Foundation and its types

foundation - definition, functions, characteristics, types based on various factors, piles, piers, caissons, well foundations, shallow foundations

1. FOUNDATION S.MANIKANDAPRABHU @ SARAVANAN

2. DEFINITION Foundation is a structural part of a building on which a building stands. The foundation of a building is that part of walls, piers and columns in direct contact with the ground and transmitting loads to the ground . The lowest load-bearing part of a building, typically below ground level .

3. FUNCTIONS Distribution of Load Reduction of Load Intensity Safety Against Undermining Lateral Stability Protection Against Soil Movements

4. FUNCTIONS Foundations distribute the non-uniform load of the super structure evenly to the sub soil. Foundation distributes the loads of the super structure, to a larger area so that the intensity of the load at its base does not exceed the safe bearing capacity of the soil. Foundation anchors the super structure to the ground, thus imparting lateral stability to the super structure.

5. FUNCTIONS It provides the structural safety against undermining or scouring due to burrowing animals and flood water. Special foundation measures, prevent or minimizes the distress (or cracks) in the super structure, due to expansion or contraction of the sub soil because of moisture movement in some problematic soils.

6. CHARACTERISTIC The foundation, including the underlying soil and rock, must be safe against a structural failure that could result in Collapse During the life of the building, the foundation must not settle in such way as to damage the structure or impair its function The foundation must be feasible both technically and economically and practical to build without adverse effect to surrounding property

7. CHARACTERISTIC All foundations settle to some extent as the soil around and beneath them adjusts itself to the loads of the building Foundations on bedrock settle a negligible amount Foundations on certain types of clay may settle to an alarming degree, allowing buildings to subside by amounts that are measured in feet or meters Foundation settlement in most buildings is measured in millimeters or fractions of an inch Most foundation failures are attributable to excessive differential settlement.

8. SETTLEMENT

9. FACTORS AFFECTING DESIGN Soil types and ground water table conditions. Structural requirements and foundations. Construction requirements . Site condition and environmental factor. Economy etc.

10. TYPES OF FOUNDATION Shallow foundation Deep foundation 

11. SHALLOW FOUNDATION The foundation provided immediately below the lowest part of the structure near the ground level, transferring load directly to the supporting soil, is known as shallow foundation. Shallow foundation is provided when stable soil with adequate bearing capacity occur near to the ground level. Requirements: Suitable soil bearing capacity Undisturbed soil or engineered fill

12. SHALLOW FOUNDATION Strip footing/wall footing/continuous footing. Spread or isolated footing. Combined footing Strap or cantilever footing. Mat or raft Foundation. Inverted arch footing Grillage foundation

13. STRIP FOOTING This is also known as Wall Footing. This footing is provided throughout the length of the wall and may be either stepped or single. These are used for light structures . E.g. Load bearing walls.

14. SPREAD OR ISOLATED FOOTING The spread / isolated / pad / column footing is generally constructed to support an individual column. The spread footing may be circular, square or rectangular slab of uniform thickness. Sometimes it may be designed as stepped or launched to spread/distribute the load over a larger area.

15. COMBINED FOOTING The combined footing is designed to support two parallel columns. It is principally used what the two columns are so close that to one another that their individual footing would overlap. By combining it with that of an interior column, the load gets evenly/uniformly distributed.

16. STRAP/CANTILEVER FOOTING A balanced footing which is also called as strap footings consists of two separate footings connected by a strap beam. Balanced footing is required where the one of the footing has limited space for bearing, or if there is any restriction over the transfer of pressure from the footing to the ground. This case may arise where there is difference in soil bearing capacity, or loose soil beneath one of the footing . The loads in a balanced footing is transferred from one footing to the other by means of cantilever action .

17. STRAP/CANTILEVER FOOTING

18. MAT OR RAFT FOOTING A mat or raft foundation is a large slab supporting a number of columns and walls under the entire structure or a large part of the structure. A mat is required when the allowable soil pressure is low or where the columns and walls are so close that individual footings would overlap or nearly touch each other Mat foundations are useful in reducing the differential settlements on non-homogeneous soils or where there is a large variation in the loads on individual columns

19. MAT OR RAFT FOOTING

20. INVERTED ARCH FOOTING It is constructed on soft soils. This type of foundation is suitable for bridges, reservoirs and tanks.

21. GRILLAGE FOUNDATION 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.

22. GRILLAGE FOUNDATION

23. DEEP FOUNDATION A deep foundation is a type of foundation which transfers building loads to the earth farther down from the surface than a shallow foundation does, to a subsurface layer or a range of depths. Deep foundations can be used to transfer the load to a deeper strata at depth if unsuitable soils are present near the surface. A pile is a vertical structural element of a deep foundation, driven or drilled deep into the ground at the building site.

