A Concrete-Filled Steel Tubular Yieldable Support for a Tunnel within Deep Soft Rock

Abstract

A concrete-filled steel tubular (CFT) yieldable support is proposed as a new passive support system in deep tunnels to improve the stability of soft rock mass, which consists of a CFT arc, a porous metal connector, and a steel tube. The connector provides a new yieldable mechanism; that is, the constant yield resistance and large deformation under compression can be determined by the void ratio and porous length of the connector. The test results indicate that the load–displacement response for the CFT yieldable support can be divided into four stages, namely, elastic stage, yieldable stage I, load transition stage, and yieldable stage II. A numerical model is then developed to investigate the deformation of a deep tunnel supported by the CFT supporting system. The results indicate that a higher concrete strength can lead to a lower deformation of the CFT yieldable support. The deformation of the tunnel roof can be effectively controlled by using higher-strength concrete. The void ratio obviously influences the deformation of the roof, and a higher void ratio tends to lead to a larger deformation. Finally, an empirical approach is suggested to predict the initial resistance and bearing capacity of the CFT yieldable support.