Study on application of displacement measurement method in 3-D physical model tests of cavern complex

Using the Shuangjiangkou hydropower station on the Dadu River in China as a background, another new physical model test of an underground cavern complex in a true 3D stress state has been conducted based on a quasi-three dimensional model test which was performed in 2007. The original experimental techniques used in last model test have been significantly developed, and some new measuring techniques have been implemented in the new model test. In order to solve the problem in measurement of small displacements in the surrounding rock masses, the digital speckle correlation method (DSCM) and special displacement sensing bars based on fiber Bragg grating (FBG) technology are adopted. Mini multi-point extensometers with high-precision grating scales are developed as transducers for displacement monitoring. We also conducted a numerical simulation with almost the same conditions, and compared the results of the model test and the numerical approaches. The study shows that the research and application of the displacement measurement methods used in the surrounding rock masses for large-scale model tests of cavern complex under 3-D stress field have achieved satisfactory results.