Bedding improvement of lining segments using geotextile tubes

Abstract

During a shield TBM excavation in hard rock, the immediate backfill of the crown immediately behind the shield is technically difficult to realize. With the advance of the cutter head a relocation process of pea gravel within the annular gap is triggered, leading to an insufficient bedding distribution of the first segments behind the shield tail and to an ovalization of the segmental lining at a certain load level. During a test application as part of an ”TBM research initiative“ of the Austrian Federal Railways geotextile tubes were integrated into the exterior surface of the segments. Immediately after leaving the shield tail, the geotextile tube, which is placed all around one ring of segments, is expanded by injection with grout. As a result, an immediate bedding between the rock mass and segmental lining is established, also preventing the rearrangement of pea gravel within the annular gap when the shield is moved forward. The displacement measurements have shown that the ring of segments equipped with geotextile tubes experiences a more rigid body motion like behaviour after leaving the shield tail with a minimal ovalization only. Numerical simulations show the influence of bedding improvement on the ovalization of the ring of segments after leaving the shield tail.