Research on multi-frequency ultrasonic scanning detecting technology of cavity in the test borehole

At present, the lack of detection technology in underground space area is the main constraint on the development and utilization of underground space. In order to solve the difficult situation of underground space exploration and evaluation, this paper presents a multi-frequency ultrasonic scanning detection technology, a large number of borehole detection data can be obtained by using the detection system to realize the accurate scanning and detection of cavity and the belly rock mass. The stability evaluation standard of cavity is established, which realizes the integration of cavity detection and stability evaluation. This paper provides an important reference for the detection of underground cavity. A scanning point position determination method based on multi-frequency ultrasonic pulse ranging is proposed in this paper, and the coordinates of scanning points are calculated accurately to realize the 3D visualization of cavity contours. Through the refined calculation of space volume, the precise control of space deformation is realized. Then, the characteristic parameters of borehole structural plane are determined after the geometrical feature combination of structural planes and the high-frequency acoustic reflection characteristics, a directional method for rock velocity measurement, is presented for the first time by means of low-frequency acoustic wave transmission. Based on the comparative analysis of echo wave characteristics, the integrity evaluation criteria of cavity are established. Finally, by analyzing the structural characteristics of cavity and upper rock mass, and the parameters which may influence the stability of cavity, combined with an engineering example, a stability evaluation system based on the multi-frequency ultrasonic scanning detecting technology of cavity in the test borehole is formed.