Annexure‐XII Clearance of derailment guards in Metro systems

1. As per para 7.1 of ‘Standards of structures for Metro Railway/MRTS system’, the derailment guard should be provided inside/outside of running rail, and the lateral clearance between the running rail and the derailment guard shall be 250±40mm. Thus the maximum clearance permitted is 290mm, and the minimum is 210mm.

In the following paras, the impact of this clearance on the safe operation of Metro systems has been analysed. Analysis has also been made to arrive at the minimum up‐stand clearance required to accommodate the various Fastening systems approved for use in the Metro systems. Based on the above analysis, recommendations for the up‐stand clearance has been arrived at. The impact of up‐stand clearance on minimum plinth width requirement has also been brought out.

2. As per SoD generally adopted by Metro systems, the following track and Rolling stock parameters adopted by Metro systems have been taken for the analysis. 2.1. Track. Gauge‐1435mm Rail head width(UIC 60)‐72mm Rail height(UIC 60) ‐172mm. Up‐stand thickness‐200mm 2.2. Rolling stock wheel set. Wheel gauge back to back distance‐1360mm Minimum projection of flange of new wheel‐28mm Maximum projection of flange of worn wheel‐36mm Maximum thickness of wheel flange‐32.5mm Minimum thickness of wheel flange‐22mm Minimum width of wheel‐135± 2.3. Wheel flange clearance to rail gauge face When the wheel set is in central position with respect to track, the clearance between rail and wheel works out to (1435‐1360‐ 2x32.5)/2=5mm. 2.4. Maximum drop of a derailed wheel. Maximum drop of a derailed wheel=214.5(ht of rail+fastening assembly)‐28(depth of flange)=186.5mm. 3. Maximum lateral movement of a derailed coachwith up‐stand clearance of 250± 40mm stipulated for Metro systems are analysed below for the two cases, viz; (a) derailment up‐stand outside track, and (b) derailment up‐stand inside track. 3.1. Maximum lateral movement of a derailed coach with derailment up‐ stand outside the Track.

Maximum lateral movement of wheel from mean position, in case of derailment, till it is stopped by the up‐stand, is as under.

(a) For up‐stand clearance of 210mm 32.5+5+72+210‐135=184.5mm.

(b) For up‐stand clearance of 290mm

32.5+5+72+290‐135=264.5mm.

3.2. Maximum lateral movement of a derailed coach with derailment up‐ stand inside Track

Maximum movement of wheel from mean position in case of derailment, till it is stopped by the up stand, is as under.

(a) For 210mm up‐stand clearance 210‐5‐32.5=172.5mm. (b) For 290mm up‐stand clearance 290‐5‐32.5=252.5mm

The results are tabulated below for the two up‐stand clearances. The up‐ stand clearances are marked‘D’ in the Table below.

Table‐1: Maximum lateral movement of a derailed coach for up‐stand clearance of 210mm & 290mm

Up‐stand Max lateral movement location For For D=210mm D=290mm Outside track 184.5mm 264.5mm Inside track 172.5mm 252.5mm

4. The effect of the above lateral movements on safety of derailed coach are analysed below. 4.1. Danger of derailed coach infringing kinematic envelope of adjoining track. The track centres are worked out such that the structure gauge of running on both tracks do not infringe. Thus, a coach running at maximum speed on one track, on derailment, will not infringe the kinematic envelope of coach on the adjoining parallel track if its lateral movement on derailment does not exceed twice the clearance of structure gauge over kinematic envelope. This value is 2x150=300mm on tracks laid on ‘at‐grade’ and on ‘viaducts’.For this lateral movement, permissible ‘D’ values are tabulated below.

Table‐2: Maximum permissible up‐stand clearance in At‐grade & elevated tracks so that a derailed coach does not infringe the on adjoining track

Up‐stand location ‘D’ value Out side track 210+(300‐184.5)=325.5, say 325mm Inside track 210+(300‐172.5)=337.5, say 340mm

Therefore, the lateral movement calculated above will not infringe the kinematic envelope on the adjoining track in ‘at‐grade’ and ‘viaducts’. In , twice the clearance of structure gauge over kinematic envelope is 2x100=200mm.For this lateral movement, permissible ‘D’ values are tabulated below.

Table‐3: Maximum permissible up‐stand clearance in tracks so that a derailed coach does not infringe the train on adjoining track

Up‐stand location ‘D’ value Out side track 210+(200‐184.5)=225.5, say 225mm Inside track 210+(200‐172.5)=237.5, say 240mm

Thus, in tunnels, maximum permissible up‐stand clearance is 240mm. 4.2. Danger of derailed coach infringing the parapet/walk way and other structures just outside structure gauge, in ‘at‐grade and viaducts With an up‐stand clearance of 210mm, maximum lateral movement of derailed coach is as per Table‐1. But the maximum lateral movement permissible is 150mm which is the clearance between the kinematic envelope and structure gauge. The up‐stand clearance permissible to prevent derailed coach hitting the walkway located just outside the structure gauge is as under.

