21 - 26 April 2018 Dubai International Convention

& Exhibition Centre, UAE

ITA - AITES WORLDTUNNEL CONGRESS

POSTER PAPERPROCEEDINGS

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The key role of underground infrastructures in the recent transformation of the city of Bilbao

José Manuel Baraibar Díez1, Pedro Rivas de Apráiz2, Iñigo Escobal Marcos3 1 Technical Director. Viuda de Sainz, S.A. (SPAIN). jmbaraibar@viudadesainz.com 2 Technical Director. Interbiak Bizkaiko Hegoaldeko Akzesibilitatea, S.A (SPAIN). pedro.rivas@interbiak.com3 CEO. Lurpeko Lan Bereziak, S.A. (SPAIN). i.escobal@lurpelan.com

Corresponding author: jmbaraibar@viudadesainz.com (José Manuel Baraibar Díez)

ABSTRACT

The urban transformation of Bilbao in the last thirty years has been exemplary, shifting from an industrial city to a friendly city based on culture and services. This internationally recognised success (Bilbao has recently been named European City of the Year at the 2018 Urbanism Awards) can be explained by a coordinated and multidisciplinary collaboration from very diverse spheres that have developed investments and projects in many areas: museums including the Guggenheim; strategic equipment, such as the Bilbao Port extension and the new Athletic Club stadium; large-scale transportation facilities, such as the Metropolitan Southern Bypass or the latest Bilbao Underground extensions; and urban renewal projects, such as the restoration of degraded areas in the riverbanks of the Nervion estuary, the opening-up of the Deusto channel and the new urban development at Zorrotzaurre.

This transformation, which is taking place today, has recently reached one of its latest stages with the inauguration of the “New Accesses to Bilbao through San Mames”. The construction of these new road accesses, in which underground infrastructures play a key role, has permitted the demolition of the viaducts in Sabino Arana Avenue, enabling the return to the city of more than 30,000 m2. This way this area, formerly subjected to severe road traffic pressure, has been reconverted for pedestrian use, in compliance with the latest urban planning guidelines.

The construction works of the “New Accesses to Bilbao through San Mames” outline a new access to the Biscayne capital, more friendly and integrated in the urban layout. It has incorporated different elements from the very early design stage in order to hide substantially the infrastructure, including 4 cut and cover tunnels, 4 viaducts, one conventional tunnel, a pedestrian emergency walkway and the burying of a 0.4-kilometre-long section of the A8 highway. The works have been completed in a densely populated area without causing any major disorder to the highway capacity, with an average daily traffic of more than 100,000 vehicles. The budget totals 156 M€, with a contract period of 5 years.

Apart from these abovementioned road accesses to Bilbao, tunnels will also play a central role in the following transport system strategic projects in the area, currently at design stage: Metro Bilbao Line 3 extension between Casco Viejo and the airport; the Access towards the Abando Station of the high-speed railway connection of the Basque Country and the new underground freight rail bypass between Bilbao Port and the French border.

Key Words: Urbanism, Restructuring, Planning, Landscape, Tunnel, City

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1. INTRODUCTION

The urban transformation of Bilbao in the last thirty years has been internationally recognised as a success [1]. One of its latest acknowledgements was the nomination as European City of the Year at the 2018 Urbanism Awards [2]. This transformation has recently reached one of its latest stages with the inauguration of the project of the “New Accesses to Bilbao through San Mames”. This project, which also transforms the A8 motorway into an urban road, has been fully funded by the regional government Diputación Foral de Bizkaia. The construction of these new road accesses has permitted the demolition of the viaducts in Sabino Arana Avenue, as shown in Figure 1, which, apart from causing a lot of noise pollution at the neighbourhood, were a clear obstacle for developing the city in compliance with the latest urban planning guidelines.

Figure 1. Demolition of the viaducts in Sabino Arana Avenue

Depending on the typology of each element forming the piles and the deck, and the closeness to streets, buildings or any kind of infrastructure, two demolition techniques were used: mechanical demolition employing hydraulic hammers and shears, or disassembly of the structure by means of abrasive and diamond wires, together with the use of a 1,350-ton crawler crane.

