Abstract:Combining the crosshole elastic wave survey with the seismic traveltime tomography, a new method to determine the microcrack zone boundary of rock masses blasting was proposed. The method of ray tracing of slowness square was briefly introduced which was used to calculate the coefficients of traveltime equations, then the weighted least-square solution of solving the large sparse linear equations and its commonly used iterative procedure were given. Based on the data of P-wave traveltime measured in six small-charge blasting experiments at Sanxia dam, the P-wave velocity distributions of rock mass before and after blasting are reconstructed and all of the microcrack depths and microcracking zone diameters in rock masses resulting from blasting were finally determined. The further research works find that the microcrack depth is much smaller than the microcracking zone radius and they almost linearly increase with the addition of charge quantity, moreover, the increment of microcrack depth is much greater than that of microcracking zone radius.

Key words: rock mass blasting　microcracking zone　measuring method　tomography