Magazines: Designs : Gabion and Fascine

Civil War Field Fortifications

Magazines

Theoretical Designs

All of the performance requirements discussed in the preceding section, proper ventilation, moisture exclusion, and storage capacity could be achieved by placing gunpowder barrels and shells in simple pitched roof sheds. But a shed, however well built, could not meet the fourth and defining performance requirement for magazines; the structure not only had to preserve its contents in serviceable condition, it also had to protect it from the destructive effects of enemy artillery fire. For a magazine to perform this most basic function it had to be constructed in such a way that enemy shot and shell delivered by horizontal or vertical fire could not penetrate into the chamber or gallery and ignite the stored materials. The interior structure of the chamber and gallery also had to be sufficiently solid and stable to withstand the concussive effects or shock waves produced by the impact of shot on the structure and explosion of shells in close proximity to the structure. Performance against artillery fire was achieved by constructing the interior chamber of relatively strong materials and joining those materials so that they could not be easily shaken apart and by covering the interior structure with layers of well rammed earth and giving this covering mass sufficient thickness to absorb and deflect the impact of shot and exploding shells well before they penetrated deeply enough to reach the interior chamber. Performance could also be increased by sinking the interior chamber and gallery into a trench which reduced the interior chamber's exposure to horizontal fire.

Engineering manuals used in the Civil War period offered a variety of designs that were intended as models that could be used as basic guides for the construction of magazines that would meet performance requirements in temporary field fortifications. These designs may be divided into three distinct categories based on the materials used to form the chamber and support the roof and weight of the covering mass: 1) gabion and fascine revetted magazines that depended on retained and rammed soil to from the walls and carry the burden of the covering mass, 2) frame and fascine magazines in which a partially framed chamber was supported by or on the earth walls surrounding it with a fascine sheathing forming the walls and roof, and 3) fully framed magazines in which the interior structure stood independent of the the earth surrounding it and carried the full burden of the covering mass. The following pages will examine specific examples of each category of magazine designs.

Gabion and Fascine Magazines

D. H. Mahan described a half-sunken magazine in which the chamber was formed by a trench about six feet wide and of the desired length with its perimeter lined with two adjoining rows of gabions. The trench was about six feet wide with its walls unrevetted and sloped on a ratio of about one in four. When gabions of the normal dimensions (about 33 inches tall and 24 inches in diameter) were used the trench would have to be about 39 inches deep to raise the ceiling of the chamber to a six foot standard height. Two adjoining rows of gabions, which would be filled with soil from the trench, were placed around the perimeter of the trench (leaving an opening about two gabions wide for the gallery) to form the upper portion of the chamber walls and to provide support for the chamber roof. The roof itself was formed by laying scantling latitudinally across the trench and topping them with two crossing layers of fascines cut to the appropriate length. The covering mass, the soil for which would be taken from a trench surrounding the magazine, was then thrown around the gabions and on top of the roof until its thickness, when well rammed, would be about three feet.

Duane's Manual for Engineer Troops, which was nothing more than a minimally attributed compilation of European engineering manuals, described a fully sunken magazine with the chamber walls revetted using a single row of gabions inside the trench. The trench itself was about 10 feet wide and six feet, six inches deep. Gabions were laid along the trench walls on a fascine footing, filled with soil from the trench, and topped by a longitudinal lining of fascines laid side by side. Joists to support the roof were made of scantling about six inches wide and 16 feet long and were sunken into the ground and extended about four feet into the undisturbed soil on either side of the trench. This arrangement helped transfer some of the weight of the covering mass off the gabions and onto solid ground around the trench. Fascines were laid on the joists in crossing layers to form the roof and the whole was covered by a rounded mound of earth to a height of about six feet. This design produced an interior chamber with a height of about four feet, six inches, which would have made handling powder barrels within the magazine extremely difficult and very uncomfortable while increasing the hazards incident to poor ventilation.

A fascine lined magazine described by Mahan could either be constructed with the floor of the chamber at ground level or with the floor well sunken in a trench. In either case the walls were about six feet apart on their latitudinal sections, six feet in height, and sloped on a ratio of about one in four to relieve pressure on the fascine lining. The fascines were cut to the appropriate length, laid in rising tiers, and well anchored with three foot long pickets which were driven through the fascine and into the soil. The scantling joists were sunken to the level of the top tier of fascines and extended well beyond the interior walls to help carry the burden of the covering mass away from the fascine revetment. Again, the roof itself was formed from crossing layers of fascines.

While these materials were suitable for temporary magazines, they were incapable of sustaining the performance requirements necessary for magazines over a prolonged period of time. Gabions and fascines were very porous and could not block the flow of water through soil. Neither fascines nor gabions were designed to bear an overhead load, both, especially gabions, tended to break down as their members loosened from the weight of the covering mass and rotted due to constant contact with the retained soil. Although both were effective revetment materials, they were very porous and not capable of blocking moisture seeping through the soil. Poor ventilation in temporary magazines designed with just one entrance and no vents, where the air was not allowed to flow freely through the structure, tended to magnify the rotting effects of moisture on magazine walls.

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