Analysis of rock quality designation (RQD) and Lugeon values in a karstic formation using the sequential indicator simulation approach, Karun IV Dam site, Iran

The hydraulic properties of hard rock and karst formations are typically highly heterogeneous. Quantification of the groundwater flow in these media is a complicated process with numerous uncertainties. There are several approaches to overcome this problem. Stochastic simulation is one of the promising approaches for quantification of the intrinsic uncertainty in karst formations. In the present research, the sequential indicator simulation was used as a tool for the simulation of the hydrogeological and geotechnical properties of a karstic formation at the Karun IV dam site, Iran. In this regard, two variables of interest, RQD and Lugeon, were considered as criteria for the development of karst. One hundred realizations of these variables were produced and then combined to obtain an expected value and the probability of exceeding a threshold value for each cell. The results showed a weak negative correlation between the expected values of RQD and Lugeon. Also, it was determined that the geologic structures (i.e., faults) and lithology play an important role in the development of karst in the study area. A decrease in the simulated values of Lugeon was observed with increasing depth of karstic layers and the distance from faults. The results of this study helped to overcome the intrinsic uncertainty in karst media and to present a conceptual model of karst development. This approach can be applied in other dams for the evaluation of risk and uncertainty of hydrogeological parameters.