Safety detection technology of roof in underground space based on sound spectrum analysis

Underground space surrounding rock mass is affected by its own joint cracks and external secondary disturbances.The roof rock is easy to fall suddenly, which poses a great threat to the safety of workers and production equipment.Aiming at the safety test of roof surrounding rock, based on the traditional “knock-up and ask top” detection principle, a knock test is performed on the roof surrounding rock with different stability on the spot to convert the characteristic parameters(sound and vibration) of the roof to a clear and intuitive spectrum figure by analyzing the spectrum characteristics and the threshold range, and the danger of roof falling is clear.The field test shows that with the decrease of the stability level of the surrounding rock in the underground space, the maximum amplitude of the audio frequency presents a non-linear increase trend, while the main frequency corresponding to the maximum audio frequency has a significant decrease.With the decrease of roof safety, the frequency domain occupied by high amplitude (30% main peak) is gradually widens, and the number of high amplitude increases gradually.As the decrease of roof stability, the amplitude of vibration (vibration sense) first decreases slowly and then decreases rapidly.This research has a certain reference significance for the non-destructive and intelligent detection of the roof.