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GREGG IN SITU, INC. ADVANCED GEO December 5, 2002 Hess DuBois 02-171 ma Stockton, Ca. In situ groundwater samples were taken at four locations. Groundwater samples were collected using a Hydropunch® type groundwater sampling system (figure 2). The groundwater sampler operates by pushing 1.75 inch diameter hollow rods with a retrievable tip. A stainless steel filter screen is attached to the tip. At the desired sampling depth, the rods are retracted exposing the filter screen and allowing for groundwater infiltration. A small diameter bailer is then used to collect groundwater samples through the hollow rod. 3.0 CONE PENETRATION TEST DATA & INTERPRETATION The cone penetration test data is presented in graphical form. Penetration depths are referenced to existing ground surface. This data includes CPT logs of measured soil parameters and a computer tabulation of interpreted soil types along with additional geotechnical parameters and pore pressure dissipation data. The stratigraphic interpretation is based on relationships between cone bearing (qc), sleeve friction ft), and penetration pore pressure (U). The friction ratio (RD, which is sleeve friction divided by cone bearing, is a calculated parameter which is used to infer soil behavior type. Generally, cohesive soils (clays) have high friction ratios, low cone bearing and generate large excess pore water pressures. Cohesionless. soils (sands) have lower friction ratios, high cone bearing and generate little in the way of excess pore water pressures. Pore Pressure Dissipation Tests (PPDT's) were taken at various intervals in order to measure hydrostatic water pressures and approximate depth to groundwater table. In addition, the'PPDT data can be used to estimate the horizontal permeability (kh) of the soil. The correlation to permeability is based on the time required for 50 percent of the measured dynamic pore pressure to dissipate 050). The PPDT correlation figure (figure 3) is provided in the Appendix. The interpretation of soils encountered on this project was carried out using recent correlations developed by Robertson et al, 1990. It should be noted that it is not always possible to clearly identify a soil type based on qc, fs and U. In these situations, experience and judgement and an assessment of the pore pressure dissipation data should be used to infer the soil behavior type. The soil classification chart (figure 4) used to interpret soil types based on•gc and Rf is provided in the Appendix. Interpreted output requires that depth of water be entered for calculation purposes, where depth to water is unknown an arbitrary depth in excess of 10 feet of the deepest sounding is entered as the groundwater depth.