Wellpoint systems

Wellpoint dewatering is the most economical and widely employed dewatering system

Wellpoint systems

     

Wellpoint dewatering is the most economical and widely employed dewatering system, especially where the water table does not have to be lowered too much (4,00 m – 4,50 m), although it is possible to achieve larger lowerings through special devices.

The most important elements of the system are vacuum and slotted screen: i.e. the wellpoint. Disposable wellpoints and compact resistant reusable wellpoints are in common use throughout the world. Each type of wellpoint has commercial advantages and disadvantages. In Lithuania, the resistant reusable weelpoints are being used in most cases.

 

The wellpoint is made up of a piercing tip at one end and a series of metallic or plastic filters. It is being made in order to deliver the maximum quantity of water per unit time without removing the solid particles. This result has been achieved by accurately balancing the areas of the pipe and their interspaces. The external perforated shell allows less water to flow than the internal shell which is provided with a textile. This difference causes a drop in the pressure between the two walls. The pressure reduction on the internal filter and on the sand which is contained between the external mesh and the internal filter will determine a low inflow speed which will be maintainedconstant during the pumping. In this manner the water filtrates through the fluid bed of highly filtering sand.

The quick flexible joint consists of a vacuumresistant transparent hose. At its ends are two quick ball semi-joints for coupling with the header semi-joints and the lifting pipe respectively. This type of pipe fitting, which is provided with a regulating cock for the water inflow, is mostly employed with moving Wellpoint system. These systems are employed in the laying out of water pipes when the pumps and pipes need to be quickly moved in order to go on with the job. Obviously, the depth and spacings of the wellpoints are determined by the kind of soil, its permeability and the depth of the lowering. Anyway, the header is provided with plugs every 1,00m in order to couple the wellpoint through the take-off points.

In UAB "Grunto nusausinimo sistemos" sales and rental equipment fleet there are pipes of different sizes pipes (2-6m). They can be assembled together, but one must clearly keep in mind that below a depth of 6,9 m the expected outputs will be low. The maximum effective practical running efficiency is about 8,5 m of vacuum, and consideration must be given to friction and air looses in the system. The system can be arranged laterally to or along the perimeter of the excavation, depending on the dimensions of the excavation and the soil profile.

The multiple-stage Wellpoint system is employed when the water table is to lowered deeper than 5,00 to 6,00 m:

The first installation is set axially or along the perimeter of the area which is to be excavated, at the top of the slopes that have to be formed, and possibly at the original ground water level. This installation may be temporary or indefinite depending upon the depth of the excavation, the kind of soil and its permeability. Once an initial drawdown is achieved, a second installation will be set at the new level of the water table. When the new installation has lowered the water table to the required depth, it may be possible to remove the perimetrical (or axial) installation above if the dewatering operations can be carried out by the deeper installation alone. An installation with 4 or 5 stages run simultaneously may be convenient when this method is employed. Should more than 1 or 2 stages be necessary, the possibility of adopting a combination of drainage systems should be examined.