Geotechnical Engineering Exam 1 Practice

The thing being tested is how particle sizes are distributed in soil and why a continuous mix of sizes matters. Well-graded soil means a broad, continuous range of particle sizes with no large gaps in the distribution, so the smaller particles can fit into the voids between the larger ones. This fills voids more effectively, allowing the soil to pack more densely, which tends to increase strength and stability and reduce compressibility and excessive permeability.

That’s why the best description is a good representation of all sizes. If you have mainly coarse particles, you don’t get the filling effect; if you have mainly fines, you can end up with high plasticity and poor drainage. A continuous mix across sizes captures the desirable packing behavior that well-graded soils exhibit.