Impact assessment of grout curtain on the hydraulic behavior in karst, based on time a series analysis

Abstract

The construction of a grout curtain in karst is a very common procedure to reduce water loss from a reservoir. Long-term and short-term monitoring of water levels was performed on the Prevoj dam (Lazici water reservoir), located in the Dinarides of western Serbia, to determine the hydraulic behavior and functionality of the grout curtain in karstic media. Different approaches of time-series analysis were applied. Based on the long-term monitoring, and by application of correlation analysis and Rescaled Partial Sums—RAPS, water table fluctuations were analyzed to obtain a general trend and relation between piezometers at the immediate zone of grout curtain. Short term, but very frequent monitoring of water table in the reservoir (SWT) and piezometers, provided considerably better insight into hydraulic behavior in karstic media. The various methods of obtaining results showed that they are all comparative or complementary. The higher order partial correlation proved to be significant in the definition of dependence between observed piezometers, by removal of possible influences of other adjacent variables piezometers. Univariate time series were analyzed by the first difference serial dependencies, which considerably changed the identification of the seasonal effect on the water table at the water reservoir. This was used as a tracer to analyze the influence of the surface water reservoir on the behavior of water table of analyzed piezometers in rock mass. An analysis of the shape of hysteresis provided valuable information related to hydraulic behavior in karst media and conditions of the functioning of the grout curtain as a barrier. Separating the rising limb from the recession limb on hydrographs and presenting adjacent piezometers on correlograms (upward and downward from the grout curtain), provided an analysis of hysteresis loops. Based on this analysis, there can be better insight of flow circulation in karst, functioning of the hydraulic barrier and better focus on certain zones and controlling of water loss from the reservoir.