Well Foundations – Pneumatic Caissons

The essential feature of a pneumatic caissons are __________
a) Tilting can be avoided and Removing water by Compressed air
b) Skin fraction is zero
c) None of the mentioned
d) All of the mentioned

Answer: a
Explanation: The essential feature of a pneumatic caisson is that compressed air is used to exclude or remove water from the working chamber at the bottom.

The method of construction of pneumatic caisson is similar to ________
a) Box caissons
b) Open caissons
c) Rectangular caissons
d) All of the mentioned

Answer: b
Explanation: The method of construction of pneumatic caisson is similar to that for open caissons (well) except that the working chamber is kept air tight.

The working chamber of pneumatic caissons are kept airtight because ________
a) To avoid tilting
b) To remove the soil
c) To prevent water from entering the chamber
d) None of the mentioned

Answer: c
Explanation: In order that sub-soil water may not enter the working chamber, the pressure of air in the shaft is kept airtight.

The allowable pressure that is allowed inside the working chamber of pneumatic caissons is _______
a) 2 kg/cm2
b) 4 kg/cm2
c) 3.5 kg/cm2
d) 7 kg/cm2

Answer: c
Explanation: Normally the tolerable air pressure under which a man can work is limited to 3.5 kg/cm2 in pneumatic caissons.

Advantage of using pneumatic caissons are _________
a) Affords easy inspection and Process is done under control conditions
b) Sinking process is easy
c) None of the mentioned
d) All of the mentioned

Answer: a
Explanation: An advantage of pneumatic caisson is that the entire process of sinking well is carried out under controlled conditions and it affords easy inspection work.

Disadvantage of using pneumatic caissons are ________
a) Process cannot be done under control conditions
b) Sinking process is tedious
c) Inspection process is time consuming
d) All of the mentioned

Answer: b
Explanation: In pneumatic caissons, the sinking of pneumatic caissons are tedious, time consuming and expensive.

In order to prevent leakage of air in the working chamber ________ is provided.
a) Arrangement of double gates
b) Air compressor
c) Air lock
d) All of the mentioned

Answer: a
Explanation: In order to prevent leakage of air, the arrangement of double gates is provided. The person enters the first gate, where pressure is atmospheric.

The limiting head of water value in pneumatic caisson is ________
a) 40 m
b) 25 m
c) 35 m
d) 50 m

Answer: c
Explanation: As the maximum air pressure is limited to 3.5 kg /cm2. the limiting head of water is given by:
hlim = 3.5/0.1 = 35 m.

In order to assist sinking of well __________ method is used in pneumatic caissons.
a) Air pressure is reduced and Using explosive
b) Using airlocks
c) None of the mentioned
d) All of the mentioned

Answer: a
Explanation: In order to assist sinking process, air pressure may be reduced for a short while. Sometimes explosive may be employed in this case, it is essential to make arrangements for the immediate removal of fall fumes.

Pneumatic caissons are closed at _________ during construction.
a) Bottom
b) Top
c) Top and bottom
d) None of the mentioned

Answer: b
Explanation: Pneumatic caissons are closed at the top and open at the bottom during construction.