TITULO SEGUNDO

Since check rails were excluded in this section, the comparison was made on both of the lines. Figures 6.18 and 6.19 illustrate the selected sites on Bakerloo and Jubilee NB lines, respectively. In order to compare the changes in damage parameters between underground (tunnel) and overground (surface) sections, the red circled regions in Jubilee line were selected in the study.

Figure 6.18: The selected reported and no reported sites on the right rails of Bakerloo NB line

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The track characteristics of the selected sites are presented in Table 6.2. The chainages, rail position and profile, curve radius, applied cant, cant deficiency and section type were provided for all sites. While the orange highlighted rows show the information for Bakerloo line, the grey rows for Jubilee line including the overground sections written in red colour. As it was mentioned in the Chapter 3.1, the cant deficiency values were significantly small and cant excess sometimes was occurred on the Bakerloo line. Since the selected sites were located in the old tunnel section of Jubilee lines, the cant deficiency values also low compared to other sections on this line. Similarly, the overground sections had small cant deficiency with the zero applied cant in Canning Town station (Site D). To identify the changes on different track positions, both high and low rail sections were selected in the study. In addition, to show the effect of unlubricated curved track, transition and different rail profiles (BH and FB) on rail damage prediction parameters, the analysis included the specific sites which were given in Table 6.2.

Table 6.2: The track characteristics of the selected sites for the curved tracks

Site Chainage (KM) Rail Position RCF Damage Condition Curve Radius (m) Applied Cant (mm) Cant

Deficiency (mm) Rail Profile Section Type

1 1+850-1+900 Low Rail Reported RCF

(Squat with T/O) 286 80 4 FB

Underground (Tunnel)

2 3+950-4+000 Low Rail No reported RCF 400 40 20 BH Underground

(Tunnel) 3 8+000-8+050 High Rail Reported RCF

(Squat with T/O) 286 100 5 FB

Underground (Tunnel)

4 9+900-9+950 High Rail No reported RCF 385 80 -9 BH Underground

(Tunnel) 5 10+450-10+500 High Rail

*Unlubricated

Reported RCF

(Squat with T/O) 364 70 -7 FB

Underground (Tunnel) 6 4+970-5+020 High Rail Transition No reported RCF 1000 70 -36 FB Underground (Tunnel)

7 5+250-5+300 High Rail No reported RCF 400 150 39 FB Underground

(Tunnel) 8 6+900-6+950 Low Rail

Transition No reported RCF 1000 60 11 FB

Underground (Tunnel)

9 10+300-10+350 High Rail No reported RCF 667 110 -10 FB Underground

(Tunnel) 10 16+050-16+100 High Rail Transition Reported RCF (Shelling on the Gauge Corner) 667 75 -9 FB Underground (Tunnel) 11 16+200-16+250 High Rail Reported RCF (Shelling on the Gauge Corner) 476 100 29 FB Underground (Tunnel) 12 21+740-21+790 Low Rail Transition Reported RCF (Shelling on the Running Surface) 435 40 45 FB Underground (Tunnel) A 0+910-0+960 High Rail Reported RCF (Shelling on the Gauge Corner) 445 35 45 FB Overground (Ballasted) B 1+340-1+390 High Rail Reported RCF (Shelling on the Gauge Corner) 325 35 45 FB Overground (Ballasted)

C 1+655-1+705 High Rail No reported RCF 1125 15 15 FB Overground

(Ballasted)

D 3+090-3+140 High Rail Reported RCF

(Squat with T/O) 1125 0 0 FB

Overground (Ballasted) *Canning Town

Station

E 32+050-32+100 Low Rail No reported RCF 575 85 45 FB Overground

(Ballasted)

F 36+000-36+050 Low Rail Reported RCF

(Squat) 775 65 0 FB

Overground (Ballasted)

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Figure 6.20 displays the comparison of Tγ and T/N results on the selected sites of the curved tracks. Whilst the green and magenta colour show the reported RCF sites, the blue and red colour indicate the no reported RCF sites on the Bakerloo and Jubilee lines, respectively. Additionally, each marker represents different contacts on the rails. As shown, most of the contacts on the reported and no reported RCF sites were clustered in two different areas as indicated by grey dashed colour boundaries. When the values were below this limit, the contacts might seem to have less effect on damage risk. Similar to the results of the previous section, the traction coefficients were limited by the selected friction coefficients. For instance, the T/N values in the reported sites of overground section cannot exceed the µ=0.25 limit. But, it is apparent that they had greater energy values than the no reported sites. Also, the 0.31-0.32 T/N played a crucial role in the underground section. In spite of the low Tγ values in this region, the RCF damage was observed for the contacts which had larger T/N values than 0.31-0.32 levels. When the contacts were particularly analysed, it was noticed that the highest results were produced on the unlubricated curve due to larger friction coefficients. Additionally, even though no cracks were recorded on the BH type of low rails, the contacts showed excessive values which mainly resulting from the higher conicity in this rail-wheel profile combination. Moreover, some reported RCF sites on the Jubilee line (magenta colour) were below the limit. This was mainly caused by the changing track geometry on the selected transition sites. Although some contacts of this site had high values, the smaller results could not pass this limit. Furthermore, when the results were compared with different defect types such as (shelling and squat), no clear response was obtained in this analysis.

Figure 6.20: The comparison of Tγ and T/N on the selected sites of curved tracks

Figure 6.21 illustrates the comparison of the creep force angle regions with reported and no reported RCF damage on the Jubilee line. As expected, the majority of high (left) rail and low rail tread contacts were on the traction region (IV:270-360) and braking regions

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(II:90°-180° and III:180°-270°), respectively. This again confirmed that the creep force direction did not seem to have an influence on damage risk since, the values primarily depended on the position of rails and route characteristics

Figure 6.21: The comparison of different creep force angle regions on the selected sites of Jubilee NB line

In the case of the Bakerloo line given in Figure 6.22, the majority of flange and high rail tread contacts were in the traction direction (I:0°-90°) and the low rails were in the braking direction (III:180°-270°). Due to difference in rails (left or right) between the selected sites, the traction region (I) generated on the right rail of the Bakerloo line, and region (IV) was generated on the left rail of the Jubilee line.

Figure 6.22: The comparison of different creep force angle regions on the selected sites of Bakerloo NB line

However, in contrast to creep force angles, the maximum contact stress results which are presented in Figure 6.23 potentially provide the opportunity to predict different damage

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mechanisms. The high values which were particularly occurred on the no reported RCF sections suggested that the high wear rate on these sites might remove the initiated cracks. Hence, no RCF defects were observed on these sites. For example, it was noticed that although the BH type of low rails exceeded the critical T/N limit, the contact stresses on this site were also high. Thus, this might give rise to wear rather than RCF damage on this site. But, the contacts both on the over-and-underground sections led to RCF cracking when they were mainly located between the two boundaries shown in Figure 6.23. The lower limit was found to be 600 N/mm2 _{and upper limit was 2100 N/mm}2_{. In addition, the}

larger Tγ values inside these upper and lower limits were seen to be more prone to RCF cracking. When the Tγ levels are less than the specified region, the contacts were less susceptible to damage.

Figure 6.23: The comparison of Tγ and P0 on the selected sites of curved tracks