Construction and Building Materials Multiple Choice Questions & Answers (MCQs) on “Classification of Caissons”.
1. A _____________ is defined as a structure which is sunk through ground or water to exclude water and semi fluid material during the process of excavation of foundations.
Clarification: A Caisson is a relatively large deep foundation and resembles is pile foundation in transferring the superstructure load to some desired depth. However, Caisson differs from a pile in size and in the method of construction.
2. A _______ becomes uneconomical in cases where the plan area of foundation work is small as compared to the depth of water.
Clarification: Under such circumstances, cofferdam becomes uneconomical. Hence, caisson would prove to be most suitable. At places where cofferdam cannot be Dewatered successfully, the Caissons are used.
3. The _________ is suitable for caissons of Open Well type.
c) Reinforced cement concrete
Clarification: New segments of cast iron are bolted as the caisson sinks. Cast iron is unsuitable for pneumatic caissons as there is risk of failures due to tension developed by the compressed air. The cost also works out to be more in relation to steel or RCC.
4. The __________ is suitable for caisson shoes.
a) Reinforced cement concrete
Clarification: Reinforced cement concrete has more weight and therefore it creates difficulties in handling and floating the Caisson in the early stage of construction. Therefore it becomes economical to construct a Steel Caisson with concrete filling.
5. The __________ is found to be the most suitable material for the construction of caisson.
b) Cast iron
Clarification: Steel is usually in the form of a double skin of Steel plating and the hollow space in then filled with cement concrete. Due to its strength and durability it is found to be most suitable material.
6. The ___________ was used as a material for the construction of caisson in the early stages of development of Caisson.
c) Cast iron
Clarification: In old days, Timber was the cheapest material due to its availability in abundance. But this material is now practically not adopted mainly because of its bulk and the risk of Fire.
7. A ______ caisson is open at top and closed at bottom.
b) Pneumatic caissons
d) Box caissons
Clarification: Box Caisson is merely a variation of the Suspended type cofferdam. The box caissons may be built of reinforced concrete, steel or timber. Condition for box caisson is that the depth of water is about 6 meters to 8 meters.
8. A ________ is a caisson which is open at top as well as at bottom.
b) Box Caisson
c) Pneumatic caissons
Clarification: Well is provided with a cutting edge at the bottom so as to facilitate sinking. The shape of a well is generally decided by the requirements of the superstructure, vertical and horizontal forces on well, base of the pier or abutment, cost of sinking, chances of tilting and shifting during execution, etc.
9. A __________ are open at bottom and closed at top.
c) Box Caisson
d) Pneumatic caissons
Clarification: The pneumatic caissons are adopted when the depth of water is more than 12 metres or so. The maximum depth of water upto which pneumatic caissons can be used is limited from the consideration of health of the workers.
10. An open _______ is a convenient form of foundation for Bridge piers.
c) Multiple wells
Clarification: Cylinder is used when depth of water is more than 12 meters or when it becomes essential go deep to avoid exposure of foundations due to scouring action of flowing water. The cylinder is a light shell which invariably become part of the permanent structure.