Pressures on a Retaining Wall by an Expansive Clay

A reinforced concrete retaining wall, 7.5 m deep, in the basement of the Gouger Street Mail Exchange, Adelaide, South Australia, supports stiff Hindmarsh clay over most of its depth. Earth pressures on the wall and soil suctions in the clay have been monitored for several years. The initial earth pressures were zero. Subsequently a pressure increase occurred at the base of the wall and moved progressively up the wall with time reaching a maximum value of five times the overburden pressure. A theoretical model using the finite element method of solution with non-linear (hyperbolic) material parameters (previously developed to analyse the load-moisture-displacement response of expansive clays) was used to check the proposed mechanism of behaviour of the wall. The model gave earth pressures on the wall comparable in both magnitude and distribution to those observed. While the interaction problem was more complex than the model used, the results suggested that the interfacial conditions between the wall and clay, the movement of the wall and the magnitude and extent of the swelling of the clay may be significant factors.