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Automation gets the most out of mining railway infrastructure

01 Apr 2006

Earlier this year, faster, heavier and fully-automatic trains began running on the El Teniente copper mine's private railway, marking the culmination of a major upgrade to squeeze the maximum daily tonnage out of the infrastructure

Thomas Salt and Kevin Mears,
Principal Consultants,
Interfleet Technology Ltd

EL TENIENTE mine in the foothills of the Andes was producing 350000 tonnes of refined copper a year in 2001, when Chile's state mining company Codelco launched a major expansion programme. This required an increase in production to 480000 tonnes, driven by dramatic rises in global demand for copper.

The project hinged on a major upgrade of the 11 km single-track electric railway which forms the backbone of the mine's ore transport. The ore loading hoppers are located inside the mine, and the standard gauge line runs underground for 7 km, surfacing for the final 4 km to reach the unloading, processing and smelting facilities.

The railway upgrade was audited and reviewed by Interfleet, who worked with Codelco to extract the maximum capacity from the route. Daily tonnage has been increased from 78000 to 120000 on a regular basis, and test runs have demonstrated that 126000 tonnes per day can be achieved. Now the railway is well on the way to achieving the upgrade's primary goal of 131000 tonnes per day.

Lengthening trains

It was realised from the start that merely increasing the number of trains would bring little benefit because of the constraints of the single-track line. Boring a second tunnel or expanding the existing tunnel for double track was not viable, so the utilisation and capacity of each train would have to be increased.

Before the upgrade five trains of 15 or 16 wagons were deployed on the line, with EMUs used to transport miners in and out of the workings. In addition there were several diesel locos for engineering trains, plus service vehicles including snow blowers and track machines.

Ore trains run in push-pull formation, with a loco at the mine end of the rake hauling empty trains uphill into the mine and propelling loaded trains down to the processing site. Before the upgrade, a guard rode in a dedicated wagon at the downhill end, using a radio to inform the driver of signal aspects and applying the emergency brakes if needed.

The railway operates two wagon types. Fine ore is carried in 100 tonne capacity bottom-discharge cars, while coarser material is moved in 80 tonne capacity side-discharge vehicles. During the upgrade six more side tippers were purchased to provide maintenance cover and extend the trains to 18 cars, the longest the loading points can handle without incurring disproportionate expense by extending tunnels.

Of greater significance than the longer trains is modification of the wagons to allow automated unloading and vehicle health monitoring. All wagons have been fitted with computers to operate the discharge doors, along with data links to the locomotive ATP and accelerometer derailment detection linked to the loco braking. Train integrity monitoring prevents a route being released behind a divided train, removing the need for the guard's dedicated end vehicles and so giving more flexible train formation.

To haul the heavier trains a replacement fleet of 1·6MW Bo-Bo locos was ordered from Schalke in Germany. Designed to withstand dust and moisture-laden mining conditions, these are ballasted to 130 tonnes to provide adhesion, have a top speed of 60 km/h and feature AC traction with totally-enclosed IGBT converters.

Driverless running

Along with the rest of the mine, the railway had traditionally ceased operations for 45min during shift changes, with all the trains brought to the surface. Codelco saw that continuous operation would bring an immediate increase in capacity, and could be achieved by automation. To free up rail capacity, buses are being used to ferry workers into the mine, though the EMUs have been retained and fitted with ATP for use in an emergency evacuation.

Automatic Train Operation has now been commissioned, and trains are running without drivers. The only human intervention is during loading, when the trains are remotely operated from the control room under the watch of CCTV. All movements are centrally controlled from two three-screen workstations, one in use and one as a standby. Each has two screens showing the railway network and one displaying alarms and alerts.

Trains are run on demand to suit the mining operations, but can also be run to a pre-defined timetable. A computer mouse is used to select start and end points of a trip, and then the automatic routing software optimises the movements and manages conflicts.

The US&S Microlok signalling and control has been replaced with Bombardier's Interflow, which was developed specifically for industrial lines and is based on similar principles to ERTMS Level 3. The track circuits were replaced with balises which provide trains with absolute position data. This is combined with measurements from axle-mounted odometers to calculate accurate locations, which are then transmitted to the interlocking by radio. Standard antennas are used in the open air, while the underground sections use duplicated and overlapping radiant cables running between repeater stations.

The interlocking monitors all train movements, radioing back movement authorities. The ATP will intervene to reduce the speed or make an emergency brake application if a train exceeds the speed profile or the geographical limits of its authority.

Increasing train speeds and tonnages has quadrupled the loading on the track, requiring changes to the infrastructure. New 67 kg/m heavy duty rail was installed in critical areas, hardwood sleepers laid and head-hardened crossings introduced. Thicker 650V DC overhead contact wires and feeds have been installed to cope with the increased power demand, the substations have been uprated, and the fuses replaced by circuit breakers to reduce costs.

The maintenance regime also needed to change. Ultrasonic inspection was increased from annually to quarterly, with a system of regular monthly track inspections in place. New maintenance machinery was acquired.

Staying safe

The demand for copper means the railway had to be kept running throughout the upgrading programme; every train carries ore containing copper worth US$70000. All upgrading had to be completed within the daily 3h maintenance windows, which initially led to problems with possessions over-running. Constant monitoring of the work was introduced, a time-consuming and demanding process but one which has ultimately paid off in the excellent safety record.

