Post-liquefaction reconsolidation and undrained cyclic behaviour of Chang Dam soil

Understanding and determination of post-liquefaction stress–strain behavior of sandy soils under monotonic and cyclic loading is essential to estimate the deformations that might occur in liquefied deposits under further loading. The undrained response of reconsolidated specimens under multilevel cyclic loading simulates the post-liquefaction behavior of soils under earthquake aftershocks and other cyclic loading conditions. In the present study, post-liquefaction reconsolidation and undrained behavior of medium dense silty-sand of Chang dam under multilevel repeated cyclic loading is explored. The soil deposit underwent severe liquefaction during the 2001 Bhuj earthquake. During the first round of loading (C<inf>0</inf>), the specimens were subjected to 50 cycles of cyclic loading at 0.4 mm amplitude (A) and 0.1 Hz frequency (f) and exhibited liquefaction. After C<inf>0</inf>, developed excess pore water pressure was allowed to dissipate, and specimens were allowed to reconsolidate. Reconsolidated specimens were then subjected to second round of cyclic loading, C<inf>1</inf> (A = 0.4 mm, f = 0.1 Hz and N = 35), and this process was continued for C<inf>2,</inf> C<inf>3</inf>, and C<inf>4</inf> loading rounds. Significant reduction in void ratio (e) was observed each time when specimens were allowed to reconsolidate after each round of undrained cyclic loading, thereby increasing the liquefaction resistance. The increase in liquefaction resistance on repeated loading was reflected in the cyclic stress ratio (CSR) calculated for every cycle for each level of cyclic applied loading. The inclination of the peak deviatoric stress envelope (instability line) for each round of loading was observed to increase with repeated reconsolidation and cyclic loading.