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Abstract
Real-time and on-line monitoring of slope and reinforcement works are useful for mastering the deformation dynamics and early warning of the landslide in time. In comparison with the conventional monitoring methods, distributed fiber optic sensing offers a number of advantages including distributed monitoring, long distance, real-time monitoring, long-term stability, et al. so as to meet the demand of early warning of landslide and health monitoring of slope engineering. The measurement principles and merits of Brillouin optical time-domain reflectometer(BOTDR) are introduced. And a novel distributed fiber optic sensor-based monitoring system for slope engineering is expounded. The relative topics about application of BOTDR in slope engineering are discussed including installation methods of optical fiber, optical fiber protection and temperature compensation method. To realize the remote distributed monitoring of the slope and reinforcement works, fiber optic sensors, which are connected with each other to form a BOTDR-based remote distributed monitoring system, are installed in the reinforcement works and the slope in some ways. Then taking a project as example, the deformation monitoring data are analyzed. And the monitoring results show that, in slope engineering, the state of deformation can be exactly reflected by BOTDR-based distributed monitoring system, which has obvious advantages in terms of slope deformation monitoring and real-time landslide prediction.
... The installation mode of optical fiber is fixed on a specific carrier has been developed by some researchers, which not only strengthened the slope, but also monitored the deformation of the slope. For instance, Sui et al. [83] designed a novel distributed fiber optic sensor-based monitoring system for slope engineering. As shown in Fig. 20 (a), the optical fiber of this kind embedded in frame beam can avoid the problems of sensing failure and inaccurate measuring result caused by a lack of protection measures and the deformation inconsistency of sensing fiber and soil, respectively. ...
... Schematic diagram of monitoring system for slope engineering: (a) sensing fiber embedded in frame beam and (b) sensing fiber installed in slide-resistant pile[83]. ...
Slope instabilities are a common occurrence in hilly areas, mine, and dam region, which bring a grave threat to the safety of transportation business and human life. The effective slope monitoring methods and instruments can provide information on the current deformation and historical trends, which is important scientific information for researchers to analyze slope stability and provide a timely warning to the public. Optical fiber sensors (OFS) have attracted many researchers to explore due to their have unique advantages in comparison with conventional electronic based sensing technologies, such as immunity to electromagnetic interference, remote transmission, easy integration and high sensitivity. This paper presents an overview of the latest development and application of OFS based slope deformation monitoring from two aspects: 1) Fiber Bragg grating (FBG) based sensing and monitoring technology; 2) Distributed optical fiber sensors (DOFS) including Brillouin Optical Time Domain Reflectometry (BOTDR) and Brillouin Optical Time Domain Analysis (BOTDA) for slope monitoring. Meanwhile, current challenges in implementing the OFS-based slope monitoring technology are discussed.
... Optical grating with different pitch can be placed in the same optical fiber, to monitor temperature, stress, and strain at the same time [3,4] . It is feasible to combine FBG technology and traditional technology for measuring borehole deviation for which can both guarantee the accuracy of the data while achieving real time monitoring [5,6] . ...
... By finding the inverse matrix, one can figure out the relation between displacement and the strain of the measuring point. As follows: (5) That is: (6) This shows that, by model simplification and assuming the clinometer, one can establish the relation between strain and displacement. In formula 6, except the strain value, which is acquired by calculating the data collected from FBG demodulator, the rest are constant. ...
Using FBG (fiber bragg grating) technology in clinometers can solve the technological problem facing by wireless transmission devices like big data transfer volume and poor stability, which has been receiving more and more attention. This paper discusses a new clinometer that is designed and transformed based on upgrading current clinometers, installing fiber grating strain gauges and fiber thermometers, and carrying out studies on such aspects as equipment upgrading, on-site setting, and data acquisition and analysis. In addition, it brings up the method of calculating displacement change based on wavelength change; this method is used in safety monitoring of the right side slope of Longyong Expressway ZK56+860 ~ ZK56+940 Section. Data shows that the device is operating well with a higher accuracy, and the slope is currently in a steady state. The equipment improvement and the method together provide reference data for safety analysis of the side slope.
