Old Railway Embankment Clay Fill – Laboratory Experiments, Numerical Modelling and Field Behaviour

Abstract

UK Railway embankments are typically more than 100 years old, and, in southern England, are generally composed of high plasticity clay fills. They were built without compaction by end-tipping loosely into place. Significant vegetation growth has developed and, depending on the vegetation type and extent, the embankments are prone to collapse or to severe serviceability problems. The paper summarises laboratory test results on block samples of clay fill. Tests were also carried out on reconstituted soils. The paper considers the varying influences of ‘structure’ on strength, stiffness and permeability characteristics. Numerical analyses were carried out which utilised a non-linear stressstrain model, both pre-peak and post-peak with strain softening towards residual strength. A challenging area is understanding the influence of vegetation; the behaviour of trees compared with grass is considered. The numerical model predictions are compared with a case history where seasonal variations in track displacement were monitored.