Abstract:As a discontinuous medium,the deformation behaviour of rockmasses is quite different from that depicted by continuous media. Based on the monitored deformation date during excavation,the deformation characteristics and mechanism are analyzed for an underground powerhouse considering its geological data and excavation process. The spatial distribution of rockmass deformation is greatly controlled by geological structural planes. Whether in horizontal direction,vertical direction or along the monitoring borehole depth,the deformation difference may exist if a structural plane is encountered;the influence of the adjacent excavations on rockmass deformation is complex,and the general rule that “the nearer the distance is,the greater the influence is” may not exist;rockmass deformation is mainly composed of the “opening displacement” of major structural planes,which constitutes 84%–93% of the monitored deformation. The characteristics mentioned above suggest the limitation of numerical methods based on mechanics of continuous media for modeling the deformation of rockmass. Therefore,application of discontinuous numerical methods such as DDA is a subject being worthy of further investigation.