Abstract
Rockburst is an unstable failure of a rock mass which is influenced by many factors. During deep excavations, the presence of nearby geological structures such as minor faults, joints, and shear zones increases the likelihood of rockburst occurrence. A shear zone has been observed in the headrace tunnel in the Neelum Jhelum Hydropower Project, Pakistan, which has played an important role in major rockburst events in the project’s history. A rockburst is a seismic event that involves the release of a great amount of energy as the dynamic wave radiated from the seismic source reaches the excavation boundary. In this paper, the FLAC 2D explicit numerical code has been used to simulate the dynamic phenomenon of rockburst near the shear zone in a headrace tunnel. The behavior of the rock mass around the tunnel has been studied under both static and dynamic loading. According to modeling results, rockburst significantly affected the upper left quadrant of the tunnel similar to the actual failure profile with a depth of approximately 5 m. The dynamic impact of rockburst has also affected the loading conditions of the support system in the adjacent tunnel. This study elucidates one of the most important rockburst controlling factors through numerical analysis and recommends yielding support measures that can withstand the dynamic impacts of rockburst in deep, hard rock tunnels.
Highlights
The rockburst is a dynamic form of damaging phenomenon that is linked with the violent ejection of rock blocks
We have numerically investigated the mechanism of rockburst in the headrace tunnels of the Neelum Jhelum Hydroelectric Project (NJHEP), which have been subjected to dynamic loading, and we have evaluated the dynamic impact of rockburst on the installed support in the adjacent tunnel
A seismic wave reached the boundary of the tunnel after travelling through the rock mass from the source point of high stress concentration near the extreme point of the shear zone as shown in Figure 6a, causing a dynamic stress rise on the already fractured zone after static stress analysis
Summary
The rockburst is a dynamic form of damaging phenomenon that is linked with the violent ejection of rock blocks. It is hazardous during the excavation of deep tunnels [1]. The severity of the damage caused by rockburst varies depending on different parameters, such as excavation depth, stress level, the quality of the rock mass near the excavation, excavation shape, excavation method, geological structures, and dynamic. The impact of geological structures on rockburst occurrence in deep hydropower tunnels is discussed in this paper. There are different geological structures such as faults, shear zones, joints, dykes, and discontinuities that encounter during deep tunneling [2]
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