A Case Study Of Rock Investigation Using Resistivity Image Profiling

The authors have developed an electrical exploration<br>technology, called "Resistivity Image Profiling", which has<br>since been applied to many sites in Japan. In this method, a<br>two-dimensional or a three-dimensional underground resitivity<br>distribution is analyzed. This method combines an accurate<br>in-situ measurement technique and automatic computer analysis to<br>obtain more detailed and reliable results than conventional<br>electrical methods. The analyzed results are displayed as a<br>color profile which shows the resistivity structures more clearly.<br>2-D "Resistivity Image Profiling" was applied in a mountainous area where construction of a highway tunnel was<br>planned. The final analysis results show a complicated<br>resistivity distribution having a range from less than 50 Ω ·m<br>to more than 5000 Ω ·m. Using the resistivity values, we<br>classified the rock properties into four general categories:<br>fresh rock, relatively fresh rock that includes many joints,<br>weathered or altered rock, and fracture zone with clayey<br>materials. Further, we estimated both underground water levels<br>and locations of faults to identify the most likely area where<br>water burst out could occur. The tunnel is now under construction and the excavation<br>results are confirming our interpretations of fault locations<br>and rock properties. The actual locations of water burst out<br>also have shown good agreement with our predictions.