Effects of grain shape on the standard penetration test and particle packing

Coarse soils can contain flaky grains in addition to rounded or angular grains, along with a varying fines content. Depending on the regional geology, however, the mica grain content can be remarkable, reaching 30 % or higher. Therefore, it is reasonable to expect that mica grains would affect the soil behaviour. In this study, soils of a delta deposit that are known to involve mica grains were examined. The river sand was considered as the host material and the mica grain contents were determined by means of the flotation technique. A correlation between the mica content as found using the flotation technique and XRD count numbers obtained using an X-ray diffraction test method for each soil sample was established. The standard penetration test (SPT) blow counts from various boreholes were interpreted from the mica content’s influence point of view. The results showed that the mica grains would reduce the SPT resistance at certain fines-content, host-sand, mica-grain combinations. The reduction in the SPT resistance as a result of the presence of mica grains might reach eight units at depths close to the ground surface. This influence is expressed by means of a dimensionless parameter (MCef); however, it diminished with an increasing effective stress and fines content. The findings of the present study show that the influence of particle shape on the overall soil behaviour deserves further study.