Seepage analysis of the fractured rock mass in the foundation of the main dam of the Xiaolangdi water control project

The foundation of the main dam in the Xiaolangdi water control project is located on the riverbed with a deep overburden layer. Here, the bed rocks have complex geological conditions and developed faults and fissures. Therefore, seepage within the fractured rock mass of the dam foundation has a significant impact on the safety operation of the dam. Using the fractured rock mass seepage theory, a three-dimensional hydrogeological model of the main dam foundation in the Xiaolangdi water control project is established in this paper which takes into account the distribution of faults and fissures in the foundation. The hydraulic conductivities of the major structures and faults are obtained by back-analyzing the data measured by osmometers embedded in the dam foundation. The model is validated by comparing measured water levels and flow rates with calculated results. On this basis, a sensitivity analysis was made of the different factors affecting seepage in the dam foundation. The following conclusions can be made: (1) Seepage is positively correlated with the reservoir's water level, but there is hysteresis in the correlation, (2) the concrete cutoff wall in the dam's foundation effectively controls the amount of seepage. Also, an increase in the curtain depth on both banks reduces seepage a certain amount. Furthermore, the right bank is clearly more impermeable than the left bank, (3) the deep-coverage layer of the foundation has a notable influence on seepage. The drainage curtain in the downstream of the dam effectively controls the amount of seepage in the dam foundation and improves the stability of the foundation seepage, (4) faults in the dam's foundation have a significant influence on seepage. If grout-strengthening technology is applied to the curtain, seepage control at the intersection between the curtain and faults should be especially highlighted, (5) the sediment deposit upstream of the dam body has no impact on the quantity of seepage from the dam's foundation, but it does significantly reduce the hydraulic head.