Summary
- A well foundation diagram illustrates the major components of a well foundation, such as the cutting edge, well curb, well cap, etc.
- Well foundations are generally employed for bridge piers, river structures, and other similar applications.
- Many different types of well foundations are used depending on the type of soil, water depth, and size of the well, as well as the structural load.
A well foundation diagram is used to represent the main parts and construction sequence of a well foundation in the construction of deep foundations. It will usually be used to refer to components such as the cutting edge, well curb, steining, bottom plug, filling, top plug, well cap, etc. This guide will explain how to read a well foundation diagram, its main types, components, and the basic construction process.
What Is a Well Foundation Diagrams?
A well foundation is a deep foundation that allows heavy loads to pass through to stronger soils below the foundation. Typically, a well foundation will be a hollow section with soil removed from inside.
- Well foundations can:
- Transport large vertical loads.
- Resist lateral forces.
- Resist bending moments.
- Work in loose or wet soil.
- Protect river beds from scouring.
Components of a Well Foundation
A well foundation must be able to sink, seal, be stable, and transfer the load.
The main components are:
- Cutting edge: Lets the well penetrate the soil during sinking.
- Well curb: Provides support and forms the bottom of the well.
- Steining: Makes up the vertical wall that bears structural loads.
- Bottom plug: Plugs at the bottom when a desired level is reached.
- Sand filling: Fills the space with sand as required.
- Top plug: Closes the top of the section filled.
- Well cap: It connects the foundation to the pier, and it distributes the load.
Types of Well Foundations
The most common types of well foundations are open caisson, floating caisson, pneumatic caisson, box caisson, and excavated caisson.
| Type of well foundation | Description | Common use |
|---|---|---|
| Open caisson | Open at the top and bottom. Soil is removed from inside as the well sinks. | Bridge piers and river works |
| Floating caisson | Constructed separately and floated to the site. | Marine works and offshore structures |
| Pneumatic caisson | Uses compressed air to keep the working chamber dry. | Deep underwater work and difficult riverbeds |
| Box caisson | Closed at the bottom and placed on a prepared foundation bed. | Shallow marine and waterfront foundations |
| Excavated caisson | A shaft is excavated to the required depth and then filled with concrete. | Certain land-based deep foundation works |
Shapes of Well Foundations
Well foundations come in a variety of shapes depending on the type of pier, direction of load, type of soil, and type of sinking. These are the round, rectangular, oblong, double D, and twin circular wells.
- Circular well: Can be easily drilled and is appropriate for evenly distributed loads.
- Rectangular well: Can be used for longer piers and abutments.
- Oblong well: Provides longer foundation length in one direction.
- Double-D well: Gives greater width to the base of large bridge piers.
- Twin circular well: Two wells that are connected and form a circle, for heavier loads.
Well Foundation Construction Process
Site investigations and plugging are the first and last steps in the construction process for a well foundation. Work should be carried out according to approved designs and project specifications.
The key steps are:
- Site investigation and setting out: Investigate soil and groundwater conditions, and also scour.
- Construction of cutting edge and well curb: The cutting edge allows the well to penetrate the soil. The well curb supports the steining to form the lower foundation part.
- Construction of steining: Construct the vertical wall, typically made of Reinforced Cement Concrete (RCC) as per specification.
- Sinking of the well: Remove soil from the well and check tilt, shift, and alignment.
- Reaching the founding level: Continue sinking till the approved soil stratum and level are reached.
- Bottom plugging: Place concrete to seal the base.
- Filling and top plugging: Fill the hole with the specified material and plug the hole on top.
- Construction of well cap: Finally, the well cap is made to tie the foundation to the pier and distribute the loads.
Read our RCC Meaning in Construction guide to understand reinforced cement concrete, its components, uses, and role in structural work.
Advantages and Disadvantages of Well Foundations
Well foundations support heavy structures. However, it may be a lengthy and complicated building process.
Pros
- Resists large vertical loads.
- Works well with large lateral forces.
- Works effectively in areas of high scour in a riverbed.
- Offers a very large, solid support base.
Cons
- Sinking requires a lot of attention.
- Can tilt and shift.
- Layers of boulders may impede excavation.
- Quality control is required when using underwater plugging.
Well Foundation vs Pile Foundation
Both well foundations and pile foundations are deep foundations. Well foundations are used for bridge and river structures, while pile foundations are used for other kinds of buildings and structures.
| Factor | Well Foundation | Pile Foundation |
|---|---|---|
| Use | Bridge piers, river foundations, and docks | Buildings, bridges, towers, and weak-soil sites |
| Form | Large hollow caisson-like structure | Slender deep elements |
| Lateral resistance | Generally high due to large size and mass | Depends on pile size, group action, and soil |
| Load capacity | Suitable for very heavy concentrated loads | Load is shared by individual piles or a pile group |
| Cost | Can be economical for major bridge foundations | Often economical for buildings and many infrastructure works |
Common Issues During Well Foundation Construction
Main issues are tilting, shifting, uneven sinking, etc. This can result in construction time issues and misalignment.
| Issue | Control Measure |
|---|---|
| Tilting | Adjust dredging and loading under expert supervision. |
| Uneven sinking | Review soil conditions and also check excavation methods. |
| Boulders or hard strata | Use an approved method to clear the blockage. |
| Sudden sinking | Control excavation and loading carefully. |
| Bottom plug issue | Prepare the base properly and also monitor concreting. |
Key Quality Checks for Well Foundation Work
Sinking and concrete quality are the key quality checks for well foundation work and alignment. These checks are to maintain stability and load transfer.
These are the major quality checks:
- Location and alignment.
- Tilt and shift during sinking.
- Cutting edge and well curb.
- Concrete grade and curing.
- Filling and top plug.
All checks should follow the applicable standards. Read our Concrete Mix Ratios guide to understand M10, M15, M20, M25, and M30 concrete grades and their common construction uses.
Choosing the Right Well Foundation for Your Project
The type of well foundation will be dependent on the type of soil, water depth, structural loadings, scour, and foundation depth. Refer to well foundation diagrams and type comparisons to confirm the final design with a qualified engineer and the applicable project standards. Working on a civil construction project in Bengaluru? Get construction materials from HomeRun with fast delivery across India.
Frequently Asked Questions
What are the different types of well foundations?
There are five basic forms of foundation: open, floating, box, pneumatic, and excavated.
What are the components of a well foundation?
The main components are the cutting edge, well curb, steining, bottom plug, sand filling, top plug, and well cap. Each part supports sinking, sealing, or load transfer.
What is a well foundation and how is it constructed?
A well foundation is a type of hollow deep foundation that is sunk to the proper founding level. Construction includes curb, steining, sinking, bottom plugging, filling, top plugging, and well cap.
How does a well foundation provide stability for heavy structures?
A well foundation transfers loads to deeper soil layers. Its large size and depth also help resist lateral forces and scour.