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The background, philosophy and approach to the problem are discussed and previous work is summarized. Measurements of the distribution of vertical stress in the subgrade for given depths of ballast, track structural configurations and loading conditions are described. It is shown that the mean maximum vertical stress in the subgrade can be predicted with reasonable accuracy by simple elastic theory. The results of laboratory work in which samples of soil were subjected to repeated triaxial loading are presented. For the cohesive soils tested a level of stress was found above which repeated applications of load caused large permanent deformations and below which permanent deformations were small and terminating. Based on these findings a method of track foundation design is developed in which the depth of ballast required to prevent excessive deformation of the subgrade can be predicted from the results of a simple laboratory repeated load test and a knowledge of the traffic loading to be carried. The Paper concludes with the results of field observations in which the actual behaviour of sites in terms of movement of the subgrade was measured for depths of construction both greater and less than those predicted by the design method. It is shown that small decreases in construction depth from the design depth produce large increases in deformation rate whilst large increases in construction depth over the design depth produce little return in terms of reduced rates of deformation. It is concluded that whilst further research is required the proposed design procedure already produces construction depths that are apparently close to the optimum for the fine grained soils so far investigated.

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The Introducers explained that Britain was preeminent in Europe in its understanding of cost causation. To ensure optimal use of its infrastructure they said it is important that British Rail (BR) accurately attributes costs between businesses where assets are used by more than one business. This requirement is particularly relevant to trainload freight (TLF) because this business uses 17 500 miles of BR's 20 300 miles but only directly owns and manages 2000. (Civil engineering costs are 28% of overall costs for TLF.) The relative lack of direct managerial control focuses attention on the ability to allocate with accuracy.