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Home My WebLink AboutHDP 2017-0001; DR. MANEA PROPERTY LOT 52; GEOTECHNICAL REVIEW OF RETAINING WALL IMPROVEMENT PLANS; 2018-05-16---'1 --ii SCST, Inc. Corporate l-leadquarters 6280 Riverdale Street San Diego, CA 92120 • 877.215.4321 619.280.4321 619.280.4717 www.scsl.com • SDVOSB. DVB!; -• ------ ------------------.. --.. - May 16, 2018 Joanne Tyler, PE O'Day Consultants, Inc. 2710 Loker Avenue West, Suite 100 Carlsbad, CA 92010 SCST No. 170106N Report No. 4 Subject: GEOTECHNICAL REVIEW OF RETAINING WALL IMPROVEMENT PLANS MANEA RESIDENCE, LOT 52 7298 SITIO LIMA CARLSBAD, CALIFORNIA O'DAY PROJECT NO. HDP 2017-0001 DWG NO. 507-7A PERMIT NO. GR2017-0059 References: 1.) O'Day Consultants (2017), Drawings: "Hillside Development Permit for La Costa Town Square Residential Lot 52 of Map 15918," dated July 11. 2.) SCST, Inc. (2017), "Geotechnical Assessment of Rear Yard Retaining Walls, Manea Residence, Lot 52, 7298 Sitio Lima, Carlsbad, California," Report No. 170106-01, dated January 10. 3.) SCST, Inc. (2017), "Geotechnical Review of Retaining Wall Improvement Plans Manea Residence, Lot 52, 7298 Sitio Lima, Carlsbad, California," Report No. 170106-02R, dated August 18. Dear Ms. Tyler: In accordance with your request, SCST, Inc. (SCST) reviewed the referenced improvements plans for the rear yard of the subject property. Provided herein are recommendations for the design and construction of the walls based on our past review of the site (referenced). SITE PREPARATION AND GRADING Site Preparation Site preparation should begin with the removal of existing wall improvements, topsoil, vegetation, and debris. If appropriate, abandoned pipelines can be filled with grout or slurry as recommended by and observed by the geotechnical consultant. Remedial Grading The existing fill, associated with the prior construction, should be removed beneath the planned retaining walls and new fills. Excavations up to about 5 feet deep are anticipated. Horizontally, - -.. -.. -----... - -... - - - - - - - - - O'Day Consultants 7298 Sitio Lima Carlsbad, California May 16, 2018 SCST No. 170106N-04 Page2 the excavations should extend at least 5 feet outside the planned perimeter foundations or up to existing improvements, whichever is less. An SCST representative should observe conditions exposed in the bottom of excavations to evaluate if additional removals are recommended. Imported Backfill Excavated material should not be used as backfill. Imported backfill should consist of predominately granular soil free of organic matter and rocks greater than 3 inches. Imported backfill should have a sand equivalent of 20 or more and should be inspected and tested by SCST prior to transport to the site. Compacted Backfill Backfill should be moisture conditioned to near optimum moisture content and compacted to at least 90% relative compaction. Fill should be placed in horizontal lifts at a thickness appropriate for the equipment spreading, mixing, and compacting the material, but generally should not exceed 8 inches in loose thickness. The maximum dry density and optimum moisture content for evaluating relative compaction should be determined in accordance with ASTM D 1557. Excavation Characteristics It is anticipated that excavations can be achieved with conventional earthwork equipment in good working order. Difficult excavation should be anticipated within rock materials. The contractor should mobilize equipment capable of excavating, breaking, and compacting hard rock. Temporary Excavations Temporary excavations 3 feet deep or less can be made vertically. Temporary excavations up to 12 feet high should be laid back no steeper than 1: 1 (horizontal:vertical) and in Type A material (i.e. weathered rock), as evaluated by the geotechnical engineer, no steeper than ½: 1 (horizontal:vertical). The faces of temporary slopes should be inspected daily by the contractor's Competent Person before personnel are allowed to enter the excavation. Zones of potential instability, sloughing or raveling should be brought to the attention of the Engineer and corrective action implemented before personnel begin working in the excavation. Excavated soils should not be stockpiled behind temporary excavations within a distance equal to the depth of the excavation. If temporary slopes are to be maintained during the rainy season, berms are recommended along the tops of slopes to prevent runoff water from entering the excavation and eroding the slope faces. Slopes steeper than those described above may require shoring. Additionally, temporary excavations that extend below a plane inclined at 1 ½: 1 (horizontal:vertical) downward from the outside bottom edge of existing structures or '1 ■ ■ii ---.. -... --- - --- -- - - - - - -- - O'Day Consultants 7298 Sitio Lima Carlsbad, California May 16, 2018 SCST No. 170106N-04 Page3 improvements will require shoring. A shoring system for a specific situation that might be used should be reviewed. Oversized Material Excavations may generate oversized material. Oversized material is defined as rocks or cemented clasts greater than 3 inches in largest dimension. Oversized material should be broken down to no greater than 3 inches in largest dimension for use as backfill, used as landscape material, or disposed of offsite. Slopes All permanent slopes should be constructed no steeper than 2: 1 (horizontal:vertical). Faces of fill slopes should be compacted either by rolling with a sheepsfoot roller or other suitable equipment or by overfilling and cutting back to design grade. Fills should be benched into sloping ground inclined steeper than 5:1 (horizontal:vertical). It is our opinion that cut slopes constructed no steeper than 2: 1 (horizontal:vertical) will possess an adequate factor of safety. An engineering geologist should observe all cut slopes during grading to ascertain that no unforeseen adverse geologic conditions are encountered that require revised recommendations. All slopes are susceptible to surficial slope failure and erosion if not carefully constructed. Water should not be allowed to flow over the top of slope. Additionally, slopes should be planted with vegetation that will reduce the potential for erosion. Surface Drainage Final surface grades around structures should be designed to collect and direct surface water away from the structure and toward appropriate drainage facilities. The ground around the structure should be graded so that surface water flows rapidly away from the structure without ponding. Site irrigation should be limited to the minimum necessary to sustain landscape growth. Should excessive irrigation, impaired drainage, or unusually high rainfall occur, saturated zones of perched groundwater can develop. CONVENTIONAL RETAINING WALLS Lateral Earth Pressures The active earth pressure for the design of unrestrained retaining walls with sloping backfill can be taken as equivalent to the pressure of a fluid weighing 32 pcf, which corresponds to an internal angle of friction of 42 degrees. These values assume a granular backfill conforming to our report section entitled Imported Backfill and drained backfill condition. '1 ■ii ---.. --- - -• -.. --- - -..,. ---------- ,-,~ - _, - -- O'Day Consultants 7298 Sitio Lima Carlsbad, California May 16, 2018 SCST No. 170106N-04 Page4 Retaining walls should be designed to resist hydrostatic pressures or be provided with drainage in accordance with regional standards to reduce the accumulation of hydrostatic pressures. Backdrains may consist of a zone of ¾-inch crushed rock and weep holes. The crushed rock should be separated from the adjacent soils using a non-woven filter fabric, such as Mirafi 140N or equivalent. Damp proofing should be considered to reduce aesthetic staining on the wall face. If you have any questions, please call us at (619) 280-4321. Respectfully submitted, SCST, INC. Emil Rudolph, PE, GE 2767 Principal Geotechnical Engineer BJG:ER:dr:hu (1) Addressee via e-mail at Joannet@odayconsultants.com II ■ ii