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TECHNICAL MEMORANDUM <br />Page 14 <br />June 3, 1992 <br />SAC31583.AC.ZZ <br />A key assumption used to estimate foundation settlement was that similar material types will <br />exhibit similar consolidation properties throughout the landfill area. Data obtained during <br />the subsurface exploration, however, indicated that the clay layers in which consolidation <br />tests were performed exhibited wide variations in density. Accordingly, because the <br />consolidation tests were performed on relatively compressible samples and relatively stiffer <br />clay zones occur at various depths, the foundation settlement estimates presented are likely <br />conservative. Also, since no geotechnical subsurface information (SPT blow -counts or shear <br />strength) was available for depths greater than 178 feet, an approximate, order -of -magnitude <br />settlement estimate was made using an elastic theory approach. Actual foundation <br />settlement values measured in the field may therefore vary from the values reported in this <br />technical memorandum. <br />Because of the anticipated landfill extension refuse loads, it is estimated that foundation <br />settlement in the clay layers will consist of both recompression settlement and virgin <br />compression settlement. A summary of the consolidation properties used in the analysis are <br />presented in Table 3. <br />Table 3 <br />Summary of Consolidation Test Results used in Foundation Settlement Analysis <br />Sample soil <br />Boring Depth Type <br />No. (ft) (USCS) <br />Slope of <br />Reoompression <br />Curve (C,) <br />Slope of <br />Compression <br />Curve (CJ <br />Preoonsolidation <br />Pressure <br />(psf) <br />Overoonsolidation <br />Ratio <br />(OCR) <br />BH4 33.0-35.5 ML <br />'. 0.01 <br />0.10 <br />14,000 <br />3 <br />BH -1 76.0-785 CL <br />0.02 <br />0.14 <br />16,000 <br />1.7 <br />BH -2 48.0-505 CL <br />0.03 <br />0.13 <br />8,000 <br />1.4 <br />The OCRs shown in Table 3 were determined based on the original groundsurface contour <br />and estimated groundwater table elevation at the time of drilling. <br />Results of Analyses <br />The greatest magnitude of total foundation settlement is anticipated to occur in the area of <br />maximum refuse height, in the area near Boring BH -1. Total, settlement at this location is <br />estimated to be up to 2 feet. Foundation settlement for interim fill conditions will be <br />smaller than this estimated settlement. Subsurface material encountered during our <br />exploration was typically very sandy, and the clay material that was encountered was <br />C <br />11 <br />