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• -t3 <br />'7) Results of water soluble sulfate tests performed on soil <br />samples from tfie site indicate a low potential for sulfate <br />attack on Portland cement concrete. Concrete exposed to the <br />on-site soils should contain Type II certient and should be air <br />entrained. <br />Deep Foundations: A deep foundation system is recommended for <br />support of the dewatering structure if minor foundation movement <br />is required. The subsoils encountered at the site generally <br />appear to become more granular with depth. Because of the coarse <br />material encountered throughout the soil strata, a heavy steel <br />section "H"-pile or drilled pier will probably be needed. Other <br />types of piling systems niay be feasible which should be evaluated <br />on an individual basis. We expect ttie piling or pier will derive <br />most of the load capacity through skin friction. Static, dynamic <br />and test loading analyses can be used to determine the safe <br />allowable load. l•!e expect that piles will be driven to a speci- <br />fied resistance. Depth of piles or piers may be on the order of <br />30 to 40 feet. Load capacities of u0 to 60 tons and digher <br />should be possible. If a deep foundation system is selected for <br />support of the structure, we should be contacted to provide geo- <br />technical review of selected alternatives. <br />Thickener Structure: We expect the steel tank will be supported <br />on a prepared subgrade and compacted base material. The base may <br />be contained by a concrete ring footing or steel band. Potential <br />differential movement of the tank, prirtiar•ily due to subgrade <br />wetting, could be on the order of a few inches which we under- <br />stand should be tolerable. A lower risk of tank movement can be <br />Chen & Associates <br />