Numerical Modeling And Analysis Of Vertical Geo-Electrical Profile Method

When we construct the civil engineering in karst region, we must find out the scale and character of shape and distributing of karst cave. The electricity character of karst cave has much difference than that of wall rock, so the surveying method of direct current can find out if there be karst cave underground. So the electrical surveying method has become one of important methods in exploring karst region.No matter what electric sounding and electric profile methods in traditional electrical surveying methods, their field layout are that current electrodes and voltage electrodes are set on the earth's surface. Vertical geo-electrical profile method is not similar to traditional electrical surveying methods, of which device is that transmitters are arranged in the borehole according to the fixed length and receivers are set on the earth's surface. In this method, for current electrodes are transmitting underground, so that the current field is less interfered and the direction of current line is directly underground to the earth's surface and the intensity of the current field is more homogeneous and great. So it can exactly reflects the depth of apparent resistivity of the anomaly. Furthermore, we can utilize geological datum from the borehole directly to calibrate the apparent resistivity anomaly near the borehole and reduce the ambiguity of the anomaly explanation. So we can increase the veracity of the anomaly explanation.In the simulation of 2D geo-electric field forward modeling, the finite element method is used great widely. We simulate the 2D various apparent resistivity anomalies of the complex geo-electric sections and regions by the vertical geo-electrical profile method using the finite element method. The computation examples show that the finite element is an effective and quick method of 2D geo-electric field forward modeling and simulation results indicate that the vertical geo-electrical profile method can directly track the extent of theapparent resistivity anomalies near the borehole, meanwhile, the arithmetic of 2D geo-electric field forward modeling is right and it satisfies the reciprocal principle to make a firm foundation for actual application. As the layout of new method is very simple and we can according to the measured data and analyses the underground rock stratum qualitatively, so it is more accurate. We can utilize the vertical electrical profile method and connect other electrical surveying methods for exploring karst to solve problem on actual engineering effectively and economically.