Optimizing seepage control for underground powerhouse caverns near a large-scale fault

Seepage control is a critical issue for construction of underground powerhouse caverns, especially when the caverns are located near large-scale, water-conductive faults that provide flow channels into the cavern area. Grouting and draining have been considered as the most effective measures for regulating leakage into the caverns, which usually calls for an optimization design to achieve a balance between the performance and cost. This study proposes to optimize both the location of an underground cavern system and the design parameters (depth and/or spacing) of seepage control system located near a large-scale fault by numerical simulations. A comprehensive site characterization is performed to quantify the permeability of the surrounding rocks, and the excavation-induced permeability variation is characterized with a strain-dependent model. The groundwater flow is described by a steady-state flow model with unilateral boundary condition for rigorous simulation of drains. It is found that both the location of caverns and the layout of grout curtains and drains can be effectively optimized in terms of the metrics including the pore water pressure distribution, the discharge into the cavern area, and the stability of fault against seepage erosion. This work underscores the importance of optimization design in regulating the groundwater flow around underground caverns located near permeable faults.