Tunnel lining is very important to the long-term stability and safety of the tunnel. Therefore, in the daily inspection of the tunnel, the inspection of the tunnel lining cracks is a normal work content. The cracks of the tunnel lining mainly include diagonal cracks, circular cracks, longitudinal cracks and network cracks, which are mainly distributed in the Various parts of the tunnel lining.
As the tunnel structure is closely related to the geological conditions and construction methods of the surrounding rock, conventional construction methods include: integral concrete lining, fabricated lining, anchor and shotcrete lining, composite lining, and double-arch lining. The inspection of the lining is divided into internal and external parts. The change of the internal structure requires professional equipment such as ground penetrating radar to check. In our daily work, we mainly check the lining part and surface materials that are visible to the naked eye.
In daily inspections, the length, width, and depth of the cracks are usually used as the main inspection basis. In actual operation, some convenient and easy-to-operate tools are used to measure the data of the cracked parts, including scale magnifiers and plugs. Ruler, ultrasonic concrete test, etc. The use of scale magnifying glass: aim the lens against the crack at the observation point, and determine the width of the crack by adjusting the lens through the scale in the lens. The use of feeler gauge: The feeler gauge is composed of several thin steel sheets. The width and depth of the crack can be obtained by observing the thickness and depth scale of the steel sheet inserted into the crack. Portable ultrasonic concrete detector: According to the speed of ultrasonic propagation in the lining concrete, the travel time curve is obtained, and then the fixed transmitter is the receiver moving in a certain direction of the lining, and the crack is calculated according to the change in the ultrasonic propagation time of the crack position. So as to achieve the non-destructive testing of the lining. The standard for crack inspection of lining structure is (mm/a per year):
- The crack width development rate is less than 1mm/a: the crack width is less than 3mm, and the length is less than 5m.
- The development rate of the crack width is less than 1~3mm/a: the crack width is less than 3mm and the length is greater than 5m, or the crack width is 3~5mm and the length is less than 5m: the cracks are more than three, and there are crossings.
- The development rate of crack width is 3~10mm/a: the crack width is 3~5mm and the length is greater than 5m, or the crack width is greater than 5mm and the length is less than 10m; there are dislocation or dislocation cracks, and the length is less than 5m: the arch part is reticular, There is a risk of falling off the lining.
- The crack development rate is greater than 10mm/a: the width of the crack is greater than 5mm, and the length is greater than 10m: there are dislocations or dislocation cracks, and the length is greater than 5m: the arch cracks are meshed, and the lining is peeled off.
The damage of the tunnel lining surface is an important reference data for the safe operation of the tunnel. Therefore, once the tunnel is found to be cracked during the daily inspection of the tunnel, it means that the structural stress level of the tunnel lining has changed, and there is a hidden safety hazard. Therefore, it is necessary to make detailed records and descriptions of the cracked part of the tunnel lining, mark the crack location and changes, and increase the inspection of the crack location to support the later repair and reinforcement of the tunnel and ensure the safe operation of the tunnel.