In-situ comprehensive investigation of deformation mechanism of the rock mass with weak interlayer zone in the Baihetan hydropower station

The weak interlayer zone (WIZ) is a type of geological structure with a loose structure, weak mechanical properties, water softening and strong extension that seriously threatens the local and overall stability of caverns. In order to better understand the mechanical mechanism of large deformation of the rock mass with a WIZ, an in-situ comprehensive investigation was carried out in a cavern of the Baihetan Hydropower Station. The technical characteristics of the WIZ (i.e. mineral composition, water physical properties, weak structure, etc.) were also systematically investigated by the laboratory tests. The in-situ investigation of the deformation process, including the spatiotemporal evolution of the rock deformation and the internal fracture extension of the rock mass with a WIZ, was recorded in a time series by sophisticated microseismic (MS) monitoring, digital borehole camera, multi-point extensometer and on-site surrounding rock failure. The experimental investigation revealed the surface deformation development and the internal fracture evolution of the rock mass with a WIZ. And the comprehensive research results showed that the large deformation of the surrounding rock of the powerhouse was mainly controlled by the WIZ. The in-situ comprehensive investigation can provide early warning of large deformations in the surrounding rock to ensure the safety and stability of the cavern.