With the development of science and technology, especially the rapid development of sensors and networks, the safety supervision of dams has gradually developed from manual inspections to intelligent, networked and profitable directions. This requires the use of high-precision, high-stability sensors as the eyes and tentacles of the intelligent monitoring system to monitor the dam on a large scale, continuously, and in real time. Dam safety monitoring mainly checks the design, improves construction, and evaluates the safety status of the dam. Monitoring the safety of the dam is the top priority. The significance of dam safety monitoring is mainly for people to accurately grasp the behavior of the dam and better play the engineering benefits, save engineering investment, and prevent major accidents. A dam is a special kind of building. It has a huge investment, but the benefits are also huge. Its overall design structure is complex, and its operating environment is more complicated. Its damage may cause severe damage to a region, even human life. Casualties. Therefore, the safety of dams deserves more attention. To accurately understand the working behavior of dams, it can only be achieved through dam safety inspection. The dam accident may be caused by excessive pressure caused by underground leakage, increased seepage flow, and excessive drop in seepage slope. It may also be caused by dam aging, material cracking, and construction quality. In recent years, some water conservancy units have mostly adopted displacement sensor products to achieve automatic measurement, provide data to the upper-level system for analysis, and understand the situation of the dam in a more timely manner. As the magnetostrictive displacement sensor
product has obvious advantages in accuracy, stability and reliability compared with other displacement products, it has gradually revealed its power in terms of displacement and liquid level monitoring.
1.Monitoring of overall dam displacement
Take a relatively geostationary reference point at each end of the dam, connect the two points with a reference line and maintain a parallel state with the dam, which constitutes a reference for the overall displacement of the dam. The relative displacement between the two is then detected by a displacement sensor installed on the dam. The magnetostrictive displacement sensor is fixed in the box and embedded in the dam. The reference line connecting the two ends of the dam is protected by a pipe to ensure that the reference line is not susceptible to other interference. A special magnetic ring is installed on the reference line, and the magnetic ring is sleeved on the sensor's measuring rod but does not contact the measuring rod. The reference line is kept in a stable state by other measures such as inert water. When the dam moves, the magnetic ring moves relative to the measuring rod, and the sensor can immediately send the measured signal to the control room, and the inspector can immediately know the displacement of the dam.
2. Monitoring of dam cracks (combined joints)
According to the relevant principles of architecture, the structure of the dam is mainly composed of dam pillars and cement walls. The piles of the dam pillars are driven deep and the cement walls are relatively shallow. Over time, cracks can occur between the dam pillar and the concrete wall, which requires monitoring. In crack monitoring applications, magnetostrictive displacement sensors are installed in the channels inside the dam (the number of channels varies with the height of the dam). One channel can be considered according to the actual internal conditions, and needs to be installed and monitored at multiple points. In actual field installation, the magnetic ring is fixed on the cement wall, and the sensor is fixed on the dam pillar. When the crack changes, the magnetic ring follows the cement wall to change its position, and the sensor transmits the new position signal generated by the movement of the magnetic ring to the control room. Because the amount of displacement in dam monitoring is small, and the change is a long-term
Due to the slow change process, the magnetostrictive displacement sensor can meet this measurement requirement in terms of accuracy and stability because of its unique principle, so it has been widely used.
3. Monitoring of dam seepage
In dam engineering, a large part of the reason is due to engineering accidents caused by seepage. In order to ensure the dam's operational safety and safety management needs, it is very important to conduct seepage detection and safety evaluation of the dam that has been completed. When the reservoir is completed, it will have a great impact on the surrounding foundations such as the dam body, dam abutment, bedrock, etc., especially after the dam has stored water, a hydraulic pressure load is generated, and the dam is affected by the difference in upstream and downstream water levels. Seepage from the body, the dam foundation and the dam. The seepage flow is the basic element reflecting the seepage state. It is an intuitive, sensitive and comprehensive factor that reflects the seepage safety problem. It reflects the working status of the impervious body in a comprehensive and timely manner. Many engineering changes reflect the seepage pressure when the seepage pressure observation is not clear enough. It is already quite obvious. Therefore, in accordance with the requirements of relevant codes, the leakage water flow through the dam body, dam foundation and cross-strait seepage measurement must be observed and measured. The seepage around the dam is generally measured by measuring in a pervious layer arranged along the bypass line or along the seepage. Press the hole to observe its water level change.
There are three methods of observing seepage:
1) When the flow is less than 1L / s, the volume method should be used;
2) When the flow rate is 1 ～ 300L / s, the measuring weir method should be adopted;
3) When the flow is greater than 300L / s or a weir cannot be set, the flow meter method or the section water level method can be used;
The water measuring weir method is widely used. Generally, the entire water measuring weir system is composed of a gully, a water measuring weir meter, and a weir plate.
Among the sensors used in water measuring weir meters, there are multiple working principles, such as capacitive, inductive, and photoelectric, but all have common weaknesses, that is, they need to be re-calibrated regularly. Poor long-term stability, easy to damage, installation Later maintenance costs are higher. A water measuring weir meter using a magnetostrictive liquid level sensor can overcome the common weakness of the above liquid level sensors. Its unique working principle determines its advantages such as high accuracy, long-term reliability, stability, and convenient installation. Water measuring weir meters are generally composed of sensors, anti-fouling pipes, mounting flanges, horizontal bubbles and so on. In actual field installation, anti-fouling pipes need to be used to protect the sensors. One is to prevent sludge from entering, so as not to affect the floating of the float, and the other is to prevent the large-scale fluctuation of the water level from causing fluctuations in the float to cause output signals. Fluctuations. The water measuring weir gauge is generally installed on the side wall of the weir groove about 1 meter upstream of the weir plate, and the anti-fouling pipe and the catchment ditch are connected to each other, so the water level of the two remains the same. When the floating ball changes synchronously with the change of the water level in the anti-fouling pipe, the sensor outputs a signal to the control room or a secondary instrument, which can directly display the amount of water level change.
In the field of dam safety monitoring, high-precision, high-stability, and high-reliability magnetostrictive liquid level sensors have been used in a variety of applications due to their unique working principles. Accurate monitoring of displacement, cracks and seepage of the dam through the measurement of sensors can better assess the safety status of the dam and avoid major accidents.
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