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HomeMy WebLinkAboutCDP 01-11; Frye Residence; Geotechnical; 2009-03-11Geotechnical Report Update - Compilation of Prior Reports and Updates Addressing: Design Criteria Geotechnical Requirements Soil Parameters % CDP 01-11 'Trye Residence 5327 Carlsbad Boulevard The Ash Company CDP 6? 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 / Mr. Dean Goetz I Owen Engineering Group Pages I I May 21, 2001 • Attachments: I ^ 1. March 6, 2001, letter to Mr. Steve Ash; June 14, 2000, letter to Mr. Jon Jensen. I ^2. March 16,1998, Updated Geotechnical Report to Mr. Jon Jensen. Excerpts from: i. March 28,1991, Geotechnical Investigation and Bluff Retreat Study prepared forM.B. Shores Corporation, Leucadia, California, "Geotechnical I • Evaluation and Recommendations", Pages 14 and 16^ — v/^4. March 28,1991, Geotechnical Investigation and Bluff Retreat Study / / I prepared for MJ0. Shores Corporation, Leucadia, California, Pages 15,16 1 17,18 and 19/ I v^ 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. I I I I I - I I u>^ OWEN ENGINEERING GROUP Civil, Geotechnical and Structural Engineering March 6,2001 Attention: Steve Ash 14 Cameo Crest LagunaNiguel, 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 . ^ j. degrees and cohesion of 100 pounds psf. ,;,Item2, , Unit soil bearing for continuous foundations located a minimum of 18 r \ ;;' ;; inches below lowest adjacent grade sfyall not exceed 2500 psf This .is a conservative value based on the Terzaghi Unit Bearing Value Formula for ;. r ; .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 maximurn of 4000 psf. 1800 Thibodo Road, Suite 320 Vista, California 02083 Telephone (760) 599 - 6767 Fax (760) 599-6070 14661 Myford Road, Suite C, lustin, California 92806 Telephone (714) 734 - 7993 Fax f7141 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 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 OK consult hi 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 Engineering Group C.J. Handle, P.E. Principal Engineer RCE 22096 CA i . OWEN ENGINEERING. GROUP (K**"Civil, Geotechnical and Structural Engineering I I June 14,2000 Mr. Jon Jensen ^ rf 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:I 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 i 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 i cohesion of 100 pounds psf. Item 2. Unit soil bearing for continuous foundations located a minimum of 18 inches below I 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 may be 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 1 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 f7J41 734-0??? I I I I 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. J 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. I i 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, I 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 I engineer. A minimum would be a 6 gauge welded wire mat or as directed by the structural engineer. 1 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 1 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. I I I 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 confonnance 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 f I I I I I I I I I I I I I I I 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 oh 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 Engineering Group C.J. Handle, P.E. RCE 22096 CA 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 September 3, 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. APPENDIX A UNIT SOIL BEARING VALUES I 1 11 I 1 1 1 1 1I 1 I 1 TERZAGHI'S BEARING CAPACITY EQUATION CONDITIONS Friction Angle 4> := 32-deg Cohesion c := 100-psf Maximum Density y := 120-pcf Footing Width B := 1-ft z := 1-ft. 1.5-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 Sc 1.0 1.3 1.3 Sc:=l Sy 1.0 0.6 0.8 (> Sy:=l N Factors (For the following values, see Terzaghi bearing-capacity values) N0:=44.90 N_:=29.5 Nv:=27.8c 1 . Y Bearing Capacity Allowable Bearing Capacity O . rJ[z\ I^C-N . .S J- n.7*J j- f) S.V.7.M ,S STT •— A n frr\ •—Tl |Tir\ / CC^^^fl'^ IVY T. a\~J '* Y T a . SF Z 1ult(z) 1a(z)2=1 ^^=25628 Ifh_:=6407 ft psf psf JON A. JENSEN & ASSOCIATES ATTORNEYS AT LAW\ 451 SOUTH ESCONDIDO BOULEVARD ESCONDIDO. CALIFORNIA 92025 TELEPHONE (760) 743-7966 FACSIMILE (760) 743-3793 RECEIVED April 2,1998 APR 0 2 1998 ENGINEERING Clyde Wickham DEPARTMENT Associate Engineer City of Carlsbad 207 Las Palmas Drive Carlsbad, CA 92009-1576 Re: Tentative Parcel Mao 98-1 and GDP 98-05 /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. I I I I 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 aLLaw JAJ/nb jaj\wickham.1 ion A. Jensen, Esq Enclosure I I I I I I I I C. J. Randle, P.E., Civil Engineer 5858 Mt Alifan Drive, Suite 235 San Diego, CA 92111 Telephone (619) 571-6271 Fax (619)571-3943 March 16,1998 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 Bluff Retreat 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+/- ;.. 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 the Ecke Site, Carlsbad, California; 1984, by Converse Consultants, Project No. 83-02299-01, dated . February 1,1984. I I I I Page 2 APN 210-120-30 March 16,1998 INTRODUCTION I 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 I of retreat, and establish building and construction set-backs relative to the top of the sea bluff. I SCOPE OF WORK " • I . 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. I Field review of the site and adjacent areas including an assessment of the nearby geological units and conditions, to include existing sea bluff conditions. I Preparation and processing of this report. In addition, our study is supplemented by our engineering services, subsurface work and I 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. I , PROPOSED DEVELOPMENT The actual plans for future development at the property are not yet complete, but include provisions j 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 I 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. I Page 3 APN 210-120-30 March 16,1993 Sf JMMARY OF REVIEW Based on our study, references 1,2, 5 and 6 adequately describe the propert^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 3.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 tenn 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 • "4uced 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 CONCLUSIONS AND RECOMMENDATIONS X 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 Should you have any questions, or require additional service please do not hesitate to contract us. Very truly yours, s VSX>*.. . ^£°y•>••'••• »!;. :< '!•"-"''•." Ernest R. Artim CEG 1084 Distribution: (3) client Charles J. RCE 22096 Ran f•• ,'?rr M.B. Shores Corporation Job No. 04-8529-001-00-00 March 28, 1991 . Log No. 1-1418 Page 14 8.0 GEOTECHNICAL EVALUATION AND RECOMMENDATIONS N, 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 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 werev. 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 potential of the bluff soils. As discussed in Section 6.4, thdfbluff retreat rate is Estimated to be 0.4 fefo per year. A factor of safety of 1.5 is applied, and the result is multiplied by 75 years.^iawiv^^t^o^^jmagd^^^etgj^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, The risk for dama*e ^creases 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 March 28, 1991 . Log No. 1-1418 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. All 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,\ 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 t 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 shouldi 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. Julie Hampton Job No. 05-8109-001-00-00 e/0 Kronunenhoek/McKeown 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 f* 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 PATE: 1953 PHOTO 04-8109-001-00-00 Julie Hampton Job No. 05-8109-001-00-00c/0 Kroaunenhoek/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 erodible 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. 05-8109-001-00-00 c/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 ersdible 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 {•fiMC 100* MMi-or-wur «*OtfO. BCCOMCO »-3O- 1*34. M OOOKm. »*ct «o orncttt GENERAL NOTES: tNCMCt* Or MMM; CMl tNONCCMMS EGAL DESCRIPTION: . . COUNIV orOf CMVO***k. *CCOM)HC K) M*» Mt>. ttUO M iMf QUtCOUMTV KfCOMfX* Of t«t MOO COUNfT. uM- 94, IfM. IOCCH«"iror tot "ir or AWCMO *CO» MCOONOA. M »< o*vC*JH.I*MI. 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