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A newly designed direct shear apparatus was developed to prevent obstacle friction which occurs between the side wall of shear box and a sand sample during a shear test under a CD-test due to dilatancy behavior of a sample. A couple of independent air jacks with load cells were mounted on the upper counter plate. This system allows the upper shear box to move up and down without tilting during shearing, and, as a result, vertical stress, σ N , can be measured correctly using the upper mounted load cells without influence of friction. A series of CD-tests using the apparatus on Toyoura sand were conducted in order to compare shear properties including shear strength obtained using an ordinary type of direct shear apparatus (Mikasa's direct shear apparatus) and an ordinary triaxial compression apparatus. It was found that strength obtained using the new apparatus gives the same strength as that obtained by CD-tests using a triaxial apparatus and that obtained by CU-tests (φ') using Mikasa's direct shear apparatus. However, CD-tests using Mikasa's direct shear apparatus give 2 to 3 degrees of excessively higher strength. This shows that the developed new system for direct shear apparatus works effectively to prevent the influence of friction problem of CD-tests on sand samples.

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