Experimental investigation on prevalent local failure mechanisms in hard rock tunnel linings using distributed optical fibre sensors

In today’s hard rock tunnel construction, the most common support system consists of rock bolts and shotcrete linings. The support system is effective to build, and structural safety has empirically been established. However, the utilization rate of shotcrete linings is usually unknown as no method exists today that determines the type and magnitude of loads acting on the linings. This paper investigates the implementation of distributed optical fiber sensors (DOFS) as a promising solution for monitoring of local loads in shotcrete tunnel linings. This approach enables the identification of local loads, facilitating targeted inspections in areas with deviating measurements and allowing for more informed repair and maintenance decisions. In the study, two typical local load conditions in shotcrete linings were analysed using strain measurements from DOFS installed in experimental specimens designed to replicate sections of tunnel linings. The results revealed that the examined load conditions can be distinguished based on the measured strains. While the lining thickness had a significant effect on the peak load capacity, the roughness of the substrate influenced the strain distribution in linings subjected to bending. It was also shown that DOFS outside the loaded area could detect load-induced strains for shear loaded specimens at low load levels, but not for flexurally loaded specimens. • Identification of loads in simplified shotcrete tunnel linings using DOFS. • Loose rock loads and distributed loose rock material loads were tested. • Novel monitoring technique for shotcrete tunnel linings in hard rock. • Evaluation of thickness, load condition, loaded area and substrate surface treatment.