Why is the stage of natural caving mining law weakening the border?

The purpose of border weakening is to:

(1) Release the horizontal stress of the original rock and destroy the natural balance arch foundation to facilitate the initial collapse.

(2) Cut or reduce the arch angle stress and improve the stability of the roadway in the high stress area near the mining boundary.

(3) Reducing the damage to the surrounding rock near the boundary, reducing the depletion of the ore, and also promoting the complete ore collapse near the boundary (especially at the corner) and reducing the loss of ore.

The method of weakening the boundary is to dig the corner patio, cut and pre-crack. In order to completely break the ore at the corner of the mining boundary (generally referred to as the sharp corner), the corner patio is burrowed at the corner. If the ore's collapsibility is poor, several layers of horizontal deep hole blasting can be drilled in the corner patio to promote the ore collapse in the corner portion. Cutting the gang is to drill one or several layers of weakened roadway at the mining boundary, and dig a cutting patio at a distance of 20~30m as a deep hole blasting free surface. From the weakening of the roadway, several rows of drilled holes are drilled to the vertical parallel deep holes to form the cutting groove, as shown in Fig. 1. Pre-cracking is to drill only a row of dense upper or lower parallel deep holes in the weakened roadway, and pre-crack deep holes with the same stage blasting as the bottom is pulled.

The method of weakening the boundary and determining the weakening height should be based on the collapsibility of the ore and the stress of the original rock. The cutting sump is generally only used in the initial stage of mining, and enters the normal collapse. It only needs to use the cornering patio and pre-cracking method.