The stability of large-scale underground caverns, such as underground openings for hydropower houses, is often affected by faults or joints located nearby. Hence, a better understanding of the mechanisms of influence, especially regarding the risk assessment of faults is required. At the department of geotechnical engineering, the influence of faults on the stability of underground opening has been investigated using numerical methods. Faults are modeled here explicitly as interface of two planes contacting each other. The interface IS represented by the stiffness in the normal and in the shear direction of the two planes. In this paper, especially the displacement behavior for different locations of a fault around the underground opening are discussed. The deformation of the fault after the excavation is also briefly presented.
Many instabilities of underground cavernsare ascribed to influence of faults located nearby. Brekke, and Selmer-olsen (1966) concluded in a survey of factors causing failures of underground excavations in Norway, that faults are often a major cause of failures. Mikula (1993) also made the same conclusion after investigating the forms of failures in open stope mining in Australia. Especially in the recent years, many reports on fault-induced problems regarding the stability of underground caverns have been published. It is obvious, that the fault-related instabilities of under- ground excavations have become a crucial issue that engineers and researchers are facing in the current time. However, owing to the fault existing, the rock mass behavior is rather discontinuous, non-linear and non-elastic. It is almost impossible to derive a theoretical solution to survey the stability of underground caverns considering the Faults. The numerical simulated method is thus the only effective way to investigate the effects of faults on the underground cavern stability. In order to establish an economical and reliable support system, a better understanding of the fault-induced behavior of underground excavations regarding the stability is required. Based on this considerations, the main objective of this work aims to insight into the effects of faults on the stress and displacement redistribution around underground openings. In order to investigate into the influence of faults, a new "interface" element of modeling the fault and a two- dimensional explicit finite difference program (FLAC2D) were employed. Furthermore, the attention was focused on assessing the effects of the mechanical properties of the faults on the stability of the excavations considering the location and the dip ofthe fault. The results obtained can offer a preliminarily guidance to the support design.
In the past several decades, different types of joint elements Have been proposed for simulating rock. Lei et al.., (1995) employed a contact-friction interface element to survey the fault influence on the stress redistribution and lining moment and normal force of lining. Steindorfer, (1998) used the ratio of longitudinal to vertical displacement to evaluate the effect of fault zones in the process of tunnel excavation. Suorincni, (1998) systematically summarized the effect of faults on stope stability in Mining engineering.
