Hydroschildvortrieb im Lauenburger Ton: Untersuchungen zur Adhäsivität des Baugrunds

Hydro shield tunnelling in Lauenburg Clay: Investigation of adhesion of the ground

In 2008/2009 the River Ems, Northern Germany had to be crossed by a gas pipeline. The river crossing was to be provided by an inverted siphon with an internal diameter of 3 m bored by a hydroshield TBM. A comparatively long section of the tunnel was intended to be in the "Lauenburger Ton", a cohesive clay layer. Regional construction experience shows the Lauenburg Clay has to be considered as potentially adhesive, with an obvious risk of the shield clogging with adhesive clay. Adhesion was investigated as part of the geotechnical survey using the test device developed at the Technical University of Darmstadt. Adhesive stresses were determined as a function of the in-situ consistency parameters of Lauenburg Clay. The results showed that there will be a serious risk of cohesive soil adhering in the shield system causing delays or worse problems to the progress of tunnelling. The evaluation of the adhesion test results impacted the design of the river crossing alignment and the set up of the tunnelling shield. On the one hand, the depth of the alignment was changed to reduce the section lengths in the Lauenburg Clay and on the other hand, additional jetting nozzles were placed in the shield to erode glued clay instantaneously. The study shows the principles of adhesion testing on cohesive soils including the interpretation and evaluation of comparative test results. Additionally, the practical use of these investigation results are demonstrated with the design of the river Ems crossing alignment and the setup of the jetting nozzles on the tunneling shield.