Investigation of differential movement at railroad bridge approaches through geotechnical instrumentation

Root cause of differential movement at bridge transition zones

“…6,7 This program included measuring wheel and tie loads with strain gages, and the measurement of permanent and transient vertical displacements as a function of depth using linear variable differential transformers (LVDTs) connected together to form a multi-depth deflectometer (MDD). 8 By comparing the load and displacement differences between and within the open track and bridge approach sites, the ''root cause'' of the observed permanent vertical displacements could be determined and is described herein.…”

“…Numerous design and remedial measures for transition zones have been suggested, they typically consist of stiffening or smoothing the stiffness difference between the open track, bridge approach and bridge [4][5][6]20 or reducing the stiffness of the bridge. 5,[21][22][23] This philosophy attempts to minimize the differential transient displacements between the transition zone and bridge.…”

“…This likely involves using multiple design features some of which are described in the literature. [4][5][6][20][21][22][23] For remediation of track geometry, tamping is a commonly used technique that involves raising the ballast; this loosens the ballast underlying the tie. The first train pass after tamping compacts the loosened ballast and creates a tie-ballast gap.…”

Recent research on the track-subgrade of high-speed railways

“…Dynamic responses of the carriages can be analyzed by this model in the case of carriages passing over curved tracks. Much research on the dynamic response of the subgrade has been conducted using analytical methods (Metrikine, 2004), 3D dynamic finite element method (Hall, 2003), 2.5D finite element method (Bian et al, 2008), field monitoring (Mishra et al, 2012;Verbraken et al, 2012;Cui et al, 2014), and model tests (Chen et al, 2013;2014a;2014b). Those studies have shown that the track-subgrade vibration is significantly associated with the train speed.…”

Evaluating tie support at railway bridge transitions

“…Instrumentation of two bridge approaches on Amtrak's Northeast Corridor (NEC) near Chester, Pennsylvania [6][7][8][9][10] with linear variable differential transformers (LVDTs) showed a strong relationship between reoccurring differential track settlement and tie-ballast gaps at the instrumented locations. 8,9 The development of tie-ballast gaps at or near bridge approaches is attributed to the inherent problem of the approach track lying on deformable earthen materials whereas the bridge deck is essentially a non-deformable man-made structure.…”