Research On The Evolution And Its Application Of Rockpressure Arch In Coal Mining

The research on evolution laws of pressure arch in coal mining has important scientific value in solving bumping pressure and soft rock support in deep mining. Based on numerical simulation, scale physical model and on site engineering practice, the formation and evolution law of pressure arch in surrounding rock during coal mining is studied; influence factor of pressure arch is discussed; effect of mining dynamic pressure on the stability of surrounding rock and bumping pressure. And then the evolution law of pressure arch is applied in prevention practice of bumping pressure. The following important results and innovations are obtained.(1) During coal mining process, the stress in surrounding rock is transferred continuously, which causes the increase of the scope of tangential stress concentration in surrounding rock and forms the pressure arch supporting the upper weight of overlying strata around the gob area. The pressure arch is approximately egg-shaped and thick-wall pressure shell structure, with long axis in the trend of working face and short axis parallel to the open-off cut. After the advance of working face, the long axis of pressure arch which is in the section of strike turns into paralleling to the work face and maintains. However the arch which is in the section of dip will remain its long axis in the vertical direction. With the increase of working face's driving distance, the outer boundary of pressure arch will extend, arch body will become thicker and stress within the arch body will increase.(2) With the advance of working face, stope stress increases gradually, stress concentration area advances and develops from the mined out area to surrounding area continuously. The stress value and its growth gradient in surrounding rock close to the face is greater than that in rock far away from the face.Stress distribution is linear in rock close to the working face, but curvilinear in rock far away. Mining dynamic pressure causes stress concentration, accumulation of elastic deformation energy and the possibility of bumping pressure. The egg-shaped spatial pattern of the arch also shows that the gate roadway is in the stress-increasing dynamic pressure area and bumping pressure is to be achieved.(3) The main factors of the pressure arch include depth of the mined out space, the width and length of the mined out space. When the width increases, the arch body will become thicker and the inner boundary of arch body will extend. When the length increases, the inner boundary of pressure arch along the strike will extend, whereas the arch pressure along the dip shift will not change. If the stope depth is large enough for the complete pressure arch, the increase of depth will not change its form, but the stress in the arch will increase.(4) With the advance of working face, the stress in surrounding rock will transfer and change continuously and pressure arch will be formed within a certain range of the heterogeneous rock mass. The space pattern and evolution law of the pressure arch is in consistent with the result of numerical simulation of homogeneous rock. Scale model test reproduces the movement and destruction of stope rock, the arching effect of in break is obvious.(5) Application of the evolution of pressure arch in project shows that before the advance of 21141 working face, the form of pressure arch was in connection with the spatial form of stope. The longer is the mined out area, the greater is the long axis, and the smaller is its flat rate. With the increase of the mined out area driving distance, the pressure arch showed dynamic change, its boundary extended forward and upward gradually. The pressure arch formed during the back stopping of 21141 working face transferred to track entry, which caused the increase of stress in the surrounding rock, the accumulation of elastic deformation energy and the raised risk of bumping pressure(6) In engineering applications, according to the space from inner boundary of arch to road way and the thickness of arch body, the dangerous area of track entry is divided based on dynamic pressure risk as the following order: 1375～1475 m >1605～1615 m>1135～1145 m>1475～1525 m>1275～1375 m. The research provides foundation for the evaluation, pevetion and control of rock burst to ensure safety of mine safety.