Answer & Solution
Answer: Option
A
Solution:
First, let's understand some terms:
Saturated Soil: Imagine a sponge completely soaked in water, so much that there are no air bubbles left in it. That's what "saturated" means for soil – all the tiny spaces (called pores or voids) between the soil particles are completely filled with water.
Pore Pressure: This is simply the pressure of the water that is trapped within these tiny spaces inside the soil.
Skempton's Pore Pressure Coefficient B: This is a value that helps us understand how much the pore pressure changes when we apply an overall squeezing pressure (called isotropic stress or all-around stress) to the soil from all directions.
Think of it as a ratio: how much the pore water pressure increases for every unit of all-around pressure you apply.
Now, let's consider a saturated soil (our sponge full of water).
When you apply an external squeezing pressure from all sides to this saturated soil, what happens to the water inside?
1. The water is almost incompressible. It cannot be squashed into a smaller volume easily.
2. The soil particles themselves are also relatively incompressible.
3. There is no air in the pores to compress.
Because of these reasons, if you apply, say, 1 unit of pressure from all directions, the water trapped inside the soil pores has nowhere to go immediately. It has to take almost the entire impact of that applied pressure.
So, if you increase the all-around stress by a certain amount, the pore water pressure will also increase by almost the same amount.
This means the ratio of the change in pore pressure to the change in applied all-around stress is approximately 1.
Therefore, for a saturated soil, Skempton's pore pressure coefficient B is 1.
So, if you apply 1 unit of all-around pressure, the pore water pressure will also increase by approximately 1 unit.
The correct answer is Option A: 1.
