Development of multi-function torsional shear apparatus and evaluation of cyclic deformation-strength characteristics of sand under various stress conditions

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In this study, low cost, high resolution and high performance direct drive motor (DDM) used as axial and torsional loading equipment of torsional shear apparatus. In this DDM,changes of position, torque, speed control mode can be done easily by signals from a computer through the RS232C during testing.To examine the effects of loading controlled conditions on the cyclic deformation characteristics of sand under wide range of strain level, axial load (torque) and axial displacement (rotation angle) controlled cyclic triaxial (torsional) shear tests were performed by the above DDM loading system. And also, displacement and load controlled undrained cyclic triaxial and torsional tests to obtain the liquefaction strength were performed.Test result showed that :1) Axial load (torque) and axial displacement (rotation angle) controlled tests under wide range of strain levels can be performed by the developed loading equipment usign DDM.2) In the load controlled undrained cyclic test, the shear modulus and the damping ratio are not continuously measured at strain revel upper about 0.1%. The reason for this is that the strain kincreases rapidly due to the decrease of effective confining pressure. On the other hand, in the displacement controlled undrained cyclic test. cyclic deformation properties are continuously measured at large strain level.3) There existed a unique rule between results of load and displacement controlld liquefaction tests. This rule was independent of the relative density, the loading cycles and the types of tests (triaxial and torsional). On the basis of this relation, the cyclic strength in load controlled tests can be evaluated to some extent by performing displacement controlled cyclic tests.