Effect of Fine-Grained Particles and Sensitivity Analysis of Physical Indexes on Residual Strength of Granite Residual Soils

Recently, stability analyses of structures built of granite residual soils, for example, earth dams or other urban structures, particularly when under vibration, are being recognized as much more important than previously imagined. In such analyses, it is emphasized that the residual strength should be utilized considering the seismic effect. Therefore, the residual strength of granite residual soils must be evaluated accurately in order to reduce the damage to structures built on them. This paper presented a laboratory study designed to examine the effect of fine-grained particles (FGPs; particle size <= 0.075 mm) on residual strength by the multistage procedure of the Bromhead ring shear test and evaluate the physical indexes forecasting the residual strength of granite residual soils using soil samples composed of fifteen different percentages of FGPs artificially adjusted from a reservoir embankment soil sample. The results showed that the residual strength decreased along with the increase in FGPs and that the residual frictional angle was rarely dependent on the ratio of FGPs when the ratio was over 90%. Even in the residual state, a small amplitude of fluctuation in shear stress still existed and was affected by the coarse-grained particles (CGPs; particle size >= 0.075 mm), such as the quartz particles in the granite residual soils. It was also found that the amplitude of fluctuation was smaller when the FGP fraction was greater. In addition, under the same normal stress, the peak strength and residual strength decreased with an increase in the ratio of FGPs. Then, they remained almost the same when the ratios of FGPs were equal to 85% and 90%, respectively, and the post-peak attenuation tended to increase initially with an increase in the FGPs and then remained almost the same. Moreover, based on the sensitivity analysis, the order of influence of physical indexes on the residual frictional angle was also ranked for the granite residual soils.