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17 <br /> 3.0 CPT DATA INTERPRETATION <br /> Interpretation of cone penetration test (CPT) data can yield information on site <br /> stratigraphy, hydrogeology, and geotechnical parameters. The following sections briefly <br /> describe data interpretation methodologies for each of these three general data <br /> categories. More detailed information on this subject is available from the references <br /> cited in the text throughout this section. <br /> 3.1 STRATIGRAPHY <br /> The most common method of obtaining CPT-derived stratigraphic information is by means of <br /> established correlations between soil type and the measured cone tip and sleeve friction <br /> resistances. The soil stratigraphy interpretations, if provided for this project, were <br /> conducted using the correlation illustrated in Figure 3. The sleeve friction value is <br /> normalized with respect to the cone tip resistance to create the "friction ratio" <br /> parameter, which expresses the sleeve fiction as a percentage of the measured cone tip <br /> -- resistance. The cone tip resistance measurement is overburden-normalized to an effective <br /> overburden pressure of 1 ton/ft2,as follows: <br /> qci - qc CN (3) <br /> Where qct = overburden-normalized cone tip resistance in tons/ft2, <br /> - qc = measured cone tip resistance in tons/e, <br /> Ch = i -log av' (minimum value of 0.4), and <br /> a„' = effective vertical overburden stress in tons/ft2. <br /> The CPT-soil type correlation shown in Figure 3 was developed through comparison of <br /> side-by-sine CPT and conventional borehole sample laboratory tests,and is based on Earth <br /> Technology's experience throughout much of the Western United States. <br /> These correlations have proved to be applicable to most natural soil deposits. When <br /> applied to a given natural site, the level of uncertainty in the soil type predictions is <br /> — often limited to the range of soil classification occupying each band of the correlation <br /> chart. If necessary, CPT-derived soil type information can be verified by conducting a <br /> single CPT adjacent to a conventionally logged borehole, thereby creating a site-specific <br /> correlation which can then be extrapolated to all of the remaining CPT locations on the <br /> 1" site. <br /> 9 <br /> 1 111111111011 1 all <br />