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HomeMy WebLinkAboutCDP 05-46; PROPOSED MOSS RESIDENCE; ADDENDUM TO REPORT OF GEOTECHNICAL INVESTIGATION; 2007-07-02^fr^^l Geotechnical Exploration, inc. SOIL AND FOUNDATON ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY CS^P^^ 02 July 2007 Mr. Steven Moss Job No. 07-9342 23679 Calabasas Road #360 Calabasas, CA 91302 Subject: LjririfSIOdliilliftJl^^ Proposed Moss Residence * 5015 Tierra del Oro Street Carlsbad, California Dear Mr. Moss: As requested, we herein provide this addendunn to our original "Report of Geotechnical Investigation and Geologic Reconnaissance" dated April 20, 2007. The property is located at 5015 Tierra del Oro Street as shown on the Vicinity Map Figure No. I. As part of this addendum report, we have responded to comments by the City of Carlsbad in letters dated, May 10, 2007 and June 5, 2007 respectively: 1. "The Geotechnical Report, prepared by Geotechnical Exploration, Inc. (April 20, 2007), does not identify the location of the bluff edge, nor does it evaluate the proposed "infinity edge" pool and its effects on the stability of the bluff. Section "E" (Pg. 18-19) ofthe report discusses the protection ofthe primary structure for 75 years, but does not include the proposed pool. Please update the report in accordance with Section 21.204.110 of the Carlsbad Municipal Code." GEI Response: As indicated in our original report, Section C, "Bluff Edge Evaluation," It appears that the bluff edge is located between elevation 15 and 20 feet above mean sea level (MSL). Refer to Figure No. II, Plot Plan and Geologic Map, and Figure No. Ill, Geologic Cross Section A-A', for the 7420 TRADE STREET* SAN DIEGO, CA. 92121 • (858) 549-7222 • FAX: (858) 549-1604 • EMAIL: geotech@gel-sd.com Proposed Moss Residence Job No. 07-9342 Carlsbad, California Page 2 bluff edge location. As depicted on the cross section, the bluff edge is believed to be a short distance east of exploratory trench HP-4. The bluff edge on the subject property Is the point at which the terrestrially eroded hillside comprised of marine terrace deposits give way to the much steeper bluff face (see Figure No. III). The bluff face is currently buried beneath the rip rap and beach sand deposits. The marine terrace, and beach sand deposits are underlain by the Santiago Formation. The bluff edge is located approximately 5 to 10 feet lower in elevation than the proposed pool and main structure and should not be affected by the proposed new construction. As such, based on the current shore protection and the estimated recession rate, it is our opinion that the proposed pool as well as main structure will be protected for at least 75 years, the assumed design life. We have performed slope stability analyses addressing the western slope down to the beach in accordance with City of Carlsbad Municipal Code, Section 21.204.110 for geotechnical reports. Included as Appendix E of our geotechnical report, we performed slope stability calculations for a typical cross section (A-A') passing through the subject property in an east-west direction and representing the proposed slope geometry. Slope stability analyses were performed utilizing the computer program GSTABL7 with Stedwin v.2.54, by Gregory Geotechmcal Software. The cross section was prepared utilizing the grading plans and pad elevation information. Excavation log geologic information and soil laboratory testing results from our referenced report were also utilized. "Provide documentation demonstrating that the rock rip rap has received a Coastal Development Permit through the California Coastal Commission". em Proposed Moss Residence Job No. 07-9342 Carlsbad, California Page 3 GEI Response: Based on discussions with the California Coastal Commission (CCC) and review of aerial photographs, the existing rock rip rap was constructed sometime between 1979 and 1987 under the jurisdiction of the CCC. The existing hp rap has provided effective protection for at least the past 20 years. Prior to the installation of this shoreline protection, we have calculated a bluff recession rate of 0.33 feet/year in the past 99 years. Using a recession rate of 0.33 feet/year yields a projected, estimated unprotected bluff recession of 25 feet over a period of 75 years. It is our opinion that the existing rock rip rap is considered to be tight and secure and based on the anticipated bluff recession rate, should be kept in place to provide protection for the new home for the life of the structure. There is no need to modify the existing rip rap, as it does not impact public beach access and it will protect the new structure and improvements for the lifetime of the project. "Pape 25 of the Geotechnical Report is recommending 'retaining walls founded on deepened conventional foundations or caissons' to support the existing fill soils in the area of the proposed pool. This requires further elaboration. Please have the Geotechnical Report revised and the plans updated to show where and how this would actually occur, how this would look and how it will affect the stability of the bluff." GEI Response: Development of the proposed pool and deck area will require removal and recompaction of existing fill and beach deposits, as well as possible construction of retaining walls to support the recompacted fill soils. Construction of the retaining walls will require either deepened conventional foundations or caissons due to the existing steep slope conditions and to satisfy the minimum distance to daylight