Experimental Study on the Uplift Bearing Mechanism of New Pneumatic Pipe Piles

To enhance the uplift resistance of micropiles used in soil slope reinforcement and ensure the stability and safety of slope structures, a novel micropile incorporating a small-scale pneumatic device and anchorage components was developed, and its uplift performance was evaluated. Through field uplift tests, the uplift load-vertical displacement relationship of the new micropile and conventional micropile in silty clay strata was compared. Numerical simulations were also conducted to reveal the uplift mechanism and analyze the influence of an anchorage component layout on the micropile's uplift resistance. The field tests showed that the ultimate uplift capacity of a 3 m long novel micropile increased by 161.7% compared to that of a conventional micropile, with a 14.7% reduction in displacement. When the anchorage components were deployed without grouting, the novel micropile achieved 70.7% of the uplift capacity of a conventional micropile, indicating a certain level of uplift resistance. Numerical simulation results indicated that the novel micropile altered the stress state of the surrounding soil, and the anchorage components changed the load transfer mechanism during micropile uplift from vertical interfacial friction to a combination of anchorage pressure and soil friction, significantly enhancing uplift resistance. For an 8 m long micropile without anchorage components, the ultimate uplift capacity was 489.9 kN. With the addition of 1 m of anchorage length, the capacity increased to 661.5 kN, a 35.0% improvement. Subsequently, each additional meter of anchorage length increased the micropile's capacity by 10.9% to 16.0%, with a cost increase of only 5.7%. The research findings provide valuable scientific references for the design and remediation of soil slope reinforcement.