In the heart of China, the Baihetan hydropower plant stands as a testament to human ingenuity and engineering prowess. However, the construction of its massive underground powerhouse cavern presented a formidable challenge: a weak interlayer shear zone that threatened the stability of the entire structure. This is the story of how a team of engineers and scientists, led by Lifang Zou from Hohai University’s School of Earth Sciences and Engineering, overcame this obstacle, paving the way for future developments in the energy sector.
The cavern in question is a behemoth, stretching 438 meters in length, 34 meters in width, and soaring 88.7 meters in height. The shear zone, a weak layer of rock, cut through this cavern, posing a significant risk to its stability, particularly on the high downstream sidewall. “The shear zone greatly modified the deformation mode of the cavern surrounding rocks,” Zou explained. “Without treatment, the deformation could have been catastrophic.”
The team’s solution was a combination of meticulous planning, advanced technology, and close monitoring. In the detailed design stage, they determined the mechanical parameters of the shear zone through laboratory experiments and site tests. Then, they used the 3D Distinct Element Code (3DEC) to predict the deformation of the surrounding rocks and the shear zone under high in situ stress conditions.
But prediction was only half the battle. The team proposed a replacement-tunnel scheme to treat the shear zone, preventing severe unloading relaxation of the surrounding rocks. “The replacement tunnels can reduce not only the unloading and relaxation of rock masses but also the maximum shearing deformation of the shear zone by 10–20 mm,” Zou said.
During the construction period, the team closely monitored the excavation responses, keeping a keen eye on the deformations of the surrounding rocks and the shear zone. They used the strength reduction method to evaluate the effect of local cracking in the replacement tunnels on sidewall stability. The results were compared with the predictions from the detailed design stage, and the agreement was striking.
The implications of this research are far-reaching. As the energy sector continues to invest in large-scale underground structures, the interaction between such structures and weak layer zones will become an increasingly important consideration. This design procedure, as Zou and her team have demonstrated, offers a robust solution.
The research was published in ‘Deep Underground Science and Engineering’ (translated from ‘深部地下科学与工程’), providing a valuable resource for engineers and scientists working in the field. The success of the Baihetan hydropower plant is a testament to the power of innovation and the importance of understanding the complexities of the earth’s subsurface. As we look to the future, this research will undoubtedly shape the way we approach the construction of underground structures, ensuring they are safe, stable, and sustainable.