Mohr-Coulomb criterion τ=c+σ tanφ.
Mohr-Coulomb: τ_f=c'+σ' tanφ'. Sands have φ'≈28–40° and negligible cohesion; clays have c' and φ' with undrained strength c_u. Tests: direct shear, triaxial (UU, CU, CD), vane shear. Drained vs undrained conditions are critical.
Dense sand with φ'=38° can support steeper slopes than soft clay.
Shear strength decides whether a soil will slide or hold, so it is the key input to slope stability and foundation design.
Mohr-Coulomb criterion τ=c+σ tanφ.
Shear strength decides whether a soil will slide or hold, so it is the key input to slope stability and foundation design.
The shear strength of soil as a combination of cohesion and friction, which depends on the effective normal stress on the failure plane.
Drained strength is for slow loading when pore water can escape. Undrained strength applies to rapid loading of clays when pore pressure cannot dissipate.
Typical applications include checking the stability of a cut slope in clay, setting the strength parameters for a retaining wall design and estimating the capacity of a foundation on sand.
Study "Consolidation" first (topic 32 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
Peak vs residual strength. Dilation of dense sand. Stress paths.
Dense sand with φ'=38° can support steeper slopes than soft clay.
The next topic is "Bearing capacity", which builds directly on this one.
It is classed as Beginner in Civil & Structural (topic 33 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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