Building the AVE high-speed line to Galicia

The arrival of high-speed rail in this region in northwestern Spain had its first historical milestone at the end of 2011, with the entry into operation of the 150-kilometre stretch between Ourense, Santiago and A Coruña. After the service commissioning of the line between Olmedo and Zamora in 2015, all that remained to complete the connection between Galicia and the centre of the Iberian Peninsula was the construction of three sections totalling approximately 230 kilometres: Zamora-Pedralba de la Pradería, Pedralba de la Pradería-Taboadela and Taboadela-Ourense.

The difficult route between Pedralba and Ourense

Built for the most part on two separate tracks, the 101-kilometre section between Pedralba and Ourense crosses the different mountain ranges that form the Central Ourensan Massif, a route that the AVE will be able to cover thanks to the construction of 32 viaducts and 31 tunnels, many of them bi-tube, or with one tube for each track. More than 60% of the route was either underground or over viaducts and required special works: in total, the section has almost 11 kilometres of viaducts, the longest of which is the Requejo viaduct (1.72 km), and 126 kilometres of tunnel (62.45 km on the right-hand track plus 55.87 km on the left-hand track and 7.84 km of double track), the longest being the O Corno tunnel (8.6 km).

The works that are covered in this report belong to this complex route between Pedralba and Ourense, which Adif Alta Velocidad constructed to provide the highest levels of railway technology, with standard-gauge double track (1,435 mm) throughout the route, and designed for speed limits of up to 350 km/h, with 2×25 kV 50 Hz alternating-current electrification, ERTMS Level 2 and Asfa traffic control systems, and a GSM-R mobile communications system.

Five of the most notable works

THIS SECTION FEATURES A NUMBER OF INFRASTRUCTURES THAT STAND OUT FOR THEIR COMPLEXITY, EITHER IN TERMS OF THE CONSTRUCTION METHODS USED, THEIR DIMENSIONS OR THEIR ENVIRONMENTAL CHARACTERISTICS.

1. The jacked caissons of the Requejo tunnel

Two caissons 80 and 100 metres long jacked under the conventional railway tracks complete the Requejo tunnels.

Several kilometres from Pedralba, the AVE works are progressing through the mountains of the Sanabria region with several notable actions, including the construction of the caissons jacked into the Requejo tunnel, structures built in situ at the western opening of the Galicia side and jacked under the railway tracks, allowing Adif to maintain rail service on the Zamora-A Coruña national gauge line, which intersects with the new high-speed line at this point.

This intersection of the high-speed line with the conventional track was resolved by constructing two reinforced concrete caissons measuring 8.5 metres high and 8.5 metres wide on the inside, with lengths of 79.5 metres for the caisson for the right-hand track and 100.5 metres for the caisson on the left.

In their final position, the caissons form the cut and cover exits of the Requejo tunnels. The execution procedure included the shoring of the conventional track and the construction of engineering structures on a sliding platform close to their final location prior to subsequent relocation by means of a hydraulic jacking across the track to their final positions.

The shoring consisted of a metal structure that allowed the caisson to be moved without affecting the track, ensuring its stability. Due to the shoring work, trains had to run at a speed limit of 30 km/h during the works, as opposed to the normal speed of the route in this area of over 100 km/h. The speed restriction was necessary as a safety measure because the level and alignment of the track in this situation can generate movements that are not compatible with higher speeds. Given the jacking lengths, the caissons were divided longitudinally into two sections that were jacked successively, each with a corresponding battery of 15 hydraulic cylinders with a force of 300 tons per cylinder. At the same time that the successive 50- centimetre thrusts were carried out, the earth was removed by mechanical means, ensuring that the stability of the tracks was not compromised, until the structures reached their final positions.

2. The Padornelo tunnels

A high-speed tunnel built just 20 metres from the longest tunnel on the entire Spanish conventional line.

Ineco provided construction management for Adif Alta Velocidad on this 6,406-metre tunnel with a 52-square metre clear cross-section, which runs parallel to the tunnel of the Zamora-A Coruña national gauge line, and is located between the municipalities of Requejo and Lubián (Zamora), below the Padornelo mountain pass.

The Padornelo tunnel is part of the Padornelo-Lubián section, and consists of the supporting layer of the single UIC-gauge track on the right, measuring 7.6 kilometres long. The left-hand high-speed track will be executed at a later stage as part of a new project that will adapt the old 5.97-kilometre Padornelo tunnel on the Zamora-A Coruña line for mixed traffic on the left-hand high-speed track and freight on the conventional line.

Construction was carried out with conventional excavation, applying supports consisting of shotcrete, bolts and trusses. Excavation was carried out by blasting the areas with the hardest terrain and using mechanical means (backhoes, hydraulic demolition hammers, etc.) in the softer ground and terrain with lower geotechnical quality.

