Effectiveness of Chemical Grouting and Stone Blowing as remedial measures to mitigate differential movement at railroad track transitions

Railway transitions like bridge approaches experience differential movements related to differences in track system stiffness, track damping characteristics, foundation type, ballast settlement from fouling and/or degradation, as well as fill and subgrade settlement. A recent research study at the University of Illinois has used advanced geotechnical instrumentation to identify and quantify different factors contributing to recurrent differential movement problems at three different bridge approaches along Amtrak's Northeast Corridor (NEC) near Chester, Pennsylvania. Field instrumentation data have indicated excessive ballast movement to be the primary factor contributing to the "bump" development at these bridge approaches. Among the different remedial measures applied to mitigate the recurrent track geometry issues were: (1) Chemical Grouting, (2) Stone Blowing, and (3) Under-Tie Pads. This paper will discuss the implementation methods using track geometry records and instrumentation data, and highlight the effectiveness of chemical grouting and stone blowing to mitigate the differential movement problem at railroad bridge approaches. According to the trends in the transient ballast deformation data collected under train loading, both remedial measures were effective in significantly reducing excessive ballast deformation, which was the primary mechanism behind the bump development at these locations. Ballast degradation and presence of excessive fine particles in the ballast layer adversely affected the ability of the grout to bond with aggregate particles. A "clean" ballast layer, on the other hand, facilitated adequate bonding between the grout and ballast particles leading to significantly improved long-term track performance.