Cyclic and post-cyclic behaviour of compacted and intact completely decomposed soils subjected to blasting vibrations

Blasting is widely used in underground construction and affects surrounding soil slopes. Its effects on soil behaviour, such as excess pore water pressure (PWP) and shear strength, have not been well understood. In this study, strain-controlled cyclic and post-cyclic triaxial shear tests were performed on four completely decomposed soils at their compacted and intact states. An analytical method was used to correlate cyclic shear strain with peak particle velocity (PPV, a key blasting-control parameter). Excess PWP increases with cyclic strain and is slightly larger in intact than in compacted specimens under comparable void ratios. At 0.05% cyclic strain (PPV=55 mm/s), excess PWP remains below 10% of the initial effective confining pressure for intact and densely compacted specimens, and below 15% for loosely compacted specimens. This ratio increases to 35% at 0.10% strain (PPV=85 mm/s) and exceeds 60% for strain above 0.20% (PPV>140 mm/s). However, cyclic loading exerts negligible effects on both peak and critical friction angles. These findings indicate that repeated blasting with PPV=55 mm/s have insignificant effects on the behaviour of tested soils and hence, the conventional static shear strength can be adopted for slope stability assessment, whereas higher PPV warrants caution due to the high excess PWP accumulation.