###### Abstract
[19] installed monitoring instruments on U-steel arches supporting roadway surrounding rock to obtain curves of the stress variation between the arches and rock, laying a solid foundation for these instruments' application. The above-mentioned research shows that in the bearing process of yield-type U-steel supports, the joint is a key part affecting bearing performance. At present, the overlapping of each section of a U-steel support mainly uses cable-clip joints, and the overlapping of each section is achieved by applying a pre-tightening torque to the cable-clip bolts. [PERSON] et al. [20] studied the mechanical characteristics of cable-clip bolt connectors and revealed the influence law of pre-tightening torque on improving the working resistance of joints. [PERSON] et al. [21] studied the slip-bearing characteristics and stable-resistance technologies of U-steel joints. The results showed that secondary pre-tightening after slippage is of great significance for maintaining a high support resistance at the joint. [PERSON] et al. [22] carried out indoor tests on the bearing performance of U-steel supports and revealed the influence mechanism of the pre-tightening force of the cable-clip bolts on the overall bearing capacity of the support; [PERSON] et al. [23] analyzed the influence of bolt pre-tightening force and groove shape on the working performance of yield-type U-steel joints through finite-element simulation and axial load testing of joints. [PERSON] et al. [24] studied numerical simulations of yield-bolt connections in U-steel arches under different torques, summarizing the relationship between clamping force and the load-carrying capacity of the component. [PERSON] et al. [25] addressed buckling failure issues in pins in U-steel supports by developing 3D models for U25 and U29 supports, obtaining deformation mechanisms, stress distributions, and details of load variation laws during support deformation, to provide a basis for design improvements. [PERSON] et al. [26] proposed a combined support system consisting of compressible U-steel and foam concrete damping layers to formulate a suitable support scheme for large-deformation soft rock roadways in coal mines, effectively controlling large deformations after application in the field. [PERSON] et al. [27] developed a \"surface-inserted\" locking unit to overcome unstable locking between U-steel arch segments, enabling effective management of roadway deformation while preventing steel support failure. In summary, secondary pre-tightening of cable-clip joints can improve the yield-pressure and bearing performance of the support. However, there is currently a lack of relevant research on the secondary pre-tightening effects of cable-clip joints on yield-type supports, and the design of the pre-tightening torque for cable-clip joints still relies mainly on experience. Based on this, this paper takes as its research object the U29 steel support, commonly used for support in deep soft rock roadways. This study considered the expression of the slip resistance of a cable-clip joint after secondary pre-tightening, conducted indoor axial compression tests on the components of the cable-clip joint, and analyzed the influence mechanism of secondary pre-tightening on the bearing performance of the joint. On this basis, a numerical analysis model of the yield-type U-steel support was established to analyze the mechanisms through which the initial pre-tightening torque, the secondary pre-tightening torque, and the timing of secondary pre-tightening influenced the bearing performance of the yield-type U-steel support, and engineering suggestions are put forward.