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Mensagem por Manuela » 05 Set 2016, 14:12

Autores: Jerry G. Rose, Ph.D., PE e Paul M. Tucker.

To be presented at the American Railway Engineering and Maintenance-of-Way Association 2002 Annual Conference & Exposition, September 24, 2002, Washington, DC.

Replacing and rehabilitating highway crossings represent a major track maintenance expense for the U.S. railroad industry. Substantial numbers of crossings deteriorate at a more rapid rate than the abutting trackbed due to excessive loadings from heavy truck traffic and difficulty with maintaining adequate drainage within the immediate crossing area. Others are replaced during out-of-face system maintenance activities such as tie and rail renewals and surfacing operations. At many crossings the disturbed track does not provide adequate support and the replacement crossings soon settle and become rough for vehicular and even train traffic.
The ideal highway crossing system is one that will maintain a smooth surface and stable trackbed for a long period of time reducing disruptions to rail and highway traffic. It will not require frequent rehabilitation and ideally, will not have to be renewed (replaced), but merely skipped, during major scheduled out-of-face track maintenance activities.
CSX Transportation and University of Kentucky researchers in cooperation with local highway agencies have developed the technology for rapidly renewing highway crossings using a panel system and premium materials. The procedure involves complete removal of the old crossing panel and trackbed materials and replacing them with an asphalt underlayment, a compacted ballast layer, a new track panel, and a new crossing surface. Numerous documented performance evaluations indicate this design provides a long-life, smooth crossing for heavy rail/highway traffic applications.
The project schedule is for the railroad to be out-of-service for a maximum of four hours and for the highway to open later in the day, typically after eight to ten hours. The importance of the cooperative effort between the railroad and local highway agency is stressed. The objective is to minimize disruption to both railroad and highway traffic during the renewal process.
Earth pressure cells have been imbedded at various locations in selected crossings to monitor trackbed pressures within the track structure under both railroad and highway loadings. Pressures vary within the crossing structure. Peak dynamic pressures develop directly below the tie/rail interface. These are typically less than 20 psi (140 kPa) at the underside of the compacted ballast layer for the 36 ton (33 metric ton) axle loads. The results of these tests and evaluations are presented in detail.
The desirability of using a high modulus, waterproofing layer to properly support the ballast layer/track panel/crossing surface within the track structure is discussed. The desirability for and proper installation of transition zones along the track and highway approaches are stressed. Also described is the benefit of pre-compacting the ballast to reduce subsequent settlement and maintain smooth crossings. Numerous case studies are presented, based on long-term performance evaluations, which indicate this practice ensures long life, economical, smooth crossings for improved safety and operating performances.
Key Words: asphalt underlayment, rail/highway crossings, trackbed pressures, fast-track.
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