All courses › Geotechnical Engineering › Total stress and pore pressure

Total stress and pore pressure

The weight of the soil above a point gives the total stress. Below the groundwater table the water in the pores is under pressure, and this pore pressure increases with depth below the water table. Both are calculated layer by layer.

\sigma_v = \sum \gamma_i\,h_i

vertical total stress

u = \gamma_w\,h_w

pore pressure

Symbols

$\sigma_v$	total stress	kPa
$\gamma_i$	unit weight of layer i	kN/m³
$u$	pore pressure	kPa
$h_w$	depth below the groundwater table	m

Example

Sand with $\gamma = 20$ kN/m³, 6 m deep, groundwater 2 m below ground:

$\sigma_v = 120$ kPa and $u = 10\cdot 4 = 40$ kPa.

Pore pressure is measured from the groundwater table, not from the ground surface.

Practise effective stress and settlement for free →

← Grain sizes and quick clay · Effective stress →

Part of Geotechnical Engineering: Effective stress and settlement.