... Zhang et al. [20] took a subway tunnel structure in Shanghai as an example, combined manual measurement and automatic monitoring methods, and found that the results of automatic monitoring were greatly affected by the natural environment and accumulated error. Sui et al. [21] designed a foundation pit monitoring system based on Brillouin Optical Time-Domain Reflectometer (BOTDR), which can accurately and stably monitor the deformation impact of foundation pit excavation on the surrounding environment. Tang et al. [22] used a precision 3D laser to automatically extract the monitoring data of a specific line of the subway tunnel, which greatly improved the monitoring efficiency. ...
The excavation of the foundation pit will cause changes in the soil stress field around the foundation pit, and that may have adverse effects on the adjacent subway tunnels. In this paper, a complex deep foundation pit excavated in different sections is taken as the research object, and the support structure of the complex foundation pit project is introduced, which accumulates experience in the selection of support structure for similar projects. The finite element models are established by MIDAS/GTS software to evaluate the influence of excavation in different sections of the foundation pit on the tunnel deformation, and the accuracy of the finite element calculation results is verified by comparing the monitoring data. The results show that: The horizontal deformation of the subway tunnel is generally smaller than the vertical deformation. Tunnel monitoring should focus more on the development of the vertical deformation of the tunnel. The maximum vertical deformation and horizontal deformation of the tunnel are both smaller than the local specification limits, and the excavation of the foundation pit in this project has little influence on the deformation of the subway tunnel.
... In recent years, fiber Bragg grating monitoring technology has developed rapidly because of it's strong resistance to external interference, high sensitivity and real-time transmission of monitoring data. Nowadays, fiber Bragg grating monitoring technology has been successfully applied in tunnels, slopes, dams, bridges and other engineering fields [2][3][4][5][6][7][8]. In the construction monitoring of soft foundation embankment, the application of this technology is still in it's infancy because of the problems of monitoring object and sensor burying technology. ...
The pore water pressure monitoring of soft ground pavement is one of the important technical links in highway construction monitoring. The use of traditional electrical measuring instruments to monitor pore water pressure has disadvantages such as low degree of automation, non-real-time data transmission, and high manual monitoring costs. However, fiber grating monitoring technology has developed rapidly due to its advantages of stable data transmission, convenient collection, and dynamic monitoring. . Therefore, relying on the soft foundation pore water pressure monitoring project of Jiujiang Ring Expressway, the monitoring principle of the fiber grating seepage pressure sensor and the buried installation technology in the soft foundation are introduced. Through the long-term monitoring practice on the construction site, it is confirmed that the optical fiber monitoring system is applied to the soft foundation. The stability of base pore water pressure monitoring provides a reference for similar monitoring projects and engineering construction.
... Deflection can be estimated by the strain on both sides of the face slab according to the methods proposed by [36][37][38]. Figure 18 shows the deflection model of the face slab during the cracking event. During the first crack of the slab in the "U"-type valley topography model, the flexural deformation of the face slab towards the downstream side formed a "D" shape, with the maximum deformation of 0.016 mm occurring near the toe wall. ...
The recent focus on water conservancy projects globally has resulted in the construction of increased numbers of concrete face rockfill dams in narrow valleys. However, valley topography impacts the deformation of a dam and further influences the distribution of stress and position of cracks on the face slab. This study conducted two centrifuge experiments to study the influence of the valley topography on the behavior of a concrete face rockfill dam from construction to impoundment. Experimental models of concrete face slab sand-gravel dams with “U”-type and “V”-type valley topographies were established. The settlement of the dam crest, the displacement of the upstream slope of the dam, and the stress on both sides of the face slab were observed. The experiment also represented the cracking of the face slab during impoundment. The results showed that the “V”-type valley topography effectively reduced the progression of dam crest settlement and influenced stress on the slab resulting from impounded water pressure. Furthermore, the flexural form of the face slab in the “U”-type valley topography took on a “D” shape and cracks progressively developed on the face slab with increased water load. The flexural form of the face slab in the “V”-type valley topography showed a “B” shape, and cracks occurred under a particular water impoundment pressure.
... Neuberx (Japan), Smartece and Omnisens (Switzerland), Micron Optics, Inc. (USA) and OZ Optics (Canada) have successively launched commercial BOTDA-based measurement systems. In the past decade, research institutions in China have conducted extensive theoretical and experimental research on BOTDA and BOTDR and used them to measure the temperature of key engineering structures and have obtained many notable achievements [6][7][8][9]. The application and research and development of BOTDA are of great significance to safety monitoring, health diagnosis and theoretical studies of key engineering structures in China. ...
