Rock breaking mechanism and the application of medium-deep hole–in-hole segmented blasting in rock roadway using digital electronic detonators

“Cutting is the key to speed” in rock roadway excavation. With the aim of addressing the challenges related to broken rock disposal, low single-cycle penetration, and high block rate in the conventional straight hole and diagonal hole excavation blasting, the method of medium-deep holein-hole segmented blasting is proposed herein. The mathematical relations for the force and resistance required in the process of rock crushing and ejection in the groove of medium-deep hole-in-hole segmented blasting, as well as that for the expected value range of the key parameters of the cutting groove, were determined. LS-DYNA was used to numerically simulate the process of medium-deep hole-in-hole and ordinary wedge cut blasting. The nature of stress wave propagation during medium-deep hole-in-hole segmental blasting and the stress characteristics of the rock at the bottom of the hole were analyzed. Furthermore, the variation characteristics of the stress wave intensity were compared for different segmental proportions, and the optimal segmental proportions were determined. The results of theoretical analysis and numerical simulation were applied to the excavation site of the rock roadway, and the blasting effect indices, such as singlecycle footage, hole utilization rate, eye mark rate, and block rate, of the medium-deep hole-in-hole segmented blasting and the ordinary wedge blasting schemes were compared. The results showed that rock can be ejected from the cavity when the dynamic force is greater than or equal to the resistance during the rock crushing and ejection process and that the resistance to rock ejection in the medium-deep holeinhole segmented blasting is less than that in ordinary wedge cut blasting, and it is easier to blast into the cavity. Best practices for achieving the complete ejection of broken rocks from the cavity are proposed, and theoretical support for determining the parameters, such as the depth of the hole, is provided. As compared to ordinary wedge cut blasting, producing a large blasting cavity through medium-deep hole-in-hole segmented blasting is easier, which is more favorable for subsequent blasting. The optimal ratio of the hole-in-hole segmented blasting was initially determined to be 0.6. Medium and deep hole-inhole segmented blasting increases the single-cycle footage, improves the utilization rate of the hole, reduces the working time, reduces construction cost, and has excellent economic and socialadvantages.