Mechanical Behavior and Constitutive Modeling of Cement–Bentonite Mixtures for Cutoff Walls

Cement–bentonite mixtures are commonly used to build cutoff walls, which limit water flow and underground transport of pollutants. These artificial materials are employed due to their very low permeability and adequate shear strength and ductility. In this paper, experimental results about the microstructure and mechanical behavior of three different cement–bentonite mixtures are presented. Specimens of these mixtures were subjected to oedometer and consolidated-undrained triaxial tests. These results were then used as a basis for the definition of a suitable constitutive framework. A quite good reproduction of the experimental results up to the peak strength was obtained using the classical Modified Cam Clay model, which could then be used satisfactorily when conventional analyses aimed at assessing the stability of cutoff walls are required. The reproduction of the strength degradation and the strains occurring in the postpeak stage requires, however, a more advanced constitutive model. To this extent, the Modified Cam Clay framework was enhanced by introducing some features commonly employed to reproduce the mechanical behavior of granular materials. This model may be useful for the real-scale analysis of more critical cases when local failure mechanisms are likely to occur and may influence the functionality of the wall.