Footings and Foundation - Engineering

7/28/2019 Footings and Foundation - Engineering

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FOOTINGSANDFOUNDATIONS


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WHAT IS FOUNDATION AND FOOTINGS

A foundation is a structure that transfers loads

to the earth.

A footing is typically concrete and reinforced

with steel. It is made to distribute the loading

of the structure to a much larger area.


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CATEGORIES OF FOUNDATION AND

FOOTINGS

DEEP FOUNDATION

SHALLOW FOUNDATION


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SHALLOW FOUNDATIONS

are usually embedded a meter or so into soil

One common type is the continuous spread

footing

Another common type is the wall footing

Combined footing


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WALL footing

Also known as Strip footing.

It is commonly is used in houses

This foundation is connected to the wall of thestructure


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COMBINED FOOTING

It is usually used when the footing is very

close to the property line

Transmits the loads from two or more

columns to the soil.


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CONTINUOUS SPREAD FOOTING

is commonly used to provide a stable base

around the perimeter of a structure or

building, supports the weight or load from the

exterior or foundation walls. The footing

thickness provides the strength to support the

weight. The wider width of the footing base

creates a large area to transfer the weight tothe ground and to prevent settlement.


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EXAMPLE SLAB-ON-GRADE FOUNDATION


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DEEP FOUNDATION

are used to transfer a load from a structurethrough an upper weak layer of soil to astronger deeper layer of soil.

can be installed by either driving them intothe ground (Driven foundation)or drilling ashaft and filling it with concrete, mass orreinforced (Drilled foundations).

can be made out of timber, steel, reinforcedconcrete and pre-tensioned concrete.


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DRILLED FOUNDATIONS

Also called drilled piers or Cast-in-drilled-

hole piles (CIDH piles) or Cast-in-Situ piles.

Construction methods depend on the

geology of the site (Dry and Wet boring

methods).

KINDS OF DRILLED FOUNDATION


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DRY BORING METHOD

employ the use of a temporary casing to seal

the pile bore through water-bearing or

unstable strata overlying suitable stable

material.

Upon reaching the design depth, a reinforcing

cage is introduced, concrete is poured in the

bore and brought up to the required level.

The casing can be withdrawn or left in situ.


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WET BORING METHOD

also employs a temporary casing through

unstable ground and is used when the pile

bore cannot be sealed against water ingress.

Boring is then undertaken using a digging

bucket to drill through the underlying soils to

design depth


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KINDS OF DRILLED PILES

Underreamed Piles

Auger Cast Piles

Pier and Grade Beam Foundations Specialty piles


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Underreamed Piles

have mechanically formed enlarged bases that

have been as much as 6 m in diameter

The form is that of an inverted cone and can

only be formed in stable soils

they allow very high load bearing capacities


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Auger Cast Piles

often known as a CFA pile

is formed by drilling into the ground with a

hollow stemmed continuous flight auger to

the required depth or degree of resistance


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Pier and Beam Foundations

In most drilled pier foundations, the piers are connectedwith grade beams - concrete beams at grade (alsoreferred to as 'ground' beams) - and the structure isconstructed to bear on the grade beams, sometimes with

heavy column loads bearing directly on the piers. In some residential construction, the piers are extended

above the ground level and wood beams bearing on thepiers are used to support the structure.

This type of foundation results in a crawl spaceunderneath the building in which wiring and duct workcan be laid during construction or remodeling.


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SPECIALTY PILES

MICROPILES

TRIPOD PILES

SHEET PILES SOLDIER PILES

SUCTION PILES


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MICROPILES

Micropiles, also called mini piles, are used for underpinning.

Micropiles are normally made of steel with diameters of 60 to

200 mm.

Installation of micropiles can be achieved using drilling,

impact driving, jacking, vibrating or screwing machinery.

Where the demands of the job require piles in low headroom

or otherwise restricted areas and for specialty or smaller scale

projects, micropiles can be ideal.

Micropiles are often grouted as shaft bearing piles but non-

grouted micropiles are also common as end-bearing piles.


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EXAMPLE OF MICROPILE

INSTALLATION


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TRIPOD PILES

The use of a tripod rig to install piles is one of themore traditional ways of forming piles, andalthough unit costs are generally higher than withmost other forms of piling, it has several

advantages which have ensured its continued usethrough to the present day. The tripod system iseasy and inexpensive to bring to site, making itideal for jobs with a small number of piles.

It can work in restricted sites (particularly whereheight limits exist), it is reliable, and it is usable inalmost all ground conditions.


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SHEET PILES

Sheet piling is a form of driven piling using

thin interlocking sheets of steel to obtain a

continuous barrier in the ground. The main

application of steel sheet piles is in retaining

walls and cofferdamns erected to enable

permanent works to proceed.


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SOLDIER PILES

Soldier piles, also known as king piles or Berlinwalls, are constructed of wide flange H steelsections spaced about 2 to 3 m apart and aredriven prior to excavation. As the excavation

proceeds, horizontal timber sheeting (lagging) isinserted behind the H pile flanges.

The horizontal earth pressures are concentratedon the soldier piles because of their relative

rigidity compared to the lagging. Soil movementand subsidence is minimized by maintaining thelagging in firm contact with the soil.


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SOLDIER PILES


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SUCTION PILES

Suction piles are used underwater to secure

floating platforms.

Tubular piles are driven into the seabed (or

more commonly dropped a few metres into a

soft seabed) and then a pump sucks water out

the top of the tubular, pulling the pile further

down.

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Footings and Foundation - Engineering