Building & engineering news . t up without interfering with the concretingof adjacent section or the excavation of the tunnel. The inside footing forms are built of wood in eight-foot fections and after stripping are re-paired and usedseveral times. The arch forms consist of 2 by 6-inch tim-lier, set longitudinally on curved steel I beams restingen the ceiling slab. The I beams are 7 inches in depthand spaced ?.0 inches centers. Two of these pneumatic mixers are now in use, one nearthe west portal, the other near the easterly end of thework. Each is set on the ceiling slab in the arch section,
Building & engineering news . t up without interfering with the concretingof adjacent section or the excavation of the tunnel. The inside footing forms are built of wood in eight-foot fections and after stripping are re-paired and usedseveral times. The arch forms consist of 2 by 6-inch tim-lier, set longitudinally on curved steel I beams restingen the ceiling slab. The I beams are 7 inches in depthand spaced ?.0 inches centers. Two of these pneumatic mixers are now in use, one nearthe west portal, the other near the easterly end of thework. Each is set on the ceiling slab in the arch section,at the tiottcm of short concrete-lined shafts tothe surface. Above the shafts are constructed the rockand sand bunkers—chutes for carrying cement alsojiass throng the bunkers and shafts Thus all materialsare fed into the measuring hopper by gravity. The conveying pipe is S-inch steel pipe with flangejoints, bolted together and is laid along the top of theceiling slab. For filling the footing forms or sidewall and. 1. 1 1 -? - 1 *-- ^\.^ .>Ielliods of Concreting. The concrete in oi)en cut work was mixed in standardrctary mixers, set up on the edge of the cuts and wasplaced with chutes and buggies. The biggest portion wasplaced direct from chutes without wheeling. Previousto the installation of pneumatic concrete mixers and con-veyors a portion of the concrete lining of the tunnel sec-tions was similarly placed. The imoiiniatic mixer used consists of a steel cylinderwitlr a Tcnc shaped liottom at the point of which is at- slab forms the pipe is led into a steel receiving hopper atthe section to be poured. This hopper is suspended fromthe arch .segments of the timber lining: from the hopperextend chutes into the forms to be filled. This hopperwas necessary as ?shooting the concrete from the pipedirectly into the forms displaced the reinforcing steel andconduits. For concreting the arch, the conveying pipe is led intothe forms; as the arch has reinforcing steel only
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