Identification of the mechanical behaviour of rammed earth including water content influence

A set of tests is proposed to contribute to the experimental identification of the failure surfaces of an elasto-plastic model for a rammed earth along different stress paths such as compression, extension and tensile stress paths. The constitutive model involves two failure surfaces reflecting two different modes of failure within the material, a shear mode of failure and a tensile mode of failure typical of quasi-brittle materials. Secondly, the influence of water content on these failure surfaces is addressed. Such an influence is important to understand when stability of walls against unexpected storage of humidity is modelled since such storage is the main cause of failure of rammed earth construction. Three different water contents were considered in this study. The results show that for the studied material, the dissymmetry of behaviour between compression and extension is far greater than another quasi-brittle material such as concrete, which is new. As a first attempt, the influence of the water content can be modelled by a mere shift of the shear and of the tensile failure surface along the hydrostatic axis. Particularly, in the range of the investigated water contents, the shape of the failure surface can be stated as independent of the water content where just the apex will shift towards smaller values.