During confined compression tests, what is the sample of soil confined by?

In confined compression tests, the soil sample is placed within a metal ring, which provides a controlled environment for assessing the mechanical properties of the soil under conditions that simulate the in-situ stresses it would experience in the field. The metal ring serves to constrain the lateral movement of the soil, thereby allowing researchers to apply a vertical load while simultaneously measuring the response of the soil to that load. By restricting the sample with a rigid structure like a metal ring, precise measurements of deformation and strength can be obtained.

This method is critical as it mimics real-world conditions where soil is subject to confinement from surrounding materials such as other soil layers or structures, creating a more realistic understanding of soil behavior under load. The use of metal ensures durability and prevents deformation that could occur if the confinement were made of softer materials.