Abstract: Internal erosion is one of the major causes of underground disasters such as sinkhole, underground cavity, loose sand body and water-rich body, which can be initiated by four erosion models. In this study, an erosion-controlled experimental method was adopted to dissolve two types of preplaced salt granules in gap-graded sand, with the aim of simulating the process of suffusion and concentrated leak erosion. Small strain shear wave velocity was measured with bender elements. Shear strength, angle of shearing resistance and dilation rate of eroded soil under different confining pressures were measured by triaxial tests. Experimental data showed that shear wave velocity decreased gradually with the dissolution of salt granules and the peak shear strength decreased significantly after internal erosion. The reduction of shear wave velocity and the shear strength increased with the level of confining pressures. Given the same mass of the erodible material, the mechanical degradation of shear wave velocity, shear strength and dilatancy during concentrated leak erosion was observed to be significantly higher compared with suffusion. The stress-strain behavior of dense sand with the relative density of 80% was strain hardening under suffusion, while the behavior of concentrated leak erosion tended to be strain softening. The volumetric strain at post erosion state was still dilatancy but with a lower trend.