Sub-Structure Works - Level 5 Detailed Description in the Building Construction Course

Sub-structure works are a critical part of the construction process, forming the foundation upon which the rest of a building is built. As part of this Level 5 Building Construction course, we will focus on providing you with in-depth knowledge and practical experience in executing sub-structure works. By the end of this module, you should be able to understand, plan, and execute the tasks involved in sub-structure works with confidence and accuracy.

1. Introduction to Sub-Structure Works

Sub-structure works refer to the construction of elements that are below the ground level of a building. These include foundations, basements, and the support structures that transfer the load from the building above to the ground below. Proper execution of sub-structure works is crucial for the stability and longevity of the building.

2. Components of Sub-Structure Works

The sub-structure typically consists of:

• Excavation: Digging the earth to create space for the foundation and ensuring the soil is prepared for load-bearing capacity.
• Foundation Construction: This includes various types of foundations such as strip foundations, pad foundations, raft foundations, and pile foundations, depending on the soil conditions and building load.
• Damp-Proofing: A key aspect of sub-structure works is damp-proofing, which involves applying materials to prevent moisture from seeping into the structure.
• Underpinning: Strengthening existing foundations to support a new or additional load.

3. Excavation Process

Excavation forms the first step in sub-structure works. This involves removing earth or soil to create space for foundations. The depth and width of excavation depend on the type of foundation chosen. Proper excavation ensures the foundation can sit on stable soil, which is crucial for preventing settlement and structural failure.

• Surveying: Before excavation begins, a site survey should be conducted to determine the excavation depth and boundary.
• Shoring and Safety: Shoring systems, such as timber or steel supports, must be used to prevent the excavation from collapsing and ensure the safety of workers.
• Soil Testing: A soil test must be done to determine the soil's bearing capacity, which will help in selecting the appropriate type of foundation.

4. Foundation Types and Construction

• Strip Foundations: These are used for load-bearing walls. A trench is dug to accommodate the foundation, and concrete is poured to form a continuous strip of foundation beneath the wall.
• Pad Foundations: Used for individual columns, pad foundations are square or rectangular slabs of concrete.
• Raft Foundations: This is a large concrete slab that supports the entire building. It is used when the soil has a low bearing capacity and can spread the load over a larger area.
• Pile Foundations: Used when the soil is too weak to support the weight of the structure, piles are driven deep into the ground to reach more stable soil layers.

5. Formwork and Reinforcement

Formwork refers to the temporary mold used to shape the concrete, while reinforcement involves the use of steel bars or mesh to strengthen the concrete. The formwork for foundations needs to be carefully constructed to prevent deformation during the pouring of concrete. The reinforcement, based on the structural design, ensures the foundation can handle the loads placed on it without cracking.

6. Concrete Pouring and Curing

Once the formwork and reinforcement are in place, concrete is poured into the foundation form. The concrete should be mixed to the right consistency, ensuring it flows into all corners of the formwork. After pouring, the concrete must be cured properly to ensure it reaches the required strength.

• Curing Techniques: This includes maintaining the right moisture level and temperature for the concrete to set and gain strength.

7. Waterproofing and Damp-Proofing

Waterproofing membranes are often applied to the external walls of the foundation to prevent water ingress. This is especially important in areas with high water tables or where basements are being constructed. Damp-proofing may involve bituminous coatings or polyethylene sheets to ensure the structure is protected from moisture.

8. Health and Safety

Throughout the sub-structure works, health and safety are of utmost importance. This includes:

• Use of personal protective equipment (PPE) such as helmets, gloves, and boots.
• Proper training for handling heavy machinery and materials.
• Adherence to local safety regulations and guidelines.

9. Final Inspection and Backfilling

After the foundation is completed, a final inspection is carried out to ensure all aspects are done correctly. If the work meets the required specifications, the area is backfilled with soil to cover the foundation and bring the site back to its original level.

Conclusion

Executing sub-structure works requires a solid understanding of construction methods, materials, and safety practices. This module will equip you with the knowledge to successfully plan, supervise, and carry out sub-structure works for various types of construction projects. By mastering these skills, you’ll contribute to the creation of stable and durable buildings that can withstand the test of time.