Spiral Cable-based Geotechnical Deformation Distributed Measurement Technology Research

Across the country in recent years, the frequent occurrence of geological disaster events constitute a serious threat to life and property safety of human being. In order to effectively analysis and risk assessment of geological disasters timely dissemination of early warning information, geological disaster monitoring system that includes various types of sensors are set up in the various geological disaster point. Geotechnical deformation monitoring sensor is an important part of the geological disaster monitoring system.At present, there are many kinds of geotechnical deformation sensors, such as GPS. The various types of sensors have their respective characteristics and application range. Due to the uncertainty of the geotechnical deformation occurred in the space, so sometimes deformation distributed measurement technology is necessary in actual geotechnical monitoring. Distributed fiber measurement techniques, due to the very limited amount of local deformation, will break in geotechnical deformation monitoring. In response to these problems, based on the research of present TDR sensing cables, a single layer spiral structure TDR sensing cable for the geotechnical deformation distributed measurement is first proposed. The sensing cable consists of silicone inner core, single layer spiral wires and external silicone rubber pipe. Compared with the traditional parallel structure probe, the spiral cable can detect distributed structural deformation caused by tensility. Compared with the coaxial cable used in measuring localized shear deformation measurement, the spiral cable can be used for the local tensile deformation measurement and is not broken in a certain tensile range. Therefore, the spiral cable is more suitable in the surface geotechnical tensile deformation distributed measurement.TDR sensing cable measurement is based on the corresponding relationship between the characteristic impedance of the measurement cables to their measured parameters. The relationship between the characteristic impedance of the parallel structure of the probe to the dielectric constant of the surrounding medium has been the in-depth study. The relationship between the deformation and the characteristic impedance of the coaxial cable cross-section has also been a theoretical analysis. To research the relationship between the tensile deformation and characteristic impedance of spiral cable becomes very important. Based on the analysis of general transmission line characteristic impedance, a theoretical calculation method of spiral cable’s characteristic impedance is proposed. The result shows that the characteristic impedance of the spiral increases in the tensile deformation. Further, the paper verify the above conclusion with precision impedance analyzer and step signal two experimental method.TDR measurement technique is divided into pulse signal time domain reflectometry and step signal domain reflectometry in the practical applications. Based on the spiral cable characteristic impedance conclusion, TDR waves are researched from the above two angles. Pulse signal TDR experiments show that the spiral cable with smaller stretching interval can effectively locate the position of the stretching interval from the reflected waveform. A difference processing method is proposed for step signal TDR waveform analysis. Based on this method, the relationship between the reflection peak amplitude and stretched length, stretching the section position, stretching interval length is analyzed. Finally, the differential step reflected waveforms is used to locate the deformation interval.