NPORS Plant Operator Theory Practice Questions - UK NPORS Plant Operator Theory Test (N001 N202) Exam

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Why does digging trench excavations in un-shored sand or gravel soil carry a significantly higher risk of sudden side cave-in compared to stiff un-fissured clay?

Granular soils create high static electricity that repels trench support boxes Sand and gravel are granular soils with minimal cohesion, relying solely on friction angle ($30^\circ-35^\circ$), causing rapid collapse when unsupported Stiff clay exerts higher lateral hydrostatic pressure than coarse gravel Sand absorbs hydraulic oil from bucket teeth, softening trench walls

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Sand and gravel are granular soils with minimal cohesion, relying solely on friction angle ($30^\circ-35^\circ$), causing rapid collapse when unsupported

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