Advances in research of rock masses containing discontinuous joints in direct shear test

Direct shear test is an effective approach for studying rock masses containing discontinuous joints;through the test,both failure models of joints and of rock bridge,when one of the principal stresses is tensile,can be simulated.Based on this test,failure mechanism has been widely researched;and shear strength criteria have been put forward,such as Jennings method,Lajtai rock theory,shear theory in fracture mechanics,combined failure theory of tensile and shear.However,the failure mechanism is not fully clear,and some parameters in shear strength criteria,for examples,compression transferring coefficient and shear transferring coefficient of rock joints,fundamental shear strength and angle of internal friction of rock bridges,etc.are still uncertain.Closing constitutive relation and shearing constitutive relation of rock masses containing coplanar discontinuous joints,as well as maximum failure strength of rock masses containing noncoplanar discontinuous joints need deeper research.Direct shear testing machine with servo system,static strain tester,acoustic emission technique,nondestructive testing technique,etc.will be greatly helpful to further research on rock masses containing discontinuous joints.