Arch as a foundation
With earth below, the arch would be even more stable and hence can take greater load, supporting the building walls.
It is interesting to note how we tend to forget what we learn. Just leaf through an old book of medicine, construction, cooking or stitching, documenting certain ideas. Only after proving itself, that idea would have been codified, written about and became part of the book. As such we may assume the written idea is a proven idea.
Let us check how many of the ideas explained in the texts are followed now. Maybe a handful or little more, not because the rest of the ideas have failed, they have been either replaced by newer ideas or have simply been forgotten.
The art of constructing a building foundation using arches is one among such ideas – simply forgotten. We continue making arches above ground but why not below ground? With earth below, the arch would be even more stable hence can take the greater load, supporting the building walls.
There are two methods to do an arch foundation – if the full foundation would be underground, the foundation trench is dug directly with arch profiles with adequate spacing between them to build foundation piers to spring the arches. This space where arches start would need a normal footing with enough width to take on two arches. The unexcavated earth stays underneath the arch as if that’s the centring support.
If the site is lower than the road, we dig only to erect the foundation piers, taking them deep enough to reach hard soil. From the top of piers which is at the site level, we can start the arches, which should be within 5 to 8 feet span for general safety. In case of uneven sites, the rise of arches can also be varied to suit the context. Arch centring is generated by filling in mud in the required profile, where using an M.S. template ensures the curved profile is perfectly suited to take the arch action.
The curved mud profile is topped with water mud mix and manually consolidated. If the top mud layer appears very brittle, a thin cement or cement-stabilised mud mortar can be applied, ensure there is a level base layer below the arch.
Now, stone or brick arches are built just like we do in any wall and cured well. Plinth beam is placed above the arches and backfilling the earth up to plinth level completes the foundation work of the building.
Architect Rajesh Jain from R-LEEF has been reviving this forgotten technology for many years now, improving it from its textbook days. Of course, it needs an engineer’s supervision, masons with arch construction skills and contractors with inclinations to explore. If the team is not interested in exploring, the idea may fail due to a badly done job.
Imagine a small plot with a dozen RCC columns and next to it a dozen arches – both take the load. To live a green future, we need to revive older ideas