Particle crushing of frozen sand under triaxial compression

Particle crushing is one of the important factors to change mechanical properties of frozen sand, which is hardly studied quantitatively so far. Triaxial compression tests are carried out on a saturated frozen sand at -0.5℃, -1℃, -2℃ and -5℃ under the confining pressure of 0.5, 2, 5 and 10 MPa, respectively. The particle crushing ratio, B_r, defined by Hardin is obtained through the particle-size distribution curves for samples before and after triaxial tests. It aims to analyze the relationship between confining pressure and particle crushing as well as the influence of the particle crushing on strength. The testing program presents a considerable particle crushing in triaxial compression of the frozen sand. There is a critical confining pressure σ_r. When σ₃<σ_r, the particle crushing ratio, B_r, increases with the increase in confining pressure; otherwise, B_r does not increase obviously with the increase in confining pressure. Previous studies as well as the test results from this work show that under -5℃, pressure melting does not play important roles in mechanical properties of frozen soils. Therefore the test results under this temperature are taken for analysis without considering pressure melting. It is found that particle crushing has a dual influence on the strength of frozen sand. Under low pressure levels, particle crushing leads to weakening and strength decreases; with the increase in pressure, particle crushing reaches the maximum and particle rearrangement tends to improve the strength.