Crown stability analysis for the right bank cavern of the Baihetan Hydropower Station, China.

Both spalling and block failure have been observed while driving the audits in the proposed locations of the cavern in the right bank at Baihetan Hydropower Project site. Severe spalling occurred primarily in the roof, and the block failures were governed by the Shear Zone C4. In addition, field investigation showed that the stress-induced spallings are spatially associated with the existence of Shear Zone C4. The occurrences observed in the audits present a strong indication that both a stress-induced problem and structure-control failure should be anticipated and may co-exist when constructing the cavern. When conducting numerical analysis of cavern stability, attention should be paid simultaneously to both the discontinuous and the non-linear behaviors of the rock mass. This paper presents the entire procedure of numerical analysis for the cavern crown. The first step in the paper is to briefly describe the site occurrences and accordingly present their indications for numerical modeling. The model inputs are then numerically examined and calibrated against the observations, which include in-situ stress regime in general, properties for both pre- and post-peak stages in the non-linear constitutive models to be employed. The numerical modeling for crown stability analysis is finally implemented. Extra attention is paid to the potential failure modes and severities, including the stress-induced failure resulting from the stress localization in the vicinity of Shear Zone C4, as well as potential ground falls governed by C4 and additional geological structures. The modeling results provide clear and solid indications for the ground support design, particularly in the required extra support element and applicable locations, in addition to the commonly-used pattern. [ABSTRACT FROM AUTHOR]