Describes Construction of Raft Foundations

2. TYPES OF RAFT FOUNDATIONS
On the basis of structural systems, they can be
classified as
1] Plain Slab Rafts
2] Beam & Slab Raft
3] Cellular Raft

5. Buoyancy Rafts are necessarily to be provided with
the basements so that the weight of the soil removed
Balances to large extent the imposed load.

6. Raft foundations are used to spread the load from a
structure over a large area, normally the entire area
of the structure. They are used when column loads
or other structural loads are close together and
individual pad foundations would interact.
A raft foundation normally consists of a concrete
slab which extends over the entire loaded area. It
may be stiffened by ribs or beams incorporated into
the foundation.
Raft foundations have the advantage of reducing
differential settlements as the concrete slab resists
differential movements between loading positions.
They are often needed on soft or loose soils with
low bearing capacity as they can spread the loads
over a larger area.
RAFT FOUNDATIONS

7. Solid slab raft foundation
Reinforcement runs in
both directions
Reinforced concrete raft
40-50 concrete blinding seals
surface and provides level platform
to fabricate the reinforcement matt
and cages
Well compacted hardcore
Solid slab raft foundation

8. Reinforced concrete raft
40-50 concrete blinding seals surface
and provides level platform to
fabricate the reinforcement matt and
cages
Downstand beams or edge thickenings can
be used to add rigidity and stability to the
raft foundation. Where brick or block walls
sit on the raft the extra load can be
accommodated by a beam within the raft.
Reinforcement cages are
constructed to act as beams
within the raft foundation
Solid slab raft foundation with
Down stand beam

9. Edge beam and reinforcement
extended to carry brickwork cladding.
Toe cast in to slab to carry
brickwork cladding. Hides
the concrete raft below the
ground
Raft foundation with extended
toe to carry brickwork

10. Based on the methods of their support, Raft can be
1] Raft supported on soil
2] Raft supported on pile
3] Buoyancy Raft

11. Reinforcement - raft foundation

12. Reinforcement - raft foundation

13. Pouring Concrete- Raft
Foundation