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Content: Objectives and function of foundation Materials used for foundation Types of foundation Causes of failure of foundation

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Building Foundation

Foundation Design Principles:

Foundation Design Principles The main objectives of foundation design are to:- ensure that the structural loads are transmitted to the subsoil safely, economically and without any unacceptable movement during the construction period and throughout the anticipated life of the building or structure

Basic Design Procedure:

Basic Design Procedure Assessment of site conditions in the context of the site & soil investigation report Calculation of anticipated structural loading Choosing the foundation type , should consider: Soil condition Type of structure Structural loading Economic factors Time factors relative to the proposed contract period Construction problem Sizing the chosen foundation in the context of loading, ground bearing capacity & any likely future movement of the building / structure

Functions of foundation:

Functions of foundation Distribution of loads Stability against sliding & overturning Minimize differential settlement Safe against undermining Provide level surface Minimize distress against soil movement

Distribution of loads:

Distribution of loads Foundation help to distribute the loads of super-structure to a large of the soil Therefore, the intensity of load at its base does not exceed the safe bearing capacity of the soil In the case of deep foundations, the super imposed loads are transmitted either through end bearing or both by side friction & end bearing Functions of foundation

Stability against sliding & overturning:

Stability against sliding & overturning Foundation imparts lateral stability to the super structure by anchoring it to the ground It increases the stability against sliding & overturning due to horizontal forces to wind, earthquake, etc. Functions of foundation

Minimize differential settlement:

Minimize differential settlement Foundation distribute the super-imposed loads evenly on the sub-soil, even in the case of non-uniform loads This can be achieved by constructing combined footing or raft foundation Functions of foundation

Safe against undermining:

Safe against undermining Foundation provide safety against scouring or undermining by flood water or burrowing animals Functions of foundation Provide level surface It provides level surface over which super-structure can be raised

Minimize distress against soil movement:

Minimize distress against soil movement Distress or failure due to expansion or contraction of the sub-soil due to moisture variation in clayey & black cotton soils are minimized by the provision of special type foundations Functions of foundation

Types of foundations:

Types of foundations


PAD FOUNDATION Suitable for most subsoil except loose sand, loose gravels and fill areas Usually constructed of reinforced concrete, square in plan Typical pad foundation types are: Isolated or pad foundation Steel grillage Rectangular pad Combined column foundation

Strip foundation:

Strip foundation Suitable for most subsoil & light structure loadings Suitable for those encountered in low to medium rise domestic dwellings where mass concrete can be used Typical strip foundation types: Traditional strip Deep strip or trench fill Reinforced concrete strip Continuous column

Raft foundation:

Raft foundation Used to spread the load of the structure over a large base to reduce the load per unit area being imposed on the ground Particularly useful where low bearing capacity soils are encountered & where individual column loads are heavy Typical raft foundation: Solid slab raft Beam & slab raft

Pile foundation:

Pile foundation Can be defined as a series of columns constructed or inserted into the ground to transmit the loads of a structure to a lower level of subsoil Can be used when suitable foundation conditions are not presented at or near ground level Classification of piles (may be classified by their basic design function or method of construction): End bearing piles Friction or floating piles Replacement piles Displacement piles

Materials used for foundation:

Materials used for foundation Foundation must be constructed of a durable material of an adequate strength The most suitable material is concrete Concrete is a mixture of cement, aggregates & water in a controlled proportion


Cement Manufactured from clay & chalk Act as a binder of the concrete mix Cement can be supplied in bags ( 1 bag = 50kg) or in bulk Air tight sealed bags requiring a dry dump free store Bulk cement delivered by tanker (12 to 50 tonnes) & pumped into storage silo


Aggregates 2 types of aggregates: coarse & fine aggregates Coarse aggregate is defined as a material which is retained on a 5mm sieve Fine aggregate is defined as a material which is passes a 5mm sieve Aggregate can be either : Natural rock which has disintegrated Crushed stone gravels


Water Must be of a good quality fit for drinking Water is added to start the chemical reaction & to give workability The amount of water used is called the water/cement ratios, usually about 0.4 to 0.5 Too much water will produce a weak concrete mix of low strength Whereas too little water will produce a concrete mix of low & inadequate workability.

Concrete mix:

Concrete mix This concrete mix expressed as a ratio, e.g., 1:2:4 or 1:3:6/20mm, which means 1 part of cement 3 parts of fine aggregates 6 parts of coarse aggregate 20mm – maximum size of coarse aggregate for the mix

Causes of failure of foundation:

Causes of failure of foundation

There are many causes of foundation failure:

There are many causes of foundation failure Soil type – especially expansive clay soil Poorly compacted fill material Slope failure, mass wasting Erosion Poor construction, and Transpiration

Causes of Foundation Failure :

Causes of Foundation Failure

Soil Type – Expansive Clay Soil:

Soil Type – Expansive Clay Soil The most common kind of expansive clay can absorb so much water that it can swell by several hundred percent. The pressure from this degree of swelling can easily lift or “heave” most residential homes. Soils expand with moisture and they contract with dessication , causing up and down movements known as differential settlement. To preserve structural integrity of the building, we have to provide underpinning for the foundation.

Poorly Compacted Fill Material:

Poorly Compacted Fill Material If the fill material on a lot is not sufficiently compacted to support the weight of the structure above it, there will be foundation problems. The problem can be from the mix of odd fill materials, and from poorly compacted fil

Slope Failure / Mass Wasting:

Slope Failure / Mass Wasting Geologists use the term “mass wasting” to describe the movement of earth downhill. It could be “creep” which is slow, or “landslides” which are sudden. Slope failure as we use it refers to “creep”.


Erosion Erosion may be the most straightforward cause of settlement issues. It can come from poor drainage, uncontrolled water flow or lack of ground cover. If not identified early, erosion can wear away the soil around foundations, creating a new need for underpinning.

Poor Construction:

Poor Construction Most towns and cities now have building codes that require soil testing and engineer certification before and during the building process, so poor construction is less and less the cause of foundation failure.


Transpiration We all know what perspiration is, but transpiration is a less commonly known word. It is the word that describes plants removing moisture from the soil. Trees withdrawing moisture from the soil in the summer can accelerate soil shrinkage in hot summer months. It is the expansion and shrinking or contraction of soils that disturb the foundation.

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