. The Americana : a universal reference library, comprising the arts and sciences, literature, history, biograhy, geography, commerce, etc., of the world . ough eitherporous material or through crevices or fis-sures in the overlying rock so that both thecompleted tunnel and the work in progressare subjected to a water pressure representedby the static head of the water above in rock tunneling under suchconditions or in stiff clay, water may flow inupon the work in quantities not too great tomake its removal by pumping , however, water enters too freely forsuch pr
. The Americana : a universal reference library, comprising the arts and sciences, literature, history, biograhy, geography, commerce, etc., of the world . ough eitherporous material or through crevices or fis-sures in the overlying rock so that both thecompleted tunnel and the work in progressare subjected to a water pressure representedby the static head of the water above in rock tunneling under suchconditions or in stiff clay, water may flow inupon the work in quantities not too great tomake its removal by pumping , however, water enters too freely forsuch procedures, compressed air must beused to keep the water out, the pressure ofair being determined by the depth of the TUNNELS AND TUNNELING work below the water surface. When tun-neling is prosecuted under these conditionsa sliield is ordinarily used, as will be de-scribed further on. An instance illustratingthe method to be followed in sub-aqueousrock tunneling will first be given. The Severn Tunnel.— This tunnel, a double-track tunnel, a little less than 4,4 rniles long,was built under the river Severn in thesouthwestern portion of England between. Fig. 5. 1873 and 1S86. Although this tunnel wasbuilt largely through rock, for a short dis-tance the material penetrated was bed of the river at the tunnel site iscomposed of strata of conglomerate lime-stone, carboniferous beds, marl, gravel andsand. The least thickness of the naturalcover over the tunnel is 30 feet of marl onthe English side of the river. At the deepestpart of the river channel the thickness of thesandstone over the tunnel is about 45 entire tunnel is lined with vitrified brickwork 214 to 3 feet thick, laid in Portlandcement, the invert having a thickness of 114to 3 feet. Much water was encountered inthe prosecution of this work which producedgrave difficulties. Indeed, at one time theentire work was flooded for a period of 13months. The water gave much trouble atother times, breaking through
Size: 1634px × 1529px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookidamericanauni, bookyear1903
