Keywords: FETI method, earth pressure, plasticity, slip surface.

The experimental and numerical research of the earth pressure problem has made significant progress during the past fifteen years by using an original medium size experimental device and advanced original software. The research has dealt with the behaviour of soil and soft rock mass during various types of movement of retaining structures. The retaining structures and soil body can be physically modelled using an experimental device filled with the soil. The device makes it possible to move the front retaining wall arbitrarily (including rotation about the bottom on top edge and translation). The displacements and failure processes of the soil as well as both components of the contact stress, i.e. the normal pressure and vertical friction at the rear face of the retaining structure, were monitored and analyzed. Also the displacement of the front retaining wall was monitored automatically and continuously.

Finally experiments were focused on the simulation of passive earth pressure which was induced by rotation of the retaining wall about the top. During the course of the experiments, one major slip surface evolved. The aim of the numerical analysis was to model the slip surface evolution. In the first approach, the finite element method and the Mohr-Coulomb plasticity model were used to describe of the response of soil in the experimental device for small angles of the front wall. The results showed that the plasticity model can be easily and sufficiently used. The numerical model determines the slip surface corresponding to the experimentally obtained surfaces. In the case of larger angles, the wedge of soil close to the front wall moves similarly to a rigid body and no additional plastic zones are developed. Only strains localized in the slip surface grow and a clear discontinuity developes.

Description of discontinuity along the slip surface requires special attention. The displacement field is not continuous and the classical formulation of the finite element method is not applicable. Various types of contact elements located in the discontinuity are very popular but difficult determination of their material parameters is the main disadvantage. Application of a suitable domain decomposition method can lead to an efficient description of the discontinuous displacement. The most suitable method is the FETI method which uses the rigid body modes. A special interface condition on the slip surface can be easily prescribed.

This paper presents the modelling of the slip surface in the non-cohesive soil using the Mohr-Coulomb plasticity model. The slip surface is taken into account during the decomposition of the finite element mesh because it is identical to the subdomain interfaces. The FETI method is used for larger angles where the wedge of soil close to the rotated wall moves similarly to a rigid body.

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