Research On Methods And Theories For Measurin Underground Displacement

The effective monitoring of underground deep displacement is not only a key means to prevent and mitigate such major geological hazards as landslide, collapse, debris flow, and subsidence, but also to guarantee quality and safety for a wide range of geotechnical and hydraulic engineering projects. Deep displacement monitoring is becoming increasingly important but less well established. Most of the existing monitoring methods have such drawbacks as high cost, low efficiency, vulnerability to missing or error in hazard prediction, and difficulty in accurately calculating the deep displacement and sliding direction. A novel method is proposed to automatically measure and remotely monitor the underground displacement based on electromagnetic underground displacement sensor group and GPRS wireless network. Two electromagnetic underground displacement sensors, that is, horizontal type (Ⅰ-type) and horizontal-vertical composite type (Ⅱ-type) are designed to meet the practical engineering needs. With regard to these two sensors, great focus is taken on the underlying theoretical research of underground displacement detecting and sensing characteristics. Three innovative measuring models suitable for hardware implementation with satisfactory estimation accuracy and calculation efficiency are constructed and derived in detail after a comprehensive research of impact of various factors and parameters on the proposed sensors. These models have been further applied for displacement parameter back analysis of Ⅰ and Ⅱ type sensors so as to predict the relative horizontal displacement, vertical displacement and tilt angle at different depth within the monitored underground soil and rock mass. A series of comparative examinations between modeling simulation and experimental tests are carried out. It not only evaluates the measuring performance of I and II type sensors, but also validates reliability of the three models and practicability of the underground displacement inversion algorithm. All of these construct a relatively complete underground displacement monitoring theory.The main research achievements and innovations are listed as follows:(1) The dissertation proposes a new underground displacement measuring method and designs a novel underground displacement measuring apparatus and a GPRS-based remote network monitoring system. With the electromagnetic underground displacement sensor group as the core, the said measuring instrument is mainly composed of a number of equally spaced integrated sensing units in series and an underground displacement measuring central processing unit, forming a measure chain of underground displacement. Its basic features include:a) Any two adjacent sensing units comprise an electromagnetic underground displacement sensor employed to measure the relative displacement and tilt angle at some given depth within the studied rock or soil mass; b) The whole measuring chain can measure the cumulative underground displacement and sliding angle from the surface to different depths within the monitored mass; and c) A GPRS-based remote monitoring network of underground displacement is developed to support the remote real-time transmission and automatic monitoring of measuring data. At the same time, to adapt to different monitoring sites, both horizontal type (I-type) and horizontal-vertical type (II-type) underground displacement sensors have been designed to serve their corresponding I-type or II-type underground displacement measuring instruments. The former is mainly applied to the underground horizontal displacement monitoring for such projects as translational sliding, sloping engineering, excavation and retaining piles, the railway roadbed. The latter is used for such applications as rotational landslide, collapse, ground subsidence and soft soil foundation that require for the underground displacement monitoring both in the horizontal and vertical directions.(2) For the I-type sensor, a mutual inductance voltage measurement model called the Equation-based Equivalent Loop Approach (EELA) has been put forward by coupling the electromagnetic formula derivation with the equivalent loop approach. It can quite accurately evaluate the complicated relationship among the I-type sensor’s mutual inductance voltage output, the relative horizontal displacement and relative tilt angle between two adjacent sensor units, and shape parameters of any two adjacent sensor units.(3) For the Ⅱ-type sensor, a mutual inductance voltage measurement model named the Numerical Integration-based Equivalent Loop Approach (NIELA) is advocated by technical fusion of the electromagnetic field formula derivation, equivalent loop modeling and numerical integration approach. It can qualitatively characterize the complicated relationship among the sensor’s measuring underground horizontal displacement, vertical displacement, and tilt angle, output of mutual inductance voltage and the geometrical parameters of two sensor units.(4) Through comprehensive application of the Hall sensing mechanism analysis,3D spatial distribution solution to magnetic field of the permanent magnet, and the multidimensional numerical calculation method, a model called the Equivalent Magnetic Charge-Numerical Integration Approach (EMC-NI) is presented and serves as II-type sensor’s Hall voltage measurement model, which provides a quantitative description of the sophisticated relationship among the sensor’s measuring underground horizontal displacement, vertical displacement and tilt angle, its Hall voltage output, the geometrical and shape parameter of sensor units and the permanent magnet.(5) A kind of underground displacement inversion algorithm based on the forward modeling and approximate optimization inversion theory is presented. It utilizes the above proposed semi-analysis measuring models (EELA, NIELA and EMC-NI) as the forward models to generate the references signals of mutual voltage and Hall voltage respectively, which is then used as entry data of the inversion system, together with the measured data of mutual inductance voltage and Hall voltage of I and Ⅱ type displacement sensors. By comprehensive application of optimization algorithm, the inversion system can finally realize the underground horizontal displacement parameters inversion for I type sensor, and the joint inversions of underground horizontal displacement and vertical displacement for the Ⅱ-type sensor, both with sound prediction precision.(6) Comprehensive examinations and comparisons have been conducted between the measured results and modeling prediction for mutual induction voltage and Hall voltage under counterpart conditions, through which not only the modeling effectiveness and calculation accuracy of the three models are objectively evaluated, but also some valuable theoretical support and guidance have served to reduce cost, speed up optimization and upgrade the proposed deep displacement sensors. Meanwhile, during this comparison process, through the implementation of optimization inversion algorithm based on forward modeling, the measured mutual inductance and Hall voltage can be directly converted to the measuring underground horizontal displacement and vertical displacement for the Ⅰ and Ⅱ type sensors.