Soil Mechanics Questions and Answers – Capillary Siphoning

This set of Soil Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Capillary Siphoning”.

1. To check the seepage of water through the body of dam, the core provided is ________
a) pervious
b) semi-pervious
c) impervious
d) hollow

Explanation: The core of the dam is provided with an impervious material to prevent the seepage of the water through the core. If a pervious material is used, then the whole structure would easily collapse.

2. To check the seepage of water through the body of dam, the outer shells of dam provided is ________
a) pervious
b) semi-pervious
c) impervious
d) hollow

Explanation: The outer shells of the dam are made of highly pervious granular soil so as to check the seepage through it. The water can rise through the capillary action through the voids of the dry soil.

3. The capillary forces can rise the water in the capillary tube against the gravity force.
a) True
b) False

Explanation: Capillarity is the phenomenon of movement of water through narrow spaces due to capillary forces. In capillary rise of water, it will hang in tension in capillary tube.

4. The maximum capillary rise at 20°C is given by ________ cm.
a) 0.1234/d
b) 0.2975/d
c) 0.3857/d
d) 0.3084/d

Explanation: The maximum capillary rise is given by,
(hc)max=4Ts/(γwd)
At 20°C, Ts=72.8 dynes/cm and γw=9.78kN/m3
∴ (hc)max=4*72.8 *10-8/(9.78*10-6* d)
∴ (hc)max=0.2975/d cm.

5. With increase in temperature, the capillary rise _______
a) decreases
b) increases
c) has no change
d) does not depend on temperature

Explanation: As the surface tension decreases with the temperature increase, the capillary rise which is directly proportional to the surface tension, would decrease with the increase in the temperature.
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6. What will be the maximum capillary rise at 20°C, if the diameter of the capillary tube is 1 cm?
a) 0.1234 cm
b) 0.2975 cm
c) 0.3857 cm
d) 0.3084 cm

Explanation: Given,
Diameter d=1cm
At 20°C,
(hc)max=0.2975/d cm
∴ (hc)max=0.2975/1 cm
∴ (hc)max=0.2975 cm.

7. The capillary siphoning will take place if the top of the core is situated at height y _______ which is above H.F.L.
a) greater than capillary rise hc
b) lesser than capillary rise hc
c) equal to capillary rise hc
d) zero

Explanation: When the height of impervious core of the earth dam is less than that of the capillary rise, then due to the capillary action, the water from one side of the dam will move to the other side over the impervious core by a phenomenon known as capillary siphoning.

8. What will be the maximum capillary rise at 4°C, if the diameter of the capillary tube is 1 cm?
a) 0.1234 cm
b) 0.2975 cm
c) 0.3857 cm
d) 0.3084 cm

Explanation: Given,
Diameter d=1cm
(hc)max=4Ts/(γwd)
At 4°C,
Ts=75.6 dynes/cm and γw=9.807kN/m3
∴ (hc)max=4*75.6 *10-8/(9.807*10-6* d)
∴ (hc)max=0.3084/d
At d=1cm,
(hc)max=0.3084/1
∴ (hc)max=0.3084 cm.

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