Extending the use of continuous welded rails by eliminating the weak points (expansion joints) of a railway track especially in sharp curves, which has resulted in increasing the operational speed and axle load of rolling stocks, enhances the special attention to the issue of track lateral resistance. In this regard, the ballast layer interaction with sleepers plays a crucial role in providing the track lateral stability. In many railway projects supplying the appropriate ballast materials has encountered serious restrictions owing to the lack of qualified ore and also their long distance to the project's site. With the development of steel industry, the quantity of production and accumulation of steel slag as a waste material has increased. In recent years, a great deal of attention has been paid to the use of this material as railway ballast. According to the physical and mechanical characteristics of steel slags, such as high specific gravity and the granular roughness respect to the limestone ballast, the usage of slag ballast can improve the track lateral stability. In this research, many field experiments were conducted on tracks with steel slag ballast and limestone ballast materials considering the same gradation. In this matter, several single tie push tests were carried out on both tracks with various ballast geometries. The ballast depth was considered as 30, 40, and 50 cm and the shoulder ballast width was equal to 30 and 40 cm. Moreover, the shoulder ballast height was chosen 0 and 10 cm. Consequently, the lateral resistance of both tracks was measured and compared in the same conditions. In overall, the obtained results confirmed a 27% increase in lateral resistance of track with steel slag ballast respect to that with limestone ballast.
Employing a dynamic model of the railway wagon in three dimensions, this paper presents the results of dynamic wheel–rail forces under the presence of track irregularities. A mathematical model of the wagon system is developed using dynamic equations of the components, taking into account the vertical (bounce), pitch and roll motions of the system. The model examines the dynamics of the wagon system under arbitrary rail irregularities. The spectra of rail surface irregularities are fed into the vehicle model to extract the time histories of dynamic forces between the wheel and the rail. Using the irregularity spectra of left/right rails, vibration of the wheelsets is studied for the bounce–roll motions. The dynamic contact forces between wheels and rails are determined for three examples of the measured irregularities. Moreover, three V-shape defects are modelled as examples of the singular defects on rail surface. The results of dynamic simulations confirm the large amounts of impact forces due to the presence of rail irregularities, particularly for the cases with much unevenness between the left/right profiles.
The lateral stability of ballasted railway tracks is a function of the lateral resistance of the sleepers created by interaction with ballast materials. Thus, one of the approaches for increasing the lateral resistance of sleepers has been to increase bottom friction and use frictional sleepers. A review of the technical literature showed that numerous experimental studies have been performed on this type of sleeper; however, no numerical analysis has been conducted on its lateral resistance. Therefore, this paper developed a finite element numerical model for investigating frictional concrete sleepers. In this regard, a hardening elasto-plastic behavior model was developed for the ballast layer and ABAQUS software was used to numerically analyze the lateral resistance of this type of concrete sleeper. Using the developed model, some sensitivity analyses were performed on the parameters that affect the lateral resistance including the thickness and extent of the ballast shoulder, and the friction coefficient between the ballast layer and sleeper. The obtained results indicated that increasing the ballast shoulder from 25 to 40 cm resulted in about a 16-22% increase in lateral resistance, whereas increasing the friction coefficient from 0.1 to 0.8 led to about a 22-28% increase in the lateral resistance. On the other hand, on decreasing the ballast layer thickness from 30 to 20 cm, the lateral resistance increased by about 12-17%. In summary, it can be concluded that, compared with conventional concrete sleepers, frictional sleepers increased the lateral resistance by about 63-70%.
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