MOBILISATION OF THE SPATIAL EARTH PRESSURE ON TBM
A novel construction of a tunnel boring machine (TBM) by Hochtief Construction AG (http://www.hochtief.de) is aimed for a continuous excavation process in soft soils. Rigid plates pushed radially from the TBM into the surrounding soil guarantee a sufficient reaction force at all driving stages. The maximum reaction force corresponds to the spatial passive earth pressure acting at the plate area. The mobilisation of the earth pressure is a function of the radial displacement, the latter being important for the design of machinery.
Large scale experiments and a 3-D FE model have been established for the study of this problem at the Institute of Geotechnical Engineering of TU Dresden, Germany (http://www.tu-dresden.de/biwigt/grundbau). The surrounding ground has been experimentally modelled by a medium sand. In the numerical simulations, the Tochnog implementation of the hypoplastic constitutive model for sand has been applied. The displacement of the plate has been approximated by velocity boundary conditions at the nodes of the plate area.
In the numerical parametric studies, Tochnog's scripting capabilities have been extensively used to generate several geometrical configurations. The attached figure shows total displacements of the soil body for one of them. A heave of the soil mass starting from the plate and reaching the ground surface cab ve recognised. The second figure depicts the concentration of horizontal stresses around the plate.