Execution was determined by the proximity of the tunnel on the Zamora-A Coruña conventional line. During the works, trains continued to run, so certain protocols were established to monitor for deformations in both tunnels, and reinforcements consisting of mesh and shotcrete were necessary in some sections of the old tunnel. 15 connection galleries were also built between the tunnels and an evacuation platform along the existing tunnel, to create the evacuation route necessary for the commissioning of the high-speed line. To carry out these works, the entire track was renovated with UIC 60 E1 rail, PR-01 concrete sleepers and type 1 ballast.

The works were accompanied by a series of specific environmental and landscape integration actions due to the proximity of two protected areas or sites of community importance (SCI):  the banks of the Tera and Tuela rivers and their tributaries. In this regard, different measures were agreed with the regional authorities to prevent the impact on the protected flora and fauna. One example was the treatment of water coming from the tunnel, which was subjected to different processes before being discharged into the waterway, in order to ensure that its physical and chemical parameters complied with legislation. In addition, from the beginning of the works, the waters of the rivers belonging to the aforementioned SCIs had their physical and chemical characteristics monitored and a follow-up assessment was carried on the area’s populations of Pyrenean desman (Galemys pyrenaicus), brown trout (Salmo trutta), freshwater pearl mussel (Margaritifera margaritifera) and aquatic macroinvertebrates.

3. The Espiño tunnels

Two large high-speed tunnels constructed using eight simultaneous excavation fronts.

The Espiño tunnels are unique in that they were excavated simultaneously from four fronts: in addition to the two end fronts, there were also two intermediate excavation fronts. To do this, an intermediate gallery was built that ended in a large cavern, from which four additional fronts could be started for excavation in the direction of Madrid and Ourense. The large number of fronts reduced the excavation times for the tunnel.

The bi-tube tunnel runs through the municipalities of A Gudiña and Vilariño de Conso in the province of Ourense. With approximately 8 kilometres on each track and connections between tunnels every 400 metres (20 emergency galleries), it is one of the largest tunnels in the section.

Both tunnels were excavated using the New Austrian tunnelling method, with top-heading and bench, from the eastern tunnel opening, from the western tunnel opening and from the intermediate galleries of attack towards both tunnel openings. The right-hand track has an exact length of 7,924 metres including 30 and 40-metre artificial tunnels in each of the openings for improved visual integration into the hillsides. The remainder (7,854 m) was mine excavated, that is, under natural terrain. The left-hand track has an excavated length of 7,838 m underground, to which 30 and 36 metres respectively were added to each of the openings as artificial or cut-and-cover tunnels, giving the left-hand Espiño tunnel a total length of 7,904 m. Cut-and-cover tunnel structures were also included for improved visual integration into the hillsides.

The presence of metal sulphides and carbonaceous matter in some slatey rock required the use of technosols to treat some of the excavated material in the waste sites. This technique made it possible to control the oxidation of these sulphides, which are capable of generating acidic water, thus creating a reducing environment and also decreasing oxidation kinetics. Technosols also act as a buffer, adsorbing any heavy metals that may be present in the runoff water in the form of leachate, and are eutrophising, which promotes eventual environmental integration.

4. The Bolaños tunnels

The only two tunnels on the Madrid-Galicia line executed BY TBM.

The Bolaños tunnels are the only ones on the entire line executed by a TBM. Bi-tube by design, they form part of the Vilariño-Campobecerros section, and consist of a 6.96-kilometre right-hand track and 7.91-kilometre left-hand track. The route runs through the municipalities of Vilariño de Conso, A Gudiña and Castrelo do Val, in the province of Ourense.

Both were executed using a TBM with the exception of the first 55.91 metres of the western opening and the first 15 metres of the eastern opening on the right-hand track and the first 76.13 metres of the western opening on the left-hand track, which were executed by conventional methods to move beyond a fault.

The dimensioning of the tunnel cross-section was limited by compliance with the UIC’s health and comfort criteria to ensure high-quality high-speed passenger transport. Following these criteria, the final open cross-section of the tunnels was 52 square metres. The excavation cross-section of the TBM was 9.80 metres in diameter, with 37-centimetre-thick segments of precast reinforced concrete lining with an internal diameter of 8.76 m. The concrete in the segments contains polypropylene fibres as a fire protection measure. The gap between the TBM excavation and segment lining was filled with two-component mortar, a mixture of conventional mortar with hydrated bentonite and silicate.

The waterproofing of the precast lining was achieved by fabricating the segments with a low-permeability concrete; installing a double waterproofing seal at the segment joints; and injecting the two-component mortar into the space that remained between the excavated surface and the ring of segments. The injected voussoir is the primary waterproofing, since, in practice, it is the first barrier encountered by groundwater on its way towards the interior of the tunnel, with secondary waterproofing being that provided by the seals.

The two tubes are connected by 18 galleries, one of which is used specifically for installations. The cross-section of the galleries has an open width of 4.70 m and a lining of 25 cm of plain concrete, with the addition of polypropylene fibres as a fire protection measure.

