Experimental and theoretical investigations of dacite under unloading lateral confining stress

To study the mechanical properties of dacite in the unloading process, this paper conducted triaxial unloading and loading acoustic emission (AE) monitoring tests under initial confining pressures (5 MPa, 10 MPa, 20 MPa, and 30 MPa), and novelty developed an unloading damage theoretical law. The main research findings showed that volumetric dilatancy and brittleness of dacite under unloading lateral confining stress were severe and the fractured samples would completely lose residual strength. Meanwhile, the deformation modulus and the cohesion strength decreased, but the Poisson’s ratio as well as the internal friction angle increased with the lateral confining stress decreasing. The AE events and the cumulative AE events also increased significantly due to energy release caused by cracks closure, friction, and slip. Moreover, the theoretical stress–strain law based on the continuum damage theory, elastoplastic framework, and flow rule agreed well with experimental results, which indicated that they were effective to characterize dacite’s unloading damage mechanical properties.