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Earth and Space Sciences · 术语表

什么是 Coulomb failure criterion?

又称: cohesion · coefficient of internal friction · angle of internal friction

Definition 16.13 University Earth and Space Sciences — Year 1 · 第 16 章 — Stress, Strain and Rheology

A rock obeys the Coulomb failure criterion if a plane through it breaks, or an existing fracture slips, as soon as on that plane

τ=C+μ σn′,σn′=σn−P,\tau = C + \mu\,\sigma_n' , \qquad \sigma_n' = \sigma_n - P ,

where C≥0C \ge 0 is the cohesion of the rock, μ\mu its coefficient of internal friction and ϕ=arctan⁡μ\phi = \arctan\mu its angle of internal friction.

Mohr’s circle in effective stresses and a Coulomb envelope. A plane whose normal makes the angle  with _1 is the point at the angle 2 from the _1 end (orange). The circle drawn just touches the envelope: the plane at the point of contact breaks, its normal at = 45 + /2 from _1, the radius there perpendicular to the envelope. Drawn to scale for C = 10\, MPa, = 0.6 and _3' = 20\, MPa, which give _1' = 97.7\, MPa.
Mohr’s circle in effective stresses and a Coulomb envelope. A plane whose normal makes the angle θ\theta with σ1\sigma_1 is the point at the angle 2θ2\theta from the σ1\sigma_1 end (orange). The circle drawn just touches the envelope: the plane at the point of contact breaks, its normal at θ=45∘+ϕ/2\theta = 45{}^{\circ} + \phi/2 from σ1\sigma_1, the radius there perpendicular to the envelope. Drawn to scale for C=10 MPaC = 10\,\mathrm{MPa}, μ=0.6\mu = 0.6 and σ3′=20 MPa\sigma_3' = 20\,\mathrm{MPa}, which give σ1′=97.7 MPa\sigma_1' = 97.7\,\mathrm{MPa}.
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