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Investigations indicate that a site on which a house is to be built has a moderately firm clay subsoil - Leaving Cert Construction Studies - Question 4 - 2006
Question 4
Investigations indicate that a site on which a house is to be built has a moderately firm clay subsoil. Consideration is being given to using either a traditional st... show full transcript
Worked Solution & Example Answer:Investigations indicate that a site on which a house is to be built has a moderately firm clay subsoil - Leaving Cert Construction Studies - Question 4 - 2006
Step 1
Show, with the aid of notes and freehand sketches, the design detailing for each type of foundation listed above.
Answer
Traditional Strip Foundation
A traditional strip foundation is typically designed as a continuous strip of concrete, poured beneath load-bearing walls. It is suitable for moderately firm clay subsoils.
Typical Dimensions:
- Width: 600 mm
- Depth: 300 mm
Sketch
Raft Foundation
A raft foundation spreads the load of the house over a large area, requiring less excavation. It is effective for soils with low bearing capacity.
Typical Dimensions:
- Thickness: 150 mm
- Extending for the entire footprint of the house
Sketch
Step 2
Recommend one of the above foundation types for the house and give two reasons in support of your recommendation.
Answer
I recommend using the Raft Foundation for the house.
- Load Distribution: The raft foundation spreads the load evenly over the entire area of the house, which reduces the risk of differential settlement, especially in soils with poor load-bearing capacity.
- Reduction of Excavation: Less excavation is needed compared to a strip foundation, making it more cost-effective and suitable for building on challenging sites.
Step 3
Identify two factors that could adversely affect the strength of concrete in a foundation.
Answer
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Improper Water/Cement Ratio: An incorrect water/cement ratio can lead to weak concrete, making it more susceptible to cracking and less durable over time.
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Inadequate Vibration/Compaction: Insufficient vibration during the pouring of concrete can cause air pockets and weak spots, leading to a significant decrease in strength and integrity of the foundation.