Mechanical characterization of lining under three-dimensional complex load during shield posture adjustment

The shield tunneling method is widely used in urban underpass construction. However, research on the mechanical characteristics of segments during construction is insufficient. Throughout the shield tunneling construction process, segments undergo a diverse range of loads, and their modes become complex. During the adjustment of the posture of the shield machine along a curved path, segments must withstand three-dimensional uneven loads from the shield tail brush and extrusion of the shield shell, in addition to conventional loads. Thus, this study delves into the mechanical characterization of the lining during shield posture adjustment. First, three-dimensional refined models of the longitudinal and circumferential joints were established to investigate their bending and shear mechanical properties. Using the joint and shield tail brush stiffness models, a nonlinear spring-connector-shell model was developed for the mechanical analysis of segments during posture adjustment. Subsequently, a three-dimensional segment load model was formulated for the construction period. The segment response under the influence of different posture adjustments was examined using a numerical model of a tunnel subjected to a complex three-dimensional load. Furthermore, a multistage model of the segment response under various posture adjustments was established. This model serves as a valuable reference for engineering applications.