What Is Inverted Arch Footing?
The Inverted Arch Footing is built in areas where the carrying or bearing capacity of the soil is very low and the load of the building is concentrated on the walls and digging is not possible. This is not a typical type of foundation. Inverted Arch Footing is built between the two foundation walls.
The walls should be thick enough and strong to withstand the outward horizontal thrust caused by the action of the arch. An Inverted Arch Footing is a civil engineering structure in the form of a modified arch, inverted in comparison with a standard arch footing.
Like flying arches, the Inverted Arch Footing is not used to support the load, such as a bridge, but rather to withstand sideways internal loads. In a standard Inverted Arch footing the dry load is facing downwards in the middle of the arch and transmits this into forces both downwards and outwards at the base of the arch.
In most cases, this sideways force is problematic and must be withstand using strong foundations or a further bowstring girder, in the form of a tied arch bridge. Inverted Arch Footing is used where sideways forces should be restrained, and where space is easily accessible beneath a construction.
Inverted Arch Footing are commonly used in railway cuttings, but are perhaps used prominently as a base of docks, especially dry docks or waterproof locks that can withstand the side thrust of their walls. Some tunnels are built in an oval section, such as the Newbold on Avon tunnel, where the lower part forms an invert for strength.
Continued use of Inverted Arch Footing to support the lengthways forces from another arch, such as a bridge or viaduct. Inverted Arch Footing is often done on poor soil for reducing ground loads. In the simplest case, the wall simply spreads the descending loads of the viaduct columns over a wide area, exactly like an inverted arch bridge.
Inverted Arch Footing was used under the Hownes Gill Viaduct, on the advice of Robert Stephenson. Inverted Arch Footing is also installed on existing bridges, to strengthen them after their banks begin to slide inwards. Such footing was used at The Iron Bridge in the 1970s.
Inverted Arch Footing is often used in conjunction with the retaining walls. This arch provides the foundation for the walls and can withstand the forces of its sides. The retaining wall also provides the vertical load required by the arch.
Where Are Uses Inverted Arch Footing?
Inverted Arch Footing is used in areas where the load-carrying capacity (Bearing Capacity) of the soil is very low. Inverted Arch Footing is also used in construction when the building load is concentrated on walls and deep excavation of the project site is not possible.
For Inverted Arch Footing an inverted arch is constructed under the foot of Piers. Usually a segmented arch with a rise of l / 5th to l / 10th of the span is used. The span of the arch will usually depend on the arrangement of the pillars. The thickness of the arch ring should not be less than 30 cm.
Advantages of Inverted Arch Footing:
The advantages of Inverted Arch Footing that can be seen in construction sites are.
- Inverted Arch Footing is constructed in soft soils due to that the depth of the foundation usually decreases.
- The entire Inverted Arch Footing is in compression.
- Bridges with Inverted Arch Footing can be very long as there is no tension in the bride.
Disadvantages of Inverted Arch Footing:
The disadvantages of Inverted Arch Footing that causes hindrance in construction sites are.
- For the construction of Inverted Arch Footing, skilled labours are needed.
- Construction cost of Inverted Arch Footing is very high.
- A cable-stayed structure must be built to hold both ends of the arch before it is joined.
FAQ
What is an Inverted Arch Footing?
An Inverted Arch Footing is a civil engineering structure designed to distribute loads in areas with low soil bearing capacity. It resembles an arch turned upside down, placed between foundation walls to resist sideways forces.
Where are Inverted Arch Footings used?
They are used in construction sites where deep excavation is impractical and when buildings exert significant loads on walls, especially in areas with soft or weak soils.
What are the advantages of Inverted Arch Footings?
- They allow for shallower foundation depths in soft soils.
- The entire structure remains under compression, eliminating tension.
- They can support long spans without the need for tension-bearing elements like traditional bridge designs.
What are the disadvantages of Inverted Arch Footings?
- Construction requires skilled labor and is generally more expensive.
- Additional structures, like cable-stayed systems, may be needed to stabilize the arch during construction.
How does an Inverted Arch Footing differ from a traditional arch?
While a traditional arch transfers loads primarily vertically, an Inverted Arch Footing also handles lateral forces, making it suitable for situations where lateral stability is crucial, such as in retaining walls or bridge abutments.
Where have Inverted Arch Footings been historically used?
They have been employed in railway cuttings, dock foundations (including dry docks), and under bridges and viaducts, notably recommended by engineers like Robert Stephenson for their stability in poor soil conditions.
What considerations are important when designing Inverted Arch Footings?
Designers must ensure that the supporting walls are robust enough to withstand the outward horizontal thrust generated by the arch. The thickness and material strength of the arch ring are critical to its structural integrity.
Are there variations of Inverted Arch Footings in use?
Yes, variations include segmented arches with specific rise-to-span ratios tailored to the project’s needs, ensuring optimal load distribution and stability.
How are Inverted Arch Footings beneficial in construction projects?
They facilitate construction in challenging soil conditions by reducing the depth and complexity of foundations, thereby streamlining the building process while ensuring structural integrity.
Can Inverted Arch Footings be retrofitted into existing structures?
Yes, they have been used to reinforce existing bridges and structures experiencing inward sliding of abutments, providing additional lateral support and stability.
What are some notable projects featuring Inverted Arch Footings?
Historically, the Hownes Gill Viaduct and the Iron Bridge are examples where Inverted Arch Footings were strategically employed to enhance stability and load-bearing capacity.
