Founding in the Sea, and the Port of Piombino
Two caisson methods for soft and rocky seabeds, with a plan of Piombino harbour
This page sets out two ways to lay a foundation underwater. On a soft bottom, two rings of piling two feet apart are packed with fat earth, drained, dug out, and founded; on a rocky, uneven bottom, four bottomless caissons joined into a square are lowered by corner capstans, hung with hemp nets and canvas that mould themselves to the rocks, and filled with gravel and lime that sets like solid wall. Leonardo adds that such a foundation should be left a full year to rise above the water before building on it. Diagrams show a netted caisson, a circular ring of piling, and, at the lower left, a plan labelled the Port of Piombino.
On this page
Four bottomless caissons lowered by corner capstans
For a rocky seabed, four large caissons the height of the water are joined into a square, and four capstans (argani) fixed on the timber-bound corners lower them. As they fill with gravel and lime their growing weight sinks them to the bottom, while hemp nets and sewn canvas hung beneath their open rims mould to the concavities of the rock.
Twin rings of piling for a soft bottom
Where the sea floor has no firm rock, two circuits of piling are driven two feet apart and the gap packed with well-rammed fat earth. The water is then bailed out of the enclosure, the ground dug out, and the foundation laid at leisure.
Leaving the foundation a year before walling above
The completed foundation is to be left for the space of a whole year, until it rises past the surface of the water. Only then may one wall above it. The lime is specified to be fresh, in whole lumps, cast as powder into the water with the gravel.
Plan of the Port of Piombino
A plan at the lower left, captioned Porto di Piombino, shows the layout of a harbour with a curved enclosing mole. It sits beside the founding studies as an application of the sea-foundation technique to a real port.