Numerical Analysis of Effects of Joints properties on Dynamic Response on Underground Opening.

Abstract

Rock masses are far from being continuum and consist essentially of intact rock and discontinuities such as joints. Presences of discontinuities affects the propagation of the stress wave in rock mass. In this paper the impact of joints properties and features on the dynamic response of underground cross-cuts to seismic loading induced during dynamic large-scale field test in Kiirunavaara mine, was numerically investigated. The numerical methods used comprise the finite element code LS-DYNA and the 2D Universal Distinct Element Code (UDEC). The LS-DYNA model simulated the blasting and acquired the crushed zone and the vibration velocities around the crushed boundary. The vibration velocities from LS-DYNA were then used as an input velocity in the UDEC model. The studies of parameters such as joint normal and shear stiffness, joint spacing and joint orientation were conducted. The vibration responses at the wall of the underground cross-cut from UDEC were analyzed and compared to observed field test results. The results show that the normal stiffness has large effects on the peak particle velocity (PPV) while the shear stiffness contributes less influence. However, changes on joint space and orientation affect the PPV at the wall of the cross-cut. The joint stiffness explains the quality of the joint to transmit the stress wave while the joint spacing, joint orientation describe the blocky in burden which explain number of times the stress wave will be reflected before reaching cross-cut wall. The analysis can be useful during designing of the blast, burden as well as cross-cut support.