SCAFFOLDING SHORING UNDER PINNING FROM WINMASTER

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• A

• B

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• D

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 Find out the incorrect statement;-

 Underpinning method adopted when   ______

a

A building with deep foundation is to be constructed adjoining to an existing building

b

A settlement of existing foundation has taken place, resulting in serious cracks in the wall

c

The Large openings are required to made in the main walls of an existing building

d

None of these

• A

• B

• C

• D

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Which of the following is the traditional method of underpinning ? 

a

Underpinning By Cantilever Needle Beam Method

b

Mass concrete underpinning method 

c

Pier and Beam Underpinning Method

d

Mini Piled Underpinning

• A

• B

• C

• D

Answer explanation

Mass concrete underpinning method is the traditional method of underpinning. The method involves extending the old foundation till it reaches a stable stratum.

The soil below the existing foundation is excavated in a controlled manner through stages or pins. When strata suitable is reached, the excavation is filled with concrete and kept for curing, before next excavation starts.

In order to transfer the load from old foundation to new one, a new pin is provided by means of placing dry sand-cement pack. This is a low-cost method suitable for the shallow foundation.

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A method of underpinning in which existing wall is divided into suitable sections of width about 1.2 m to 1.5 m

a

Pile method

b

Pier method

c

Freeze method

d

Pit method

• A

• B

• C

• D

Answer explanation

Pit method : -
● In this method, the existing wall is divided into suitable sections of width about 1.20 m to 1.50 m.
● The holes are made in the wall.
● The needles with bearing plates are then inserted through these holes and supported on jacks.
● If space to support needles on outside is not available, the cantilever needles, projecting inside and provided with fulcrums and loadings.
● A hydraulic jack is placed between the needles and fulcrum

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Method of underpinning effectively used in water logged areas

a

Pile method

b

Pier method

c

Both A and B

d

Pit method

• A

• B

• C

• D

Answer explanation

Pile method: -

● In this method the piles are driven along both the sides of the existing wall and then needles in the form of pile caps are provided through the existing wall.
● Useful in clayey soils and waterlogged areas

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The Method which is  effectively used  in clayey soil and in waterlogged areas

a

Pile Method of underpinning

b

Pit Method of underpinning

c

Mini Piled Underpinning

d

None of these

• A

• B

• C

• D

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In ______ method, the underpinning is carried out by vibrating the sand.

a

Cement grouting

b

Vibroflotation

c

Chemical consolidation

d

Freezing

• A

• B

• C

• D

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In _________ method, the freezing pipes are driven below the existing footing and the soil is frozen.

a

Vibroflotation

b

Cement grouting

c

Chemical consolidation

d

Freezing

• A

• B

• C

• D

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In _____ method, the soil under the existing footing is consolidated by using chemicals.

a

Chemical consolidation

b

Freezing

c

Cement grouting

d

Vibroflotation

• A

• B

• C

• D

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Method which  is used to restore slab or pavement which has settled.

a

Cement grouting

b

Freezing

c

Vibrofloatation

d

Guniting

• A

• B

• C

• D

Answer explanation

Grouting: is a process of ground improvement attained by injecting fluid like material into subsurface soil or rock. 

Holes are drilled in a slab and then cement grout is forced under pressure through these holes.

Freezing : Ground freezing is a process of making water bearing strata temporarily impermeable and to increase their compressive and shear strength by transforming joint water into ice.

Vibrofloatation: Vibroflotation is a ground improvement technique used at a considerable depth that by using a powered electrically or hydraulically probe, it strengthens the soil. 

The vibroflotation will compact the soil making it suitable to support design loads. It involves the introduction of granular soil to form interlocking columns with surrounding soil. Vibroflotation increases the density of soil which ultimately results in the increase of bearing capacity of soil. 

This method is useful for granular or sandy soil and before the processing of underpinning start, the building or any of its structure component is shored carefully.

Guniting is the most effective process of repairing concrete work which has been damaged due to inferior work or other reasons. It is also used for providing an impervious layer. 

The gunite is a mixture of cement and sand, the usual proportion being 1:3