Effect of high in-situ asymmetric stress on the brittle failure of the boundary of an underground powerhouse
摘要
Brittle failures often emerge around the boundaries of deep excavations due to high in-situ stresses. This study focuses on the Shuangjiangkou Hydropower Station’s underground powerhouse, which encounters some of the highest in-situ stresses globally (up to 37.8 MPa before excavation). Using artificial intelligence, the three-dimensional in-situ stress was determined. Prior to excavation, the major stress component was approximately parallel to the excavation axis, and this orientation remained largely unchanged post-excavation. As a result, the post-excavation tangential stress σθ, which exceeds the pre-excavation major stress, becomes the dominant stress. Traditional criteria, such as the σ1/σc ratio, may not effectively predict rockburst intensity due to this shift. True triaxial compression tests on cuboid specimens simulated excavation-induced stresses and revealed that post-excavation stress distribution is asymmetric. Shearing failure is observed in the arched upstream spandrel, where curvature is high and bearing capacity is minimal, while tensile failure occurs in the straight downstream sidewall with negligible curvature. The minor stress enhances rock strength and ultimate stored energy, whereas the intermediate stress accelerates brittle failure. Crack initiation and damage align with the ultimate stored energy and peak strength, with anisotropic deformation evident, showing a more pronounced Poisson’s ratio in the σ3-direction, leading to bulging and slabbing, while fractures develop along the σ2-direction.
Highlights• Boundary failure in an underground powerhouse depends on in-situ stress directions.
• A high σ2/σ3 ratio induces the hard rock to deform anisotropically.
• Shear failure occurs at arch-shaped shoulder; tensile failure arises at straight sidewall.
•σ3 greatly enhances the strength of the rock but σ2 accelerates its brittle failure.