What type of sampler is most widely used for obtaining undisturbed soil samples?

The Shelby tube sampler is favored for obtaining undisturbed soil samples because it is specifically designed to minimize disturbance to the soil structure during the sampling process. This type of sampler consists of a long, thin-walled tube that is driven into the ground, capturing a cylindrical section of soil. The thin walls of the tube help to preserve the soil's natural density and moisture content, which is crucial for accurate testing and analysis.

Compared to other sampling methods, the Shelby tube provides a clearer representation of the soil's in-situ conditions, making it ideal for engineering studies where understanding the soil's properties is vital. It is particularly effective for cohesive soils, such as clays, where maintaining the sample's original state is essential for reliable testing.