The URL can be used to link to this page

Home My WebLink About1584 E Santa Clara Ave - Soils Report€ Leighton and Associates, lnc A LEIGHTON GROTJP COMPANY June 7, 2018 Project No. 11932.003 Taylor Morrison Services, lnc. 100 Spectrum Center Drive, Suite 1450 lrvine, CA 92618 Attention: Mr. Sean Doyle Subject:Geotechnical Review of Precise Grading Plans Proposed Residential Development Avery at the Grove, Tnct'i.7231 City of Santa Ana, California ln accordance with your request, Leighton and Associates, lnc. (Leighton) has reviewed the precise grading plans for the subject project. lt should be noted that Leighton has been retained as the geotechnical consultant of record for the project as documented in our referenced report (Leighton, 2018b). The precise grading plan was reviewed with respect to the geotechnical aspects of the project. The reviewed plan set, Precise Grading/Plot Plan, Lyon Street, Buffalo Avenue and Santa Clara Avenue, Tract 17231 , 1584 E. Santa Clara Avenue, Santa Ana, California, with Delta 1 revisions, was prepared by Hunsaker & Associates lrvine, lnc. and dated May 29, 2018. The reviewed plan set contains eight (8) sheets, and was received electronically by us on May 3'l , 2018. The plans indicate precise grading details for the residential lots for the project, including the model lots (Lot Nos. 22 and 23) and associated temporary parking lot for the model homes. ln addition, the plans indicate erosion control details. \ \\ N U\I T h \ N',. \il r-l INTRODUCTION PRECISE GRADING PLAN 11932.003 Review of Sheet 4 of 8 indicates a short retaining wall (3 feet tall) at the rear of Lots 13 and 14 with a minor 2:1 (horizontal:vertica l) slope ascending beyond the wall to the residential lots behind Lots 13 and 14. These walls were added to the plans as part of the Delta 1 revision. lt was noted that the previous geotechnical investigation report for the project by Alta (2015) did not include geotechnical design recommendations for sloped backfill above retaining walls; therefore, we are providing supplemental geotechnical recommendations in this letter to support design of the proposed retaining walls associated with Lot Nos. 13, 14 and 16. lt is our understanding that the retaining walls shown on the plans along the southern boundary of the development and the short section of retaining wall along the western boundary at Lot 2 have already been constructed. PLAN REVIEW ANO RECOMMENDATIONS Based on our review, the reviewed precise grading plan set is considered acceptable from a geotechnical standpoint provided the following recommendations are incorporated with regard to the design of the planned retaining walls and driveway pavement for the project: Desiqn Recommendations for Retaininq Walls Review of precise plans indicates the planned retaining walls are typically 3 to 4 feet in height. The wall along Lots 13 and 14 is located at the back of the lots with the adjacent properties being somewhat higher in elevation. The wall along Lot 16 is located along the western side of the lot with the lot being somewhat higher in elevation than the adjacent street and sidewalk right-of way. Backfill Retaining structures planned al the site should be backfilled with granular (SE > 30), very low expansive (El < 20) free-draining soil throughout the zone of lateral pressure influence. All backfill should be mechanically compacted in layers; flooding should not be permitted. Proper compaction of backfill will be necessary to minimize settlement of the backfill and to minimize settlement of overlying slabs, concrete flatwork, and paving. Backfill should be compacted to at least 90% of the maximum dry density obtained by ASTM Test Method D1557. The excavated soils may be used in the compacted backfill; however, cobbles larger than six inches in diameter should be omitted from the backfill to minimize possible damage to the walls. Also, cohesive soils with significant clay content should not be used for backfill behind walls. The soils used in the upper foot of the backfill zone are recommended to consist of low expansive onsite soils. 2 € Leighton 1 1932.003 Late ra I E a rth Pressures The following parameters are recommended to be used for the design of retaining structures less than 6 feet in height based on the assumed type of low expansive, granular backfill material as described above. Table 1 - Retaining Wall Design Parameters Condition Equivalent Fluid Unit Weight (psf/ft) Active Earth Pressure At-Rest Earth Pressure Allowable Passive Earth Pressure Coefficient of Sliding Friction Unrestrained walls that are free to rotate or deflect may be designed using the active earth pressure. The at-rest condition should be used for restrained walls that are fixed against rotation. The atrest pressure should also be used for design of walls supporting settlement-sensitive structures, such as adjacent roadways and structures. Resistance to lateral loads will be provided by the friction acting along the bottom of the footing and the passive pressure along the front of the foundation and footing key (if included in design). The lateral passive resistance should be used in design only if the footings are cast in direct contact with vertical side walls within structural compacted fill and the support characteristics of the soils in front of the footing will not degrade with time. Protection of the soils typically consists of covering the ground surface with an impervious surface. The above-recommended lateral pressures were based on a soil total (compacted) unit weight of 125 pounds per cubic foot (pcf) and an angle of internal friction of 32 degrees. Revision to the parameters may be necessary if the soils used in construction exhibit different properties. Backfill for retaining walls should be compacted to a minimum of 90 percent relative compaction based on ASTM Test Method Dl557. Relatively light construction equipment should be used to backfill the retaining walls and the walls are recommended to be externally supported during backfilling and compaction operations. 