211 1.The proposal of mechanical rock breaking gravity slag removal technology Currently, according to the different rock breaking methods, well construction is mainly divided into blasting tunneling and mechanical rock breaking drilling. Usually, the construction method from top to bottom is adopted. The broken rock and soil at the working face needs to pass through the already constructed well hole and overcome gravity to be directly discharged from bottom to top to the ground. The large-diameter well blasting method mainly uses a rock grabber to load the broken rock slag into a bucket, and then lifts it to the ground for slag removal by the hoisting system. The existing vertical shaft tunneling machine mechanical rock breaking slag lifting is similar to the drilling and blasting method, still using the method of lifting rock slag to the ground by bucket. The slag removal is not continuous and it is difficult to coordinate with the rock breaking process. 1.1 Mechanical rock breaking fluid slag removal process The commonly used circulating medium for fluid slag removal is mud. In addition to fulfilling the function of circulating slag removal, mud also has a temporary wall protection function to maintain the stability of the surrounding rock of the well formed by rock breaking drilling. Depending on the diameter of the drilled well, the fluid slag removal method is also different. For example, small diameter boreholes usually use positive circulation slag removal, while large diameter drilling usually uses compressed air reverse circulation slag removal. Small-diameter boreholes utilize the positive circulation cutting removal principle, as shown in Figure 1. A mud circulation pump installed on the ground applies pressure to the drilling mud medium. The mud is forced through the drill pipe's central hole to the drill bit position, mixing the rock fragments broken by the drill bit with the mud. This cuttings-laden mud mixture returns to the surface via the annular space between the drill pipe's outer wall and the borehole, where it undergoes sedimentation and solid-liquid separation. The separated clean mud is then recycled back into the mud circulation pump's intake port. Figure 1 - The positive circulation slag removal principle in small-diameter well drilling Figure 2 - The principle of reverse circulation slag removal in large-diameter drilling
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