Failure mechanism of floor heave and supporting technology of soft rock roadway

Control of roadway bottom heave in soft rock is always one of the key problems in soft rock support system.The problem of roadway bottom heave affected by mining pressure is particularly prominent in mining roadway. This re- search was conducted by aiming the technical problem of large deformation of soft rock in Shanghaimiao mining area of Shandong Energy Linyi Mining Group. Firstly,the mechanical model of roadway floor heave with shear dislocation was established based on the constitutive relation of surrounding rock and the stress action mode by using Rankine pressure theory,and then an analytical formula for calculating the force source P0 which caused the roadway bottom heave was derived. According to the calculation of the model,it was found that the rock mass of roadway floor will have shear ex- pansion and dilatational deformation,which makes roadway floor squeezes into the roadway space when the pressure P0 of bottom heave is greater than the ultimate strength of floor rock mass,which eventually leads to floor heave with the increase of time effect. Secondly,combined with the mechanical model of bottom heave,a new type of anti-bottom arch control technology which is suitable for the mechanics mechanism of bottom heave in the shear-staggered roadway was developed,and the theoretical analysis was made on the functions of three parts,including the overhang of anti-bottom arch,floor prestressed bolt and the main section of anti-bottom arch in the process of bottom heave control which re- veals the controlling mechanism of bottom heave. By using the numerical calculation and orthogonal experiment,three main parameters of the new inverted arch structure were optimized. Simulation results show that the main factors affect- ing the index of floor heave are the overbreak depth of the floor and the length of the overhang of the anti-bottom arch, and the main factors affecting the index of convergence of two ribs of the roadway is the length of the overhang of the anti-bottom arch. Finally,based on the stress checking of the floor under the original support condition for track gate- way at the 13803 working face of Yushujing coal mine,it was determined that the coupled effect of the rock pressure of floor and mine drainage was the main reason which caused the bottom heave. Then,according to the optimized floor treatment scheme,a field industrial test was carried out in the track gateway repair section of 13803 working face of Yushujing coal mine. The engineering practice shows that the new technology has a good effect on controlling the road- way bottom heave and walls deformation in soft rock and it effectively guarantees the roadway stability during the work- ing face extraction.