Tunnelling has been used for several purposes for thousands of years. In the coming years the world's population will increase in the urban areas. So, the urban centres will have to adapt, in order to guarantee that their future population will have the necessary and sustainable growth. Due to the constraints for surface construction, also connected to environmental issues, this population growth will imply a greater use of the underground. With this optimal growth, the population of the cities will have better mobility, quality of life, and economic and social sustainability. In a first phase, this report will present a historic approach to tunnelling and its foreseeable future. Afterwards, we will present some considerations on the three factors which tunnelling impacts: mobility, quality of life and social sustainability. As a case study, we will analyse the 2nd phase of the construction of the Marão Tunnel (TDM) -the longest ever built in the Iberian Peninsula-and describe the options made regarding each of those factors. In this case study, the options implemented made it possible to successfully execute the works. For the industry, this work is important because it describes a successful management of the aspects under analysis.

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The investment in tunneling shows an worldwide expansion trend. Reduction of risks, as part of the financial strategy of the stakeholders, has been the focus of several research studies. This paper aims to describe the construction risk prevention, in terms of occupational accidents and diseases, of the 2nd phase of the Marão Tunnel (Portugal) -the longest roadway tunnel in the Iberian Peninsula excavated with Sequential Method -with the particularity of the works being interrupted, leaving the tunnel only with primary lining for three years. The methodology is based in: 1) identification, by literature review, of most typical preventive measures and assessement of their applicability in the case study; 2) description of new preventive approaches. The paper will start with a history of work accidents, followed by the case study and, finally, it will delve into the preventive measures applied, as well as the new approaches, such as over-runs, falling blocks and risks associated with the suspension of works. Measures identified in literature were implemented and their validity was assessed. New approaches provided an safer and quickest way to work. This study is relevant to future tunnelling sites, since it is a good example of risk management using new approaches.Key words: New Austrian Tunneling Method (NATM), Sequential Excavation Method (SEM), risks, safety, tunneling. ResumenLa inversión en construcción de túneles muestra una tendencia de expansión mundial. La reducción de los riesgos laborales, como parte de la estrategia financiera de las empresas, ha protagonizado varios estudios científicos. Este artículo describe la seguridad laboral implementada durante la construcción de la 2ª fase del Túnel de Marão (Portugal), el túnel carretero más largo de la Península Ibérica ejecutado mediante el Método de Excavación Secuencial, con la particularidad de que su ejecución fue interrumpida durante tres años manteniendo el túnel sólo el revestimiento primario. La metodología se basa en: 1) identificación, mediante revisión bibliográfica, de las medidas preventivas más habituales y evaluación de su aplicabilidad al caso de estudio; 2) descripción de nuevos enfoques preventivos. El artículo comienza analizando un histórico de accidentes, seguido por el estudio de caso y finaliza profundizando en las medidas implementadas y en los nuevos enfoques, como sobrecargas, caída de bloques y riesgos asociados a la suspensión de las obras. Se implementaron medidas identificadas en la bibliografía y se evaluó su validez. Los nuevos enfoques proporcionaron una manera más segura y rápida de trabajar. Este estudio es relevante para el futuro de la construcción de túneles por la aplicación de nuevos enfoques.

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