A Preliminary Study on the Detections of Potential Support Degradation in Deep Hydraulic Tunnels.

Understanding the time-dependent performance changes in tunnel supports through the monitoring data is crucial to predict the long-term stability of deep hydraulic tunnels. This paper provides an analytical solution for assessing the long-term stability of the diversion tunnels from the perspective of support permeability degradation. An evaluation factor R_gl, which denotes the ratio of the hydraulic conductivities of the grouted rock and the concrete lining, is proposed to analyse the degradation characteristics of tunnel support performance over time. The time-dependent changes in R_gl and its controlling factors are discussed using the monitoring data of the Jinping II diversion tunnel. The results show that there are ascending or descending trends of R_gl over time, linking to the evolutions of hydraulic conductivity in the grouted rock and the lining. The reliabilities of the analytical model for explaining the changes in tunnel support permeability are examined using numerical methods. The comparisons between the numerical solutions and monitoring results show good agreements in the hypothetical cases characterising the potential degradation of support of the diversion tunnel. Highlights: Ratio of hydraulic conductivities between grouted rock and lining was proposed for diversion tunnels. Time-dependent hydraulic performance in support of the Jinping II diversion tunnel was analysed. Hydraulic conductivity degradations of diversion tunnel supports were simulated. [ABSTRACT FROM AUTHOR]