The initial ease of digging and subsequent increase in difficulty is likely due to a change in the soil composition and/or the presence of an impermeable layer at depth. The top layer of soil is generally looser and easier to dig, while deeper layers may contain compacted soil, partially weathered rocks, or bedrock, making it more challenging to excavate. Additionally, encountering an impermeable layer, such as a clay layer or a layer of water-saturated soil, would likely make digging very difficult or impossible beyond a certain depth.
Here’s a more detailed breakdown:
Soil Structure:
The topsoil is often characterized by a loose, organic structure, making it easier to move with a shovel or digging tool. Deeper down, the soil becomes more compact, with less organic matter and more mineral particles. This compaction increases resistance to excavation.
Rock and Bedrock:
As the digger goes deeper, they may encounter partially weathered rock or bedrock. These are more dense and harder to break down than the topsoil, requiring more force to remove them.
Impermeable Layer:
If the man encounters an impermeable layer like a layer of clay or a water-saturated layer, digging becomes very difficult. This is because the tool cannot penetrate the solid, dense material. Water saturation can also make it difficult to dig due to the increased weight and the potential for the soil to become unstable.
Soil Composition:
The type of soil also plays a role. Sandy or loamy soils are generally easier to dig than clay or heavy clay soils.
The fact that the man could not dig beyond 5 feet suggests that he may have encountered a dense layer of compacted soil or bedrock, or an impermeable layer like clay, which made further excavation impossible or extremely difficult.