NASCLA Accredited Commercial General ContractorSite WorkMedium
A construction project involves the excavation of a large pit for a new underground detention basin. The project specifications require dewatering to maintain a dry work area. The soil consists primarily of fine silts and clays. Which dewatering method is most effective for this soil type?
- AEjector systems
- BVacuum dewatering
- CDeep wells
- DWellpoints
Show answer & explanationAnswer & explanation
Correct answer: B. Vacuum dewatering
Fine silts and clays have low permeability, making traditional gravity-driven dewatering methods like deep wells or wellpoints less effective. Vacuum dewatering creates a negative pressure to draw water from these tight soils more efficiently.
Why the other options are wrong
- A. Ejector systems are suitable for low permeability soils but vacuum dewatering is generally more efficient for fine silts and clays.
- C. Deep wells are best for high permeability soils like sands and gravels.
- D. Wellpoints are effective in moderately permeable sands, not fine silts and clays.
Vacuum Dewatering
A dewatering technique that uses a vacuum pump to create negative pressure in a system of wellpoints or drains, effectively extracting water from low permeability soils.
- Ideal for fine silts and clays.
- Increases the hydraulic gradient to draw water.
- Requires airtight connections for efficiency.
Memory trick: Suck the Sludge with Vacuum, Sand is Simple with Wells.