wellpoint
A small well consisting of a tube hammered into the ground, that can drain water from a construction site.
wellpoint: a driven tube that drains water from building sites
A wellpoint is a small diameter tube, typically 50 mm or 75 mm, driven vertically into the ground to depths of 5 to 10 metres. The lower end terminates in a screened section that allows groundwater to enter while blocking soil particles. The tube connects to a centrifugal pump via a common header pipe, creating a temporary dewatering system that lowers the water table around an excavation or foundation pit.
The tube itself is usually steel or aluminium with the pointed driving head, or shoe, hardened for impact resistance during hammer installation. The screen section uses stainless steel mesh or similar, and the annular space between tube and soil is backfilled with sand or pea gravel to maintain permeability. Wellpoints are installed in clusters, with 20 to 40 points commonly spaced around a perimeter to achieve steady drawdown.
When and how they fail
The most common problem is screen clogging from silt and fine sand migration, which reduces flow and increases pump discharge head. This occurs when the surrounding soil lacks sufficient natural filter material or when the gravel pack becomes contaminated. Driving tubes into cobbles or fractured rock may damage the shoe before reaching required depth, leaving the wellpoint ineffective. Corrosion of steel tubes accelerates in acidic or saline groundwater, particularly where site conditions expose metal for months.
Wellpoints occupy a distinct position in construction dewatering. They work best in sands and fine gravels where screens can remain open and intake is easy; they struggle in silts and clay. For deeper excavations (beyond 10 metres) or in poor soils, contractors shift to jet wells or deeper well systems. Sumps and pumped exclusion remain cheaper for very shallow, small-volume seepage, while sheet pile cutoffs and chemical grouting address problems wellpoints cannot solve.
The term reflects the dual nature of the device: it is a well in function, drawing water from surrounding soil, but also a point, literally a sharp tip that breaks ground. Installation crews often refer to the apparatus by its assembled form as a wellpoint system, understanding that isolated tubes are worthless without the pump, header, and manifold that give them purpose.