The floating slab has been the primary method for mitigation of underground noise and vibrations in the Washington Metropolitan Area Transit Authority's (WMATA's) Metrorail system. Because of one type of defective polyurethane isolator pad supporting the floating slabs, about 18,800 track ft of floating slabs have settled unevenly, causing operation and miantenance problems. As an emergency measure, WMATA's maintenance forces raised the rails to the proper elevations by inserting shims under the rail fasteners on the floating slabs. There are about 80,000 ft (15 mi) of floating slabs in the WMATA operating system. About 22,400 ft (4.2 mi) are resting on this type of polyurethane pads, and 18,800 ft (3.5 mi) require new pads. Replacing pads under a 60 ton, 60 ft long floating slab segment, under restricted working conditions, presents a real challenge. The working hours are limited to nonrevenue hours between midnight and 5:00 a.m. Many techniques of repair have been developed and tried with the assistance of De Leuw, Cather and Company, WMATA's General Engineering Consultant. Two techniques have been successfully tried and are being used to lift the floating slabs for pad replacement. The retrofit has been performed by a Design Build team consisting of the Office of Engineering and Architecture and the maintenance forces from the Office of Track and Structure. For the circular tunnel sections, the technique is called window cutting with jacks and beams. For the box sections and passenger stations, the technique is called window cutting with jacks and stools. For the crossover and turnout areas, the technique has not been developed. It will probably be a variation of the window cutting with jacks and stools technique. As of December 1994, about 5,241 ft (1 mi) of floating slabs have been retrofitted by these two techniques with new natural rubber pads. To complete the retrofit, track alignment survey, noise and vibration measurements, and structural restoration are being performed after the pad replacement. The work is continuing wherever the track-right is available and may take the rest of the century to complete.


  • English

Media Info

  • Features: Figures; Tables;
  • Pagination: p. 118-126
  • Monograph Title: Public transportation 1995: current research in operations
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00715535
  • Record Type: Publication
  • ISBN: 0309061652
  • Files: TRIS, TRB
  • Created Date: Dec 29 1996 12:00AM