In shield engineering, the determination and control of the preload of shield segment bolts is a crucial link, which directly affects the connection quality of shield segments and the stability of tunnel structure.
The determination of the preload of shield segment bolts needs to take into account multiple factors. The first is the load borne by the shield segment, including soil pressure, water pressure, and equipment and personnel load inside the tunnel. Through detailed analysis and calculation of these loads, the required preload can be preliminarily determined to ensure that the segments can be tightly connected and jointly bear the external load.
Secondly, the material and size of the segment will also affect the determination of the preload. Segments of different materials and sizes have different strength and stiffness characteristics, which will affect the effect of bolt preload.
Furthermore, construction technology and environmental conditions are also factors that need to be considered. For example, temperature changes during construction may cause thermal expansion and contraction of materials, thereby affecting the actual effect of preload.
There are many methods to control the preload of shield segment bolts. One common method is to use a torque wrench. By setting the torque value of the torque wrench, the predetermined preload can be achieved when tightening the bolt. However, this method requires attention to the accuracy of the torque coefficient, because the torque coefficient is affected by factors such as the friction coefficient of the bolt and nut, the thread shape, etc.
Another method is to use a tensioner. The tensioner can directly stretch the bolt to accurately control the preload. This method is relatively more accurate and reliable, but the equipment cost is higher.
In actual construction, in order to ensure accurate control of the preload, it is usually necessary to detect and monitor the preload. Ultrasonic detection technology can be used to calculate the preload by measuring the change in the length of the bolt before and after preload.
At the same time, the operating skills and experience of the construction personnel also play an important role in the control of the preload. Strict training and standardized operating procedures can reduce the preload deviation caused by human factors.
For example, in a shield tunnel construction project, due to the inaccurate control of the preload in the early stage of construction, tiny gaps appeared between some segments, affecting the waterproof performance of the tunnel. Later, by improving the control method of preload, strengthening detection and monitoring, and timely adjusting the construction process, the quality of the segment connection and the safety and stability of the tunnel were finally guaranteed.
In summary, determining and controlling the preload of the shield segment bolts requires comprehensive consideration of multiple factors, and adopting appropriate methods and technical means, while strengthening construction management and quality control to ensure the safety and reliability of the tunnel structure.
