Which bearing plane should trenches installed parallel to footings not extend below?

The correct choice highlights the importance of maintaining structural integrity in relation to the bearing planes of footings or walls. The 45° bearing plane of the footing or wall is critical because it represents the angle at which pressure is distributed from the load above through the footing and into the soil below. Trenches installed parallel to footings should not extend below this 45° plane to ensure that the loads are properly supported and to prevent issues such as settlement or undermining of the footing.

When trenches extend below this bearing plane, it can lead to instability in the footing, as the pressure distributed through the footing could be disrupted, potentially causing structural failure. Therefore, adhering to the 45° bearing plane ensures that the load is adequately conveyed to the soil without compromising the structural support provided by the footing.

Understanding the bearing plane is essential for safe trenching practices in plumbing and construction, as it protects against the risks associated with undermined footings.