The bottom of the Maoping Reservoir Dam in a county in Hunan Province has been leaking for many years. The local water conservancy department has taken many measures and detection methods but failed to find the cause of the leakage. They had no choice but to grout the entire dam in the hope of plugging the leak. Hundreds of tons of cement have been grouted into the dam, but there is still no effect. The water quality at the bottom of the leak has not changed at all. The water quality is still clear and the water volume has not changed. The leaking position from the top of the dam to the bottom is about 30 meters high. The construction team used a core drill to drill holes at the top of the dam and drilled to the bedrock to take out the complete core. The pigment tracking liquid was poured into the hole. It was not until more than 6 hours later that there was a leak. We tracked the leakage of fluid but couldn't find the cause at all. There was no way they could find us after seeing our dam leakage detection video on the Douyin platform and invited us to do an inspection for them to find and analyze the cause and location of the leakage. We drove to the scene with the dam leakage detector PQ-227A independently developed and produced by ourselves. After arriving at the scene, we learned the details and the leakage location from the construction party, inspected the on-site situation, and combined with some of the measures they have taken, we preliminarily analyzed and judged that the cause of the leakage should not be due to damage to the internal dam body, but to the cracks or broken water-bearing structures in the bottom bedrock and the abundant groundwater that caused the water to bubble up and flow out from the bottom of the dam.
To verify this analysis, we conducted a comprehensive inspection of the dam using a PQ-227A embankment leakage detector.
The PQ-227A levee leakage detector is an efficient geophysical exploration equipment carefully designed by the Puqi Geological Exploration Equipment Research Institute. It is mainly used for the safety detection of water conservancy facilities such as river levees and reservoir dams. It uses the exploration principle of natural electric field frequency selection method, measures and analyzes the law of potential difference changes of the dam body, measures N electric field components of different frequencies in the natural electric field, and analyzes the abnormal changes of the dam body based on the collected data to determine whether there is a pipe leakage problem in the dam. The detector can accurately find the leakage points of dam pipes, ant holes, and bedrock foundations. It has excellent detection effects in the exploration of engineering disasters such as dams, and provides scientific technical support for levee safety.
First, we collected data on the dam's backwater slope using the equipment's rapid detection mode three-frequency measurement, using a gradient measurement method with a pole spacing of 10 meters and a point spacing of 5 meters. The principle is to use three fixed frequencies to measure the measured area at three depths, with each frequency corresponding to a depth level. The equipment automatically generates a graph of the three frequencies, and finds abnormal areas through the regular changes of the curves. The measurement speed is fast and the work efficiency is high. It only takes a few seconds to collect data at one point, which is suitable for finding abnormal areas over a large area and determining the range of abnormalities.
The measurement results are as follows:
According to the measurement results, we found abnormal reflections in the area of points 5-9, and the three curves showed regular changes in this area. Next, we used the abnormal verification mode of the equipment to measure in this area, and arranged the survey lines in the abnormal area. The equipment can simultaneously collect data from 18 points on a survey line at a time. After the collection is completed, curve graphs, profile graphs and 3D renderings can be generated in real time, which is convenient for on-site analysis of the results.
The abnormal verification results are as follows:
Technical Analysis:
Through the analysis of our measurement results, the abnormal structure under the dam body is obvious. The structure above 30 meters is basically intact and no abnormal reflection is found. There are obvious low-value abnormal reflections at 7-10 o'clock and 14 o'clock below 30 meters. The dam body structure is above 30 meters. Before the construction of the reservoir, this place was a canyon sandwiched between two mountains. The rock type here is a granite area. From the outcropping of the mountain, it is observed that the weathering is serious and the cracks are well developed. Water can be seen flowing out of the rock cracks with the naked eye, which shows that there is abundant groundwater in the area. This verifies the problem of leakage that we analyzed and judged before. At the same time, it also explains why the grouting work done by the water conservancy department before has no effect on the leakage amount and water quality. It can also be reasonably explained that the tracking fluid did not flow out from the leak until 6 hours after it was injected into the borehole. It is because the tracking fluid did not flow out until it penetrated into the groundwater position and contacted the groundwater. The measurement was very successful and the equipment was very accurate. It solved the problem of finding the cause of the leakage of this reservoir that has plagued this reservoir for many years and provided scientific and technical support for the later governance of the local water conservancy department.
Hunan Puqi Geological Exploration Equipment Research Institute Technical Service Department
April 29, 2025
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