# Study on Gage Widening Methods for Small-Radius Curves
## 4 Adaptability Analysis of Gage Widening Standards
### Influence of Gage Widening on Maintenance Workload  
On 22 November 2019, we communicated with the Shijiazhuang Section of the Beijing Railway Bureau to understand the use and maintenance situation of the Shijiazhuang-Taiyuan Railway. The Shijiazhuang-Taiyuan Railway is mainly used for freight cars, with only a few regular-speed passenger cars. Heavy trucks run on the upline, and empty trucks run on the downline. The annual transportation volume of the upline is about 140 million tons. The length of the Shijiazhuang-Taiyuan Railway in the Shijiazhuang section is 117 km. The main line contains 149 small-radius curves with a radius of smaller than 400 m (75 upline and 74 downlines). Table 19 lists the distribution of curves with different grades of radius, wherein majority curves have a radius of 300 m or smaller, constituting over 60% of the total radii, whereas the smallest radius is 278 m. According to the current gage widening standard, six curves need to be widened: three uplines and three downlines. As the rails in the curve section with a radius of 300 m or below cannot be polished by a polishing train, the upper strand side of the rail is severely worn, and the lower strand is collapsed and deformed into a flat shape, accompanied by obvious peeling pieces, as shown in Figure 17. The severe wear and contact fatigue caused the rail life to be considerably reduced. Table 20 lists the rail life statistics results. The downline mainly runs empty cars, and the rail life generally exceeds six years. The life of the rails on the upline is significantly lower. When the radius range is the same, the U78 CrV heat-treated rail is significantly longer than the U75V heat-treated rail. Replacing rails has become the primary task, which requires substantial labor and material resources. Owing to the limited number of personnel in the work areas, guaranteeing daily inspection and maintenance is difficult. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Radius**} & \multicolumn{2}{c}{**Upline**} & \multicolumn{2}{c}{**Downline**} \\ \cline{2-4}  & **U78 CrV** & **U75V** & **U78 CrV** & **U75V** \\ \hline
350 \(<\) R \(\leq\) 400 & 3.42 & 2.67 & 9.64 & 9.57 \\
300 \(<\) R \(\leq\)350 & 3.33 & 2.4 & 8.07 & 7.41 \\ R \(\leq\) 300 & 2.42 & 1.34 & 7.61 & 6.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 20: Statistical results on curved rail life (years). Figure 17: Surface damage situation of a small-radius-curve rail. (**a**) Upper strand; (**b**) Lower strand. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Radius** & **Upline** & **Downlines** \\ \hline
350 \(<\) R \(\leq\) 400 & 6 & 7 \\
300 \(<\) R \(\leq\) 350 & 24 & 19 \\ R \(\leq\) 300 & 45 & 48 \\ \hline \hline \end{tabular}
\end{table} 
Table 19: Distribution of curves. According to the current gage widening standard, curves with radii less than 295 m should be widened. Most of the curves on the Shijiazhuang-Taiyuan Railway do not need to be widened. The maintenance regulations stipulate that the gage limit for temporary repairs should not exceed 16 mm. It is known that both rail wear and fastener structure deformation cause the gage to expand. When the rail side wear reaches 10-11 mm, the gage usually reaches 1450 mm. At this time, the work department restores the gage to 1435 mm; when the rail wear reaches the limit value of 19 mm, the rail is replaced. Therefore, the rail gage needs to be adjusted once in the lifecycle of the rail. The rail maintenance process is shown in Figure 18a. The gage varies in the range of 1435-1450 mm, the average gage is 1442.5 mm, and the equivalent widening amount is 7.5 mm. According to the original gage widening standard (before 2014), the gage should be widened if the radius is less than 350 m. The small radius of the Shijiazhuang-Taiyuan Railway would need to be widened by 5 mm, and the nominal gage size is 1440 mm.