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HomeMy WebLinkAboutTract Map 20879-1 LOT 71 Soils ReportGeotechnical C Geologic C Coastal C Environmental 18451 Collier Avenue, Suite A, Lake Elsinore, California 92530 TEL: (951) 471-0700 - FAX: (951) 471-0702 www.geosoilsinc.com May 9, 2024 W.O. 8806-A-SC Premier Pools & Spas 26499 Jefferson Avenue, Unit E Murrieta, California 92562 Attention:Mr. Jon Slivick Subject:Geotechnical Retaining Wall Design Recommendations for 31920 Vineyard Avenue, Lot 71 of Tract 20879-1, City of Temecula, Riverside County, California (APN 953-073-024) Dear Mr. Slivick: In accordance with your request and authorization, GeoSoils, Inc. (GSI) is presenting geotechnical retaining wall design recommendations for the subject lot in the City of Temecula, Riverside County, California. The scope of our services has included review of available geologic data for the area, a site reconnaissance and soil sample collection, associated laboratory testing, analysis of data, and preparation of this summary report. SITE CONDITIONS AND PROPOSED DEVELOPMENT The residential property is located at 31920 Vineyard Avenue in the City of Temecula, Riverside County, California. The property was residentially developed as Lot 71 within Tract 20879-1. According to historical Google Earth Imagery and the Riverside County Information Technology “Map My County” website (RCIT, 2024), the overall tract was developed on hillside terrain, and construction was complete within the subject tract in 1987. No previous geotechnical or grading reports are currently available for review. Our review of the RCIT (2024) website, and mapping by the California Department of Conservation, California Geological Survey (CGS, 2018), indicates that the subject site does not lie within a County designated or State designated Alquist-Priolo fault zone, nor is the site susceptible to liquefaction. Based on the plans provided, it is our understanding that the property is proposed to be improved by the installation of a swimming pool, and approximately 6- and 8-feet tall retaining wall structures. The plans indicate a proposed concrete deck area between the two (2) proposed retaining walls to expand the usable areas of the rear yard. Currently, no specific retaining wall or structural plans have been provided for our review; however, the pool details site plan shows all three structures in plan-view. The need for import of fill APPROVED BY CITY OF TEMECULA PUBLIC WORKS david.pina 11/07/2024 11/07/2024 11/07/2024 11/07/20 soils for the proposed retaining wall backfill is currently not anticipated at this time, based on need for the wall foundation trenching and the existing excavated backcuts for the wall structures. OBSERVATIONS AND SAMPLE COLLECTION On April 25, 2024, GSI’s personnel performed a site reconnaissance of Lot 71 within Tract 20879-1 (31920 Vineyard Avenue), which included visual observations of the existing retaining wall backcuts, tactile probing of the proposed wall footing locations, and general soils conditions within the area of the proposed retaining walls. Observations and tactile probing indicated that the wall subgrade materials were excavated into firm and unyielding sedimentary bedrock materials. In addition, a representative soil sample was collected for appropriate laboratory testing. SOIL CONDITIONS General The earth material unit that was observed/exposed in the proposed retaining wall area, and mapped at the subject site (Tan and Kennedy, 2000), consisted of sedimentary bedrock of the Quaternary-age Pauba Formation. A general description of the material type is presented below. Quaternary-Age Pauba Formation As encountered/observed onsite, and as mapped by Tan and Kennedy (2000), sedimentary bedrock deposits assigned to the Quaternary-age Pauba Formation underlie the subject site. These sediments generally consist of light brown to brown sandstones and siltstones, with minor amounts of clay, are dense to very dense, and are considered suitable for supporting settlement-sensitive improvements and planned fills in their existing state. LABORATORY TESTING Classification Soils were classified visually according to the Unified Soils Classification System. The soil is classified as a clayey SAND (SC). Premier Pools & Spas W.O. 8806-A-SC 31920 Vineyard Avenue, Temecula May 9, 2024 File:e:\wp21\murr\rc8800\8806a.grw Page 2 Expansion Testing A representative sample of the near-surface site soils was evaluated for expansion potential. Expansion index (E.I.) testing and expansion potential classification were performed in general accordance with ASTM Standard D 4829. The results of the expansion testing are presented in the following table: SAMPLE LOCATION AND DEPTH (ft)EXPANSION INDEX EXPANSION POTENTIAL Grab Sample @ 0 - 1 21 Low E.I. = 0 to 20 - Very Low Expansion Potential; E.I. = 21 to 50 - Low Expansion Potential; E.I. = 51 to 90 - Medium Expansion Potential; E.I. = 91 to 130 - High Expansion Potential; E.I. > 130 - Very High (Critical) Expansion Potential WALL DESIGN PARAMETERS General Recommendations for the design and construction of conventional masonry retaining walls are provided below. Recommendations for specialty walls (i.e., crib, earthstone, mechanically stabilized earth [MSE], gravity, etc.) can be provided upon request, and would be based on site-specific conditions. Conventional Retaining Walls The design parameters provided below assume that either very low expansive soils (typically Class 2 permeable filter material or Class 3 aggregate base) or native onsite materials with an expansion index up to 50 are used to backfill any retaining wall. The type of backfill (i.e., select or native), should be specified by the wall designer, and clearly shown on the plans. Building walls, below grade, should be waterproofed. Waterproofing should also be provided for site retaining walls in order to reduce the potential for efflorescence staining. Retaining Wall Foundation Design Foundation design for retaining walls should incorporate the following recommendations: Minimum Footing Embedment - 18 inches below the lowest adjacent grade (excluding landscape layer [upper 6 inches]). Minimum Footing Width - 24 inches Premier Pools & Spas W.O. 8806-A-SC 31920 Vineyard Avenue, Temecula May 9, 2024 File:e:\wp21\murr\rc8800\8806a.grw Page 3 Allowable Bearing Pressure - An allowable bearing pressure of 2,500 per cubic foot (pcf) may be used in the preliminary design of retaining wall foundations, provided that the footing maintains a minimum width of 24 inches, and extends at least 18 inches into approved engineered fill overlying dense formational materials. This pressure may be increased by one-third for short-term wind or seismic loads. Passive Earth Pressure - A passive earth pressure of 250 pcf with a maximum earth pressure of 2,500 pounds per square foot (psf) may be used in the preliminary design of retaining wall foundations, provided the foundation is embedded into properly compacted silty to clayey sand fill. Lateral Sliding Resistance - A 0.35 coefficient of friction may be used for a concrete to soil contact when multiplied by the dead load. When combining passive pressure and frictional resistance, the passive pressure component should be reduced by one-third. Backfill Soil Density - Soil densities ranging between 125 pcf and 135 pcf may be used in the design of retaining wall foundations. This assumes an average engineered fill compaction of at least 90 percent of the laboratory standard (ASTM D 1557). Any retaining wall footings near the perimeter of the site will likely need to be deepened into unweathered bedrock deposits for adequate vertical and lateral bearing support. All retaining wall footing setbacks from slopes should comply with Figure 1808.7.1 of the 2019 CBC. GSI recommends a minimum horizontal setback distance of 7 feet as measured from the bottom, outboard edge of the footing to the slope face. Restrained Walls Any retaining walls that will be restrained prior to placing and compacting backfill material, or that have re-entrant or male corners, should be designed for an at-rest equivalent fluid pressure (EFP) of 55 pcf and 65 pcf for select and very low expansive native backfill, respectively. The design should include any applicable surcharge loading. For areas of male or re-entrant corners, the restrained wall design should extend a minimum distance of twice the height of the wall (2H) laterally from the corner. Cantilevered Walls The recommendations presented below are for cantilevered retaining walls up to 10 feet high. Design parameters for walls less than 3 feet in height may be superceded by City of Menifee standard design. Active earth pressure may be used for retaining wall design, provided the top of the wall is not restrained from minor deflections. An equivalent fluid pressure approach may be used to compute the horizontal pressure against the wall. Appropriate fluid unit weights are given below for specific slope gradients of the retained Premier