Many studies on the mechanical phenomena of soil in box shear test have been done, but few studies on the structures of the shear layers in the test have been done.
The structures gradually change with proceeding of the test. The author prepared three types of the shear layer at different three stages of the test (1st: stress of about three fourths of shear strength, 2nd: shear failure, 3rd: creep). And in order to take X-ray stereoradiographs of the structures, contrast media were pulled into the voides in the soil samples. The results of this study are shown bellow.
The shear layers at the 2nd and the 3rd stage have fully developed and the layers are formed with very many small shear planes which link together in chains. And the chains crowd together like branches of tree. The shear layers at the 1st stage have not yet developed in many cases.