A comprehensive investigation of engineering geological characteristics of interlayer shear weakness zones embedded within Baihetan hydropower station.

• Engineering properties of ISWZs investigated considering genesis and fabric. • The Baihetan ISWZs are divided into single-layer and multilayer structures. • A new multi-index engineering rock mass properties classification method is proposed. • A strength parameters estimation method is proposed for the small-scale ISWZs. The interlayer shear weakness zones (ISWZs), which are a kind of large-scale infilled discontinuity, are frequently considered the most hazardous potential slip surface in the rock masses. Based on laboratory and field investigations, the engineering characteristics of ISWZs (i.e., genesis, fabric, structure, mineral composition, water-physical properties, shear strength properties, and engineering classification) embedded in and around the Baihetan hydropower station area are systematically examined. The results of the laboratory and field show that ISWZs have complex occurrence features, undulating and spatial inconsistency in thickness, and variation in mineral composition, fabrics, and structures. Moreover, based on variabilities in various features and extend, ISWZs are categorized into single-layer structures (Type-A) and multilayer structures (Type-B). An engineering geological classification approach for large-scale ISWZs is developed based on the two essential index such as clay proportion and infilled ratio. This classification method not only involves the influence of the undulating state of ISWZs on their shear properties but also considers the physical and mechanical properties of weak interlayer materials. The results of this investigation contribute to a proper understanding of mechanical properties and rock mass classification, especially for large-scale ISWZs. [ABSTRACT FROM AUTHOR]