End friction effect and initial defect of sample both can cause inhomogeneous deformation

then form macroscopic shear band in soil test. The triaxial equipment of GDS is improved based on digital image processing technique

and used to do drained test of sand. The strain nephogram and local stress-strain complete curve at each sampling time point are recorded; then end friction effect is researched. The result shows that the end friction has significant effect on mechanical properties of sand sample. The radial strain error reaches 10%. The macroscopic inhomogeneous sample is got by putting silt clay block into sand sample; and the formation process of shear band is tested. The evolution of shear band during the loading process shows that the discontinuation of stiffness formed at interface of two materials; with inhomogeneous deformation developing

the macroscopic shear band is fully formed

so as to fracture.