Which type of grading indicates that soil has a range of particle sizes?

The concept of grading in soil mechanics refers to the distribution of particle sizes within a soil sample. When a soil is described as well graded, it means that it contains a wide range of particle sizes. This range allows for the smaller particles to fill the voids between larger particles, creating a dense and stable structure. Well-graded soils are often capable of achieving higher densities and better compaction because they can better fit together, which is advantageous in various construction and engineering applications.

In contrast, uniformly graded soils contain particles that are similar in size, leading to larger void spaces and less stability. Coarse graded soils primarily consist of larger particles, and uniform grained soils have a specific and consistent size of particles. Each of these does not demonstrate the beneficial characteristics associated with a range of particle sizes, which is a hallmark of well-graded soils. Thus, well-graded is the correct choice as it directly aligns with the definition of having a variety of particle sizes.