L1 - Construction Technology - Foundations Flashcards
What is substructure?
All elements of work that are undertaken below the damp proof course (DPC) that provides the basis for the superstructure to be constructed upon.
Substructure includes: Foundations up to and including the DPC, lowest floor assembly below the underside of the screed or the lowest floor finish, basement excavation and basement retaining walls up to and including the DPC.
What are foundations?
Foundations provide support for structures by transferring loads to layers of soil or rock that have sufficient bearing capacity and suitable settlement.
What affects the design of foundations?
Nature of the load requiring support
Ground conditions
Presence of water
Availability of space
Accessibility
Sensitivity to noise and vibration
What are the different categories of foundations?
Shallow foundations - loads imposed by a structure are low relative to the BC of the surface soils. Less than 3m.
Deep foundations - BC of surface soils is not adequate to support loads of structure, so loads need to be transferred to deeper layers of soil with higher BC. Higher than 3m.
What different types of shallow foundations are there?
Strip foundation
Pad foundation
Raft foundation
What is a strip foundation?
Strip foundation: Continuous strip of support to a linear structure such as a wall. It is designed for a continuous load equal along the whole strip. It is suitable for most subsoils and lightweight loading.
What are pad foundations?
Pad foundation: Circular / square block or slab used to spread the load from a heavy column.
What are raft foundations?
Raft foundation: Used to spread the load from a structure over a large area. They are often used on loose soils with low BC as they can spread the loads over a larger area.
What different types of deep foundations are there?
Piled foundations
What are pile foundations?
Pile foundations are long members that transmit foundation loads through soil strata of low BC to deeper soil having higher BC.
How do friction piles work?
Piles rely on the friction between the piles and the soil for its bearing. It doesn’t need a solid base.
What are end bearing piles?
End bearing piles are loads transferred through soft strata directly onto firm strata to develop their load bearing capacity.
What types of piling installation is there?
Displacement / driven
Replacement / bored
How does displacement piling work?
Piles are driven, this displaces soil laterally
How does replacement / bored piles work?
Casing is bored, drill excavates soil, reinforcement / rebar placed in bore, pile is casted using concrete, casings are then removed
What are some risks of using bored piles?
Risk for PQS cost plan as unknown depth of piles, utilise D&B to transfer the risk
What are some advantages and disadvantages or driven piling?
Advantages
- Cost effective
- Wide variety of buildings
- Steel / precast concrete
- Pre-fabricated
Disadvantages
- Noisy and vibrating
- Not appropriate for ground with poor drainage
What is CFA?
CFA is continuous flight auger and it is a cast in situ method of piling. It is 1 continuous operation enabling faster installation than bored piling. Rebar is placed into the wet concrete after casing
What are secant piled walls?
Guide walls with male / female, drilling rig into every other hole, CFA auger, drill piles inbetween
What are advantages of CFA piling?
Low levels of sound and vibration
Compared to bored piles, they are installed quickly and economically
Have high load bearing
Piling rigs can be adapted to operate in different conditions
