Determination of cohesive properties for mode I fracture from compacted clay beams

Tensile fracture in mode I occurs in many geotechnical applications such as in slope stability, desiccation cracking, borehole pressuremeter testing, etc. The cohesive crack model is a powerful and versatile tool that can be used to numerically analyse mode I fracture, that has had very limited usage in geomechanics to date. This research reports findings from testing on single-edge notched beams manufactured from compacted clay fractured in three-point bending. Specimens were tested at a range of moisture contents to determine several fracture parameters including the parameters defining cohesive cracks. The properties for the cohesive crack were back-calculated by matching the numerically modelled load–load point displacement curve obtained using a hybrid continuum distinct element program with the ones obtained experimentally. It was found that the cohesive crack method could be successfully used in matching the load–load point displacement curves for a range of consistencies of the clay from soft to very hard. It is tentatively suggested that linear softening curves may be sufficient for modelling clay fracture, unlike for concrete, which typically displays distinctly bi-linear softening behaviour. Further research and testing along the discussion presented in this paper could be beneficial in numerically analysing geotechnical applications with mode I fracture.