requirement. Refer to Figure No. Ill for proposed retaining wall locations. Assuming the foundation recommendations in the geotechnical report are followed, it is our opinion Proposed Moss Residence Carlsbad, California Job No. 07-9342 Page 4 that this area is well suited for the proposed new improvements and will not have an affect on the underlying bluff stability. LIMITATIONS The findings, opinions and conclusions presented herein have been made in accordance with generally accepted principles and practice in the field of geotechnical engineering within the City of Carlsbad. No warranty, either expressed or implied, is made. If you have any questions regarding this letter, please contact our office. Reference to our Job No. 07-9342 will help expedite a response to your inquiry. Respectfully submitted, GEOTECHNICAL EXPLORATION, INC. Jaijjie-ArCerros, P.E/ R.C.E. 34422/G.E. 2007 Senior Geotechnical Engineer LesTTe D. Reed, President C.E.G. 999[exp. 3-31-09]/R.G. 3391 VICINITY MAP Thomas Bros Guide - San Diego County pg. 1126 Moss Residence 5015 Tierra Del Sol Carlsbad, CA. Figure No. I Job No. 07-9342 0) > _J o a> oo c D 0) > o .Q < c O D > 0) LJJ © D E •>? 2 a a < CROSS SECTION A-A' Geologic Legend Moss Residence 5015 Tierra Del Oro Carlsbad, CA. A' Qaf Qb Qt- Tsb Artificial Fill Beach Deposits Terrace Deposits Santiago Formation ROOF ELEV - 69.0' 60 —I •ROPERTY UNE 40 M 20 — APPROX. MEA. HIGH TIDE UNE _l MATCH JN AT FLOWLINE 0" CURB Relative Horizontal Distance | Feet) Scale: 1" = 20' (Horizontal and Vertical) Figure No. Ill Job No. 07-9342 07-9342-XS-2 NOTE: This Cross Section is not to be used for legal purposes. Locations and dimensions ore approxi- mate. Actual property dimensions and locations of utilities may lie obtained from the Approved Building Plons or tlie "As—Built' Groding Plans. Geotechnical Exploration, Inc. June 2007 ifriBi G^echnical Exptoration, Inc. SOIL AND FOUNDATON ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY 04 October 2007 Mr. Steven Moss Job No. 07-9342 23679 Calabasas Road, Ste. 360 Calabasas, CA 91302 Subject: Response to Carlsbad Enoineerina Deoartment Proposed Moss Residence 5015 Tierra del Oro Street Carlsbad, California Dear Mr. Moss: As requested, and as required by Ms. Kathleen Farmer with the City of Carlsbad Engineering Department in a letter dated September 25, 2007, we herein respond to her comment "the soils engineer, Geotechnical Exploration, Inc. is to revise page 23 of their April 20, 2007 soil report to address alternative shoring methods with respective factors of safety in order to prevent distress during and after construction to the adjacent property to the south" A third party review of the revised soils report will then be required. We are getting a proposal for this review. I will contact you with further information". The City of Carlsbad letter referenced above was addressed to Natalie Roderick of Hoffman Planning who is working with you on this project. The same letter was copied to David Hauser, David Rick, Frank Jimeno, Jason Goff, and John O'Donnell at the City of Carlsbad. Based on a previous letter dated August 22, 2007, from Jason Goff, Associate Planner of the City of Carlsbad Planning Department addressed to Natalie Roderick, it was our understanding that the Engineering Department had notified Mr. Goff 7420 TRADE STREET* SAN DIEGO, CA. 92121 • (858) 549-7222* FAX: (858) 549-1604 • EMAIL: geotechiligei-scl.com Moss Residence Job No.07-9342 Carlsbad, California Page 2 that they had no further comments regarding the resubmittal of the project dated July 6, 2007. We are surprised that after our geotechnical addendum report dated July 2, 2007, and based on the August 22, 2007, letter that the City Engineering Department now requires another letter to address further comments. In addition, the City usually uses Esgil as a third-party to review all documents not reviewed by the Engineering Department and does not request another third-party reviewer. This has been our experience on all other projects built in the same area and for which we have provided geotechnical engineering services. GEI Response On page 23 of our April 20, 2007, geotechnical report for the project, we state, "Excavation for the basement will result in the removal of most of the existing fill/topsoil at the proposed basement location, however, approximately 2 feet of loose sandy terrace soil may require removal and recompaction below the basement level elevation. In addition, shoring may be required along the north, south and east property lines if temporary steep cuts at the recommended inclinations are not allowed due to space constraints. This is especially a concern in the southwest corner of the proposed structure, where the existing fill soils have settled, causing separations between the house and wood deck. Special care should be given to excavations made along the south property line wall". It should be noted that our discussions with Mr. Frank Jimeno at the City of Carlsbad clarified that the settlement damage observed is related to the Moss residence and deck, not the neighbor to the south. To date, we are not aware of any damage to the neighbor's property. In other parts of the report, such as on page 34, we state, "Temporary shoring/underpinning or special phased construction procedures will most likely be needed to ensure that the adjacent properties to the Moss Residence Job No.07-9342 Carlsbad, California Page 3 north and south will not be affected by the basement excavation or where the