High Speed Railway Structure Research Articles

Thermal-mechanical coupled XFEM simulation of low temperature cracking behavior in asphalt concrete waterproofing layer

Asphalt concrete waterproofing layer (ACWL), which is used to reduce the moisture impact on high-speed railway structure, tends to crack at low temperatures and thus reduces its durability. Therefore, understanding the low-temperature cracking behavior of ACWL from both the material and structure perspectives is of great significance. In this study, thermal-mechanical coupled simulation based on extended finite element method (XFEM) was employed for research on this aspect, with the experimental and numerical monotonic-loading overlay test (ML-OT) to determine the fracture parameters of railway asphalt concrete materials and full-scale model to characterize the thermal cracking behaviors of ACWL. The results firstly showed that both the ML-OT and thermo-mechanical simulation on ACWL structure presented a four-stage fracture process, i.e. elastic response, crack initiation, crack propagation and final failure stage, at the temperature of −20 °C. Secondly, the effects of material formulation and structure design on the low-temperature cracking resistance was investigated: 1) In terms of material formulation, the binder B and gradation AC-13 was superior to their counterparts; 2) In terms of structure design, the ACWL layer thickness of 8 cm was the most unfavorable in the range of 6–16 cm, and the increased temperature difference accelerated the thermal cracking propagation in ACWL at the average temperature of −20 °C. In addition, two thermal stress mitigation strategies, namely laying the geotextile at base joints and setting expansion joints, were found to effectively prevent and delay the emergence of thermal cracks in ACWL at low temperatures. For recommendation, the developed thermal-mechanical coupled simulation framework, the custom-designed railway asphalt concretes, and the recommended ACWL thickness of 12 cm were applicable in future studies and engineering projects.

A tentative test for measuring the sub-millimeter settlement and uplift of a high-speed railway bridge using COSMO-SkyMed images

This paper analyzed the dynamic behaviors of a high-speed railway (HSR) bridge and evaluated the possibility of measuring the sub-millimeter settlement and uplift using COSMO-SkyMed images. The capability of synthetic aperture radar interferometry (InSAR) technologies with the purpose of sub-millimeter deformation monitoring without ground control points has rarely been studied. In this paper, we conducted a tentative test for measuring the sub-millimeter settlement and uplift of a HSR bridge. Persistent scatterer (PS) and distributed scatterer (DS) were jointly detected to increase the point density. The temperature model was introduced to separate the thermal expansion and linear deformation. By analyzing the HSR structure and time-series deformation, we infer that PS points correspond to double-bounce scatterers mainly generated by the interactions between the girder and track slab and between the girder and fender, and DS points correspond to single-bounce scatterers generated by the bridge girder surface. The accuracy of linear deformation velocity and time-series deformation were evaluated, respectively. Under the assumptions by qualitative analysis, the results demonstrate that COSMO-SkyMed is capable of achieving sub-millimeter accuracy in linear deformation velocity. However, the leveling validation implies that it is difficult to achieve sub-millimeter accuracy in time-series deformation because of the uncertainties from incorrect ground data, location and time difference between the InSAR and ground data, the presence of lateral deformation, improper removal of the atmospheric phase screen, and inconsistency between the air temperature and bridge temperature.

PSD of ballastless track irregularities of high-speed railway

The calculation method, fitting function and fitting spectrum of power spectral density (PSD) of track irregularity were proposed in the paper. To improve the calculation accuracy of PSD of track irregularity, a linear interpolation method and a wavelet analysis method are given and used to eliminate the outliers and trends in the track irregularities. The paper describes the window function, window length and PSD estimation method to calculate track irregularity PSD. For comparison the track irregularity power spectral densities (PSDs) calculated with different window functions, window lengths and PSD estimation methods. Combing the above mentioned results and the data from the high speed comprehensive inspection train, the paper determines the track irregularity PSD fitting equation and introduces the frequency multiplication energy table to reflect the impact of track periodical structure of High Speed Railway. PSD of ballastless track irregularities of high-speed railway includes fitting spectrum and frequency multiplication energy table, which provides basis for maintenance and optimization design for High Speed Railway.

Settlement Control and Impact Analysis of the Subway Shield Under-Passing Beijing-Shanghai High Speed Railway Bridge

When the shield tunnel go through the bridge structure of high speed railway, it will affect the high speed railway bridge structure, thus influence to the bridge of track structure and ballastless track. Based on the Beijing subway tunnel go through the Beijing-Shanghai railway bridge section engineering examples, for the first time to shield under through the high speed railway caused the bridge pier settlements are analyzed. Combined with the actual monitoring data, the isolation pile during the period of construction bridge pier and Shield during through bridge pier during the period of settlement regularity of construction bridge pier, settlement regularity of Isolation pile as well as settlement regularity of the surface land are summarized analysis. During the construction of high-speed rail bridges and the soil to produce a certain degree of deformation, Shield Zone just above the soil settlement with a large deformation, both sides of the deformation gradually decreases, but the deformation is controlled. The use of the isolation pile reinforcement measures significantly reduced the influence by the Shield Construction and it can satisfy the requirement of high speed railway control standards