CONSTRUCTION OF TUNNELS WITH HORIZONTALLY STEERED SHIELD DRILL : TECHNIQUE FOR DRIVING LARGE GALLERIES UNDERGROUND

For driving tunnels in weak soils a number of drilling-techniques have been developed. One of these is the shield method: a drill head (the shield) is thrusted horizontally through the ground, excavating soil on the front side of the head, while the tunnel is being constructed at the rear. With the shield method tunnels with large diameters can be constructed. This article considers the principle of the shield method, in which various techniques for controlling the ground water and the excavation process are discussed. To construct the tunnel wall simple segments of high-quality concrete are mostly used nowadays. This is cheaper than the formerly used double wall system (inner and outer lining). Finally the assessment of the depth position of the shield tunnel is briefly discussed. (TRRL)