. Shield and compressed air tunneling . Lining.—The weight of cast iron liningdepends on the design and, therefore does not follow any definite LININdS FOR SUIKLI) DRIVEN TUNNELS 10!) law. Figure 3G shows the weight per linear foot of tunnel inpounds in relation to the external diameter of various tunnels inLondon (lay and also a curve having the equation W = UJ) (28) where 11 is the weight of the lining in pounds per linear foot of tun-nel and D the external diameter in feet. This curve approximately _ 20,000 15,000 10,000 5,0 OO —1 —1 ^ —\ ~ ~ ~~ _ ir, Y ~ ~ ~ ^~ / / < ... / y ~ ^ - - /t
. Shield and compressed air tunneling . Lining.—The weight of cast iron liningdepends on the design and, therefore does not follow any definite LININdS FOR SUIKLI) DRIVEN TUNNELS 10!) law. Figure 3G shows the weight per linear foot of tunnel inpounds in relation to the external diameter of various tunnels inLondon (lay and also a curve having the equation W = UJ) (28) where 11 is the weight of the lining in pounds per linear foot of tun-nel and D the external diameter in feet. This curve approximately _ 20,000 15,000 10,000 5,0 OO —1 —1 ^ —\ ~ ~ ~~ _ ir, Y ~ ~ ~ ^~ / / < ... / y ~ ^ - - /t _^ _ - / . ^ ^ i: ^ ^ < ^ ^ . X- •x ;^^^ - — — — ? 1 1 _ _ _ 10 15 20 15 E)<fernal Diame+er in feet 30 35 Fig. 36.—Cast iron lined tunnels in London clay. Relationship betweendiameter and weight of cast iron. satisfies the actual weights. Figure 37 shows a similar curvefor tunnels in firm waterbearing ground, having the equation W = 19D (29) and also the actual weights of various tunnels in waterbearing 20,000. 10 15 eo 25 Ex+ernal Diameter in feet 30 Fig. 37.—Cast iron lined tunnels in water bearing ground. Relationshipbetween diameter and weight of cast iron. ground. Figure 38 shows the same relation of tunnels in HudsonRiver silt and a curve having the equation 110 SHIELD TUNNELING W = 22Z)2 (30) These curves should be used only for establishing a provisionalvalue of W and they should not be used for tunnels larger than30 ft. in diameter without further investigation. 20,000 T 5,000 J / / / / / A-18 J^ / / / / A-h / */4-/7 ? ? ^ ^ ^ ^ _ _ _ ^t _ _ _ _ — _ _ _ — _ _ — ? t= CD 1— 1— 1— 1— 1— 1— 1— 1—- L- 1— <— L- L- L-J 10 15 20 25 External Diameter in feet 30 35 Fig. 38. -Cast iron lined tunnels in Hudson River silt. Relationship betweendiameter and weight of cast iron. 44. Specifications for Cast Iron Tunnel Lining.—In the follow-ing the specifications for cast iron hning used for rapid transittunnelsin N
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