This set of Construction and Building Materials Multiple Choice Questions & Answers (MCQs) focuses on “Underpinning and its Types”.
1. The placing of new Foundation below and the existing foundation of the process of strengthening the existing Foundation is known as the ___________ of foundation.
a) Shoring
b) Underpinning
c) Grouting
d) Scaffolding
View Answer
Explanation: Following are the situations demanding underpinning: A building with deep Foundation is to be constructed at joint to an existing building; The settlement of existing Foundation has taken placed, resulting in serious cracks in the wall; The basement is to be provided to an existing building.
2. In __________ method of underpinning, the existing wall is divided into suitable sections of width about 1.20 metre to 1.50 metre.
a) Pit Method
b) Pile Method
c) Miscellaneous Method
d) Chemical Method
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Explanation: In Pit Method, the holes are then made in the existing wall. The needles with bearing plates and then inserted through this holes are supported on Jack. The pit is excavated and the existing foundation is taken up to the required level.
3. In _________ method, the piles are driven along both the sides of existing wall and the needle in the form of pile caps are provided through the existing one.
a) Pit method
b) Pile method
c) Miscellaneous method
d) Vibroflotation
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Explanation: Pile method is useful in clayey soils and for waterlogged areas and for walls carrying heavy loads. For underpinning very light structures, the piles are driven along the structure and then brackets or cantilever needles are provided to carry the structure.
4. __________ method is used to restore slab or pavement which has settled.
a) Vibroflotation
b) Freezing
c) Chemical consolidation
d) Cement grouting
View Answer
Explanation: The operation of Cement grouting is simple. The holes are drilled in a slab and then cement grout is forced under pressure through these holes. The pressure is maintained until the cement grout has set.
5. In _________ method, the soil under the existing footing is consolidated by using chemicals.
a) Chemical consolidation
b) Freezing
c) Cement grouting
d) Vibroflotation
View Answer
Explanation: The procedure for chemical consolidation is as: The perforated pipe are driven in an inclined direction. The inclination slopes are so adjusted that the entire area under the existing putting comes under the command of the inclined pipes; The chemical reaction takes place between two chemicals and the soil is consolidated.
6. _________ method is useful when the soil consists of sand or granular material.
a) Vibroflotation
b) Chemical grouting
c) Chemical consolidation
d) Freezing
View Answer
Explanation: Here, the cost of consolidation depends on the nature of soil, depth of consolidation, site of work, etc. In this method, the soil under the existing footing is consolidated by using Chemicals. The chemical reaction takes place between two chemicals and hence the soil is consolidated.
7. 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
View Answer
Explanation: Freezing is really adopted, mainly because of two reasons: it is expensive and more time is required for the installation of the freezing pipes.
8. In ___________ method, the underpinning is carried out by vibrating the sand.
a) Cement grouting
b) Vibroflotation
c) Chemical consolidation
d) Freezing
View Answer
Explanation: 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 components is shored carefully.
9. When one building is higher than the other _____________ may be provided on the horizontal shores.
a) Raking shore
b) Pile Underpinning
c) Flying shore
d) Pit Underpinning
View Answer
Explanation: Whereas, the flying shores are generally erected at a distance of about 3 m to 5 m in plan and horizontal Struts are introduced, if necessary, to act as a lateral bracing between the adjacent line shores.
10. A large factor of safety should be adopted in the design of __________ as it is difficult to assess the actual loads.
a) Vertical shores
b) Pit method
c) Horizontal shore
d) Pile method
View Answer
Explanation: In Flying or horizontal shore arrangement, the horizontal supports are given to the parallel walls which have become unsafe due to the removal or collapse of the intermediate building.
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