Salinity effect on the compaction behaviour, matric suction, stiffness and microstructure of a silty soil

To better understand the salinity effect on the compaction behaviour of soil, standard Proctor compaction test was conducted on soil samples with different salinities. Matric suction and small-strain shear modulus, G(max), were determined and pore size distribution was also investigated on samples statically compacted at different water contents. Results showed that with the decrease of soil salinity from initial value of 2.1 parts per thousand (g of salt/kg of dry soil) to zero, the maximum dry density increased and the optimum water content decreased, whereas there was no significant change with the increase of soil salinity from 2.1 parts per thousand to 6.76 parts per thousand. Interestingly, it was observed that G(max) also decreased when the soil salinity decreased from initial value of 2.1 parts per thousand to zero and kept almost constant when the soil salinity increased from 2.1 parts per thousand to 6.76 parts per thousand, for dry samples with similar matric suction and also for samples compacted at optimum state and on wet side whose matric suctions were slightly different due to the difference in remoulded water content. Furthermore, the effect of salinity on compaction behaviour and G(max) decreased for samples compacted from dry side to wet side. The pore size distribution exhibited bi-modal characteristics with two populations of micro- and macro-pores not only for samples compacted on dry side and at optimum state, but also for those compacted on wet side. Further examination showed that the modal size of micro-pores shifted to lower values and that of macro-pores shifted to higher values for saline soil compared to the soil without salt. (C) 2021 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.