Pools & Spas W.O. 8806-A-SC 31920 Vineyard Avenue, Temecula May 9, 2024 File:e:\wp21\murr\rc8800\8806a.grw Page 4 material. These do not include other superimposed loading conditions due to traffic, structures, seismic events, or adverse geologic conditions. When wall configurations are finalized, the appropriate loading conditions for superimposed loads can be provided upon request. Although not anticipated, the structural consultant/wall designer should incorporate any surcharge of traffic on the back of retaining walls where vehicular traffic could occur within horizontal distance “H” from the back of the retaining wall (where “H” equals the wall height). The traffic surcharge may be taken as 100 psf/ft in the upper 5 feet of backfill for light truck and cars traffic. This does not include the surcharge of parked vehicles, which should be evaluated at a higher surcharge to account for the effects of seismic loading. Equivalent fluid pressures for the design of cantilevered retaining walls are provided in the following table: SURFACE SLOPE OF RETAINED MATERIAL (HORIZONTAL:VERTICAL) EQUIVALENT FLUID WEIGHT P.C.F. (SELECT BACKFILL)(2) EQUIVALENT FLUID WEIGHT P.C.F. (NATIVE BACKFILL)(3) Level(1) 2 to 1 38 55 50 65 (1) Level backfill behind a retaining wall is defined as compacted earth materials, properly drained, without a slope for a distance of 2H behind the wall, where H is the height of the wall. (2) SE > 30, P.I. < 15, E.I. < 21, and < 10% passing No. 200 sieve. (3) E.I. = 0 to 50, SE > 30, P.I. < 15, E.I. < 21, and < 15% passing No. 200 sieve. Seismic Surcharge For engineered retaining walls with more than 6 feet of retained materials, as measured vertically from the bottom of the wall footing at the heel to daylight, GSI recommends that the walls be evaluated for a seismic surcharge (in general accordance with 2022 CBC requirements). The site walls in this category should maintain an overturning factor-of-safety (FOS) of approximately 1.25 when the seismic surcharge (increment) is applied. For restrained walls, the seismic surcharge should be applied as a uniform surcharge load from the bottom of the footing (excluding shear keys) to the top of the backfill at the heel of the wall footing. This seismic surcharge pressure (seismic increment) may be taken as 16H, where "H" for retained walls is the dimension previously noted as the height of the backfill to the bottom of the footing. The resultant force should be applied at a distance 0.6 H up from the bottom of the footing. For the evaluation of the seismic surcharge, the bearing pressure may exceed the static value by one-third, considering the transient nature of this surcharge. For cantilevered walls, the pressure should be applied as an inverted triangular distribution using 16H. For restrained walls, the pressure should be applied as a rectangular distribution. Please note this is for local wall stability only. The 16H is derived from a Mononobe-Okabe solution for both restrained cantilever walls. This accounts for the increased lateral pressure due to shakedown or movement of the Premier Pools & Spas W.O. 8806-A-SC 31920 Vineyard Avenue, Temecula May 9, 2024 File:e:\wp21\murr\rc8800\8806a.grw Page 5 sand fill soil in the zone of influence from the wall or roughly a 45° - N/2 plane away from the back of the wall. The 16H seismic surcharge is derived from the formula: Ph = d C ah C (tH Where:Ph =Seismic increment. ah =Probabilistic horizontal site acceleration with a percentage of “g.” (t =Total unit weight (125 to 135 pcf for site soils @ 90% relative compaction). H =Height of the wall from the bottom of the footing or point of pile fixity. Retaining Wall Backfill and Drainage Positive drainage must be provided behind all retaining walls in the form of gravel wrapped in geofabric and outlets. A backdrain system is considered necessary for retaining walls that are 2 feet or greater in height. Details 1, 2, and 3 present the backdrainage options discussed below. Backdrains should consist of a 4-inch diameter perforated PVC or ABS pipe encased in either Class 2 permeable filter material or ¾-inch to 1½-inch gravel wrapped in approved filter fabric (Mirafi 140 or equivalent). For select backfill, the filter material should extend a minimum of 1 horizontal foot behind the base of the walls and upward at least 1 foot. For native backfill that has up to E.I. = 20, continuous Class 2 permeable drain materials should be used behind the wall. This material should be continuous (i.e., full