Detecting the status of shield segment bolts is crucial to ensure the structural safety of shield tunnels. Here are some common detection methods and techniques:
1. Appearance inspection
Appearance inspection is one of the most basic detection methods. Observe the surface of the bolts with the naked eye to check whether there are obvious defects such as corrosion, deformation, cracks, etc. For bolts exposed to the external environment, you can also check whether their coating is intact and whether there is any peeling. In addition, you can also check whether the connection between the bolt and the segment is tight and whether there are any signs of loosening.
2. Torque detection
Torque detection is a commonly used method to detect the preload of bolts. Use a torque wrench or torque tester to test the bolts to determine whether the preload of the bolts meets the design requirements. If the torque value is too small, it means that the bolt may be loose and needs to be re-tightened; if the torque value is too large, it may cause the bolt to be overloaded or even broken. Therefore, accurately controlling the torque of the bolt is the key to ensuring the firm connection of the shield segment.
3. Ultrasonic detection
Ultrasonic detection is a non-destructive detection method that can detect defects inside the bolts. By emitting ultrasonic pulses, when the ultrasonic wave encounters defects inside the bolt, a reflected wave is generated. By analyzing the characteristics of the reflected wave, it can be determined whether there are defects such as cracks and inclusions inside the bolt. Ultrasonic testing has the advantages of fast detection speed, high accuracy, and no damage to the bolt, and is a very effective detection method.
4. Magnetic particle testing
Magnetic particle testing is also a non-destructive testing method, which is mainly used to detect defects on the surface and near the surface of the bolt. After the bolt is magnetized, magnetic powder is sprinkled on its surface. If there are defects on the surface of the bolt, the magnetic powder will gather at the defect to form an obvious magnetic mark. By observing the shape and distribution of the magnetic mark, the type and location of the defect on the bolt surface can be determined. Magnetic particle testing has the advantages of simple operation and high detection sensitivity, but it can only detect bolts made of ferromagnetic materials.
5. Stress detection
Stress detection can monitor the stress changes of the bolt in real time during use by installing strain gauges or stress sensors on the bolt. If the stress of the bolt exceeds its design strength, it may cause the bolt to break or fail. Stress detection can help engineers discover potential problems with the bolt in a timely manner and take appropriate measures to deal with it.
In short, detecting the status of shield segment bolts requires the comprehensive use of multiple detection methods and technologies. Through regular inspections, defects and problems of bolts can be discovered in time, and effective measures can be taken to repair and replace them to ensure the structural safety of the shield tunnel.
