Investigation of the evolutionary process of a reinforced model slope using a fiber-optic monitoring network

The stability condition of a reinforced slope is influenced by many factors, such as surface loading, adjacent excavation, groundwater seepage, rainfall infiltration, and earthquake. In order to investigate the evolution of stability condition of a soil slope reinforced with soil nails, a physical model test at 1 g condition was conducted in the laboratory. In the model test, an innovative quasi-distributed fiber-optic sensing network based on the fiber Bragg grating (FBG) technology was developed to monitor the strain distributions of the soil nails, the slope subsurface displacements, and the internal strains of the soil mass, together with laser displacement transducers for surface displacement measurement. The sensor installation and temperature compensation methods of the monitoring system were presented in detail. During testing, the surcharge loading was applied on the slope crest in stages using hydraulic jacks and the slope behavior was carefully monitored. The simplified Bishop's method was performed beforehand to obtain the factors of safety and the critical slip surfaces of the model slope. It is found that the measured strains of the model soil nails had a close relationship with loading magnitudes. The bending stiffness of the model soil nails contributed to the stability of the model slope when considerably large deformation occurred. The variation of slope movements and the distribution pattern of internal strains in the active and passive zones were further discussed, which indicates the progressive evolutionary process of the reinforced slope. It is verified that the fiber-optic monitoring data can identify the evolutionary stages of a reinforced slope effectively.