SHALLOW FOUNDATION

PREPEARED BY MOHAMMAD SHAHIDB.ARCH 3RD YR

INTRODUCTION TO FOUNDATION

The lowest part of a structure is generally referred to as foundation.

FUNCTION OF FOUNDATION To transfer load of the superstructure to the soil on which it is resting

REQUIREMENTSA properly designed foundation is one that transfers the structural load throughout the soil without overstressing of soil which can result in either excessive settlement or shear failure, both of which can damage the structure.

Types of loads on foundations Dead, live, wind, inclined thrusts and uplift, water table and earthquake forces

Types of settlements Uniform and differential - Differential settlement must be minimized, depends on site soil conditions and distribution of loads on columns supporting the building

LOADS AND SETTLEMENT OF FOUNDATIONS

TYPES OF FOUNDATION

Foundations are classified as

SHALLOW FOUNDATION AND DEEP FOUNDATION 1. Shallow foundation- It has a smaller depth limited to the depth

of the footing. It spreads the load from superstructure on a larger area of soil.

They are classified asa. Isolated footing b. Combined footing

An isolated footing supports one wall or one column .either flatOr stepped which distribute the Load of wall to the soil. An Isolated footing supporting a Single column is commonly Used where the loads on column are Small and columns are not closely Spaced. They are of the following Shapes.

Footing for column Footing for wall

SQUARE SPREAD FOOTINGS / PAD FOUNDATION

support a single centrally located column use concrete mix 1:2:4 and reinforcement the reinforcement in both axes are to resist/carry tension loads.

RECTANGULAR SPREAD FOOTINGS

Useful when obstructions prevent construction of a square footing with a sufficiently large base area and when large moment loads are present

CIRCULAR SPREAD FOOTINGS

are round in plan viewmost frequently used as foundation for light standards, flagpoles and power transmission lines

Also known as a footer or footing

It’s an enlargement at the bottom of a column/ bearing wall that spreads the applied structural loads over a sufficiently large soil area.

Each column & each bearing wall has its own spread footing, so each structure may include dozens of individual footings.

SPREAD FOOTING FOUNDATION

SPREAD FOOTING

The spread foundation consists of concrete slabs located under each structural column and a continuous slab under load-bearing walls. For the spread foundation system the structural load is literally spread out over a broad area under the building

It is most common type of foundation used due to their low cost & ease of construction.

COMBINED FOOTINGS

Combined footing supports two or more columns.Combined footing supporting two columns may be used for column on property lines.

When the bearing capacity of the soil is low , then continuous strip footings supporting more than two columns in a row are provided. Such strip footings more than two columns in both the directions are known as grid foundation.

GRID FOUNDATIONS

A foundation system in which essentially the entire building is placed on a large continuous footing.

It is a flat concrete slab, heavily reinforced with steel, which carries the downward loads of the individual columns or walls.

Raft foundations are used to spread the load from a structure over a large area, normally the entire area of the structure.

It is normally consists of a concrete slab which extends over the entire loaded area.

It may be stiffened by ribs or beams incorporated into the foundation.

Raft foundations have the advantage of reducing differential settlements as the concrete slab resists differential movements between loading positions.

They are often needed on soft or loose soils with low bearing capacity as they can spread the loads over a larger area.

RAFT FOUNDATION

PLAN

ELEVATION

VIEW

DEPTH AND LOCATION OF FOUNDATION

Depth and location of foundation depends on 1. Zone of significant volume changes in soil.

2. Adjacent structures and property lines.

3. Ground water

4. Underground defects

Structures may be damaged by the construction of new foundations, as a result of vibrations, undermining by excavation or lowering of the water table. After new foundations have been constructed, the (new) loads they place on the soil may cause settlement of previously existing structures as a result of new stress pattern in the surrounding soil.

Adjacent structures and property lines.

In general, deeper the foundations and closer to the old structure, greater will be the potential for damage to old structures.

Part existing property line

Property line

Ground water

Presence of water reduces soil bearing capacity, larger footing size more cost. During construction pumping is necessary – adds to the cost of construction.

Thank you