Semicircular Vault
This vault has been built in the campus of the Auroville Earth Institute. It is used as a precasting shed on the ground floor and as a trainee’s dormitory at the first floor. This semicircular barrel vault had been built also to experiment the optimisation method developed by the Auroville Earth Institute. The vault has been built in 37 days with 4 masons and it presents these features:
• Weight: about 40 tons
• 6 m span, 3 m rise, 11 m long, 36.5 to 7 cm thick
• It has been built free spanning with a combination of horizontal and vertical courses
The condition of safe stability for a barrel semicircular vault of this size requires normally 1.2 m thickness. With our method, the vault has been optimised with a decreasing thickness of only 36.5 cm thickness at the bottom up to 7cm at the top.
Note that the vault stability is first calculated without the weight of the waterproofing. The waterproofing of such a vault is done with stabilised earth plaster, which has been researched and developed by the Auroville Earth Institute. The weight of such a waterproofing was around 6 tons and it was spread over the entire vault area. Therefore this load, which was added a few months after completion of the vault, changed the location of the line of thrust in the structure. Therefore, the geometry of the vault was be done in such a way that it is stable with or without load:
– When the vault is built, the line of thrust is sometimes at the inside limit of the middle third of the vault.
– With the weight of the waterproofing, the line of thrust moves slightly outside in some parts to become limit at the outside of the middle third.
