Back-analysis approach for the determination of hydraulic conductivity in rock caverns

• The model for computed water inflow Q is established by a semi-analytical method.
• The hydraulic conductivities kjkj are back-analyzed by minimizing the error function E.
• The function E represents the discrepancy between measured Q and computed results.
• The defined incorrect ratio a represents the effectivity of back-analysis solution.
• The maximum a of computed Q in case study is 35%, 92% of them are less than 15%.

Water seepage related problem is often the major geological hazard in underground rock excavation. In order to reduce the risk associated with extensive seepage, a reliable hydro-geological model should be established based on the in-situ investigation data. One of the challenges for establishing a reliable hydro-geological model is on how to determine the hydraulic conductivities of the fractured rock masses using the limited in-situ investigation data. In this study, a back-analysis approach for the determination of the hydraulic conductivities along a rock cavern is presented. To take the advantages of both the analytical solutions and the numerical methods, this paper proposed a semi-analytical approach for prediction of the water inflow into caverns with the horseshoe section, and the semi-analytical solution is used for the back-analysis of the hydraulic conductivity around a rock cavern based on the in-situ monitoring data. The hydraulic conductivities are obtained by using the EXCEL spreadsheet’s build-in optimization routine SOLVER to minimize the error function. The computed water inflow into the cavern is compared with the in-situ measured data. The results indicate that the derived hydraulic conductivity is acceptable.