Mechanical Properties and Structural Evolution of Sludge-cured Lightweight Soils Subjected to Freeze-thaw Cycles

Abstract

The rational and effective disposal of sludge has always been a key topic of interest. Freeze—thaw cycles can change the mechanical properties and structural characteristics of soils, leading to a range of engineering geological problems. The sludge curing technology can be used to transform municipal sludge into a new type of sludge-cured lightweight soil. The effects of the number of freeze-thaw cycles and freezing temperature on the unconfined compressive strength and compression modulus of the improved sludge-solidified lightweight soil were investigated by unconfined compressive strength and one-dimensional compression tests. A structural quantitative parameter that considers the freeze-thaw cycles, i.e., the freeze-thaw structural potential, is proposed. The variation pattern of the freeze-thaw structural potential under the influence of different factors was analysed. The test results show that the strength and compression modulus initially rapidly decreased, and then tended to be stable with the increase in the number of freeze-thaw cycles. A lower freezing temperature led to smaller strength and compression modulus. The first two freeze-thaw cycles had a greater influence on the freeze-thaw structure potential. The influence of freezing temperature on the freeze-thaw structural potential is significant when the pressure and number of freeze-thaw cycles are small, and diminishes as the pressure and number of freeze-thaw cycles increase. It was found that there was a good non-linear relationship between the freeze-thaw structural potential and both the unconfined compressive strength and compressive modulus. On this basis, models for the freeze-thaw structural potential as a function of the unconfined compressive strength and compression modulus, taking into account the effects of freezing temperature and the number of freeze-thaw cycles, are proposed respectively, and the accuracy of the models is further verified. The results can provide a reference for the applications of solidified light soil in various fields including engineering fillings in seasonally frozen areas.