Failure Mechanism of Back-Break in Bench Blasting of Thin Terrane

Abstract

The shape of a free surface is an important factor that determines the effect of bench blasting. The structural dynamics theory was applied to establish a structural failure model of the layered rock considering the impact of a blasting gas intrusion. Combined with the continuous-discontinuous element method (CDEM), the influence of rock strata on the failure mechanism of back-break was analyzed. The results show that structural failure characteristics of stratum with different dip angles are different. The bending failure characteristics of dipping-in-face stratum are stronger than that in dipping-out-of-face stratum. With the increase of the dip angle and height of rock stratum, the bending failure length of dipping-in-face stratum increases and the maximum value reaches 5.24 m. The trend of failure along the stratum surface towards the bottom increases, which is an important reason for the formation of an unfavorable shape of free surface. However, the failure depth of the gently dipping stratum and dipping-out-of-face stratum is relatively uniform; the average value is about 0.5 m. Finally, combined with the results of the bench blasting field test of the Changjiu (Shenshan) limestone mine, which is the largest in the production of sand and gravel aggregates, we verify the correctness of the theoretical analysis results. Relevant research results can provide a theoretical basis and technical support for controlling the bench blasting effect.