Abstract
Abstract The performance of railroad structure has a tremendous influence on the safety and stable operation of high-speed trains. Strong vibrations and the degradation rate of the track are the main factors affecting the transport safety of a railroad built over a weak soil. Geogrid reinforced embankment supported by pile structure is a new efficient construction technique used to ensure the stability and enhance the performance of the railroad system; but only a few studies are oriented to its behavior under train operation. This paper investigates the dynamic response of geogrid reinforced embankment supported by cement fly-ash gravel pile structure during a high-speed train operation. The establishment of a realistic simulation model for railroad subjected to a moving train load, is an important first step towards the reliable design of geogrid reinforced embankment supported by pile structure. Thus, a 3D nonlinear FEM has been established to simulate the instrumented Harbin-Dalian railway test section. Each train carriage was modeled as a transient dynamic load through a user-defined Dload subroutine. The developed model was successfully validated by the dynamic response recorded from the field test section. The improvement of the railroad structure by the CFG piles and geogrids contributed significantly to the reduction of the vibration in the structure, which attenuates 1.2 times faster with the structure depth, even under overload conditions. Moreover, the phenomenon of resonance observed when the train reaches speeds of 100 and 260 km/h were annihilated. The analysis of the stress distribution within the embankment revealed that a dynamic arch is formed in the embankment at 2 m from the ground. The stress onto the pile was 16 times greater than that acted on the soil and the tensile stress developed in the geogrid was high at the piles edge below. In addition, the coupling effect of geogrid with various tensile strengths and the piles with different strength grades indicated that the combination of a high-strength pile and geogrid significantly reduces the displacement gap due to the variation of train speed. As a result, the vibrations of the track were almost constant during the train operation; thus, ensuring comfort to passengers and reducing the risk of derailment.
Highlights
The development of the high-speed railroad in recent years has improved the transportation system around the world and has contributed immensely to countries’ economies
To evaluate the role of the pile and geogrid in a railroad dynamic response built over weak soil, the geogrid reinforced embankment supported by CFG pile structure condition was compared to the case of the conventional embankment when the train speed was 200 km/h
Since strong dynamic amplification can be observed in the railway structures when the train approaches a certain speed depending on the properties of ground material [1, 22], this study shows that the pile and geogrid, because of their stiffness, provides the embankment with a certain rigidity to slacken the propagation of vibration induced by the train
Summary
The development of the high-speed railroad in recent years has improved the transportation system around the world and has contributed immensely to countries’ economies. The dynamic response of the geogrid reinforced embankment supported by pile structure during the passage of the train is a very complex phenomenon. It is unfortunate, that very few experimental and numerical studies have given a comprehensible explanation on it. It is necessary to explore the dynamic characteristics of the geogrid reinforced railroad embankment supported by CFG pile and to better elucidate the mechanism of the system components interaction, which is of great importance to the establishment of stringent guidance for the railroad design over weak soil. This section includes the description of a three-dimensional model of the railroad embankment reinforced by geogrid and supported by pile, the material parameters, the dynamic train load model, the mesh and boundaries conditions
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