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Effective Stress Parameter of Unsaturated Soils from Multiphase Lattice Boltzmann Simulation
The effective stress parameter chi in Bishop's equation for unsaturated soils can be measured grain by grain by summing the suction and surface-tension forces each grain feels, extracted from a single-component multiphase lattice Boltzmann simulation of the two fluid phases in the pore space. Students learn how this pore-scale force balance yields the chi versus degree-of-saturation curve over a full wetting and drying cycle, why chi exceeds the saturation everywhere except the endpoints (with maximum divergence at the pendular transition), and why the curve is hysteretic - larger during imbibition than drainage because surface-tension forces contribute more.