Rail construction is a sequence of steps that takes laborious amounts of time in each step and finally results in a wonderful and safe system for transport for many decades to come that requires minimal maintenance over that period. The first step in the construction process is the approval for new line itself. This is typically the responsibility of the government to do it. Once a approval is given for rail connectivity between two points then the role of engineering kicks in.
The first step in the process is the alignment. Alignment is nothing but the path in which the track is laid between the two points. Typically one end point is an existing railway station. Deciding on alignment has a number of factors that the designers consider. While trying to fix an alignment there are a large number of factors that needed to be considered. First the length and the economy of building that length. For instance, the basic geometric sense says that the shortest distance between any two points is a straight line. However this straight line alignment between two points may have to go through hills, valleys, agricultural fields, water bodies, urban areas and others. This is where the meandering starts. The cost of construction of a tunnel is very high and avoided if technically and economically feasible. Valleys, streams and rivers need a bridge. Bridge essentially needs to be perpendicular to the flow of water. So the alignment before and after is also to be carefully matched. Agricultural fields and urban settlements are a serious problem that the owners may not give easily like to give up on their lands. Then finally there are also political influences and need to fulfil electoral politics or even aspirations of the local people. All these factors now influence the alignment and finally there are a few alternates that drawn and initial rough estimates arrived at.
Depending on the rough estimates one final alignment is arrived at and approval got from appropriate authorities. Occasionally public opinion is also taken to ensure that there is overall acceptance of the alignment in the minds of the people at large. This step is crucial in the construction of the rail road because this will have future implications when land needs to be acquired for the project by the project authorities.
The next immediate step in the process is financial closure for the project. The project may be funded by the railway company or the government or a financial institutions like banks. Some ties organizations like the world bank also get involved in the funding of the project.
One there is a financial closure and the project is assured of the capital that is required the real work on the ground start. The first step is the reconnaissance survey followed by the detailed survey. During both the surveys pegs are driven, survey benchmarks are constructed. Once this is done the project gets on the drawing board for a detailed design. In the detailed design every kilometre is designed and the alignment fixed. All the aspects are laid out to the last detail as per the Permanent Way Standards. Bridges, Culverts are identified and designed. Cross water works if necessary are also identified and designed. After the completion of all aspects of design finally, the work on the ground starts.
The first work on the ground for the railway line to be built is the marking of the alignment on the ground. This is done using the sophisticated survey techniques and drawn out on the ground. Permanent markers are fixed and this becomes the reference point for the field construction, and monitoring staff.
Once the detailed marking is done, the ground preparation is begun along the complete length of the alignment. Digging and filling are taken up where required as per the design requirements. Then the ground compaction starts using a variety of techniques including rolling and mechanical compacting. Extensive equipment is used in this stage to accelerate the preparation of the substratum.
Preparation of the substratum is the most important step in the laying of a permanent way, because any collapse in the substratum at any point in time for any reason will lead to extensive loss to the rail operations at a later time. Great caution is exercised to make sure rain water flows away from the substratum that could lead to the collapse of the substratum. Extensive drainage works are undertaken to ensure total drainage of rain water and other precipitation from the permanent way at all time.
Great care is exercised to ensure there is no flooding that happens on the permanent way. 100 years of data is taken to consider the flood levels, the maximum flood level etc. are considered before deciding on the height of the substratum from the ground level. Same factors are also considered while deciding on bridges across water bodies and valley. Aesthetic factors to ensure the bridge structures merge well with the surroundings is taken to while designing the bridges
.Preparation of the substratum takes the longest amount of time in a railway project along with drainage and cross-drainage works. It is during this time bridges, culverts and other structures are built and prepared for the next step in the building of a permanent way.
Once the substratum is cleared by the safety authorities then the ballasting, sleeper laying happens. Once the sleeper laying is finished, right behind it laying of track happens. It is during this phase that the electrical pillars required for electrical traction are also laid. After laying the rails, they are smoothened out and the fixing of rails happens with careful checking for track accuracy. Visually the track must look like a smooth curve or a line. Correction is done till this is achieved and the distance between the two rails for the track is achieved. This distance is constantly monitored and checked to ensure accuracy.
After this step the Overhead electrification (OHE), signalling and communication works are undertaken. Signage are fixed at this juncture all along the track as required by the permanent way standards. Once this happens the construction is certified by the safety inspectors and the permanent way inspectors. After this the track is permitted to be loaded with empty rolling stock and the track is test driven. After successfully rolling empty rolling stock, loaded rolling stock is driven on the track and all aspects are tested for speed, safety and accuracy. Then there is a final inspection and the track is cleared for rolling as under regular operations and the track is handed over the operations staff.
