Abstract:Jiji quarry is one of the candidates in Beishan area,Gansu province—the preselected area for Chinese high-level radioactive waste repository. Data of 13 012 joints of granite are mapped by comprehensive joint survey method in Jiji quarry. According to the two faults,Jiji quarry is roughly divided into three regions where the structure of rockmass is homogenous and two regions which are influenced by the two faults. Based on the theory of the circular sampling window,the computing program is developed and is used to analyze the diversity of the mean joint trace length and joint trace midpoint density in the both sides of the faults. The boundaries of the rockmass structure homogenous region are determined according to the influential range of the faults;and the mean trace length and trace midpoint density of each rockmass structure homogenous region is calculated. The optimal joint sets of each rockmass structure homogenous region are obtained by rose diagram method and equal-area upper hemisphere projection method. The probability distributions of joint dip and dip angle can be effectively fitted by normal function;and the joint dip angles are mostly steep. The joint spacing of each set of joint is calculated and can be effectively fitted by negative exponential function. According to “suggested methods for quantitative description of discontinuities in rock mass”(ISRM,1978),the joint spacing of each rockmass structure homogenous region is wide. In this study,attention is focused on the rockmass joint characteristics,such as orientation,trace length,trace midpoint density and spacing. The quantitative parameters which can be used to describe the rockmass joint characteristics are obtained. They are essential for further research of the mechanical and seepage characteristics of rockmass.