Dynamic Response of Artificially Structured Residual Soils Under Undrained Cyclic Loading

The geotechnical behaviour of residual soil is fundamentally different from that of sedimentary soil because of the weathering pedogenesis of the former, thereby posing significant difficulties in predicting soil response under cyclic loads. In this study, the cyclic behaviour and post-cyclic structural degradation of artificially structured tropical residual soils were investigated. Consequently, tests were conducted to ascertain the development of soil structure or bonding by treating residual soils with 1% of Portland cement. The test results reveal that the soil’s cohesion was significantly improved, and soil structure was developed. Furthermore, strain-controlled undrained cyclic triaxial tests were conducted to evaluate the dynamic behaviour and structural degradation of the artificially developed tropical residual soils under cyclic loads. The specimens exhibited a rapid decrease in stiffness, and inelastic behaviour within the first 10 cyclic loads at all the confining pressures (50–200 kPa). The post-cyclic behaviour indicated significant deviator stress degradation indices (DSDI) > 0.3 at all the confining pressures and significant loss of energy absorbing capacity (> 30%). Under these cyclic loads, the specimens show partial disruption of bonds as evidenced by a maximum pore water pressure ratio of 0.16%. The post-cyclic behaviour shows that the soil possessed significant resilience to cyclic loads due to the presence of residual bond structure. The study recommends the use of soil improvement techniques such as cement stabilisation, fibre reinforcements and incorporation of degradation indices in the design of geotechnical infrastructures, specifically in weakly cemented residual soils, which are prevalent in tropical and subtropical regions.