In shield tunnel construction, the preload setting of shield segment bolts is a crucial link, which is directly related to the stability of the tunnel structure.
First, the preload setting method needs to consider multiple factors. It should be determined based on the material properties, size specifications and design loads of the shield segment. Generally speaking, the preliminary preload value is obtained through theoretical calculation, for example, the friction and shear force required by the bolts are calculated based on the circumferential and longitudinal pressures of the segment, so as to estimate the preload size. At the same time, numerical simulation analysis is carried out with the help of advanced simulation software to simulate the stress state and deformation of the segment under different preloads, so as to optimize the preload value. In addition, it is also necessary to consider construction environment factors, such as the influence of temperature and humidity on the performance of bolts and segment materials, and make appropriate corrections to the preload to ensure its accuracy.
Secondly, the appropriate preload has a positive effect on the stability of the tunnel structure. During the tunnel excavation process, the segment is subjected to complex loads such as pressure from the surrounding soil, groundwater pressure and the jack force of the shield machine. When the preload force of the segment bolts reaches the set requirements, the segments can be tightly connected to form an integral ring structure. This integrity effectively resists external loads and reduces the occurrence of segment misalignment, cracking and other defects. For example, sufficient preload force can prevent the segments from leaking under high water pressure, because it ensures the sealing of the segment joints and maintains the dry environment inside the tunnel, thereby ensuring the durability and stability of the tunnel structure.
Furthermore, insufficient or excessive preload force will have an adverse effect on the tunnel structure. If the preload force is insufficient, the segments are not tightly connected. Under the action of external loads, the segments are prone to relative displacement and deformation, resulting in excessive convergence and deformation of the tunnel, and may even cause local collapse accidents. Excessive preload force will cause the bolts to bear excessive stress, increase the risk of fatigue fracture of the bolts, and may also cause local extrusion damage to the segments, weaken the bearing capacity of the segments, and also endanger the safety and stability of the tunnel structure.
Finally, during the construction process, the bolt tightening operation must be carried out strictly in accordance with the set preload force, and professional torque wrenches and other tools must be used for precise control. At the same time, strengthen the monitoring of preload, regularly check the tightening status of the bolts, and promptly re-tighten if the preload is found to be attenuated. Only in this way can the preload of the shield segment bolts fully play its role in protecting the stability of the tunnel structure and ensure the safe construction and long-term stable operation of the shield tunnel.
