BUILDING COMPONENTS Sub structure Super structure

Sand Filling Brick Masonry Floor Finish Foundation concrete Ground Level Step Plinth Floor Concrete Basement Door Lintel Roof Slab Parapet Weathering Course COMPONENTS OF A BUILDING Damp Proof Course Foundation

FOUNDATION

Foundation is the part of the structure which is in direct contact with the ground to which loads are transmitted.

A weak foundation destroys the work which is built upon it.

Functions of foundation Even distribution of load Reduction of load intensity Reduction of differential settlement Safety against sliding and overturning Safety against undermining Provide firm and level surface Protection against soil movement

Requirements of a good foundation Constructed to sustain dead load and imposed load and transmit them to underlying soil Rigid-to avoid differential settlement Taken to sufficient depth Performance should not be affected due to any unexpected future influence

Factors for the design Ultimate bearing capacity Safe bearing capacity Allowable bearing capacity Uniform settlement Differential settlement Bearing capacity of the soil 2. Settlement of foundations

BEARING CAPACITY Supporting power of soil without any failure Depends on : Properties of soil Position of water table Physical features of foundation like type, size & shape Ultimate Bearing Capacity : minimum gross pressure intensity at the base of foundation that the soil fails in shear Net Ultimate Bearing Capacity : minimum net pressure intensity at which the soil fails in shear Net safe bearing capacity : obtained by dividing the net ultimate bearing capacity of the soil with a suitable factor of safety Safe bearing capacity : Maximum pressure the soil can carry safely without the risk of shear failure

Settlement of foundations No settlement Total settlement Differential settlement Uniform settlement is usually of little consequence in a building, but differential settlement can cause severe structural damage.

Settlement of foundation means the sinking of foundation as a consequence of compression or deformation of the soil under the foundation Equal Settlement : The structures settles by uniform amount at each and every portion of the structure Unequal Settlement: The amount of settlement is different at different parts of the building

Causes of differential settlement: Causes of settlement: Due to weight of the structure transmitted to the soil Due to increased load on the surrounding soil Due to excavation near the foundation Lowering of water table Vibrations from moving machineries Deterioration of concrete by the chemical action of soil, seawater etc… Due to mining and tunnelling operations Causes of differential settlement: Non uniform load distribution on foundations Non uniformity of soil types Percolation of water Overlap and concentration of stresses due to presence of adjacent foun dations

Causes of foundation failure Unequal settlement of subsoil under the foundation Unequal settlement of the masonry Lateral movement of earth Shrinkage of soil bed due to seasonal variation of moisture content The penetration of the roots of trees Atmospheric action Lateral escape of the soil beneath the foundation Horizontal movement of the soil adjacent to the structure

Types of Foundations Shallow Foundations D<=B Deep Foundations D>B D - Depth of foundation B – Width of foundation

Shallow foundations Types of shallow foundations Isolated or column footing Wall or strip footing Combined footing Continuous footing Cantilever footing Raft or mat foundation

Isolated or column footing When the load on the column is less, a spread is given under the column

Wall or strip footing The foundation which is provided through out the length of a continuous structure is called strip footing.

Combined footing When a foundation or footing is constructed for two or more columns is called as combined footing Two individual footings overlap When bearing capacity is less when footings are constructed near boundaries of the plot Trapezoidal footing – when column loads vary considerably

Continuous footing A single continuous reinforced concrete slab is provided as foundation for three or more columns in a row. Continuous footing is more suitable to prevent the differential settlement in the structure and for the safety against earthquake.

Continuous footing

Cantilever Footing (Strap) Consists of an eccentric footing for the exterior column and a concentric footing for the interior column. A strap or a cantilever beam connects them.

Strap footing

Raft or mat foundation A raft foundation is a combined footing which covers the entire area beneath a structure and supports all the walls and columns

Raft or mat foundation

Mat foundation

Raft or Mat Foundation

Raft foundations are suitable when The building loads are heavy The allowable soil pressure is small Individual footings would require more than half the building area In highly compressible soil Weak spots and loose pockets in soil mass are suspected

Deep Foundation The foundations having very large depth compared to width are called deep foundations E.g. Pile foundations Well foundations

Pile Foundation Piles are long slender members driven into ground or cast at the site. Pile foundations are common where the soil conditions are unfavorable for the use of shallow foundations

Suitability of pile foundations Loose foundation soil but hard strata is available at a depth of 10-15 m Heavy dead and live loads Near seashore or riverbed where scouring action of water occurs Position of water table is likely to fluctuate appreciably Canals or deep drainage lines near by

Classification of Piles Method of load transfer Function or action Composition and material Installation

Classification based up on method of load transfer End bearing Piles Friction Piles

End bearing piles End bearing piles-Used to transfer load to a suitable bearing stratum

Friction piles Friction Piles- used to transfer the loads to a depth by friction along the surface area of the piles.

