Which method is best suited for obtaining an undisturbed clay sample?

• A. Pennetration test
• B. Pressure meter
• C. Split spoon
• D. Shelby Tube

Answer: (D)

The Shelby Tube is the best method for obtaining an undisturbed clay sample because it is specifically designed for that purpose. This method utilizes a thin-walled, cylindrical tube that is driven into the ground to capture the soil sample. The design of the Shelby Tube minimizes disturbance to the soil structure as it is inserted into the ground, allowing for the collection of intact samples that accurately reflect the in-situ conditions of the clay.

When the Shelby Tube is retrieved, it provides a cylindrical sample of the clay with minimal disturbance, which is critical for laboratory testing, such as determining the plasticity, compressibility, and shear strength of the soil. These tests are important in geotechnical engineering for designing foundations and assessing soil behavior.

Other methods, such as penetration tests and split spoon samplers, may result in disturbed samples due to the driving force applied or the nature of their design. While pressure meters are used to assess in-situ stress conditions and flow parameters, they do not provide soil samples conducive to testing in the same manner as a Shelby Tube. Thus, the Shelby Tube stands out as the preferred choice for obtaining undisturbed clay samples.