What are common causes of pavement failure?

The most accurate choice regarding common causes of pavement failure is linked to the concept of an unbound subgrade. An unbound subgrade refers to layers of unsealed, loose material that may not adequately support the loads applied on the pavement surface. Such materials lack the cohesion and stability needed to provide a solid base for the pavement. When subjected to traffic loads, an unbound subgrade can compress, shift, or erode, leading to surface cracks, ruts, and premature deterioration of the pavement. The weakness of the subgrade significantly contributes to the overall failure of the pavement structure.

In contrast, a strong subgrade would generally support the pavement effectively, helping to extend its lifespan. Improper design of pavement can lead to issues, but it primarily relates to calculations and specifications rather than the physical characteristics of the subgrade itself. Poor drainage systems can also contribute to pavement failure by allowing water to accumulate and weaken the pavement structure, but the concept of an unbound subgrade captures a fundamental structural flaw that directly leads to failure under load.