After four decades of intense traffic and years of protests of the neighbours from the district of Basurto [3], where the viaducts were built, a new access to the Biscayne capital, more friendly and merged in the urban layout has been opened to traffic, enabling a strategy of sustainable landscape integration.

It has incorporated different elements from the very early design stage in order to hide substantially the infrastructure, including 4 cut and cover tunnels, 4 viaducts, one conventional tunnel, a pedestrian emergency walkway and the burying of a 0.4-kilometre-long section of the A8 highway, as shown in Figure 2. The works have been completed in a densely populated area without causing any major disorder to the highway capacity, with an average daily traffic of more than 100,000 vehicles.

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Figure 2. Location of works

Among the underground works, the 344-metre-long Altamira tunnel is highlighted, whose construction has entailed tremendous technical complexity, as in very few metres several supporting techniques have been required due to some great geotechnical difficulties such as shallow overburden, the presence of buildings over the tunnel, the adverse structure of the rock mass, a high grade of tectonization and severe levels of soil alteration in some sections.

A complete description of the construction of this tunnel, as well as the procedures used to face all its geotechnical difficulties, are included in the following section. 2. THE ALTAMIRA TUNNEL

2.1 General description

The Altamira tunnel is 344 metres long. It has two artificial tunnels both at the beginning and the end of its profile totalizing 447 metres. It has a curved path plan with a super elevation up to 7%, hosting a 4.00 metres width main carriage way, two 2.50 metres and 1.00 metre road shoulders and two 0.75 metres width paths. The total width of the platform is therefore 9.00 metres. Its transverse geometric section is a polycentric oval, with a main vault radius of 5.13 metres and a height over the platform of 7.14 metres, as shown in Figure 3.

Figure 3. Transverse geometric section (left) and final appearance (right)

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As an additional security measure during its operation, a pedestrian gallery was also foreseen. With a length of 102 metres and a mean slope of 12%, it connects the middle point of the tunnel with the surface, offering a safe route for pedestrians in case of emergency. Its transverse geometric section is a semi-circular vault with straight side walls, adopting a width of excavation of 4.10 metres for execution reasons [4].The construction project defined a system of advance employing the top-heading-and-bench method, using an excavator hydraulic hammer for the excavation as blasting was strictly prohibited. Two possible supporting sections have been specified for the short and long term stabilisation of the tunnel, according to different geological characteristics of the ground that can be found in each position of the profile, consisting on shotcrete, steel ribs and radial rock bolts, as shown in Table 1.In addition, the installation of several special ground treatments was foreseen in order to eventually deal with possible situations that may appear, but due to their random nature it was not possible to precisely determine their position or maximum amount (treatments for front stabilization, treatments for vault stabilization, treatments against water infiltration, treatments for karstic terrains, injections and treatments for limiting subsidence).

Table 1. Characteristics of the basic support types

2.2 Geology and geotechnics of the body of ground in which excavation occurs

The new connection passes through several Cretaceous sedimentary materials, typically found in the surroundings of Bilbao. There are basically two formations: • Ereza formation: calcareous sandstone with alternation of calcareous siltstone.• Arraiz formation: set of grey limestone with rudistes, corals and detrital limestone.

The contact between the Ereza and Arraiz formations takes place along a fault line with a strong dip, as shown in Figure 4. This fault greatly affected the surrounding materials, bringing rock masses with very high grades of alteration (degree IV-V) and a strong tectonization, or even materials with degree VI of alteration, behaving as soils. Due to the curved path plan of the tunnel, the fault affected most of the tunnel profile.

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Figure 4. Geologic profile and soil cover in Altamira tunnel The main geotechnical constraints that appeared during the tunnel construction are listed below:• High levels of alteration and intense tectonization of the rock mass.• Overburden less than one diameter in very altered materials or totally

decomposed.• Intense karstification of the materials excavated in the Arraiz formation.• Mixed excavation faces with very altered materials in the upper zone of the

section and fresh rock mass at the bottom of the section.• Presence of buildings on the surface throughout all the tunnel ground layout.

