Experimental Research On Fracture Toughness K_IC Of Remolded Clay

The traditional theories of strength of soils,such as compressive and shear strength,cannot satisfy the requirements for solving the fracture-induced problems.Thus,more attention has to be paid on the characteristics of soil fracture.However,there have been no relevant standards on the apparatus and testing method for soil fracture toughness yet.In order to study the fracture toughness Kic of remolded clays,a new apparatus was developed on the basis of the strain-controlling direct shear apparatus,which eliminates the influence of self-gravity of the samples existing in the traditional three point bending test.A series of experiments have been conducted on remolded clay samples.The effect of initial fracture morphology,water content,dry density,particle gradation,sand content and loading rate on the fracture toughness Kic were investigated through the tests and the results of the tests were analyzed.The following conclusions can be drawn:(1)The new developed apparatus can be effectively used to measure the soil fracture toughness,and the corresponding mold can be used to prepare reliable samples.The experimental results of new developed apparatus have a good stability.(2)The initial crack morphology can affect the value of fracture toughness of remolded clays.The samples with U-shaped initial cracks have the greatest frature toughness,while the samples with V-shaped initial cracks have the smallest fracture toughness.(3)The change of water content and dry density has a significant effect on the value of fracture toughness of remolded clays.With the increasing water content,the fracture toughness of soil samples first increases and then decreases,showing that there exists an optimal water content where the fracture toughness of soils is the greatest.As the dry density increases,the value of the fracture toughness almost increases linearly.(4)The increase of sand content and coarse grain content in the sample has a significant negative effect on the fracture toughness of remolded clays.With the increasing sand content or coarse grain content,the fracture toughness value of the samples decreases,and the influence of sand content on the soil fracture toughness is more obvious than that of coarse grain content.(5)In the range of loading rate used in the experiments,the change of the loading rate has little influence on the fracture toughness of remolded clays,which can be neglected.