No abstract

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

No abstract

No abstract

No abstract

SUMMARYStrain localization developing inside soft rock specimens is examined through experimental observation and numerical simulation. In the experimental study, soft rock specimens are sheared at different strain rates under plane strain conditions and deformation and strain localization characteristics are analysed. Transition of localization mode from highly localized mode for higher strain rate to distributed and diffused mode of strain localization for lower strain rates was observed. In the numerical study, simulations of plane strain compression tests are carried out at different strain rates by using an overstressed-type elasto-viscoplastic model in finite element computations. The role of strain rates on setting gradients of strain fields across shear band is clarified. The probable mechanism for transition of localization mode is discussed.

This paper describes the development of a new digital image-based deformation measurement system for triaxial tests on soils. Three digital cameras placed on radii at intervals of 120° viewed on plan outside a transparent triaxial cell were used to capture images of a deforming cylindrical soil specimen at various instants. A digital image correlation program was written to analyze the captured images, using ray tracing to take account of image distortion due to refraction at the interfaces between the cell fluid, the cell wall, and the atmosphere. The technique is validated with reference to a sand specimen tested in drained triaxial compression. Typical implementations of the system to study surface deformation characteristics (e.g., barreling, onset of localization, and shear band evolution) of deforming soil specimens are illustrated.

No abstract