Founding a Sea-Wall: Lowering Caissons onto the Rock
Sinking clay-filled boxes to the seabed and bonding masonry directly to bare rock
The note completes a method for building a foundation directly on the sea floor. Around each sunken caisson a free beam lets the box slide down like a portcullis until it settles on the uneven rock, after which the box is packed with potter's clay up to the waterline and shored against the waves. Once secured, the enclosed bottom is cleaned of weed and rubble and filled with gravel and lime, or walled with large stones, so that the masonry bonds permanently to the rock. A small pen sketch at the lower left shows the open box-frame of such a caisson.
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Sliding the caisson down to rest on the sea floor
A free beam set around each caisson lets it descend by itself, working like a portcullis or floodgate, until it comes to rest on the unevenness of the rock masses of the sea bottom. It is then packed with fat potter's clay up to the surface of the water or higher, so the fury of the sea cannot overtop its rims. A clay-smeared canvas palisade may be added to break the waves.
Bonding the wall permanently to the rock mass
Once the caisson is shored, the bottom within its circuit is cleaned and the rocks stripped of weed and other nuisances, then filled with gravel and lime or walled with large stones. Because no canvas or rope net is interposed, the masonry stays joined to the rock mass and, Leonardo claims, remains eternal together with it.
Sketch of the open caisson frame
A quick pen drawing at the lower left of the sheet shows the open, bottomless timber box of the kind described in the text, drawn in perspective as a rectangular frame of uprights. It illustrates the caisson lowered onto the seabed.