Publié le 06/02/2017 - Mis à jour le 28/08/2017
Passer la zone des réseaux sociaux


Ropes, harnesses, climbing crampons … you need to be a bit of a mountain climber to reach the Mercues Rock Face in the Lot department, three kilometres from Cahors. Yet it is here that SNCF Réseau undertook major safety works throughout the entire year in 2016. The works took place on the side of a cliff and required exceptional human and equipment resources.

A high-perched project

A deafening sound fills the air around Mercues. There is a helicopter flying above the SNCF railway line which connects Montauban to Abrais on the Paris-Orléans-Limoges-Toulouse (POLT) route. Looking down, it is also possible to see the Castle of Mercues, in the same field of vision as a rock wall where workers with orange safety vests are busily moving around.

It has been a year since SNCF Réseau and its partner company - ROC Aménagement – started working on this imposing site. The aim of their work has been to upgrade and ensure the technical compliance of the warning system used in case of a rock fall. The old system had become outdated and the installation of new detector nets will make train traffic safer.

22 May 2012: part of the retaining wall on the rock face collapsed. The very next morning 40 cubic metres of rock were removed to make it safer. The train tracks were repaired and railway traffic resumed a few days afterwards.



“Special procedures were required due to the geological and cultural nature of this site”, explains Karine Castet, Director of Operations responsible for this project. “The fact that the Castle of Mercues is situated nearby meant that it was necessary to apply to the Historic Monuments of France for building permission.”

The specialized staff of ROC Aménagement are authorized to work at great heights and were located 10 to 25 metres above the train tracks. “The challenge of this project is to carry out complex works under dangerous conditions.”

Special procedures were required due to the geological and cultural nature of this site


Wide-ranging safety systems

Working on the Mercues Rock Face had become quite difficult. The net detection system was old and maintenance personnel were exposed to risky conditions as they needed to climb up poles to reactivate the system after each warning alert.

Initial works focused on foundational elements, mainly:

  • compliance upgrade of the net detection system for rock falls in order to provide warning alerts and stop all railway traffic in case of rock falls
  • installation of a protection system on the rock wall via a wire meshing which is anchored and pressed against all parts of the wall not covered by the net detection system
  • creation of a path to enable safe access to the net detection system during emergency and maintenance use

Infrastructure protection was also renovated. The rock wall along railway line 1 (Toulouse to Paris) was reinforced through an anchoring system and the enhancement of the bricked portions, thanks to the resources provided by the Gauthier works company.


  • 4 January 2016: start of buttressing works
  • August 2016: start of infrastructure rehabilitation works
  • 18 October 2016: deployment of the first series of net detectors following technical tests conducted by the Toulouse-based PRI Regional Engineering Centre and the local Electric Signalling Centre
  • 18 November 2016: completion of infrastructure works
  • 1 December 2016: deployment of second series of net detectors
  • First half of December 2016: installation of new access paths (metal structures including step ladders, caged ladders, etc.)
  • 3rd week of December 2016: closure of works site



High level partners

For passengers travelling on the Paris-Orléans-Limoges-Toulouse line, the low-angle view of the Mercues rock face is quite impressive. A nearly vertical 20 metre high rock wall with railway lines at its bottom. “This is one of the complexities of the project”, says Karine Castet.

Specialised partners were selected to help SNCF Réseau carry out this project. “The supplier selection process began in the early part of the summer of 2015”, says Gaëlle Morin, an expert buyer in the Procurement Division (Atlantic Region.) “Due to the specialised nature of the works, we had to go outside of our usual working scope and find trusted companies which had not yet become approved suppliers. We knew that ROC Aménagement would be a highly competent partner with experience both in working at heights and in compliance with stringent safety standards defined by SNCF Réseau.”

The rock fall detection system and the implementation of wire meshing to ensure the safety of the Mercues rock face.


An exceptional project

Due to the physical layout of the area, ROC Aménagement contracted with a helicopter transport firm to fly out the rubble and residue, and to fly in the required equipment to the works site. A very unusual operation represented by the following figures:

  • over 400 “big bags” of rubble and residue were flown out between January and May 2016, with each one weighing about 800 kg
  • 300 poles measuring 5 to 6 metres in height and weighing 180 kg were installed
  • 49 cable drums, each one with 500 metres of cable to install
  • over 3,000 pulleys to position
  • 1,500 metres of access paths to the railway safety system were re-designed
  • 20 staff dedicated to this project on a full-time basis
  • project cost of €5 million, 100% financed by SNCF Réseau

We knew that ROC Aménagement would be a highly competent partner with experience both in working at heights and in compliance with stringent safety standards.

An impressive – and complex - geological landscape


Dense train traffic to be managed during the works

Different project teams worked together on the specific characteristics and challenges of these railway works:

  • Operational Project Ownership was assigned to the Midi-Pyrénées Project Agency
  • the role of General Contractor for technical studies was handled by the Toulouse Regional Engineering Centre
  • the role of General Contractor for works was managed by Infrapole, Infralog and the Midi-Pyrénées Infra-Traffic Centre

Project management on a daily basis was a real challenge as the POLT railway line is a major transportation route. The different participants involved in the project had to be managed, while also taking into account frequent train traffic. “We had to plan railway traffic interruptions in advance during different periods of the day. At times, only traffic on line 1 was stopped. An automatic address system allowed trains to travel on line 2 (Paris to Toulouse) in both directions. If necessary, train traffic on both lines was interrupted at the same time.”

Thanks to this ongoing cooperation, the buttressing works project for the Mercues Rock Face was able to start and end at the scheduled times. “Every day we had to meet new challenges! During the month of August, a second company – Gauthier – arrived on site to work on the infrastructure, at the same time as ROC Aménagement. For safety reasons, simultaneous vertical work by two parties is not authorized. As a result, they had to work in linear fashion. We were therefore obliged find new solutions, change our ways and ensure that all the teams involved could successfully carry out this project.”

Every day we had to meet new challenges!

Good team cohesion ensured the successful execution of the project


Project fully managed by SNCF Réseau

The Mercues Rock Face project is part of the greater programme to modernise the POLT railway route. This includes works dedicated to railway switches, train track renewal and tunnel rehabilitation. In total in 2016, nearly €9 million were allocated by SNCF Réseau to this strategic railway route in the Midi-Pyrénées region. In Mercues the works lasted until December 2016.

Many railway works scheduled to be completed on the POLT route by the end of 2016


An innovative approach to procurement

The works carried out on the Mercues Rock Face were most definitely not like a normal project! In general, the requests for proposals (RFP) are sent to partner companies previously approved by SNCF Réseau. These companies are registered and approved to work on specific segments of the railway network. The process for the Mercues project was somewhat different. “We had to create a new selection process. Only 3 companies qualified to work at heights were registered in the SNCF Réseau Supplier Qualification Programme”, explained Gaëlle Morin, an expert buyer in the Procurement Division (Atlantic Region). “Given the distinctive geological characteristics of this project, and because we needed a partner specialised in working on ropes, we first very precisely defined our needs with the General Contractor for technical studies. We then decided to challenge the existing group of approved suppliers to provide a customised solution”. On the basis of technical and financial selection criteria, ROC Aménagement was awarded the contract.