Behavior of hybrid system of soil-nailing and compression anchor

This paper presents the mechanical behavior of a hybrid system of soil-nailing and compression anchor; the model is composed of a nailed steel bar and an anchor with two PC strands, and it takes advantage of conventional soil reinforcement methods such as soil-nailing and earth anchor. Pre-stress is applied to the strands, resulting in compressive stress to the steel bar. It mitigates tensile stress of the bar during pullout, and thus increases the reinforcing capacity of the system. However, this hybrid system uses two reinforcing materials. The steel bar yields earlier than PC strands because the elongation rate of the bar is less than that of PC strands. Therefore, it is needed to match the yielding time of the two materials in order to maximize the design load of hybrid system. Nine field pullout tests were performed with two conditions: soil-nailing only; hybrid system with pre-stresses ranging from 0 kN to 196 kN. The load transfer mechanism of the system was analyzed, and the optimized pre-stress was investigated. It was found that the compressive stress of the steel bar induced by pre-stress decreases the slope of load-strain curve for the bar, compensating tensile stress of the bar. As the load-strain curves of both the strands and the bar get closer, the total pullout load increases. The pullout load was maximized when the load-strain curve for the bar becomes close to that of strands. It was recorded that the pullout load of the hybrid system could be almost twice as much as that of the soil-nailing system.