Temperature monitoring is an important component of structural health monitoring of mass concrete after pouring. This study investigates temperature measurements of mass concrete based on Brillouin optical time-domain analysis (BOTDA). First, the fundamental principle of using BOTDA-based distributed optical fiber sensing (DOFS) technology to measure temperatures is provided. Then, a temperature-measuring system is introduced. Finally, a case study on an engineering structure was conducted to explore issues relating to the practical application of BOTDA-based DOFS technology, including optical fiber cable laying and protection, measurement and results analysis. In addition, point temperature sensors and precision thermometers were used to measure the temperatures at several points along the optical fiber cable and the ambient temperature, respectively. The measurement results were compared with those measured by the optical fiber cable. Our study shows that BOTDA-based DOFS technology can be used to take accurate distributed temperature measurements of mass concrete structures. This temperature-measuring method provides an effective means for measuring the temperature of mass concrete structures.
In order to solve the problem of foundation settlement monitoring, this paper presents a monitoring program of substation foundation settlement, which is based on the distributed optical sensing technology. The composition of the hardware monitoring system and the wiring scheme of stress optical cables were described. The results of simulation experiment showed that the Brillouin optical time domain analysis could well meet the precision requirements of substation settlement monitoring. Moreover, the temperature reference optical fibers should be laid for temperature compensation. This paper can provide the basis for further prevention of substation foundation settlement.
The construction method of a box culvert being pushed to replace two pipe roofs is initiated as a city tunnel excavation method in China. This method is complex, and soil deformation is the key factor to test whether the construction method is successful or not and to guarantee the tunnel safety. The soil deformation sensors are introduced based on the distributed fiber sensing technology, their performances are tested in the laboratory, and a three-dimensional deformation monitoring network is designed according to the model tests. The test results and the monitoring data are analyzed. The soil deformation characteristics during the pipe-roofs pushing and box culvert replacement are summarized. This study will play an important role in perfecting the intelligent monitoring system, improving this construction method and analyzing the deformation of engineering soils.
In order to get the internal force distribution data of anti-sliding piles and evaluate their working state, distributed optic fiber sensing technique was used in landslide engineering monitoring strains of anti-sliding piles. Research results show that the process of strain variation from pile casting to push acting on pile is monitored; The strain in arbitrary depth of anti-sliding pile body is successful collected. Strain variation of anti-sliding pile because of the shrinkage of concrete achieves stable time about 4 months. Selecting the strain of the stable time as an initial value, according to the calculation theory of reinforced concrete, anti-sliding pile axial stress is computed and the current state of the safety evaluation of anti-sliding pile is obtained.
The geological condition and climatic condition are complicated in the plateau region of Yunnan Province, where potential safety hazards, such as the instable geological structure, the deformation of electric power transmission tower, and the overtemperature of the hidden parts of power transmission/transformation equipment, exist in most montanic electric substations. This situation endangers safe operation of the electric power system. The non-electricity full optical fiber sensor network and the intelligent information online monitoring system, which can realize detection and signal transmission, was constructed based on the special physical properties of the fiber Bragg grating (FBG), such as electric insulation, anti-interference, high precision and long service life, with consideration of the requirements of montanic transformer substation and transmission/transformation equipment. Consequently, accurate real-time monitoring of the geological structure, the power transmission tower deformation and the working temperature of the hidden parts of power transmission/transformation equipment were implemented. The FBG sensing technology has been applied successfully to the 220 kV Yanjin transformer substation of Zhaotong Power Supply Bureau of Yunnan Power Grid Corporation.
After analysis of the shaft damage reasons, the different reinforcement measures and the corresponding construction plan have been taken for the engineering characteristics of different rock segments. The influence of mining underground to the shaft repaired has been studied by establishing a numerical model in the identical condition of reinforcement measures, the corresponding geological conditions and mining order. The Numerical simulation experimental results showed that the shaft is a certain degree damage risk with the deeper mining. According to the engineering distribution between the shaft and ore bodies, the distributed optical fiber sensing technology has established a dynamic monitoring system for long-term monitoring and predicting rock mass deformation accurately.
