Development and preliminary application of a new temperature-controlled triaxial test system for unsaturated soils

In order to study the influence of temperature on the hydraulic, mechanical and acoustic properties of unsaturated soils, a temperature-controlled triaxial apparatus with the bender element system (BES) and precision volume change measurement is developed. The instrument can accurately control and measure temperatures by adding a temperature-controlled inner pressure chamber into the stress path unsaturated triaxial testing system of geotechnical digital systems. A differential pressure sensor and the temperature-controlled inner pressure chamber are combined to achieve the precision measurement of volume change of specimens under different temperatures, whilst the BES is equipped to perform the real-time wave velocity tests. A series of experiments are carried out on the sand in Hangzhou Bay, including the triaxial shear tests under four temperature levels and the wave velocity tests under the same temperature level. The results show that the new instrument can control the temperature stably and accurately measure the volume change and the real-time wave velocity of the specimens under different temperatures. The performance of the instrument is satisfactory. Additionally, the instrument has the advantages of simple integral structure, convenient assembly and disassembly, and the function to perform freely the switching tests between the conventional and the temperature-controlled for unsaturated (saturated) soils without mutual interference. The successful development of the instrument will provide a convenient and effective testing device for the study on the hydro-hydraulic-mechanical-acoustic coupling characteristics of unsaturated (saturated) soils.