Volume 29, Issue 5 (September 2006)
Development of a Direct Shear Apparatus with Rock Joints and Its Verification Tests
A new direct shear apparatus for natural rock joints and artificial joints has been developed that can achieve constant normal stress (CNS), constant normal load (CNL), and infinite normal stiffness (INS). The CNS condition during shear is maintained by changing the normal load corresponding to a reduced contact area with shear displacements. The deformation of the apparatus due to normal loading is excluded in order to obtain the pure displacement of the specimen. The deformation of the apparatus due to shear loading included in the total displacement is also minimized by measuring the relative displacement between the upper and lower shear boxes. Four degrees of freedom are employed in this study: two transitional motions of the upper and lower shear boxes and two rotational motions of the upper shear box. A series of tests for CNS, CNL, and INS conditions have been performed to verify the accuracy of the control system for the same roughness. Other tests have also been performed on saw-tooth joints with asperities having inclinations of 16.7° and 26.6°, and JRC values of 10 and 15 were obtained from the tests, respectively. The maximum dilation angle occurs at peak shear strength, which shows a good agreement with Barton's model.