Transient Groundwater Response to Pumping in a Confined Aquifer during Deep Circular Excavation Dewatering

Vertical circular excavations are widely used in practical engineering due to their higher structural stiffness and construction efficiency compared with other plan geometries. The dewatering well and partial penetration cutoff wall are generally adopted for groundwater control to ensure the safety of the circular foundation pit and its nearby environments. Current studies on transient flow response in confined aquifers with cutoff walls due to pumping have primarily focused on numerical methods, with a lack of analytical methods that offer ease of implementation and computational efficiency. This study proposes a new analytical model to assess the transient flow behavior associated with constant-rate pumping during circular excavation dewatering, taking into consideration the existence of a partial penetration cutoff wall in confined aquifers. The semianalytical drawdown solution is developed for both inside and outside the cutoff wall at specific locations and times. The transient total discharge through the wall opening, extending from its base to the bottom of the confined aquifer, is obtained. The developed solution is verified through numerical solution employing COMSOL Multiphysics (version 6.0), existing solutions, and a field pumping test. The results demonstrate that wall penetration depth and dewatering well structures have a significant effect on drawdown inside the foundation pit. The total discharge curve with respect to time is divided into three distinct stages. During Stage I, there is no flow across the wall opening. In Stage II, the total discharge gradually increases as the pumping duration advances. In Stage III, the flow flux through the wall opening equals the well discharge, and flow balance is achieved. The discharge across the wall opening exhibits an uneven distribution, with larger values of discharge close to the base of the installed wall in contrast to the remaining section of the opening.