Experimental Investigation for Determining Explosive Consumption and Researching Effect of Rock Fragmentation by Blasting During Shield Tunneling

Abstract

Blasting pretreatment is commonly used to break boulders before shielding to ensure shield machine tunneling safely. Considering that rock fragments after blasting should be met the special dimensional requirement of shield machine’s mucking system, so the explosive consumption is usually larger than explosive charge of conventional blasting and should be determined accurately. However, explosive charge is usually determined based on empirical formula and regulation of rock fragment distribution is unknown, resulting in that the blasting effect is unsatisfactory. In order to solve these problems, model test of blasting is carried out and the following contents are studied. The contents conclude: the explosive consumption corresponding to the average size of rock fragment; the relation between explosive charge and the overburden depth; the relation between explosive charge and regulation of rock fragment distribution. There results show that: the explosive consumption of blasting at land is 5.4–6.5 times that of conventional blasting when the size of rock fragmentation after blast is less than 30 cm. The explosive consumption increase linearly with depth of overlying stratum in double logarithmic coordinates and the relation between average size of rock fragment and depth of overburden is quadratic polynomial. The influences of explosive charge and depth of overburden on average size of rock fragment after blast is different. Explosive charge is the main influence factors for average block degree when the boulder is buried in a shallower depth, but thickness of overlying stratum’s influence on average block degree will exceed that of explosive consumption when the boulder’ buried depth exceed a certain value.