Effective dewatering: wellpoints, the principle of their operation and the advantages of using

High-lying groundwater significantly hampers economic activity, pours foundation pits for future objects, complicates the construction process, reduces their reliability and durability, eroding the foundation. To make this or that site suitable for construction, preliminary water reduction is carried out. Needle filters used to reduce the water level, allow to realize the assigned tasks even in the most difficult hydrogeological conditions.

The basic principle of water loss

The choice of a specific method for controlling high groundwater depends on parameters such as the size and depth of the excavation, the design of the future building, the current geological and hydrological conditions, etc. However, any water-reducing technology is used for one purpose: lowering the level of occurrence of groundwater to such a depth , On which they will not be able to obstruct construction work.

The general principle of all water-lowering methods is the creation of a depression funnel. With constant pumping, the water in the soil layer forms a kind of funnel. In the place where dewatering is performed, the wellpoints form the center of the depression. The difference between the required water level and the bottom point of the funnel-shaped depression is called the depression funnel.

Depth and radius of the depression funnel is set depending on specific requirements and conditions. These parameters are maintained during the entire period required for construction operations. It is important that dewatering with needle filters is of a permanent nature, since if pumping is stopped, the groundwater will rise to its original level.

Design of wellpoints

These devices consist of a pipe at the suction end of which a filter is installed. Due to the presence of a filter, solid particles (soil, sand, fragments of various rocks, etc.) do not enter the needle-filtration plants.

The diameter and length of the pipes are determined depending on the depth of the future excavation, the properties of the soil and the required throughput.

Algorithm of the work of the wellpoints

Calculation of the number of wellpoints is carried out taking into account the required diameter of the funnel. In an upright position, the equipment is installed in the ground at the site where the dewatering will be carried out. The needle filters are connected via a pipeline to a pump for pumping water. The pipeline can be made of rubber, metal or other types of pipes. The main thing is that they are reliable.

The extent to which the water loss of needle filters will be effective depends on the correct selection of the pump's power and the correct calculation of the number and diameter of the suction pipes. However, sometimes it is not possible to completely drain the aquifers, as a result of which a certain layer of water (0.5-1 m) remains above the water column. Its removal is usually carried out by arranging temporary open water diversions and using mobile pumping units for pumping water out of them.

Techniques of water reduction by needlepoints

There are various methods for reducing the level of groundwater with the help of needlepoints.

• If for construction work requires a small amount of water loss, wellpoints and self-priming pumps are used light. Such equipment will be able to reduce the level of occurrence of groundwater to a depth of 4.5-8.5 m. If it is necessary to carry out the dewatering operation to the maximum depth, special wellpoints with a multi-tiered structure are used.
• If the level of groundwater is to be reduced to a depth of 18-20 meters, ejector needle-filters with a special water jet pump-ejector-are used.
• Deep centrifugal pumps of high power are used for dewatering to a depth of over 20 meters.
• The vacuum method is based on the use of special ejectors, which create a vacuum at the locations of the filters. Such systems can effectively reduce the level of groundwater in hydrogeological conditions of increased complexity.

The choice of a specific method of depreciation is based on the characteristics of the soils, the conditions of their occurrence and the thickness of the aquifer. In addition, the required filtration factor, the area of the depleted zone, the technology of construction or mining works, the duration of dewatering and the characteristics of the dewatering equipment are taken into account.

Mounting of wellpoints

The choice of the method of installing the water-lowering equipment depends on the characteristics of the soil at the site of future construction works.

• Hydraulic installation method is used when it is necessary to reduce the water level in sandy and fine-grained soils. This technology involves pumping water into the filtering device, which then falls into the ground.
• The mechanical method of installing needlepoints is recommended for water depletion in gravel and clay soils. For drainage pre-drill wells with special equipment.

The optimal way to install the wellpoints and their number is determined by the size of the drainage area and ground features.

Advantages of using needlepoints

• Availability of water-reducing equipment.
• Mobility and ease of installation of the system.
• Absence of the need for the use of electric power (wellpoints operate on diesel fuel).
• Efficiency of work.
• Low cost of depreciation in comparison with other methods.
• High efficiency.