Design and construction of impervious system in foundation of Yele embankment dam

摘要

Yele Dam is the highest embankment dam (125.5 m) with asphalt concrete wall in Asia, located in the Nanya River in Sichuan Province south west of China, and is under construction. Due to the complicated geologic condition and high earthquake intensity (VIII), there are a lot of particular difficulties in design and construction of the foundation treatment. Yele Dam is placed on the highly asymmetrical ground bed. Its left abutment is on the quartz diorite, but the main body and the right abutment as well as the right upland plain is on the loam and sandy gravel interbedded strata with the depth of more than 420 m. To control the seepage of the foundation, compositive measurements in design have been adopted. From left to right, the curtain grouting in rock (left grouting gallery), cut-off wall plus lower curtain grouting in rock (left abutment), cut-off wall (in bed and right abutment) and cut-off wall plus lower curtain grouting (in the right bank upland plain) are used. The upland plain cut-off wall is 140 meters deep and is divided into two parts, the upper wall and the lower wall, connected by a construction gallery functioning as the work place to build the lower wall and the lower curtain grouting. The lower curtain grouting is 60 meters deep beneath the bottom of the lower cutoff wall, so the total depth of seepage control is 200 meters. To build the cut-off walls in so deep overburden foundation, some difficulties must be resolved, such as bentonite slurry stable wall, hole deviation control and ring budding of the adjacent holes as well as the choose of proper drill machines (the twin wheels milling machine, chopping drill, and hammer drill with reverse circulation are adopted in different geologic condition). To execute the grout curtains, some difficulties such as the proper drilling equipment, the grouting pressure, water cement ratio, quality inspection and acceptance criterion, etc must be overcome. Yele Dam and the power house will be completed and put into production in 2005. The total acreage of cut-off walls in the dam is 55000m~2, in which 30000m~2 has been completed and the tests demonstrated that results were satisfactory. This paper will detailedly describe the successful options in the design and construction of foundation treatment of Yele Dam.