3 € Leighton 38 (Level Backfill) 64 (2H:1V Backfill) 55 (Level Backfill) 92 (2H:1V Backfill) 250 with a maximum of 2,500 psf (Level grade in front of wall) 0.30 1 1932.003 Lateral pressures from other surcharge and superimposed loads (for example, from vehicle traffic and adjacent structures) should be added to the above recommended lateral earth pressures if the loads fall within a projected area of an imaginary line extended at an angle of 45 degrees from the wall foundation. The surcharge may be modeled as a uniform lateral pressure equal to 33 percent of the surcharge pressure for unrestrained walls and 50 percent of the surcharge pressure for restrained walls. The foundations for walls located within the proposed development (e.9., Lot Nos. '13 and 14) and not along the perimeter of the development may be designed for a maximum, net allowable soil bearing pressure of 2,000 pounds per square foot (psf) provided the footings extend at least 1 foot into suitable beaning soil and are supported at least 18 inches below finish adjacent grade. The minimum foundation width is recommended to be 18 inches. Design of the foundations for the retaining walls along the property lines will require careful evaluation of the soil conditions exposed in footing excavations to verify suitable bearing conditions exist. Due to lhe locations of these walls along the property line, the actual lateral and vertical extent of fill placed during rough grading cannot be verified cannot be established from the available grading report. Therefore, wall construction is anticipated to require increase in footing embedment depth to verify embedment in suitable bearing native soils. However, care must be used to avoid undermining adjacent properties thereby requiring deepened trenches to be excavated in a slolcut manner with the deepened trenches backfilled with a lean cement slurry to planned bearing grade. The individual slots are recommended to be no greater than 6 to 8 feet in length depending upon the actual required depth of excavation. The allowable passive equivalent fluid pressure is recommended to be 200 pcf to a maximum of 2,000 psf. 4 € Leighton Foundation Desiqn Based upon the grading operations reported to have been performed and documented during rough activities (Alta, 2017c), suitable bearing structural compacted fill is expected to exist at nominal bearing grade. The minimum depth of structural compacted fill below foundations is recommended to be 3 feet. Based on the reported grading activities, the structural fill requirements are anticipated to exist without the need for additional overexcavation and recompaction, but field conditions should be verified during construction. 11932.003 Drainaqe The lateral active and at-rest pressure values presented in Table 1 are based upon drained conditions behind the wall. Therefore, design of the retaining walls should include provisions for drainage such as a permanent subdrain at the base of the wall that is sloped at a minimum of one percent toward an approved non-erosive outlet. The subdrain is recommended to consist of 4-inch diameter perforated pipe (perforations at bottom) embedded within a free-draining, clean %-inch nominal diameter crushed aggregate (typically 1 cubic foot per lineal foot) wrapped in filter fabric. Surface drainage should be designed to direct water away from foundations and toward approved drainage devices. lrrigation of landscaping should be controlled to maintain, as much as possible, consistent moisture content sufficient to provide healthy plant growth without ovenltratering. Review of the precise grading plans indicates the garage driveways will consist of Portland cement concrete of a thickness in accordance with the recommendations of the geotechnical engineer. Recommendations specific to driveway pavement were not presented in the referenced geotechnical reports by Alta (2015, 2017a,2017b,2017c and 2018). Therefore, we recommend that the driveways consist of a minimum S-inch thick Portland cement concrete pavement supported by a properly prepared subgrade. Preparation of the subgrade prior to concrele placemenl is recommended to include scarification, moisture conditioning as necessary followed by recompaction of the soils to a minimum of 90 percent of the ASTM D1557 maximum dry density. Unless superseded by the recommendations presented in this report, the recommendations presented in our previous report (Leighton, 201 8b) and the referenced reports by Alta (2015, 2017a, 2O17b, 2017c and 2018) remain valid and should be incorporated in the design and construction of the project. 5 € Leighton Drivewav Pavement Desiqn Considerations 1 '1932.003 CLOSURE We appreciate the opportunity to be of service to you on this project. lf you have any questions, or if we can be of further service, please contact the undersigned at your convenience. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC )- J Jeffrey M. Pflueger, PG, CEG 2499 Associate Geologist John E. Haertle, PE, GE 2352 Associate Engineer JMP/JEH/lr Attachment: References Distribution: (1 ) Addressee € JEFFRFTM. PFLUEOER No.2/tS t* OF l,lo. 2352 OF * m * ao6 6 Leighton $5-=-- 1 1932.003 Alta California Geotechnical, lnc., 2015, Preliminary Geotechnical lnvestigation, Tentative f racl 17231, Santa Clara Avenue, City of Santa Ana, California, Project No. 1-0173, dated September 14, 2015. _, 2017a, Rough Grading Plan Review, f racl 17231, Located Off Santa Clara Avenue, City of Santa Ana, California, Project No. 1-0173, dated February 14, 2017. _, 2017b, Precise Grading Plan Review, Tract 17231 , Located Off Santa Clara Avenue, City of Santa Ana, California, Project No. 1-0173, dated October 3, 2017. _,2017c, Project Grading Report, Lots 2 through 15 and 20 through 23, Tentative f racl 17231 , Santa Clara Avenue, City of Santa Ana, California, Project No. 1- 0173-G, dated December 15,20'17 . _,2018, Pavement Design Recommendations, Santa Clara Avenue, Lyon Street and Buffalo Avenue, f racl 17231, City of Santa Ana, California, Project No. 1- 0173-G, dated January 4,2018. Leighton and Associates, lnc., 2018a, Geotechnical Due Diligence Review, lracl 17231 , 1585 Santa Clara Avenue, Santa Ana, California, Project No. 'l 1932.002, dated March 7,2018. _, 2018b, Change of Consultant Letter and Geotechnical Review of Foundation Plans, Proposed Residential Development - Avery at the Grove, ftact 17231, Phases 1 & 2 and Models, Lots 3-15 and 22-23, City of Santa Ana, California, Project No. 1 1932.003, dated May 11 ,2018. € Leighton REFERENCES