Under what conditions is a 'subgrade' considered stable?

A 'subgrade' is considered stable when it possesses sufficient shear strength. The shear strength of a soil or subgrade material directly affects its ability to support loads without undergoing deformation or failure. When a subgrade has adequate shear strength, it can resist potential shearing and slipping, which is crucial for the structural integrity of pavement and other constructions placed upon it. This stability is essential during construction and in the long-term performance of engineered structures, ensuring that they can bear the stresses imposed by traffic, environmental factors, and the weight of the materials above.

Inadequate moisture, for instance, can lead to weakening of the soil structure, which compromises shear strength. Similarly, while aggregate composition may contribute to overall stability, it is the shear strength that ultimately determines the subgrade's capacity to support loads effectively. Furthermore, an untested subgrade may not have defined shear strength characteristics, making its stability ambiguous and unreliable for structural support. Thus, having sufficient shear strength is the definitive condition under which a subgrade can be considered stable.