Study on shaft damage control technology of water inrush and sand burst in drilling process with thick topsoil and thin bedrock

Aiming at the technical problems of comprehensive treatment and repair of sand burst and water gushing in drilling wellbore in thick surface and thin bedrock strata, taking a coal mine auxiliary shaft under construction in Lianghuai Mining Area as an engineering background, the analysis shows that the bending and subsidence deformation of the overburden strata of ingate under repeated disturbance is the main cause of the damage of the auxiliary shaft.The damage of main shaft and air shaft is secondary damage caused by auxiliary wells. In line with the principle of paying equal attention to repair and prevention, a comprehensive control scheme for injection, freezing, repair and prevention wellbore is formulated. That is to say, ground grouting can improve formation performance and prevent bending deformation of lower bedrock; compound shaft lining can be formed by sleeve shaft lining and original shaft lining to improve the structural safety of the shaft in this complex stratum condition; freezing surrounding rock of existing shaft can be used as sleeve shaft lining measure engineering to provide safety guarantee for its construction. Research and development of a series of wellbore and ingate repair construction technology: ①downward drilling and injection combined with leakage, multi-stage casing flexible formation grouting hole construction and grouting technology; ②auxiliary wells, drainage holes are respectively local and full depth freezing, main and air wells are full depth freezing, hydrological pressure relief holes are set in the freezing shaft lining, temperature measurement data and numerical model, combining with the control freezing technology to predict the development of freezing shaft lining; ③adopting different repair methods according to the damage degree of shaft shaft lining; ④ the construction technology of inner steel plate shaft shaft lining, such as assembling and welding of composite steel plate, preparation of high performance concrete(steel fiber concrete); ⑤and strengthening surrounding rock of ingate by grouting behind the shaft lining, breaking ingate super-strong composite permanent support control surrounding rock, layered repair and erection technology on both sides at the same time. The comprehensive monitoring results show that the surface subsidence in the industrial square is stable; the internal force of the sleeve shaft lining and the pressure between the auxiliary wellbore are less than the design value after repair; the water inflow of the main and air wellbore is about 1 m3/d, and the water inflow of the auxiliary wellbore is about 4 m3/d. The main, auxiliary and air wellbore repaired by this scheme meets the requirements of relevant specifications and are in safe operation state.