Keywords: asphalt, contact, deformation loading, FEM, foundation, friction, laboratory tests, shear stress, sliding joint.

If a structure is in a direct contact with other elements or structures and free deformation cannot occur, friction and shearing stress appear on the contact surfaces. At the same time, internal forces in the structure increase. This situation is typical of foundations where the structure cannot deform freely because of the subsoil. The source of the horizontal relative deformation can be the foundation structure itself (creeping, shrinking, temperature changes, prestressing) or the subsoil (mining activities). Generally, the internal forces may reach considerable values. For the sake of structural reliability, the structure must be reinforced with many reinforcements.

Application of a rheological sliding joint can considerably decrease the friction between the foundation and soil and can result in lower internal forces and higher structural reliability. It was proved in the 1980s that the sliding joints in foundation structures would reduce the friction. If the asphalt felts are exposed to the shear load, they have a specific behaviour that generates a viscous flow. The calculation method developed in those years is, however, rather outdated now and can be used for very approximate or general estimates only. Furthermore, the calculation method mentioned can be applied to a rather limited group of asphalt felts but technologies used for production of the asphalt felts differ considerably from those used in the past.

The sliding joint consists of a loosely laid or melted bituminous felt on a levelling concrete layer. Another possibility is to use molten mastic asphalt or a plastic foil. The sliding joint is either covered with concrete finish or the foundation structure is placed directly on that felt.

Consequently it was decided to look for new calculation methods based in particular on the finite element method and to test advanced asphalt felts. Contact elements represent an alternative that makes it possible to model realistic behaviour in a foundation bottom and a foundation bottom with a sliding joint with a certain accuracy. Functions of the model have been verified for a practical example by the deformation of a strip foundation on the subsoil In the calculation, time sequences of specific loads have been taken into account. The result is that if the sliding joint is applied the internal forces determined in the two-dimensional model do not differ too much from the three-dimensional model.

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