This project (realized as subproject in the frame of collaborative research center SFB837) mainly focuses on the investigation of hydro-mechanical interactions induced by mechanized tunneling in normally consolidated structured clays (1st and 2nd phases of subproject) as well as over consolidated clay rocks (in the 3rd phase). In this frame, a hierarchical constitutive model for natural structured soft clays in the frame of bounding surface plasticity is developed and an automatic constitutive model adaption technique is proposed to analyze the hydro-mechanical (HM) coupled interactions in the near field around the tunnel. The current third phase of A5 aims to study the feasibility of TBM tunneling in swellable clay shales and to develop an adequate numerical model for mechanized tunnel excavation in such soft rocks with the potential of swelling upon water uptake. Special attention is being paid to the variation of HM properties (e.g. shear strength and permeability) of the material in the excavation damage zone (EDZ) by focusing on the saturation of the clay rock due vapor-water fluid flows in the clay matrix (micro and macro pores), bedding planes and fractures. Furthermore, the evolution of the swelling pressure with deformation of the grout and lining segments will be investigated for the purpose of optimal lining structural design. For the validation of the swelling model that is governed by suction, saturation and deformation a series of tests have to be conducted. For this purpose, an innovative swelling test device for tunneling relevant boundary conditions is developed that allows conducting swelling pressure test under fully controlled HM boundary conditions. In these cells, the samples can be saturated with water (advection) or vapor (diffusion) while the deformation (e.g. strain) or stress can be controlled during the test to mimic various tunnel support reactions (e.g. rigid and flexible supports). In the numerical part, the shape and size of the EDZ is studied by numerical simulations with a higher order gradient model to account for microstructure effects such a dilation and permeability increase on the shear bands. Various boundary conditions relevant to mechanized tunnel are examined, in particular to study the swelling pressure development for tunnel support with different rigidities. The results will be validated using in situ measurements from the new Belchen tunnel in Switzerland that is excavated in Opalinus clay shale.
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Last update: Sep 08, 2022