Large-scale triaxial tests of dense gravel material at low confining pressures

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The results of a series of large-scale triaxial tests performed on dense, prismatic gravel specimens, with a height of 50cm and a cross-section of 23cm×23cm, are described. The specimens were prepared at a density equal to approximately 95% of the maximum density at the optimum moisture content. Deformations were measured locally using vertical and horizontal local deformation transducers. Stress conditions with selected levels of very low confining pressure were used to simulate specific conditions in the case of road and railway embankments. Particular attention was paid to the bedding error at the top and the bottom ends of the specimens, and to fixing transducers onto the membrane to be used under low confining pressure. The confining pressure was applied by vacuum and varied from 10kPa to 75kPa. Unsaturated specimens were tested under drained triaxial compression using monotonic and cyclic loading with frequencies in the range of 0.5–5Hz. The effects of a large number of load cycles and of specimen preloading were investigated.