Development of a tunnel electrical resistivity prospecting system and its application

Abstract

It is very important to understand the constructing ground condition in detail at the design stage in order to have successful underground and long tunnel construction. Therefore, before designing an underground structure (with the tunnel representing underground structure), site investigation must be performed in order to know the conditions of the ground around the tunnel. The site investigation methods that are performed at the tunnels include conventional investigation methods, like boring, and, most recently, geophysical exploration surveys. However, these methods have limits in accurately understanding the condition of the grounds that have underground structures or deep tunnels due to limited resolution and limited ground conditions. This is because the conventional geophysical exploration methods are performed on ground surface. For this reason, the unexpected occurrence of anomalies, such as weak zones, fault zones and cavities, may cause tunnel accidents due to the collapse of tunnel face and the relaxation of tunnel ceiling. And the cases of tunnel accidents, as well as construction delays and casualties, have also been frequently reported. Therefore, the Tunnel Electrical resistivity Prospecting System (TEPS), which can accurately understand the rock conditions ahead of tunnel face and predict minutely anomalies existing ahead of tunnel face under tunnel construction, is developed to solve those problems. TEPS consists of analytical equations, rock mass classification system, inverse programs, control systems, and measurement systems. The analytical equations, which lead to predict anomalies existing ahead of tunnel face, can obtain electrical resistance values measured on tunnel face as the methods that performs the measurement after first performing the analysis, differently to conventional methods, in case of generating the voltage in the rock existing ahead of tunnel face. The analytical equations consists of the electrical resistance equation...