The principle of effective stress, first formulated by Karl von Terzaghi, governs the strength of all fine dust soils.
Effective stress equals total normal overburden stress minus pore water pressure: p’ equals sigma minus u.
When pore water pressure rises until it equals the overburden weight, the effective contact stress between single soil grains drops to total zero.
Friction angle vanishes. Cohesive shear strength dissolves.
A soil that could support a castle ten minutes earlier suddenly transforms into a dense, thick, sticky liquid with the bearing capacity of chicken broth.
When twenty thousand gallons per minute of white-hot four-hundred-degree earth-heat blowdown water soaked the loose river-bottom mud of the eastern approach plain, Terzaghi’s equation showed up with total, exact brutality.
The thirty massive war-crawlers of the Ironfang Legion rolled straight into the liquefaction zone.
The lead crawler, weighing forty tons, crossed the boundary marker at four miles per hour.
