Small Drills Building Large Tunnels.
The range of applications of microtunnelling systems has been substantially extended by the pipe arch process. In this process the actual tunnel is systematically excavated under the protection of previously constructed pipe jackings. The pipe arch process is the safest and most efficient way of constructing large diameter tunnels over short distances.
Common applications of this method include tunnelling under railway lines or the construction of new metro stations. In such projects microtunnelling is carried out on a large scale. In this technique steel tubes are used in most cases which are pushed forward to create a kind of "safety roof" around the tunnel to be constructed. An ingenious gate mechanism enables the machine to be retracted after tunnelling a short distance into the launch tunnel so that it can start work on the next tunnel from the same side.
Dependent on the geological conditions, freezing plants can be fitted in the steel tubes to freeze the ground below to form a stable "water-soil-casing". Protected in this way the actual tunnel can be systematically excavated and supported. Dependent on the requirements of the project, the jacking frame can be attached to a horizontally and vertically movable platform in order to facilitate the large number of drillings required. The main advantage of this method of construction is that the tunnel to be constructed can be excavated without ground settlement, thus avoiding the need to alter the height of the rail track system.
