A recent study has delved deep beneath the surface of hydropower engineering to explore the complex mechanisms of ground deformation during tunnel excavation under high crustal stress. Conducted on the right bank diversion tunnel at the dam site of the Lancang River hydropower station, the research highlights significant challenges faced by engineers when excavations interact with the surrounding hard and brittle rock.
The study aims to address the longstanding issues of rock mass deformation—an area fraught with unknowns particularly when subjected to high geo-stress conditions. High ground stress, coupled with the degree of fracture development within the rock, emerges as pivotal factors impacting how surrounding rock behaves during and after excavation.
Researchers observed two distinct phases of damage to the tunnel walls as excavation proceeded layer by layer. Following the removal of the first layer, they noted extensive but shallow surface damage characterized by the formation of thin, plate-like cracks. This localized deterioration required immediate attention, as it posed risks for subsequent excavations. The preliminary findings indicated, "The main conditions for surrounding rock deformation in the diversion tunnel are a high ground stress environment and the degree of surrounding rock fracture development."
Once the second and third excavation layers were removed, the relationship between the rock’s condition and the support systems put in place became even more clear. Damage from earlier layers exacerbated existing fractures with significant reductions in support effectiveness, demonstrating how interconnected the excavation phases are. The researchers stated, "Layered excavation leads to 'time-dependent' changes in the yield characteristics of the surrounding rock."
These findings offer compelling insights for engineers developing underground structures, especially those relied upon for large-scale water conservation projects. Past experiences with similar projects have often ended in failure due to insufficient support measures. This research reinforces the necessity for careful monitoring and proactive reinforcement systems, as it is emphasized, "If the support system fails to provide sufficient support force, the surrounding rock will deform."
Field data gathered during the study indicated stress concentrations at various points along the tunnel—a natural byproduct of excavations subjected to uneven stress distributions. The effect of support systems was assessed through numerical simulations, which aimed to recreate real-world conditions encountered within the geological formations at the dam site. Notably, the incidence of high-stress failures upon the arch shoulder confirmed earlier assessments and predictions made by the simulation models. For example, "High-stress failure occurred in the surrounding rock at the arch shoulder, verifying the consistency between the numerical analysis and the engineering reality."
Moving forward, the researchers propose enhanced reinforcement strategies to mitigate risks associated with excavation under high stress. The potential risks highlighted throughout the study lend credence to the fact this domain of engineering requires constant updating of methodologies based on developing research and technological capabilities.
This investigation not only contributes to our theoretical knowledge of tunnel excavation mechanics but also provides actionable strategies for practitioners aimed at increasing safety and efficiency within the engineering field. The lessons drawn from the Lancang River hydropower station could influence future hydropower projects, reinforcing the link between advanced research and practical engineering solutions.
The interplay of high ground stress and the configuration of surrounding rock is at the forefront of tunnel construction challenges today. With continued efforts to explore and refine these mechanisms, future engineering projects might achieve greater structural integrity and operational efficiency, hence optimizing the role of hydropower as a sustainable energy resource.