Leakage detection of urban water supply pipe network is an important topic in the water industry, and it is also a worldwide problem. Therefore, it is necessary to comprehensively use multidisciplinary methods, combine advanced and cutting-edge technical concepts, and carry out high-quality and efficient pipeline network leakage detection work in an all-round way according to the characteristics of abnormal points of water supply network leakage. This paper will focus on introducing new methods for pipeline network leakage detection based on other principles, including:
(1) Flow monitoring method based on the principle of water balance;
(2) Pressure monitoring method based on the principle of pressure change;
(3) Gas tracer method based on the principle of gas concentration change;
(4) pipeline endoscopic method based on closed-circuit television imaging principle;
(5) Ground-penetrating radar method based on the principle of electromagnetic wave detection;
(6) Surface temperature measurement method based on the principle of infrared thermal imaging;
(7) Radar satellite imaging method based on the principle of electromagnetic wave detection;
(8) Pipeline under-pressure detection technology based on the principles of acoustics, closed-circuit television imaging, optical cable communication, and temperature sensing;
It is hoped that through the series of elaborations in this article, readers will be helped to establish an understanding of the international advanced and cutting-edge pipeline network leakage detection methods and science and technology, and provide diversified solutions for pipeline network leakage detection.
1.1 Sky-penetrating radar method
1.1.1 Basic mechanism
Ground-penetrating radar is a geophysical method that uses antennas to transmit and receive high-frequency electromagnetic waves to detect the properties and distribution of materials inside the medium. Since the UHF short-pulse electromagnetic wave propagates in the medium, its propagation path, electromagnetic field strength and waveform are related to the electrical properties and geometric shape of the passing medium. The ground penetrating radar method is to judge the characteristics of the underground structure through the analysis of the received reflected wave data. Or man-made structural features, and then infer the method of water leakage.
1.1.2 Scope of application
The ground penetrating radar method can be used to detect water leakage points in pipelines that have formed wetted areas or empty areas. However, if the water supply pipeline is located below the groundwater table, or the medium around the water supply pipeline is seriously uneven, the ground penetrating radar method is not suitable.
1.1.3 Technical points
The ground penetrating radar method should meet the following conditions: first, there is a significant electrical difference between the wetted area or void area formed by the water leakage point and the surrounding medium; field resolution.
Ground penetrating radar detection equipment should meet the following requirements: First, the maintenance and calibration of equipment should be carried out in strict accordance with regulations; second, the transmission power and anti-interference ability of detection equipment should meet the detection requirements; third, the antenna frequency used by detection equipment should be consistent with Match the buried depth of the pipeline.
In order to ensure the application efficiency of the ground penetrating radar method, the method test should be carried out in the detection area or adjacent known leaking points before detection to determine the effectiveness of the detection method and determine the best working parameters in the field. Working parameters should include working frequency, dielectric constant, time window, sampling interval, etc.
When the ground penetrating radar method is used for detection, the arrangement of measuring points and measuring lines should meet the following requirements: first, the measuring lines should be arranged perpendicular to the direction of the water supply pipeline to be tested, and at least three measuring lines should pass through the abnormal water leakage area; The distance between the measuring points should ensure the effective identification of the reflected wave anomalies and their interface in the abnormal water leakage area; thirdly, the measuring lines should be densely arranged in the abnormal water leakage area. The extent of the void area. Because the difference in electrical properties of the underground medium varies greatly, sometimes fine-tuning the position of the radar profile will cause a relatively large change in the radar waveform. Therefore, if necessary, the survey line can be arranged in a grid to improve the detection accuracy of the ground-penetrating radar method.
When the ground penetrating radar method is used for detection, the ground penetrating radar system should adopt working parameters such as working frequency, dielectric constant, and propagation velocity determined through the method test, and should adjust the working parameters in time according to changes in the field conditions. When the detection conditions are complex, two or more antennas with different frequencies should be selected for detection, and the working parameters should be adjusted in time according to the interference situation and image effect.
On-site geophysical conditions may affect the quality of data recorded in the field, and processing through necessary data processing methods can improve the quality of images and facilitate the identification of target anomalies. Data processing methods can choose to delete useless traces, normalize the horizontal ratio, gain adjustment, terrain correction, frequency filtering, fK dip filtering, deconvolution, offset homing, spatial filtering, point averaging, etc.
When interpreting the data based on the analysis of various parameter data, the following regulations should be met: first, it should follow the principle of moving from known to unknown, easy before difficult, combining point and surface, and qualitative guidance; second, it should be based on the principle of pipeline The conditions of the surrounding medium, the possible drainage channel and scale of the leakage shall be comprehensively analyzed; the third is that the radar image involved in the interpretation shall be clear, and the interpretation result data shall include the radar section image, the position and depth of the pipeline, and the wetting or emptying caused by the leakage. Area map.