Soil mechanics terminology – pore pressures under loading: In geotechnical engineering, the pressure that develops in the pore water immediately due to an increment of load on the soil mass is termed as what?

Introduction / Context:
When a load is applied to a saturated or partially saturated soil, water within the voids initially carries part of the stress. This generates a transient increase in pore-water pressure above the equilibrium value. Understanding this “excess pore pressure” is central to consolidation theory, slope stability during rapid loading, and earthquake-induced soil behavior.

Given Data / Assumptions:

• No numerical values are required; the question asks for the correct term.
• Hydrostatic pore pressure refers to the equilibrium pressure due to the water column alone.
• Excess pore pressure is the additional component created by load or disturbance and dissipates with time as water drains.

Concept / Approach:
Immediately after loading a low-permeability soil (e.g., clay), the soil skeleton cannot compress quickly, so the pore water takes the extra stress, creating excess pore pressure u_excess. Over time, drainage reduces u_excess and transfers effective stress to the soil skeleton, causing settlement. In rapid shearing (undrained), u_excess may persist and can reduce effective stress, leading to instability.

Step-by-Step Solution:

Verification / Alternative check:
Piezometer readings during construction often spike above hydrostatic immediately after embankment placement, then decline as consolidation proceeds—direct evidence of u_excess generation and dissipation.

Why Other Options Are Wrong:

• Excess hydrostatic pressure: hydrostatic is an equilibrium state, not the transient rise from loading.
• Hydrodynamic pressure: used for flowing fluids around structures, not for consolidation response.
• “All of the above” is incorrect because only the first term is standard.
• Neutral pore pressure at initial equilibrium is the baseline, not the increment.

Common Pitfalls:
Confusing total pore pressure with its components; assuming u_excess is always positive (it can be negative in dilative soils).

Final Answer:
Excess pore pressure