Laser /GNSS automatic deformation and settlement monitoring system
The monitoring items of the dam safety monitoring automation system include: dam deformation monitoring, slope monitoring and environmental monitoring, which are mainly composed of monitoring instruments (sensors), monitoring data acquisition system (including automatic data acquisition and monitoring subsystem and electronic manual inspection and maintenance management subsystem), monitoring data management system, safety early warning and evaluation system and user interface system.
The system adopts a combination of relative and absolute measurements for overall monitoring of the dam and nearby bank slopes, utilizing multiple new technologies such as ring grid laser collimation technology with independent intellectual property rights, laser automatic leveling compensation technology, laser ring grid spot CCD image recognition technology, and high-precision Beidou/GPS dual frequency receiver.
Among them, dam monitoring includes three subsystems: horizontal/vertical monitoring of dam crest, Beidou /GPS three-dimensional displacement monitoring of dam crest, dam leakage and environmental monitoring. Other monitoring data of upstream and downstream water level, rainfall, temperature and other environmental quantities can be shared through the monitoring information management system by using the monitoring data of water regime forecasting system.
A, dam crest horizontal/vertical monitoring subsystem
Two patented technologies, ring grating laser collimation and laser ring grating spot CCD image recognition, are adopted, and the horizontal and vertical displacement of dam crest are monitored at the same time by laser long chord measurement method, which has the characteristics of high precision, fast monitoring speed, low failure rate, simple structure and easy maintenance.
1. Measuring principle
A high-precision collimated laser beam composed of concentric rings with alternating light and dark is emitted from the laser emitting end. The images of light spots at different distances are shown in the following figure:
The laser beam passes through the CCD digital receiving target installed at each monitoring point in turn, and the spot image is identified and the spot center (x, y) is calculated by the digital receiving target, and the horizontal displacement and vertical displacement can be obtained by comparing with the initial value. The horizontal displacement calculation method is as follows:
2. System composition
2 laser leveling monitors
1 laser ring grating collimating light source
3 CCD digital receiving targets at monitoring points
3 reference end CCD digital receiving targets
3. Main technical indicatorsThe resolution of CCD digital receiving target is 0.01mm and the accuracy is 0.05 mm. The observation accuracy of the laser displacement monitoring system is 0.6mm, and the automatic observation time is 2min. It completely meets the requirements of Technical Specification for Dam Safety Monitoring Automation (DL/T 5211-2005), Technical Specification for Concrete Dam Safety Monitoring (DL/T 5178-2003) and Technical Specification for Earth-rock Dam Safety Monitoring (SL 60-1994).
4. System software
5. According to the measured data of dam crest displacement, the displacement process curve drawn is shown in the following figure:
Second, the dam GNSS three-dimensional displacement monitoring subsystem
With the improvement of GPS system and the completion of the networking of Beidou II system in China, the receiver of Beidou /GPS/GLONASS system has been successfully commercialized. At present, Beidou /GPS can be used for precision deformation monitoring and will gradually replace the conventional measurement methods, which is a technological revolution in the field of precision deformation monitoring. Beidou /GPS receiver with China's independent intellectual property rights is the guarantee for the safety of major national infrastructure.
The principle of Beidou /GPS automatic monitoring scheme is to use Beidou /GPS carrier phase high-precision relative positioning for three-dimensional positioning. Using precise ephemeris and software jointly developed with Tsinghua University, the accuracy of the solution can reach millimeter level by using the observation data of two-hour dual-frequency Beidou /GPS receiver.
1. Measuring principle
A reference station is set up at a firm place on the dam slope, and a high-precision Beidou /GPS dual-frequency receiver is placed. The receiver signal is transmitted to the monitoring center regularly through optical fiber or special digital communication network. Beidou /GPS high-precision dual-frequency receiver is placed at the monitoring point of dam crest displacement to be measured. The monitoring receiver signal is sent to the monitoring center regularly through optical fiber or special digital communication network. The information received by the monitoring center from the reference station and the monitoring station is solved by Beidou /GPS high-precision baseline processing software, and the coordinate difference between the reference station and the monitoring station is obtained. The result is the coordinate difference in WGS-84 geocentric coordinate system. The change of coordinate difference measured at different times reflects the three-dimensional deformation of monitoring points.
2. System composition
1) Beidou /GPS reference station and monitoring stationBeidou /GPS reference station receives Beidou /GPS satellite signals for baseline calculation. The monitoring station is placed at the displacement point, receives the Beidou /GPS satellite signal, and can measure the deformation of the displacement point by positioning relative to the reference station.
