Bolaños Rail Tunnel – Railway Technology

This article delves into the engineering and construction of the Bolaños rail tunnel, a critical component of the Madrid-Galicia high-speed rail line in Spain. The project showcases advanced tunnel boring machine (TBM) technology, innovative ground stabilization techniques, and the successful execution of a complex undertaking in challenging geological conditions. The aims of this analysis are to examine the technical challenges overcome during construction, highlight the employed methodologies and technologies, and assess the overall project’s efficiency and effectiveness in delivering a crucial segment of this major high-speed rail infrastructure. Understanding the Bolaños project provides valuable insights for future large-scale rail tunnel projects, emphasizing the importance of pre-construction planning, appropriate technology selection, and risk mitigation strategies in complex geotechnical environments. The subsequent sections will detail the project’s scope, construction methodology, and challenges, culminating in an assessment of its success and lessons learned.

Project Overview and Scope

The Bolaños rail tunnel, with its twin 9.9m-diameter tubes, constitutes a significant part of the 7.9km Vilariño-Camobecerros section of the Madrid-Galicia high-speed rail line. This section also incorporates a viaduct spanning the Val de Parada River. The tunnel’s design includes two twin viaducts (each 41m long), two flyovers, six longitudinal drainage trenches, and a 5m² free section beneath the platform. The two tunnel bores are interconnected by 18 communication galleries. The project’s challenging geological profile includes shales, quartzite, phyllite, and sandstones, demanding sophisticated engineering solutions. The project involved the construction of approximately 35km of power lines and an on-site water treatment plant, in addition to other auxiliary infrastructure.

Construction Methodology and Technology

Construction commenced in August 2012, employing a Herrenknecht S-511 single-shield TBM (Tunnel Boring Machine). This machine, equipped with a rotating cutter-head and disc cutters (each applying up to 32t of force), efficiently excavated the twin tubes. Water jets were utilized to cool the cutting tools and minimize dust generation. An organo-mineral grout injection system addressed unstable ground conditions, facilitating smooth TBM operation. The tunnel lining consists of precast segments (370mm thick, 1.6m long), joined using a double-joint system for enhanced structural integrity. A double-component backfill method, using bentonite, cement, water, and silicate additives, filled the annular gap between the tunnel lining and the excavated rock. This method created a high-quality, gelatinous consistency, ensuring rapid bonding and a strong, stable backfill. Rock bolting techniques were employed to secure the surrounding rock mass, preventing distortion and collapse.

Geotechnical Considerations and Risk Management

The project faced significant geotechnical challenges due to the varying geological formations and high overburden (approximately 200m, with a water load of 140m). To mitigate these risks, an R&D+i (Research and Development + Innovation) solution involved implementing a ground stabilization system in geologically unstable zones. PRO GEO Geotechnical Consultants played a crucial role in providing geotechnical expertise, designing cross-passage tunnels, and developing landfill geotechnical designs, crucial in ensuring the safety and stability of the tunnel construction. The careful planning and execution of these geotechnical solutions were integral to the project’s success.

Project Performance and Timeline

The first tunnel bore was completed in 11.5 months, achieving an average daily excavation rate of 19.40 linear meters. The second bore was completed even faster, in just 9.5 months, with an average daily excavation rate of 24.32 linear meters. This improved efficiency demonstrates the effectiveness of the chosen construction methods and the experience gained during the construction of the first tunnel. The overall project’s rapid execution showcases a high level of project management and execution.

Conclusions and Lessons Learned

The Bolaños rail tunnel project represents a significant achievement in railway engineering and construction. The successful completion of this project, despite the complex geological conditions and high overburden, highlights the effectiveness of using advanced TBMs coupled with innovative geotechnical solutions. The rapid construction times, exceeding initial expectations, underscore the importance of detailed planning, meticulous execution, and a collaborative approach among the project stakeholders. The utilization of a double-component backfill method significantly enhanced the stability and durability of the tunnel lining. The project’s efficient use of resources and innovative solutions offers valuable lessons for future large-scale rail infrastructure developments. The successful integration of R&D+i initiatives, in particular the ground stabilization system, demonstrated the critical role of innovation in overcoming technical challenges and ensuring project success. The application of advanced TBM technology, combined with effective geotechnical engineering and rigorous project management, resulted in a safe, efficient, and cost-effective construction process, delivering a crucial link in the high-speed Madrid-Galicia rail line. The project demonstrates a model of best practices for future tunnel projects, emphasizing the synergistic impact of technological advancements, geotechnical expertise, and diligent project oversight.

Company Information:

• FCC Construcción: A major Spanish construction company.
• Contratas y Ventas: A significant Spanish construction company.
• Construcciones y Obras Llorente: A Spanish construction company.
• Herrenknecht: A German manufacturer of tunnel boring machines.
• PRO GEO Geotechnical Consultants: A geotechnical engineering consultancy.