tunnels and mobility structures

In general, land transport infrastructures require specific unique structures, such as tunnels, viaducts, bridges, overpasses, and underpasses, to overcome geographical obstacles along their route or to allow safe intersections and connections between the different infrastructures.

Tunnels are underground constructions artificially opened to establish a communication route between two external points through a mountain, under a river, even seas and oceans, or any other obstacle.

Depending on the use for which the tunnel is built, it will have a different section. Thus, road and rail tunnels have large cross-sections, allowing continuity of the track layout without reducing the standard cross-section. In contrast, the cross-sections of tunnels for hydraulic or fluid transport works are usually much smaller.

Tunnel construction has evolved dramatically throughout history thanks to technological innovation. However, traditional construction methods are still in use and have remained virtually unchanged since the construction of the first tunnel in the 6th century BC.

It could be said that tunnelling is the underground excavation of unknown and unpredictable terrain without the system collapsing.

Tunnel construction techniques

The most commonly used techniques when excavating tunnels are the Belgian method or classic Madrid method, which is a traditional way of excavating a tunnel gallery followed by the formwork from top to bottom of the excavated section; the new Austrian method or sequential methodwhich takes advantage of the resistance of the ground to support the structure; the use of tunnel boring machines; or drilling and blasting, which is the method used if the tunnel route runs through rocks.

Over the past fifty years, Sando Infraestructuras y Proyectos has excavated tunnels using a variety of techniques and set international records in tunnel construction, such as the use of tunnel boring machines to build high-speed rail tunnels.

Tunnel construction involves a complex methodology. Before excavating the tunnel, it is essential to have a detailed knowledge of the ground on which it will be built An exhaustive prior investigation must be carried out at the geological level to know the type of materials that make up the subsoil and at the geotechnical level to see how these materials will behave when handling them and carrying out the excavation This will be necessary to know the feasibility and scope of the project.

In addition to an adequate knowledge of the terrain and its characteristics, other fundamental factors must be taken into account, such as the presence of the water table, as this will condition the choice of excavation method. When digging a tunnel, the forces of nature are being challenged. Therefore, it is also imperative to know in advance the length and dimensions of the infrastructure to be built to choose the method of execution and the necessary and appropriate safety elements.

Although some tunnelling methods have remained virtually unchanged in recent years, tunnelling companies such as Sando have introduced improvements in tunnelling machines, such as tunnel boring machines, rock drills, hydraulic hammers or drills, which have generally increased tunnelling efficiency. Thanks to technological and innovative developments, these machines have made excavation actions impossible before, adding improvements such as sensors that let you know whether you are digging inside or outside the defined section.

Bridges, viaducts, overpasses, underpasses and large structures, in general, are the unique elements that form part of transport infrastructures to overcome many obstacles along their route. As with any element specifically designed to solve a problem, these large structures are often technically complex and require advanced technologies and innovative ideas to meet and overcome the technical challenges posed by their construction.

Depending on the materials used in their construction, these structures can be reinforced concrete, prestressed concrete, metal or mixed.

Reinforced or post-tensioned concrete structures are usually built entirely on-site. In contrast, prestressed concrete, steel or composite structures are partially built in workshops or precasting plants, with the beams and other precast parts transported to the site for assembly.

Introducing prefabricated elements in the construction of large structures allows a certain degree of industrialisation in the civil works construction sector, enabling cost and time reductions.

Once the underground construction has been completed, an ongoing phase begins: infrastructure conservation. In this regard, Sando Conservación y Energía focuses its efforts on ensuring efficient maintenance that enables predictive maintenance of tunnels throughout their entire service life. We have extensive experience in inspecting and carrying out repair work on highway structures, including viaducts, underpasses, and overpasses across the various highway sectors we maintain.

In road tunnels, the regulations are stringent, where lighting installations, fire extinguishing, etc., are essential for road safety. Through the Ministry of Transportation, which is investing in bringing all tunnels into compliance with Royal Decree 635/2006 of May 26, Sando Conservación y Energía is carrying out several projects, such as those in the La Cerradura, Despeñaperros, Cantera, La Miel, and Santa Lucía tunnels. Province of Jaén.