Nfluence of the concrete joint on the spacer system of the excavation under accidental impact

Introduction. Due to the increasing use of underground space in cities, deeper excavations are increasingly being used. These excavations contain more elements and increase the chance of failure of one of the elements. When excavations collapse, there is economic damage and possible loss of life. The current level of research regarding the protection of excavations from progressive collapse and the accidents that have occurred are reviewed. The purpose of the study is to evaluate the influence of modelling of concreting joints between trench wall sections on the redistribution of forces in case of an accidental impact in the form of failure of one strut.

Materials and methods. Numerical finite element modelling of a 16 m deep excavation constructed under the protection of a wall in the ground with a spacer system was carried out. The joints were modelled by interface elements taking into account their deformability and strength.

Results. The modelling of the concreting joints results in a redistribution of the forces in the struts within the same wall section. In the case of normal load combinations, the forces in the struts do not change on average depending on the joint modelling, but in the case of accidental impact, the forces in the design case with concreting joints increase. In the case of progressive collapse within the wall, the direction of action of the bending moments changes. The displacements of the ground surface in the case of joint modelling are smaller than in the traditional modelling method.

Conclusions. The results obtained will allow more accurate modelling of excavation enclosures, making their use more predictable and safer. As further research, more advanced models of concrete contact behaviour are envisaged. The use of identical reinforcement meshes on opposite faces of the wall in the ground is also recommended as a structural measure to prevent progressive collapse.

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