Three years ago we were asked to trek up to Fort Ticonderoga to examine the deteriorating fort walls. Originally built in the mid-18th century, the fort overlooks Lakes Champlain and was a strategic stronghold for various armies. The barracks and defensive constructions fell apart or were dismantled over the years, but in 1908 the fort was rebuilt following the original construction techniques. The fort is rectangular with four bastions, one at each corner. Two demi-lunes protect the landward faces to the north and west; these are separate triangular bastions connected via raised bridges to the main parade ground.
The fort walls are two to three feet thick, composed of outer wythes of stone set in mortar and an inner fill of fine rubble. The terreplein sits on barrel vaults spanning between the walls. Theoretically, the terreplein is sloped for drainage and water that runs into the walls escapes through weep holes and drips down the face of the wall. When we took a look in 2020, many walls of the demi-lunes and main curtain walls had suffered partial collapse. Water infiltrating the wall had washed out the mortar and the walls’ rubble infill, meaning there was nothing left to anchor the outer wythe of stones and they began to fall out. Freeze-thaw cycles quickened this process, the expansive ice trapped in voids in the wall pushing the stones out. In some areas this was just a few stones; in others, wide swaths of the wall were now gaping open. This failure leaves only one unstable wythe of stones behind and it was evident that immediate rebuilding was necessary. As we developed repair details for the work, conditions worsened. The extent of the partial wall collapse had notably spread when we revisited this summer.
It was decided that the scope of the current work would pertain to the north demi-lune. We developed a repair sequence: insert stainless steel through-ties to hold in place a wire mesh over the remaining rubble infill. This would keep it in place and provide a small amount of tensile strength against movement out of plane. Then rebuild the outer wythe of the wall. Finally, with shoring in place to combat hydrostatic pressure, the wall would be grouted to replace the rubble fill and solidify the wall. In areas where the veneer stone has not yet fallen out, ties would be inserted and the wall would be repointed and grouted. The repair work began earlier this year and is progressing nicely.