Development and experimental research of the cable bolt constant resistance device by using composite expansion pipe

Abstract

Under the conditions of deep high stress, weak surrounding rock, and strong mining influence, the surrounding rock of deep-buried roadway frequently experiences large deformations, the controllability of large deformation support for this type of surrounding rock is generally poor, and the conventional anchor bolts often break or fail to anchor due to their low elongation rate, which cannot adapt to the large deformation of the roadway, resulting in the risk of roof caving in the roadway. The constant resistance device by using composite expansion pipe (CRD-cep) used in conjunction with cable bolt has been invented. The main structures include a stop end cover, an expansion pipe, an integrated tray and a conical lock. The conical lock overcomes the approximately constant composite resistance generated by the “expansion grinding” of the expanding pipe, thus, the constant resistance of the cable bolt during the large deformation process of the surrounding rock is achieved. The mechanical characteristics and working stability of the resistance stabilizer are improved by theoretical analysis, numerical simulation and static tensile testing and other comprehensive research methods, and the influence of the expansion increment and lock cone angle of the composite expansion tube constant resistance device on the deformation of the expansion pipe and the composite resistance of the CRD-cep has been understood. The test results indicate that the composite resistance of the CRD-cep is mainly divided into two processes: the fast rising resistance stage and the near constant resistance stage, and the nearly constant resistance section as the main stage reaches 85% to 90% of the entire test process. The lock cone angle and expansion increment directly affect the deformation of the expansion pipe and the mechanical characteristics of the CRD-cep. When the lock cone angle is less than 20°, the deformation of the expanding pipe is uniform and the composite resistance of the CRD-cep is stable. The expanding increment determines the size of the CRD-cep. The required constant resistance of the cable bolt can be obtained by adjusting the expanding increment. When the diameter of the anchor rope used is 17.8 mm, the lock cone angle is 15° and the expansion increment is 5 mm, the constant resistance of the CRD-cep is about 265.92 kN, when the diameter of the anchor rope used is 21.8 mm, the lock cone angle is 15° and the expansion increment is 8 mm, the constant resistance of the CRD-cep is about 424.15 kN, and the working state is stable and reliable, which can better meet the constant resistance support requirements of large deformation roadway. The CRD-cep has the characteristics of strong working stability, adjustable constant resistance stroke and resistance, simple structure, and convenient installation, which is an effective supplement to the control technology of surrounding rock in large deformation roadway.

Keywords

• large deformation roadway
• composite expansion pipe
• cable bolt constant resistance
• tensile test