1. GENERAL

➢ Any building, it consists of two main components .

1. Sub structure: The structure which is below the ground

level.

2. Super structure: The structure which is above the

ground level.

CONTINUED….

Substructure Superstructure

The structure which is below

the ground level.

The structure which is above

the ground level.

It takes the load from

superstructure and transmits

the same to soil below it

over large area.

It provides shelter to users.

Usually foundations are

categorized under this.

Walls, columns, beams,

roofs, floors etc.

2. COMPONENTS OF BUILDING

CONTINUED….

1. Foundation: Substructure which transmits the load from

substructure to subsoil.

2. Plinth: The structure at ground level which connects

adjacent columns.

3. Walls: It divides area into several rooms.

4. Columns: Vertical components which transfers load

from beam and slab to footing.

5. Floors: Horizontal component which creates a platform

to users.

6. Doors: It provides accessibility to the users.

7. Windows: It provides accessibility to air and sunlight.

8. Ventilators: This is for ventilation.

CONTINUED..

9. Stairs: It provides accessibility between different floors.

10. Roofs: It is a horizontal member which protects and

covers the building from sun, wind and snow etc.

11.Building Finishes: Plastering and painting are provided

to protect from external agencies like sunlight, rain and

wind etc. It also increases the esthetic appearance.

12.Building services: Services like, water supply, drainage,

sanitation, electricity, heating, and air condition etc are

categorized under this.

3. FOUNDATION

➢ It is a substructure which transmits the load from

superstructure to subsoil.

PURPOSE OF FOUNDATION

➢ It distributes the load to the soil over large area.

➢ It avoids unequal settlements.

➢ It supports superstructure.

➢ To prevent lateral movement.

➢ It provides a rigid base and resists earthquake forces.

TYPES OF FOUNDATION

➢ Foundation are classified into two types

1. Shallow foundation: Depth of foundation is less than or

equal to width of foundation

2. Deep Foundation: Depth of foundation is greater than

width of foundation.

TYPES OF SHALLOW FOUNDATION

➢ Spread Footing

➢ Combine Footing

➢ Mat or Raft Foundation

➢ Grillage Foundation

➢ Strap Footing

➢ Stepped Foundation

SPREAD FOOTING

1. It is a common type of foundation provided in alluvial

or ordinary soil.

a. Wall Footing

b. Column Footing

c. Inverted Arch Footing

WALL FOOTING

➢ It is constructed by brick or stone.

➢ 50mm outside offset is provide on either side.

➢ Depth of each coarse is 100mm.

➢ 75mm outside offset is provided on either side for stone

masonry.

➢ A PCC layer is applied below the footing of thickness

100mm to 150mm.

WALL FOOTING

COLUMN FOOTING

➢ They are used to support individual columns.

➢ For heavy loaded columns steel reinforcement columns is

provide in both the directions in concrete bed.

➢ Based on shape.

It is classified as

a) Square Footing.

b) Circular Footing.

c) Sloped Footing.

d) Square Footing with Pedestals.

COLUMN FOOTING

INVERTED ARCH FOOTING

➢ It is used in structure like bridges.

➢ In this foundation, contact area of foundation increases

hence intensity of pressure reduced.

➢ It reduces depth of excavation.

➢ Series of inverted arches may be provided along the row

of piers.

➢ It depends on nature of soil and type of load coming on

the pier.

INVERTED ARCH FOOTING

COMBINED FOOTING

➢ A common footing is provided for two columns.

➢ This is of rectangular or trapezoidal in plan.

CONTINUED……

It is provided under following conditions.

➢ When two Columns nearer to each other.

➢ When SBC of soil in less.

➢ When the column is located near the property line, in

order to restrict footing line over property line.

➢ To have same pressure intensity trapezoidal footing is

provided.

3.MAT OR RAFT FOUNDATION

➢ Mat or raft foundation covers entire area of structure.

➢ It consists of slab and beams.

➢ It is suitable when heavy loads are to be carried and

when SBC of soil is very less.

➢ The area is well consolidated necessary reinforcement is

provided.

➢ It is suitable for public buildings, schools, office etc.

MAT OR RAFT FOUNDATION

CONTINUED….

