Experimental Study On The Suitability Of TDR Technology In Landslide Deformation Monitoring

China is a country with increasing landslide geological hazards.According to statistics,the property loss of landslide hazard is nearly up to 10 billion yuan and thousands people was dead every year.In recent years,with the development of the monitoring methods and monitoring instruments,the Successful prediction on landslide geological hazards greatly inreased by monitoring work.Therefore,it is necessary possible to carry out on the landslide hazard monitoring and forecasting.Although there are some defects such as the heavy workload and low-level automation,the deep displacement monitoring is a very critical and important issue in studying the landslide prediction research on geological disasters.As for the advantages of fast,accurate,remote control and so on,The Time Domain Reflectometry technology as a new type of deep displacement monitoring is more and more related to the researcher increasingly.It can understand and grasp the process of dynamic change of deep displacement in landslide by TDR technology in time,so that it can realize to monitor the dynamic deformation of landslide.However,there are still have some controversialso in if the TDR technology is feasibility to applicate to the landslide deformation monitoring.Based on this,combining with the National Natural Science Foundation project we carried out research work under the guidance of instructors.Firstly,It is aimed at demonstrate the feasibility in landslide deformation monitoring. Moreover,this paper also wants to monitor the quantitative relationship between the signal and the landslide deformation.Based on the previous studies and research work before this article,we discussed the formation of landslide mechanisms and methods of the existing landslide monitoring.Then,we detailed introduce the methods of deep displacement monitoring,and compare the advantages and disadvantages.Next,we detailed summary and discusses the methods of TDR monitoring systems,signal rules and the factors that lead to signal loss.Based on the above theory,this paper proposed a complete set of TDR monitoring system.Then the key part of the system is described in detail,such as electromagnetic excitation device,signal sampling and processing system,and so on.Based on the Maxwell theory,the wave equation of the electromagnetic wave in transmission medium is derived and solved.And then the impedance and the reflection coefficient are obtained which can descript the status of transmission line.Finally,the reflection model of coaxial cable signal is established.Then theoretical foundation was established that can be betterly promote the application for TDR technologies.In this paper,the specific research, ideas and research findings were as follows.Then,the author uses the TDR monitoring instruments to carry out shear and tensile test by coaxial cable in laboratory.Through laboratory testing we verify the practical feasibility of TDR technology.However,because of TDR monitoring system itself and the impact of the external environment,making the monitoring data is often mixed with some interference factors.As result,the laws and characteristics of TDR signal was not obvious.In order to accurately reflect the development of TDR signal changes,the paper introduced the best analysis of the signal de-noising tools-wavelet analysis.Through detailed analysis and comparison of wavelet transform methods,and finally this paper come to a combinational methods which is suitable to de-noise the TDR signal.The methods is used the db3 wavelet basis,three-tier system decomposition and fixed form threshold.Through the practical application it shows that the combination is feasible and practical.In laboratory test,there are three deformation forms of coaxial cable,extrusion deformation, shear deformation and tensile deformation.De-noising by using wavelet transform for the experimental data of TDR,we found that extrusion deformation has two stages:the first is slow changing signal and the second is rapid changing signal.The overall trend is that the signal amplitude increases as the deformation.In addition,the signal amplitude is also increases with the cable deformation at the stage of shear deformation.However,at the stage of tensile deformation,the signal amplitude is decreased with the tensile deformation increasing.Base on the regression analysis statistics and the result of three deformation types of laboratory test,we concluded respectively four formulas and three the confidence interval of the signal amplitude to the deformation that fitted for each deformation.And then,this paper give the conditions of application for the four formulas.At the stage of extrusion deformation,the first and second fitted formula can be used to calculate the actual deformation when range of the TDR signal amplitude is about 0～14.5mv.At the stage of shear deformation,the third fitted formula can be used to calculate the actual deformation when range of the TDR signal amplitude is about 12.5～17mv.In addition,as the cable may occur tensile deformation,we must to calculate the tensile deformation by the fourth fitted formula when the range of the TDR signal amplitude is larger than 9mv.In contrast,we also can estimate the state of coaxial cable by the scope of signal amplitude changes.In addition,the confidence interval of the TDR signal in three stages in this paper provides a reference for the practical application of TDR system.In order to verify the application of TDR monitoring system in landslide site,we take the YUhuangge landslide and Xiakou landslide as the test field to test the applicability and the accuracy of the system on site.Based on identifying the geological conditions of Xiakou landslide,the geological structure model of the landslide was abstracted which is used to calculate.The result of the stability evaluation informed that the landslide is in a critical state during the natural state.Otherwise,we also come to the conclusion that the slide may initiate creep phenomenon in the natural situation through numerical simulation.To make matters worse, the landslide will slide in part or in whole once there are external conditions affect,such as heavy rains,earthquakes and so on.Nest,TDR system is used to monitor the landslide deformation which is arranged in the landslide body by drilling.As the analysis of monitoring data show, TDR technology can accurately position the location of sliding surface and forecast the trend of landslide deformation.Comparing with the monitoring value of borehole inclinometer,the deformation calculated by the second fitted formula is the value of 69.4%～73.6%.To be sure, both methods predict the development trend of decline is basically same.By contrast the tiltmeter monitoring,we found the displacement calculated by laboratory fitting formula is smaller than the actual monitoring value.So the fitting formula was amended.TDR monitoring system in YUhuangge automatic monitors the deep displacement of landslide which takes one day as a monitoring cycle to.Therefore the technology realizes the monitoring in real-time and dynamic.In this paper we analyzes the TDR monitoring data for deep slide zone of the YUhuangge landslide which from June to December in 2008.The results show that TDR can be accurately reflected the deformation change when the Three Gorges Reservoir develops the 175m impoundment water tests from October to November.Further it evidence that the TDR monitoring system can be used in monitoring the landslide.Moreover, TDR is more accurate to capture the small deformation than the borehole inclinometer.The results show that the revised formula is a reasonable to use in the YUhuangge landslide monitoring.Through the study the YUHuangge landslide,we find the TDR can provide long-term effectiveness and accurate information for the situation of landslide deformation.In this paper,TDR technology was continued to spread by discussing of theoretical derivation,laboratory test and field test.Finally,we draw a conclusion that the TDR technologies definitely can be used in the landslide monitoring.In addition,TDR technologies can accurately determine the slip surface and forecast development trend of the landslide deformation.In one word,the TDR fully reflects the advantages of rapid,accurate,remote control,etc.Through discussion we can see that the theoretical basis of TDR technology is perfect and suitability.It can be said that the technology is valuable for popularized application and prospect.In a word,the innovative research work mainly manifested in:The method of standard wavelet de-noising was put forward through laboratory test.Moverever,the deformation of coaxial cable has three states extrusion deformation,shear deformation and tensile deformation.In this paper,the innovative research work mainly manifested in:The method of standard wavelet de-noising was put forward through laboratory test.Secondly,the deformation of coaxial cable has three states extrusion deformation,shear deformation and tensile deformation. otherwise,we found that extrusion deformation has two stages:the first is slow changing signal and the second is rapid changing signal.Thirdly,by the regression analysis statistics and analysis the result of three deformation types of laboratory test,this paper put forward the the confidence interval of three deformation state.Also,we propose and amendment the conversion formulacan which can be used for TDR landslide deformation monitoring.