What Is Well Point System?
A Well point system contains a series of smaller diameter wells, installed by water jetting, rotary drilling, or augering techniques, connected by a header pipe that is further connected to a centrally located suction pump.
Dewatering is the operation carried out using a well-point system as they are applicable to a wide range of excavations and groundwater conditions. In many projects, dewatering of water plays an important role in deciding the overall completion period of the project.
Many pump sets are available at a specific distance as per site requirements. For the well point dewatering system to be more efficient or effective, the ground strata require to generally be permeable to allow the well point to draw the groundwater.
Read More: 10 Dewatering Methods in Construction
Types of Well Point System
The following are two main types of well point systems.
- Single Level Well Point
- Multi-Leve Well Point
These systems are briefly described in the following;
1. Single Stage Well Point System
A Single level well point is prepared by a 50 mm dia and 1 m long pipe. It has perforations, which are protected with a fine screen to prevent clogging of silt particles in it.
A jet nozzle is fixed at the bottom of the system and it is also working as a point of drive for dewatering. This nozzle also acts as a driving point. A ball valve is also fixed to the bottom of the pipe which permits water flow in a single direction.
A riser pipe of equal diameter is connected to a well point pipe at the lower level of the system. The Riser Pipes are fixed the longitudinal pipes at the ground level surface which is also called the head pipe of the system.
The well point pipe is kept at a distance of 0.6m to 1.5m intervals. During the installation of well point system, water is forced with a jet in a downward direction to reach to the required depth.
Once the above whole mechanism is installed at the project site, pumping is started continuously till the excavation or groundwork is completed.
A systematic diagram of the well point system is shown in fig,
2. Multilevel Well Point System
Multi-stage or multi-level good point is mostly preparable where the excavation depth is more than 15 feet and there is a chance of slope failure to excavation.
Firstly, the well point is operated to lower the water table by 15 feet depth from the level of installation. Again the water table lowered soil excavated to the depth of 15 ft after the 2nd installation. In a multilevel well-point system, well points are fixed in stages or in different grades.
The setup of the system is shown below figure,
The water table is again lowered by 15 feet from the 2nd-second installation of a system In a multistage well point system, excavation is carried out till the excavation reaches about 45 ft. By the well point system, method excavation greater than 45 ft cannot be made.
Application of Well Point System
The following are well-point system applications,
- Excavation of foundations for building
- Deep sewer lines Laying
- Tunnel Excavation work
- Subways Construction
- Hydro projects
- Construction of Basement
- Water Distribution projects
- Reclamation of Land projects
- Construction of Canal
- Thermal Powerplant Structures
- Underground Water tank construction
- Construction of Bridge
Read More: Types of Water Distribution System
Well Point Dewatering System
To draw down groundwater, the well point method for dewatering is chosen and improves working conditions in shallow excavations, typically less than 6 meters in depth. For deeper excavations (more than 6m depth) several strategies, such as staged and multi-tier well point systems can be utilized.
Well point dewatering system consists of small diameter wells, installed by water jetting, auguring, or rotary drilling techniques joined with a header pipe connected to a centrally located suction pump. Groundwater is abstracted via the well point from a vacuum generated by the pump.
A well point is efficient for drawing water below the ground up to a depth of 6 meters and is perfect for shallow excavations, basements, pipelines, confined spaces, underpasses, and tunnel excavations. Pumping facilities include surface electric or diesel suction pumps and super-silenced models of suction pumps for residential areas.
Well-point dewatering systems can be installed quickly in moist ground conditions and are easy to maintain for the duration of the project.
PVC Types Well Point
PVC well point is the economical and properly installed system that will be drained and stabilize the soils up to smaller depths. In this method, punch casing and jet rod can be re-utilized in future stages of dewatering, hence there is a considerable saving in material uses.
The top of the well point will generally be a minimum of six feet below the proposed line to get the maximum drawdown of water. A well point uses the PVC screen, Which permits the max. the flow of water flows min. space of fine materials. This PVC screen gets cleaned by itself with flushing water in opposite direction.
PVC well points are injected around the perimeter of the site from ground level and later connected to a common header pipe. These points draw water from beneath the excavation.The header pipe is connected to a pump to maintain a continuous vacuum.
Atmospheric pressure enforce the water through the ground with a header system into the pump where it is discharged to the approved location.
Well Point Installation
There are three types of wells namely bored/drilled, dug, and driven. Well, points are used for driven well types. How deep the well point needs to be determined by how deep the water table is. When using well point, location is important. The moist soil strata may be preferable for the ease of installation of the well-point system.
To accurately install your well point, the entire point must be below the water table, or else the pump will only suck up air. Another thing to keep in mind while installing the well point is that the water table will eventually lower as the pump runs, so the point will have to be below the capacity of the pump to draw the water table down.
Make sure the entire length of the well point is immersed and if able at least 2 feet beyond that to account for variations in the water table.
Advantages of Well point System
The following are well-point system advantages,
1. More Effective
In a case where the deep well dewatering system is not suitable, a well point can be selected to reduce the water level table to the specified excavation level.
2. Less Cost
Dewatering and well-point systems equipment can be taken on lease for short and long periods, and individually, to satisfy the builder’s dewatering requirements.
3. Quick Deploy
Well-point systems can be utilized on any construction site very efficiently and effectively to reduce the downtime of the construction work.
The wellpoint dewatering method is most suitable for a depth of up to 12 ft in soil that has high permeability and also for a place excavation required more.
Dewatering on any construction site is only required when excavation is to be done on the subsoil water table. Wellpoint dewatering is the most effective method for shallow excavations (up to 4m) to achieve adequate dewatering in permeable soils.
5. Design Criteria
Well point system offers various methods of dewatering among then we can select the most efficient method for your particular job or site.
6. Area of Application
This is the most efficient method as it covers a large area of land than others. This method is capable to work consistently at 100 m3/h capacity of water and it is also discharged airflow with a head up to 60 ft.
7. Groundwater Management
The main goal of using a dewatering system is to lower the water table in that area below the working platform and maintain this level up to work underground is completed.
Well point System Disadvantages
Disadvantages as follows,
- The wellpoint dewatering system is recommended for lower 5 to 6 meters water table only.
- For deeper excavations, it is advisable to adopt the caisson foundation method.
- In well point, It is a prime requirement that well point should run continuously till the required water is lower.
- For running well point system in soil which is having big boulders, clay, and gravel use of machine drilled hole is essential which will increase the cost of installation.
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