| As the coal mining develops gradually towards the deep,the breaking and deformation analysis of deep soft coal and proper supporting issue have become particularly important.In order to select proper support and its arrangement to keep the deep soft coal roadway stable and to solve the difficulty of complexity and low accuracy with the method of loosen zone thickness measurement for deep soft coal,combination of site test and numerical simulation is adopted.Firstly,main factors(primary rock stress,roadway section size and coal lithology)affecting deep soft coal breaking and deformation are determined through theoretical analysis and then values of physical mechanics parameters of coal are measured with relevant test(elastic modulus,Poisson ratio,cohesive force and inner friction angle).Reasonable FLAC3 D numerical calculation model is built,meshing is performed and five typical directions are selected(a A,b B,c C,d D and e E).This paper focuses on the analysis of displacement field distribution characteristics of deep soft coal under different primary stresses P(10MPa,12 MPa,14MPa,18 MPa and 20MPa)and different coal lithology(I,II,and III)in the typical directions,of the residual strength distribution characteristics in typical directions under different conditions and of the displacement gradient distribution characteristics and breaking-expansion degree of the deep coal under different conditions.The fitting equation is obtained with the numerical simulation results,the displacement values in each direction obtained from Tecplot post-processing software and by fitting of displacement with software Origin.The loosen zone thickness and distribution are determined by analyzing the surrounding rock zone when the soft coal strength attenuates to residual strength and site test is adopted to verify the reasonableness of the test.Further the influence of roadway arrangement parameters like roadway depth,coal lithology and section size on the loosen zone thickness and arrangement is analyzed.The results show that roadway arrangement parameters affect significantly the loosen zone thickness and arrangement,different positions of deep soft coal large section roadway all have large loosen zone thickness which is particularly obvious in the middle of two sides of the roadway.Therefore,the support strength shall be significantly improved and key position support shall be enhanced in particular.Relevant coefficients are obtained by analyzing the displacement field distribution of soft coal in different directions and by regression of displacements in different typical directions,and then the displacement gradient values are obtained and the critical allowable displacement gradient values in critical state of coal loosening and breaking are determined.The results show that the loosen zone thickness of deep soft coal is significantly affected in different conditions,but the critical values above are basically the same,which is generally about 10.0;the loosen zone thickness when critical allowable value is taken for coal displacement gradient can be estimated by coal regression equation of coal displacement field distribution and relevant regression equation coefficients.The loosen zone thickness is estimated by measuring the coal displacements at different positions in engineering practice and better effect is achieved.The breaking-expansion degree of the coal is determined by analyzing the displacement gradient of the coal at different typical positions in different conditions,and average breaking-expansion ratio of the surrounding rock of the roadway in different typical directions is determined by the displacement where the loosen zone is and by the displacement of surrounding rock surface.The results show that large scale of breaking is produced at different positions of the deep soft coal,but the average breaking-expansion at the middle of roadway sides is significant and there is extremely excessive expansion in large scale in the area close to the roadway surface.Long anchor cables are adopted to support the roadway and the roof,and anchor cables are locally added closely and short anchor rods are arranged at the middle of roadway sides so as to ensure effectively that the roadway deformation is stable. |
