Experimental study on fracture toughness and tensile strength of a clay

Fracture toughness KIC is an important mechanical parameter of a material to indicate its ability to resist fracture failure under mode I load conditions in fracture mechanics. The method to determine KIC of geomaterials and the relationship between KIC and other mechanical parameters such as tensile strength σt were paid close attention by many studies. In this study, the KIC of a clay, which is the core material of a high earth-rock fill dam in Western China, was determined by an improved 3-point bending beam loading assembly on single edge cracked soil beams. The testing results indicated that linear elastic fracture mechanics is suitable for investigating the fracture behavior of the clay. The values of the KIC of the clay vary from 7.10 to 31.43 kPam0.5 with changing water contents or dry densities of the soil beams. The σt of the clay was investigated by a uniaxial tension loading assembly on cylindrical compacted specimens. The testing results indicated that the tensile failure of the soil columns is brittle, and the strain before failure can be neglected. The values of the σt of the clay vary from 19.00 to 90.00 kPa with changing water contents or dry densities of the soil columns. Based on testing data, an empirical linear relationship between the KIC and the σt of the tested clay, which is KIC = 0.3546 σt, was suggested. By analyzing other studies, it was found that the fracture toughness and tensile strength of many geomaterials such as cohesive soil, frozen soil, soft rock and hard rock are also linearly correlated. But the proportionality coefficients are different for different soils or rocks and testing methods.