Transient Electromagnetic Technology Applied Research In The Tunnel Geological Prediction

Unfavorable geologic bodies such as faults, caverns and fracture zones, andsoft formations filled with water or mud are often met in the dig of the tunnel, which can lead to the jet of water or mud, and fall of the tunnel. These unfavorable geologic bodies can affect the plan of the dig, and even make serious event of safety. Thus the work of advanced forecast of geology in tunnel is important. Presently, the advanced exploration is realized with the combination of geologic method, the geophysical method and geologic drill in the world. And the geophysical methods include TSP, Ground Penetrating Radar (GPR), seismic negative apparent velocity method, HSP an d so on and these method have their own advantage each other. But there is an unsolved problem in the exploration of unfavorable geologic bodies filled with water in the advanced forecast of geology in runnel.This article introduce a new method of advanced forecast of geology in tunnel at the basis of the methods used at present—the method of Transient Electromagnetic Method(TEM). The new method is sensitive to the unfavorable geologic bodies filled with water or mud such as faults, caves and zones of rock fracture. The key techniques of the exploration in tunnel such as the impact of tunnel background and the transient process of the cane", and one of its important steps-the pick up of the parameter m, was improved using the Genetic Arithmetic (GA), and so that reduce the equivalent range and increase the accuracy of explanation consequently.In the article different styles of tunnel are displayed to show the effect of the advanced forecast with TEM method. In the Baziling cavern on the railway from Yichang to Wanzhou, there met many fractures filledonfiguration itself have been solved successfully through the study of the key technique, and so the TEM method can be used successfully in the advanced forecast of geology. The explanation method chose in the article is the method of "equivalent conductive pl with mud during the dig, and the exploration result is accord with dig result. It is proved that TEM is sensitive to the fractures filled with mud. In the auxiliary tunnel in JinPing, there is much water jet out from the working face and sidewall, which proved later fracturewater. The exploration result is consistent with the fact, which can prove that TEM is sensitive to fractures filled with water. As to the highway Changdangzi tunnel in Fengjie County, we met a super cavern filled with water and mud, and the exploration result is consistent perfectly with the actual cavern. From the examples in this article, we can see that the accuracy of exploration for unfavorable geologic bodies filled with water or mud which have a scale are less than 10%. So we can draw the conclusion than TEM is effective to do the advanced forecast of geology in tunnel.Both the result of digital modeling of geoelectric model and the processed results of the field data show that it is effective and successful to use the TEM method to explore the unfavorable geologic bodies filled with water or mud in tunnel.