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Geotechnical Engineering and Geological Hazard Study Lincoln Elementary School Modernization Project Manteca, California Page i i 7.2.: Engineered Fill Materials Engineered fill used for the project should be either 1) select import engineered fill, or 2) general on-site sandy soils with 'less than 3 percent organic content. Select import engineered fall should be inorganic, have an R -value of at least 50, and plastic index less than 4. In addition, select import engineered ill should meet the following particle -size gradation: Sieve Opening Percent Passing, by Dry Weight 4 -inch square 100 3/4 -inch square 70 minimum U.S. No. 4 60 minimum U.S. No. 200 40 maximum Fill material that does not meet the above criteria should be tested under the direction of the Geotechnical Engineer of Record to determine if it has engineering properties equivalent to, or better than, the existing site materials. Samples of any proposed imported fill material should be submitted to the Laboratory of Record for testing and approved by the Geotechnical Engineer of Record prior to being brought to the site. General on-site engineered fill should be inorganic, contain no rocks greater than 4 -inches in least dimension, and be free of deleterious materials. Soils containing more than 3 percent by weight of organic material should be considered organic. Our subsurface data and laboratory test data indicate that the near - surface soil encountered in the borings generally meets the criteria for on-site engineered fill. However, the deeper soils are also classified as clay or silt containing more than 50 percent passing the No. 200 sieve and should not be placed in the upper 2 feet of subgrade. 7.2.5 Engineered Fill Placement Engineered fill should be placed in a series of horizontal layers not exceeding 8 inches in loose thickness, uniformly moisture -conditioned, and compacted to achieve a minimum relative compaction of 90 percent of the ASTM D1557 maximum dry density. Non -expansive fill soils and native silts and sands should be uniformly moisture conditioned to between I and 3 percentage points above the optimum moisture content. Fill soils composed of clays (such as deep utility backfill) should be uniformly moisture conditioned to between 3 and 5 percentage points above the optimum moisture content. Additional fill Iifts should not be placed if the previous lift did not meet the required relative compaction or if soil conditions are not stable. Discing, tilling, and/or blending may be required to uniformly moisture - condition soils used for engineered fill. The upper 12 inches of pavement subgrades should be compacted to at least 95 percent relative compaction by the CAL 216 test procedure. 7.2.6 Excavations Excavations will typically encounter compacted engineered fill and unconsolidated silts and sands. These materials can be easily excavated with conventional earthmoving equipment. We anticipate that temporary excavations less than 5 feet deep and above groundwater may be cut as steep as 1''/2H: IV (horizontal to vertical). Deeper cuts should be considered on a case-by-case basis. All open cuts should be in compliance with applicable Occupational Safety Health Administration (OSHA) regulations (California Construction Safety Orders, Title 8) and should be monitored for evidence of incipient instability. The final inclination of both permanent cut and permanent fill slopes above the groundwater level should be made no steeper than 2H:1 V. N9