TRACK MODULUS MEASUREMENTS AT THE PUEBLO SOFT SUBGRADE SITE

Abstract

At the Pueblo test facility a clay subgrade layer 1.5 m (5 ft) thick was installed to provide a low modulus track. The performance and maintenance requirements of this track under accumulated traffic (with a 170-kN or 39-kip wheel load) were compared with those of an adjacent track section with natural stiff subgrade. In this way the effect of substructure condition on track performance was distinguished. It was determined that the low modulus track produced a more variable support condition than did the stiffer track. Larger variation in support provided more differential settlement and, therefore, required more smoothing maintenance. Track deflection under load provides information regarding substructure support and related track maintenance needs. Three ways of characterizing the load-deflection characteristics of track were considered: track deflection, track stiffness, and track modulus. The results of these measurements are shown and compared, and the implications of using each are discussed. Whichever technique is used, a system that can take measurements on a continuous basis is recommended to determine the support characteristics along the track. Such a system could be used to identify those sections requiring differing amounts of maintenance and those that may need rehabilitation to increase the modulus to an acceptable level.