The Experts below are selected from a list of 8076 Experts worldwide ranked by ideXlab platform
David D. Davis - One of the best experts on this subject based on the ideXlab platform.
-
ballast Settlement ramp to mitigate Differential Settlement in a bridge transition zone
Transportation Research Record, 2015Co-Authors: Yu Qian, Erol Tutumluer, Youssef M A Hashash, Jamshid Ghaboussi, David D. DavisAbstract:Differential Settlement in railroad track transitions, often associated with differences in track stiffness, may apply considerable impact load and may cause rapid deterioration of track geometry. Such Differential Settlement commonly seen in bridge approaches may lead to problems in ride comfort, track safety, and reliability. Ballast and subballast layers have been identified as a major cause of Differential Settlement related to the particulate nature of the aggregate deformation behavior causing degradation and breakdown associated with increased track usage. This paper describes an innovative field approach that successfully demonstrated the use of engineered ballast materials for reducing or mitigating the Differential Settlement problem in a bridge transition zone. Discrete element method (DEM) simulations were used to predict full-scale track deformations of four ballast materials having different gradations and aggregate shape properties. An imaging device was used to create accurate particle siz...
-
Track Differential Settlement Model
ASME IEEE 2007 Joint Rail Conference and Internal Combustion Engine Division Spring Technical Conference, 2007Co-Authors: David D. Davis, Steven M. ChrismerAbstract:A study of track Settlement behavior at critical transitions such as road crossings and bridge approaches has yielded a model to predict the amount of Differential track Settlement at these transitions caused by ballast and subgrade deformation. This AAR ballast and subgrade deformation model has been developed from field and laboratory test data, and has been validated with field Settlement measurements at bridge approaches where the ballast and subgrade properties were well documented. As an analytical tool the model can determine the rate of track Differential Settlement at transitions with traffic loading and to predict when tamping is required to correct track geometry. Also the model can determine the relative amount of deformation from the individual ballast and subgrade layers. These capabilities provide a means to assess whether the main source of deformation is the subgrade or the ballast and the best means to reduce Differential Settlement and decrease the frequency of tamping at these track transitions.© 2007 ASME
Ming Liang - One of the best experts on this subject based on the ideXlab platform.
-
geometry mapping and additional stresses of ballastless track structure caused by subgrade Differential Settlement under self weight loads in high speed railways
Transportation geotechnics, 2019Co-Authors: Hongguang Jiang, Xinliang Li, Jizhe Zhang, Ming LiangAbstract:Abstract Rail irregularities caused by subgrade Differential Settlement will accelerate track degradation and lower ride comfort and safety. Since the track substructure is normally inaccessible, these problems are hard to be detected early. To study the mapping characteristics of deflection profiles in the ballastless track-subgrade system, a 3D FEM model considering the contacts between different layers was established to simulate different Settlement scenarios. The numerical results were first validated by the comparisons of rail deflections with a full-scale physical model testing. Then the influences of subgrade Differential Settlement on the CRTS II type ballastless track were analyzed, including the deflection profiles, additional tensile stresses and contact stresses. The Settlement transfer characteristics from the subgrade surface to the rail were revealed, which were largely dependent on the track equivalent flexibility. A unified formula in terms of the Settlement amplitude and track equivalent flexibility was proposed to describe the geometry mapping relationship. The scenario of hanging track structure occurred at the subgrade Differential Settlement with wavelengths shorter than 15 m, or wave-length between 15 m and 20 m and amplitude larger than 15 mm. The thresholds of unacceptable Settlement wavelengths for the additional stresses were 10–20 m for the concrete base and 10–15 m for the subgrade with the Settlement amplitudes smaller than 15 mm. Differential Settlement with shorter wavelengths was more vulnerable, and the critical scenarios of soil yielding at subgrade surface happened earlier than the concrete cracking in the track structure. Subgrade maintenance works, such as Settlement restoration and soil improvement, were suggested to be implemented before the wavelength reached 10 m to avoid further development of Settlement and potential threats to the track structure.
Wei Wang - One of the best experts on this subject based on the ideXlab platform.
