Porewaterdruk

Porewaterdruk, in geotechnical engineering commonly written as pore water pressure, is the pressure exerted by groundwater within the pore spaces of a soil or rock. In saturated soils it is denoted by u and interacts with the total stress to determine the soil’s effective stress.

The effective stress principle, formulated by Terzaghi, relates total stress, pore pressure, and shear strength: sigma' = sigma - u. This means that higher pore water pressures reduce the effective stress and thus the soil’s shear strength. Conversely, lowering pore pressure through drainage or unloading increases effective stress and strength.

Pore water pressure can arise from several sources. In static conditions, it follows hydrostatic flow and increases with depth. It can be elevated by rapid loading, infiltration, seepage, or inadequate drainage, and may decrease as soils consolidate or are drained. In unsaturated soils, suction can create negative pore pressures, contributing to apparent stiffness.

Measurement and assessment are typically done with piezometers or vibrating-wire transducers installed in the ground. Standpipe piezometers or more advanced instruments can monitor pore pressure changes during loading, drainage, or surface water variations. Pore pressure is often expressed as a pressure ratio ru = u / sigma'v, used in liquefaction and slope-stability analyses.

Significance and management: porewaterdruk influences bearing capacity, settlement, slope stability, and liquefaction resistance. Engineering measures to control pore pressures include drainage and dewatering, preloading, installation of vertical drains, and proper design of drainage paths. Understanding porewater pressure is essential for safe foundation design, earthworks, and groundwater management.