height) behind the wall, and it should be constructed in accordance with the enclosed Detail 1 (Typical Retaining Wall Backfill and Drainage Detail). For limited access and confined areas, (panel) drainage behind the wall may be constructed in accordance with Detail 2 (Retaining Wall Backfill and Subdrain Detail Geotextile Drain). Materials with an expansion index (E.I.) potential of greater than 20 should not be used as backfill for retaining walls. Retaining wall backfill materials should be moisture conditioned and mixed to achieve the soil’s optimum moisture content, placed in relatively thin lifts (6 to 10 inches), and compacted to at least 90 percent relative compaction. For more onerous expansive situations, backfill and drainage behind the retaining wall should conform with Detail 3 (Retaining Wall And Subdrain Detail Clean Sand Backfill). Outlets should consist of a 4-inch diameter solid PVC or ABS pipe spaced no greater than 100 feet apart, with a minimum of two outlets; one on each end. The use of weep holes only, in walls higher than 2 feet, is not recommended. The surface of the backfill should be sealed by pavement, or the top 18 inches compacted with native soil (E.I. # 50). Proper surface drainage should also be provided. For additional mitigation, consideration should be given to applying a waterproof membrane to the back of all retaining structures. The use of a waterstop should be considered for all concrete and masonry joints. Premier Pools & Spas W.O. 8806-A-SC 31920 Vineyard Avenue, Temecula May 9, 2024 File:e:\wp21\murr\rc8800\8806a.grw Page 6 12 inches (1) Waterproofing membrane Provide surface drainage via an engineered V-ditch (see civil plans for details) (5) Weep hole Proposed grade sloped to drain per precise civil drawings (4) Pipe (3) Filter fabric (2) Gravel 2:1 (h:v) slope 1:1 (h:v) or flatter backcut to be properly benched Slope or level Native backfill Very Low to Low Expansive soils, E.I. <50, P.I. <15 (1) Waterproofing membrane. (2) Gravel: Clean, crushed, 3 4 to 1 1 2 inch. (3) Filter fabric: Mirafi 140N or approved equivalent. (4) Pipe: 4-inch-diameter perforated PVC, Schedule 40, or approved alternative with minimum of 1 percent gradient sloped to suitable, approved outlet point (perforations down). (5) Weep holes: For CMU walls, Omit grout every other block, at or slightly above finished surface. For reinforced concrete walls, minimum 2-inch diameter weep holesspaced at 20 foot centers along the wall and placed 3 inches above finished surface. Design civil engineer to provide drainage at toe of wall. No weep holes for below-grade walls. (6) Footing: If bench is created behind the footing greater than the footing width using level fill or cut natural earth materials, an additional "heel " drain will likely be required by geotechnical consultant. Footing and wall design by others (6) Footing Structural footing or settlement-sensitive improvement H H/3 CMU or reinforced-concrete wall 6 inches (1) Waterproofing membrane (optional)Provide surface drainage via engineered V-ditch (see civil plan details) (5) Weep hole Proposed grade sloped to drain per precise civil drawings (4) Pipe (3) Filter fabric (2) Composite drain CMU or reinforced-concrete wall 2:1 (h:v) slope 1:1 (h:v) or flatter backcut to be properly benched Slope or level Native backfill Very Low to Low Expansive soils E.I. <50, P.I. <15 (1) Waterproofing membrane (optional): Liquid boot or approved mastic equivalent. (2) Drain: Miradrain 6000 or J-drain 200 or equivalent for non-waterproofed walls; Miradrain 6200 or J-drain 200 or equivalent for waterproofed walls (all perforations down). (3) Filter fabric: Mirafi 140N or approved equivalent; place fabric flap behind core. (4) Pipe: 4-inch-diameter perforated PVC, Schedule 40, or approved alternative with minimum of 1 percent gradient to proper outlet point (perforations down). (5) Weep holes: For CMU walls, Omit grout every other block, at or slightly above finished surface. For reinforced concrete walls, minimum 2-inch diameter weep holesspaced at 20 foot centers along the wall and placed 3 inches above finished surface. Design civil engineer to provide drainage at toe of wall. No weep holes for below-grade walls. (6) Gravel: Clean, crushed, 3 4 to 1 1 2 inch. (7) Footing: If bench is created behind the footing greater than the footing width using level fill or cut natural earth materials, an additional "heel " drain will likely be required by geotechnical consultant. (6) 1 cubic foot of 3 4 -inch crushed