Revetment, Vertical Post

According to John G. Barnard's Report on the Defenses of Washington plank revetments turned out to lack the durability necessary for semi-permanent fortifications and some other means had to be found to form revetments that would last as long as the forts guarding the approaches to Washington were needed. Plank revetments in some forts were replaced by sod revetments, which were, since the material was not subject to rot, quite durable. Other forts' old plank revetments were replaced by specially developed vertical post revetments.

This type of revetment was formed by carefully positioning timber posts on end along the foot of an interior slope and fixing them in place and anchoring the posts to the parapet with a horizontal capping timber joined to an anchoring log buried in the body of the parapet. Timber posts were between 4 and 6 inches in diameter and cut to a length of 5 1/2 feet. Posts were fixed in place by planting them in a 2 feet deep trench excavated along the foot of the interior slope; they could either be laid in contact with the bottom of the trench or placed on a 2 inch thick horizontal ground sill laid into the trench. Once in place, the posts were cut off at a point 16 inches below the interior crest and the tops shaped to receive the capping timber. The interior slope above the level of the cap was allowed to fall at the natural angle of the soil from the interior crest to the top of the revetment or was revetted with sod. Capping timbers were six inches in diameter split into half-rounds. An anchoring tie was dovetailed into the center of the capping timber and notched onto an anchoring log which was buried parallel to the interior crest inside the body of the parapet.

This type revetment, much like a well made post and plank revetment, required a great deal of time and labor to execute properly and would have been quite unsuitable for use in a hastily constructed field work or one that would not see almost indefinite use. But it was quite handy for renewing the revetment of an existing parapet. Barnard claimed that it had the advantages of increased durability and was much better at receiving shot penetrating through the body of a parapet. Such a penetrating shot could knock out two or three posts, but it also sent them rotating about a vertical axis, that is, spun them around. This, again according to Barnard, would cause a great deal less damage to the revetment then a penetrating shot striking a plank revetment which would rotate on a horizontal axis and inflict relatively more injuries from splinters and large pieces of plank on troops lining a banquette over a longer stretch of the interior slope.

[This page originally appeared as a Detailed Notes Page on the old Civil War Field Fortifications Website.]

January, 2004