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Luizkv Associates Development. LP - Geotechnical Investigation <br />MACTEC ProJect 4953-03-2631 <br />September 18.2003 <br />due to arching in the soils. For clear spans of up to 8 feet, we recommend that the lagging be <br />designed for a semi-circular distribution of earth pressure where the maximum pressure lS 400 <br />pounds per square foot at the mid-line between soldier piles, and 0 pounds per square foot at the <br />soldier piles. <br />6.11 GRADING <br />Because of the expansive nature of the on-site clay soils, precautions should be taken to reduce the <br />potential heaving of concrete slabs-on-grade. A layer of relatively non-expansive, predominantly <br />granular soils is recommended immediately beneath the floor slabs, and all concrete walks and <br />slabs. This select non-expansive granular soil should contain sufficient fines so as to be relatively <br />impermeable when compacted. <br />*A 2-foot-thick layer of.non-expansive soils would normally be considered adequate. However, if it <br />is desired to provide even greater protection against heaving of such slabs, a thicker layer of non- <br />expansive soils could be used. (Based on our experiences at nearby projects in Santa Ana, Irvine <br />and Costa Mesa non-expansive soils up to four feet in thickness have been used where the slab is <br />considered critical to differential movement; this greater thickness may be used if considered <br />appropriate by the client.) <br />Good drainage of surface water, preferably away from the proposed Data Center, should be <br />provided by providing adequate slopes to all graded and paved surfaces. Where good surface <br />drainage is not possible, subdrains should be provided within planter and other irrigated areas to <br />prevent accumulation of water within the upper soils. Proper drainage will be important to <br />minimize infiltration of water into the subgrade soils. Cut-off walls achieved by deepening curb <br />sections or grade beams around planters and landscaping or other comparable barriers are also <br />recommended to minimize lateral flow of irrigation water beneath adjacent slabs and paving. <br />If grading is performed during the rainy season, the subgrade soils may become wet and soft. It <br />may then be necessary to place a layer of crushed rock or a geo-membrane, or both, over the <br />exposed soils to provide a competent base for the compaction of overlying fill. In this case, the <br />natural soils should be carefully excavated prior to placing the crushed rock layer or geo- <br />30