Interlayer staggered zones at Baihetan hydropower station are characterized as loose structures

poor water-physical properties

weak mechanical properties and large spatial distribution. The weak structural surfaces in the surrounding rock of underground space determine the deformation and failure of the surrounding rock mass. Based on a large number of geological exploration and experimental results of interlayer staggered zones in the Baihetan project area

they are divided into joint zones

lining zones and muddy zones. The formation mechanisms

macrostructural and microstructural features

mineral compositions

water-destructible properties and shearing mechanical properties in the C2 and C4 zones are studied. It is concluded that the interlayer staggered zones are mainly tectonic genesis

and the differences in clay mineral content

microstructure and hydrologic properties are obvious in different sub-zones. The shear mechanics curves of the interlayer staggered zones presents an ideal elastic-plastic. In the end

we analyze the effect of geological characteristics of interlayer staggered zones on the engineering rock mass during construction. Three main failure modes block collapse

shear slip

and seepage failure in the surrounding rock mass of underground powerhouses and caverns are observed.