Casting a mast with proper alignment in the OHE foundation is called grouting process. Grouting is an important and careful process. Once grouting is done incorrectly, it cannot be easily corrected. Therefore, it is essential to keep the following points in mind before carrying out the grouting work.
- Type of Mast & it’s Implantation
- Embedment Length
- Part of mast below & above the Rail level
- Reverse Deflection
Type of Mast & it’s Implantation
Before grouting work, Ensure that you determine/check the type of mast from CSD; otherwise, once grouting is done, the mast may either get damaged or both the mast and OHE foundation could be useless.
- Minimum implantation should not be less then 2.90 metres.
- Minimum implantation should not be less then 4.75 metres in platform area.
- Maximum implantation should not be more than 4.80 metres for single mast. In case of upright it may be more than 4.80 metres.
Embedment Length
Embedment length is the length of mast which is inserted into the OHE foundation. Before mast erection, ensure that embedment length is sufficient for grouting work.
- Minimum embedment length should not be less then 1.35 metres for single mast(B-series mast, BFB mast, RSJ mast, TTU upright etc.
- Minimum embedment length should not be less then 1.45 metres for portal upright grouting.
Portion of mast below/Above the rail level
At the time of mast alignment, we must ensure that the required length of mast is above the rail level(7.65 meters) or required length of mast is below the rail level(1.85 meters in IR).
Portion of mast above the rail level = Mast Length – (Step Distance + Embedment Length)
ML = L – (SD + EL)
L= 9.5 meters in IR, 9.8 meters in DFCCIL project
SD = 0.50 meter in IR, 0.80 meter in DFCCIL Project
EL = 1.35 m for normal mast, 1.45 m for Portal Upright
Reverse Deflection
The bending of OHE mast from its vertical position is called reverse deflection. Generally reverse deflection value are 0, 30 & 60.
Actually OHE mast should be straight without any deflection after the erection of final load such as brackets, boom & wires. This is the reason we provide reverse deflection in the OHE Mast. If we don’t provide reverse deflection, OHE Mast will lean after erection of brackets, wires & others load.
- Deflection is depend upon employment schedule.
- Reverse deflection is given with either +sign or -sign. +sign denoted that the OHE Mast will bend in opposite direction of the track centre, while –sign denoted that the OHE Mast will bend towards the track centre.
- In case of inside curve track, reverse deflection should be in –sign.
(it means mast will bend towards the track center)
- In case of outside curve track, reverse deflection should be in +sign.
(it means mast will bend opposite direction of the track centre)
- In case of tangent track, reverse deflection may be either 0 or in +sign. It will be depend upon load applied on the OHE Mast.
- In case of portal upright grouting, reverse deflection will be “0”.
How to check revers deflection practically
Following materials will required for Alignment & deflection checking of OHE Mast-
1)Wooden or Angles , 2) Plumb bob with thread, 3) Scale or Vernier Callipers, 4) Twist rotator(mostly BT or ST pipe are used)
Following procedure will do for deflection checking-
- First, check the deflection value from the CSD or LOP. Generally reverse deflection value are 0, 30 & 60.
- Let us consider value of deflection is +30. It means mast will be 30mm bend opposite site of the track.
- Take 1.5 meters of chord plumb and check X mm gap between face of the mast & plumb ball as per picture shown in below.
Now, we will calculate the value of X.
- Calculation
Length of mast (L) = 9.5 meters
Length of mast above the foundation level
FL = L – EL
FL = 9.5 – 1.35
FL = 8.15 meters
Deflection (D) = 30 mm or 0.03 meter
Let us consider X mm deflection required for 1.5 meters of plumb.
If value of deflection is 0.03 meter for 8.15 meters of mast
Then value of deflection for 1 meters = 0.00368 meters
So, value of deflection for 1.4 meters of plumb = 0.0051 meter or 5 mm.
Value of X = 5 mm
- As per given calculation we will take 5 mm gap between face of the mast & plumb ball.
That’s why, as per plumb image we can check 30 mm gap between face of the mast & centre point of plumb ball.
X+25 mm = 5 mm + 25 mm = 30 mm
- We can take various value of deflection as per length of plumb bob.
| Sr. No | Length of Plumb | Value of X |
| 1 | 1.3 m | 4.7mm ~ 5mm |
| 2 | *1.4 m | 5.1mm ~ 5mm |
| 3 | 1.5 m | 5.5mm ~ 5 mm |
| 4 | 1.6 m | 5.8mm ~ 6mm |
| 5 | 1.7 m | 6.2mm ~ 6 mm |