Cracking of unsaturated clays using a newly developed small-beam bending apparatus and analysis by digital image correlation

This research presents a comprehensive investigation on the impact of initial imposed suction both on the applied tensile force and the cracking phenomenon of unsaturated clayey soil samples. The proposed experimental approach is based on using a new developed apparatus for testing the indirect tensile force on small-beam bending. Several sets of bending tests have been carried out on small clay beams initially submitted to different levels of suction (361 MPa, 110 MPa and 38 MPa). The approach consisted first to study the global behaviour by estimating the maximum tensile force Fmax which controls the initiation of tensile cracks. The results show that Fmax varies with the initial imposed suction level as well as the consolidation stress direction representing the initial loading applied to the sample during the stage of clay core preparation. Then, unload–reload cycles allowed to describe the reversibility of beam’s behaviour versus the initial imposed suction. Finally, by using digital image correlation technique, the formation and propagation of cracks were precisely captured through the measurement of the local strain variations, especially close the crack tip. •Relationship between the global behaviour and the local behaviour of clay under bending using DIC method.•Analysis of the reversibility of the behaviour under several unload–reload cycles after the first tensile load and effect of the initial imposed suction.•An original approach by estimating the local suction around the crack especially at the tip to study the crack initiation and propagation mechanisms.