Northwest Rail link
The Northwest Rail Link project is a wonderful rail project that is setting new records for rail construction in Australia. Though the project length is just 23 km is the largest work underway in Australia. It is expected to be complete in late 2019 and is expected to serve the population of approximately 360,000 and likely to grow to 485,000 by 2021. This rail link will provide a train every 5 minutes during peak hours. This rail road is expected to reduce 14 million car trips as it becomes operational and is expected to go up to 20 million by 2026.
There are 16 construction sites in the entire projects spread along the length of the alignment of the rail line. At any site and stage of construction the sites may have multiple functions running there. Between the 16 sites there are three overarching core working zones identified, viz., Epping to Bella Vista Station (for tunnel work), Bella Vista Station to Rouse Hill Station (for embankment and sky train work), and finally Rouse Hill Station to Tallawong Road (for surface or bridge and viaduct structures and Rapid Transit Rail works.)
A large number of construction activities are likely to be undertaken at the tunnel boring points including establishment of high voltage electrical lines, support systems like water, construction of access shafts and allied structures, Water recycling systems, spoil storage areas and others.
There will be a range of construction site activities at each of the station (summarized in the table)
A number of factors have been considered while designing of stations in this rail line like the following to ensure this rail line remains as a positive reinforcement in the lives of future generations:
- The components must essentially contribute to the good public spaces, which can provide high quality experience for the users. The locations must be direct, equitable, safe and convenient to use. They must also provide integration with the spaces closeby.
- The facilities at the stations and service facilities must integrate into the environment easily and holistically. They must be easy to maintain.
- Since the entire track is in the urban locations it must facilitate retailing, services around the stations and contribute to active public spaces with excellent landscaping and environment friendly parking space.
- The design must eliminate blind spots totally as well as other possible dangerous areas.
- The materials used for design as well as finishing must be easily maintainable and also take into account of dust, rain, heavy traffic, and graffiti
- The stations must have easy noise cancellation measures.
Tunnels in this project are between Epping and Bella Vista, which will be the longest tunnel in Australia. The entire tunnelling will be done in Sydney Sandstone and shale rocks. In the normal circumstances the two tracks are designed to be 13 m apart, however depending on the construction limitations and rock conditions this could vary. Combination of tunnel boring machines and road header machines are being used. Most of the work will be done by the tunnel boring machines, they are quick and efficient. Road header machines will be used to build sections linking new tunnels to the existing ones.
The tunnel boring machines look like giant worms about 120 m in length. They consist of the mechanical cutting head and balance of the backup mechanism. Each of the machines would weigh about900 tonnes. The tunnelling machines will use extensive power. They will use about7 km of conveyors to remove the debris from the site. The machines work as under:
- The Grippers move to rock surface, allowing the cutting head to move forward. The Rock is pulverized by high strength alloy steel discs placed on the cutter head.
- The crushed rock debris is picked into machine’s head and loaded on to a conveyor belt.
- The conveyor moves the rock right through the machine shield and exits the tunnel behind it
- Precast concrete ring segments are then delivered to the ring building area for ring building.
- Concrete ring is then built. Putting together precast segments using a special vacuum lifting equipment.
- The ring once completed, about 1.7m in length, is joined to the last concrete ring and then pushed out of the back of the shield section.
- The gap between the concrete ring and the rock is filled with grout, to keep water out of the tunnel.
- The machine moves 1.7m forward and then the whole process starts all over again.
Safety is being given the paramount importance in the rail project. The complete tunnel will be compliant with 4 hour structural fire resistance rating. The tunnels will have emergency lighting, CCTVs and public address speakers. There will be fire hydrants right through the length of the tunnel. The tunnels are so designed that in case of an emergence the passengers can get off the train either from the back or the front and walk along the rails. Stations will act as the primary escape points with the facility of fire stairs at the end of the stations. Effective smoke control systems have been installed.
The massive building is likely to have impact on the environment. Intense efforts are being made to ensure such impacts are minimal including mitigation strategies and actions.
