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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British Railways (BR) is structured into eight commercial businesses of which six have to trade profitably without any government subvention. The most profitable passenger one is InterCity which is managed through sub-sector or route profit centres. Two of these dominate the trading results: the West Coast which was electrified between 1956 and 1967 (London to the West Midlands and the North West) and extended to Glasgow during 1970 to 1974; and the East Coast which is the subject of this paper. The InterCity network is shown in Fig. 1; the West and East Coast routes are indicated. InterCity was the sponsor of the electrification project.

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