Compared with SP, SW sand is described as:

• A. More permeable
• B. Less permeable but still more permeable than silt/clay
• C. Equally permeable
• D. Non permeable

Answer: (B)

Permeability in soils depends on how big the pore spaces are and how easily water can move through them. In sands, gradation matters: poorly graded sand has a relatively uniform grain size, which tends to leave larger, more open pore channels and easier flow. Well-graded sand, on the other hand, contains a mix of grain sizes that can pack more tightly, filling gaps and creating more tortuous flow paths, so it generally conducts water less readily than poorly graded sand. But both types of sand still allow much more flow than silt or clay, which have much finer particles and very low permeability due to tiny, poorly connected pore spaces. So, compared with poorly graded sand, well-graded sand is less permeable, yet still more permeable than silt or clay.