Internal blast loading in a buried lined tunnel

The paper presents a comprehensive approach to simulate an explosion occurring inside a buried axisymmetric lined cavity. The approach considers all the stages of the process: detonation of the internal charge; the shock wave propagation in the internal gas and its following interaction with the cavity's shell lining including multiple reflections; soil–structure dynamic interaction, including multiple gap opening/closure and wave propagation in the surrounding medium. The cavity's lining is modeled as a Timoshenko elastic plastic shell. The soil is modeled by the Grigoryan model that takes into account both bulk and shear elastic plastic behavior, including the effect of soil pressure on the yield strength for the stress tensor deviator. The gas-dynamics problem is solved by the modified Godunov method, based on a fixed Eulerian mesh with the so-called mixed cell. The variational difference method is applied to solve the problem in the soil and in the shell domains. The contact pressures acting on the lining due to both the detonation products on the internal side and the soil on its outer side are computed by solving the coupled system of finite differences equations of gas, shell and soil dynamics using a simple iteration method. The problems of a blast-hole charge and of a periodical system of spherical blast charges that are placed at equal distances from each other were solved. The explosion occurs within a cylindrical steel pipeline, surrounded by an elastic plastic loess soil. The effect of the soil elastic plastic pressure-density behavior and its shear properties on the soil–structure interaction (including the gap opening/closure process) was studied.