Study On The Controlled Perimeter Blasting Of The Fracture Zones In Guanjiao Tunnel

Based on the shattered fault zones blasting construction of Qinghai-Tibet railway Guanjiao tunnel, according to the special geological conditions of tunnel, adopting one type of controlling blasting excavation to shattered fault zones, attain to reducing out break, improving outline quality, and reducing the effect which rock blasting causes to the stability of surrounding rock.Theoretically, study on the fracture mechanics sew theory, Griffith brittle failure theory and mixed mode gas wedge effect. In line with the different of initiate crack formation mechanism and pattern on hole, discussing the notched directional splitting controlled blasting, shaped cartridge directional fracture controlled blasting and cutting seam cartridge directional fracture controlled blasting, in addition, illustrating the rock strength criterion of high stress fracture broken. Also, provide theoretical basis for numerical simulation and field test.Draw support from finite element analysis software ANSYS/LS-DYNA, by using the method of numerical simulation, numerical simulation of smooth blasting and directional splitting controlled blasting, controlled perimeter blasting results show that the effective stress around the seam increased, vertical direction of blast-hole decreased, and provide favorable conditions for the form of crack on blast-hole attachment, simultaneously, which provides theoretical basis for the optimization design of the site blasting parameters.In the field experiments, by contrasting the ordinary smooth blasting with peripheral holes blasting technique, it is not hard to find that by using peripheral holes blasting technique can improve the cross-section quality, the random radial crack around the hole reduced Significantly, this shows the energy gathered at seam, making the effective stress around the seam increased, and having priority to format crack. in the meantime, the blasting vibration effect reduced obviously, it suggests the effective stress of outside blast-hole attachment obviously reduced, which is consistent with the results of numerical simulation.In the process of blasting excavation, selecting typical section for field test, according to blasting seismic wave, analysis test results to determine the blasting seismic wave propagation of high stress broken tunnel, and propose the security standard for controlling rock damage...