recommended temporary slopes cannot be constructed due to surcharge or space constraints". On page 37 of the same report, we state, ^^Shoring walls may be designed based on the described equivalent fluid weights already indicated. If soil parameters are used, we recommend that a friction angle of 32 degrees, a cohesion of 50 psf, and a unit weight of 128 pcf be used". We understand, based on the current available project plans, that basement walls will be 6 feet away from the north and south property lines and approximately 10 feet from the east property line. Therefore, temporary slopes will not be able to be developed and shoring will be required. Shoring calculations and plans will be provided by the project shoring contractor, who typically retains a structural engineer or uses an in-house engineer for the shoring design. The shoring design is not prepared until all the architectural, structural and grading plans are completed, so that the shoring designer knows where the improvements, foundations and walls will be located. The shoring design and evaluation is typically performed during preparation and submittal of the construction plans, not at this level of planning approval. The structural designer ofthe shoring knows to provide adequate factors of safety against bending, foundation settlement, soil shear, etc. to help control or prevent excessive soil deformation that could impact the adjacent properties as well as the workers safety. The structural shoring designer, the shoring contractor, the owner, and all the other parties involved with the soils, shoring, foundation and construction take measures to ensure that no damage is caused to other properties and/or persons. All of these parties make sure that their participation is performed in accordance with current building codes and standards of practice. Therefore, once the structural design ofthe shoring is prepared, the City's pertinent departments and reviewers will verify that the shoring design is made in accordance with city requirements and building codes. The City reviewers may Moss Residence Carlsbad, California Job No.07-9342 Page 4 then approve or reject the shoring design if it is not in compliance. Typically the plan checker or an engineer in the engineering department reviews the plans and calculations. Our soil design parameters for the shoring design were provided in the April 20, 2007, report. If you or your shoring designer have any questions regarding soil design parameters for the shoring design may contact our office. All other recommendations presented in our report dated April 20, 2007, remain applicable unless superseded in writing by our firm. LIMITATIONS The findings and opinions presented herein have been made in accordance with current generally accepted principles and practice in the field of geotechnical engineering within the City of Carlsbad and County of San Diego. No warranty, either expressed or implied, is made. If you have any questions regarding this letter, please contact our office. Reference to our Job No. 07-9342 will help expedite a response to your inquiry. Respectfully submitted, GEOTECHNICAL EXPLORATION, INC. Jaime A. Cerros, P.E. R.C.E. 34422/G.E. 2007 Senior Geotechnical Engineer cc: Ms. Kathleen Farmer, City of Carlsbad Engineering Department Ms. Natalie Roderick, Hoffman Planning Mr. Jason Goff, City of Carlsbad Planning Department i Geotechnical Exploration, Inc. SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY 09 October 2007 Mr. Steven Moss 23679 Calabasas Road, Ste. 360 Calabasas, CA 91302 OCT 12 21 DEPARTMENT Job No. 07-9342 Subject: Addendum to Geotechnical Report and Response Carlsbad Enoineerino Department Proposed Moss Residence 5015 Tierra del Oro Street Carlsbad, California Dear Mr. Moss: As requested, and as required by Ms. Kathleen Farmer with the City of Carlsbad Engineering Department in a letter dated September 25, 2007, we herein respond to her comment that ''...the soils engineer, Geotechnical Exploration, Inc. is to revise page 23 of their April 20, 2007 soil report to address alternative shoring methods with respective factors of safety in order to prevent distress during and after construction to the adjacent property to the south." A third party review of the revised soils report will then be required. We are getting a proposal for this review. I will contact you with further information". The City of Carlsbad letter referenced above was addressed to Natalie Roderick of Hofman Planning who is working with you on this project. The same letter was copied to David Hauser, David Rick, Frank Jimeno, Jason Goff, and John O'Donnell at the City of Carlsbad. However, based on a previous letter dated August 22, 2007, from Jason Goff, Associate Planner of the City of Carlsbad Planning Department addressed to Natalie Roderick of Hofman Planning, it was our understanding that the Engineering 7420 TRADE STREET* SAN DIEGO, CA. 92121 • (858) 549-7222* FAX: (858) 549-1604 • EMAIL: geotech@gei-sd.com Moss Residence Job No.07-9342 Carlsbad, California Page 2 Department had notified Mr. Goff that they had no further comments regarding the resubmittal of the project dated July 6, 2007. GEI Response On page 23 of our April 20, 2007, geotechnical report for the project, we state, "Excavation for the basement will result in the removal of most of the existing fill/topsoil at the proposed basement location, however, approximately 2 feet of loose sandy terrace soil may require removal and recompaction below the basement level elevation. In