Abstract: To investigate the swelling and softening characteristics of expansive rocks, swelling test and conventional triaxial test were carried out. The scanning electron microscopy (SEM) and nitrogen adsorption (NA) techniques were conducted before and after soaking water. Undisturbed expansive rock samples were selected to fully consider the cementation among the particles inside the expansive rock and original structure. Experimental results show that the expansion has apparent anisotropy and the axial expansion is 1.5 times of the radial one. With the increase of relative water content, the peak strength decreases rapidly and then slowly decreases, the elastic modulus and cohesion decrease. Under the condition that the confining pressure remains unchanged, the deformation form of the expansive rock changes from tensile failure, tensile-shear failure to shear failure, and surface cracks increase when the expansion rock fails. SEM results show that the microcracks of the expansive rock increases after the water soaking, and the pore development is obvious, which is the softening fundamental of the expansive rock.

Key words: expanded rock, mechanical properties, softening characteristics, microstructure