Final answer:
The slope limits of footings depend on the angle of repose of the material used, such as 30° for sandstone and over 40° for shale, and must also comply with local building codes and soil conditions.
Step-by-step explanation:
The question concerns the slope limits that apply to the top and bottom surfaces of footings in construction and engineering. Footings are designed to support building structures and must be constructed with stability in mind. The primary consideration for footing slopes relates to the angle of repose, which is the steepest angle at which a sloped surface formed of a particular loose material is stable.
For example, when considering different materials, such as sandstone with an angle of repose around 30° or shale, which can exceed 40°, the slope of footing surfaces must not exceed these limits to prevent material from cascading or sliding. In engineering practices, the exact slope limits can also be influenced by local building codes, the specific type of soil and sediment present, the foundation design, and overall stability requirements of the structure.
This is similar to how solifluction or soil creep on hillside terraces can affect soil stability. Sediments and soil move differently based on their composition and the slope's angle, a principle that also applies to the design of footings in engineering projects.