Final answer:
The intermediate layer, also known as the B horizon or subsoil, holds the most critical influence on the slope of the excavation in layered soils.
Step-by-step explanation:
The layer of soil that holds the most critical influence on the slope of the excavation in layered soils is the intermediate layer. The intermediate layer, also known as the B horizon or subsoil, is an accumulation of mostly fine material that has moved downward. It forms a dense layer in the soil which can greatly affect the slope stability of an excavation in layered soils.
In contrast, the topsoil layer (A horizon) is the surface layer of soil that is rich in organic material and the bottom layer (C horizon) consists of the parent material and organic and inorganic material broken down to form soil. The bedrock layer lies beneath the C horizon and is considered separate from the layered soils.