Terreplein

Terreplein. . , Fort Knox's roof, or terreplein, has emplacements for thirty cannons. These cannons would have been smaller than the guns planned for the casemates on the main level below., The 30 gun circles on the terreplein were all laid and ready for guns in September 1864. The fort was not fully armed, however, and the terreplein's cannon emplacements never received guns. Other areas, such as the batteries and the main level's casemates, proved of higher priority for the fort's defense and received most of the 74 cannons that were eventually mounted at the fort., The terrepleins of forts like Fort Knox were most often covered with earth. This material has both practical and strategic advantages. It was inexpensive and could be leveled easily. If shells from enemy ships fell on the terreplein, an earthen covering could absorb the impact. In addition, earth was not easily damaged by vibrations from the firing of the fort's own cannons., A New Approach , A major project began in 1996 to waterproof Fort Knox's terreplein, repair damaging leaks below, and improve drainage. This project created a new concrete surface and drainage just below the terreplein's earthen fill in order to bypass the deteriorated drainage system deep inside the fort structure., Machinery removed the terreplein's fill down to the top of the casemate arches in the main level below. Originally, these arches had been coated with concrete and mastic to prevent leaks through the brick masonry. Engineers and workers in the 1860s had also installed vertical drains between each casemate to collect water from the terreplein and direct the water outside the fort or to cisterns inside., The upper parts of the vertical drains between the casemates are shown in the photograph above, which dates from the 1996 project. When they were first built, these drains were capped with removable circular drain covers so that the drains could be inspected., Once the terreplein's fill was removed in 1996, a concrete slab was poured, waterproof membrane applied, and drainage mat and drain pipes installed. The terreplein's earthen fill was then replaced and grass planted.