Which risk increased during Roman road construction when a clay layer was overlaid directly atop unstable ground?

💡 Explanation

When clay is directly laid atop unstable ground, consolidation settlement occurs because the clay compresses the underlying weak soils non-uniformly under load, resulting in uneven roadbed settlement. Therefore subsidence increases, rather than heave, dust, or overuse, which are related to different factors like temperature, environmental management and incompetence respectively.

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