Abstract:Long-term observations for tunnels have shown two interesting aspects:an increase in leakage for watertight tunnels;and a decrease for leaking tunnels. An increase in leakage may exceed the capacity of drainage system and a decrease in leakage cause unexpected water pressure on the lining. Both excess leakage and additional water pressure are detrimental to running tunnels. Therefore,during tunnel operation,the flow behaviors around tunnel should be appropriately controlled. One of the most significant key elements in evaluating tunnel safety is the development of water pressure on the lining due to the deterioration of the drainage system. The increased water pressure on the lining is termed here as “residual water pressure”. The subsea tunnels generally need strict and careful monitoring of hydraulic effect to keep safe operation. Establishment of a well-organized maintenance program is therefore essential during operation. However,most aged-subsea tunnels do not have well-equipped monitoring systems,in addition even in new tunnels,the monitoring systems are often malfunctioned just after several years of operation. In this study,a new indirect and nondestructive method evaluating residual water pressure on the lining is proposed based on a characteristic water pressure curve obtained by numerical analysis. If the amount of water inflow,the height of water table and average ground permeability are known,the water pressures on the lining can be evaluated using the proposed analytical equations and the characteristic curves. It is shown that the method is particularly useful for tunnels of which measured data are not available and particularly for the aged-tunnels without monitoring systems. Applicability of the proposed method is illustrated by solving an example problem.