Impact of Ground Water Flow on design of Open Underground excavation-Paper

Paper

Pdf Summary

The paper examines how groundwater flow affects the design and construction of deep open excavations, using an underground metro station in India as a case study. The 17.62 m-wide, approximately 180 m-long station is constructed top-down, with 24 m-deep diaphragm walls that also serve as permanent station walls.<br /><br />PLAXIS 2D finite-element analyses model the construction sequence and compare phreatic conditions, steady-state seepage, and fully coupled transient flow-deformation analyses over one- and two-year periods. The study evaluates seepage, groundwater drawdown, ground settlement, wall deformation, and diaphragm-wall bending moments and shear forces. It also considers a deep-well dewatering system and examines the sensitivity of results to soil permeability and groundwater-table level.<br /><br />Calculated total seepage is similar across the main flow scenarios, at approximately 98–99 m³/day for the station. However, groundwater-flow analyses predict greater surface settlement than the phreatic analysis: steady-state settlement reaches about 66 mm, compared with about 40 mm under zero-drawdown conditions. Maximum drawdown is approximately 1.7–1.8 m. Diaphragm-wall bending moments and shear forces remain broadly comparable across the analyses, as do maximum wall deformations, which range from about 47 to 50 mm.<br /><br />The authors conclude that groundwater-flow and dewatering effects should be explicitly assessed when designing deep excavations. Steady-state and transient analyses are important for estimating settlement and seepage, while sensitivity studies help inform the dewatering design.

Keywords

groundwater flow

deep excavation

metro station

diaphragm walls

finite-element analysis

seepage

groundwater drawdown

ground settlement

dewatering system

PLAXIS 2D