This system shares four high-precision Beidou /GPS receivers, including one reference station and three monitoring stations. Two monitoring stations are installed on the main dam, one monitoring station is installed on the auxiliary dam, and one reference station is installed in the reservoir management office.
2) Wireless communication networ
Function of wireless communication network: transmit Beidou /GPS satellite signals received by reference stations and monitoring stations to the central station in real time. The central station monitors the working conditions of reference stations and monitoring stations through the communication network; And send monitoring commands to reference stations and monitoring stations.
Central station function:
A, responsible for the management of the whole system and monitoring the working conditions of Beidou /GPS receivers in reference stations and monitoring stations; Send control instructions and set working parameters to the receivers of reference stations and monitoring stations.
B, collect original data observed by Beidou /GPS receiver of reference station and monitoring station in real time.
C, automatically extract that data of corresponding reference station and monitoring stations from the database according to the set time, and the data proces center automatically calculates the three-dimensional coordinates of the monitoring points.
D, analyzing the calculation results of the data processing center in real time, and drawing the displacement change time-history curve and settlement change curve of each monitoring point. Analyze the deformation of monitoring points and give an alarm to the out-of-limit points with large deformation.
3. System accuracyThe accuracy of deformation output by the system: 24-hour solution is less than 1mm, and 4-hour solution is less than 3 mm.
4. Data analysis
Analyze the accuracy, reliability and precision of monitoring data.Analyze the law of monitoring quantity changing with time or space.Distinguish the abnormal value of monitoring quantityAnalyze the stability of the variation law of monitoring quantity.Apply mathematical model for analysis, and propose or adjust monitoring indicators when necessary.The integrity and stability of dam structure and the effectiveness of seepage control and drainage facilities are analyzed.Evaluate the working state of the damDraw the displacement process curve according to the monitoring data as follows:
During the operation period, the mathematical model generally includes three parts: water pressure component, temperature component and aging component. The changing form of aging component is an important basis for evaluating whether the effect quantity is normal or not. The following figure shows three forms of aging component, representing three working states.
5. System characteristics
Beidou /GPS technology is completely feasible for dam appearance deformation monitoring and landslide monitoring. Compared with conventional monitoring methods, it has the following advantages:All-weather monitoring and monitoring time synchronization can be realized.
The monitoring accuracy is high, and the accuracy can reach 1 mm, which can meet the requirements of dam displacement monitoring.Can be continuously observed and used for a long time, and has long service life.
The observation results are digital results, which can automate the whole monitoring process.Three-dimensional displacement can be measured simultaneously.It can greatly improve the production efficiency and reduce the consumption of manpower, material resources and financial resources.Three, dam leakage and environmental monitoring subsystem
1. The arrangement position of leakage monitoring subsystem and its instrument working principle.Automatic collection of monitoring data: various sensors such as osmometer, rain gauge, water temperature gauge, upstream and downstream water level gauge, etc. adopt automatic monitoring (self-reporting type) and forced monitoring (response type) for patrol measurement, selective measurement and manual measurement.Data communication: there is bidirectional communication between the measurement and control unit and the workstation.Data analysis and management: display, store and print the monitoring data, establish engineering files, realize online and offline processing, make charts in time, and analyze and evaluate the engineering performance.
2. Observation of leakage: The leakage reflects the integrity of the dam body, the water-stop structure of dam joints and the working state of seepage-proof curtain, which is of great significance for understanding the operation state of the dam. Combining with the actual seepage situation of the reservoir, two measuring points are arranged, and the water collecting wells behind the dam are measured by measuring weirs, that is, one measuring weirs are respectively arranged in the water collecting wells behind the main dam, and the water head on the weir is measured by using ultrasonic water level meter, so as to obtain the leakage. This system is equipped with a leakage observation instrument.
3. Rain gauge: A tipping bucket rain gauge is installed on the roof in dam management. The working principle is: when it rains, the tipping bucket rotates once, and the magnetic switch is turned off to give the MCU a pulse signal, then the MCU counts the signal of each pulse and turns it into rainfall. This system is equipped with a rain gauge.
4. Monitoring of dam seepage pressure: The seepage pressure is observed by vibrating string osmometer. The sensing element of the osmometer is a piano string attached to the membrane, which is excited by the winding magnet to change the pressure of the string. The tension is proportional to the resonance or natural frequency of the steel string, and then it is converted into water pressure data through frequency signal measurement. There are 20 osmometers in this system. See the CAD plan for details.
5. Arrange two water temperature meters.
6. Arrange two water level gauges.
Fourth, the video monitoring subsystem
Two video cameras are installed on the main dam and the auxiliary dam respectively, which can monitor the gate, spillway and dam body 24 hours a day, and at the same time play the role of safety monitoring of dam body monitoring equipment.
