Study on the technology of inner steel plate concreteshaft lining for thick topsoil wellbore repair

In order to solve the damage question of shaft in thick topsoil caused by water inrush and sand burst, in view of its failure characteristics such as vertical fracturing, flange opening and wellbore deflection, adopting the repair and reinforcement scheme of full deep casing wall, which combines reinforced concrete shaft wall with inner sleeve steel plate (steel fiber) concrete shaft wall structure.Taking auxiliary shaft of a coal mine under construction in huainan mining area as the engineering background, combining with the failure form of wellbore and the mechanism of water inrush and sand burst, the design principle and structure form of wellbore sleeve are put forward; the thickness of sleeve wall and the stress of steel plate and concrete are calculated according to the deformation of wellbore in situ and relevant codes; by analyzing the calculation results and combining with the actual situation in the field, the sleeve wall construction scheme is formulated; vibration string sensor method is used to monitor the wall pressure, circumferential reinforcement stress and deformation of the repaired inner sleeve, and observing the water level of the inspection hole for a long time.The results show that,①according to the formula of composite tube, the stress range of steel plate (steel fiber) concrete composite shaft lining structure steel plate is 187.6～ 292.0 MPa, and that of concrete is 32.8～ 51.0 MPa, which all meet the design requirements;② after completion of construction, the maximum monitoring values of wall pressure and circumferential reinforcement stress are 3.2 MPa and 113.4 MPa respectively, which are within the safe range;③after repairing, the wellbore water inflow is about 4 m3/d, the waterproof effect of the inner steel plate concrete composite wellbore structure is outstanding, and the wellbore structure is safe and stable;④ in the 315.0～567.7 m deep section, the borehole is damaged in many places, mainly by deflection, the maximum deflection value is 1 154 mm, in the severe deflection section, the inner sleeve wall is constructed vertically by mode division, deflection following and fine-tuning, so as to solve the difficulties of the transition construction of each model steel plate stubble connection.The scheme utilizes the advantages of single-layer inner steel plate (steel fiber) concrete composite shaft lining structure, such as high strength and good waterproofing performance, not only greatly reduces the thickness of inner sleeve shaft lining, but also ensures the safe and stable operation of repaired shaft lining.