Stability Analysis Of Key Blocks Under Blasting

The underground engineering rock mass is cut by the structure surface and t he excavation surface,forming mosaic blocks of various sizes and shapes,which will often cause local instability of the cavern Stability of blocks is always anal-yzed by static methods.There are some differences about the block action effect between the static excavation and the dynamic excavation,and the effect of blast-ing is also an extremely important and complex problem.In this paper,the infl-uence of blasting effect on the stability of the underground cavern block was an-alyzed by a three-dimensional model of underground cavern block,and the result-s are compared with the results of pseudo static method.The main achievement-s of this paper are as follows:(1)Based on the practical problems in the actual project,according to the o rientation of the structural plane,the pyramidal blocks are formed by the mutual cutting between the structural plane and the excavation face of the cavern,and b-lock theory is used to determine the movability of the blocks.Then the instable type of the block was obtained by using the full space stereographic projection a-nd the block kinematics.(2)The effect of various factors on the stability of blocks and the sequence of significance were analyzed by orthogonal numerical tests.The range of cohesion,internal friction angle and blasting vibration in range analysis are:0.79,0.73,and 0.84,respectively.It can be seen that the order of influence of various factors on the stability of the block is:blasting vibration?cohesion?internal friction angle.Secondly,in order to distinguish the differences in test results from the factor level changes or experimental errors,and to find out the key and secondary factors affecting the results on the basis of range analysis.Through the analysis of variance,the F values of cohesion,internal friction angle and blasting vibration are 64.3972,54.9178,and 72.7123,respectively,which are all greater than the critical F value 19,indicating that all factors have a significant effect on the stability of the block,and the impact of blasting vibration on the stability of the block is the most significant,the cohesive force is the second and the internal friction angle is the least.(3)The effect of key blocks under the action of blasting dynamic loads was studied by the dynamic time history method,and the stability determination me-thod is established by vector transformation of coordinate axes.The change of stress at the measuring point and the time history of the safety factor of the block cut by the weak structure surface of the 0.5m,1.0m,and 1.5m under the action of blasting were obtained.The safety factor for the case 1 is 11.9.case 2 is 12.5,case3 is 13.4.It is learned that the larger the width of the structural weak surface,the more obvious the energy barrier and the greater the safety of the block.(4)By analyzing the shear stress characteristics and the safety factor of the pseudo-static method structural plane and comparing it with the dynamic time c-ourse.it can be seen that the shear stress decreases with the increase of the wi dth of the weak surface of the structure;and the existence of the structural plan e in the rock mass will obstruct and absorb the blasting wave energy,resulting i-n the attenuation of the energy transmitted through the structural surface.The ef-fect on the block would be reduced and the safety of the block would increase.