Development and validation of three-way rigid true triaxial apparatus for soils

The intermediate principal stresses have a significant effect on the stress-strain behavior of soils. To describe the stress-strain behavior of soils more accurately, it is necessary to carry out true triaxial tests in the field of soil mechanics. A new three-way rigid loading true triaxial apparatus independently developed by Xi'an University of Technology is introduced, including the pressure chamber composed of four bottom rolling and side sliding rigid plates, a rigid specimen cap and a rigid bottom plate, the three-way servo-hydraulic stepping motor loading control system, the computer and storage intelligent control system, and the water-air suction control system panel. By dividing the rectangular soil samples into true triaxial rectangular shear layer specimens and soil blocks of the transfer layer, transferring the vertical principal stresses through the end of the transfer layer acting on the rectangular shear layer and applying the orthogonally bi-directional principal stresses with the side sliding rigid plate, the technical problem of interference in using the traditional three-way rigid plate loading is solved. Through the verification tests on the remolded loess and saturated sand, the rationality of the apparatus is validated, and the failure mode of the samples and the cause of the test errors are summarized. The proposed apparatus has the advantages of simple operation, uniform deformation and intelligent control of automatic loading.