Auteur: Pandrol

Engineering a solution in an earthquake zone

Santiago Metro (Metro de Santiago) is one of the largest and most advanced underground railway networks in Latin America. It currently has six lines, 107 stations, running across 118 km and carrying around 2.5 million passengers every day. Pandrol currently has a package of work which is part of a 20 year contract for the construction and maintenance of lines 3 and 6.

The Challenge

As Santiago is one of the locations in the world where earthquakes are most prevalent, the customer required a fastening solution that allowed for potential future adjustment of the track. In the last 12 months, there have been 67 earthquakes in Santiago, therefore the project requirements were for a +30 mm adjustment capability. The project required a fastening solution for 50 km of track and the requirements were for a lightweight baseplate and under-the-track rubber mats for noise and vibration mitigation.

Pandrol Solution

Pandrol delivered a multifaceted track solution including fastenings, catenary and floating slab mats. The unique and challenging requirements led to Pandrol developing a new composite plastic baseplate, the SEE-SD. This baseplate is designed to be embedded into fresh concrete or by wet pour methods. This would be more cost effective than a traditional aluminium/steel casting and would be easier to handle and install on the track. The SEE-SD provides adequate resilience (stiffness) to attenuate to the concrete slab and provides large vertical adjustments to the rail position. The Pandrol air evacuation system prevents trapped air entering under the baseplate. The SEE-SD plastic baseplate has a special feature of vents and channels that optimise insertion into concrete and ensures excellent resistance to lateral forces.

Once the system was developed, Pandrol’s technical team carried out rigorous tests to demonstrate to the customer that their solution could meet both performance and cost requirements. This required technical validation of the system, including a complete and fully tested assessment of Pandrol’s recommended solution.

The SEE-SD assembly is designed to give a typical vertical dynamic stiffness of around 60 MN/m. It offers a wide range of pad stiffness levels, making it suitable for meeting noise and vibration mitigation requirements on this project. It also meets all requirements of the latest updates of EN 13146 and EN 13481-5 standards. In addition, its performance relating to electrical insulation complies
with EN 13146-5:2012.

The baseplates used in the SEE-SD design is made from glass fibre reinforced polyamide material in order to provide maximum resistance to lateral loads. The baseplate is not ‘laid’ on the concrete but ‘anchored’ and integrated into the slab. There is consequently no risk of slippage. The stress level in the screws is significantly reduced even on tight curves, as a result of the anchoring system, which is based on the use of two screws.

The SEE-SD was designed for use with the SD clip, with its screwed design that optimises track construction costs and provides very high technical performance. SD stands for ‘safely driven’ which relates to the controlled clip guidance from the ‘parked’ to the ‘in-service’ position.

SD insulated blocks are designed to offer lateral adjustment of the track gauge in increments of 1.25 mm. The method to adjust the gauge is managed simply by adapting the insulated block combination. SEE-SD meets the requirements for all urban rail networks, from tram lines
to modern light rail and high capacity metro applications.

Over the lifetime of the project Pandrol has manufactured more than 200,000 SEE-SD fastenings systems to the French rail consortium ETF and Colas Rail on behalf of Metro de Santiago.

Mitigating Vibration

To meet with vibration minimisation requirements, Pandrol supplied its Floating Slab Mats (FSM), which are continuous resilient mats used for the isolation of train-generated vibrations in concrete slabs. These FSMs are manufactured from high quality resin-bonded rubber to achieve vibration attenuation, with a low resonance frequency.

Pandrol QTrack® embedded rail system was also supplied to Santiago Metro depots to help in achieving a maintenance free slab structure.

Rails were elastically supported and fastened while embedded providing free and safe movement of workers and maintenance vehicles. Pandrol QTrack® system can also be developed to completely encapsulate the switches and crossings of a depot in the same manner as a regular track.

Electrification

Electrification was a major part of the Santiago Metro project too, which was completed in 2017. Santiago Metro required 60 km of Rigid Catenary for this project, for which we designed and manufactured the whole system. This was supplied mainly for use within tunnels. Our rigid catenary system was specified as it offers low maintenance, high performance and enhanced safety.

The project involved providing technical support and training to the contractor installing the system. This included on-site training and members of our technical team were present during installation to ensure the process ran as smoothly as possible.

Rigid Catenary is an overhead contact system that has advantages over the third rail or suspended bimetallic T-rail. It is manufactured via an aluminium alloy profile, which accommodates the copper contact wire, with a great cross section for the current that allows operative OCS voltages from 750 to 1.500 V, without any feeding supply.

Rigid Catenary offers many advantages over traditional flexible catenary system, including no traction stress as it allows more contact wire wear without the risk of it breaking off. Rigid catenary provides no mechanical stress on the contact wire, so there is less wear and fewer maintenance issues.

Summary

It is common practice that in earthquake zones around the world, once an earthquake is detected, trains are immediately stopped, after which operation is continued at reduced speeds or is suspended, depending on the strength of the shock.

Metro de Santiago has invested in an infrastructure which mitigates the impact of frequent earthquake activity, whilst ensuring their long term performance and resilience. An 8.8 magnitude earthquake shook the southern part of Chile back in 2010 but the majority of the Metro survived well. More recently in April 2017, an earthquake of magnitude 7.1 reached Santiago after starting around the Chilean coast, whilst the Metro remained largely unaffected.