When it comes to the "carriageway" product in the Gotthard Base Tunnel

The exceptional event in the Swiss project of the century was honoured with high-ranking representatives of Alp- Transit Gotthard (ATG), Swiss Federal Railways (SBB), the Federal Office of Transport (FOT) and the Canton of Uri in a formal ceremony with the installation of the "Golden Sleeper" opposite the contractor Bahntechnik Transtec Gotthard.

This technical article (Part 1) describes the success factors of quality control on site, with which the project team of ARGE Fahrbahn Transtec Gotthard AFTTG, sub-group of Transtec Gotthard for the track work, successfully implemented this first stage of the slab track project in the Gotthard Base Tunnel.

Initial situation

AlpTransit Gotthard, a subsidiary of the Swiss Federal Railways (SBB), is responsible for the planning and construction of the new transalpine rail link (NRLA). The NRLA is the centrepiece of the north-south axis of the European EU transport corridor from Rotterdam to Genoa. The Gotthard Base Tunnel project, with two 57-kilometre-long tunnels and the 35-kilometre-long north and south access routes, is the central construction project within the NRLA. Another main railway engineering project, the Ceneri Base Tunnel at the southern end of the axis, was awarded to Swiss construction consortia for implementation at the end of 2014. With the completion of the NRLA, Switzerland will be integrated into the European high-speed network.

Transtec Gotthard is responsible for the planning, implementation and commissioning of the entire railway technology system in the Gotthard Base Tunnel project. The consortium consists of the four shareholders Alpiq, Alcatel-Lucent/Thales RSS, Balfour Beatty Rail and Renaissance Construction. In addition to the temporary installations, such as the construction of installation sites, ventilation/cooling and construction logistics, TTG's service portfolio also includes the permanent installations of track, traction current 16.7 Hz, power supply 50 Hz and cable installations, as well as telecommunications and safety installations.

Project organisation ARGE Fahrbahn Transtec Gotthard

ARGE Fahrbahn Transtec Gotthard (AFTTG) is responsible within Bahntechnik Transtec Gotthard (TTG) for the performance of all services to be rendered under a contract for work and services for the railway track. It was founded by the two shareholders Balfour Beatty Rail and Renaissance Construction.

In its organisational structure (Fig. 1), all necessary functions/roles are listed which are required by the customer ATG for the fulfilment of the work contract. A special feature here is the Q organisation, which has an independent role within ATTG vis-à-vis construction.

The customer has not installed permanent and external quality control/construction supervision. The general contractor for railway engineering (TTG) and its trade organisations assume overall liability for the railway engineering work in the Gotthard Base Tunnel as part of the general contractor contract. The Construction line is responsible for the production of quality. The Quality Control line is responsible for monitoring quality production. In organisational terms, these lines are separated within the organisation and each reports directly to the project management.

The Q-organisation of the AFTTG is therefore the "eye" of the customer and the quality insurance for all required and expected product characteristics.

AFTTG has also implemented a certified management system according to ISO 9001:2008. Concrete production is monitored internally in accordance with factory production control as per SN EN 206-1:2000 and has been certified by the Swiss Certification Body for Construction Products S-CERT.

Quality planning

In order to ensure the high demands on the product quality of the ballastless track, a quality plan was drawn up. (Fig. 2). It is part of the project-related quality management system (PQM) in accordance with SIA 2007 - Quality in Construction, which applies in Switzerland. As an inspection basis for the "inspection on site", the work contract requirements were transferred into an inspection plan, taking into account the applicable regulations and codes of practice. In a further step, the specific requirements for each stage of the assembly process were broken down into test instructions. They are a binding basis between the building contractors and the quality inspectors. Quality assurance is thus simplified into a controllable and standardized task for the employees. Audits and inspections of suppliers and service providers, sampling of prototypes, factory inspections of individual components are just as much part of the PQM as the quality inspections in the slab track installation process. However, they are managed at a higher level and not at the assembly level.

Quality control

The slab track installation process in the Gotthard Base Tunnel is divided into 21 successive process steps. The process begins with the inspection of incoming goods and continues with the laying and welding of rails, laying of concrete single-block sleepers, track grid installation, rough and fine measurement, concrete production, concreting and the remaining work after concreting has been completed. This installation process is repeated every 20 days (rolling installation procedure) with an installation length of 2160 m of finished FF track. This 20-day rhythm was repeated approximately 53 times in the 2 tunnel tubes and resembles an industrial production process along a line construction site.

The quality control is divided into 3 phases. In phase 1, quality controls are carried out in the ongoing assembly process of the track grating up to the start of concreting. The quality inspectors monitor compliance with the tolerance specifications for each process step. The objective in this phase is to identify early detection of undesirable developments and to initiate preventive measures to ensure a fault-free and continuous assembly process at all times. Immediately before the start of concreting of the track grating, a final quality check is carried out. The "Technical Release for Concreting" is issued jointly by the Construction Foreman, the Surveyor and the Track Installation Quality Inspector. The Technical Release has the character of a formal acceptance and concreting release. This stopping point is an essential point for risk control, as once the concrete has been poured the track position can no longer be corrected, or only with a great deal of effort.

In phase 2, the concrete is produced and placed. Fresh concrete is produced directly in the tunnel at the construction site using a mobile concrete mixing plant (concrete train), monitored and transferred to the paving tip by means of a concrete shuttle. Concrete production is monitored by the concrete quality inspector and formally released to the construction foreman for placement by concrete delivery note. A mobile concrete testing laboratory is set up in the area of the concrete mixing plant for carrying out the fresh concrete tests and taking samples for the hardened concrete tests.

In phase 3, the remaining work after concreting is carried out and accepted. A survey of the actual condition of the concreted track is carried out, drill cores are taken from the hardened concrete, the air bubble content under the individual concrete block sleepers is checked and other tests are carried out. All tests are verifiably documented and linked in the requirement tracing system (RTS) with the corresponding work contract requirement. The verifications at the assembly process level are only a subset of all verification documents in the overall project. Component qualifications, factory tests, supplier inspections, audit reports, etc. are also entered into the RTS and linked to the WK requirements.

The test basis for the assembly process is the respective test instruction for each process step. Control point, test method, measuring equipment, test frequency, nominal value, tolerance value, error measure, verification document and responsibility are defined in the test instructions.

Summary

Systematic quality planning is required for the structured process of quality control on the object in complex general contractor construction projects. Standardization of complex assembly processes enables efficient and industrial manufacturing and quality assurance on line construction sites. The "factory" moves along the product. To keep maintenance costs low in the system life cycle, high initial quality is required. Maintenance costs are a significant influencing variable in the life cycle consideration for ballastless track, since the manufacturing costs are about twice as high as for ballasted track.