Ground and Groundwater Responses Due to Shaft Excavation in Organic Soils

Abstract

Excavation of a 16-m deep shaft was suspended due to groundwater drawdown of about 4.5 m that led to nearby ground subsidence and settlement of infrastructure. As a remedial measure, a deep-ground recharge system comprising multipoint recharging wells was conceived and then designed to mitigate the detrimental effects caused by the groundwater drawdown on nearby infrastructure. In the three-dimensional (3D) finite-element model, fully coupled flow-deformation analyses have been successfully developed and used. The results of the numerical analyses show that the predicted and measured ground and groundwater responses achieved reasonably good agreement due to (1) successful understanding of the anisotropy of underlying site condition, (2) sound 3D modeling technique, and (3) sound engineering remedial design. The simulation of this case study evidenced the detrimental effect of anisotropy in permeability of organic soil during groundwater drawdown, in which the soil permeability in the horizontal direction is, on average, five times higher than the permeability in the vertical direction.