The Udhampur-Srinagar-Baramulla Rail link Project (India)
This is one of the most challenging Railway Engineering Projects ever executed anywhere in the world. This is a project that links Jammu with the Kashmir valley and has many political and national interests behind it. It is a 293 km long broad gauge rail line (5’6” apart) running 148 km over the two treacherous and precipitous mountain ranges of Shivaliks and Peer Panjal. 75% in this 148 km stretch over these two ranges needed to be in tunnels. It has the longest tunnel that is 11 km long and many in 6 – 7 km lengths. Accessibility to the construction sites is the fundamental problem and actually the final survey was done without these access roads!
River Chenab that has its origins in Himachal Pradesh flows west through Jammu and Kashmir. Pir Panjal ranges are very steep. Though the horizontal distance between Chenab and Kashmir valley is only 40 km the level difference is about 1000 m. This makes the choice of alignment difficult. A survey in 1973-74 suggested two alternate alignments with ruling gradients of 1 in 100 and other 1 in 50.
The biggest challenge as mentioned earlier in the document, the construction sites were not accessible because of the lack of access roads. Innovation was the key to success and many innovative approaches were used to implement the building of access roads. The land for the roads was taken on contract from the landowners before the final acquisition of the land by the government. Construction of the approach roads was made the part of the rail contracts! A 1m tracer paths (picture below) were first built to check feasibility and the strata along the road alignment. After marking of alignment on topo-sheets pegging was done to develop L and X sections.
Then the challenge was to design the cross section of the tunnels for single rail road. In India typically a D section is used for all single rail roads in India. For the terrain and geological conditions an elliptical section was used. It is 300% more load efficient. For longer tunnel lengths over 3 km an horse shoe section was preferred that gave space for a 3 m wide motorable road for emergency evacuation and rescue measures. It was essential to make extensive studies on the slope before the entry and exit points were decided to ensure slope stability during excavation.
Another challenge in the entire stretch of the rail road project was availability of space for the station yards. This constraint comes because of the hilly terrain. Station at Reasi is built on a 93 m high viaduct. The slopes excavated for station yards are mostly in Muree and Dolomite formations that required extensive protection.
The tunnels along the alignment are passing through many soft, medium and hard rocks therefore each posing its individual engineering challenges. The tunnels pass through extensive shear zones and cavities. Tunnelling in these areas had a custom challenges and they were overcome based on the following guidelines:
In case of loose soil, no muck is to be removed but the walls to be supported using earth filled gunny bags till a cut off is achieved. The cut off is achieved with proper drainage of the site and driving forepoles, cement grouting and back fill concreting. The objective to drain water 5 – 10 m away from the tunnel face.
1:3 cement-sand mix is pumped into the cavities using concrete pumps and transit mixers. This system is advantageous in filling large cavities. 15 m long drain pipes were driven into dolomite stone to drain water and create access to the cavities. Only after the area is stabilized then the face is opened in multiple openings till the cavity is passed.
There were other engineering challenges in the form of bridges over River Chenab and Anji Nallah. The challenge was terrain without a precedence. Anji Bridge was a steel arch of 265 m and 189 m high above the river bed. The Chenab bridge was 485 m arch with 359 m above the river bed.
This made the Indian Railways a kind of pioneers in tunnelling technology in the world.
Some of the important lessons from an engineering perspective from this project are:
- A road network must be first built before contemplating a rail road project, especially so in the difficult terrains like mountains.
- Alignment finalization must use all technology at disposal and then a detailed foot by foot survey is important
- Tunnel portals must always be located in hard rock
- Tunnelling operations must not be initiated before a detailed geo-technical analysis.
- Commercial angle must be thoroughly examined before the beginning of such difficult tasks.
Bibliography
Davies Alan Is this rail line too good to be true? [Online] // Crikey Independent Media, Independent Minds. - 26 July 2012. - 14 October 2014. - http://blogs.crikey.com.au/theurbanist/2012/07/26/is-this-too-good-to-be-true/.
JRTT Railway Construction Tecnologies [Online] // JRTT. - 2012. - 14 October 2014. - http://www.jrtt.go.jp/11English/pdf/p_rw_010.pdf.
NSW Government North West Rail Link Corridor Strategy [Online] // NSW Planning and environment. - 2013. - 14 October 2014. - http://www.planning.nsw.gov.au/north-west-rail-link-corridor-strategy.
Turner and Townsend Breaking records in Australia with the North West Rail Link [Online] // Turner & Townsend. - 12 September 2014. - 14 October 2014. - http://www.turnerandtownsend.com/NWRL/_NWRL.html.