addition, shoring may be required along the north, south and east property lines if temporary steep cuts at the recommended inclinations are not allowed due to space constraints. This is especially a concern in the southwest corner of the proposed structure, where the existing fill soils have settled, causing separations between the house and wood deck. Special care should be given to excavations made along the south property line wall". Based on a meeting with representatives of the City of Carlsbad, we understand that they were concerned that soil movement on the Moss property was causing separations and potential damage to improvements on the neighbor's property to the south. We clarified in discussions with Mr. Frank Jimeno at the City of Carlsbad that the separations noted in our soils report were between the Moss residence and a wood deck on the Moss property. The movement was caused by minor settlement of existing fill soils under the southwest corner of the residence and is considered surficial in nature. The minor fill soil settlement is not considered to be a deep-seated soil or bluff instability problem. To date, we are not aware of any damage to the neighbor's property. It should be noted that the existing structure on the Moss property will be removed and the site is being developed to receive a new residential structure with a basement. Moss Residence Job No.07-9342 Carlsbad, California Page 3 However, due to the observed conditions, it was mentioned in our geotechnical report so that special precautions would be taken in the planning and installation of required shoring in this area. The shoring will consist of drilled soldier beam and wood lagging that is installed before the excavation of the new basement along the north, south and east property lines. In other parts of the report, such as on page 34, we state, "Temporary shoring/underpinning or special phased construction procedures will most likely be needed to ensure that the adjacent properties to the north and south will not be affected by the basement excavation or where the recommended temporary slopes cannot be constructed due to surcharge or space constraints". On page 37 of the same report, we state, ''Shoring walls may be designed based on the described equivalent fluid weights already indicated. If soil parameters are used, we recommend that a friction angle of 32 degrees, a cohesion of 50 psf, and a unit weight of 128 pcf be used". We understand, based on the current available project plans, that basement walls will be 6 feet away from the north and south property lines and approximately 10 feet from the east property line. Therefore, temporary slopes will not be able to be developed and shoring will be required. Shoring calculations and plans will be provided by the project shoring contractor, who typically retains a structural engineer or uses an in-house engineer for the shoring design. The shoring design is not prepared until all the architectural, structural and grading plans are completed, so that the shoring designer knows where the improvements, foundations and walls will be located. The shoring design and evaluation is typically performed during preparation and submittal of the construction plans, not at this level of planning approval. The structural designer of the shoring should provide adequate factors of safety against bending, foundation settlement, soil shear, etc., to help control or prevent excessive soil deformation that could impact the adjacent properties as well as the workers safety. The structural shoring designer, the Moss Residence Job No.07-9342 Carlsbad, California Pa9^ ^ shoring contractor, the owner, and all the other parties involved with the soils, shoring, foundation and construction take measures to ensure that no damage is caused to other properties and/or persons. All of these parties make sure that their participation is performed in accordance with current building codes and standards of practice. Therefore, once the structural design of the shoring is prepared, the City's pertinent departments and reviewers will verify that the shoring design is made in accordance with city requirements and building codes. The City reviewers may then approve or reject the shoring design if it is not in compliance. Typically the plan checker or an engineer in the engineering department reviews the plans and calculations. Our soil design parameters for the shoring design were provided in the April 20, 2007, report. If you or your shoring designer have any questions regarding soil design parameters for the shoring design may contact our office. All other recommendations presented in our report dated April 20, 2007, remain applicable unless superseded in writing by our firm. LIMITATIONS The findings and opinions presented herein have been made in accordance with current generally accepted principles and practice in the field of geotechnical engineering within the City of Carlsbad and County of San Diego. No warranty, either expressed or implied, is made. Moss Residence Carlsbad, California Job No.07-9342 Page 5 If you have any questions regarding this letter, please contact our office. Reference to our Job No. 07-9342 will help expedite a response to your inquiry. Respectfully submitted, GEQXECHNICAL EXPLORATION, INC. -isrme'KTCerros, P.E. R.C.E. 34422/G.E. 2007 Senior Geotechnical Engineer cc: Ms. Kathleen Farmer, City of Carlsbad Engineering Department Mr. David Hauser, Deputy City Engineer, City of Carlsbad Mr. Bob Wojcik, Hofman Planning