What defines the "haunch zone" of an excavation?

The "haunch zone" of an excavation specifically refers to the area surrounding the pipe, particularly where the pipe meets the surrounding soil. This zone is critical for the stability and support of the pipe. In the context of a pipe installation, it refers to the arched section on either side of the bottom half of the pipe, which plays a crucial role in distributing the load from the soil above and ensuring the pipe is properly supported.

This is particularly important because the soil's load-bearing capabilities directly impact the integrity of the pipe and the overall system. Understanding the haunch zone helps in determining how to properly backfill and support the pipe to prevent issues such as sagging or settling over time.

The other choices do not accurately describe the haunch zone. The section above the trench relates more to surface soil than to excavation support. The area directly below the surface of the ground may encompass various zones but does not specifically define the haunch. The sloped walls of the trench pertain to excavation safety and methods, primarily focused on preventing cave-ins rather than the specific support dynamics of the installed pipe.