Abstract
Some important modifications were made to an existing triaxial testing apparatus to more accurately evaluate the stress-strain behavior of geomaterials for wide ranges of strain and strain rate. An electro-mechanical loading device was specifically designed to control strain states and stress paths and to study the quasi-elastic properties of geomaterials at any given stress state. The device is now driven by an a-c servo motor, allowing for changing the strain rate about three orders of magnitude without any intermission in each test. A 16-bit A/D card has been adopted also to increase the resolution in data acquisition. The long-term stability of a local axial gage, LDT, has been ensured to evaluate creep deformations as well as post-creep behavior of geomaterials, which should be properly understood for many practical engineering applications. High performance of the system is demonstrated by presenting some typical results from undrained cyclic tests at very small strain levels for a wide range of strain rate and an undrained monotonic loading test for a wide strain range, both on a compacted silty sand. It is shown that the equivalent Young's modulus and damping ratio at very small strains have a clear sensitivity to both strain rate and ageing period. For monotonic shearing tests in a wide range of strain, the isotach property and the effects of changes in the strain rate are also presented.
