Subgrade modulus is often called which set of terms?

• A. k-value, soil modulus, Westergaard's modulus, foundation modulus
• B. Young's modulus
• C. Poisson's ratio
• D. Shear modulus

Answer: (D)

Subgrade modulus describes the stiffness of the soil reacting under a foundation in a Winkler-type model, where pressure is proportional to settlement. It is commonly referred to by several interchangeable names that capture that same idea of soil stiffness: k-value, foundation modulus, Westergaard's modulus, and simply soil modulus. These terms emphasize the soil’s reaction to load, not the material’s intrinsic elastic properties.

In contrast, Young's modulus and shear modulus are fundamental material properties (stiffness in axial and shear deformation, respectively), and Poisson's ratio is a ratio of lateral to axial strain. Those terms describe general material behavior, not specifically the subgrade reaction used to model settlement under a foundation.

So the set that names subgrade modulus with terms like k-value, soil modulus, Westergaard's modulus, and foundation modulus is the best fit.