Changes of small strain shear modulus and microstructure for a lime-treated silt subjected to wetting-drying cycles

Lime treatment can enhance the workability and hydro-mechanical properties of soil through different physical-chemical reactions. Nevertheless, the beneficiary effect of lime treatment can be altered when the soil was exposed to wetting-drying cycles, depending on the wetting fluid and soil state. In the present study, the changes in small strain shear modulus (Gmax) and microstructure of a compacted lime-treated silt under wetting-drying cycles were studied. The untreated state of soil was also considered for comparison. Meanwhile, the effects of wetting fluid (deionized water and synthetic seawater) and maximum soil aggregate size (Dmax = 0.4 mm for S0.4 and 5 mm for S5) were investigated. Results showed that Gmax increased significantly for the lime-treated soil over curing, and increased slightly for the untreated soil. The untreated specimens were softened and damaged by wetting-drying cycles, while the lime-treated specimens exhibited good resistance with the pore size distributions almost kept reversible along the wetting-drying paths. The subsequent more intensive drying resulted in a significant fabric alteration with occurrence of shrinkage-related fissures of the clay part. However, these fissures were almost healed with rewetting. Thereby, the Gmax of lime-treated soil showed a constant decreasing trend with wetting and an increasing trend with drying. Moreover, Gmax decreased slightly with wetting-drying cycles for the lime-treated specimens wetted by deionized water, suggesting that the wetting-drying indeed softened the soil. However, Gmax increased for the lime-treated specimens wetted by synthetic seawater, due to the more production of cementitious compounds promoted by salts. The lime-treated specimens S0.4 wetted by synthetic seawater had higher Gmax than those wetted by deionized water, while the wetting fluid had insignificant effect on the Gmax of specimens S5 due to the limited promotion of pozzolanic reaction and negligible soil aggregation induced by salts.