Hollow cylinder apparatus for testing unbound granular materials of pavements

Unbound granular materials used in pavement structures are subjected to a complex stress path which includes rotational stresses. Hollow cylinder apparatuses (HCAs) are suitable laboratory devices for reproducing stress paths found in the field. However, as the size of the HCA depends on the size of the granular particles, their use for testing unbound granular materials for pavements has not been reported in the literature. This paper presents the development of a new large size hollow cylinder apparatus designed to study the response of unbound granular materials subjected to stress rotation. This large HCA has hydraulic actuators for vertical movement and torsion while shear and vertical stresses are servo-controlled to reproduce stress paths produced by a heavy vehicle moving on a pavement structure. Confining stress is applied through the use of rings with controllable stiffness. This paper highlights the role of ring stiffness on stress paths. The results show the capabilities of the large HCA for studying the behaviour of unbound granular materials used in pavement structures.