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7.A. - Page 65 <br />■ site grading, including criteria for fill quality and compaction <br />■ the appropriate foundation type for the proposed building <br />■ subgrade preparation for secondary slab -on -grade construction (such as exterior walkways, steps, and <br />approach ramps) <br />■ retaining walls <br />■ excavation and shoring <br />■ dewatering considerations <br />■ stormwater infiltration/bioretention considerations <br />■ utilities (trenching for utility infrastructure) <br />The above interrelated issues are detailed in the geotechnical report, which also includes the technical data and <br />analysis of one exploratory boring and three cone penetration tests performed on the project site, and installation of <br />one vibrating wire piezometer (VWP) for long-term groundwater monitoring. The summary below is intended to <br />give the reader an overview of the primary geotechnical issues. The professional engineering -level discussion is in <br />the original report by ENGEO. <br />The geotechnical report (cover letter and p. 5) concludes, "[Tjhe site is suitable for the proposed development <br />provided the recommendations and guidelines provided in this report are implemented during project planning, <br />design and construction. " The report's conclusions and recommendations (pp. 5 through 18) focus on the following <br />project -specific geotechnical concerns, based on laboratory testing of on-site soil samples and the application of <br />City and State regulations: <br />■ potentially liquefiable soil <br />■ groundwater depth <br />■ presence of soft to medium stiff clayey deposits <br />The following information is taken directly from the ENGEO geotechnical report. The report recommends feasible <br />solutions to the identified issues and concerns. For example: <br />Potentially Liquefiable Soil <br />■ Depending on the depth of the garage finished grade, potentially liquefiable soil ranging from I to 2 feet thick <br />may be exposed at bottom of the excavation resulting in an unstable soil condition and the potential for <br />liquefaction -induced ground softening at the base of the foundation. The risk of liquefaction -induced ground <br />softening may be reduced by over -excavation and recompaction of the potentially liquefiable soils exposed at <br />the base of the excavation. (p. 8) ENGEO recommends that the garage foundation level be supported on at <br />least 2 feet of engineered fill to reduce the risk of liquefaction -induced ground rupture and differential soil <br />movement, or as an alternative, the garage pad can be chemically treated. (p. 13) <br />Groundwater Depth <br />■ Depending on the depth and time of year of construction, excavations for the parking garage and deep utilities <br />will likely encounter groundwater; and temporary dewatering measures would be necessary. (p. 8) <br />Presence of Soft to Medium Stiff Clavev Deposits <br />■ Major considerations in foundation design for this project are the potential impacts of liquefaction, shallow <br />groundwater conditions, and the potential presence of soft to medium stiff clayey deposits. In order to reduce <br />the effects of these geotechnical concerns, the foundation should be sufficiently stiff to move as a rigid unit with <br />tolerable differential movements. ENGEO recommends a mat foundation for the proposed structure. (p. 12) <br />Other Recommendations <br />Ground Shaking: All structures should be designed using sound engineering judgment and the latest California <br />Building Code (CBC) requirements, as a minimum (p. 6). <br />Foundation Settlement: Thin layers of silty sand and soft to medium stiff clayey deposits were encountered <br />between 10 to 15 feet bgs (below ground surface) and at approximately 25 feet bgs. Depending on the finished <br />grade of the lowest garage level, soft clayey deposits may be exposed at foundation elevation. ENGEO <br />recommends contract specifications (see Appendix F of the ENGEO report) that prescribe measures and <br />standards for erosion control and soil reinforcement; excavation, fill, and subdrains; and other items related to <br />earthwork materials and procedures. These recommended contract specifications would be subject to City <br />review and approval. (p. 9) <br />Expansive Soils: The highly expansive soil would be excavated and off -hauled during construction. Highly <br />expansive soils underlying the base of the foundation are not expected to exhibit significant shrink -swell action <br />due to the level of saturation and the weight and mass of the building (permanent building loads). (p. 9) <br />18 <br />