Research on grading support of deep shaft construction in expansive soft broken rock strata

When a kilometer-deep shaft through expansive soft broken rock strata in an overseas copper-gold mine, the surrounding rock has a great expansion pressure in water, and there have been two cases of wellbore collapse and cracking, which has a great impact on the construction progress and the safety of construction workers. To address this issue, the related literature and similar construction cases at home and abroad are searched, the fracture mechanism of wellbore through expansive soft broken rock strata is analyzed, and the repair scheme of wellbore fracture is formulated. On this basis, the engineering geology and hydrogeology of the construction site are further investigated. Through analysis and summary, the construction and grading support scheme of deep shaft in bad rock strata is put forward. The grading table of the surrounding rock of the expansive soft broken rock strata through which the shaft passed is formulated, and the corresponding construction and specific support scheme is put forward according to different rock mass grades. Through the repair of the two fractures, there are no cracks and water leakage for a long time, and the repair effect is good to reach the expectation; on the other hand, after the subsequent construction of the shaft using the hierarchical support scheme, the shaft smoothly passed through the bad rock strata with a thickness of more than 500 m, and achieved good results in terms of construction period, quality and safety, ensuring the construction quality and safety of the deep shaft engineering. The project has accumulated valuable experience for the deep shaft tunneling construction in the expansive soft rock, and has certain reference significance for similar projects.