Mountain tunnels may be subject to deformation, cracking or other abnormalities caused by ground pressure after they are put into service (Fig. 1). Although such damage requires appropriate maintenance along with future servicing, no method has yet been established to predict how tunnel damage will progress over time. A technique is therefore developed to simulate the progress of tunnel damage caused by ground pressure.

This simulation technique expresses ground fracture and damage/fracture of tunnels by inputting the decrease in ground strength over time. An actual damaged tunnel in use was analyzed to reproduce abnormalities with this technique. The results confirmed that type, location and time of damages obtained by this method are respectively in good agreement with its measurements (Fig. 2). The method enables to predict when abnormalities including cracking occur, as well as the appropriate timing for the implementation of remedial work (Fig. 3).

To reduce the burden on designers in applying the method to actual design work, a nomogram is also created to get easily values to be input for simulation analysis from measurements of the ground strength and the convergence speed.