Research On Application Of Integrated Electric Prospecting Methods In Ash Dam Detection

Hydraulic ash disposal ash dam of thermal power plant differs from reservoir Water Conservancy Project, and have its own characters. Reservoir services for water storage, but ash dam for drainage. The quantity of stored ash is increasing year by year after thermal power plant has been operated. To increasing the ash stored capacity of ash dam, ash dam is necessary to be heightened commonly under the geological conditions, dam body quality and water seepage conditions. Before design and construction, it is necessary to investigate, interpret and demonstrate the ash dam quality, reservoir area geology and hydrology situation. This exploration project directly relate to the economy benefit of thermal power plant, it ensures ash dam safety and ash storage efficiency, also relate to downstream residents life.This thesis combines with the soakage line exploration of ash dam of Jilin Xinli thermal power plant, analyze the space variety character of soakage line, ash blocked and seepage condition basing the exploration data, gathered geology and hydrological data. The thesis takes the research of soakage line distributing character on the dam and reservoir area as research emphases.This research adopts integrated geophysical method combined with ground penetrating radar method and resistivity imaging surveys to detect and interpret water level and soakage space distribution of work area. Ground penetrating radar method is a high resolution detecting method. The detection theory bases on the electromagnetic wave propagation change between up soakage line and down, because the water content differ from each other up and down of the soakage. Ground penetrating radar can widely detect the soakage line of ash dam. Ground penetrating radar is a nondestructively detecting technology with high exploration efficiency and low cost. Because it uses wide-band high frequency electromagnetic wave as active source to carry out detection, it takes high resolution of exploration. Ground penetrating radar id convenient and flexible in use and great practicability, and can carry out measurement over the ash dam area fleetly with mesh mode. It is effective to control the position of soakage line (surface) distribution over the ash dam area. Resistivity imaging survey is a traditional geophysical method. It bases on static electric field theory, and takes the electricity diversity of shallow objects as detecting precondition. Using resistivity imaging survey can determine the under detecting objects space distribution if the electricity character of the under detecting object differ from around medium. In the ash dam region and ash dam body itself, the resistivity or the conductivity of medium upside of the soakage face and water level take great difference from the downside, this satisfy the applied condition of resistivity imaging survey. The data gather of resistivity imaging survey carry out automatically or half automatically, cost low and have high efficiency. Resistivity imaging survey obtains abundance information and is easy to interpret, all this avoid the mistake arising by handwork operation.This application research projection had carried out two exploration, and obtain seventeen ground penetrating radar detecting profile and seven resistivity imaging survey profile; two radar of them are obtain in the supplement exploration and two resistivity profile of them too.According to the exploration data of ground penetrating radar, electromagnetic wave abnormity character of soakage face can be summed as four: along the survey line direction, in-phase axis relatively continuum; radar wave phase change; reflection wave energy vary more or less; reflection wave frequency also change, usually change to low. According to the change character of parameter, we can determine the reflected wave position caused by soakage line (face), and compute out the depth of soakage line (face) with the electromagnetic wave (0.08m/ns) of dry ash. Because the geological conditions of ash pond are differ from that of ash dam body and road surface under the ash dam, the exploration setting parameter and data processing method applied to them is also different, and then, we take the profiles carried out on ash pond and profiles carried out on the ash dam body process and interpret separately as they have different detecting character, in the ash dam, in-phase axis of reflected wave in ground penetrating radar exploration result preferably has continuity, its energy varies quite greatly, that is easy to recognize. The results of radar show that local water level change up and down more or less, it is necessary to take appropriately smooth when pick up the value of soakage line (face). Radar detecting results on the ash dam body show out that the water lever clarity. The water level in the middle of ash dam change not too much, but slightly down, two side of that gradually shoal. At around of soakage line, radar wave show clearly, not only the in-phase axis continence but also the energy and frequency change much. Resistivity imaging survey is a assistant method, the detecting result is relatively intuitive, but it's depth determination is not nicety than radar, and that the grounding resistivity on the ash dam body is too big to carry out survey, beside the dam is not half-space medium condition, so resistivity imaging can not carry out over there. Resistivity imaging survey are carried out over the top of ash dam and ash pond. five profile were obtained over the first exploration and two over the supplement. The reason to carry out supplement measurement is that the fist exploration work was carried meeting raining, the rain may caused the soakage line hoist, and then the steady soakage line (face) maybe have indetermination. there had be no rain until July twenty five, and thermal power plant had changed the ash emission place, and then the soakage line may descend and go to be steady, so it is necessary to carry out supplement measurement to ensure the position of soakage line (face).Exploration result imaged that the soakage face of ash dam is different between the two side of ash dam, and show to be discontinuity. At the ash dam bam backward position, flow-water gradually assemble, and its range also gradually become small; moreover, at the ash pond, soakage face depth gradually decrease when far from the ash dam axis, it show to be a anomalistic curve. On the curve, the max depth can be reach over 10 m, and the mini shallow is close to water level which go to 0 m. at the 33 m, 50 to 60 m etc place, the soakage depth appear to change quite quickly. Multifactorial analysis indicate that soakage line in the ash pond area distribute steadily, ash pond area water seepage and drainage is all right. This applied research also reflects that geophysical method combined with ground penetrating radar method and resistivity imaging surveys to detect and interpret water level and soakage space distribution of ash dam can obtain a good application effect.