New mixed boundary, true triaxial loading device for testing three-dimensional stress-strain- strength behaviour of geomaterials

This paper presents a brief review of true triaxial apparatuses (TTAs) developed in the past and their advantages and limitations. Considering the limitations of previous designs, a new true triaxial loading device that provides mixed boundary conditions for a true triaxial apparatus (TTA) is introduced. This loading device consists of four sliding rigid plates and two flexible loading faces. The setup of the loading device together with the whole true triaxial system is de- scribed. Frictions between sliding plates and the soil membrane surfaces in the new loading device are examined. A three- dimensional finite element (FE) modelling study is carried out on the stress and strain distribution of a soil specimen subjected to loading from two different loading devices. It is found that stresses and strains of a soil specimen subjected to loading from the new sliding plates are far more uniform than those subjected to loading from nonsliding plates with pre- set gaps. Finally, the paper presents the applications of the present TTA with the new loading device for testing studies of a completely decomposed granite soil and a geofoam. Typical results are presented and discussed. It is found that the present mixed boundary loading device is very suitable for true triaxial testing on both soils and geofoam, especially under large strains or compression without corner contact problems.