05-8109-001-00-00c/o Krommenhoek/McKeovm Log No. 9-2248
NoVember 6, 1989 Page 10
during extremely high tides and high surf. Additional
erosion occurs as a result of ground water seepage at the
contact between the terrace deposit and Santiago
Formation bedrock
The other major factor in bluff stability is the effect
of surface water erosion. The mesa area above the bluff
generally drains to the west. As the sheet flow nears
the bluff top it is concentrated into shallow gullies.
As the gullies coalesce, they become deeper. Where the
gullies dump over the bluff top, the gullies are over 5
»
feet deep. Over time the gullies migrate up-gradient
(eastward) and laterally, effectively moving the top of
the bluff eastward.
6.3 Bluff Retreat Rates
Bluff collapse or block topples are episodic and
catastrophic. There are long periods when there are no
failures followed by one or two events where tens of feet
of bluff may retreat. Aerial photographs taken in 1929
and 1953 (figures 2 and 3) were compared with photographs
taken by Gerald Kuhn in 1978 and 1983 and maps prepared
in 1984. The base line for measurements were the
railroad tracks east of the site (Location Map, Figure
1). The photographs indicate that there has been little
retreat of the bluff top in the vicinity with the
exception of the "cove" area described by Converse
Consultants (1984).
The anomalous retreat in the "cove" area is a result of
a lack of a bedrock bench to protect the erodible terrace
deposit in that portion of the bluffs. Additionally,
1929 PHOTO
: 04-8109-001-00-00 IOATE:
1953 PHOTO
04-8109-001-00-00 DATE: kl L "" ]November 1989 FIGURE:3
Julie Hampton Job No. 05-8109-001-00-00
c/0 Krommenhoek/McKeown Log No. 9-2248
November 6, 1989 Page 11
there is an offshore channel that refracts unbroken waves
into this section of beach. Without the benefit of an
offshore reef to dissipate wave energy, the "cove" is
subject to more violent wave attack.
The bluff top within the subject property does not appear
to have retreated in the past 61 years. The storm in
August, 1983, -did remove roughly 20 feet from the base
of the upper bluff without collapse of the bluff top.
The result was to steepen the bluff above the bedrock
bench.
»
Future retreat of the bluff at the subject site will be
controlled by several factors:
a. A large reef is located just offshore from the
property. Waves break on the reef rather than on
the beach or against the bluffs thereby reducing
their energy significantly.
b. The bedrock bench has not been undermined and does
not contain open joints or other structural
weaknesses. The bench is 20 feet wide and 5 feet
above the present beach. The bench should protect
the more credible terrace deposit and fill by acting
like a natural sea wall. Direct wave attack on the
base of the upper bluff would only occur when the
tide and storm surge is in excess of +13 feet of
present mean sea level.
c. The fill present in the old erosional gully and
exposed in the upper bluff face within the property
contains chunks of concrete and asphalt. The fill
Julie Hampton Job No. 05-8109-001-00-00c/0 Krommenhoek/McKeown Log No. 9-2248
November 6, 1989 Page 12
appears to be draped over the erodible portion of
the terrace deposit. The fill will act, to a
certain extent, as rip-rap. While the fill is
erodible, it appears much less erodible than the
friable sand in the terrace deposit.
d. .The subject site is roughly 100 feet north of the
"cove" area. Further erosion in the "cove" will
not likely affect the proposed development for well
beyond the economic life of the residence.
»
A structural setback has been established for the subject
property based on the historical bluff retreat in the
area and a 75 year economic life of the residence.
Although the bluff top does not appear to have retreated,
the 20 feet of erosion at the base of the upper bluff has
been extrapolated over the 61 years of documentation to
estimate a average retreat rate of 0.33 feet per year.
A factor of safety of 1.5 is applied and the result is
multiplied by 75 years to arrive at the 40 foot setback
from the bluff top shown on Plate I.
7.0 SEISMICITY
7.1 General
The site is considered to be a seismically active area,
as can all of southern California. There are, however,
no known active faults either on or adjacent to the
project site. Figure 4 shows the known active faults
and major earthquake epicenters in the region and their
geographic relationship to the site. Because these
active faults are at a substantial distance, the seismic
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