The Research On The Joint Monitoring Technology Of Complex Optical Fiber Transducers For Soil Landslide

Landslide is a very harmful geological hazard.Effective acquisition of early warning information of landslide can provide early warning and prediction for landslide.Scientists have explored a large number of monitoring methods to obtain early warning information of landslides,but there is still no monitoring method that can predict landslides very accurately.According to the data of China's environmental monitoring website,only 3.76% of landslides have been successfully monitored and predicted in recent years.The reason is that the mechanism of landslide is complex,and the existing monitoring methods have not realized the effective correlation between the early warning information of landslide and the state of landslide,so they can not make accurate early warning and prediction of various states of landslide process.Therefore,it is of great social value and practical significance for landslide early warning and prediction to study the scientific method of monitoring landslide early warning information and establish a monitoring model of effective correlation between landslide early warning information and landslide state.The purpose of this paper is to use optical fiber sensing technology to develop composite optical fiber devices for landslide monitoring and early warning.Compared with traditional technology,optical fiber sensing technology(OFST)has obvious advantages in monitoring landslides: Firstly,optical fiber itself is not only a sensing medium,but also a carrier of sensing information;secondly,optical fiber has strong anti-electromagnetic interference ability and is not affected by environmental and climatic conditions;finally,low-cost optical fiber can realize distributed laying on the surface or inside of landslides,and can sensitively monitor early warning information: displacement.Stress,etc.However,how to design an economical and universal monitoring device to monitor the early warning information of landslide and how to establish a scientific model to effectively correlate monitoring data with the process of landslide incubation need to be solved urgently.It is found that the current optical fiber monitoring method only monitors the displacement change information of landslide body or the stress change information of landslide body.Because the displacement and stress changes in the process of landslide are complex,diverse and cross-influence,these single monitoring methods alone can not make the monitoring data effectively correlated with the state of landslide.In this paper,two kinds of composite optical fiber devices(COFT)and the early warning and discriminant method combining displacement and landslide thrust are proposed for the specific field of soil slope.Composite optical fiber devices include: one is to make Bowknot-COFT to monitor creep displacement information of landslide by using optical time-domain reflection principle;the other is to use FBG(Fiber Bragg Grating)to form FBG-COFT to monitor shear displacement and thrust information of landslide,in which FBG-COFT is used to monitor shear displacement and thrust information of landslide.COFT has designed and manufactured three kinds of sensing devices.These four sensors constitute a joint monitoring system to acquire the displacement and thrust precursor information of landslide stereoscopically.The correlation mechanism between the precursor information of displacement and thrust and the state of landslide is analyzed through experimental study.Displacement-Thrust(D-T)is proposed to comprehensively judge and realize the early warning of landslide.The Joint Monitoring Technology of COFT(JMT-COFT)is constructed around four kinds of sensing devices and displacement-thrust early warning discriminant method of two kinds of composite optical fiber devices.It is used in indoor model test and outdoor test to monitor the displacement and thrust information of landslide.The test shows that the combined monitoring technology of composite optical fiber devices can better monitor the displacement and thrust information of landslide.The early warning information of landslide can also be realized.The combined monitoring technology of composite optical fiber devices can realize the three-dimensional displacement monitoring of the surface,middle and deep layers of landslide,and real-time monitoring of the shear thrust of landslide.The combined monitoring technology of composite optical fiber devices has the characteristics of high initial measurement accuracy and large measurement range.The direction of landslide can be determined by combining displacement and thrust,and the three stages of landslide process can be distinguished,and the boundary points of landslide can be warned.The main work of this paper has the following aspects:(1)The first composite fiber optic device(Bowknot-COFT)based on the fiber-optic bow is used to measure the displacement.The device mainly measures the superficial displacement of the landslide body.The Bowknot-COFT composite fiber optic device was applied to the indoor test,and achieved good results.(2)A composite fiber optic device based on fiber Bragg grating is designed to measure the shear thrust and deep displacement of the landslide body.The composite fiber optic device based on fiber grating is divided into force sensing transducer and Shear output measuring transducer(SDMT),and the optical fiber inclinometer is composed of fiber Bragg grating and strain gauge(FBG-inclinometer)is used to measure the distribution of landslide displacement on the vertical line.(3)Exploring the Joint Monitoring Technology of COFT(JMT-COFT)based on optical time-domain reflection(OTDR)and fiber gratings to analyze the soil slope displacement information and mechanical information,Whichlaid the foundation for revealing the internal factors and mechanics of landslide.(4)Carry out the indoor model box test based on the joint monitoring of the composite optical fiber device,and carry out the field in situ test based on the joint monitoring of the composite optical fiber device.Based on the deep slope of the slope,the displacement of the superficial part and the variation law of the shear thrust,the characteristics of the three stages of the landslide are analyzed,and the slipping boundary of the soil slope is predicted based on the time coordinate.Through research,the combined monitoring technology of composite optical fiber devices can optimize the advantages of each monitoring device.The technology combines the composite optical fiber devices,whose main characteristics are that three kinds of composite optical fiber devices are developed to monitor the displacement changes of the landslide surface,middle and deep,and the thrust grating force sensor is developed for the thrust changes of the landslide.By using the combined monitoring technology of composite optical fiber devices,three stages of landslide incubation process,Creep sliding,Uniformsliding and Speed sliding are clearly judged and divided.The composite optical fiber device combined monitoring technology realizes the effective monitoring of the early warning information of soil landslide,studies the internal relationship between the early warning information and the state of the landslide,and achieves the purpose of early warning of the landslide.For the follow-up research work,we need to continue to explore how to further increase the measurement range of sensor devices and how to achieve the integration of multiple devices.