Foundation, Concrete and Earthquake Engineering

Raft Foundation Construction Method

Raft foundation is reinforced concrete Slab which founds the entire supporting member of structure like column, shear wall etc. Foundation construction of this type is required where made up ground, expansive clay soil or marshy site are chosen to found a heavy structure.

Raft foundation slab generally covers entire contact area of structure like a floor and foundation slab projects 30 cm to 45 cm distance from outer wall/basement wall of the structure towards all sides.  But  when  property line merges with basement wall, the projections are sometimes avoided.
excavation protection for raft foundation slab with steel arragement
If the bearing area exceeds the above defined area, the projection may be changed and depending on the eccentricity due to lateral load moment and unsymmetrical axial loads on column and shear wall the symmetry of projection may be changed. The excavation is done around the area defined above to designed depth and necessary protections are taken to excavation related hazard and to give safety to neighbor buildings.
steel arrangement for inverted beam in raft foundation slab
The excavated area is well consolidated and if required necessary treatment is applied to soil to achieve desired bearing capacity depending on soil investigation data. The consolidated and treated surface is the base upon which raft slab will cast. In case of inverted foundation beams (both main and secondary beams) as discussed in previous post, the beams are cast after the slab with necessary precaution to provide construction joints. Further continuation is commenced after the proper curing of the raft slab and beams.


  1. Construction method of raft is too mild.
    What precautions should have been taken prior to commencing excavation?
    What method should be employed from safety viewpoint?
    What about de-watering if so required?
    How to ensure that soil capacity is acceptable?
    How to reach soil to required capacity?
    How to protect excavation & other buildings adjacent?
    What distance should be a minimum for basement from other building line?

  2. any one have drawing of inverted filter to be done in raft foundation of bridge.
    pl mail

  3. So nice to see the walls going up !!! we are also construction company in london.

    Central London Basements