Optimization of Sardasht Dam Sealing System Using UDEC Software

Summary In this paper, the capability of foundation and support for the Sardasht dam is investigated. Finally, according to the results of numerical modeling in UDEC software, the diameter and distance of grout injection boreholes and dimensions and angle of seal curtain of the dam foundation dam have been suggested.   Introduction The injection is a process whereby a cement slurry is pushed into rock formations through a borehole, thereby reducing the permeability and deformation of the rock mass and increasing its resistance. The rocks are almost impermeable and rock mass permeability is often a function of discontinuity systems. Due to the different and unpredictable behavior of rock masses, there is no specific law for determining the distance of injection holes and generally relies on the experience and judgment of the design engineer when deciding on the borehole distance. So, it is proposed to use numerical methods in predicting the radii of injection for grouting material and also determining the ideal spacing between adjacent holes. As the main results of this study, the optimum pattern for drilling sealing systems for different locations of the Sardasht dam was determined and compared to the empirical models using the discrete element method in UDEC. The optimum deviation angle of the holes was investigated, too.   Methodology and Approaches The Sardasht dam is a trench with a clay core with a height of about 106 meters and a length of 280 meters. The total embankment volume of the dam body is estimated to be about 3 million cubic meters and the volume of clay core is about 516000 cubic meters. The water diversion system consists of two tunnel strings with an inner diameter of 7m and lengths of 627m and 682m in the right support and its height is about 46m. The right tunnel is used as the lower evacuator during the operation period. In order to investigate the in-situ condition of rock mass in Sardasht Dam area, rock mechanical parameters including rock mass quality index (RQD), specific gravity, uniaxial compressive strength, and geometry and resistive properties of discontinuities have been determined and measured. Then, the quality of grout injection in walls and foundation of the Sardasht dam was modeled, using numerical modeling in UDEC discrete element software.   Results and Conclusions The results of this study show that the appropriate borehole spacing for the walls and the foundation should be taken as 3m and 5m, respectively. Also, the results obtained from the numerical modeling of the optimum injection pressure in the construction area of the Sardasht dam were determined for different depths. Based on the numerical modeling results in order to minimize water leakage from the Sardasht dam foundation, the optimum angle of curtain installation should be 17 degrees.