Abstract:

The excavation depth of Meizizhou air shaft for Nanjing Weisan Road Yangtze River Tunnel is about 48 m, the soil layers beneath the excavation bottom are highly permeable silty sand layer and gravel layer, and the groundwater has a direct and stable hydraulic connection with the river water. Besides, the clear distance between the air shaft and the flood embankment is only 18 m. So, the shaft excavation is faced with extremely complex engineering geological and hydrogeological conditions. The actual experiences of the excavation mentioned in this paper are as follows: 1) For the ultradeep excavation in which the excavation depth and confined aquifer thickness are so large that it is difficult for the waterproof curtain to penetrate the confined aquifer, the application of underwater excavation can prevent the water inrush effectively and can improve the forced and deformation state of the retaining structure greatly; 2) The underwater bottomsealing concrete can bear the high confined water pressure acting on the bottom of the foundation pit, which is the key measure to ensure the successful implementation of the project.

Key words: ultradeep excavation at riverside, pumping test, high confined water, water inrush, underwater excavation, underwater bottomsealing