Shear Mechanical Behavior of Geogrid-Reinforced Calcareous Sands under Inclined Reinforcement Effects

Geogrid-reinforced calcareous sand (GRCS) is an attractive alternative to enhance the bearing capacity and stability of geotechnical structures in island and coastal areas. Understanding the geogrid–particle interaction and shear mechanical behavior is the current challenge. This work investigated the shear mechanical behavior of the GRCS under the influence of inclination angle, stress level, geogrid type, and the number of geogrids employing large-scale direct shear tests. The results revealed that the shear strength of the three-layer inclined reinforcement increased by an average of 81% and 59% compared to the unreinforced and horizontally reinforced conditions, respectively. The internal friction angle and the pseudo cohesion at the shear plane were particularly sensitive to the inclined reinforcement condition, with maximum values of 54.7° and 55 kPa, respectively. The increased inclination angle and geogrids enhanced the initial volume shrinkage and maximum dilation during the shear process, which is essentially governed by the rotation and alignment of the particles. The shear stress level primarily influenced particle crushing, with a maximum relative breakage index of 2.18%. In addition, a simplified calculation of the equivalent additional stress provided by the geogrid–particle interface was further developed under the horizontal and inclined reinforcements. Further, the potential correlations between the shear stress transfer coefficient and the determined parameters were clarified by analyzing the force and deformation characteristics of the geogrids. The presented findings are highly significant for understanding the geogrid–particle interaction mechanisms and the future application of reinforced geostructures in calcareous sand regions.