Study on Strength Characteristic of Unsaturated Undisturbed Lateritic Clay

Abstract

To investigate the effect of suction on strength characteristic of undisturbed lateritic clay, obtained from Jinhua-Quzhou Basin, the suction-controlled triaxial compression tests were carried out on undisturbed specimens under different suctions and net confining pressures, respectively. The obtained results show that the peak strength continues to increase with an increase in suction. Meanwhile, the stress-strain curves vary from strain-hardening to strain-soften for specimens gradually with an increase in suction. Correspondingly, the failure mode changes progressively from plastic failure with barrel deformation to brittle failure with localized deformation gradually. The variations of cohesion and internal friction angle with suction indicate that the cohesion increases linearly and nonlinearly with suction in semi-logarithmic coordinate before and after threshold suction (suction corresponding to abrupt change in variation tendency). On the contrary, the internal friction angel is almost the same with increasing suction before the threshold suction, while it increases significantly when the suction exceeds the threshold suction. Then, mercury intrusion porosimetry (MIP) was carried out to obtain pore size distributions (PSDs) of specimens with different suctions, to investigate the mechanism about the variations of strength parameters (cohesion and internal friction angel) with increasing suction. The MIP results indicate that typical unimodal PSDs exhibit in undisturbed lateritic clay. The peak of pore size distribution declines with an increase in suction, while the distributions of micro-pores are not affected by increasing suction. Moreover, the delimiting suction (suction corresponding to the delimiting diameter of macro- and micro-pores) calculated from the PSDs, is consistent to the threshold suction deduced from triaxial compression tests. Consequently, it can speculate that the different mechanism of suction effects on cohesion and internal friction angle, can be attributed to the fact that the cohesion is mainly influenced by the capillary water distributed in macro-pores, while the internal friction angle is mainly affected by the bound water distributed in micro-pores.