Advantages of Mat or Raft Foundation:

➢ It is suitable for soft soil and marshy (watery soil).

➢ Overall settlement can be reduced.

➢ Load distribution is uniform.

➢ It carries more load.

GRILLAGE FOUNDATION

➢ It is applicable when the load of the structure is heavy

and SBC of soil is poor.

➢ It avoids deep excavation.

➢ Normally it is used for steel stanctions or columns.

➢ It consists of steel ‘I’ sections (Rolled mild steel joists)

➢ I sections are inter connected by spacer bar.

CONTINUED…

DIFFERENCES BETWEEN MAT FOUNDATION

AND GRILLAGE FOUNDATION

SLNo Mat Foundation Grillage Foundation

01 Casted over large area, no

columns are erected over

mat foundation.

It is provided for single

steel columns.

02 It is used when Isolated

column is not suitable.

Used in factory or

workshop sheds.

STRAP FOOTING

➢ In strap footing two or more footings are connected

together by a strap beam.

➢ It is provided when the soil is soft and subjected to heavy

load.

➢ The load on the boundary line column is balanced by

load on the inner column through a cantilever beam.

➢ The strap beam does not transfer any load to the soil but

it avoids differential settlement.

CONTINUED….

STEPPED FOUNDATION

➢ This type of foundation is provided in hilly areas.

➢ Plinth beam is constructed above the highest footing.

➢ Timber or steel pile is driven to avoid slipping of the

building.

WIDTH AND DEPTH OF SHALLOW FOUNDATION

Total Load = Dead Load + Live Load + Wind Load +

Snow Load.

Where t- Thickness of wall

x - Extension

1.

2.

Greater value of 1 and 2 is selected as width of footing

DEPTH OF FOUNDATION

It is calculated by Rankine’s formula.

Where

Df = Minimum depth of foundation in meters.

P0= SBC of soil in kN/m2

Γ = Density of soil per unit weight of soil in

kN/m3

Ø= Angle of repose.

DEEP FOUNDATION

➢ The foundation in which depth of foundation is very

large compared to width of foundation.

➢ When SBC of soil is very poor, when the area is

restricted to increase the width of footing then deep

foundation is laid.

➢ It increases durability and stability of the structure.

CONTINUED….

Types of deep foundation.

1. Pile Foundation.

2. Well or Cassion Foundation.

PILE FOUNDATION

➢ It is provided for buildings, bridges, flyovers etc.

➢ Pile is an element made of timber, concrete or steel etc.

➢ These are precast elements driven into the soil.

➢ When the soil is very loose pile foundation is preferred.

➢ The load transferred either by end bearing or by friction

developed on sides of piles.

APPLICATION OF PILE FOUNDATION

➢ It is applicable in water logged areas, compressible soils,

it can be used to any structures like buildings, docks and

harbors.

CONDITIONS AT WHICH IT IS USED

➢ When water table is at lower depth.

➢ Load is heavy.

➢ Other foundations are uneconomical to use.

➢ Loose soil to greater depth.

➢ To construct in marine structures.

TYPES OF PILES

1. Bearing pile

2. Friction pile

3. Sheet pile

4. Fender pile

5. Anchor pile

6. Batter pile

7. Compaction pile

8. Screw pile

BEARING PILE

➢ Piles are driven in to the soil

up to hard strata.

➢ These type of piles are

adopted when hard strata is

located at considerable

depth.

➢ This increases SBC of loose

soil to greater extent.

FRICTION PILE

➢ Piles are driven into the soil, piles bear the load from

friction developed on skin of piles and surrounding soil.

➢ When it is uneconomical to provide bearing piles to

greater depth then friction piles are driven.

➢ Piles are driven up to a depth when friction developed

will be equal to load transmitted on the pile.

➢ Friction can be increased by increasing the diameter of

pile, making the surface rough, by increasing the length

of pile.

CONTINUED….

DIFFERENCES BETWEEN BEARING PILE AND

FRICTION PILE

SL

No

Bearing Pile Friction Pile

01 Load transmitted to

hard strata.

Load transmitted by

friction developed by the

skin of pile.

02 Pressure of water does

not effect

Pressure of water reduces

friction

03 End Bearing piles Skin Friction piles

CONTINUED…..

