Research On Application Of Multi-electrodes Resisitivity Imagining Survey

Recent years, the application of multi-electrodes resistivity imaging survey (MRIS) become more and more widely. MRIS is based on the electric conductivity of rock and soil and is a kind of method of electrical survey method which is researching the conduction current distribution law of the rock and soil imposed artificial stable current field. Therefore, the theoretical foundation between MRIS and routine electrodes resistivity is the same. Actually, MRIS is one of array method of electrical survey methods. It will need to lay out all electrodes on the survey section. Then according to preset method of the work, each electrode should be supplied electricity and measured by auto-controlling. So it is achieving automatic data collection on the whole radiometric profile.Compared with other exploration methods, MRIS is more efficient and visual and has higher degree of automation. It is broadly used and has good results in metal and non-metallic mineral, engineering geological prospecting, geological hazards, karst exploration, archaeology, and many other fields.The MRIS can use pole-pole, pole-dipole, wenner, dipole-dipole and schlumberger array to collect data. Every array has its own advantage and disadvantage: the Pole-Pole array has the widest horizontal coverage and the deepest depth of investigation. However, it has the poorest resolution, which is reflected by the comparatively large spacing between the contours in the sensitivity function plot. The pole-dipole array also has relatively good horizontal coverage, but it has a significantly higher signal strength compared with the dipole-dipole array and it is not as sensitive to telluric noise as the pole-pole array. The pole-dipole array also requires a remote electrode, the B electrode, which must be placed sufficiently far from the survey line. Among the common arrays, the wenner array has the strongest signal strength. This can be an important factor if the survey is carried in areas with high background noise. One disadvantage of this array for 2-D surveys is the relatively poor horizontal coverage as the electrode spacing is increased. With the proper field equipment and survey techniques, dipole-dipole array has been successfully used in many areas to detect structures such as cavities where the good horizontal resolution of this array is a major advantage.Therefore, in practical work which array to choose should be based on the specific situation.But some problems and shortcomings were found in the process of use MRIS. For example, the location of target geological body in the display image by 2-D survey has large displacement with actual location, which is because of Volume effect. Therefore, when the isolated target geological body be detected, the 3-D MRIS Which can restrict the geological body in three dimension should be used.The pole-pole, pole-dipole and dipole-dipole arrays are frequently used for 3-D surveys. This is because other arrays have a poorer data coverage near the edges of the survey grid. In the three array, pole-pole array has the poorest resolution. This article establish cuboid model and Plate model from the engineering geological investigation of the practical applications, by studying the result of the forward numerical simulation modeling and inverse modeling to analyze the resolution of 3-D MRIS to the resistivity of isolated target geological body and the size of isolated target geological body, to select suitable acquisition parameters for the actual reference to the engineering investigation.The conclusion is made after the forward numerical simulation modeling and inverse modeling: three-dimensional MRIS can be more accurate in determining the location and size of geological body and serve engineering investigation better. To detect cuboid geological body by three-dimensional MRIS, the ratio of geological body and background should be greater than 2, the ratio for the size of geological body and electrode space should be greater than 4; when to detect plate geological body by three-dimensional MRIS, the ratio of geological body and background should be greater than 1.5, the ratio for the size of geological body and electrode space should be greater than 2.Finally, introduce two-dimensional and three-dimensional MRIS in details combine Examples and test engineering, and analyze the result to validate the numerical simulation.