The leakage occurs during operation of the dam in Liuhuanggou reservoir. It’s a threat to the safety of the people’s lives and property in downstream. In order to eliminate the hidden danger of reservoir, ensure the safety of the dam, play better the function of flood control and water storage of the reservoir etc., we apply the 3D electrical resistivity tomography detecting technology and volume rendering image processing technology, make the measurement in field, process the data and combine the field survey to find out the leakage channels inside the dam. The results show that the 3D resistivity images appear the low resistivity zone corresponding with the leakage channels. There are two main leakage channels that come from different location inside the dam. It is feasible to diagnose the leakage in earth rock-fill dam by applying 3D electrical resistivity tomography.
Early electrical resistivity tomography (ERT) is 1D and divided into electrical sounding and electrical profile. The vertical electrical and horizontal electrical changes in different underground depth are reflected by the two methods respectively. They can obtain the geoelectric data too little to reflect the complicated geological conditions. With the development of CT imaging technology, some scholars have applied the technique of tomography to electrical exploration. Loke, M.H. [
Flood and drought disasters occur frequently that cause heavy losses in China in recent years, and the irrigation and water conservancy infrastructure are exposed very weak. We must vigorously strengthen the construction of water conservancy. We must consolidate the reinforcement results of large and medium-sized dangerous reservoirs, and speed up the reinforcement pace of small dangerous reservoirs, as soon as possible to eliminate the hidden danger of reservoirs, recover the control capacity of flood, and enhance the regulation capacity of water resources. China plans to reinforce the water conservancy project that has been the built during the period of “the 13th Five-year”. Within the next two years, China’s average annual investment is expected to reach 600 billion. This series of measures for the normal operation of the national economy and the guarantee of national sustainable development has played an important role, but also makes full use of the comprehensive benefits of the water conservancy facilities for flood control, irrigation, power generation etc. In a word, the state pays more attention to water conservancy project reinforcement. The leakage is a common dangerous in earth rock-fill dam. Through access to literature, we find that many water conservancy projects are not properly dealt with the leakage problem results in a series of accidents. The problem of the leakage in the dam is more and more serious in Liuhuanggou reservoir, and the space distribution of the leakage channel is understood by 3D electrical resistivity tomography detection technology, which provides a scientific basis for the next step of the treatment [
The theory of 3D electrical resistivity tomography is consistent with the common electrical method that conductive of underground material differences as the prerequisite, make underground is full of electricity and observe of subsurface electric field distribution, so as to solve different geological problems. Compared with 3D electrical resistivity tomography the 2D high-density electrical resistivity tomography still exist some problems: when the survey line doesn’t layout in the hidden the underground objects cannot be reflected, which brought difficulty in field test and there is more difficult to detect complex leakage channels especially; Accuracy also have difference by using several 2D cross sections at the same time in an interface to open for forming a quasi 3D images between obtained true 3D images after 3D inversion. The 3D inversion divided the subsurface into a number of small rectangular to build geoelectric model [
where:
Comparing the accuracy between the measured resistivity value and the theoretical value to determine the results of the inversion calculation if it meets the requirements. When the requirements don’t meet, it is required to recalculate the theoretical value until the difference is in the proper range.
Reservoir locate in Jinping village the town of Tiaoshi Chongqing Banan district, dam locate in YiPing Rive the primary tributary of Yangtze River in the right bank. Liu Huanggou reservoir is type of a small (2) water conservancy project with flood control and irrigation. 0.2 km2 control basin area in Liu Huanggou reservoir, the main river channel length 0.8996 km, average down more than 95.92 per thousand. Dam is a homogeneous earth dam, with the maximum dam height 13.25 m, total capacity 14.06 million∙m2, normal storage capacity 12.46 million∙m2, dead storage 0.51 million∙m2, designed irrigation area 980 acres, the effective irrigation area 900 acres. The reservoir for V small (2) water conservancy project, the permanent main building engineering for level 5, secondary structure for level 5, temporary buildings for level 5.
In field investigation the five conditions of exit section the leakage gradient less than the allow leakage gradient J = 0.45. It shows that the leakage stability of the dam is satisfied with the requirement of the standard and will not occur leakage failure. But it is still found that there are two leakage areas in the downstream of the dam. La Youting five survey lines that each survey line using 60 electrodes and the electrode spacing is 1m in the downstream slope. Electrode made of copper that connects the host through a cable with 32 core, the measurement controlled by program-controlled multichannel conversion switch in the host that also equipped with a RS232 interface and a LCD screen 160 × 128 pixels. Putting electrodes into the dam accuracy with tape to make sure contact with it well. The horizontal spacing of each survey line is 3 m, which is layouted in parallel [
The test data are collected by duk-2b high-density electrical instrument, and combined with the terrain condition select Werner array, each survey line under the condition of Wenner array instrument can collect 552 points and each point can get the voltage, current and the resistivity data, five survey lines obtain 2760 points. Each line near the left bank is set to start electrode 1, the minimum and maximum isolation coefficient are 1 and 16.
Putting the data into the computer and calculating the coordinate of each point, then open the software, aftert inverting the test results are shown in
In the direction along the dam axis, the resistivity distribution is shown in
reflected. We can find low resistivity area is wide that shows the leakage seriously in deep inside dam in the first layer resistivity profile. From the inside to the outside, we can find that there are two low resistivity zones in the third layer and fourth layer resistivity profile, the two low resistivity zones in the fourth layer resistivity profile is basically consistent with the leakage area of the downstream slope. It shows that again there is an inclined channel to the downstream slope.
Selecting three resistivity profiles in the direction of the vertical axis as shown in
Two low resistivity zones can be found in the fourth layer of
1) The 3D electrical resistivity tomography can be used to understand the development of the leakage channel
and the diagnosis effect is good when earth rock-fill dam is leaking.
2) In the analysis of the leakage channel in earth rock-fill dam use of volume rendering image processing tec- hnology, to further understand the spatial form of the leakage and provide help to find leakage.
3) 3D electrical resistivity tomography in the application can provide a wealth of data. The results are intuitive, easy to explain and the results are valid. 3D electrical resistivity tomography will be more widely used in the future.
This paper is funded by National Natural Science Foundation of China (51279219).
Xin Zhang,Mingjie Zhao,Kui Wang,Pan Liu,Huan Liu, (2016) Application of 3D Electrical Resistivity Tomography for Diagnosing Leakage in Earth Rock-Fill Dam. Engineering,08,269-275. doi: 10.4236/eng.2016.85023