Abstract

The selection of grouting timing is of great significance for reducing the dam uplifting and fracturing risk under construction period. The Wudongde powerstation is the seventh largest and the second largest under construction in the world, which faces challenging problem on how to determine the grouting time order between the dam transverse joint and riverbed foundation, and avoid dam uplifting and fracturing risk. This study first feedback determine the equivalent grouting pressure of the dam foundation surface, and then analyze the effect of grouting uplift on dam working behaviors and fracturing risk during the construction period. Finally, the optimal grouting time order for the dam transverse joint and riverbed foundation was proposed. Numerical and monitoring results indicates that zoning grouting has few effect on dam working behavior. It is suggested that the grouting timing should be dynamically adjusted from Sept. to Oct., 2017, the dam height should be 30∼50m and the actual maximum grouting pressure should be 3.5MPa. It also summaries the reinforcement grouting process with cover weight, guides the control of grouting uplift gradient deformation, and to ensure compliance with grouting design requirements.

1.
Introduction

Many high arch dams have been built with the rapid development of hydropower engineering in China in the past two decades. The quality of the foundations is of great importance to the stress and deformation states of the dams(Lin et al., 2015; Wang et al., 2007). In the case where the design requirements cannot be met, it is necessary to reinforce the foundations by grouting, anchoring or other treatments in order to improve the stability of the dam (Zhou et al., 2008). It is noted that uplift at the base of the dam often occurs during grouting, which is equivalent to reducing the self-weight of dam structure and has a negative impact on its overall stability (Serafim, 1968). Both grouting pressure and grouting timing play an important role in the grouting process (Lombardi &Deere,1993; Eduardo et al., 2013; Hässler., 1993; Babak & Morteza,2009), but they are very difficult to determine.

The Wudongde powerstation is the seventh largest arch dam in the world. The project is located on the Jinshajiang River, Ninang County, Sichuan Province, southwestern China. The normal water level is EL 975m, and the height of the double-curvature arch dam is 270 m. Both sides of the site are very steep slopes but they are quite stable. The foundation consists of limestone and marble, which are mainly composed of type II rockmasses with a few type III1 rockmasses. The riverbed foundation distribute gently dipping fracture rock mass locally. Thus, it is necessary, although difficult, to strengthen consolidation grouting and take structural measures to meet the stability requirements.

In this paper, the equivalent grouting pressure of the dam foundation surface is determined base of feedback, and then the effect of grouting uplift on dam working behaviors and dam fracturing risk is analyzed. Finally, the optimal grouting time order for the dam transverse joint and riverbed foundation is summarized and proposed.

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