Dewatering practice: a single-stage well-point system can effectively lower groundwater and dewater an excavation down to approximately what maximum depth?

Introduction / Context:
Well-point systems are widely used for lowering groundwater around shallow excavations. The achievable drawdown in a single lift is limited by suction and pump performance.

Given Data / Assumptions:

• Conventional single-stage well points connected to a header and a vacuum-assisted pump.
• Permeable soils where well points are effective.
• We seek the practical maximum depth of effective drawdown per stage.

Concept / Approach:
Atmospheric pressure limits suction lifts to roughly 7–8 m under ideal conditions. Accounting for losses and field reality, the practical drawdown per stage is typically about 4.5–5.5 m. Hence, a single-stage system is generally capped at about 5 m. Deeper excavations require multi-stage well points or deep wells.

Step-by-Step Solution:
Relate suction limit to groundwater drawdown capability.Apply field allowances: adopt ≈ 5 m for a single stage.

Verification / Alternative check:
Manufacturers’ data and method statements frequently recommend further stages for depths exceeding ~5 m.

Why Other Options Are Wrong:

• 10–25 m: exceed practical single-stage limits; would require deep wells or staged systems.
• 15–20 m: similarly unrealistic for single-stage well points.

Common Pitfalls:

• Confusing deep well pumping (submersible pumps) with vacuum well points.

Final Answer:
5 m