Construction Tech Flashcards
Bonded Screeds
which are laid on to a ready prepared rough, cleaned concrete base.
Unbonded Screeds
which are laid on to a sound clean bitumen damp proof membrane.
Floated Screed
which is laid with steel or fibre reinforcements on to the insulating board, which in turn can be laid on to a suitable damp proof membrane.
Resin bonded screed
which is laid on to a clean, rough pre-prepared concrete base. The resin acts as a ready installed damp proof membrane to the top screed.
Sheet piles
a. Deep trench is excavated and concrete is poured in situ
b. Piles can be used to form basement walls or act as retaining walls
Secant Piles
a. Interlocking piles provide a combination of foundations and basement walls
b. Support in providing a waterproof structure and are often seen when top down construction methods are used
Bored piles
- Bored piles
a. An auger is used to excavate the soil and then concrete is poured once complete
Pre-cast piles
- Pre-cast piles
a. Hammered into the ground (not often favoured due to high noise and lack of flexibility in depth)
What are the different ways that the piles transfer their load to the surrounding ground?
- End bearing piles - transfer load through low bearing capacity soil to a strong stratum such as rock or very dense sand.
- Friction piles - bear on frictional resistance between their outer surface and the soil in contact.
- Settlement reducing piles - usually incorporated beneath the central part of a raft foundation in order to reduce differential settlement to an acceptable level.
- Tension piles - resist uplifting forces that might otherwise cause the structure to be extracted from the ground due to uplifting forces such as hydrostatic pressure, seismic activity or overturning movement.
What is the difference between bored vs. pre-cast piles?
- Bored piles are defined when the process for removing the spoil to form the hole for the pile is carried out by a boring technique.
- They are used primarily in cohesive subsoils for the formation of friction piles and when forming pile foundations close to existing buildings where the allowable amount of noise and/or vibration is limited.
- Pre-cast Concrete piles are generally used where soft soil deposits overlie firmer strata. These piles are usually driven using a drop or single action hammer.
- Issues can arise due to the noise levels associated with the installation method of pre-cast piles.
What is a raft foundation
- Raft foundations spread the load of the superstructure over a large base and reduce the load per m2 of the area.
- Raft foundation solutions are useful in low bearing capacity soils.
- They can be a solid raft slab or beam and slab raft such as a ground beam system and suspended PC concrete ground floor.
When would raft foundations be used?
- A raft can be used for lightly loaded buildings on sites with poor soils.
- Heavy loads to the raft have the potential to cause the raft to move sideways as a result of raft foundations not being very deep.
What is a strip foundation?
- Strip foundations are formed by creating a shallow continuous excavation to support the perimeter and internal walls.
- They are also referred to as strip footings and are suitable for most subsoils and a light structural design.
What are pad foundations?
- Pad foundations provide a base for reinforced concrete or steel columns.
- They are usually formed by making an isolated excavation in the shape of a square or rectangle.
- They often have reinforcement mesh as part of the construction and spread the load to a layer of bearing soil or rock below.
What is powder coating?
- A durable factory applied coating on metals, such as aluminum or galvanized steel which is available in many colours.
- This application is sprayed on and is followed by heat curing to give a film thickness of 50 to 100 microns.
- Any holes and cutting should be carried out before the coating is applied.