Displacement measurement techniques and numerical verification in 3D geomechanical model tests of an underground cavern group

In this paper, the stability of an underground cavern group is investigated on the basis of large-scale 3D geomechanical model tests and numerical simulations. Multiple measurement techniques are developed to measure the convergence of deformation in the cavern, displacements at key points in the side wallsand the damage pattern during the excavation simulation process. The digital photogrammetric technique and fiber Bragg grating (FBG) based displacement sensing bars are applied to measure displacements in the surrounding rock masses. Mini multi-point extensometers with high-precision grating scales are developed as transducers for displacement monitoring. Afterward, a nodal-based Discontinuous Deformation Analysis (NDDA) method is applied to simulate the whole process of the physical model tests and to compare with experimental results. The variation process and law curves of the displacements in the surrounding rock and at key points in the side walls are obtained atexcavation stages. The study shows that the application of the displacement measurement methods used in the surrounding rock masses for large-scale model tests of cavern group under true 3-D stress state have achieved satisfactory results.