During the tunnel excavation, a large amount of water was generated by the construction processes, and it was necessary to treat it in a large treatment plant in order to comply with the parameters required by the competent bodies. The suspended solids present in the water were removed using a separation process, with the help of coagulants and flocculants. The pH was adjusted through the use of CO₂ (for basic process water) or caustic soda (for acidic process water).

5. The Teixeiras viaduct

A 100-metre-high central arch over the Arroyo Teixeiras.

The Teixeiras viaduct, for which Ineco was in charge of works and environmental management, is without a doubt the most spectacular structure on the entire Madrid-Galicia HSL.

The deck of the Teixeiras viaduct was executed using self-launching formwork, and has a length of 508 metres distributed in eight spans (56 m + 4×66 m+56 m). Its uniqueness lies in the construction procedure chosen to negotiate the Arroyo Teixeiras with maximum respect for the environment. The foundations of the central piers (which are more than 90 metres high) are shared by two half arches, which were erected and angled inward to meet at a fixed point under the deck, providing a separation between piers of 132 metres, equivalent to two spans, which, in addition to minimising the impact on the environment, gives the structure greater transparency and beauty. The Arroyo Teixeiras, a tributary of the Támega River, has protected riverbank vegetation and, on the surrounding slopes, a forest consisting of native species with large chestnut and oak trees.

The construction of a large structure like the Teixeiras viaduct requires large auxiliary areas to house the facilities that support the construction: from large cranes to site huts; from storage yards to vehicle car parks. For this site, ways of minimising the impact of this area were studied thoroughly. Detailed analysis was carried out on the opening of roads with steep slopes to reduce their grade, areas of auxiliary facilities on bends or between foundations, work platforms adjacent to jobs with strict occupation limits, etc. All of these installations were located on both hillsides that, in addition to being very steep, had soils made up of highly fragmented materials with high potential for displacement of soil that would reach the waterway below in the case of rain.

In order to prevent or mitigate the effects that this soil displacement could have on the water quality of the Arroyo Teixeiras, an ingenious anti-displacement system was implemented, basically consisting of a network of pipes (concrete ditches, pipes, sandpits, settling pools, intermediate reservoirs, etc.) deployed along the access roads to the foundations, which converge at pumping reservoirs located very close to the waterway. To reduce earthwork and facilitate subsequent integration, metal containers were used as pumping reservoirs so that they could be easily removed after the completion of the works.

In the event of heavy rain, sediment-laden runoff was redirected –by means of powerful pumps– to a treatment system located at the height of abutment 2 of the structure, expanding the response capacity in the case of a heavy rains. In this treatment system, coagulants and flocculants were also be used to accelerate separation if necessary.

By the Ineco construction managers Arturo Pastor, Iago Rodríguez-Lorasque and Noelia Cobo, technical engineer Jesús Pena, and environmental worksite managers Iñaki G. Seoane, Enrique M. Agüera and Luis Álvarez-Pardiñas with the collaboration of Raúl Correas, deputy director of Construction V at Adif Alta Velocidad.

Load tests: ready for action

Prior being put into operation, Ineco carried out the load testing of 25 structures and inspection of 70 bridges for Adif on the Olmedo-Pedralba section of the Madrid-Galicia high-speed line.

By Pablo Sánchez Gareta, civil engineer

During the months of March and April 2019, a team of seven specialists from Ineco carried out an important task for Adif Alta Velocidad prior to the commissioning of the new Olmedo-Pedralba de la Pradería section: load testing and inspection of the bridges and viaducts over which the complex route of the Madrid-Galicia HSL runs, all with satisfactory results.

Load tests were carried out on a total of 25 structures, in addition to the main inspections of 70 bridges (14 viaducts, 2 pergolas and 54 underpasses). In the case of the bridges, and since they were newly constructed, the data collected during the inspections provides a baseline situation (zero state) for subsequent analysis and monitoring of the evolution of the structure.

During the tests, which are compulsory for all new bridges with spans 10 metres or longer, actions of actual use of the works are reproduced under controlled conditions.

In other words, checks are carried out to ensure that the bridge is safe, well built and able to withstand the loads of the trains that will travel over it over time. For these verifications, static and dynamic tests are carried out with loaded trains running at different speeds. Data collected by sensors installed on the structure is analysed and the actual and expected responses are compared. The results are sent to the Railway Safety Agency, which is responsible for authorising the entry into operation of the section.

One of the most representative structures that was tested was the Ricobayo viaduct over the reservoir of the same name, measuring 368 metres long and consisting of four spans of between 50 and 155 metres long. For the test, 2 locomotives and 20 hopper wagons loaded with ballast weighing a total of 1,863 tons were used. On the spectacular viaduct over the Tera River, measuring 645 metres long and consisting of nine spans of between 60 and 75 metres, two trains with eight hopper wagons each, weighing a total of 1,536 tons, travelled at speeds of between 10 and 80 km/h.