Middle East Sewage and Draining Services (MESDS) offers a complete range of dewatering services using the latest techniques, the highest quality of de-watering equipment, a highly skilled staff and many years of experience in all sectors of construction de-watering. MESDS also monitors and maintains the system throughout the operating period.

Type of Dewatering

There are various factors that determine the type of shoring and de-watering solution employed. Some of the main factors are:-

• Soil Condition
• Depth of Excavation
• Water Table Level
• Nature of Structure
• Duration of De-watering
• Type of perimeter retention system

Dewatering methods may be broadly classified as follows.

• Wellpoint System
• Deep Well System
• Gravity Drain System
• Open Sump Pumping

Wellpoint System

In this system, individual small wells - called wellpoints - are secured to the end of riser pipes of appropriate length and are washed into the soil at close centers using high-pressure water. These are set around the proposed excavation area and connected via a suction header pipe to a centrifugal pump fitted with an air exhauster system capable of handling large quantities of air. The wellpoint screen, together with carefully placed filter media when required prevent surrounding soils - even extremely fine particles - from entering the wellpoint. Wellpoints are placed in subsoil to pre-determined depths, generally 4 to 6 meters and spaced 1-2 meters apart. The site investigation, the calculations and the prevailing sub-soil conditions determine the precise location of each wellpoint.

Wellpoints system may be further classified into Single-Stage or Multi-Stage wellpoints. Where it is required to excavate below 7 meters in water bearing aquifer, multi-stage system is implemented. Where bulk excavation is required the most frequently employed method of wellpoint de-watering involves the enclosure of the excavation area by a ring of header pipe. This is a Ring Installation as opposed to the Line Installation employed for trench excavation.

Deep Well System

Deep bored pumping wells are employed in situations where it is necessary to achieve de-watering in a single stage to much greater depths than that achieved using conventional wellpoints. This system consists of a perforated well liner surrounded by a suitable sand filter, with an electro-submersible pump placed at the bottom of the well to pump the water to the surface.

Sacrificial / Dead System

A buried/sacrificial system of wellpointing is adopted in circumstances where the wellpoints need to be located under the foundation due to site conditions. In this case the well points are left in place and disposed once the construction is over.

Gravity Drain System

This system is also known as gravity drain system. A trench or a network or a ring of trenches is dug around the proposed area where de-watering is required. The bottom of these trenches is sloped to some predetermined drain points, and the trenches are filled with gravel. Ground water gets collected at the drain points through the trenches from where it is pumped away.

Open Sump Pumping

Here an open sump created for the surrounding water to seep in. The water collected is then pumped out.