What classification represents poorly graded clean sand?

The classification that represents poorly graded clean sand is indeed SP. This classification is part of the Unified Soil Classification System (USCS), which categorizes soils based on their grain size and distribution characteristics.

Poorly graded clean sand is defined as a sand that has a relatively uniform particle size distribution, meaning that the majority of the sand grains are of similar size and there are few fines (smaller particles). This results in a soil that has low cohesion, making it susceptible to shifting and difficult to compact effectively. The designation ‘SP’ stands for "Poorly Graded Sand," indicating that the soil lacks the variability in grain sizes that would help in achieving better compaction and stability.

In contrast, other classifications such as GM (silty gravel) and GC (clayey gravel) indicate the presence of significant amounts of finer particles, which are not characteristics of clean sand. The classification ‘SW’ indicates well-graded sand, which contains a range of particle sizes that enhance its packing and stability. Hence, selecting SP accurately reflects the nature of poorly graded clean sand as per the USCS.