Effective stress with groundwater and surcharge

The governing relationship

Vertical effective stress is the total vertical stress minus pore-water pressure: σ'v = σv - u. Total stress includes the overburden and applicable surface surcharge. Below the water table, hydrostatic pore pressure is based on the vertical depth beneath the water table and the unit weight of water.

Reliable solution sequence

• Draw the soil profile and mark the water-table elevation.
• Compute total stress from the stated surcharge and the total unit weight of each layer.
• Compute pore pressure only over the depth below the water table.
• Subtract pore pressure from total stress and report the result with units.
• Check whether a surcharge may reasonably be treated as uniform at the point of interest.

Common failure modes

Frequent mistakes include using submerged unit weight in the total-stress sum and then subtracting pore pressure again, applying pore pressure over the full depth rather than only below the water table, or assuming a local surcharge creates its full surface intensity at depth without a stated influence model.