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Geotechnical Engineering and Geological Hazard Study Lincoln Elementary School Modemization Project Manteca, California Page 1? 7.3 UNDERGROUND UTILITY TRENCHES Unless concrete bedding is required around utilities, pipe bedding should consist of sand with a sand equivalent of at least 30 or the pipe manufacturer's requirements, whichever is more restrictive. The pipe bedding should extend from 6 inches below the invert of the pipe to 1 foot above pipe the crown of the pipe. The pipe bedding material should be compacted to a minimum of 90 percent relative compaction or the manufacturer's recommendations if more stringent. Trench backfill above the pipe bedding zone should be placed in the same manner as required in Section 7.2.5, Engineered Fill Placement. On-site fill soils and "non-organic" native soils may be used as backfill in trenches above the pipe bedding. Utility trench backfill should be placed in layers not exceeding a loose lift thickness of 8 inches, uniformly moisture conditioned, and compacted to a minimum of 90 percent relative compaction. Compaction criteria for trench backfill above the bedding zone may be decreased to 85 percent relative compaction in landscape areas at least 5 feet beyond structural improvements, except in areas overlain by pavements, sidewalks, or other hardscapes. In landscape areas overlain by pavements, sidewalks, or other hardscapes, we recommend that the trench backfill be compacted to a minimum of 90 percent relative compaction to within 1 foot of the finished subgrade surface. The upper 1 foot should be compacted to 95 percent relative compaction in areas to receive AC pavement. 7.4 SURFACE DRAINAGE CONTROL Surface drainage should be planned to prevent ponding and to enable water to drain away from building foundations, slabs, and edges of pavements toward suitable collection of discharge facilities. A positive surface drainage of at least five percent should be provided within 10 feet of all building foundations. Elsewhere, positive surface drainage of at least two percent is recommended to allow for rapid removal of surface water. Pavements should also be designed with minimum gradients of about 2 percent in their principal direction of drainage, unless drainage reaches are short. Roof drainage systems should be planned to direct rainwater away from building foundations. A detailed drainage plan is outside the scope of this report but should be included in the preparation of the grading plans for the project. 8.0 FOUNDATION RECOMMENDATIONS 8.1 GENERAL FOUNDATION RECOMMENDATIONS All foundation improvements should be designed and constructed in accordance with the 2013 California Building Code, Title 24, Chapter 17A (Structural Tests and Special Inspections), Chapter 18A (Soils and Foundations), and all other sections applicable to the proposed structural improvements. Note that all stated preliminary bearing pressures in Section 8.0 are net values, and the weight of concrete in the portion of the foundations that extends below grade can be neglected in proportioning the foundations. Further evaluation of the subsurface may be warranted based on any other specific foundation designs not considered in this report. Site characteristics considered in selection of appropriate foundation system include the presence of (1) potentially liquefiable deposits under much of the Site. The use of engineered fill beneath shallow foundations systems, as described in Section 6.2.2, is recommended to improve the ability of the foundations and floor slabs to resist the adverse effects of seismically -induced ground deformation. Piping and utility connections should be designed to accommodate the estimated maximum foundation settlements. 13