What Do You Mean By Well Point System
A Well Point System serves as a dewatering tool, as all the deep excavations are now corresponding with the expulsion of subsoil water for construction foundations of structures or any underground construction.
Wellpoint dewatering systems are situated around the perimeter of the project site against excavation shoring and are connected with a perimeter discharge line via a pump set.
What Is Well Point System?
A Well point system contains 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. In the wellpoint dewatering system to be more efficient or effective, the ground strata require to generally be permeable to allow the wellpoint to draw the groundwater.
Read More: 10 Dewatering Methods in Construction
Types of Well Point System
There are two types of well point dewatering systems to remove subsoil water namely,
- Single Stage Well Point System
- Multi-stage Well Point System
These systems are briefly described in the followings;
1. Single Stage Well Point System
- A single-stage wel lpoint system consists of a pipe about 1m long and 50mm in diameter. It has perforations, which are covered with a screen to prevent clogging of silt particles in it.
- At the bottom end, a jetting nozzle is provided. This nozzle also acts as a driving point.
- A ball valve provided near the lower end allows the water to flow only in a downward direction during the installation of the well point system.
- A riser pipe having a similar dia. as the well point system has to connect with the wellpoint at its bottom end.
- The riser pipe is connected to a horizontal pipe, known as the header pipe, at the ground level. The header pipe is coupled to a pumping unit.
- The well points are spaced at every 0.6m to 1.5m intervals. The well points are placed to the desired depth by jetting water through riser pipes in the downward direction.
- Once the above whole mechanism is installed at the project site, pumping is started continuously till the excavation or groundwork is completed.
- A functional diagram of the single-stage well point system is shown in the below figure.
- A single-stage well point system is generally utilized when the depth of excavation is less than 4.5m. This system is very effective in granular soil.
- By the single-stage well point system method, the water table is lowered by about 4.5m. This method is suitable for soils having a coefficient of permeability between 10-2 to 10-4 cm/sec.
2. Multistage Well point System
- Multistage well point systems are usually preferred if the depth of excavation exceeds 4.5meters and where there is a chance of slope failure.
- In a multistage well point system, well points are installed in stages or in different grades.
The setup of the system is shown in below figure,
- First of all, well points are installed to a depth of approximately 4.5meters and put into action till the water table is decreases by about 4m.
- Then the area is excavated up to this 4m depth. After this, well points are installed within the area, which is excavated already.
- The water table is further lowered by another 4m.
- In a multistage well point system, excavation is carried out till the excavation reaches about 15m. By the well point system, method excavation greater than 15m cannot be made.
Application of Well Point System
At the following construction or project sites well point system can be adopted,
- Excavation of foundations for building
- Basement construction
- Laying of deep sewer lines
- Tunnel work
- Construction of subways
- Hydro projects
- Water supply projects
- Land reclamation projects
- Canal construction
- Structures for thermal power plant with not too deep foundations
- Underground tank construction
- Bridge construction
Read More: Types of Water Distribution System
Well Point Dewatering System
- To draw down groundwater, the wellpoint 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.
- Wellpoint dewatering system consists of small diameter wells, installed by water jetting, auguring or rotary drilling techniques, joint with a header pipe which connected to a centrally located suction pump.
- Groundwater is abstract via the wellpoint from a vacuum generated by the pump.
- A wellpoint 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 Well Point System
PVC well point is the economical and properly installed system that will be drained and stabilize the soils up to smaller depths.
This method of wellpoint consists of a series of well points usually jetted into place and utilized when a jet rod or punch casing is reused in a well point system.
The top of the wellpoint will generally be a minimum of six feet below the proposed line to get the maximum drawdown of water.
PVC well point screen, which allows maximum water flow with minimum passage of fine materials. This PVC screen gets self-cleaned by reverse flushing while jetting.
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 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.
Installation of Well point System
- There are three types of wells namely bored/drilled, dug, and driven. Well points are used for driven well types. How deep the wellpoint needs is to be determined by how deep the water table is.
- When using wellpoint, location is important. The moist soil strata may be more preferable for the more ease of installation of the well point system.
- To accurately install your wellpoint, 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 wellpoint 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 to.
- Make sure the entire length of the wellpoint is immersed and if able at least 2 feet beyond that to account for variations in the water table.
Well Point for Shallow Well
- In a shallow well application, the maximum depth to draw water is up to 25′. The utilization of a wellpoint in a shallow well is commonly not a good source of potable water.
- Shallow wells are more exposed to pollution like fertilizer, animal waste, and dry wells.
- In a shallow well system, if a wellpoint is being used for a source of potable water, you should refer to your applicable local well and plumbing codes.
- Also, regular testing will be necessary to ensure that it’s free from harmful chemicals and safe for drinking and other use.
- It’s good to be aware of the ground from which the wellpoint has to travel.
- For example, coarse sand is the best strata to drive a point where fine sand is extremely hard since the fine sand would grip the point.
- For shallow wells, steer clear of a location near any marshy areas or septic tanks that could cause contamination to the water.
- If there is a sewer line close by, it is important to stay at any wellpoint at least 50 feet away.
Advantages of Well point System
Followings are the unique advantages of the well point system due to which this method is commonly more preferable over other dewatering methods;
1. More Effective
At construction projects where deep well dewatering is not required, a wellpoint dewatering system is an effective and economical way to reduce the level of the water table to the required excavation level.
2. Less Cost
System of wellpoint method and dewatering equipment can be taken on lease for short and long periods, and individually, to serve the builder’s dewatering requirements.
3. Quick Deploy
Well-point systems can be placed on the project site very efficiently and effectively to reduce the downtime of the construction project.
4. Technical Background
Dewatering is commonly required on-site when excavations are to extend beyond the subsoil water table. For shallow excavations (up to 4m) wellpoint dewatering is often the most effective method to achieve an adequate drawdown in permeable soils. (i.e. sand, clayey sand, etc.)
5. Design Criteria
Well point system gives you a different method to adopt and selection of the most efficient method for your particular job or site.
6. Area of Application
Well point system is usually most efficient to cover more land area than other as this system cover more area with a constant capacity of 100 m3/h of water, air or water, and air mixture is discharged against a head of 20 meters.
7. Groundwater Management
The main purpose of any dewatering practice is to draw down the water table below the working platform and maintain the depressed level for the duration of the dewatering period.
Disadvantages of Well point System
Followings are some disadvantages of well point system:
- Wellpoint dewatering system is suitable for lowering water table by 5 to 6 meters only. For deeper excavations, where the water table is to be lowered for a greater depth caisson method required for that particular site.
- It is essential to continue pumping once it has started until the excavation is complete. If it is stopped in between, it may prove to be tragic.
- In the case of ground consisting of stiff clay, gravel, or boulders, well points are installed in drilled holes, which increases the installation cost.
Q.1 What is well point system?
A Well-point system is one with series of smaller diameter wells, installed by water jetting, rotary drilling, or auguring techniques, connected by a header pipe that is further connected to a centrally located suction pump.
Q.2 What are the different types of Well Point systems?
There are two types of Well Point Systems, termed as;
1. Single Type Well Point System: generally utilized when the depth of excavation is less than 4.5 meters.
2. Multi Type Well Point System: usually preferred if the depth of excavation exceeds 4.5 meters.
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