rock (7) Footing Footing and wall design by others Structural footing or settlement-sensitive improvement (1) Waterproofing membrane Provide surface drainage (5) Weep hole Proposed grade sloped to drain per precise civil drawings (4) Pipe (3) Filter fabric (2) Gravel CMU or reinforced-concrete wall 2:1 (h:v) slope 1:1 (h:v) or flatter backcut to be properly benched Slope or level (8) Native backfill (1) Waterproofing membrane: Liquid boot or approved masticequivalent. (2) Gravel: Clean, crushed, 3 4 to 1 1 2 inch. (3) Filter fabric: Mirafi 140N or approved equivalent. (4) Pipe: 4-inch-diameter perforated PVC, Schedule 40, or approved alternative with minimum of 1 percent gradient to proper outlet point (perforations down). (5) Weep hole: For CMU walls, Omit grout every other block, at or slightly above finished surface. For reinforced concrete walls, minimum 2-inch diameter weep holesspaced at 20 foot centers along the wall and placed 3 inches above finished surface. Design civil engineer to provide drainage at toe of wall. No weep holes for below-grade walls. (6) Clean sand backfill: Must have sand equivalent value (S.E.) of 35 or greater; can be densified by water jetting upon approval by geotechnical engineer. (7) Footing: If bench is created behind the footing greater than the footing width using level fill or cut natural earth materials, an additional "heel " drain will likely be required by geotechnical consultant. (8) Native backfill: If E.I. <21 and S.E. >35 then all sand requirements also may not be required and will be reviewed by the geotechnical consultant. (6) Clean sand backfill H ±12 inches H/2 minimum Heel width (7) Footing Footing and wall design by others Structural footing or settlement-sensitive improvement Wall/Retaining Wall Footing Transitions Site walls are anticipated to be founded on footings designed in accordance with the recommendations in this report. Should wall footings transition from cut to fill, the structural consultant/wall designer may specify either: a)A minimum of a 2-foot overexcavation and recompaction of cut materials for a distance of 2H from the point of transition. b)Increase of the amount of reinforcing steel and wall detailing (i.e., expansion joints or crack control joints) such that a angular distortion of 1/360 for a distance of 2H on either side of the transition may be accommodated. Expansion joints should be placed no greater than 20 feet on-center, in accordance with the structural engineer’s/wall designer’s recommendations, regardless of whether or not transition conditions exist. Expansion joints should be sealed with a flexible, non-shrink grout. c)Embed the footings entirely into native formational material (i.e., deepened footings). If transitions from cut to fill transect the wall footing alignment at an angle of less than 45 degrees (plan view), then the designer should follow recommendation "a" (above) and until such transition is between 45 and 90 degrees to the wall alignment. CONCLUSIONS Based upon our site reconnaissance, the test results obtained, and review of onsite geologic conditions, it is our opinion that the subject lot within Tract 20879-1 (31920 Vineyard Avenue) appears suitable for the proposed retaining wall improvements, so long as the design recommendations provided herein are properly implemented. SUMMARY OF RECOMMENDATIONS REGARDING GEOTECHNICAL OBSERVATION AND TESTING We recommend that observation or testing be performed by GSI at each of the following construction stages: •During excavation. •During placement of subdrains, toe drains, or other subdrainage devices, prior to placing fill or backfill. Premier Pools & Spas W.O. 8806-A-SC 31920 Vineyard Avenue, Temecula May 9, 2024 File:e:\wp21\murr\rc8800\8806a.grw Page 10 •After excavation of retaining wall footings, prior to the placement of reinforcing steel or concrete. •Prior to pouring any slabs or flatwork, after presoaking/presaturation of lots and other flatwork subgrade, before the placement of concrete or reinforcing steel. •During retaining wall subdrain installation, prior to backfill placement. •During slope construction/repair. •When any unusual soil conditions are encountered during any construction operations, after to the issuance of this report. •When any developer or owner improvements, such as flatwork, walls, drainage devices, etc., are constructed, prior to construction. •A report of geotechnical observation and testing should be provided at the conclusion of each of the above stages in