1. SANKALCHAND PATEL COLLEGE OF ENGINEERING,
VISNAGAR
FOUNDATION
SUB: BUILDING COUNSTRUCTION ( )
PREPARED BY:
PANDYA RUCHA H
GUIDED BY:
MR.AKSHAY B.PATEL

2. foundation
A foundation is the lowest part of a building or structure which is in the direct contact with ground to which the load are transmitted.
Types of foundation
Shallow foundation
Deep foundation

4. Spread footing Single footing for a column
Stepped footing for a column
Slopped footing for a column
Wall footing without step
Stepped footing for wall
Grillage foundation

6. Single footing for a column
A spread footing for a single column is either know as the isolated footing
The footing may be consist of simple concrete block projecting out from the column face on all sides.
The thickness of concrete block should at least be equal to side offset from the column face.

7. Stepped footing for a column
If the column load is more or if the safe bearing pressure of the soil is less ,the base area will be larger.
In such a case it is necessary to provide masonry offsets, to achieve larger spread, before the load is transferred to the concrete base .
Slopped footing for a column
Due to the low bending strength, the footing constructed with brick, stone or plain concrete require considerable depth to be safe to carry heavy load.
The depth of plain concrete footing can be reduce by providing reinforcement at its base.

8. Stepped footing for wall
When the wall carries heavy loads and the safe bearing pressure of the soil is not very high, the base width required much greater.
The masonry offsets are provided to achieve larger spread, before the load is transferred to concrete base.
If the walls having thickness ‘t’ cm the foundation width is equal to (2t + 30) cm and depth is equal to or more than the width of foundation.

9. Grillage foundation
A grillage foundation is an isolated footing provided when heavy structural loads from columns, piers or steel stanchions are required to be transferred to a soil having low bearing capacity
It is lighter and more economical for which deep excavation is not required and provides more area at the base, so that the intensity of pressure can be reduce within safe bearing capacity of soil.
Types of grillage foundation
Steel grillage foundation
Timber grillage foundation

11. Steel grillage foundation
Steel grillage foundation consists of steel joints or beams which are provided in single or double tiers.
In double tire grillage, the top tier is laid at right angles to the bottom tire.
The beams of each tier are held in position by 20 mm dia spacer bars with 25 mm. dia pipe separators.
A minimum clearance of 8 cm is kept between the beams, so that concrete can be poured easily and compacted properly.
A minimum cover of 10 cm is kept on the outer sides of the external beam.
The depth of concrete below the lower tier should be atleast 15cm.

13. Timber grillage foundation
It is provided for heavily loaded masonry walls or timber columns. This foundation is specially useful in waterlogged areas, where the bearing capacity of the soil is very low and where the steel beams may get corroded due to subsoil water.
The foundation uses timber planks and timber beams in the place of steel joints. No concrete is embedded between the timber joints.
Over platform, a tier wooden beams, 15*10 cm in size spaced at 30 to 50 cm is laid at right angles to the direction of the planks.
Over the top of this layer, a timber beam of same section as that of the wooden post is placed at right angles.
Timber post is fixed vertically to timber beam.

14. Combined footing

15. Combined footing

16. Combined footing

17. Combined footing
A combined footing is a single footing, which supports two columns. A combined footing is provided under the following circumstances:
When the column are very near to each other, so that their footing overlap.
When the bearing capacity of soil is less, requiring more area under individual footing
When the end column is near a property line so that its footing cannot spread in that directiont.
The aim of combined footing is to get uniform pressure distribution under the footing

18. Strap footing

19. Strap footing
A strap footing consists of two or more footing of individual columns, connected by a beam called strap.
The strap beam connecting the spread footing of the two column does not remain in contact with soil and thus does not transfer any pressure to the soil.
The strap beam is subjected to bending moment and shear force and it should be designed to withstand these.
Strap beam is to transfer the load of heavily loaded outer column to the inner one.

20. Raft foundation
A raft is combined footing, which covers the entire area below the whole building or structure and support all the walls and column
A raft foundation is preferred in the following situation:
When the allowable soil pressure is low or the building load are heavy and the use of spread footing cover more than one half of the area .
A raft foundation is also needed to reduce settlement on highly compressible soils, by making the weight of structure and raft approx equal to the weight of the soil excavated

21. Raft foundation consists of the thick reinforced concrete slab covering the entire area of the structure like a floor. The slab is reinforced with bars running at right angles to each other both near the bottom and top face of the slab.
Some times, it is necessary to carry the excessive column load by an arrangement of inverted main beams and secondary beams, cast monolithically with the raft slab.

22. Foundation in black cotton soil
Construction of building on black cotton soils is very much dangerous due to its volumetric changes with the change of atmospheric condition.
When the black cotton soil become wet, it will swell excessively and when become dry it will shrink excessively.
The differential settlement of the building, caused by the movement of the ground due to the alternate swelling and shrinkage, result in formation of cracks.

23. Precautions for foundation in black cotton soils
The minimum depth of foundation should be atleast 1.50m.
If the depth of black cotton soil does not exceed 1.5m, the entire layer of black cotton soil may be removed.
The bed of the foundation concrete or masonry work should not be in direct contact with the black cotton soil.
The construction in black cotton soil should be carried out during dry season
The external walls should be provided with plinth protection at ground level, so that moisture does not enter in foundation

24. Type of foundation in black cotton soils
Strip or pad foundation
Pier foundation
Under reamed pile foundation
Under reamed pile are bored cast in situ concrete piles of shallow depth, having bulb shaped enlargement near the base
The piles having one bulb known as single under reamed or two bulbs known as double under reamed piles, may be having 15 to 50 cm. diameter and spaced at 2 to 4 m
The pile are connected by rigid capping beam.

25. Under reamed pile foundation