Surrounding rock mass stability monitoring of underground caverns in a geomechanical model test using FBG sensors

Abstract

Fiber Bragg Gratings (FBG) sensor is widely accepted as a structural stability device for all kinds of geomaterials by either embedding into or bonding onto the structures. The physical model in geotechnical engineering, which can accurately simulate the construction processes and the effects on the stability of underground caverns on basis of satisfying the similarity principles, is an actual physical entity. Due to a large number of restrained factors, a series of experiments are difficult to be carried out, in particular for how to obtain physical parameters during the experiments. Using the geo-mechanical model test of underground caverns in Shuangjiangkou Hydropower Station as a research object, the FBG sensors were mainly focused on and adopted to figure out the problem how to achieve the small displacements in the large-scale model test. The final experimental results show that the FBG sensor has higher measuring accuracy than other conventional sensors like strain gages and mini-extensometers. The experimental results agree well with the numerical simulation results. In the process of building the model, it's successful to embed the FBG sensors in the physical model through making a reserved pore and adding some special glue. In conclusion, FBG sensors can effectively measure the small displacement of monitoring points in the whole process of the geomechanical model test. The experimental results reveal the deformation and failure characteristics of the surrounding rock mass and make some guidance for the in-situ engineering construction.