Experimental study on the static and dynamic characteristics of straw-lime reinforced saline soil under freeze–thaw cycles

Abstract

The engineering properties of frozen saline soils gradually deteriorate with increasing freeze–thaw cycles, adversely affecting the safety of foundations and geotechnical structures. The static and dynamic characteristics of straw-lime reinforced saline soil (SLRSS) under freeze–thaw action were investigated in this study. Firstly, the unconfined compression strength (UCS) tests were adopted to evaluate the effect of freeze–thaw cycles on the UCS of SLRSS. The results indicate that the optimal reinforcement effect is achieved at the straw length of 15 mm, straw content of 0.6% and lime content of 6%. As the number of freeze–thaw cycles increases, the UCS increases first and then decreases, reaching its peak at 1 freeze–thaw cycle and gradually stabilizing after 5 cycles. Secondly, the dynamic triaxial tests were performed to obtain fitting curves of dynamic elastic modulus ratio against dynamic strain and damping ratio against dynamic strain for SLRSS. Calculation formulas for the freeze–thaw correction coefficients of initial dynamic elastic modulus and maximum damping ratio were presented. The results indicate that the number of freeze–thaw cycles is negatively correlated with dynamic elastic modulus and dynamic elastic modulus ratio, and positively correlated with damping ratio and maximum damping ratio. As the number of freeze–thaw cycles increases, the correction coefficient of initial dynamic elastic modulus decreases, whereas that of maximum damping ratio increases, with both trending to stabilize after 5 cycles. Finally, the scanning electron microscopy (SEM) was adopted to investigate the effects of different freeze–thaw cycles on the microstructure of SLRSS and analyze its pore evolution characteristics. The results show that significant differences in crack propagation and pore distribution are observed between the fiber-soil interface and non-fiber-soil interface.