Which of the following statements about wet clay is NOT true?

The assertion that wet clay should be mixed with sand to improve its properties is not universally true, particularly in every application of excavation and grading. While it is sometimes practiced to mix sand with clay to enhance drainage and workability, it may not be necessary or beneficial in all situations. Mixing can alter the plasticity and workability of the clay, depending on the specific characteristics of the clay itself, its moisture content, and the intended use in construction. In certain cases, adding sand could lead to a less stable mixture, especially if the primary requirement is to achieve proper compaction.

The other statements regarding wet clay highlight its characteristics accurately; for instance, re-rolling can be a technique used if compaction fails, wet clay has poor drainage properties, and the presence of water can aid in aligning clay particles, enhancing compactability. Each of these points is grounded in the physical behavior of clay when subjected to moisture and mechanical compaction forces.