Experimental Study on Axial Force Safety Monitoring of Plate Buckle Steel Pipe Support on Tunnel Roof

In recent years, the application of disc buckle steel pipe support in tunnel roof construction is becoming common. The conventional way is to use the rear loading method to monitor the vertical rod axial force, and adjusting the vertical rod top support when installing the sensor leads to the redistribution of axial force and the lack of monitoring axial force accuracy. In this paper, the preloading method is proposed for monitoring. Through the actual monitoring cases, the monitoring control tests are carried out by using the preloading method and the conventional afterloading method, and the axial force values are calculated by comparing the standard theory, the monitoring results are compared and analyzed, and the axial force monitoring method of disc buckle steel pipe vertical rod is explored. The results show that: (1) compared with the conventional postloading method, this paper proposes that the preloading method is closer to the actual axial force of the high-support die vertical rod. (2) the theoretical calculation value of the axial force of the high support die in the JGJ231-2021 code is larger than that of the actual monitoring axial force in this test, which verifies that the axial force calculated by the code is safe. (3) there is a big difference between the axial force value of the vertical rod obtained by the afterloading method and the preloading method, and the axial force value obtained by the postloading method is 15.64% smaller than that of the control group and 37.8% smaller than the reference point. (4) the axial force value of the preloading method is closer to the theoretical axial force value than that of the rear loading method. The ratio of axial force value of preloading method to theoretical value MA/N is 0.49, and the ratio of axial force value of conventional afterloading method to theoretical value is 0.419 and 0.309 respectively. It is proposed that the preloading method is closer to the actual stress situation, and the research results can correct and supplement the conventional high-supported formwork monitoring and construction.