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.

Segmental vault, 10.35m span, 2.25 m rise
Built free spanning in 3 weeks

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.

Starting the horizontal courses

Laying 3 to 5 mm mortar on the vertical side joint Laying a triangular mortar for the horizontal joint
Pressing the block on the side

Pressing the block on the previous course
The trowel cannot go in the joint if the block is well laid
Laying the half block outside for the bond pattern
Filling the joint of the first courses

Horizontal courses going ahead

Starting an arch window with a centring used as a guide
Reversing the centring to build the arch window
Starting the arch of the window

Arch of the window being built

Arch of the window in progress

Blocks corbelling for the arch of the window
Building the arch of the window

Building symmetrically the arch of the window
Arch of the window near completion
Corbelling blocks of the window

Laying the bottom side blocks of the window
Completing the bottom side of the window
Window arch completed

Horizontal courses around the arch window

Horizontal courses going on above the arch window

Building symmetrically with horizontal courses till the limit of stability
Horizontal courses completed
Limit of stability with horizontal courses
Starting the vertical courses
Building vertical courses
Vertical courses in progress
Vault near completion
Competing the vault

Laying the last blocks of the last course
Checking the last course

Vault completed in 37 days
Vault completed
Casting the waterproof earth plaster
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