Interaction Mechanism between Two Large Rock Caverns

Abstract

Long-term stability of geotechnical structures is critical to any engineering design. Design of underground structures is initially planned using empirical approaches based on the rock mass–classification system. This design is mainly based on limited data obtained from boreholes and surface geological mapping. However, this design needs to be continuously updated based on the information gathered as the excavation work progresses. Over the last few years, geotechnical monitoring has emerged as a major engineering tool for engineers to review and update their existing design configuration based on the actual behavior of excavated rock mass. This paper presents a case study of the interaction of two large unlined rock caverns that were excavated using a drill-and-blast technique with a heading-down benching approach. The mechanical response of the two caverns was numerically modeled and studied in terms of the stress-deformation behavior of the excavated caverns and rock support installed, taking into account the actual sequence of heading and benching followed during parallel excavation activity at one of the construction sites. It was observed from the analysis that the crown/wall junction is sensitive to displacements under both good and fair rock-mass conditions. Limited comparative study was also carried out between the measured and calculated displacements; this showed encouraging results. Progressive buildup of forces in the rock bolts and development of the stresses in pillars were also studied as part of the interaction response of two caverns.