Anacostia River Tunnel Project Groundwater Drawdown Effects from the Deep Well Depressurization System at the CSO-019 Drop Shaft

摘要

The Anacostia River Tunnel with a length of 12,300 feet (2.33 miles) and internal diameter of 23 feet will be excavated using an Earth Pressure Balance Tunnel Boring Machine (EPBM) in the hard/stiff clays and silts/sands of the Potomac Formation. This paper presents the design of a depressurization system at the CSO-019 Drop Shaft and shows that the use of laboratory derived properties will result in excessive estimates of settlement. This paper shows that more reasonable settlements can be obtained with pressuremeter data; furthermore, when the predicted settlements are compared to field measurements, it is found that the rapid vertical movement of the ground monitoring points in response to depressurization changes come from settlement or rebound in the aquifer, not the aquitard.