A sand box or sand jack is a device used for removing the

centering Centring, centre, centering"Centering 2, Centring 2" def. 1. Whitney, William Dwight, and Benjamin E. Smith. ''The Century dictionary and cyclopedia''. vol. 2. New York: Century Co., 1901. p. 885., or center is a type of formwork: the temporary str ...

of an arch. Each

prop A prop, formally known as (theatrical) property, is an object used on stage or screen by actors during a performance or screen production. In practical terms, a prop is considered to be anything movable or portable on a stage or a set, distinc ...

is mounted on a sand box. After the plug is removed, the sand pours from the box, causing the centering to move downwards, diminishing the pressure from the arch, and enabling to ultimately remove it.Ashok Kumar Jain, B.C. Punmia, ''Building Construction'', Firewall Media, 2005, p. 435.

References

{{Reflist Arches and vaults Sand Tools