Research On Forward Modeling And Dispersion Characteristics Of Rayleigh Waves Of Geological Anomalies

The advanced geological forecast is the most realistic and effective technical means to guarantee the safety of underground construction at present.It is listed as the necessary,technical link in most underground engineering projects,Rayleigh wave exploration technology is a kind of geophysical exploration.Because of its many advantages,such as rapid economy,wide application range,easy detection,easy excitation acquisition,high signal-to-noise ratio,and high resolution,Rayleigh wave exploration technology is applied to the prediction of underground engineering,and the forward modeling of Rayleigh wave,the extraction of dispersion curve and the de-noising and purification of Rayleigh wave in underground engineering are studied.On the basis of analyzing the present situation,development trend and main problems of Rayleigh wave exploration at home and abroad,according to the basic principles of Rayleigh wave exploration,launching Rayleigh wave forward modeling of typical geological anomalies,the extraction of dispersion curves and the de-noising and purification of typical geological anomalies are studied in this paper.The obtained results are summarized as follows.(1)In order to study the influence of geological parameters on Rayleigh wave dispersion curve under the condition of underground engineering geological anomaly,the Rayleigh wave forward modeling is studied in this paper.The characteristics of dispersion curves under different geological conditions are analyzed and compared.The study shows that the occurrence of the "zigzag" of Rayleigh wave dispersion curve is related to the existence of geological anomaly bodies.The dispersion curve of Rayleigh waves is determined by the size,location and nature of the qualitative anomaly.The location of the take-off position of the "zigzag" character of the dispersion curve basically reflects the location of the geological anomaly.The smaller the size of the fault fracture zone,the deeper the buried depth and the less prominent the low-velocity zone,the smaller the "zigzag" deformation span in the Rayleigh wave dispersion curve;contrariwise the larger.The dispersion curve of Rayleigh waves in voids is discontinuous and is divided into three sections.The deeper the cavity is buried,the larger the transverse coordinate of the first breaking line of the dispersion curve is.(2)With the help of the existing conditions of a geophysical prospecting technology research base in Fujian,this study conducted field experiments on the front face of the bunker with a Rayleigh wave detector to conduct an advance test of the water bunker in a water-free and watery condition,and studied the corresponding changes and laws of the Rayleigh wave dispersion curves.The results show that:the"zigzag" of the obtained dispersion curve can be used to reflect the geological lithologic changes and tectonic development in front of the face of mine excavation.The dispersion curve of Rayleigh wave is distributed in three sections when it detects empty water silo.Water-rich geological zones usually show a decrease in seismic wave velocity.(3)In this paper,the dispersion characteristics of Rayleigh waves are discussed based on the generalized s transform.The feasibility analysis,the discussion of the influence factors and the improvement of the algorithm are discussed in this paper.The research shows that:Compared with STFT and WVD,the dispersion curve obtained by GST is more accurate in the judgment of shallow strata,and the error between the actual value and the theoretical value is only 5%,and the curve obtained by using GST is more smooth and stable.The Rayleigh wave signal under the typical stratigraphic model is analyzed by using the slope of the Rayleigh wave extreme point fitting line to estimate the phase velocity corresponding to a certain frequency.The experimental results are compared with the theoretical dispersion curves calculated by the fast scalar transfer algorithm.The curves are still the reflection of the multi-order mode dispersion curves,and the dispersion curve is smoother and more stable than the single-channel GST method.According to the characteristics of generalized S-transformation,a new method for the refinement of Rayleigh wave signal based on the generalized S-transformation multiple filtering method is proposed.The theoretical calculations,simulation experiments and engineering examples show that GSTTF-MT processing of detection signals is a very effective method for purifying Rayleigh wave signals,and has the advantages of reliability,stability,and simple calculation.