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Types of foundation

Types of foundation. Prepared by : Prof. Alka M. Shah Civil Engineering Department Nirma University. What is Foundation ?. Lowest part of a structure directly in contact with the ground and transmits all the loads to the sub-soil below it .

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Types of foundation

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  1. Types of foundation Prepared by : Prof. Alka M. Shah Civil Engineering Department Nirma University

  2. What is Foundation ? • Lowest part of a structure directly in contact with the ground and transmits all the loads to the sub-soil below it. • Majority of structure fails due to failure of their foundation PURPOSE • To support structure • Distributes the loads over a larger area • Minimizes the differential settlements • Increases stability & prevents overturning • Distribute non-uniform load uniformly to the soil

  3. Foundation and Footing are same? • Foundation: Part of the structure which is in direct contact with the ground to which the loads are transmitted. • Footing: Lower most portion of foundation which is in direct contact with the sub soil is called footing.

  4. Types of Foundation

  5. SHALLOW FOUNDATION Suitability of FOUNDATION • Bearing capacity of soil is more. • ground water table(W.T) is low. • dewatering of foundation is not required. • top layers of soil are uniform and stable. • Load on the structure is less. Deep FOUNDATION • Bearing capacity of soil is low. • ground water table(W.T) is high. • dewatering of foundation is costly and difficult. • top layers of soil are non uniform and unstable. • Load on the structure is more.

  6. TYPES OF SHALLOW FOUNDATION 1) SPREAD FOOTING i) Continuous footing (strip or wall) ii) Isolated column footing a) Square b) Circular c) Rectangular iii) Inverted arch footing iv) Reinforced concrete footings 2) STRAP FOOTING 3) COMBINED FOOTING i) Rectangular ii) Trapezoidal 4) RAFT FOUNDATION 5) GRILLAGE FOUNDATION

  7. 1) SPREAD FOOTING • Carries a single column • Used to spread out loads from walls of columns over a wider area • Consists of concrete slabs located under each structural column and a continuous slab under load-bearing walls. • Commonly used due to their low cost & ease of construction. • Used in small to medium size structures with moderate to good soil condition. • For high rise buildings it is not efficient.

  8. Wall Footing Simple wall footing without masonry offsets (SBC is high) Wall footing with masonry offsets (Stepped wall footing) (SBC is low)

  9. STRIP/WALLFOOTING • A spread footing for a continuous wall is called strip footing. (Used to support load bearing walls)

  10. Inverted Arch footing • Used on soft soils to reduce depth of foundation. • End columns must be strong to resist outward pressure caused by arch action.

  11. Reinforced Concrete footing • Used where the walls are subjected to heavy loads & soil bearing capacity is low

  12. ISOLATED COLUMN FOOTING • Used to support individual columns.

  13. 2) COMBINED FOOTING • Supports two columns • the two columns are so close to each other that their individual footings would overlap • one column is placed right at the property line • C.G. of column load and centroid of the footing should coincide

  14. COMBINED FOOTING • Rectangular footing • Trapezoidal footing

  15. A combined footing will deform as shown in fig below • The eccentric loading condition upon the left end, due to the restrictions of a property line, will generate tensile stresses on the top of the footing.

  16. 3) CANTILEVER/STRAP FOOTING • Two isolated footings connected with a strap or beam • Connects in such a way that they behave as one unit • The strap acts as a connecting beam and does not take any soil reaction. The strap is designed as rigid beam. • It does not provide bearing

  17. to connect an eccentrically loaded column footing to an interior column. • Used to transmit the moment caused from an eccentricity to the interior • Can be used instead of combined footing if the distance between two columns is large • More economical than combined footings

  18. 4) RAFT FOUNDATION • Large reinforced concrete slab supporting no. of columns & walls • area of spread footings or combined footings exceeds about 50 percent of the gross area of the building • Greater weight & continuity of a mat provides sufficient resistance

  19. RAFT / MAT FOUNDATION

  20. RAFT / MAT FOUNDATION

  21. Raft/Mat Foundation is suitable under following conditions • Structural loads are heavy or the soil condition is poor • Soft or loose soils having less bearing capacity • Foundation soil is non-homogeneous and prone to excessive differential settlements • Lateral loads are non-uniform • Columns are so close that their individual footings would overlap • To resist water pressures when groundwater extends above the floor level of the lowest basement of a building • There is a large variation in the loads on individual columns

