Compressed Air Work And Diving 1909

SINKING. 47 skins which do not require to be concreted up, this can be most conveniently applied in the form of water, which can be pumped in or out as the circumstances of ticle level may demand. In soft ground the caisson may be allowecl to sink gradually into the ground without any lowering of the air unless the skin friction becomes too great, but a lock- out must be kcpt for large boulders and old piles or pile heacls. The two latter are often found at a consider- able depth below ground level, and will often clo a good cleal of damage if not noticed in time. If the cutting edge should get bent in at all, it will be necessary to keep the line of excavation some distance behind it in orcler to prevent the caisson jambing as it clescencls. Pipes are fitted for biowing out any water that may get into the working chamber when the excavation has been carried below the cutting eclge. Air should be allowed to mix with the water, and then it can be blown out over the sides of the caisson considerably above the level of the water outsicle. If this is not done, the water in the pipes will only rise to outsicle water level. A con- venient methocl is to introduce a pipe of smaller diameter into the mouth of the blow-out pipe, so that the latter can be kept below the water in the caisson, and will not require adjustment as the level of water is reduced. The other end of such a small pipe will be merely left open so that the air in the working chamber can enter it. In the diagram, Fig. 3, which has been introduced to illustrate this chapter, the concrete is shown at the top of the roof girders, but in actual practice the air- tight ceiling will come at the bottom of the girders and the space between them will be fillecl with concrete. The sloping walls at the sides may either be filled with concrete