Spatial resolution is one of the important parameters for Brillouin scattering based distributed optical fiber sensing. The results of constant tensile load test were analyzed, and the strain distributions of point-by-point fixed fiber measured by two different spatial resolution respectively were compared. Then the influence of spatial resolution on measured strain was analyzed. Two spatial resolution calibration methods, including 10%~90% step-function method and hot-spot method, and their applicability were discussed. The dissimilar-fiber-splicing method was proposed to calibrate the spatial resolution. Dissimilar-fiber-splicing means two variant peak frequency fibers are alternately spliced in series with segments of different length. The calibration experiment shows that dissimilar-fiber-splicing method is accurate, objective, and comparative.
Fiber optic sensing is a newly-developed distributed monitoring technology; it has great potential in slope engineering. A new method to evaluate the stability condition of slope based on strain distribution of slope mass measured by sensing fiber in real-time is proposed. A slope model test is conducted in laboratory and the Brillouin optical time-domain analysis (BOTDA) technology has been used to measure the horizontal strains at different depths of the slope model subjected to loading on the slope crest. The test results show that the tight-buffering optical fiber packaged by heat-shrinkage tubes can be used for monitoring strain distribution within the slope. In order to take temperature compensation into consideration and achieve the purpose of accurate positioning, the installation of loose fiber sections at key locations along the sensing fiber is recommended. The potential slip surface can be estimated based on the distributed strain monitoring results. The deformation behavior and stability condition of the slope model during testing was analyzed in detail. It is found that there is an empirical relationship between the averaged maximum horizontal strains and the factor of safety of slope, so as to provide a new approach to evaluate slope stability and perform early warning of landslides.
The monitoring method for deformation force of continuous concrete wall during the excavation processs of a foundation pit is introduced by using the BOTDA distributed optical fiber sensing technology. Through the distributed optical fiber on the continuous concrete wall of steel and H steel, this technology can automatically acquire the data of strain, bending moment, deflection of piles during the excavation process. The monitoring method adopts double-line measurement and has the capability to self temperature compensation.
Aiming at the problems in the deep deformation monitoring of anti-slide piles, the Brillouin optical time domain reflectometer(BOTDR) technology is proposed to monitor deep deformation of anti-slide piles. Based on the monitoring data, the displacement is determined. Through the analysis of relationships between displacement and other physical quantities of anti-slide pile and the strain characteristics by BOTDR technology, the quadratic integral function relation between displacement and strain is established; and the analytical process and boundary conditions are given based on the hypotheses. Taking the anti-slide pile project of the landslide No.1at Hongyan Village of Zhu-Yong Expressway in Zhejiang Province as the background, the optical fiber sensor and inclinometer are installed at different locations and the displacements are calculated based on the monitoring data. Comparing the calculation displacements with inclinometer monitoring results, the rationality of model for determining anti-slide pile displacement based on BOTDR monitoring data is verified. The results show that: BOTDR technology applied to monitor deep deformation of anti-slide pile is feasible; the model for determining anti-slide pile displacement can meet the needs of engineering to some extent; through arranging optical fiber along the reinforcement, the calculation displacements based on the monitoring data are more accurate. Finally, the locations of installing optical fibers for determining displacement of anti-slide pile based on BOTDR technology are recommended. The study has reference value for the application of BOTDR monitoring technology in anti-slide pile and relational monitoring and data processing in pile foundation engineering.
BOTDR technology is used to monitor surface deformation overcoming defects of conventional monitoring means and technology. The authors research on fixation and temperature compensation of fiber in the process of monitoring implementation, emphatically introducing laying means in the Guanjia slope of Longli freeway in Zhejiang Province. Based on characteristics of engineering environment, implanted fixation is used on slope volume. Introducing quasi-distributed monitoring concept, special clamps are used to fix fiber in fixed-point on front slope face. The monitoring results show that tight coated fiber of relatively small outer diameter is suitable for implanted fixation to ensure sync coordinate deformation and sensitivity of fiber is improved because of smaller sheath effects. Big outer diameter is suitable for fixed-point. When temperature field changes a little, temperature compensation could be neglected. In contrary, it could be carried out by selecting similar monitoring environment and laying relaxed fiber to measure temperature changes. At the end it is discussed about fiber laying measures improvement and temperature compensation means.