  22. 5) GRILLAGE FOUNDATION • Used to transmit heavy loads from steel columns to a soil having low bearing capacity • Avoids deep excavation • Reduces pressure intensity • Lighter & economical • Used in masonry bridge seat, bus stands, railways etc • Made up of a rolled steel joints (RSJ) known as grillage beams Types of Grillage foundation • Steel grillage foundation • Timber grillage foundation

  23. A type of foundation often used at the base of a column. It consists of one, two or more tiers of steel beams superimposed on a layer of concrete, adjacent tiers being placed at right angles to each other, while all tiers are encased in concrete. • This is dependable foundation and is used in those place where the load of the structure is pretty and bearing capacity of soil comparatively poor • The grillage foundation helps in distributing the load over a wider area of subsoil. • The grillage foundation helps in avoiding deep excavations as the necessary base area is provided for the load of transmission • This type of foundation generally used for heavy structure columns piers and steel stanchions etc.

  24. GRILLAGE FOUNDATION

  25. Steel Grillage foundation • Consists of rolled steel joists in single or double tiers

  26. Timber Grillage foundation • Uses timber planks & timber beams • No concrete is embedded between the timber joists • Used in waterlogged areas

  27. Grillage foundation for Wooden/Timber Post

  28. SHALLOW FOUNDATION Advantages: Cost (affordable) Construction Procedure (simple) Material (mostly concrete) Labour (doesn’t need expertise) Disadvantages: Settlement Foundation gets subjected to pullout, torsion etc Irregular ground surface(slope, retaining wall)

  29. TYPES OF DEEP FOUNDATION • PILE FOUNDATION • 2) CAISSONS OR WELL FOUNDATION • 3) COFFER DAMS

  30. 1) Pile foundation • Pile: Column-like foundations going deep into the subsoil. • Piles are structural members that are made of steel, concrete or timber. • Preferred: • i)When soil bearing capacity is poor. • ii) Non availability of proper bearing strata at shallow depth. • iii) pumping of sub soil water would be too costly. • iv)Heavy loads from super structure for which shallow foundation will be uneconomical.

  31. 1) Pile foundation Classification of pile foundation • Based on function: • -End bearing: Transfer load to through soil or water… • -Friction: Transfer load by means of skin friction… • -Compaction: Compacting loose granular material and thus increasing SBC… • -Tension(uplift): Anchor down the structures subjected to uplift due to hydraulic pressure or due to overturning…

  32. 1) Pile foundation Classification of pile foundation -Anchor: Provide anchorage against horizontal pull… -Fender and dolphins: Protect against impact from ships. -Sheet: To reduce seepage and uplift under hydraulic structures like dams…

  33. Under reamed piles • Under reamed piles are bored cast-in-situ concrete piles having one or more number of bulbs formed by enlarging the pile stem. • These piles are best suited in soils where considerable ground movements occur due to seasonal variations, filled up grounds or in soft soil strata. • Provision of under reamed bulbs has the advantage of increasing the bearing and uplift capacities. It also provides better anchorage at greater depths. • These piles are efficiently used in machine foundations, over bridges, electrical transmission tower foundation sand water tanks

  34. Caissons • The word caissons derived from the French word caisse meaning a box • Box like structure, round or rectangular which sunk from the surface of either land or water to some desired depth • Used for placing foundation under water

  35. Types of Caissons Pneumatic caisson (closed at top and open at bottom) Box caisson (open at top and closed at bottom) Open caisson or wells (open at top and bottom) Single, Multiple and Cylinder

  36. Box caissons • Strong water tight vessel • Built on land and floated up to site and then sink in to the water • Used when loads are not heavy • Bearing stratum is available at shallow depth • Water depth is 6 to 8 m • Foundation bed not required • Material is loose

  37. Open or Well caissons ( Well Foundation) • Used for buildings and bridge where soil liable to scour • No firm bed is available

  38. Pneumatic caissons • It is useful when well foundation is not possible • Depth of water 12 to 35 m

  39. Cofferdams • Cofferdam is a temporary structure which is built in a river, lake or dam to remove water from the area and make possible to construct • Require in dams, docks and bridge pier

  40. Types of Cofferdams 1. Earth fill cofferdam

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