EARTH PRESSURES ON AN INTEGRAL BRIDGE ABUTMENT: A NUMERICAL CASE STUDY

DAVID MUIR WOOD and DAVID NASH

ABSTRACT: Earth pressures are generated on the abutment wall of an integral bridge as a result of thermal expansion of the bridge deck. This provides an example of soil: structure interaction where a rational result can only be obtained if the relative stiffness of the fill and the structure is taken into account. The problem must be understood and analysed as a whole. A numerical case study is described in which analyses of a typical integral bridge are used to show that, for the flexible abutment wall being considered, the development of earth pressure is primarily controlled by the stiffness of the fill and is hardly influenced by its strength. Comparisons are given between computed earth pressures and those proposed by design guides. The fill is described as an elastic-Mohr Coulomb perfectly plastic material. Typical stress paths for elements behind the wall indicate that the nature of the loading is dominated by compression rather than shearing. The selection of stiffness properties-for which very little reliable information will usually be available-is discussed and a possible range of values is proposed.

Key words: abutment, bridge, design, lateral pressure, (IGC: E12/E2/D6)