TUNNEL ENGINEERING

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20.2 n Section Twenty Dry Packing. Filling a void with a stiff mortar, placed in small increments, each rammed into place. Evasé Stack. An air-exhaust stack with a cross section increasing in the direction of air flow at a rate to regain pressure. Face. The surface at the head of a tunnel excavation. A mixed face is a condition with more than one type of material, such as clay, sand, gravel, cobbles or rock. Grommet. A ring of compressible material inserted under the head and nut of a bolt connecting tunnel liners to seal the bolt hole. Heading. A small tunnel, or tunnels, excavated within a large tunnel cross section which will be enlarged to the full section. Jumbo. A frame that rolls on tracks or rubber wheels and carries drills for excavation of rock tunnels. Lagging. Timber planks or steel plates inserted above tunnel-supporting ribs to hold back rocks or soil. Liner Plate. A steel segment to support the interior of a tunnel excavation. Lining. A temporary or permanent structure made of concrete or other materials to secure and finish the tunnel interior or to support an excavation Mucking. Removal of excavated or blasted material from face of tunnel. Pilot Tunnel. A small tunnel excavated over part or the entire length to explore geological conditions and assist in final excavation. Pioneer Bore. (See Pilot Tunnel.) Poling Boards. Timber planks driven into soft soil, over timber supports, to hold back material during excavation. Scaling. Removal of loose rocks from tunnel surface after blasting. Shield. A steel cylinder of diameter equal to that of the tunnel, for excavation of tunnels in soft material to provide support at the face of the tunnel, to provide space for erecting supports, and to protect workers excavating and erecting supports. Spiling. (See Poling Boards.) TUNNEL ENGINEERING 20.2 Clearances for Tunnels Clearance in a tunnel is the least distance between the inner surfaces of the tunnel necessary to provide space between the closest approach of vehicles or their cargo or pedestrian traffic and those surfaces. Minimum tunnel dimensions are determined by adding the minimum clearances established for a tunnel to the dimensions selected for the type of traffic to be accommodated in the tunnel and the space needed for other requirements, such as ventilation ducts and pipelines. Clearances for Railroad Tunnels n Individual railroads have different standards to suit their equipment. But on tangent tracks, clearances for single- and double-track tunnels should not be less than those shown in Fig. 20.1. (Clearances shown are those in the “AREMA Manual” American Railway Engineering and Maintenanceof-Way Association, 8201 Corporate Drive, Suite 1125, Landover, MD 20785, (www.AREMA.org). In rail tunnels, clearances for personnel are required on both sides where niches are not provided. These clearances should be at least 6 ft 8 in or 2 m high and 30 in wide each side of the vehicle clearance diagram, although a 24-in minimum is permitted on some lines. In highway tunnels, a 3 ft or 0.9 m clearance from face of curb is used where walkways are provided. In both road and rail tunnels, it is common practice to provide a walkway along the common wall between adjacent ducts to facilitate emergency evacuation between ducts and to prevent people from emerging directly into the path of oncoming traffic. On curved tracks, the clearances should be increased to allow for overhang and tilting of an 85ft-long car, 60 ft c to c of trucks, and a height of 15 ft 1 in above top of rail. (Distance from top of rails to top of ties should be taken as 8 in.) The track should be superelevated at curves according to AREMA standards. Clearances for pantograph, third-rail, or catenary construction should conform to diagrams published by the Electrical Section, Engineering Division of the Association of American Railroads. The latest clearance standards of AREMA should be checked for new construction. Local legal requirements should govern if they exceed these standards. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.
Circular tunnels should be fitted to the clearance diagrams, with such modifications as may be permissible. Clearances for Rapid-Transit Tunnels n There are no general standards for clearances in TUNNEL ENGINEERING Tunnel Engineering n 20.3 Fig. 20.1 Clearances specified by AREMA for railway tunnels on a tangent. rapid-transit tunnels. Requirements vary with size of rolling stock used in the system. Figure 20.2 shows the normal-clearance diagram of the New York City BMT and IND Division 267 ft cars. Figure 20.3 gives the clearances established for the San Francisco Bay Area Rapid Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.
Page 1: 20 Lars Christian F. Ingerslev, Art
Page 5 and 6: Fig. 20.3 Clearance diagram for San
Page 7 and 8: 20.5 Preliminary Investigations Sur
Page 9 and 10: The ventilation system also must be
Page 11 and 12: from larger fires. Supply semi tran
Page 13 and 14: adjustments to meet variable demand
Page 15 and 16: generator sufficient for minimum re
Page 17 and 18: interior. The length of each of the
Page 19 and 20: tunneled with tunnel boring machine
Page 21 and 22: Fig. 20.9 Tangent Piles. deep. The
Page 23 and 24: unless the rock is highly abrasive,
Page 25 and 26: more economical because of their st
Page 27 and 28: layers may be sprayed on as needed.
Page 29 and 30: Steel liner plates are available in
Page 31 and 32: should be restricted. Personnel acc
Page 33 and 34: hoe is used to loosen the soil and
Page 35 and 36: A safety screen placed in the upper
Page 37 and 38: conditions. Stone or brick masonry
Page 39 and 40: effective. Bolts are tightened with
Page 41 and 42: Fig. 20.20 Stresses in liner ring m
Page 43 and 44: ground are directly related to the
Page 45 and 46: deep, as long as risks from ship an
Page 47 and 48: stressed together longitudinally fo
Page 49 and 50: in two directions. Self-compacting
Page 51 and 52: constructed to the correct grade. T
Page 53 and 54:
seismic hazard at a tunnel site can
Page 55:
is not an option, then the tunnel m
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TUNNEL ENGINEERING

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