A large commercial building project involves extensive foundation work, requiring the excavation of a deep pit in an area with a high water table. To ensure a stable and dry working environment, the contractor decides to use a dewatering system that creates a continuous barrier around the excavation to prevent groundwater inflow. Which dewatering technique involves constructing a physical barrier to achieve this?
- ASlurry wall
- BEjector system
- CDeep well system
- DWellpoints system
Show answer & explanationAnswer & explanation
Correct answer: A. Slurry wall
A slurry wall is a type of cutoff wall constructed by excavating a trench and filling it with a bentonite-water slurry to maintain trench stability. Concrete or other impermeable materials are then placed within the stabilized trench, forming a continuous, low-permeability barrier (a 'cutoff wall') that physically prevents groundwater from entering the excavation. This is distinct from pumping methods.
Why the other options are wrong
- B. Ejector systems actively pump water, often used in low permeability soils, but do not create a physical barrier.
- C. Deep well systems actively pump water from larger wells, they do not create a physical barrier.
- D. Wellpoints actively pump water from multiple small wells, they do not create a physical barrier.
Slurry Wall (Cutoff Wall)
A dewatering and excavation support technique that involves constructing a continuous, low-permeability barrier around an excavation by excavating a trench under a bentonite slurry and then backfilling with impermeable materials (e.g., soil-bentonite, cement-bentonite, concrete).
- Creates a physical, impermeable barrier.
- Prevents groundwater inflow.
- Can also provide excavation support.
- Used in high water table conditions.
Memory trick: Pumps pull water, walls block water, choose your battle with the flow.