Experimental study on the ultrasonic nonlinear damage characteristics of expansive soil during constant amplitude dry-wet cycles

Dry-wet cycles can cause fatigue damage to expansive soil, and various control parameters of the dry-wet cycles (initial moisture content, number of dry-wet cycles, cycle amplitude, etc.) can affect the development of soil damage. Therefore, it is important to study the fatigue damage characteristics of expansive soil under dry-wet cycles of constant amplitude. This paper considers expansive soil from Baise in Guangxi, China, as the research object. Based on tests of the P-wave velocity and low-stress shear strength of expansive soil under 0-6 constant amplitude dry-wet cycles, the attenuation laws for the P-wave velocity were analysed, the damage variable of expansive soil was characterized by P-wave velocity, and the rationality of this damage variable was verified by measuring the low-stress shear strength values of expansive soil specimens. Based on the experimental P-wave velocity results, a nonlinear empirical model of fatigue damage for expansive soil was constructed. The results illustrate that the P-wave velocity of an expansive soil sample decreases nonlinearly with an increasing number of dry-wet cycles and that the damage degree increases nonlinearly with an increasing number of cycles. The P-wave velocity can be successfully used to define a representative damage variable for expansive soil.