shallow foundation

A shallow foundation is a type of building foundation that transfers building loads to the earth very near to the surface, rather than to a subsurface layer or a range of depths as does a deep foundation. Shallow foundations include spread footing foundations, mat-slab foundations, slab-on-grade foundations, pad foundations, rubble trench foundations and earthbag foundations.

1. SHALLOW FOUNDATION Presented By A.Bharat kumar

2. FOUNDATION Lowest part of the Sub-structure. Provides a base for the super structure. Transmits the load on the structure including the dead weight of the structure itself to the soil below.

3. SHALLOW FOUNDATION Foundation placed immediately lowest part of the super structure. Used to distribute the structural load over a wide horizontal area at a shallow depth below the ground level. According to Terzaghi , a foundation is shallow if its depth is equal to or less than its width.

4. TYPES OF SHALLOW FOUNDTION Isolated spread footing Wall footing Combined footing Cantilever or Strap footing Raft or Mat foundation

5. ISOLATED SPREAD FOOTING Structural members are used to support columns and to transmit their loads to their loads to the soil.

6. SPREAD FOOTING

7. TYPES OF ISOLATED SPREAD FOOTING W all footing Reinforced footing Inverted arch footing Column footing

8. Wall footing Supports wall that may either be bearing or non bearing walls. Required to support direct concentric loads. Used in low rise buildings.

9. Reinforced concrete footing Relatively heavy loading than wall footing. Bearing capacity of soil is low. Reinforcing steel is placed in the bottom of the footing in a direction perpendicular to the wall.

10. Inverted arch footing Used to resist sideways, in wards loads. Used in conjunction with retaining walls.

11. Column foundation Most economical type of footing. Used when columns are spaced at relatively long distance. Carries heavy loads. Used to support single column. Distribute the load uniformly.

12. Combined footing Usually supports two or three columns not in a row. Used when two columns are so close that single footings cannot be used or when one column is located at or near a property line.

13. Combined footing

14. Cantilever or strip footing A strap footing is used to connect an eccentrically loaded column footing to an interior column. The strap is used to transmit the moment caused from an eccentricity to the interior column footing so that a uniform soil pressure is generated beneath both footings. The strap footing may be used instead of a rectangular or trapezoidal combined footing if the distance between columns is large and / or the allowable soil pressure is relatively large so that the additional footing area is not needed.

15. Cantilever or Strip foundation

16. Raft / Mat Foundation Consist of a thick reinforced concrete slab covering the entire area of the bottom of the structure (like a floor). Base soil has low bearing capacity or Column load are so large that more than 50% of the area covered by conventional spread footing. Resist unequal settlement due to earthquake. Quickness of construction work.

17. Raft / Mat Foundation

18. Types of Mat Foundation Flat plate mat Plate thickened under columns Two-way beam and slab Rigid frame mat Piled raft Plate with pedestal

19. Advantages of shallow foundation Quick process compared to others construction work. Economically cheaper. Can resist ground water absorption. Damage due to earthquake is lesser than any other type of foundation. Consist of reinforced concrete slab which is more thicker than footing foundation. Prevents unequal settlements.

20. Disadvantages of shallow foundation Spread footers being installed is too shallow (2-3 feet below), which does not eliminate the effects of expansive soil. Foundation repair will last longer than a week as the excavations are made and the concrete will have to be cured before the holes can be refilled. A huge amount of earthwork is to be done in mat foundation. Ground water may come out when earthwork is done. Limited to dealing with point loads.

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