Research On The Optimizing Method Of Blasting To Control The Tunnel Overbreak

In recent years, with the rapid development of national economy, all kinds of engineering construction scale is also growing. Across the country, there are many tunnels and underground engineering in the railway and highway, especially in the construction of highways and many urban subway.During tunnel construction, in order to reduce tunnel surrounding rock damage, especially in the surface of the building damage, or excessive disturbance, it is necessary to adopt blasting technology with less vibra tion intensity. It will affect the stability of surrounding rock if the tunnel blast-induced damage zone is too large. The Influence of blasting on the tunel surrounding rock stability is divided into three areas: one is blasting at the close zone(crushing zone); Second is blasting in the central zone(fractured zone); Three is blasting in far zone(vibration zone). By controlling the three zone of the superposition of the damage of surrounding rock zone, to achieve the goal of controlling the tunnel overbreak.This paper is based on the houziyan tunnel project to study o n damage of surrounding rock blasting parameters by theoretical analysis and ANSYS/LS-DYNA finite element program,, the main contents and results are as follows:①In the invariable condition of explosives and peripheral eyes resistance, numerical simulation analysis was based on the soft rock through changing the blast hole diameter and blast hole spacing to determine reasonable blasting parameters of blast hole spacing and balst hole diameter values.②Based on the reasonable blasting parameters values to estimate the range of surrounding rock damage caused by smooth blasting;③According to the result of monitoring measurement, obtaining the peak vibration velocity attenuation formula of the area near blasting source, without considering the influence coefficient of group of hole, according to the vibration velocity safety limit to determine the range of the smooth blasting damage.④Through comparative analysis between the numerical simulation of houziyan tunnel and the result of monitoring measurement to get the error range.⑤Through comparing damage zone of numerical simulation and the desigen of the control of overbreak values to determine whether the selection of blasting parameters is reasonable.