Highway & Rail Transit Tunnel Maintenance & Rehabilitation Manual
Chapter 1: Introduction
In 1999, the Federal Highway Administration (FHWA) created an office to focus on management of highway assets. Part of this office is responsible for providing guidance and technical assistance to state and local highway agencies on structure management issues, including highway tunnels. Similarly, the Federal Transit Administration (FTA) is responsible for providing guidance on tunnel management to rail transit owners. Because of this common interest in tunnel management procedures, the two agencies decided to jointly sponsor the development of a Tunnel Management System for both highway and rail transit tunnel owners.
To avoid future potential major operation problems due to deferred maintenance, FHWA and FTA sponsored this project to develop inspection procedures and guidance for maintenance practices within highway and rail transit tunnels and to assist tunnel owners in maintaining their tunnels. Along with the Inspection Manual and this companion Maintenance and Rehabilitation Manual, a computerized database system was also developed to assist with the storage and management of tunnel condition data and for prioritizing repairs. It is the intent of the FHWA and FTA that these products be furnished to each highway and rail transit tunnel owner across the nation, and to be placed in the public domain.
Phase 1 of this project involved the development of an inventory database of the nation's highway and rail transit tunnels that included such information as location of the tunnel, tunnel name, age, length, shape, height, width, the construction method employed, construction ground conditions, lining/support types, and types of mechanical/electrical systems. The data received from highway tunnel owners responding to the questionnaire revealed that more than 32 percent of reported highway tunnels are between 50-100 years old, with 4 percent greater than 100 years old. Although it is more difficult to categorize rail transit tunnels by percent, inventory information collected to date, plus data known to exist for certain agencies that had trouble segmenting all of their tunnels according to the questionnaire, suggests that there are approximately 346 km (215 miles) of rail transit tunnels greater than 50 years old. This data is sufficient to indicate that these older highway and rail transit tunnels contain elements that are deteriorating and in need of repair.
Groundwater infiltration through joints and cracks in tunnels is the number one cause of deterioration of the various tunnel elements. In addition, for concrete tunnels more than 50 years in age it is highly likely that the concrete was not air-entrained and; therefore, tunnels subjected to temperature gradients may have suffered damage over the years due to freeze-thaw actions. Since numerous tunnels have been subjected to these conditions for many years, it is vitally important that tunnel owners commence regular preventive maintenance and repair procedures for correcting deficiencies such that each tunnel can continue to function as originally designed.
The purpose of this manual is to provide highway and rail transit tunnel owners with guidelines and practices for preventive maintenance of both the tunnel structure and the mechanical/electrical/track systems within. Suggested repairs to the tunnel structure for various deficiencies are provided. These repairs include guidelines for controlling water infiltration into the tunnel, the number one cause of deterioration.
To promote consistency of definition of particular elements, this manual contains several chapters that explain the various types of elements that exist within the tunnel. For example, the description of tunnel components such as tunnel configuration, liner types, invert types, ventilation systems, lighting systems, tunnel finishes and other systems/appurtenances (track, traction power, signals and communications) are each provided in separate sections to assist tunnel owners in educating their inspectors as to the particular system existing within the tunnel.
The incorporation of the guidelines presented herein and the use of a documented maintenance and inspection program (via the software provided) will help tunnel owners to program needed maintenance and rehabilitation costs. It is important to note that the guidelines and practices included are intended to supplement existing programs and procedures already in place. It is not the intent to replace current practices unless the tunnel owner decides to do so as a benefit to his/her program.