. Shield and compressed air tunneling . ion is generally done by mechanical power, and the imple-ment used for this purpose is called an erector. The erectorconsists essentially of an arm which swings on a horizontalshaft parallel to the longitudinal axis of the tunnel and which maybe shortened or lengthened as desired. 51. Location of Erector.—The erector may be carried on aseparate stage behind the shield, as shown in Fig. 72, but in mosttunnels it is mounted on the shield. The principal advantage ofthe latter arrangement is that the erector is moved forward withthe shield and no adjustment
. Shield and compressed air tunneling . ion is generally done by mechanical power, and the imple-ment used for this purpose is called an erector. The erectorconsists essentially of an arm which swings on a horizontalshaft parallel to the longitudinal axis of the tunnel and which maybe shortened or lengthened as desired. 51. Location of Erector.—The erector may be carried on aseparate stage behind the shield, as shown in Fig. 72, but in mosttunnels it is mounted on the shield. The principal advantage ofthe latter arrangement is that the erector is moved forward withthe shield and no adjustment is required to bring it into properposition for erecting the lining. On the other hand, if the erectoris mounted on a separate stage, the proper adjustment is mademore readily, when the lead is great, without straining the erectorarm and when out of repair the erector may be removed withoutinterfering with the work at the shield. When mounted on theshield theturning axis of the erector usually coincides with that 160 SHIELD TUNNELING. TUNNEL SHIELDS Ki of the shield, but in a few instances two erectors have l)eenmounted symmetrically on the shield, each with its turning axison the horizontal diameter of the shield. The purpose of usingtwo erectors has been to speed the work of erection, but it isdoubtful if the efficiency is increased. With two erectors thearm of each should ho able to reach rather more than one-half thecircumference of the lining. With one erector the arm must beable to make a complete revolution.
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Keywords: ., bookcentury1900, bookdecade1920, bookidshieldcompre, bookyear1922
