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8/10/2019 shoringandunderpinning-140225074015-phpapp02

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SHORING AND UNDERPINNING


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SHORING

It is the means of providing support to get stability of a structuretemporarily under certain circumstances during construction,repair or alteration.

Such circumstance arises when

1. The stability of a structure is endangered due to removal of adefective portionof the structure.

2. The stability of a structure is endangered due to unequalsettlementduring construction itself or in long run.

3. Certain alterationsare to be done in present structure itself. Eg:remodeling of walls, changing position of windows,etc.

4. Alterationsare carried out in adjacent buildingfor remodeling,strengthening of foundation, etc.


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INSTALLATION OF SHORING

For shoring timber or steel tubes may be used. Sometimesbothareused in combination. If timberis used its surfaceshould be coatedwith a preservative so as to protect against wet rot.

The shoring should be designedbased on the loadit has to sustain

and durationof load. Shoring may be given internally or externallydepending on the

case and in certain cases they may be provided on either side ofthe wall to produce additional stability.

Shoring should be installed only after getting thepermissionifnecessary, of the local authorities.

There is no time limit to which the shoring has to be kept, it mayrange from weeks to years depending on the case.


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TYPES OF SHORING

Raking or inclined shores

Flying or horizontal shores

Dead or vertical shores


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RAKING OR INCLINED SHORES


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FLYING OR HORIZONTAL SHORING


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DEAD OR VERTICAL SHORING


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UNDERPINNING

It is the method of supporting the structures while providing newfoundations or carrying out repairs and alterations withoutdisturbing the stability of existing structures. It is carried underfollowing conditions:

1. When abuildingwith deep foundation is to be constructed

adjoining a building which is built on shallow footings. Here theshallow footings should be strengthenedfirst.

2. In order toprotectan existing structurefrom the danger ofexcessive or differential settlementof foundation.

3. In order to improve thebearing capacity of foundation so as to

sustain heavier loads for which deepening or widening offoundation is done.

4. In order toprovide abasementfor an existing structure.


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PRECAUTIONARY MEASURES

Before implementing appropriate underpinning measures thefollowing important points should be carefully attended:

The existing structure should be fully examined carefully andappropriate underpinning method should be adopted.

All poor masonry work, such as joints, cracks, plasteringshould be rectified before.

Necessary shoringand struting should be done such thatexisting structure is safe.

Urgent repairlike grouting of cracks, insertion of rod

between walls , etc. should be carried out beforecommencing underpinning.

Adequate careshould be taken to ensure that there should beno movement of structure for which levelsshould be marked.

Underpinning process is not a science but an art should be

exercised depending on the situation.


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METHODS OF UNDERPINNING

Pit method

Pile method

Chemical method

Other method


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PIT METHOD


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PIT METHOD


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PILE METHOD


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CHEMICAL METHOD

In this method the foundationsoilis consolidatedby

employing chemicals. Perforatedpipesare driven in an inclined directionbeneath

the foundation . The slopesareprovidedsuch that the entire

areaunder the existing footingcomes under the area used to

be strengthened. After the pipes are installed, solution of sodium silicate in

water is injectedthrough the pipes. This is a two-injection

method. The pipes are withdrawn and at the time of

withdrawal of pipes, calcium or magnesium chloride isinjected through pipes.

Chemical reaction takes place between these two chemicals

and the soil is strengthenedby consolidation. This method is

suitable for granular soils


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OTHER METHODS

Other methods are cement grouting, freezing, vibrofloatation,

etc.


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