Vertical Pressure Distribution in the Ballast Section and on the Subgrade Beneath Statically Loaded Ties

A program to obtain more nearly definitive measures of ballast pressure distribution utilizing modern types of earth pressure cells and laboratory simulation of a well-compacted subgrade under the ballast was undertaken in the Civil Engineering Department of the University of Illinois during the period of February 1965 through June 1996. The study was given financial sponsorship by the Railway Maintenance Corporation of Pittsburg, Pennsylvania, pressure cells were loaned by the Research Center, Association of American Railroads, Chicago, Illinois and rails, ties, ballast and subgrade materials were donated by the Illinois Central Railroad, The hydraulic loading jacks, 12-channel pressure cell recorder and working site were provided by the Civil Engineering Department of the University of Illinois. The ballast section in its primary functions of distributing wheel load from the cross ties, anchoring the track, providing immediate drainage, and contributing resilience is one of the most important elements in a railroad track structure. A suitable depth of ballast is needed in order to get a uniform pressure distribution on the subgrade under the rail and a unit pressure distribution imposed on the subgrade within the allowable limits of the subgrade bearing capacity. If ballast pressures are not uniformly distributed on the subgrade, some of the ballast particles will be forced into the subgrade leading to instabilities and formation of ballast pockets.