Using the Shuangjiangkou hydropower station in the Dadu River in China as a background, physical model tests were conducted to investigate the stability of a cavern complex, which contains a power house, a transformer house, a tail water surge chamber as well as other openings under high in-situ stresses. During the study, a steel structural frame of the physical model, a hydraulic pressure system, a rock analogy material, measuring technology and elements, fabricating and embedding technology of pre-stressed cables and rock bolts were developed and excavation and measurement of the cavern complex were implemented. The test results from this study were analyzed and compared well with those from the numerical simulations. This research obtained the expected effects and provided guidance for the design and construction of the power station.
In the study of the stability of the surrounding rock masses in large underground cavern complex, a large number of numerical methods have been used, such as the finite element method (FEM) , the boundary element method (BEM)  , the finite difference method (FDM) , and the discrete element method (DEM)  , and so on. However, physical model tests are still very important and necessary especially for some complicated circumstances, in which physical model tests can be used to validate numerical simulations. Furthermore, physical model tests can be used to study failure mechanisms, processes, and forms. In recent years, geotechnical engineers and researchers have developed a number of test methods and measuring technologies in physical model tests. Li et al.   developed several new technologies in physical model tests, such as the masking excavation technology, the endoscope measuring technology, etc., which were successfully used in the 3D physical model test of the underground complex of the Xiluodu hydropower station. Chen et al.   developed a new 3D steel frame, which can be used to apply triaxial loading with a uniform or inverted trapezoid distribution. Zhang et al.  developed another type of steel structural frame for 3D geo-mechanical model tests. This frame has apparent technical advantages such as high stiffness, great stability, and flexibility of assembly, and easy adjustment of its dimensions. Wang et al.  developed a new type of analogy material called IBSCM, which can simulate different types of rock masses. Zeng and Zhao  introduced a physical model test of underground caverns in a hydropower station and obtained the stress distributions, displacement distributions, and failure modes and mechanisms of the surrounding rock masses. Shen  introduced the characteristics and development tendency of the geo-mechanical model tests and considered that new mechanisms could be found and mathematical models could be verified. Jiang and Cao  adopted a 3D geotechnical model test to simulate the whole Goupitan Double-Curved Arch Dam and obtained the failure mechanisms and the capability of the dam under overloading. Ma et al.  developed another analogy material called NIOS and used it in a 3D geo-mechanical model test of the underground caverns of Xiluodu hydropower station. Su et al.  developed a steel structural frame for simulating the state of plane stress of underground mining roadways.