Types of Underpinning and Timbering
In building construction, temporary and strengthening techniques are often required to ensure safety and stability of structures and excavations. Underpinning and timbering are two such important methods. In the ITI Draughtsman Civil trade, understanding these techniques is essential for safe construction practices and preparation of accurate drawings.
Underpinning is used to strengthen or deepen existing foundations, while timbering is used to support the sides of trenches and excavations to prevent collapse.
Underpinning
Underpinning is the process of strengthening an existing foundation or increasing its depth when it becomes weak or when additional load is to be supported. It is commonly used during renovation, extension, or repair of buildings.
Need for Underpinning
- Weak or damaged foundation
- Increase in load due to additional floors
- Change in use of building
- Settlement of foundation
Types of Underpinning
1. Mass Concrete Underpinning
This is the most common and simple method. Concrete is placed below the existing foundation in stages to increase its depth.
- Suitable for shallow foundations
- Simple and economical
2. Beam and Base Method
In this method, beams are constructed below the existing foundation to transfer load to a new base.
- Used when foundation requires more support
- Provides better load distribution
3. Mini Piled Underpinning
This method uses small diameter piles to support the structure.
- Suitable for weak soil conditions
- Used in restricted spaces
4. Cantilever Underpinning
A reinforced concrete beam is used to transfer load from existing foundation to a new support.
- Used when access is limited
- Requires careful design
Advantages of Underpinning
- Strengthens existing structures
- Prevents settlement and failure
- Allows modification of buildings
Timbering
Timbering is the process of providing temporary support to the sides of trenches or excavations using timber or other materials. It prevents the collapse of soil during construction work.
Purpose of Timbering
- To protect workers in trenches
- To prevent soil collapse
- To maintain stability of excavation
Types of Timbering
1. Stay Bracing
Used for shallow trenches with firm soil.
- Simple and economical
- Suitable for small excavations
2. Box Sheeting
Timber boards are placed closely together to support trench sides.
- Used in loose soil
- Provides continuous support
3. Vertical Sheeting
Vertical boards are used with horizontal supports.
- Used for medium depth trenches
4. Runner System
Vertical planks (runners) are supported by horizontal members.
- Used in deep excavations
5. Sheet Piling
Steel or timber sheets are driven into the ground to support soil.
- Used in waterlogged or loose soil
- Provides strong support
Components of Timbering
- Poling Boards: Vertical boards supporting soil
- Wales: Horizontal supports
- Struts: Provide lateral support
Safety Measures
Proper precautions must be taken while using underpinning and timbering:
- Use good quality materials
- Ensure proper installation
- Regular inspection
- Provide safety equipment for workers
Importance in Construction
Underpinning and timbering are essential for:
- Strengthening existing structures
- Ensuring safety during excavation
- Preventing structural damage
Importance in Draughtsman Civil Trade
Knowledge of underpinning and timbering helps draughtsmen in preparing detailed drawings and planning construction work. It ensures safety and efficiency in building projects.
Conclusion
Underpinning and timbering are important techniques used in construction for strengthening foundations and supporting excavations. Understanding their types and applications is essential for safe and efficient construction.
For students of the ITI Draughtsman Civil trade, this knowledge is crucial for designing safe structures and managing construction activities effectively.