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Split spoon penetration testing in gravels Daniel, Christopher Ryan

Abstract

The widely used "Standard Penetration Test" (SPT) is considered unreliable for gravel deposits because gravel particles can be larger than the opening of the SPT split-spoon sampler and because drilling methods normally employed for SPT in sands are often impractical in gravels. The "Large Penetration Test" (LPT) potentially reduces the effect of the former through the use of oversized split-spoon samplers. This thesis presents a method of predicting SPT from LPT blow counts so that currently available empirical design methods based on the SPT may be used in gravel deposits. The proposed method considers input energy and sampler dimensions and can be used with any LPT system (i.e. any combination of hammer and split-spoon). The results of the proposed method are compared to those of an existing correlation method and to empirical SPT-LPT correlation factors from the literature, including correlations for the "Japanese LPT" (JLPT) and "Italian LPT" (ILPT). In addition, three field research programs were conducted to develop an empirical correlation factor between the SPT and the "North American LPT" (NALPT). Field tests revealed that the proposed correlation method requires an empirical correction factor of 0.82. Review of the JLPT data set revealed that the SPT-JLPT correlation factor might be unreliable. If the JLPT data is excluded and if the empirical correction factor is applied, it is found that the correlation factors predicted using the proposed method range from 83% to 96% of those observed in sands. The equivalent range for the existing correlation method was 39% to 73%. The author attempted to obtain preliminary insight into the problem of grain size effects using the available test data. The observed SPT-NALPT and SPT-ILPT correlation factors appear to decrease with increasing grain size. Data illustrating a fair relationship between the observed correlation factor and the portion of the soil that is too coarse to enter the SPT split-spoon is presented.

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