Evaluating shear test methods for stabilised rammed earth

Abstract

Rammed earth is an accessible, sustainable and increasingly popular building material. Owing to a lack of research, current design standards for rammed earth have taken a conservative stance on material attributes like shear strength. Evaluating the shear strength of rammed earth is particularly important in seismic areas because of the material's high mass, low ductility and propensity to fail in shear. Shear test methods designed for other materials have typically been used in practice to determine the shear strength of rammed earth. In this research the design shear strength guidance available in current earth building standards was compared with experimental shear strength results for stabilised rammed earth. The triaxial (geotechnical) and triplet (masonry) tests were used to evaluate specimens reinforced with natural fibres: sisal and New Zealand flax. Both shear test methods showed that the shear strength capacity of cement-stabilised rammed earth was greater than the current guidance provided in the earth building standards. Recommendations were made to use the triaxial test to evaluate the shear strength of stabilised rammed earth and to allow the use of design shear strength equal to 7% of the compressive strength.