Canadian Pre-Configuration

Here in the picture you can see a sort of pre-configuration of voussoirs being arranged at a bridge we built near Montreal. 

Having spent time sorting through the pile of material and choosing the best ones, rather than fitting them one at a time over the actual bridge form, we pre-fit them in an assortment of rows according to size nearby first. This way it was possible to choose all the similar width stones and prop them up together in rows to see how they would fit. 

If you decide to do this, choose a flat area and lay plywood out wide enough to accommodate the dimensions of the form which is a rectangle the 'width of the bridge' by 'the length of the arc over the span' This length will be slightly longer than the span across the bottom of the form.

Lay the stones face down on as if you were pitching cobblestones on a path, only upside down

The idea of preparing all the voussoirs beforehand to one side of the bridge is to be able to work together as a group better. Sorting and moving them around is more convenient. It also facilitates a variety of configurations to be tried out rather than having no opportunity to undo the rows that would have been placed on the bridge if they hadn't been pre-configured. 

It also means more people can work on the project at the same time, rather than all be crowded around waiting to put stones over the arch one at a time. 

The putting together of the arch takes less time since the voussoirs can be easily moved one by one and re-fit on the form. When they are set over the bridge form, each voussoir is spread with small wedges so that they all fan properly,



Care should be taken when people are transferring the individual stones to the bridge, not to mix up the rows, or reverse the sequence of voussoirs left-to-right. 

Numbering them or spraying coloured dots on the stones helps remove confusion.       Or does it?