Soft sediments are best sampled with a ______ to obtain undisturbed samples.

• A. Shelby tube
• B. Split-spoon sampler
• C. Piezometer
• D. Grab sampler

Answer: (A)

Preserving the in-situ structure of soft, cohesive sediments is essential when you want undisturbed samples. A Shelby tube is a thin-walled, piston-driven sleeve that is pushed into the soil and then retrieved with the soil still inside. This design minimizes disturbance to the soil fabric, moisture content, and density, so the sample can be extruded and tested for properties like moisture content, Atterberg limits, and shear strength with confidence. The other devices disturb the soil: a split-spoon sampler is driven into the ground and tends to smear the fabric, yielding a disturbed sample; a grab sampler collects surface material and does not maintain the natural structure; a piezometer is used to measure pore-water pressure rather than to collect a sample. For soft sediments where maintaining original structure is key, the Shelby tube is the best choice.