A novel experimental study to investigate the interface properties of rammed earth

Rammed earth is a monolith structure constructed by compacting partially saturated soil in layers within a formwork. Few studies have pointed out the lack of experimental data on rammed earth layer interface strength and their importance in design consideration. Currently available testing procedures such as shear box, triaxial, triplet, push-over and diagonal compression tests have their own limitations, mainly their cost, which make them unlikely to become a standard procedure. This paper introduces a wedge tool technique to explore interface shear strength properties with ease. Three pairs of metallic wedges with different testing inclination angles (45, 30 and 20°) were designed and tested for two soils. Specimens tested at these inclinations provide a combination of shear and normal stress acting on the interface. Tests on two different soils showed that the new device can measure cohesion and the angle of internal friction with a correlation coefficient higher than 0·8; the results were found to be consistent with values classically obtained for these kinds of materials. The indirect shear test procedure developed is a robust way of measuring shear parameters while being simpler and less expensive than existing devices.