Discussion on key technical problems of water cutting off engineering in submerged roadway with large-cross section

When a water inrush occurs in a coal mine,the usual way to control water hazard is to build a water blocking wall by pouring aggregate into the water passage.This paper discusses the hydraulic status during the aggregate filling period,the mechanism of accumulation growth and roof connection,the construction parameters of closure,the stress state of wall and the optimization of construction.Some conclusions are as follows:① The closure process is divided into four stages:before aggregate perfusion,paving and filling,roof connection and grouting.Using two phase flow numerical model,the dynamic distribution effect of the flow during closure is verified in space and time.② The aggregate distribution is screened by the flow field,and the accumulation height and length is closely related to the flow rate.When the aggregate feeding process matches the flow rate,the stacking height and length can increase simultaneously,and grow reverse to the upstream until the successful closure.If the flow speed is too low,it will connect the top in advance and leave a cavity between the holes.③ The starting speed is positively correlated with the uphill angle and negatively correlated with the downhill angle.Under the same conditions,the accumulation length and height are the largest and the lowest in the downhill perfusion,which are not conducive to the control of project cost and time limit.④ The accumulation quantity is analyzed from three aspects of energy criterion,seepage breakthrough and slurry initial setting time.The prediction method is analyzed and the influence of dip angle,branch pathway and scour effect on the necessary accumulation is pointed out.The influence range of maximum stress under 5 MPa water pressure is not more than 50 m,which indicates the key reinforcement area is near the upstream.⑤ It is proposed to avoid adverse factors as far as possible to design the construction scheme.In the construction process,the grouting process can be adjusted or the number of boreholes can be increased according to the feedback in the boreholes,so as to achieve the best effect with the minimum input.