Experimental analyses of an optimized shear load transfer in the circumferential joints of concrete segmental linings

The coupling of subsequent rings in the circumferential joints of tunnel lining systems is of particular interest in mechanized tunnelling and a controversial issue in discussions. On the one hand, interlocking systems such as "cam & pot" can be of use in limiting the lining's deformation. But on the other hand, unfavourable conditions often lead to repetitive and significant damage that decreases the tunnel's lifetime. This paper describes the experimental results of a three-part optimization concept (structural analysis, topological optimization and experimental verification) that was tested for concrete linings using the example of the shear coupling mechanism. First, geometrical dependencies are analysed which reveal predominantly stronger cams than corresponding pots. Hence, pot bearing capacities are increased, transferring topological optimization results to reinforcement concepts featuring micro-mesh reinforcement, steel fibre cocktails and rebars welded to anchor plates. The latter especially resulted in comparatively stronger pots along with considerably better ductility. Nevertheless, pots still represent the weaker part and are crucial for the design. Therefore, a concept with steel dowels and predefined static boundary conditions was tested. The results are characterized by a significantly lower scatter of bearing capacities accompanied by much better ductility.