Terzaghi's principle: σ'=σ-u controls soil strength and deformation.
σ'=σ-u, where u is pore water pressure. Soil strength and volume change depend on effective stress, not total. Rising water table reduces σ' and strength. Capillary rise increases it in fine soils.
At 5 m depth in saturated soil with γ_sat=19 kN/m³, σ'=95-49=46 kPa.
Effective stress governs how soil carries load, since water pressure reduces the stress between particles and the strength of the soil.
Terzaghi's principle: σ'=σ-u controls soil strength and deformation.
Effective stress governs how soil carries load, since water pressure reduces the stress between particles and the strength of the soil.
Total stress minus pore water pressure, and it is the stress that acts between soil particles and controls strength and deformation.
Higher pore pressure reduces effective stress, which can weaken slopes and cause heave or instability in excavations.
Typical applications include explaining why a saturated soil loses strength when water pressure rises, estimating the settlement of a clay layer under a new load and checking the stability of a slope after heavy rain.
Study "Permeability" first (topic 30 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
Total stress σ=γz. Hydrostatic u=γ_w z_w. Principle behind consolidation and liquefaction.
At 5 m depth in saturated soil with γ_sat=19 kN/m³, σ'=95-49=46 kPa.
The next topic is "Consolidation", which builds directly on this one.
It is classed as Beginner in Civil & Structural (topic 31 of 112). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.
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