OPERATION AND MAINTENANCE PHASE

6.1. Operation and Maintenance

After construction the railway line will start to operate according to its original scope, i.e. fulfilling the need that gave rise to the construction of the line in terms of traffic throughput at a given axle loading, train speeds, train lengths etc. There will probably be a ramp-up phase to the maximum design capacity (full system operation).

The operations phase may be longer than 30 years (the track life) and with continual maintenance and material replacements may well exceed 50 years before the next phase, track renewal, is required where the formation may need to be rehabilitated as well as replacement of some track material, especially sleepers which will probably be replaced for the first time. With modern track maintenance and rehabilitation machines the distinction between the phases have become vague since formation rehabilitation can commence without closing the line for a lengthy period, i.e. rehabilitation can be carried out in a series of longer maintenance windows in areas where such is required and the line opened again every day for traffic in-between the rehabilitation windows. The maintenance function is discussed in more detail CHAPTER 7 and the maintenance management process in CHAPTER 5.

6.2. Track Life Stages

In this thesis three track life stages are identified during the operations and maintenance phase being early-, mid- and late life stages (Figure 15 ‘A’). The maintenance requirements and maintenance machinery features, type and mix of machines will change during these stages. The lifecycle phase illustrations in the rest of this chapter were partly inspired by a publication of Haas et.al

Figure 15: Operations and Maintenance Life Stages (Adapted from Ebersöhn, 1997)

6.2.1. Early Life Stage

These are the initial years in the life of the track. It starts shortly after rehabilitation of the formation and renewal of track material or newly constructed line. Under normal operating conditions staying within the scope and design of the line (capacity, throughput, axle loading, train length and speed, etc.), there should be few material replacement requirements during the early life stage.

However, some infrastructure material, especially electrical and signalling components, may follow a failure probability pattern (see CHAPTER 4 paragraph 7.3) where the probability of failure is highest during the initial stage of the component’s life. Therefore, some material replacements may already occur during the early life stage. This material failure may also be the cause of some early emergency maintenance. This type of failure mechanism normally does not give a warning of potential failure and would therefore not constitute corrective maintenance (by definition of this thesis in CHAPTER 5 paragraph 2.4).

Preventive mechanised maintenance activities such as infrastructure measuring and recording, ultrasonic rail flaw detection, ballast tamping and stabilising, ballast profiling, rail profiling, overhead electrification system (OHE) maintenance, etc. will already start early after opening the line. Depending on the maintenance strategy followed, these initial maintenance activities could be at a high frequency level (short intervention cycles) due to tight maintenance intervention levels. Refer to CHAPTER 4 paragraph 5, Figure 34.

6.2.2. Mid-Life Stage

During the mid-life stage the track components will show wear or fatigue deterioration which will signal the start of some material replacements such as rails, fastenings, rail pads etc. Where maintenance windows are required to replace rails for example as part of the preventive replacement programme, it may be necessary to replace some other components such as rail clips or pads prematurely as it may not be possible to get a maintenance window at the same section soon again. See CHAPTER 6 on maintenance windows. All costs involved need to be considered at the time such as cost for early replacement versus cost of consequential damage for late replacement and cost of an additional maintenance window at a later stage.

Potential failures (CHAPTER 4 paragraph 7.2) of some track components may be witnessed if the preventive replacement programme falls short of timeous replacement. If potential failure of sections of the formation becomes visible, it may mean that the track or a section thereof is already in the late stage of its life and re- evaluation of the maintenance strategy may be required.

Preventive maintenance such as rail grinding, ballast -tamping, - regulating, -replenishment, etc. will continue during the mid-life stage. Ballast management may increase in importance during the mid-life stage since the ballast bed would have developed several areas of excess and deficit in ballast volume over time. This can make high production ballast regulating and management machines such as the Plasser & Theurer BDS system economically viable and beneficial and a consideration for procurement. Refer to Zaayman (2016), Chapter 13, paragraph 6. This machine may incorporate material conveying systems such as the MFS allowing the transportation of large volumes of ballast between areas of excess and deficit ballast.

Ballast cleaning will also start during the mid-life stage which will only then require the procurement of ballast cleaning machines. Refer to Zaayman (2016), Chapter 14. If it was a new line, ballast deterioration might be fairly homogeneous along the length of the line. To avoid some sections of the line only being ballast cleaned very late (high levels of contamination) due to resource availability and availability of maintenance windows, some sections will require ballast cleaning prematurely to remain within a reasonable maximum contamination for the entire section to avoid consequential deterioration of other track components and rapid track deterioration. The life of the formation is to a very large extent dependent on the condition of the ballast bed and if the formation is damaged as a

result, there is no easy repair and the financial consequences and impact on train operations will be significant.

Emergency maintenance is omnipresent but it can be limited if a good preventive maintenance programme is maintained. Corrective maintenance will increase to correct defects that may occur between preventive maintenance activities. See definitions of maintenance tactics in CHAPTER 5 paragraph 2.4.

6.2.3. Late Life Stage

Even if preventive maintenance is reduced towards the end of the track life in terms of the maintenance strategy (CHAPTER 4 paragraph 5), it does however not necessarily mean that the demand for mechanised maintenance machinery will reduce as well. Corrective maintenance is likely to increase which may have an even greater demand on mechanised maintenance machinery. It could actually require additional lower production machinery or spot maintenance machinery to be spread along the length of the line to work in-between trains addressing short defects, rather than fewer very high production machines.

During the late life stage potential failures (CHAPTER 4 paragraph 7.2) may increase as the track standard is reduced by lowering the maintenance intervention level towards renewal (if that is the strategy). Material replacement will therefore concentrate more on corrective replacement rather than preventive replacements and premature replacement becomes less likely. See Figure 15 ‘B’.

If potential failures are detected in the formation (Figure 16 ‘B’), the track is nearing the end of its economic life and would require renewal. The P-F Interval depicted (Moubray, 1997) is discussed in more detail in CHAPTER 4 paragraph 7.2. However, depending on the track alignment, topography, climate, length etc., the formation on some sections of the line may have a remaining life beyond the original design horizon. Track renewal using modern mechanised methods can therefore become an integral part of track maintenance effort starting during the late life stage which blurs the distinction between the track life phases and stages. The demand for ballast cleaning could potentially be reduced as track renewal starts.

Figure 16: Potential Failure of the Formation Indicates End of Track Life [Adapted from Haas et.al (1994), Ebersöhn (1997) and Moubray (1997)]