FOUNDATIONS RAFT FOUNDATIONS TYPES AND ADVANTAGES rea of soil and Raft foundation isa thick reinforced conerete slab which spreads over a are provides support for several columns and load bearing, walls It is also called as mat foundation which are widely used foundation system. Raft foundation is # 9° of shallow foundation. Fig 1: Raft or Mat Foundation Types of Raft Foundation Following are different types of raft foundations, 1. Flat Plate Type Raft Foundation 2. ‘Thickened Flat plate Type Raft Foundation 3, Beam and Slab Type Raft Foundation 4. Piled Raft Foundation 5, Cellular Raft Foundation 4, Flat Plate Type Raft Foundation ness covering Flat plate type rat foundations consist a reinforced concrete slab of uniform thick the whole bearing area. This suitable when the columns a laced with uniform space between them and carying equal and small loads. Reinforcement 9 slab is provided in both directions in the form of steel mesh, Two mesh are reinforced at oP ‘and bottom ofthe slab to balance upward Page 115P FOUNDATIONS rete slab in di d \) mm is provided for cone! 304 is provide id nding forces. Maximum thickness of 300 n and downward bending . ase of raft foundation, Fig 2: Flat Plate Type Raft Foundation 2. Thickenead Flat plate Type Raft Foundation thickness also helps to receive heavy loads.FOUNDATIONS m and Slab Type Raft Foundation In case of Beam and slab type raft foundation, beams are laid in perpendicular directions and All ofthese beams connected by ral slab. Columns are situated exactly on intersections of beams of raft foundation, This type rat foundation is suitable when the columns are carrying lunequal loads and there is large space between them. Integral edge beam Ground Fig 4: Beam and Slab Type Rafi Foundation. 4, Piled Raft Foundation In case of piled raft foundation, raft sla is preferred for soils of high compressibility and high water table. These are well suitable for supported by piles in soil. This type of foundation high rise buildings. Provision of piles under the raft reduces the amount of settlement and also controls the effect of buoyancy. Ultimate load capacity of foundation also increases. Fig 5: Piled Raft Foundation Page 35) FOUNDATIONS 5. Cellular R, Celtul aft Foundation ar raft foundation fou iS also known as box type raft foundation or rigid frame raft Aation. tn this type each bo, Of foundations, boxes lke structures are formed where the walls of acts as thks an beams and these ae connected by slabs at top and bottom. The beams and ATE united in suc 7 . found Sich a way that their cross section look like section. This type of ations can resist S ver : 5 Settlement "sty high bending stresses and suitable for loose soils where ‘Ment is Uneven, {ivr ie new, course sonnet Fig 6: Cellular Raft Foundation Advantages of Raft Foundation The advantages of raft foundation are as follows: * Rafi foundations are constructed for shallow depths hence, it requires less excavation + Well suitable in soils of low bearing capacity + Loads coming from superstructure are distributed over a larger area + Differential settlement of soil can be reduced. Disadvantages of Raft Foundation The disadvantages of raft foundation are as follows: * Insome cases, large amount of reinforcement is required for raft foundation which increases the cost of project. ml Special attention on raft foundations is required in case of concentrated loads, 1 of edge erosion. isa chanc + If they are not treated properly, there i ir isr ,ouNDATIONS f 4 Skilled workers are required to construct the raft foundations.