In USCS, SP describes which sediment type?

• A. Poorly graded sand, which is well sorted (small range of grain sizes), very permeable
• B. Well graded sand, which is poorly sorted (wide range of grain sizes)
• C. Low porosity clay with high cohesion
• D. Fine-grained silt with low permeability

Answer: (A)

In USCS, the symbol SP identifies sand with poor gradation, meaning the grain sizes are fairly uniform with little variation. This narrow range of particle sizes is described as being well sorted. Because there aren’t many fine materials to fill the voids, sands with this uniform size distribution typically have high permeability, allowing water to flow through easily. So, describing SP as poorly graded sand that is well sorted and highly permeable fits the characteristic pattern. The other options describe either clay or silt, or a sand with a broad range of grain sizes (well graded), which does not match SP.