freight was carried over the (227,000 km) railroad network. nation’s nearly 141,000-mile The average freight car weight has increased to 129 tons (117 metric tons) with most new cars having gross weights of 143 tons (130 metric tons). The importance of developing and specifying premium track structures and components to adequately carry the increased tonnage is a current reality of the industry. Failure of the track structure and components results in difficulty maintaining track geometric features necessary for efficient and safe train operations. Maintenance costs and track outages increase due to frequent maintenance and renewal cycles. The inability of the track structure to adequately carry the imposed loadings can be categorized into two primary failure types. The first one is failure of the subgrade when the pressure transmitted to the subgrade is higher than the inherent hearing capacity of the particular subgrade. The subgrade to accommodate loading soil’s ability pressures is a function of its shear strength, cohesion, plasticity, density, and moisture content. A well-compacted subgrade soil that is confined and maintained reasonably dry will normally perform adequately for an indefinite period of time. A possible exception is a highly compressible soil such as peat. Subgrade failures adversely affect track geometry and are normally difficult and expensive to correct. The second type of trackbed failure occurs when one or more of the trackbed structural components fail to perform satisfactorily for a reasonable period of time. This is commonly manifested by the subballast, and particularly the ballast, becoming clogged (fouled) with excessive quantities of fine size material. This lowers the shear strength of the ballast and bearing capacity of the subballast. Fouling is normally due to degradation of the ballast, infiltration of subgrade soil particles, extraneous droppings
freight was carried over the nation’s nearly 141,000-mile (227,000 km) railroad network. The average freight car weight has increased to 129 tons (117 metric tons) with most new cars having gross weights of 143 tons (130 metric tons). The importance of developing and specifying premium track structures and components to adequately carry the increased tonnage is a current reality of the industry. Failure of the track structure and components results in difficulty maintaining track geometric features necessary for efficient and safe train operations. Maintenance costs and track outages increase due to frequent maintenance and renewal cycles. The inability of the track structure to adequately carry the imposed loadings can be categorized into two primary failure types. The first one is failure of the subgrade when the pressure transmitted to the subgrade is higher than the inherent hearing capacity of the particular subgrade. The subgrade soil’s ability to accommodate loading pressures is a function of its shear strength, cohesion, plasticity, density, and moisture content. A well-compacted subgrade soil that is confined and maintained reasonably dry will normally perform adequately for an indefinite period of time. A possible exception is a highly compressible soil such as peat. Subgrade failures adversely affect track geometry and are normally difficult and expensive to correct. The second type of trackbed failure occurs when one or more of the trackbed structural components fail to perform satisfactorily for a reasonable period of time. This is commonly manifested by the subballast, and particularly the ballast, becoming clogged (fouled) with excessive quantities of fine size material. This lowers the shear strength of the ballast and bearing capacity of the subballast. Fouling is normally due to degradation of the ballast, infiltration of subgrade soil particles, extraneous droppings