Centrifuge model test on soil slopes reinforced with micropile–anchor composite structure

Micropile–anchor composite structures (MACSs) are effective in slope stabilisation by combining the active resistance of anchor cables with the passive reinforcement of micropiles. However, the reinforcement mechanism of MACS under prototype conditions remains unclear, as existing studies have focused on small-scale 1-g model tests. This study conducted three centrifuge model tests on soil slopes reinforced with double-row micropiles and double/single-row MACS, respectively, based on a highway slope in Shandong, China. The development of earth pressure, pile bending moment, anchor axial force, and slope deformation was systematically analysed, and crack propagation and failure characteristics were examined. The results demonstrate that MACS significantly improve slope performance by reducing earth pressure and restricting deformation. Lateral earth pressure is redistributed between front and rear micropile rows, and load sharing is affected by reinforcement configuration. Anchor cables enhance the plastic deformation capacity of slopes and inhibit surface crack growth, while double-row micropiles obstruct sliding surface coalescence. Furthermore, micropiles row influence slope deformation at the failure stage, with double-row MACS-reinforced slopes remaining stable with minor surface cracks, whereas single-row MACS-reinforced slopes fail as crushed blocks along a circular sliding surface initiated by main cracks. These findings contribute to understanding the reinforcement mechanism of MACS.