Experimental investigation on anti-sliding performance of grouted micro-pipe pile groups

As a common geohazard, landslides may cause enormous losses of human lives and properties. It is necessary to prevent landslides by effective technical measures. The grouted micro-steel-pipe pile group is a typical composite anti-sliding structure applied in landslide-stabilization engineering, where the micropiles and the surrounding geomaterials interact to resist the landslide thrust. In this study, laboratory experiments were carried out to investigate the anti-sliding performance of a kind of 3 x 3 grouted micro-pipe pile group anchored in bedrock at different row spacing of micropiles. The results indicate that the grouted micro-pipe pile group shows a relatively large anti-sliding capacity at row spacing of 4-8 times the micropile diameter. The active earth pressure on micropiles induced by soil movement shows an approximately triangular distribution. More of the thrust load transfers from the rear pile row to the middle and front pile rows gradually as the thrust load increases, where the ratios of earth thrust among the rear, middle and front pile rows can reach up to 1:0.60:0.44. The maximum bending moment occurs at the anchoring segment close to the bedrock surface. As the thrust loading increases, the maximum bending moment of the rear pile row will first increase to a peak value and then rapidly decrease, implying the micropile group is about to lose its anti-sliding ability. The development of deformation can be characterized as three stages including the slow deformation stage, accelerating deformation stage and unstable deformation stage. It is recommended that the horizontal displacement of pile head should be less than 1% of the loading depth for actual engineering design.