Influence of Freezing-Thawing Cycles on Mechanical Properties of Tailing Soil at Yunnan-Guizhou Plateau

In order to study how the mechanical properties of tailing soil evolve during the freezing-thawing process in open environment, a series of triaxial consolidated undrained (CU) shear tests were carried out with different numbers of freezing-thawing cycles and confining pressures. In the tests, 0, 1, 5, 10 and 15 freezing-thawing cycles were set and the groups of confining pressures including 50, 100, 200 and 300 kPa were applied. Based on test results, the mechanical indexes, including the shear strength, the peak value of shear strength and elastic modulus are finally analyzed. The results indicate that the influence of freezing-thawing on mechanical properties of tailing soils is significant. As the number of freezing-thawing cycles increases, the stress-strain curves gradually transform from the strain-softening type into the work-hardening one, whereas the brittle failure pattern turns into plastic failure, and the negative growth of pore pressure during the shearing process becomes weak till disappears; the peak shear strength, cohesion, internal friction angle and elastic modulus gradually decrease; during the process, tailing soils are affected most by the first cycle of freezing-thawing, of which the effective cohesion and effective internal frictional angle is reduced by 30.55% and 6.33%, respectively; and the average reduction ratios of the peak shear strength and elastic modulus are 42.66% and 33.61%, respectively. The mechanical indexes of tailing soils tend to stabilize after 10 freezing-thawing cycles, and from 10 to 15 cycles of freezing-thawing, the effective cohesion and effective internal frictional angle are reduced by 2.94% and 0.37% respectively; and the average reduction values of the peak shear strength and elastic modulus are 2.53% and 4.03%, respectively. The mechanical indexes of 10 freezing-thawing cycles are proposed as the reference for engineering design.