24. DEEP FOUNDATION Selection of pile foundation types and length depends on following conditions: Soil conditions Loads from structures Nature of loads Number of piles to be used Cost of construction Installation Method

25. TYPES OF DEEP FOUNDATION Pile foundation Pier foundation Well foundation

26. PILE FOUNDATION Pile foundations are common type of deep foundation. These  are relatively long, slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. In  addition to supporting structures, piles are also used to anchor structures against uplift forces and to assist structures in resisting lateral and overturning forces.

27. NEED FOR PILE FOUNDATION Top layers of soil are highly compressible Depth/Width >4 Low Bearing Capacity of soil . Non availability of proper bearing stratum at shallow depths. Heavy loads from the super structure for which shallow foundation may not be economical or feasible. Lateral forces are relatively prominent. In presence of expansive and collapsible soils at the site. Offshore structures Strong uplift forces on shallow foundations due to shallow water table can be partly transmitted to Piles.

28. CLASSIFICATION OF PILE FOUNDATION Based on material Concrete Steel Timber Based on Load transfer mechanism End bearing piles Friction/Floating piles Bearing cum Friction piles

29. CLASSIFICATION OF PILE FOUNDATION Based on method of construction/installation. Driven /Displacement Pre cast Piles Driven/Displacement Cast in Situ Piles Bored/ Replacement Pre cast piles Bored/ Replacement Cast in situ piles. Based on inclination Vertical Piles Inclined/ raker Piles

30. TIMBER PILES Timber piles are mainly used to support light to moderate loading structures. They are widely used for compaction of soils and for the construction of temporary structures. They are also used in the protecting water- front structure . The main advantages of timber piles are, they are easy to handle, low initial cost, durable in non-fluctuating weather conditions. 

31. TIMBER PILES

32. CONCRETE PILES Concrete piles are the widely used for heavily loaded structures. Concrete piles can be pre-cast or cast in-situ piles. The precast piles may use ordinary reinforcing bars or pre-stressed bars depending on the usage and the loading conditions The main advantage is the higher loading capacity and ease in construction . Disadvantages include high initial cost, requirement of treatment when used in corrosive areas, marine environment and splicing in case of prestressed piles.  

33. CONCRETE PILES Disadvantages include high initial cost, requirement of treatment when used in corrosive areas, marine environment and splicing in case of pre-stressed piles.

34. STEEL PILES   Steel piles of various cross sections such as Hollow steel tubes, Box sections,  H-sections, built -up sections are available and have to be chosen carefully according to the site conditions. Steel piles are easy to splice, handle and install where deep penetrations are required. They can withstand high driving forces and any damage to the pile head can be rectified by trimming them and splicing with a newer section . Steel piles are best suited where ground heave and lateral displacements are to be avoided.

35. STEEL PILES  

36. PRE-CAST CONCRETE PILES These piles are manufactured in factory. The precast concrete piles are generally used for a maximum design load of about 80 tons. They may be reinforced to withstand handling stresses. It can be driven under water, if the subsoil water contain sulphate the concrete for cast insitu piles would not set. It is highly resistant to biological and chemical reaction of subsoil.

37. PRE-CAST CONCRETE PILES

38. BASED ON LOAD TRANSFER MECHANISM End Bearing Pile If the pile transmits the load from the structure to a considerable strong stratum mainly through the resistance developed at the bottom or tip of the pile, then it is called as end bearing pile. Friction Piles If the prominent load transfer is primarily by  friction along the surface of the piles, then they are termed as frictional piles. Friction piles are generally used in low to medium dense sand and where hard strata is not available at reasonable depth. End Bearing cum Frictional Piles In few cases, the load transfer will be a combination of both end bearing and frictional resistance.

39. BASED ON LOAD TRANSFER MECHANISM

40. Based on Load transfer mechanism End bearing Friction Pile

41. Based on Load transfer mechanism End bearing Friction Pile

42. BASED ON METHOD OF CONSTRUCTION Driven pre-cast pile: The pile is casted in a yard brought to the site and driven by some mechanism into the soil. Driven cast-in-situ pile: A casing plugged at bottom is driven into the ground and then the pile is casted by removing or retaining the casing. Bored pre-cast pile: A bore is made and the soil inside is removed and then a pile casted in some yard is put into the bore. Bored cast-in-situ pile: A bore is made the soil is removed and the pile is casted at site in the bore.

43. BASED ON INSTALLATION TYPE - REPLACEMENT PILES These piles are either bored and cast in-situ piles or drilled-in tubular piles. In both the cases, the earth is removed where the pile has to be installed and is then filled with reinforced concrete or precast sections are erected. Steel liners, bentonite slurry may also be used according the prevalent soil condition in the site. These replacement piles do not provide any additional consolidation or displace the surrounding soil and hence ground heaving is avoided. Due to no displacement during installation, there is no heave in the ground.