Geological structure health in mountainous area substation is complex, and the climate is changeable, it is easy to appear the geological disasters like landslide and subsidence in substation, Aiming at the strong electromagnetic interference in substation and other factors, to monitor of slope surface strain of mountainous area substation with FBG strain sensor, in order to reflect the stability of the slope. Combined with the actual situation of slope of Yunnan 220kV mountainous area substation, the surface type FBG strian sensors are installed on the surface of upstream and downstream slope of mountainous area substation, the lower reaches of the substation, the serial network forms a quasi distributed optical fiber sensing network. they form a quasi-distributed optical fiber sensing network through the serial networking methods.When the slope surface occurs deformation due to the soil sliding, it will drive the FBG strain sensor and transfer the equal strain to the FBG strain sensor. By measuring the center wavelength shift of the FBG strian sensor, the strian value of slope surface at each point can be reflected. The monitoring results show that, the period from May 9th to June 6th, the maximum strain of upstream slope is 171uɛ, it appears at the location of marked as US4 FBG strain sensor, the maximum strain of downstream slope is 112uɛ,it appears at the location of marked as DS1 FBG strain sensor.
The mountain landslide has been the disaster which makes great harm in the nature. People have been looking for better monitoring of the preceding information to the landslide. A number of commonly used monitoring methods have been developed, but they have both advantages and disadvantages. With the development of optical fiber sensing technology, it is found that monitoring optical fiber has many advantages comparing with traditional methods. In this paper, the basic principal of optical fiber sensing technology is described; and technologies of optical power consumption, Optic Time Domain Reflectometry (OTDR), Brillouin Optic Time Domain Reflectometer (BOTDR) and Fiber Bragg Grating (FBG) are analyzed. A new composite optical fiber testing device based on optical fiber monitoring method is proposed. The device based on optical time domain reflectometry can achieve high initial accuracy, large range and direction of the judge.
By analyzing the problems of determining landslide thrust at present and requirements of thrust characteristics of landslide, calculation method of landslide thrust is proposed based on BOTDR monitoring data. By arranging optical fiber sensors on anti-sliding piles to monitor their continuous deformation under thrust, landslide thrust was determined based on the function relationship among strain of anti-sliding piles, bending moments and force on piles. The results show that this method is not only able to determine modes and values of landslide thrust on anti-sliding pile, but also to determine the force on the piles and the presence of slip surfaces. According to the results of calculation, thrust distribution of the landslide on the piles has segment characteristics. The modes make a great difference. When the piles are close to landslide spindle line, landslide thrust is the largest which has the mode approximate parabola. The effect of landslide thrust on marginal segmentation is weaker. So, from central to marginal segmentation, the direction of landslide thrust generates deflection.
The fiber Bragg grating (FBG) technology was studied based on the current monitoring status of the highway soft ground settlement, such as the low degree of automation, the unsatisfied accuracy of the device, the slow data transmission and the greater measurement errors. The development of the long range optical fiber displacement sensor as well as its burying techniques which are suitable for soft ground settlement monitoring was analyzed. Both of them were applied in Dechang Highway D10 subject. The results show that the long-range optical fiber displacement sensor is able to meet the requirements of the soft ground monitoring. And data can be accurately monitored by means of real-time or on-line continuously.
In the area of Longnan, Gansu province, slope engineering safety issues have become increasingly prominent, and it is necessary to monitor and warn the slope works. A comprehensive three-dimensional automatic slope monitoring system was established, based on a high slope reinforcement works instance of Zhouqu reconstruction project after a disaster. Through monitoring and analyzing on the slope of stress and displacement, we found the slope's changes in the characteristics and laws during the construction and operational phases. During the initial phrase, the slope support, stress, and displacement amplitude are greater. With the mutual adjustment of internal support structure and rock slope, both changes were stabilized. Since the end of the slope support, maximum displacement speed is 0.24 mm/d,<0.5 mm/d, and maximum displacement accumulated variation is less than 10mm. Maximum acceleration is 0.31 mm/d2; the force and deformation of lattice beams are in the elastic range; the slope changes of internal horizontal displacement are small. Integrated the monitoring results, it can be drawn that an anchor lattice beam can play an effective reinforcement role, and that during the operational phase, this slope is in a stable state. The test has certain reference value for the reinforcement design and monitoring analysis of similar slopes in the future.
