SANDBAG-FILLING

Hauraki Plains Gazette, Volume 51, Issue 3156, 12 August 1942, Page 6

SANDBAG-FILLING

GOOD, MEDIUM AND POOR HINTS FOR PROTECTION In view of the fact that it is months since there has been an E.P-S. trial in Thames and that the expeetanev of such a trial has faded from the thoughts of local citizens, it may be well to recollect some of the things worth knowing in case of an air raid. For instance, a circular issued by the National Service Department mentions that the materials used for filling sandbags may be classified thus: —

Good: Ballast/ blast furnace slag, broken stone, coarse sand, dry earth, gravel, shingle. Medium: Broken brick, chalk, coal in lumps, fine sand, foamed slag. Poor: Boiler ash, coal dust, plastic clay, pit heap material, sharp flints, and material with lime adhering. It is difficult to build a firm screen wall if the bags are filled with a fine powdery material, as the bags tend to a'ssume a ball shape, and the filling is liable to escape through the fabric. Some materials, such as flints, have such sharp edges that they cut the bags and are unsuitable. Other materials will corrode and should not be used if the bags are to be placed in contact with steel.

The resistance of the filling to penetration by bomb fragments is important; it is roughly proportional to the weight per cubic foot of the materials. For materials of the same density the coarser the grain the less the penetration.

The addition of a little cement to any of the granular fillings has the advantage of causing the whole to bind into a solid which may be stable even if the bag decays.

As between possible materials the choice. would naturally be determined by final cost and availability, remembering that thickness must be increased if penetrative resistance is reduced. For example, for lateral protection 2ft thicknesses of ballast or broken stone is equivalent to a thickness of 2ft 6in of earth or sand. For a sandbag wall 2ft thick at the top, vertical at the back and with a front slope of four to one, the number of sandbags required per foot run of wall is roughly 30 for a height of Oft; 36 for 7ft; 40 for Bft; 50 for Oft; 60 for 10ft; 75 for lift; and 85 for a wall 12ft high. Where, however, the sandbag wall is being built to make a 9in brick wall proof against bomb splinters, a reduction may be made of roughly one-third of the above number of sandbags per foot run required. A cubic yard of sand or earth will fill approximately 48 sandbags.