Pore Water Pressure in the Capillary Zone

Pore water pressure is the pressure exerted by the water present in the soil pores. In the capillary zone, the pore water pressure is negative. Let's understand why.

Capillary Zone

The capillary zone is the region in the soil where the pore size is small enough to create capillary forces. Capillary forces are the forces that cause water to rise in a small-diameter tube due to the adhesive forces between the water and the tube's surface.

Negative Pore Water Pressure

In the capillary zone, the pore size is small enough to create capillary forces that cause the pore water pressure to be negative. The negative pore water pressure occurs due to the following reasons:

- Adhesion: The water molecules adhere to the soil particles due to which the water level in the soil is lower than the water level in the free surface.
- Surface Tension: The surface tension of water causes it to stick to the soil particles and reduce the pore water pressure.
- Attraction: The soil particles attract the water molecules, causing the water level to be lower than the free surface.

Conclusion

In conclusion, the pore water pressure in the capillary zone is negative due to the capillary forces, adhesion, surface tension, and attraction between the soil particles and water molecules.

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