# Capillarity of soil

In general, capillarity arises due to surface tension between two materials. In general, capillarity arises due to surface tension between two materials.

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## What is capillarity?

In general, capillarity arises due to surface tension between two materials. There is a capillary rise if adhesion between materials is greater cohesion.

Example: You might have seen capillary rise of water when a small diameter tube is inserted into the container of water. This is because adhesion between glass molecules & the liquid is greater than cohesion between the liquid molecules

## What is capillarity of soil?

In soils due to capillarity, water rises upto some distance above the water level and some part gets saturated fully above to that some other part gets partially saturated.

Pressure at the water level is the atmospheric pressure and below to that is hydrostatic pressure.
• Capillarity water is held above the water level due to the surface tension
• At the interface of two states generally the capillary develops.

## Empirical correlation

Below to the water level, water will be in compression and above to the water level it would be in tension. Empirical correlation is given below for sands and silts

### Factors affecting capillarity rise in soils

Capillarity rise doesn’t depend upon the grain size, but it does depend upon the pore size. We consider compression as positive and tension as negative

### Summary Points

• Water is held in soils due to gravity and capillarity
• Capillarity arises due to surface tension between two materials
• In soils due to capillarity, water rises upto some distance above the water level and some part gets saturated fully above to that some other part gets partially saturated.
• Capillarity rise doesn’t depend upon the grain size, but it does depend upon the pore size.

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