Most of them are more than 50 years old.

Those factors have constrained the tunnel execution, particularly in the following aspects: controlling the excavation perimeter by means of heavy micropile umbrellas, in some cases with armed injections (selective and repetitive injection through the micropile); controlling the excavation face by sealing it with shotcrete and even reinforcing it with self-drilling rock bolts; employing heavy-duty machinery being able to break competent rock masses; controlling the deformations of the tunnel itself, reflected on surface, by means of micropile underpinning while excavating the top heading and reinforcing the support with 9-metres long self-drilling rock bolts and active anchors and geotechnical controlling and monitoring of ground deformations on surface.

Despite all these geotechnical difficulties, a fast and efficient response was undertaken in accordance with all the Sponsor requirements, especially concerning rates of progress (see Figure 5), performance and geotechnical and qualitative control of the excavation [4].

Figure 5. Average rates of progress in Altamira tunnel

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2.3 The construction stage

The tunnel excavation is divided into three different phases: • Top heading, with a height of 6.00 metres and advance steps of 1-1.50 metres

depending on the support type. In the areas of less geotechnical quality, stabilization of top heading excavation with “elephant foot” systems.

• Bench excavation, with a height of 3.40 metres, divided into two stages, IIa and IIb, with a minimum 3-metre offset and keeping a 3V:1H slope between them.

• Tunnel invert. In the areas of less geotechnical quality a definitive tunnel invert was built. The steel ribs supports corresponding to the bench excavation were extended, embedding them into a concrete cube excavated under the tunnel invert side joint, in order to fully ensure the stability of the structure during its construction. Subsequently, central sections of the tunnel invert were excavated and poured in stages.

The beginning of the tunnel invert took place simultaneously with bench excavation. Figure 6 shows the concrete pouring of the tunnel invert lateral joints and, at the back, the face of the bench excavation.

Figure 6. Tunnel invert lateral joints and bench excavation The tunnel execution starts from the exit portal, until the top heading is completed. On the other hand, the bench excavation and tunnel invert where carried out from both fronts, in order to control and limit the settlement caused by these tunnelling operations. Given the geotechnical conditions already described and with the purpose of minimizing possible impacts on surface, it was necessary to arrange systematic micropile umbrellas in most of the tunnel profile. A total of 29 sets of micropile umbrellas were drilled, some of them with valves permitting repetitive injections through their steel section. Thanks to carefully coordination of these different tasks, the rate of progress was satisfactory.

The starting and ending sections of the Altamira tunnel, as shown in Figure 7, were especially demonstrative of its great geotechnical difficulty. The limited overburden, less than one diameter, the high rate of terrain alteration near the crown and the existence of intense karstification of the limestone generated large movements on surface, around 20 centimetres, with the risk of causing a chimney that was finally avoided.

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Figure 7. Altamira tunnel entrance portal during construction

In the central section of the tunnel, despite the fact that the rock mass were of better geotechnical quality, the auscultation tracking system detected a direct relation between the movements of the crown of the tunnel and the subsidence on surface which could affect the buildings over it. This obliged to reinforce the top heading support.

Figure 8 shows the vertical movements measured in the crown of the tunnel and on surface. In the first section moderate movements were found, following a normal behaviour within the typical limits for this kind of terrain [5]. In the central section, movements were higher than expected, both of them being very similar. In the final section, with limited overburden and karstic terrain, the settlement measures were extraordinarily high. Despite this fact, the movements of the crown did not show great magnitude, due to the high rigidity of the supporting system.

