Volume 27, Issue 5 (September 2004)
Triaxial Testing System for Measuring Loading-Rate Effects During Cyclic Tests of Sand
A triaxial testing system is described for obtaining reliable data for measuring stiffness and damping of a sand by applying cyclic load in the frequency range between 0.005 and 2.0 Hz. The system is equipped with LDTs to measure axial deformations locally, gap sensors (GSs) to measure axial and radial deformations, and a load-cell. The data acquisition units of these components were critically examined for the possible existence and the influences of time lag in the stress-strain responses of cyclic load. For the measurement of a pair of corresponding stress and strain, data acquisition systems consisting of various electronic transducers must be identical to each other. Damping ratio evaluated with axial strain by the inductive-type sensor GS was found unreliable when used with a strain-gage type load cell to measure deviator stress. The problem was totally absent in the pair of load cell and LDTs as they are strain-gage type devices having similar data acquisition units. Using the latter combination, the stiffness was observed independent of frequency, while damping showed noticeable dependency on the frequency of loading.