PE Civil Transportation Practice Exam

A Shelby tube is specifically designed to collect undisturbed soil samples, particularly from clayey subsoils. The design of the Shelby tube ensures minimal disturbance to the soil structure during the sampling process. When the tube is pushed into the ground, it maintains the in-situ conditions of the soil, preserving water content and the arrangement of soil particles. This is crucial for geotechnical investigations, as undisturbed samples allow engineers to accurately assess the soil's properties, such as strength and compressibility, which are vital for foundation design and other engineering applications.

In contrast, options focused on taking disturbed soil samples, obtaining groundwater samples, or measuring soil plasticity do not accurately reflect the primary function of the Shelby tube. Disturbed samples would imply significant alteration of the soil structure, which is contrary to the purpose of using a Shelby tube. Groundwater sampling requires specialized devices to access water from below the soil surface, while soil plasticity measurements typically involve laboratory testing of specific samples rather than sampling techniques.