Charactreristics Of Structure Evolution And Mining-induced Stress Distribution Affected By Multiple Faults

The geological conditions in the vicinity of fault zone are extremely complex,which presents several features,such as weakness,crushing and so on.Because the fault breaks the continuity of rock strata,the stress distribution varies and abnormity affected by fault cutting,especially in the affected-zone of multi-faults or fault groups.It easily induces the severe dynamic disaster accidents(i.e.rock burst,shock bump,coal outbur)and has large effect on safety production of underground coalmines.In this paper,by using the methods of theoretical analysis,UDEC numerical and FLAC3D numerical,a numerical model with two faults occurrence is established,and then the mining operation process with different distance between the two fault and different mining directions are simulated.After that,the evolution law of overlying strata and distribution characteristics of mining-induced stress are studied and analyzed.Finally,a case engineering in filed regarding to the microseismic monitoring is used to verify the fore-mention results.The main study results are presented as follows:(1)In this paper,two faults in fore-mention numerical model are setup and three zones caused by faults cutting are divided by these two faults cutting which can defined as upper region(UR),middle region(MR)and lower region(LR).It can be concluded that the distance between these two faults has little effect on overlying strata structure of UR and MR when a working face mines from LR to UR,while it affects the structure of MR notably.When the distance is large,the structure evolution of overlying strata can present as follows:Trapezoid-shape in LR—Triangular-shape in LR—r-shape in MR—Trapezoid-shape in MR—Triangular-shape in MR—Trapezoid-shape with small range in UR.When the distance is less than 60 m,a triangular-shapes structure is formed and slips notably in MR.(2)When a working face mines from UR to LR,the overlying strata structure presents successively as Inverted-trapezoid-shape in UR—Triangular-shape in MR—Inverted--triangular-shape in MR—Triangular-shape in UR.With the distance decreasing,the evolution has no much change and no notable slipping which infers that it is more safe compared to the analysis condition of conclusion.(3)The effect of mining directions and distance between the two faults on the mining-induced stress in UR and LR is small,while that of on MR is large.When the distance is large,it has little effect on peak stress value in MR and the position of the peak value is same.Meanwhile,when the distance is less than 60 m,the peak stress value reduces with the distance decreasing and its position moves forwards.