This paper describes model tests carried out to investigate the contribution to the resistance to 11 the lateral movement of a railway sleeper attributable to the ballast shoulder, for a range of 12 shoulder widths and heights. During the tests, the deflection and resistance were measured 13 and photographs taken. Photographs were analyzed using a digital image correlation 14 technique to identify the zones of ballast surface disturbance, these demonstrate that a bulbed 15 failure volume is mobilized at the ultimate limit state. An idealised three dimensional failure 16 mechanism is proposed and resistances are calculated using the limit equilibrium approach. 17The calculation is found to provide a reliable estimate of the measured resistance. The work 18 identifies the optimum shoulder width and height. The calculations are extended to 19 demonstrate that when a number of sleepers are moved simultaneously the sleeper end 20 resistance may be 1/3 less per sleeper than that indicated in tests on an isolated sleeper. The 21 image analysis and limit equilibrium calculations show that this is due to the overlapping of 22 mobilized failure volumes from adjacent sleepers. 23
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