-
influence of Differential Settlement on pavement structure of widened roads based on large scale model test
Journal of rock mechanics and geotechnical engineering, 2011Co-Authors: Xiaolin Weng, Wei WangAbstract:Abstract This study introduced at first the background of numerous highway widening projects that have been developed in recent years in China. Using a large ground Settlement simulator and a fiber Bragg grating (FBG) strain sensor network system, a large-scale model test, with a similarity ratio of 1:2, was performed to analyze the influence of Differential Settlement between new and old subgrades on pavement structure under loading condition. The result shows that excessive Differential Settlement can cause considerable tensile strain in the pavement structure of a widened road, for which a maximum value (S) of 6 cm is recommended. Under the repetitive load, the top layers of pavement structure are subjected to the alternate action of tensile and compressive strains, which would eventually lead to a fatigue failure of the pavement. However, application of geogrid to the splice between the new and the old roads can reduce Differential Settlement to a limited extent. The new subgrade of a widened road is vulnerable to the influence of dynamic load transferred from the above pavement structures. While for the old subgrade, due to its comparatively high stiffness, it can well spread the load on the pavement statically or dynamically. The test also shows that application of geogrid can effectively prevent or defer the failure of pavement structure. With geogrid, the modulus of resilience of the subgrade is increased and inhomogeneous deformation can be reduced; therefore, the stress/strain distribution in pavement structure under loading condition becomes uniform. The results obtained in this context are expected to provide a helpful reference for structural design and maintenance strategy for future highway widening projects.
Hongguang Jiang - One of the best experts on this subject based on the ideXlab platform.
-
geometry mapping and additional stresses of ballastless track structure caused by subgrade Differential Settlement under self weight loads in high speed railways
Transportation geotechnics, 2019Co-Authors: Hongguang Jiang, Xinliang Li, Jizhe Zhang, Ming LiangAbstract:Abstract Rail irregularities caused by subgrade Differential Settlement will accelerate track degradation and lower ride comfort and safety. Since the track substructure is normally inaccessible, these problems are hard to be detected early. To study the mapping characteristics of deflection profiles in the ballastless track-subgrade system, a 3D FEM model considering the contacts between different layers was established to simulate different Settlement scenarios. The numerical results were first validated by the comparisons of rail deflections with a full-scale physical model testing. Then the influences of subgrade Differential Settlement on the CRTS II type ballastless track were analyzed, including the deflection profiles, additional tensile stresses and contact stresses. The Settlement transfer characteristics from the subgrade surface to the rail were revealed, which were largely dependent on the track equivalent flexibility. A unified formula in terms of the Settlement amplitude and track equivalent flexibility was proposed to describe the geometry mapping relationship. The scenario of hanging track structure occurred at the subgrade Differential Settlement with wavelengths shorter than 15 m, or wave-length between 15 m and 20 m and amplitude larger than 15 mm. The thresholds of unacceptable Settlement wavelengths for the additional stresses were 10–20 m for the concrete base and 10–15 m for the subgrade with the Settlement amplitudes smaller than 15 mm. Differential Settlement with shorter wavelengths was more vulnerable, and the critical scenarios of soil yielding at subgrade surface happened earlier than the concrete cracking in the track structure. Subgrade maintenance works, such as Settlement restoration and soil improvement, were suggested to be implemented before the wavelength reached 10 m to avoid further development of Settlement and potential threats to the track structure.
Xiaolin Weng - One of the best experts on this subject based on the ideXlab platform.
-
influence of Differential Settlement on pavement structure of widened roads based on large scale model test
Journal of rock mechanics and geotechnical engineering, 2011Co-Authors: Xiaolin Weng, Wei WangAbstract:Abstract This study introduced at first the background of numerous highway widening projects that have been developed in recent years in China. Using a large ground Settlement simulator and a fiber Bragg grating (FBG) strain sensor network system, a large-scale model test, with a similarity ratio of 1:2, was performed to analyze the influence of Differential Settlement between new and old subgrades on pavement structure under loading condition. The result shows that excessive Differential Settlement can cause considerable tensile strain in the pavement structure of a widened road, for which a maximum value (S) of 6 cm is recommended. Under the repetitive load, the top layers of pavement structure are subjected to the alternate action of tensile and compressive strains, which would eventually lead to a fatigue failure of the pavement. However, application of geogrid to the splice between the new and the old roads can reduce Differential Settlement to a limited extent. The new subgrade of a widened road is vulnerable to the influence of dynamic load transferred from the above pavement structures. While for the old subgrade, due to its comparatively high stiffness, it can well spread the load on the pavement statically or dynamically. The test also shows that application of geogrid can effectively prevent or defer the failure of pavement structure. With geogrid, the modulus of resilience of the subgrade is increased and inhomogeneous deformation can be reduced; therefore, the stress/strain distribution in pavement structure under loading condition becomes uniform. The results obtained in this context are expected to provide a helpful reference for structural design and maintenance strategy for future highway widening projects.