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.