Application of Geocell Track Substructure Support System to Correct Surface Degradation Problems Under High-Speed Passenger Railroad Operations

Abstract

Ballast fouling and associated degradation of track geometry is a serious problem for railway systems in general and high-speed passenger rail systems in particular. This paper presents the results of a field test on Amtrak’s Northeast Corridor where a long-term problem area existed near Oakington Road, Havre de Grace, Maryland, near MP 63.7 between Philadelphia and Washington DC. This test looked at the application of a new generation of three-dimensional cellular confinement systems (geocells) in reducing the rate of track geometry degradation, particularly in poor subgrade and ballast locations which require frequent, expensive, track surface maintenance. The field test compared two distinct sets of rebuilt track conditions, to include zones with and without a layer of geocell material. Both zones were rebuilt with improved drainage and a good, well-defined track structure and substructure (to include a well-defined depth of clean ballast). The test measurements included pre-maintenance and post-maintenance track geometry measurements together with comparative subgrade pressure measurements inside and outside the geocell cell zones. The pressure cell measurements, which looked at subgrade pressure under left and right rails in both the geocell zone and the control (non-geocell) zones, included measurements under both Acela high-speed trains and lower speed regional trains. In all cases, the subgrade pressures in the geocell zone were approximately half of those for the cells in the control zone (no geocell). Track geometry measurements were made using Amtrak’s track geometry vehicle which measures key track geometry parameters at 1-ft intervals along the track. There were several well-defined locations in the overall test zone that experienced significant track geometry degradation; these were all corrected during reconstruction. In the zones with no geocell material, these geometry variations reappeared within 6 to 7 months with the same if not greater amplitudes. By contract, in the geocell zone, the “after” geometry variations were significantly smaller than the pre-reconstruction geometry variations. Furthermore, the rate of geometry degradation was signficantly less for the geocell zones compared to the pre-geocell time periods for the exact same track. This indicated the effectiveness of the geocell material in reducing the rate of track geometry degradation and extending the surfacing maintenance cycles. Analysis of the rate of degradation showed that the effect of installing the geocell material was to significantly reduce the rate of degradation (and thus increase the surfacing cycle) by a factor of 6.7 times the pre-geocell installation surfacing cycle.