A new double-cell system for measuring volume change of a soil specimen under monotonic or cyclic loading

For accurately measuring the volume change of a soil specimen under monotonic and cyclic loading, a new double-cell system is described in this paper. This newly designed double-cell system is equipped with local linear variable differential transformers (LVDTs) and can also accommodate large specimens. Careful calibrations, including the effect of cell pressure change, creep of inner cell volume, the effect of temperature fluctuation, and loading ram movement, are presented and discussed by comparing the possible errors with those of other existing apparatuses. This system exhibits superior performances in volume change due to cell pressure, temperature sensitivity, and accuracy of loading ram movement. Three monotonic compression tests under saturated and unsaturated conditions were conducted to evaluate the performance of volume change measurement and local LVDTs. Moreover, six different frequencies were used to verify the workability and accuracy of this system in conducting cyclic testing. The results indicate that the maximum frequency this system can achieve, with a satisfactory precision, is 0.2Hz, which is four times higher than what the previous systems could achieve. Finally, several suggestions are made on how to improve the system's performance even better.