There are a total of 147 slots in underground continuous wall in the eastern Yanshan stope, each slot wall is 6.5 m long, with a total length of 811.5 m; Wall thickness is 0.6 m, the top of the wall above the highest water level of the new river is not less than 0.5 m, which is 22.5 m. Foundation of

1 INTRODUCTION

Yanshan Iron Mine is an important iron ore production base of Hebei Iron and Steel Group Mining Co, Ltd, which is an open-pit mine, with an annual output of 7 million tons. Luan River lies there and flows southward into the Gulf of Bohai. There contains strong permeability sand and gravel layers with large amount of water. Majority ores are buried beneath local erosion base level and covered by Quaternary topsoil. The layer thickness is 10 m∼30 m, the thickest is about 65 m, eastern quaternary is alluvial sand as well an sand and gravel layer, pore phreatic aquifer is strong water permeable and rich aqueous. The new path of Luanhe, which is about 60 m away from the stope, will serve as the constant head water supply. Large amount of water gushes to the stope from the new river through its east side as water channel and the stability of the east slope is severely affected.