1468 defective geological structures such as faults, cavities, fractures and voids in the stratum, so as to improve the structural strength of the strata traversed by the shaft and reduce the permeability of the stratum. This method can be redefined as a structural stratum modification method. Thus, the two methods can be collectively referred to as stratum modification methods. Conventional shaft sinking by drill-and-blast adopts a short-bench combined excavation and lining operation process, which involves drilling with umbrella drills, manual charging, rock loading with grab loaders, hoisting with skips, and concrete shaft lining pouring with integral formwork. This method requires a large number of personnel to work in the complex environment inside the shaft, facing safety risks such as collapse, water inrush, gas leakage and equipment accidents, which are prone to cause serious occupational injuries to personnel. Therefore, exploring non-blasting rock-breaking shaft sinking methods has become the development direction of shaft sinking technology. To address the challenges of shaft construction in deep water-rich alluvial strata in central and eastern China, specialized large-diameter shaft drilling rigs have been developed by drawing on the technologies of oil well drilling, and a relatively mature shaft sinking method by drilling has been established, which enables unmanned operation underground. Aiming at the problems of low shaft sinking efficiency, long construction period and high cost caused by high risks of blasting rock breaking, complex processes of rock slag collection and hoisting at the shaft bottom, and mismatched rock breaking-slag removal processes during the shaft sinking of large-diameter shafts by the drilland-blast method, research on technical equipment and processes of mechanical rock breaking drilling for largediameter shafts based on gravity-driven slag discharge was carried out. Therefore, the authors analyzed the advantages and challenges of the mechanical rock breaking and gravity-driven slag discharge shaft sinking method, systematically sorted out the existing technical equipment system of mechanical rock breaking and gravity-driven slag discharge drilling, and constructed an integrated shaft construction process combining multiple processes. This research is of great significance for the transformation and innovation of shaft construction towards safety, green development, economy and intelligence. 2. 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. 2.1 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.
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