Building Foundation, Types of foundation

We all know the building has two main parts, i.e.Foundation or Sub-Structure and superstructure.

The foundation or sub-structure is the lowest part of the the structure which directly transmits the load to the soil.

While the lowermost portion of the foundation which is in direct contact with the sub-soil is called footing.

 Types of foundation –

Types of foundation

The foundations may be broadly classified as shallow foundation and deep foundation.

Again shallow foundations can be subdivided into four categories –

1.       Spread footing

1.       Combined footing

1.       Strap footing

1.       Mat foundation.

Deep foundations may be following types –

1.          Deep strip, rectangular or square footing

1.          Pile foundation

1.          Pier foundation

1.          Well, foundation.

Also Read:- Ground-improvement-technique-in-soil.

The foundation must be considered sound and stable against What are the basic criteria for the design of the foundation?

The following criteria are given below –

1. Shear failure.
2. The soil at the foundation must not settle beyond tolerable limits.
3. The soil must not be subjected to local erosions due to flow of water, underground defects e.g. cavities, unconsolidated filled up the soil, GWT, expansive soils, etc.
4. The design loads including dead, wind load, seismic loads lateral pressures on the embedded structure, the effect of dynamic load also governs the foundation design.

What are the uses of the Foundation?

Types	Uses
Pile foundation	To compact a loose soil layer.  To hold structures subjected to uplift.  To provided anchorage against the horizontal pull.  To protect waterfront structures.  To resist oblique compressive loads.
Well, foundation or open caissons.   Box caisson Open caisson Pneumatic caisson	Where bearing structure is at shallow depth and where loads are not heavy. Used for bridge foundation. Used to prevent the entry of water and to permit excavation in dry.
Pier foundation or drilled caissons.	Used to accommodate the bridge piers.

Also, Read- one-example-analysis-of-rate.

What are the essential requirements of a good foundation?

The foundations shall be constructed to sustain the dead and imposed loads and to transmit these to the subsoil in such a way that pressure on it will not cause settlement which would impair the stability of the the building or adjoining structures.

Foundation base should be rigid so that differential settlement are minimized, especially for the case when super-imposed loads are not evenly distributed.

Foundations should be taken sufficiently deep to guard the building against damage or distress caused by swelling or shrinkage of the sub-soil.

Foundations should be so located that its performance may not be affected due to any unexpected future influence.

Also Read:- Rise and Fall method in Surveying.

How you will determine the width and depth of the foundation?

 Width of foundation: It is obtained by dividing the total load including dead load, live load and wind load by the allowable bearing capacity of the soil.

B = T/P

Where,

           B = Width of the foundation in m

           T = Total load per meter run in kg.

           P = safe bearing capacity of soil in kg/m³

Depth of Foundation:

The minimum depth of foundation is obtained by Rankine’s formula

D =   P/W(1- sinƟ/1+ sinƟ)²

Where,

            P = safe bearing capacity of soil in kg/m³

           W = unit weight of soil in kg/m³

           Ɵ = angle of repose of the soil in degrees.

           D = Minimum depth of foundation in m.

What are the causes of failure of foundation?

1. Unequal settlement of the sub-soil under the foundation
2. Unequal settlement of the masonry
3. Lateral movement of earth, increasing horizontal pressure which tends to over-turn the structure.
4. Horizontal movement of the soil adjacent to the structure
5. Shrinkage of the soil bed due to seasonal variation of  moisture content
6. Lateral escape of the soil beneath the foundation
7. Atmospheric action.

Follow us on Facebook:- totalcivilstudy/facebook


Subscribe our youtube channel:- Specialised Civil