Hydraulic head difference at two sides of suspended waterproof curtain during multi-grade dewatering of excavation

Abstract

This paper proposes an approach to calculate the head difference at two sides of suspended waterproof curtains during multi-grade dewatering. The seepage during the dewatering process can be subdivided into three regions: (i) seepage in pit, (ii) seepage between curtains, and (iii) seepage outside the pit. The flow rate of the first region is equal to the pumping rate, and the flow rate of the second and third regions can be obtained by numerical analysis. A numerical model is established to simulate the seepage in the second and third regions and its performance is validated by using the measured data of a series of field tests. The flow rate of each region is then used to derive formulae for the head difference in conventional dewatering, which can be used to determine the head difference at two sides of each waterproof curtain during multi-grade dewatering. The proposed formula expresses the head difference as a function of the relative depth of the curtain inserted into the confined aquifer, the thickness of the aquifer, the distance between two curtains, and the anisotropy of the hydraulic conductivity of the aquifer. The proposed numerical approach is further validated by using data derived from numerical analysis. The validation results demonstrated that the predictions of the proposed approach are acceptable and convenient.

Keywords

• Head difference
• Multi-grade dewatering
• Suspended waterproof curtain
• Confined aquifer