Sandpit (construction)
A sandpit was previously used in the construction of structures in order to adjust or lower posts or supports loaded with heavy weights.
The principle is based on the fact that dry, clean sand can practically not be compressed. If you put the foot of a post or a support (on a support plate) in a filled sandpit with a hole closed with a plug at the bottom, the sand slowly trickles out when the plug is pulled, but the hole can be closed again at any time. In this way, the post or the support can be lowered by the millimeter.
Sand boxes were mainly used to slowly lower a falsework after the completion of the bridge arch that weighs on it, until the arch supports itself and the falsework can then be safely removed. But they were also used during the construction of the Eiffel Tower to precisely adjust heavy iron girders.
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- Paul Séjourné: Construction des ponts du Castelet, de Lavaur et Antoinette . Annales des Ponts et Chaussées 1886, Volume II, XII, pp. 409-549, in particular pp. 439 ff. Digitized on BnF Gallica
- Gustave Eiffel : Une tour de trois cents mètres , Lemercier, Paris 1900
