Studies On The Signal Response Of Transient Rayleigh Waves In Detection Of Underground Pipes

Rayleigh wave test and analysis techniques have been widely used in engineering geological survey, the current function which mainly for layering and velocity divided in layered geological structure. But for the some geological structure that similar to underground pipelines is still lacking of theoretical analysis of Rayleigh wave test, practical engineering testers often tend to use single-channel vibration test images of underground pipes, and the longitudinal wave reflection is agreed.Rayleigh wave is a kind of elliptical polarized wave and on the contrary the direction of propagation, due to the complexity of its vibration, it is difficult to directly analyze the signal characteristics of similar to underground pipeline structure, which limits the application of this method in practical engineering. Compared with longitudinal wave, Rayleigh wave has a remarkable characteristic that is strong energy. Researching underground pipelines and local geological structure signal characteristics of Rayleigh wave response has important theoretical significance and practical application value.This paper Uses ANSYS/LS-DYNA the numerical simulation method of finite element, simulation of dynamic response characteristics of Rayleigh wave encounter underground pipeline. Successfully solve the finite element simulation of model size, the selection of the vibrating force, the division of the grid size and boundary conditions and the data format conversion and storage. Calculated by finite element model of a series of different operating conditions, and combined with practical engineering, summarizes the pipe laying environment parameters, acquisition system parameters setting on the influence law of Rayleigh wave response signal.Proposing a new method of Rayleigh wave seismic influence method detecting underground pipeline, through simulation found that Rayleigh wave encounter underground pipeline will be presented the arc of the reflected signal waveform on earthquake tract set oscillogramBy calculating a series of finite element model of underground pipes, fitted pipeline depth h and the Rayleigh wave velocity VR, the reflection characteristics of the signal with the top time in the history of the relationship Δt for determining pipeline depth quickly provide a quantitative standard and has been verified in the engineering examples. By calculating the models of the different thickness of pipeline overlying rigid surface and different exciting frequency, the rule was summarized, that the change of the rigid surface thickness and the exciting frequency influence on Rayleigh wave signal response, providing the theoretic basis and reference for the reasonable selection of exciting forms in geotechnical investigation.We summarized that the law of Rayleigh wave signal response in different shapes and diameters of pipes, providing the theoretic basis and reference for setting the field data acquisition system parameters and the analyzing the exploratory data, and the law was verified in practical engineering.We summarized that at the law of Rayleigh wave signal response in different cannon separation distance and road separation distance.3D simulation model of underground pipeline is established, and then to relative space position relation of line and the pipe for pipeline response to study the influence law of response signal.