order to provide concise and clear documentation of site work, or to comply with code requirements. LIMITATIONS The materials encountered on the project site and used for our analysis are believed representative of the area; however, soil and bedrock materials vary in character between excavations and natural outcrops or conditions exposed during mass grading. Site conditions may vary due to seasonal changes or other factors. Inasmuch as our study is based upon our review and engineering analyses and laboratory data, the conclusions and recommendations are professional opinions. These opinions have been derived in accordance with current standards of practice, and no warranty, either express or implied, is given. Standards of practice are subject to change with time. GSI assumes no responsibility or liability for work or testing performed by others, or their inaction; or work performed when GSI is not requested to be onsite to evaluate if our recommendations have been properly implemented. Use of this report constitutes an agreement and consent by the user to all the limitations outlined above, notwithstanding any other agreements that may be in place. In addition, this report may be subject to review by the controlling authorities. This report brings to completion our scope of services for this portion of the project. Premier Pools & Spas W.O. 8806-A-SC 31920 Vineyard Avenue, Temecula May 9, 2024 File:e:\wp21\murr\rc8800\8806a.grw Page 11 The opportunity to be of service is sincerely appreciated. If you should have any questions, please do not hesitate to contact our office. Respectfully submitted, GeoSoils, Inc. Todd A. Greer Stephen J. Coover Engineering Geologist, CEG 2377 Geotechnical Engineer, GE 2057 TAG/SJC/ef Enclosure:Appendix - References Distribution:(1) Addressee (PDF via email) Premier Pools & Spas W.O. 8806-A-SC 31920 Vineyard Avenue, Temecula May 9, 2024 File:e:\wp21\murr\rc8800\8806a.grw Page 12 APPENDIX REFERENCES American Concrete Institute, 2015, Guide to concrete floor and slab construction (ACI 318-15): reported by ACI Committee 302, dated June. _____, 2014a, Building code requirements for structural concrete (ACI 318-14), and commentary (ACI 318R-14): reported by ACI Committee 318, dated September. _____, 2014b, Building code requirements for concrete thin shells (ACI 318.2-14), and commentary (ACI 318.2R-14), dated September. American Society of Civil Engineers, 2018a, Supplement 1 to Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE/SEI 7-16), first printing, dated December 13. _____, 2018b, Errata for Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE/SEI 7-16), by ASCE, dated July 9. _____, 2017, Minimum design loads and associated criteria and other structures, ASCE Standard ASCE/SEI 7-16, published online June 19. _____, 2010, Minimum design loads for buildings and other structures, ASCE Standard ASCE/SEI 7-10. Bryant, W.A., and Hart, E.W., 2007, Fault-rupture hazard zones in California, Alquist-Priolo earthquake fault zoning act with index to earthquake fault zones maps; California Geological Survey, Special Publication 42, interim revision. California Building Standards Commission, 2022, California Building Code, California Code of Regulations, Title 24, Part 2, Volumes 1 and 2, based on the 2021 International Building Code, effective January 1, 2023. California Code Of Regulations, 2011, CAL-OSHA State of California Construction and Safety Orders, dated February. California Department of Conservation, California Geological Survey (CGS), 2018, Earthquake fault zones, a guide for government agencies, property owners/developers, and geoscience practitioners for assessing fault rupture hazards in California: California Geological Survey Special Publication 42 (revised 2018), 93 p. County of Riverside Transportation and Land Management Agency, Building and Safety Department, Planning Department, Transportation Department, 2000, Technical guidelines for review of geotechnical and geologic reports. Riverside County Information Technology (RCIT), Graphic Information Services (GIS), 2024, M ap M y C ount y, w e bsi te: ht tp://mmc.rivco it .org/M M C _Publi c/ Viewer.html?Viewer=MMC_Public. State of California, 2024, Civil Code, Sections 895 et seq. Tan, S.S. and Kennedy, M.P., 2000, Geologic map of the Temecula 7.5' quadrangle, San Diego and Riverside Counties, California: a digital database, California Division of Mines and Geology, version 1.0. Premier Pools & Spas Appendix File:e:\wp21\murr\rc8800\8806a.grw Page 2