The fiber Bragg grating (FBG) technology is studied based on the current monitoring status of the highway soft ground settlement, for instance, the low degree of automation, the unsatisfied accuracy of the device, the slow data transmission and the greater measurement errors. The limited measuring range and the difficult situations of the soft ground burying and installing of the fiber optic sensor still need to be addressed. This thesis has analyzed the development of the long range optical fiber displacement sensor as well as its burying techniques which are suitable for soft ground settlement monitoring. Both of them have been successfully applied to De Chang Highway D10 subject. The study also shows that the long range optical fiber displacement sensor is able to meet the requirements of the soft ground monitoring. And data can be accurately monitored by means of real-time or on-line continuously. This is of great significance in pushing forward the development of the fiber optical monitoring technology in the field.
Based on briefly introducing the works of BOTDR, article studied on dike strain monitoring by using the distributed optical fiber measurement system produced by OMNISENS in Swiss. Builded the dike model, monitored the dike strain changes influenced by seepage and loading, we try to verify the feasibility that the distributed optical fiber measurement system can basically reflect the dike deformation. It can be an important direction for the development of dike strain monitoring.
In order to clarify some of the important issues on slope performance, a full-scale slope monitoring experiment has been conducted at a being constructed slope, Hong Kong. The experiment adopts a number of instruments, including soil moisture probes, tensiometers, open standpipes, piezometers, inclinometers, earth pressure cells, and a rain gauge. etc. A high proportion of instruments are connected to dataloggers for automatic monitoring of the slope performance. The design and installation of the instrumentation system for the slope monitoring experiment are presented in detail.
An example of soil-nailing support is introduced for a high weak rock slope and the information from construction monitoring is analyzed based on the principle of soil-nailing support. Based on the construction monitoring, the most dangerous failure surface of high weak rock slope is provided. The slope is designed and analyzed by theory of limit equilibrium. The support parameters are adjusted and the construction period is shorted in time. The sidewall deformation is controlled at every construction stage and the whole slope stability is ensured.
The distributed-optic-fiber strain sensors based on the Brillouin scattering is one of the key problems in the monitoring of industrial structures and equipments and in the diagnosis of faults, and it has wide applications in not only the optic fiber communication, and intellectualized-structure-systems but also the space/aeronautics, civil construction, dam, and bridge construction etc engineering. The Brillouin frequency-shift caused by the optic-fiber strain in the sensor was analyzed and discussed theoretically, and on this basis, the relationship between the strain and frequency-shift was established which has been checked to be in good agreement with the experimental results available in literature.
A newly developed fiber optic sensing net is presented in this paper. Optical fiber (cable) was weaved into a fiber optic sensing net. The distribution of strain experienced by the net was measured by a BOTDR (Brillouin Optical Time-Domain Reflectometer). The flexible fiber optic sensing net laid on the surface of a slope can deform along with the slope surface. Therefore, the surface deformation of the slope can be monitored by measuring the strain of the fiber optic sensing net. The Lab. experiment showed that the net was sensitive to the surface deformation caused by loading. By analyzing the strain of optical fiber (cable) and the position of loading, a 3-D simulation was made.
This paper introduces the development and application of an integrated automatic slope monitoring system. The system combines (a) advanced conventional instruments and (b) accurate global positioning instruments. The development includes selection of all instruments, technical requirements, integration method and post-process of monitoring data, etc. This system has been installed in a real loose fill slope to verify its functions and reliability of the integrated system including remote data acquisition. Preliminary monitoring data are presented and discussed.
250 and 3 873 bundles of prestressed anchor cables with grade of 1 000 kN and 3 000 kN respectively, have been employed to stabilize the high slope of the TGP permanent shiplocks and 113 sets of stress monitors have also been installed to monitor the stress state of these anchor cables. It is rare to have so many anchor cables and stress monitors for a slope in the world. Based on the interpretation and analysis of stress monitor data, the stress state of anchor cables, stabilization effect and loss of prestress are discussed, which will facilitate the safety judgment of high slope stabilization and provide practical experience for other similar projects.
