The design of lining and un lining of a water pressure tunnel is carried out through the detailed estimation of rock mechanical and hydrological factors and the establishment of the design guideline. The field investigation for rock mass rating and joint pattern, laboratory rock test, numerical analysis on mechanical stability using UDEC, wedge analysis for the estimation of rock block falling according to joint pattern, and hydrological analysis for the lining and un lining conditions are carried out. The design criteria are evaluated for the factors such as support pattern related with RMR range, hydraulic jacking and leakage according to the condition of rock stress and inner/outer water pressure. With these guidelines, the lining and un lining sections are designed for the water pressure tunnel with the diameter of 2.6m and the length of 5.3km. This assessment technique and the design criterion can be used as a guideline in the design of lining and un lining of the water pressure tunnel.
The lining of a water pressure tunnel has a role in the increase of mechanical stability, the prevention of rock fall at tunnel crown, the suppression of hydraulic jacking and ground water leakage, and the improvement of water now by reducing the frictional resistance between water and tunnel wall. On the contrary to these advantages, additional cost for lining must be increased. In design of lining and un lining, therefore, various aspects should be considered such as tunnel stability, efficiency of water now, and the purpose and maintenance of tunnel. Many water pressure tunnels in Norway have been constructed without lining(Broch 1985, 1988, Selmer-Olsen 1985). This is mainly based on two aspects. One is that the rock condition in Scandinavia peninsula is very hard. The other is the basic concept of support design that some small rock fall is allowable as far as this does not influence on the tunnel stability, head loss of water pressure and maintenance of water flow channel, of course, there are some cases of collapse of unlined tunnels. In construction of water pressure tunnel recently in Korea, the lining is basically included in the support design after the experience of rock fall accident of an unlined water tunnel a few years ago. The water tunnel to be considered here is also designed as lining for the whole tunnel length at the initial design Stage. However, rock is found out very fresh and hard during actual excavation and so the initial lining design turned to be re- considered. for the re-design of lining and un lining pattern of this water pressure tunnel, the detailed estimations of rock mechanical and hydrological factors are carried out and the guideline of the lining design is established. The field investigation and laboratory test for the rock mass classification, the numerical analysis using UDEC and UNWEDGE code for the estimation of mechanical stability, and hydrological analysis for the estimation of the water now efficiency are carried out. The basic design criteria are evaluated.