Classification based up on function or use Compaction Piles Tension or uplift piles Anchor Piles Fender Piles Sheet Piles

Compaction Piles

Anchor Piles and Tension piles Used to anchor structures subjected to hydrostatic pressure (against pilling or pushing forces) Anchor Piles and Tension piles

To protect water front structures like docks, harbours etc… against impact from ships Fender Piles

Used to retain the sides of excavation, to prevent seepage below dams, to construct retaining walls etc. Sheet Piles

Classification based up on material and composition Timber Piles Steel Piles Concrete Piles Composite Piles

Timber Piles perform well both in dry condition and in submerged condition

Used to resist lateral or horizontal forces. More durable. Steel Piles

Concrete Piles

Used when part of the pile is submerged under water Used when part of the pile is submerged under water. Made up of concrete and steel Composite Piles

Classification based upon installation Precast Piles Cast In Situ Piles

Precast Piles

CAST IN SITU PILES CASED CAST IN SITU PILES UNCASED CAST INSITU PILES

Well Foundations A well foundation is a well type structure, which built at the ground level and sunk into the soil at the required level. The bridge pier will be resting on the top of the well foundation. The bottom of the well is plugged with concrete. The top is covered with a well cap which is a thick concrete slab

The bottom edge of the well foundation consists of a cutting edge The bottom edge of the well foundation consists of a cutting edge. The different c/s adopted for well foundations are Circular Twin circular Double D Dumb bell Twin hexagonal Rectangular

Components of well foundation Well curb Cutting edge Steining Bottom plug Top plug Well cap

WELL CAP TOP PLUG STEINING SAND OR SOIL FILLING WELL CURB BOTTOM PLUG CUTTING EDGE

Well curb Cutting edge Steining Bottom plug Top plug Well cap Support the wt of the well Cutting edge Sharp angle for cutting the soil without making it too weak Steining Walls of the well Bottom plug Concrete plug provided to balance the soil pressure Top plug Concrete plug provided above the sand/soil filling Well cap Serves as platform for the supporting members of the superstructure

Well sinking operations Laying the well curb Construction of masonry in wall steining Well sinking Completion of well

Soil excavation

Construction of well cap

Machine foundation To support the dynamic forces produced by the operation of the machine To avoid large settlements at resonance, natural frequency of foundation should be different operating frequency of the machine

Types of machines Impact type Reciprocating type Centrifugal type Presses, forge hammers Reciprocating type Compressors, engines Centrifugal type Motors, turbines Miscellaneous types Machine foundation

BLOCK TYPE BOX TYPE WALL TYPE FRAMED TYPE

DETERMINATION OF BEARING CAPACITY

Plate load test

Plate load test

PLATE LOAD TEST It is a field test used to determine the ultimate bearing capacity of soil A pit is dug up to the foundation level A square plate of 300mm x 300mm & 25 mm is placed at the centre of the pit A dial gauge is connected to the test plate Now weights in the form of sand bags are placed on the platforms in equal increments. The test is continued till the failure occurs or the plates settled by 25 mm whichever occurs earlier The load settlement curve is then recorded.

Load v/s settlement graph

Standard Penetration Test

STANDARD PENETRATION TEST Test is conducted in a bore hole 50 to 150 mm in diameter Split spoon sampler (pipe-like weight) is driven into the ground by a weight of 65 kg weight is repeatedly raised and dropped a distance of 750 mm to drive in sampler number of blows required to drive the sampler for a penetration of 300mm is recorded The number of blows is known as penetration number (N Value) There are empirical charts from which the bearing capacity can be calculated based up on the N Value

Methods for improving Bearing Capacity Compaction Drainage Vibratory methods Chemical stabilisation Grouting Geotextiles