What is Wellpoint Dewatering?
A Wellpoint Dewatering system is a versatile, cost-effective pre-drainage solution that features individual wellpoints which are closely spaced around the excavation.
This technique utilizes vacuum to assist in lowering groundwater levels to create a stable, dry working environment. Wellpoints are especially suited to shallower excavations or excavations taking place in fine-grained soils.
Wellpoint System Design
Wellpoint systems consist of a series of small-diameter wellpoints installed at a pre-determined depth (usually 23ft deep or less) on relatively close centers. They are quick to install & can handle a wide range of flows.
The pump serves three basic functions:
- Creates vacuum & primes the system
- Separates air/water
- Pumps water to the discharge point
Wellpoint Installation
- Jet/Drill boreholes at the spacing designed for the excavation
- Install wellpoints & place designed filter pack in the boreholes
- Set the header pipe
- Connect wellpoints to the header pipe with swing joints
- Set the wellpoint pump & connect the header pipe to it
- Start pumping
- Optimize, monitor & adjust the system
- Lower the water table
- Excavate
Single & Multi-Stage Systems
Wellpoint systems are limited by suction lift and can only lower water below grade to a certain point (depending on the altitude). Systems are often installed as a Single-Stage or Multi-Stage because of these limitations:
Single Stage
When excavations are 18ft deep or shallower, one row of wellpoints may be used to draw the groundwater below subgrade. Careful consideration should be given to the project altitude as higher altitudes will mean less available drawdown.
Multi-Stage
Wellpoints can be used on much deeper excavations, but multiple stages are required. If necessary, two or more rows of wellpoints are installed at different elevations. This is needed when the excavation is deeper than 18ft or when the altitude would prevent dewatering with a single wellpoint stage.
Advantages & Limitations
Advantages
- Quick installation & easy maintenance
- Cost-effective
- Used in low & high permeability soilds
- Suited for shallow aquifers
Limitations
- Deep excavations (due to suction lift limits)
- Lowering water table near bedrock
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