Limit of crack depth in KIC testing for a clay

Fracture toughness (KIC) is a very important parameter to evaluate fracture behavior of materials. Three-point bending (TPB) test on a single edge cracked beam (SECB) is often used to determine the value of KIC of soils. Depth of initial crack (a) of the SECB specimen may affect the tested value of KIC, limit of crack depth is therefore necessary in order to obtain the value of KIC. In this study, a red clay, distributed widely in south-west of China, was used to investigate the limit. Three-group TPB tests on 63 SECB specimens with different dimensions and properties were carried out. Based on the testing results, the limit of crack depth for the clay, i.e. the ratio of initial crack depth to specimen width a/W = 0.3-0.6, was suggested.