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"Important NOTE!!!" Information Provided On This Website Is Intended For... "GENERAL INFORMATION
ONLY!!!" And Must Be Only Be Used Only As A "GUIDE!!!" It Must Not Be Used For Decision Making, Or
Be Used For Any Building Purposes Or Legal Proceedings. Refer To Our Policies On This Website.

An Under-pinning Design!!! Is The Process By Which The Foundation
Of An Existing Building Or Structure Is Strengthened A
nd Stabilized.

It is an important part of civil engineering... and is carried out due to many reasons.

Some of the reasons which warrant  an Under-pinning design are:

* The original foundation has become weak and unstable.

* The structure is being used for a different purpose from what it was originally designed for.

* The soil under the property structure has changed its abnormality or the soil properties were not properly analyzed during the original construction.

* Nearby construction excavation has led to weakening of soil under the foundation.

* The cost of under-pinning works out cheaper than constructing a new building, or shifting elsewhere.

The basic strategy of under-pinning is to extend the depth and breadth of the foundation, so that it's
supported by more stable soil!!! and the load is spread over a larger area.

There Are Many Methods Associated With An Under-pinning Design.

Some of the methods are:

* Mass concrete under-pinning.

* Beam and base under-pinning.

* Mini piled under-pinning.

MASS CONCRETE UNDER-PINNING:

This is the good old method... and has been used by civil engineers for more than one hundred years.

The advantage off this method is... its simplicity and low cost.

The added advantage is!!! that it can be carried out even when the existing structure is in use.

Basically, this type of under-pinning uses manual methods. It strengthens the existing foundation by
manually digging boxes underneath it... and pouring concrete into the excavation.

Boxes are dug in sequential order!!! and concrete is poured into the box.

The sequence of the boxes and the pouring of concrete etc. depend on site conditions. Since heavy machinery is not used, all that's required is... labor and hand held tools.

Work can proceed even in tight spaces.

BEAM AND BASE UNDER-PINNING:

This method has its root in the old mass concrete under-pinning method. It is technically more advanced,
and a greater strength can be achieved in the under-pinning process.

A new reinforced concrete beam is constructed, either above or below, the existing footing.

A number of concrete bases are constructed in strategic places!!! and the newly constructed beam
transfers the load to the bases.

This reduces the load on the existing foundation... as the under-pinning acts as a support.

The base size, depth and locations vary according to the site conditions. The beam is designed by taking
into consideration!!! the applied load, as well as the shape of the building.

When there is a potential expansion of the soil, e.g. clay soil, then anti-heave measures must be
incorporated into the design!!! to ensure stability and integrity of the under-pinning phase.

MINI PILED UNDER PINNING:

This technique of under-pinning... is used in the following site conditions:

* Ground conditions are very variable.

* There is restricted access to the work site.

* There are significant environmental pollution aspects.

* Where movement of structural elements should be kept to the minimum.

This type of under-pinning is used when loads from the foundation!!! has to be transferred to stable soil, which is available at depths of 5 meters or more.

The diameter of standard mini-piles varies from 150mm to 300mm.

They are usually steel cased or augured. Engineers use special rigs, which have been designed for use
in places with restricted headroom and limited space.

They are small enough to be taken through the narrow confines of a standard home doorway.

Using these specially designed rigs, it is possible to construct piles!!! up to a depth of 15 meters.

The small diameter of the mini-piles is a abnormality of this type of under-pinning design. They are further
stabilized by anchoring them to an existing structure or rock, by using anchoring or tie backs.

Depending on its location, the mini-piles may be under compression or tension and are designed taking
this into consideration.

In addition, other variables such as settlement, bursting, cracking etc. must be taken into consideration
when the mini-piles are being designed.

There Are Various Types Of Mini-pile Under-pinnings Designs In Use Today.

Some of the frequently used types are:

* Pile and beam - they use pairs of piles on either side of the wall and are linked with a pile cap support to
the wall.

* Cantilever pile-caps - are used so that the original building is undisturbed.

Uses tension and compression piles to each cap and are linked by a beam.

* Pile raft systems - this method is used when the entire building foundation has to be strengthened.

Under-pinning is a useful strategy to strengthen the foundation of an existing building or structure.

Whether you use mass concrete under-pinning or its more modern cousins, it is a cost effective and
ingenious method, widely used in the construction industry.


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Underpinning 3 By Civplex Structural Engineers Pty Lty

Underpinning 4 By Civplex Structural Engineers Pty Ltd

"Important NOTE!!!" Information Provided On This Website Is Intended For... "GENERAL INFORMATION
ONLY!!!" And Must Be Only Be Used Only As A "GUIDE!!!" It Must Not Be Used For Decision Making, Or
Be Used For Any Building Purposes Or Legal Proceedings. Refer To Our Policies On This Website.

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