Table‐4: Maximum permissible up‐stand clearance in At‐grade & viaduct tracks so that a derailed coach does not infringe the walk way Up‐stand location ‘D’ value Out side track 210‐(184.5‐150)=175.5, say 175mm Inside track 210‐(172.5‐150)=187.5, say 190mm

4.3. Danger of derailed coach infringing the walkway/tunnel structure in tunnels. In tunnels, the up‐stand clearance permissible to prevent derailed coach hitting the walkway located just outside the structure gauge is as under.

Table‐5: Maximum permissible up‐stand clearance in tunnel tracks so that a derailed coach does not infringe the walk way

Up‐stand location ‘D’ value Out side track 210‐(184.5‐100)=125.5, say 125mm Inside track 210‐(172.5‐100)=137.5, say 140mm

The above values of up‐stand clearances are not workable, as the minimum clearance required for entrapping a derailed wheel is about 160mm.If up‐ stand is to be effective in tunnels, walk way and other structures in tunnels should be kept with a clearance of structure gauge over kinematic envelope, of 150mm .

4.4 Danger of derailed vehicle capsizing.

Since the drop of wheel is by 186.5mm only, the tilt of coach with one wheel on rail and one on plinth is not appreciable to cause capsizing. When both wheels and rest on plinth, there will be no tilt. The gap between rail and up‐stand has a locking effect on the derailed wheel, preventing the tilting of the coach. However, the plinth width will have to be adequate to support the derailed wheel flange. 5. Minimum up‐stand clearance required for accommodating approved Fastening systems

Up‐stand clearance required for the 3 approved Fastening systems are tabulated as under for a rail of 1 in 20. The up‐stand clearance provides for 20mm additional allowance for construction allowances.Explanatory sketch is also given below.

Table‐6: Minimum up‐stand clearance required to accommodate the standard fastening systems approved by Railway Board for use in Metro systems. Note: Rail cant of 1 in 20 has the effect of 8.6mm tilt(172/20) of rail top with reference to rail bottom Fastening Half Up‐stand clearance to Recommended up‐stand system width of accommodate bearing plate clearance bearing plate(w) Up‐stand Up‐stand Up‐stand Up‐stand inside=w/2‐ outside=w/2 inside=w/2‐ outside=w/2 8.6‐36 +8.6‐36 8.6‐36+20 +8.6‐36+20 Fastening 196mm 151.6mm 168.8mm 171.6, say 188.8, say system‐ 175mm 190mm 336 245mm 200.5mm 217.7mm 220.5, say 237.7, say 220mm 240mm Delkor‐ 212.5mm 168mm 185.2mm 188, say 205.2mm, Alt‐1 190mm say 205mm

Fig‐3: Figure showing minimum up‐stand clearance for accommodating the base plate of approved fastening systems‐up‐stand inside track

Fig‐4: Figure showing minimum up‐stand clearance for accommodating the base plate of approved fastening systems‐up‐stand outside track

Thus, from considerations of accommodating the approved Fastening systems, the clearance required is 240mm. 6. Maximum Up‐stand clearance from various considerations. The conclusions arrived at in paras 4&5 are tabulated below.

Criteria Up‐stand Up‐stand out inside side Viaduct‐non infringement of adjacent 340 325 track Tunnel‐ non infringement of adjacent 240 225 track Viaduct‐non infringement of walk way 190 175 Tunnel‐ non infringement of walk way 140 125 Minimum width to accommodate 220 240 bearing plates of approved fastening systems Minimum width to trap derailed wheel 165 165 7. Conclusions. 7.1. The Railway Board directive to provide up‐stand clearance of 210‐ 290mm needs review. Most world Railways adopt a clearance of 180‐ 190mm. The guard rail clearance adopted in some of the Metro systems are as under. (i) BTS/Bangkok‐194mm (ii) Kaohsiung Metro‐180mm (iii) Singapore Metro‐180mm. 7.2. Absolute minimum clearance to trap a derailed coach is 165mm. 7.3. The plinth width has to be minimum to reduce dead load on sub‐ structure. With larger up‐stand clearance, the plinth width gets increased. Thus, up‐stand clearance of 180‐240mm is expected to meet the requirements of the Metro system. 7.4. The plinth width should be sufficient to accommodate both the derailed wheels in case of derailment so that one of the derailed wheels does not fall on the viaduct deck causing possibility of overturning of the coach. 8. Proposal. “The lateral clearance between the running rail and the derailment guard/up‐stand shall be 180‐240mm.The Metro system shall decide the clearance within the above limits, taking in to consideration the requirements specific to that Metro. The plinth width shall be adequate to contain both the wheels in case of a derailment.”