Experimental study on evolution law of dynamic characteristic parameters during the tunnel surrounding rock block collapse process

Tunnel surrounding rock block collapse is one of the most common geological disasters in the fractured rock tunnel. Due to its sudden characteristics, the traditional monitoring methods such as displacement monitoring cannot be effective, which seriously threatens the safety of tunnel construction. In this paper, the monitoring experiment research of the whole rock block collapse process is carried out, by introducing a number of timedomain and frequency-domain dynamic characteristic parameters such as Vibration Peak Value, Crest Factor, Natural Vibration Frequency, etc. The experiment results show that the evolution law of dynamic characteristic parameters such as the Vibration Peak Value, RMS Value, Crest Factor, Natural Vibration Frequency in the whole rock block collapse process can be clearly divided into three stages: Stability phase, Detachment phase, Accelerated destruction phase. Moreover, the strength and transfixion rate of the main structure plane have a great influence on the dynamic characteristic parameters of the block, but the dynamic characteristic parameters have no obvious relationship with the transfixion position of the main structure plane. In view of the tunnel engineering, this paper proposes a three-color early warning method for the tunnel surrounding rock block collapse based on dynamic characteristic parameters with Crest Factor and natural vibration frequency as the main monitoring indexes. The method is applied in the K97 + 860.1 section of Qingshan Tunnel in Jinan Ring Expressway, and the collapse disaster is warned 12 min in advance, which verifies the feasibility of this method. This research provides a new way for the monitoring and early warning method of tunnel surrounding rock block collapse disaster, and can provide important support for the active prevention and control of block collapse disaster.