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Geotechnical Investigation Report 03/11/2025 2234 S Lowell St., Santa Ana, CA 92707 Page | 11 After clearing and grading the site, excavate at least two (2) feet below the building’s footprint, scarify the upper 8 inches of the soil, bring the moisture content to near optimum moisture (around 8%) and compact it to at least 90% of relative compaction, then replace the removed soil using 6-8 inch-thick lifts compacted to at least 95% of relative compaction. Upon completing the over-excavation work, the foundation trenches can be excavated to the recommended foundation depth. The foundation bottom surface should be the over-excavated soils. The on-site soils may be used as trench backfill provided, they are screened of rock sizes over 6 inches in maximum dimension and organic matter (in case encountered). Trench backfills should be compacted in uniform lifts (not exceeding 8 inches in compacted thickness) by mechanical means to at least 90 percent relative compaction (based on ASTM D 698). CONCRETE SLABS Interior concrete slabs should have a minimum thickness of 4 inches and be underlain by a 10- mil visqueen moisture retarder barrier underlain with a 2-inch layer of clean sand (sand equivalent of at least 30). The visqueen moisture barrier should be overlain by a 2-inch layer of clean sand to aid in concrete curing. All slabs should be constructed with preferred minimum reinforcement consisting of No. 3 bars placed mid-height in the slab and spaced on 18-inch centers in both directions. Crack control joints should be provided in accordance with the recommendations of the project structural engineer. Exterior concrete flatwork (sidewalks, etc.) should have a minimum thickness of 4 inches, be underlain by a 2-inch layer of clean sand, and reinforced with a minimum. No. 3 bars placed mid- height in the slab and spaced 18-inch on centers in both directions. Care should be taken by the contractor to ensure that the reinforcement is placed and maintained at slab mid-height. We recommend that crack control joints for exterior flatwork be provided with a minimum spacing of 12 feet and a maximum of 15 feet, or in accordance with the structural engineer's recommendations. We also recommend that every third control joint be converted to an expansion joint. Some slab cracking due to shrinkage should be anticipated. The potential for this slab cracking may be reduced by careful control of water/cement ratios. The contractor should take appropriate curing precautions during the pouring of concrete in hot weather to minimize cracking of slabs. We recommend that a slipsheet (or equivalent) be utilized if crack-sensitive flooring is planned directly on concrete slabs. All slabs should be designed in accordance with structural considerations. SURFACE AND SUBSURFACE DRAINAGE We recommend that measures be taken to properly finish grade the site, such that surface drainage is directed away from structure foundations, floor slabs, and tops of slopes, at a 2 percent minimum grade for a minimum distance of 5 feet for subgrade, and 1 percent minimum grade for a minimum distance of 5 feet for hard finish surface (pavement, walkways etc.). Ponding of water should not be permitted, and installation of roof gutters which outlet into a drainage system is considered prudent. Planting areas at grade should be provided with positive drainage directed away from all buildings.