Relationships between induced polarization relaxation time and permeability of sandstone.

During the excavation of tunnel construction, there are often delays or threats to personal safety due to water inflow. Detecting permeability distribution in front of a tunnel face in advance can provide a basis for preventing water inflow, thereby ensuring safety in tunnel construction. Based on the complex petrophysical relationship between the geoelectric properties and the permeability, we have compared the existing induced polarization (IP) models for permeability prediction. The relaxation time, which is one of the induced polarization parameters, is the most critical parameter for predicting the permeability coefficient based on the induced polarization. Many researchers have proposed predictive models applicable to surface hydrological investigations; however, the tunnel environment is impacted by excavation and tectonic movements, and the permeability coefficient varies over a wider range than the surface strata. Therefore, we selected 50 artificial sandstone samples with the permeability varying over a wide range for common tunnels to measure the IP attenuation curve, and we obtained multiple IP parameters, such as the relaxation time and chargeability, to construct a predictive model based on induced polarization parameters suitable for the tunnel environment. The nature of the correlation between IP parameters and permeability is that both are affected by pore structure and fluid ion concentration. Considering this, we introduced formation factors and ion concentrations into the prediction model to improve prediction accuracy. [ABSTRACT FROM AUTHOR]