NTT Access Network Service Systems Laboratories has developed a system for monitoring road disasters by using optical fiber sensing technology. This technology allows linear measurement over long distances, which is advantageous when the length to manage is long and risk locations are difficult to determine in advance. This article describes various sensors developed for monitoring road disasters and software for controlling the measuring devices, processing data, and performing other tasks.
Anti-slide pile is an important method for slope treatment, especially when the slide face is certain and the subterrane is stable, the method is proved to be prior. But if there exist more weak terrains under the slide face, a new slide face may be formulated after being reinforced and ideal reinforcement effect can not be achieved. Monitoring and analysis of anti-slide piles reinforcement effect on the west area slope of Chengchao Iron Ore are analyzed. The results indicate that there are shallow-layer and deep-layer slide faces in the slope after reinforcement. At first, there is only a shallow-layer slide face found before reinforcement, but a new weak face on the base of the first shallow-layer slide face is found after reinforcement and then, shallow-layer and deep-layer slide faces are found. However, anti-slide pile has effects only on the shallow-layer slide face because of its length. It is pointed out that the influence of ground water is an important factor for slope deformation.
The principle of Brillouin optical time domain reflectometer (BOTDR) is introduced and its application to the strain monitoring of the strain distribution of reinforced concrete beam is studied. The experimental results show that the strains measured by BOTDR optical fiber sensor are in good agreement with that by strain gauges. By comparing the measured strains of the steel bar inside the concrete with that attached on the concrete surface at the same level, the damage is detected when the load reaches 25 kN. The deflection of the beam is calculated with the strain distribution measured by BOTDR. It is concluded that, as an advanced distributed optical fiber sensing technology, BOTDR is good for measuring the strain distribution of reinforced concrete structures. It is accurate and feasible to be used in the fields of deformation monitoring and damage detection of reinforced concrete structures.
Distributed fiber optic sensing technique is being considered as a promising method to monitor continuously structural behavior such as the detection of crack, and the measurements of crack widths and overall deformation with a real-time manner, because current structural inspection technologies are not capable of responding to many of the monitoring needs pertinent to concrete structures. In this paper, in order to investigate and improve the monitoring capability of fiber optic sensors with BOTDR, first of all, several kinds of installation methods are proposed. Moreover the effectiveness is verified through testing instrumented RC beam specimen where the fiber optic cable is installed with the proposed methods. It is realized that the loop type of installation methods of fiber optic sensors can be effectively used to measure the crack damage within a relatively local area and the fixed point installation method of fiber optical sensor is capable of measurement of strain due to one or two localized cracks within a distance of lm resolution.
SUMMARY Since river levee collapse causes great damage, it is socially very important to prevent such disasters by using a monitoring system which can detect changes in the state of a river levee. To investigate the possibility of detecting the collapse of a levee slope at an early stage, we performed an experiment in which we used artificial rainfall and penetration to collapse a full-scale levee model, and measured the change in the levee state using a detection system during collapse. The system consists of sensor plates, a distributed fiber optic strain sensor, and a per- sonal computer. With this system, the stretching produced in the sensor plates by the force resulting from the movement of the soil on the levee slope face is detected as strain by a sensing optical fiber fixed to the plates. Since the distributed fiber optic strain sensor can measure strain continuously and for a long distance along a fiber, it is suitable for monitoring civil structures such as river levees. The experiment confirmed that a change in a levee can be clearly detected when the slope face collapse progresses near the place where the sensor plates are buried. The results suggest the feasibility of being able to foresee the collapse of a levee slope.
Due to the large measurement range, distributed optical fiber sensors are very effective in the monitoring of large structures. Brillouin distributed optical fiber sensors, which measure strain by using Brillouin frequency shift, show some measurement error for non-uniformly distributed strain because of their spatial resolution characteristics. They require compensation of measured values and positions in the end-parts of the measurement range because measured values are not distributed over all the positions of the spatial resolution range. In this paper, we present the strain measurement characteristics of Brillouin distributed optical fiber sensors and the compensation method in the end-parts of the measurement range. A deflection measurement method for a beam subjected to a bending load using Brillouin distributed optical fiber sensors is also presented. This is verified by a three-point bending experiment employing an 8 m aluminum beam. The experimental results showed that the measured value agrees with the one expected by Brillouin measurement theory.