By: Sr vini

# Before starting lessons 3 of Capillary Water Tension it’s highly recommended to read lesson 1st and 2nd by click below link, it gives a good idea about the topic.

## Capillary action due to Tension

Dear Friends, Basic Phenomena of the earth is When Pressure applied, in Direction of Gravity Force called positive pressure. Now understanding the term capillary water tension.

the previous lesson, we see a Capillary tube in which water on the inside is hanging to Surface of the tube.

Let’s show a capillary tube Fig.

The pressure of point a is atmospheric pressure because of a free surface.

Now pressure (p) of top point T is (p = ρ g h) now because it acting upward its again the general earth law of pressure so it’s written as p = -(ρ g h)

So here we can say in Tube water is tried to remain sticky on the wall and gravity tried to pull downward.

from the above statement, we can say a tension force produced between them, and these tension in a capillary tube is known as capillary water tension.

Friends the same Phenomena is work in the soil,

soil mass also contains small dia interstice which behaves like a capillary tube of small dia.

so the water rises in the soil above the water level.
From all the above visualization and from the previous lesson, we can say

* Because the capillary pressure act upward (also say negative) it increases the effective stress-bearing capacity of the soil.

### Capillary action give Tension During Drying and wetting

Dear Friend above we learn capillary tension in the tube or soil above the water table. in this article, we consider the soil mass capillary zone is at the ground surface.
fig show soil mass particle which Saturated throw top means of capillary water

in the first type, fig soil is saturated by capillary action throw top.

now when the temperature increase water evaporates and soil particle look like fig-2

further increase in temperature increase soil dry amount and this case give interstices water reduction, and water tries to collapsing the soil particles and particle tries to remain in the same place.

so a capillary tension is introduced due to this drying. but further drying case Zero tension and soil particles behave like dry sand mass.

now if we wetting these soil a reverse cycle of above is continues. and you visualize what happened.

so its all about Capillary Tension During Drying wetting.

### Soil Suction and Water Content relation

you can also learn an extra things soil suction and drying wetting relationship. I thig it’s very easy to understand what goes on the graph by reading the previous lesson and today topic.