44. Cast in-situ piles may be cased or uncased (by removing casing as concreting progresses). They may be provided with reinforcement if economical with their reduced diameter. Enlarged bottom ends (three times pile diameter) may be provided in cohesive soils leading to much larger point bearing capacity. Example: Bored cast in situ or pre casts pile BASED ON INSTALLATION TYPE - REPLACEMENT PILES

45. BASED ON INSTALLATION TYPE REPLACEMENT PILES

46. Displacement piles are either solid sections or hollow sections with a closed end driven into the soil, thus displacing the soil around them. They are mainly used where there are no restrictions on ground heaving and lateral displacement of soil. Displacement piles are mainly preferred in marine structures . Displacement piles are either solid sections or hollow sections with a closed end driven into the soil, thus displacing the soil around them. They are mainly used where there are no restrictions on ground heaving and lateral displacement of soil . BASED ON INSTALLATION TYPE - DISPLACEMENT PILES

47. In loose cohesionless soils Densifies the soil upto a distance of 3.5 times the pile diameter (3.5D) which increases the soil’s resistance to shearing The friction angle varies from the pile surface to the limit of compacted soil In dense cohesionless soils The dilatancy effect decreases the friction angle within the zone of influence of displacement pile (3.5D approx.). Displacement piles are not effective in dense sands due to above reason. BASED ON INSTALLATION TYPE - DISPLACEMENT PILES

48. In cohesive soils Soil is remolded near the displacement piles (2.0 D approx.) leading to a decreased value of shearing resistance. Pore-pressure is generated during installation causing lower effective stress and consequently lower shearing resistance. Excess pore-pressure dissipates over the time and soil regains its strength. Example : Driven concrete piles, Timber or Steel piles BASED ON INSTALLATION TYPE - DISPLACEMENT PILES

49. Piles Larger than 600mm in diameter are called Large Diameter Pile. Size 300 to 600mm are called normal or small diameter pile. Pile 150 to 250mm are called mini piles. Pile less than 150 mm diameter are classified as micro piles. BASED ON SIZE

50. PIER FOUNDATION TYPE Pier foundations may be of the following types: Masonry or concrete pier Caissons .

51. PIER For homes and light commercial building, concrete piers or concrete column that are formed by pouring liquid concrete into holes drilled into the ground.

52. TYPES OF CAISSON Box Caissons Excavated Caissons Floating Caissons Open Caissons Pneumatic Caissons Sheeted Caissons

53. BOX CAISSONS  Box caissons are watertight boxes that are constructed of heavy timbers and open at the top. They are generally floated to the appropriate location and then sunk into place with a masonry pier within it.

54. EXCAVATED CAISSONS  Excavated caissons are just as the name suggests, caissons that are placed within an excavated site. These are usually cylindrical in shape and then back filled with concrete.

55. FLOATING CAISSONS Floating caissons are also known as floating docks and are prefabricated boxes that have cylindrical cavities.

56. OPEN CAISSONS Open caissons are small cofferdams that are placed and then pumped dry and filled with concrete. These are generally used in the formation of a pier.

57. PNEUMATIC CAISSONS Pneumatic caissons are large watertight boxes or cylinders that are mainly used for under water construction.

58. WELL FOUNDATION Well foundation is a type of deep foundation which is generally provided below the water level for bridges They are quite appropriate for alluvial soil in rivers and creeks where maximum depth of scour can be quite large They are also known as caisson foundation or pier foundation

59. WELL FOUNDATION Caisson is a cylinder or hollow box that is sunk into the ground to a specified depth by auguring a deep hole into the strata. The cylinder or box is then back filled with concrete, thus creating the foundation

60. WELL FOUNDATION

61. ADVANTAGES It is easily adaptable to varying site conditions. This means that no matter where the structure is being constructed, caissons can be easily put in place. The hardest part of placing them is the drilling of the holes. High axial and lateral load capacity for these foundations. The weight of the structure can be easily held by the piers and is very sturdy. They are very economical. The cost to drill and install the caissons is minimal when compared to the cost to any traditional foundation .

62. Piers minimize the need for pile caps. Because the piers are filled with concrete, pile caps are really not necessary. The caisson foundation will reduce vibrations and has slightly less noise. Since the foundation is based on piers, there are less vibrations that will upset the structure. ADVANTAGES

63. There is a lack of expertise of these types of foundations. Construction managers and crews are not as familiar with the procedures and protocols related to caissons. Piers cannot be placed on contaminated sites. Due to the amount of drilling required to place the caissons and pour the concrete, they cannot be placed in an area where the soil has been contaminated The construction procedures for placing caissons is very sensitive. This is why there are not many construction managers who are willing to work on a job requiring caissons to be placed. There is a major lack of inspectors who are qualified to inspect the construction of caisson foundations to ensure that they are safe and secure. DISADVANTAGES

64. Cutting edge Well curb Bottom plug Steining Top plug Well cap SECTIONS OF WELL FOUNDATION

65. DIFFERENT SHAPES OF WELL FOUNDATION Circular Double D Double Octagonal Twin Circular Rectangular Double Rectangular The choice of a particular shape of well depends upon the size of the pier, the care and cost of sinking, the considerations of tilt and shift during sinking and the vertical and horizontal forces to which well is subjected.