What should be considered when classifying soil in a layered system?

Classifying soil in a layered system requires careful consideration of the weakest layer of the system because it often dictates the overall stability and performance of the soil structure. The weakest layer is critical in determining the potential for failure under load, as it is typically the layer that will deform or yield first when stress is applied. Engineers and operators must identify the properties of this layer to ensure safe excavation practices and to design foundations or structures that adequately account for the soil's bearing capacity and behavior.

In a multilayered system, while the strengths of the individual layers and their average might provide useful information, it is the weakest layer that presents the most risk. For example, if a strong layer is present above a weak layer, even if the average strength appears adequate, the presence of the weaker layer could lead to issues such as settlement or instability under load conditions. Therefore, focusing on the weakest layer ensures a more conservative and reliable approach in excavation and construction scenarios.