New safety risks are presented by automation. Miners formerly had relatively unrestricted movement around the site, with train drivers warning anyone in the vicinity of their presence. Removing the drivers means a different approach, with the erection of safety barriers, fences and warning signs, and the creation of special procedures for dealing with emergency repair works and rescuing failed trains.

The most likely time for an accident is at the commencement of automated running, and so automatic operation has begun with crews still on board for an overlap period while Codelco ensures that the safety measures are fully effective. The driver has a standard ERTMS user interface, displaying the actual and target speeds and the distance-to-go.

Codelco made it clear that no-one would be made redundant by the automation, helping to ensure the co-operation of the train crews during the changes. The staff are being retrained to service the trains and carry out other railway duties, including providing back-up if the automated system is unavailable. Codelco also recognised the importance of retaining their collective operating experience.

The mine has traditionally maintained all its equipment in-house, but this model was seen to be unsuitable for the new technologies. Maintenance contracts have been signed with suppliers Bombardier and Schalke, who will provide labour, spares and future upgrades.

Getting even more out

The upgraded railway now runs for 21h a day, with a shut-down for maintenance between 11.00 and 14.00 during the least productive shift. Daily tonnage regularly reaches 120000, and tests have shown that 126000 tonnes can be achieved. Codelco will achieve the primary goal of 131000 tonnes per day, while the automation is keeping operating costs down.

Even before the upgrade was completed, an increase to 150000 tonnes was being considered. This is more than the mine's current output, but an advance study was needed to give time for either a second railway or conveyors to be provided if the current railway had reached its absolute limit.

Interfleet was asked to identify the pinch points in the system, and calculate how much more capacity could be squeezed out of the system. Extending the tunnels was deemed prohibitively expensive, so the focus was on optimising the operating pattern, timetable and track layout at the unloading point.

The mine's production plan defined the quantities of ore to be moved and where it would be loaded, setting the routing and frequency of the trains. There are inherent vagaries in mining, and the railway has to be flexible enough to adapt. To compile a full picture of the current operating performance, Interfleet looked at the 2006 production plan, and developed an operating plan to deliver the required tonnage. The 2006 plan assumed 137000 tonnes of ore per day, which is refined to 1512 tonnes of copper, worth about US$6m.

Weighbridge statistics showed that the wagons did not always carry their maximum load, and so when reviewing the upgrade plans, Interfleet calculated the capacity on the basis of a 65 tonne load to obtain a more realistic figure.

We had to determine the total train cycle time, how the single-line section is used, times for each section of line, and loading and discharge dwell times. The Interflow package provides a complete record of all train movements, which was invaluable in developing our understanding of the current operations. In addition, Codelco provided loading and discharge times for all trains over a two-month period.

Opentrack software was used with the real timings to produce a simulation of the existing system, which was then optimised through a series of small incremental changes to the operating plan. We found that the optimal cycle time was 76min. This was being bettered on some occasions, but overall efficiency was being compromised because there was not the consistent regulation needed to ensure that all trains could maintain these timings.

We then analysed other limiting factors to determine the potential total tonnage. This produced a recommendation of some additional track works, including installation of a length of movable OHLE at a loading point to enable more flexible pathing by allowing through trains to reach other loading points without needing two pantograph adjustments.

Allowing for the 4h maintenance period we developed a 20h operating plan which covered seven trains operating 15 x 76min cycles, and six trains operating a partial 60min cycle. The plan details the precise order of the trains, their movements and how they should be regulated. The plan delivers 55800 tonnes of fine product on two trains each running 15 and 16 cycles per day, while five trains of 18 side-tipper wagons would each complete 16 cycles, delivering 93600 tonnes of coarse ore and giving a total traffic of 149400 tonnes of ore per day. The cycles were validated using OpenTrack, ensuring there were no conflicting movements.

We found that under ideal conditions the railway could theoretically handle up to 150000 tonnes per day with the existing rolling stock and infrastructure, assuming a 4h maintenance shut-down. Once we factored in an allowance for production difficulties, train reliability and any stoppages, we determined the realistic average capacity as 137000 tonnes/day, in line with the 2006 requirements. Our study concluded that any further expansion would require considerable investment in most areas of the railway.

Supplier Schalker Eisenhütte
Type Bo' Bo'
Gauge mm 1435
Length over couplers mm 15 640
Width mm 2 900
Height above rail mm 4 000
Weight tonnes 130
Max speed km/h 60
Power supply V 650
Drive Three-phase IGBT converter
Nominal performance 8 x 200 kW
Control Siemens S7
Braking electro-dynamic, air/spring-loaded
  • CAPTION: A fleet of new electric locos (top) has been acquired from Schalke of Germany to replace the older units (below). The trains are worked in push-pull mode, and before the introduction of ATO a dedicated end wagon was provided for the guard (below right)
  • CAPTION: With the introduction of ATO, all movements are centrally controlled from two three-screen workstations in the dispatching office (below left), one in use and one as a standby. The new locos (below) are fitted with Interflow ATP equipment based on ETRMS Level 3 principles
  • CAPTION: ATP location-monitoring reports and movement authorities are transmitted to and from the control centre, trains and lineside interlockings using digital radio