Abstract: To investigate the performance of gypsum rock softened by water in the tunneling, gypsum rocks from Lower Triassic Jialing River Group were immersed by fresh water within different times for softening tests. The variations of uniaxial compressive strength, shear strength, elastic modulus and Poisson’s ratio of gypsum rocks with increasing immersion time were analyzed. The study indicated that, with the increase of the immersion time, the uniaxial compressive strength, shear strength and elastic modulus of gypsum rock exhibited a decline trend as a negative exponent, while Poisson’s ratio presented a linear increase trend under certain conditions. On the basis of damage mechanics, a softening damage evolution equation was deduced by considering time effect of gypsum rock. The relationship between the brittleness coefficient and softening-damage variable was revealed, and the softening-depth model at different immersion time was established. This study can be used to identify the softening area of surrounding rock caused by groundwater in the tunneling through gypsum layer.

Key words: gypsum rock, compressive strength, shear strength, fresh water immersion, softening-depth model