Introduction of Well Point System
The well point system has more than one point near the trench or around the excavation site to dewatering water from the trench. All points of this system are connected to the common header pipe. This header is used to pump water out of the pipe.
Common and complex problems like groundwater can be controlled by various water techniques. Ignoring water dewatering during project planning can lead to construction project delays and cost overruns.
The main purpose of dewatering techniques is to allow the construction of the foundation in dry conditions. Wellpoint system makes pre-drainage of soil possible. In addition, there is a change in groundwater control, and properties such as land physical change are formed.
If the issues of dewatering for groundwater should be properly considered at the stage of investigation and design. The purpose of the well point system is to temporarily reduce excavation and groundwater tables in arid climates.
What Is the Well Point System?
The various parts of the wellpoint system include well point, screen, riser pipe, and jetting. This system has a header pipe for the water inlet. The water is pumped through this header pipe.
A well point pump is a combination of two pumps that pump water out of a header pipe. The wellpoint system has a vacuum pump to remove air. Air control plays an important role in a well point system because excess air reduces the efficiency of the pump.
The dewatering pump used in the wellpoint system is specially designed for dewatering function. Dewatering pumps are available in sizes of 4 ”to 10” of different capacities.
A well point system is used for a stable working construction site to reduce groundwater levels in the foundation area of the excavation site. Wellpoint system is used for a shallow foundation, trench work and dewatering utility.
The well point system consists of a set of shallow wells of small diameter. The various riser pipes of the well point are connected to the main header pipe, and the water in this header pipe is pumped by a high-efficiency vacuum dewatering pump.
The diameter of the riser pipe is kept from 38 to 50 mm. The bottom of the riser pipe is fixed with mesh, which enables to draw of water using a pump.
The material used for the size of the slots or openings in the riser pipe is the size of the grain used.
When the installation is done using drilling techniques in the wellpoint system, large quantities of water cannot be obtained from Well Point. It can be dewatering about 3 gallons of water per minute.
Very low water flow can be obtained in silt sand from well points system. While in coarse sand and gravel, large streams of water can be dewatering.
Types of Well Point System
There are two main types of well point systems
- Single-Stage Well Point System.
- Multi-Stage Well Point System.
Single-Stage Well Point System
In this type of well point system, perforated pipe, 1 m long and 5 cm in diameter, are installed in the ground. The riser pipe is covered with a screen to prevent debris. The jetting nozzle is fixed to the lower end of the riser pipe.
The Cone steel drive point is fixed at the lower end of the well point to provide easy installation. In this type of well point a ball valve is fixed near the lower end, which allows water to flow after installation.
Riser pipes of different well point 15 to 30 cm. Of diameter. Which is fixed with a header pipe
The header pipe is connected to the pumping unit. In a well point system, the distance of the well point is kept according to the type of soil and the depth of water. The distance between two well points is kept between 1 to 3m as required.
The header pipe-connected pumping unit is continued continuously until the excavation work is completed.
It is advisable to use a single-stage well system when excavation depth is less than 4.5 m on the construction site.
Multi-Stage Well Point System
A multistage well point system is commonly used when the excavation depth above the construction site is more than 4.5 m. Also, a slope is used where there is a high chance of failure.
In a multistage well point system, various well points are installed in stages.
The stage-wise installation of the system is shown in the figure.
In the first phase, various well points are installed at the construction site to a depth of 4.5 meters. By pumping, the water level of water is reduced to 4.5 meters.
In a multistage well point system, the excavation reaches about 15 mm till dewatering is done by the stage-wise well point system. It is possible to dewatering up to 15 meters by the multi well point system.
PVC Well Point System
PVC well point system can be installed economically and easily, which is capable of dewatering water to a shallow depth.
Uses jet rods in PVC well point system. This type of well point riser can be reused by pulling because this type of method uses couplings.
The use of PVC well point system has increased due to its corrosion-proof quality and cost-effectiveness, and flexibility. PVC has a lightweight and easily installable component in a well-point system. In addition, it creates less friction force.
Advantages of Well Point System
The various types of dewatering in the project provide significant advantages through wellpoint installation methods which are as follows.
- The maintenance cost of a well point system is low.
- The well point system can be easily installed.
- They can be used for industrial, commercial, high rise etc. projects.
- The well-point system works effectively at the construction project site.
- Wellpoint dewatering system for deep foundations in construction projects can be done to reduce water level during required excavation as per stage.
- Individual, wellpoint systems and systems of water appliances can be leased to meet the builder’s water needs.
- The most efficient method for the site can be adopted from various methods in the well point system.
- The well point system is generally easier and able to cover more land area than other systems. Water can be dewatered at 10 m3 / hour through this system.
Disadvantage of Well Point System
- Once in the construction project, it is necessary to continue pumping until the excavation is completed. If pumping is stopped in the middle, the water is more likely to refill.
- It is very expensive to install well points in an area with hard clay, gravel or stones.
- Wellpoint dewatering can be done up to 15 meters from the dewatering system.
- It is expensive to install a well point system for deep depth. As it has to do stage wise dewatering.