CASSION’S FOUNDATION

➢ It is a special type of foundation used to construct piers

in bridges.

➢ It is a box like structure which will be water tight.

➢ It is placed inside the river with the help of cranes.

➢ It is made up of steel, timber or RCC.

FOUNDATION IN BLACK COTTON SOIL

➢ Black cotton soil is not suitable for construction because

SBC of soil is very less.

➢ It undergoes volumetric change due to change in

moisture.

➢ Soil develops wide cracks due to shrinkage.

➢ Crack develops up to greater depths.

PREVENTIVE MEASURES IN BLACK COTTON SOIL

➢ The SBC of soil must be from 50 to 100kN/m2

➢ Deep excavation is done.

➢ Water is not allowed up to the bottom of foundation.

➢ If depth of black cotton soil is up to 2m depth, whole soil is

replaced by imported soil.

➢ Bottom of foundation is compacted well by ramming.

WHEN DEPTH OF BLACK COTTON SOIL IS VERY

LARGE THEN

➢ When depth is from 1 to 1.5m and rain water does not

penetrate into the soil.

1. Excavation is done up to a depth of crack + 300mm.

2. The allowable SBC of soil must be less than 150kN/m2

3. Trench is rammed well and a layer of gravel is speeded over

the trench.

4. A layer of concrete bed is laid to a depth of 300 to 500mm

deep above the gravel.

5. The space left in between trench and wall is filled by sand.

ALTERNATIVE METHOD

It is used when depth of black cotton soil is quite large and

rain water may reach the bottom of trenches.

1. Trench is excavated up to 2m deep.

2. Side portion of trench is size filled with concrete of

250mmm x 250mm.

3. The space between concrete block is filled with sand.

4. A RCC slab of thickness 120 to 150mm is constructed

to complete width of trench.

CONTINUED…..

CONTINUED…

5. The space between masonry and trench faces is filled

with sand.

6. To drain off the water from bottom of trench pipes are

introduced between masonry at an interval of 1.5m.

These are pipes are led from the plinth level.

It is plugged at the top.

CONTINUED…

UNDER REAMED PILES

➢ These are most suitable for black cotton soil.

➢ The diameter of pile vary from 150mm to 500mm.

➢ Piles re driven with the help of machines.

➢ Reinforcement is provided inside the piles to bear all

types loads.

➢ Bulbs are introduced to increase the grip.

➢ SBC of soil can be increased by increasing number og

bulbs.

UNDER REAMED PILES

CAUSES FOR FAILURE OF FOUNDATION AND

PREVENTIVE MEASURES

➢ Unequal settlements of subsoil.

➢ Unequal settlement of masonry.

➢ Horizontal movement in adjoining soil.

➢ Moisture removal from subsoil.

➢ Lateral pressure on the superstructure.

➢ Action of atmospheric agencies.

CAUSES AND PREVENTIVE MEASURES

SL

No

Causes Preventive Measures

01 Eccentric loading Avoid eccentric loading

02 Load is not uniform. Foundation must rest on

rigid strata.

03 Low cement content . Use mortar of proper

portion 1:3.

04 Volumetric change in soil Depth of foundation must

be increased.

05 Reduction of water table

results in shrinkage.

Trees must be away from

the buildings (horizontal

distance =1.5x height of

tree.

NECESSITY OF SHORING AND STRUTTING IN

FOUNDATION

➢ If the foundation trenches are deep and the soil not firm,

the sides of trenches may be suitably sloped or it must be

supported by wooden planks.

➢ Ehen properly line is nearer to excavation, shoring is

provided.( When depth of trench is greater than 2 meter)

➢ If excavation is done in sandy type of soil

➢ When the soil is of clayey nature.

➢ It is provided in loose type of soil.

PROCESS OF DEWATERING

➢ When the water table is very high or in case of deep

excavation water is filled due to seepage water.

➢ Dewatering means removal of excess water from

saturated soil.

➢ Dewatering can be done by

1. Pumping.

2. Sumps.

3. Well Point.

Prepared by,

Naveen Kumar B.S.

Lecturer,

Department of Civil Engineering,

Government Polytechnic, Raichur