Answer:
To determine the change in vertical effective stress at a point 4m below the surface of the sand due to the flooding, we need to consider the effect of the added water. The change in vertical effective stress (Δσ'v) can be calculated using the following equation:
Δσ'v = γw * Δh
Where:
- γw is the unit weight of water.
- Δh is the change in effective stress due to the added water.
Given:
- Total density of sand (γ) = 1.7 t/m³
- Depth to the water table (h) = 2m
- Depth to the point of interest (depth) = 4m
- Change in water depth due to flooding (Δh) = 2m
First, we need to calculate the effective unit weight of the sand (γ'):
γ' = γ - γw
Next, calculate the change in vertical effective stress using the equation:
Δσ'v = γ' * Δh
Substitute the given values into the equation to find the change in vertical effective stress.
This calculation represents the change in vertical effective stress due to the added water from flooding. It's important to note that the water table has risen, resulting in increased pore water pressure. As a result, the effective stress at the point 4m below the surface will decrease, indicating a reduction in the vertical effective stress. The calculated value of Δσ'v will reflect this change.