An inverted arch footing is a specialized foundation system used in situations where the soil's load-bearing capacity is poor, particularly when concentrated loads are applied over walls, and deep excavations are impractical. It's essentially an upside-down arch built into the ground.
How it Works
Instead of transferring loads downwards, as with a typical footing, an inverted arch distributes concentrated loads horizontally along its base. This spreads the load over a larger area, reducing the pressure on the underlying soil. The curved shape of the inverted arch efficiently redirects the concentrated load from the walls or columns it supports into a distributed load along the base of the structure. Think of it as flipping a typical arch upside down.
Applications and Advantages
- Poor Soil Conditions: Ideal for sites with weak or unstable soil where conventional footings wouldn't be sufficient.
- Concentrated Loads: Effectively manages high concentrated loads from walls or columns.
- Reduced Excavation Depth: A significant advantage is that it often requires less excavation than other deep foundation solutions. This reduces construction time and cost.
- Improved Stability: Distributes loads more evenly, enhancing the overall stability of the structure.
The inverted arch footing's construction often involves materials like brick, stone, or concrete, forming an inverted arch shape beneath the structure. (See Figure-8 in the TestBook article for a visual example). This allows for significantly reduced foundation depth compared to alternatives in soft soils. (The Construction Civil)
Disadvantages
While effective in specific scenarios, inverted arch footings are not without drawbacks. Their design and construction can be more complex than traditional foundations, potentially increasing the overall cost. Furthermore, their use is limited to situations where the specific soil conditions and structural requirements are suitable.
Examples
An example of an inverted arch footing is shown in Figure 62 of the Poplar Heights Farm article (https://www.stone.poplarheightsfarm.org/footings.htm), illustrating two piers connected by a brick-and-concrete inverted arch.
