Numerical simulation of control blasting with borehole protecting and water jet slotting in soft rock mass

The drilling-blasting method dominated in the excavation of tunnels and mine works. However, there exists some serious problems such as poor profile flatness, severe under excavation and great damage to surrounding rock after blasted. How to improve the blasting effect and reduce the damage of blasting to surrounding rock becomes an urgent issue. Especially for soft rock tunnel, how to achieve safer and lower-damage excavation in tunneling has been a study hot spot. In this paper, a new method of directional fracture controlled blasting with borehole protecting and water jet slotting in soft rock mass was proposed based on previous achievements of soft rock blasting. Depending on the mechanism of the blasting, a FEM software ANSYS/LS-DYNA is used to numerically simulate the stress field distribution during the blasting process. The result shows that the distribution of stress filed can be changed by the slots and protecting pipes. Rock cracks appear and extend along the jet slot direction because of tensile stress concentrated at the tip of the jet slot. This method of blasting can greatly decrease damage causing by load of explosives and make full use of explosion energy in excavation.