Rock mass classification and prediction ahead of tunnel using electromagnetic wave

Abstract

As all kinds of industrials have been developed increase of demands for various natural resources has led many researchers to find effective methods to detect them buried in the earth. One of prominent methods is a geophysical exploration using electrical resistivity. Although the electrical resistivity-based geophysical exploration has been commonly used for site investigation, the majority of such application is restricted to rough description of underground condition and only a few researchers tried to correlate electrical resistivity with rock mass classification, such as Q-system and RMR, playing an important role in practical rock engineering designs. On the other hand, during tunnel construction ground failures often occur due to the existence of weak zones, such as faults, joints, and cavities, ahead of tunnel face. It is hard to detect effectively the weak zones, which can lead underground structure to fail after excavation and before supporting, by using conventional characterization methods. Thus, the main goal of thesis is to explore the correlation between rock mass classification system and electrical resistivity, and to develop an enhanced analytical method of predicting weak zones ahead of tunnel face using electromagnetic wave. Electric field in intact rock and jointed rock mass are analyzed with considering the characteristics of elastic fields subjected to rock mass from Coulomb``s law and Gauss`` law. The results show that electrical resistivity measured by two electrodes is governed by the electrical resistivity of intact rock and joint, the interval of joint and the thickness of joint. An attempt is made to correlate electrical resistivity of rock mass with Q-system and RMR-system theoretically. Each factor in Q-system and RMR-system is interrelated to electrical resistivity. The analytical method suggested for classification of rock mass using electrical resistivity is verified through experimental tests. The assembly of concrete blocks, ...