Development of shear device for large deformation of sand

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A new shear device for sand was developed which can study the granular movement of sand particles prior to and after the peak strength and during the state of residual strength.The shear device houses a specimen which measure 5^<**>5^<**>10cm^3in size. A vacuum pressure is introduced into the specimen in order to produce an effective confining pressure. This measure makes pressure cell unnecessary and enables a microscope to directly approach the specimen. The microscopic observation of granular movement is made further easier by covering one of the side faces of the specimen with a transparent acryl plate. The microscope employed in the present study has CCD transducers of digital type which make it possible to analyze the observed data by a computer.The present research revealed the following issues. Firstly, granular movement prior to the peak strength consists of falling of grains into adjacent large voids. This phenomenon occurs more or less uniformly in the specimen. In contrast, after the peak strength, shear movement of grains is concentrated in a narrow domain which is often called a shear band. The width of the shear band is approximately 10 times the grain's diameter. Both shear and rotational movements are significant in the shear band. In particular, the rotational movement was found to be irregular, occurring in both positive and negative directions. The dilatant motion was also found more important in the shear band than outside of it.