Shield segment bolts play a vital connection role in shield tunnel construction, and their service life is affected by many factors.
First of all, the choice of material is one of the key factors. High-quality steel has better strength, toughness and corrosion resistance, and can withstand the complex environmental pressure and chemical erosion inside the tunnel. If poor quality materials are used, bolts are prone to fatigue cracks, corrosion and other problems, thus shortening their service life.
The quality of installation also has a significant impact on its longevity. During the installation process, if the pre-tightening force of the bolts is insufficient or uneven, it will cause the connection between the segments to be loose, causing additional stress and vibration during the shield advancement process, and accelerating the wear and fatigue of the bolts. Conversely, too much preload may cause the bolt to overstretch, reducing its load-bearing capacity.
The environmental conditions inside the tunnel cannot be ignored. The chemical nature of groundwater may be corrosive and will corrode the surface of the bolt over time, causing it to rust, thin, or even break. In addition, changes in temperature and humidity in the tunnel will also have an impact on the bolts, and the high temperature and high humidity environment may accelerate the corrosion process.
Dynamic loads during shield construction are also an important factor. The propulsion force of the shield machine, the pressure of the surrounding soil, and the vibration during tunnel operation will subject the bolts to repeated stress. Long-term alternating stress can easily cause fatigue cracks in bolts. As time goes by, the cracks continue to expand, eventually leading to bolt failure.
The maintenance and upkeep of bolts is equally critical. Regular inspection, tightening and anti-corrosion treatment can detect and solve potential problems in time and extend the service life of bolts. Without effective maintenance, small problems can gradually worsen and eventually affect the performance of the entire bolt.
For example, during the construction of a certain subway tunnel, due to the uneven pre-tightening force of some Shield segment bolts during installation, and the strong corrosiveness of groundwater in the tunnel, these bolts experienced serious corrosion and loosening after a period of operation. Large-scale replacement and repair had to be carried out, which increased the cost and construction period.
In addition, the reasonable design of the bolt will also affect its life. For example, if the thread shape, pitch, head and tail structure of the bolt are not designed properly, stress concentration may occur and cracks may easily occur in these parts.
To sum up, the service life of Shield segment bolts is comprehensively affected by many factors such as material, installation quality, environmental conditions, dynamic load, maintenance and design. In practical applications, these factors need to be fully considered and corresponding measures taken to ensure the long-term stable operation of the bolts and the safety and reliability of the shield tunnel.
