<i>MDC</i> score values.

The Gansu Beishan area is a preselected candidate site for a high-level radioactive waste repository in China. The development of surface rock mass discontinuities in this region is crucial for ensuring the long-term stability and safety of the project. The survey line method was employed to investigate these discontinuities. Fault geometry information was defined based on the characteristics of traffic routes and exploratory trench wall fault gouge. Optimal joint sets were identified using rose diagram equal-area upper hemisphere projection methods. Statistical analysis shows that the dominant joint orientations in each group follow a normal distribution. Using the circular sampling window theory, the mean trace length and trace midpoint density of joints for each outcrop were calculated. A Multiscale Discontinuity Comprehensive (MDC) index was proposed to evaluate the degree of surface rock mass discontinuity development based on discontinuity geometry parameters. The results of the surface rock mass discontinuity development were analyzed according to the tectonic stress and mechanical formation mechanisms of the discontinuities. These research findings provide critical data to support the ongoing development of high-level radioactive waste geological disposal.甘肃北山地区是中国高放废物处置库（high-level radioactive waste repository）的预选候选场址。该区域地表岩体结构面的发育特征，对保障该工程的长期稳定性与安全性至关重要。本次研究采用测线法对该区域的岩体结构面开展调查：断层几何信息依据交通沿线及探槽壁的断层泥特征进行厘定；通过玫瑰图-等面积上半球投影法识别优势节理组。统计分析表明，各组优势节理的产状服从正态分布。基于圆形采样窗（circular sampling window）理论，计算得到各露头节理的平均迹长与迹线中点密度。本研究提出多尺度结构面综合（Multiscale Discontinuity Comprehensive, MDC）指数，依托结构面几何参数对地表岩体结构面发育程度进行评价。结合构造应力与结构面形成力学机制，对地表岩体结构面发育特征的分析结果展开深入解析。上述研究成果可为高放废物地质处置（high-level radioactive waste geological disposal）的后续推进提供关键数据支撑。