A unified failure criterion for unstabilized rammed earth materials upon varying relative humidity conditions

• Impact of the hygroscopic conditions on the strength of earthen constructions is analyzed.
• Compressive and tensile strengths are determined on earthen materials upon varying relative humidity.
• Suction plays an important role on the strength of the material.
• A unified failure criterion including the effect of the suction inside the stress state is proposed.

Uniaxial compression tests and indirect tensile tests are performed on compacted clayey silt samples upon varying suctions in order to assess the influence of changes in the relative humidity conditions on the strength of unstabilized rammed earthen building materials. The results show that suction plays an important role on the strength of the material. Also the ability of the Belgian clayey silt to develop sufficient mechanical strength to be used as an unstabilized earthen construction material is demonstrated whatever the relative humidity conditions, excepted the fully water saturated state. The experimental data are interpreted in the context of unsaturated soil mechanics using the generalized effective stress concept. This constitutive framework allows defining a unified failure criterion predicting the strength of the earthen building material as a function of the environmental hygroscopic conditions.