| With the continuous promotion of urbanization in China,the production of domestic waste continues to increase,and sanitary landfill has become one of the important ways of waste disposal.To prevent waste leachate from polluting the surrounding groundwater resources,landfills usually use HDPE membranes for impermeable treatment.However,during the construction or operation stages of landfills,HDPE membranes are prone to different degrees of breakage due to various factors,resulting in continuous leachate leakage.Therefore,how to quickly and accurately locate the leakage position of HDPE membrane and repair it in time has become the focus of researchers in various countries.At present,the methods for locating leaks in the impermeable layer of operating landfills are divided into electrical and acoustic methods.The electrical method is to lay detection electrodes or grid-like conductive fibers under the impermeable layer to locate the leakage point according to the distortion of electrical parameters in the leakage area,but the electrical method has a low safety factor and the conductive fibers are prone to misalignment.The acoustic method is to lay multiple stress wave sensors under the impermeable layer and use the sensors to receive transient break signals from HDPE membranes to achieve positioning,but it does not consider the inversion of wave velocity of the media layer and is prone to cause missed detection.At the same time,the above methods do not achieve the recognition of HDPE film breakage shape.In order to solve the above problems,this thesis proposes a leakage location model based on elastic wave velocity inversion,which is mainly applied to the landfill operation stage to monitor and locate the integrity of HDPE membrane in real time,and at the same time identify the shape of the leakage point to provide location information for subsequent accurate repair.Firstly,the HDPE membrane leakage localization model is established,which is distinguished into breakage point and leakage point localization according to different detection principles.When the HDPE membrane is broken,the sensor is used to receive its transient signal for spectrum analysis,and the signal generator actively excites this signal for localization wave velocity inversion,which is combined with passive linear localization and Geiger algorithm to realize the broken point localization.When the breakage signal and leakage detection occurs,according to the elastic wave velocity distortion of the leakage area,the combined algorithm of BPT and SIRT is used to perform wave velocity laminar inversion analysis of the sub-membrane detection layer to realize the leakage point location.Secondly,the method to improve the performance of the leakage location system is studied,and the EMD algorithm is used to analyze the spectrum and reduce the noise of the elastic wave signal.At the same time,aiming at the identification and extraction of the initial P-wave signal,the traditional STA / LTA algorithm is improved,and the threetime window method model is proposed,and the AIC algorithm is combined to realize the accurate picking of the initial P-wave.Finally,the simulation of leachate transport was carried out,and the test platform was built to test and verify the HDPE membrane leakage localization detection and leakage point shape identification.The test results show that: the difference of medium wave velocity between HDPE membrane leakage and non-leakage state is significant,and the wave velocity distortion rate is 3.7%~5.6%,which can provide good resolution for the positioning model;the maximum deviation of distance between the actual breakage point and the positioning coordinates in XY plane is 3.12 cm,and the maximum deviation of distance between the actual leakage point and the inverse inferred position is9.26 cm,both of which meet the engineering error requirements.The wave velocity inversion region can effectively identify both linear and circular leakage points. |
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