Design of mini multipoint extensometer in geomechanical model test of cavern group and its application

Geomechanical model tests play important roles in stability analyses of large-scale underground cavern groups. However, the application of this type of test was restricted by a number of factors, in particular the measurement of physical quantities during the test. A large-scale geomechanical model test was conducted under three-dimensional stress state. To measure small displacements in the surrounding rock masses, a mini multipoint extensometer measurement system was developed. The variation process and regular curves of the displacements of surrounding rock masses during excavation can be obtained. In addition, 3D numerical simulation was performed to simulate the whole process of the physical model tests. The comparison between experimental and numerical results leads to conclusions on the stability of the underground cavern group. The study shows that design and application of the mini multipoint extensometer measurement system have achieved satisfactory results.