Strength and volume change behaviour of a sand–bentonite mixture

Abstract

Triaxial and one-dimensional swelling tests have been performed at pressures up to 3 MPa on a compacted sand–bentonite mixture with potential use for containing nuclear and other toxic wastes. The material expands in a low stress range up to 0.6 MPa, with the volumetric expansion depending on the confining pressure and the duration of the tests. Swelling is inhibited by confining pressures in excess of 0.8 MPa. The strength of the material corresponds to that of the bentonite fraction. The material is dilatant at low stresses (below about 0.8 MPa) and compressive at higher stresses. Normalized bulk moduli are significantly affected by stress level, whereas normalized tangent shear moduli at 0.5q max decrease with increasing confining stresses. The data suggest a modified critical state model for the stress–strain–time behaviour of the material. Key words: bentonite, sand–bentonite, mixtures, compaction, triaxial, strength, compressibility, critical state, nuclear waste, containment.