Stationary Analysis And Effective Extraction Of Microtremor Signals In Urban Underground Space

In order to meet the ever-increasing demand for electricity in densely populated areas of the city,the more scientific and rational location of substations has become an important task in promoting the sustainable and healthy development of the power industry and even ensuring people's livelihood.The location of the substation should avoid natural karst caves,seismic fault zones and other areas with bad geological conditions,but the underground space of most cities still has the problem of unknown geological conditions.Therefore,the geological situation of the urban underground space has been identified to determine the location of the substation The design of the general plan,the treatment of bad foundation soil and construction suggestions play a decisive role.The microtremor detection technology is an investigation method based on a stationary random process.It requires no labor,has no damage to the environment,has strong anti-jamming capability,and is convenient for construction.It has good prospects for identifying the geological structure of the underground space of urban substations.However,due to the complexity of the urban environment,when there is strong interference,the stability of the microtremor signal will be destroyed.At the same time,the effective signal and the interference signal are mixed together,so it is difficult to identify the effective signal,resulting in poor data analysis effect.In view of this,this paper proposes a RT-STI based microtremor signal stability analysis method,and proposes an effective extraction method for microtremor signals based on ICEEMDAN and S-G for signal-to-noise confusion.Through simulation and practical experiments,the feasibility of the method for analyzing the smoothness of fretting signals and the correctness of the effective signal extraction method are proved.The main contents of this article are as follows:(1)Two typical data processing methods for microtremor detection are analyzed.One is to use the H/V spectrum ratio method observed at a single station to analyze the excellent frequency(peak frequency)and shear wave velocity of the observation site by extracting the H/V spectrum ratio curve from the microtremor signal;one is to use multiple stations The spatial autocorrelation method(SPAC),adopts a nested triangular array to collect microtremor signals,and inverts the shear wave velocity of the stratum structure through the extracted dispersion curve.(2)Two methods of stationarity test for mathematical statistics based on wide stationarity are improved.The Run Test method(RT)is efficient,but it has the disadvantage that some stationary signals are misjudged as non-stationary.The Space Time Index method(STI)can accurately identify the smoothness of the signal,but the algorithm is more complicated and the operation time is longer.This paper improves the computational efficiency of the STI method,proposes the RT-STI method that combines the advantages of the two methods,analyzes the doppler noise signal with distance as a single variable,and accurately and quickly identifies its stability.(3)Effectively extract the smooth microtremor signal.The Savitzky-Golay filter can better maintain the amplitude and bandwidth of the signal,but it can only attenuate high-frequency interference and cannot be completely filtered out.This paper analyzes the advantages and disadvantages of empirical mode decomposition and its improved methods,and proposes an improved complete ensemble empirical modal decomposition with adaptive noise(ICEEMDAN).This method has a small reconstruction error(on the order of 10-16).Complete characteristics,and fast calculation speed.In this paper,ICEEMDAN with S-G method adopts S-G filter to smooth some high order modal components decomposed by ICEEMDAN method,and reconstructs with residual signals,which solves the problem of effective signal loss caused by abandoning high frequency components and avoids incomplete filtering of high frequency interference(4)The effectiveness of the method in this paper is verified through simulation and actual experiments.The H/V spectral ratio curve and the SPAC dispersion curve of the measured fretting signal before and after effective extraction are compared,and the results show that the smooth fretting signal after effective extraction is closer to the excellent frequency of the actual observation site and better reflects Shear wave velocity structure of actual formation.In view of the shortcomings of human experience in judging the stability of microtremor signals and the inadequacy of the identification of effective signals,the proposed method of microtremor signal stationary analysis and effective signal extraction can improve the accuracy and efficiency of microtremor detection of urban underground space,further provide effective guidance for the selection and design of substation sites.