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Benefits of providing raft foundation for basement

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Basements for buildings are arranged for architectural and occupancy requirement. It provides us lots of spaces and accommodation inside the buildings. Besides, the removed soil naturally provides low stress on the soil below.

So basements are provided after removing soils and some sections of them are built up underneath water table in adjoining soils. But, sometimes basement faces issue with water tightness.

Given below, the construction process of basement :-

The lowest portion of basement gets in touch with soil underneath them. The upper levels (basement floor) do not get in touch with soil below; only basement wall or foundation wall have connected with soil on their sides.

The bottom most sections of basement belong to essentially a foundation or a portion of foundation. The basement is built up with column footings, the footings are attached with slab that is normally usually thin since bearing pressure is provided mostly underneath footings.

Another option is again a thin connected slab that is spaced for pile caps. Sometimes piles raft foundation is also implemented. The raft foundation is utilized as basement of a building.

The thin slabs do not have the capacity to provide water tightness to basement. Under these circumstances, stress concentration is produced at intersection of the footing to slab or basement wall to raft (slab) that results in creating cracks.

So raft foundation will be effective in place of such weak slabs. The basement should be arranged over the ground water table (assume ground water-table is low).

Also Read: Live Demonstration of Raft Foundation Construction Process

Even under this situation, water is entered from surface through rainfall, irrigation etc., the same problem of water proofing is found.

When water is stored for a prolonged time over impermeable soils (permeability < 0.1 mm/sec), sever issue is raised and if clayey soil has expansive character, the condition becomes worst; particularly when the building site contains sloping ground where water discharges toward building with large contact area to foundation soil.

Basement wall should be designed to acquire the strength of cantilever retaining wall not getting support from floor immediate over it.

While construction of basement wall it becomes complicated to provide supports by raking struts (temporarily) until supports of upper floor (may be intermediate basement or ground floor) is finished.

Benefits of providing raft foundation for basement