A triaxial swelling test apparatus

Abstract

This paper describes a new triaxial swelling test apparatus, and presents some of its applications to testing procedures. The apparatus was developed to simulate in-situ stress state in laboratory specimens, and to determine the three-dimensional swelling characteristics of clay-bearing rocks. The cell is based on the oedometer principle, but places a specimen within its jacket, so that various levels of confining pressure can be applied. Its main parts are: (1) loading platens including porous stones; (2) rubber jacket and its seating cylinder; (3) end caps. The apparatus can be used to determine: (1) axial swelling stress under various confining pressures; (2) axial swelling strain under various confining pressures; (3) axial swelling stress as a function of permitted axial swelling strain under various confining pressures. The first two tests are simple, and give results that are useful in preliminary analyses. Only the third test describes the complete stress-strain behaviour. The complete swelling stress-strain tests were performed for a marl sample, whose results are given in the paper, and for some other samples. A simple mathematical expression is derived for the 'three-dimensional swelling behaviour' of clay-bearing swelling rocks. Its parameters depend on the type and amount of clay minerals, initial water content, and other variables.