307.5 Trench location. Trenches installed parallel to footings shall not extend below the 45-degree (0.70 rad) bearing plane of the footing or wall.

FIGURE 3.8 Line of loadbearing distribution plane.

A footing requires a minimum loadbearing area to distribute the weight of the building. This loadbearing distribution plane extends downward at approximately a 45-degree angle from the base of the footing. Water and sewer piping may not be installed below this loadbearing plane, nor may excavation for the installation of the pipe extend below the plane in order to not negatively influence the load capacity of the footing, or cause the excavation to collapse.