Multiaxial failure of low-cohesive frictional materials: fracture behaviour and size dependency

Abstract

An experimental investigation concerning the size effect in quasi-brittle materials under multiaxial compressive loading was carried out. Laboratory results are presented concerning the size effect and fracture mechanisms in hollow cylinders using two cement-based model materials. Hollow cylinders in a size range 1 : 4 were tested under external hydrostatic pressures while monitoring their inner-hole deformations. A mild but notable size effect was observed during the tests with strength decrease as specimen size increases. Fracture mechanisms for hollow cylinders during failure were investigated using impregnation techniques and their results indicated the occurrence of splitting type, which encircled the inner holes in a rather uniform manner. Numerical simulations using the distinct element code PFC^2D were performed in order to provide insight into the experimental findings. The model was capable of replicating the failure mechanisms and damage pattern in the hollow cylinder tests. In terms of size effect, the model showed similar trends as those observed during Brazilian splitting tests with a decreasing nominal strength as size increases. The simulation results suggested a statistical effect to be noteworthy for the observed size effects in tension, which was further demonstrated from a good agreement between these results and the predicted size effect from the Weibull theory. In compressive test simulations, a slight increase in strength with size was observed for confined and unconfined compression tests simulations on rectangular assemblies.

Acknowledgements

The professional assistance provided by Ing. G. Timmers in designing and performing the experiments is sincerely appreciated. The financial support by the Dutch Technology Foundation (STW) is gratefully acknowledged.