Figure 8. Settlements along the tunnel profile [6]

2.3.1 Execution of karstified section with shallow overburden At the beginning, the tunnel execution team faced a 78-metre-long section in a limestone rock mass intensely karstified in the upper zone of the section but extraordinarily competent at the ground level. In addition, there was a shallow overburden in that section (only 0.65 times the diameter) with very high grade of alteration (degree IV-V). This section is characterized by the existence of mixed excavation faces, as shown in Figure 9. The crown, in a ratio of 66% to 20% is composed of weak silty clay. The rest of the face is composed of compact limestones (degree I-II). Because of the high level of rock alteration, behaving as

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a soil, in this section it was difficult to obtain the RMR parameters. Besides, there was a risk of instability in the excavation face. In this section, surface settlements were monitored by means of subsidence markers, installed at regular intervals of 5.00 metres. Approximately each 25 metres additional markers were installed, forming transverse subsidence sections. Because of the poor geotechnical quality of the rock mass and the shallow overburden, from the beginning of the excavation high settlement measures were found, between 60 mm and 230 mm, with a volume loss between 2.3% and 7.8% [6].

Figure 9. Mixed excavation faces. Silty clay at the top and compact limestone at the bottom

Although the magnitude of this deformation was relatively high, it was decided to implement conventional solutions intended to ensure the stability of the excavation face, in spite of implementing intense ground treatments. The face stability was ensured with the installation of 15-metre-long self-drilling rock bolts in a mesh size of 1.00 m. x 1.00 m. and systematic sealing of it with shotcrete. In order to ensure the stability of the crown, subsequent sets of 12-metre-long self-drilling steel micropile umbrellas were installed, with a radial spacing of 0.35 metres. Each micropile umbrella was made up of 40 micropiles. The associated supporting section was founded on ‘elephant foot’ systems [6].

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2.3.2 Execution of the fault line section

The tectonization of the contact between Arraiz and Ereza formations caused that a 30-metre-long section of the tunnel were intensely fractured and weathered. RMR values ranged from 18 to 24, with overburdens about 1.7 times the diameter of the excavation. The settlements measured on surface were much smaller than those registered in the karstified section. Nevertheless, vertical displacements of 45 mm. were found, with a volume loss around 1.5%.

In this case, the proximity of the buildings recommended the intensification of the monitoring of the stability in the crown of the tunnel. In this sense it was decided to double the micropile umbrellas, increasing the overlapping between them and installing regulating valves for eventually permitting repetitive injections through their steel section.

2.3.3 Supporting reinforcement in the central section

In the central section of the tunnel, calcareous sandstone from the Ereza formation (degree III-IV), with compact sandstone metric blocks, was excavated. While executing the tunnel, another subparallel fault was found. In this case, the degree of alteration was less severe, but due to the curved path plan of the tunnel, this fault affected a 60-metre-long tunnel section.

The overburden in this area is higher than 30 metres, reaching a maximum of 42 meters. This section corresponds to the zone of most building density over the tunnel. Leaving aside a five-story building recently built and a church, the other surrounding buildings are not robust and more than 50 years old. Given the geotechnical quality of the rock mass and the presence of the buildings, the excavation was completed under the shelter of a successive 15-metre-long micropile umbrellas, with an overlapping of 3.00 metres. The spacing between micropiles varied between 0.35 m. and 0.50 m. In all the section, the top heading support was founded on a rock bedding, so the use of ‘elephant foot’ systems was not necessary. The excavation in this section went smoothly. Nevertheless, the monitoring systems installed in the tunnel showed vertical movements measured in the crown of the tunnel around 45 mm. In spite of that fact, tunnel convergences did not show great deformations, as the maximum value only reached 20 mm.

Parallel to this process, important settlement was detected on surface. The level of deformation on surface was the same order of magnitude as the observed on the tunnel crown. The monitoring points on the buildings over the tunnel also registered those movements. Given this behaviour, a numeric analysis of the interaction between the tunnel and the settlement measurements was conducted. This analysis showed the great influence that the fractured structure has over the settlement on surface, so it was decided to reinforce the supporting system before the bench excavation, during a 70-metre-long section under the buildings. A systematic installation of 9-metre-long self-drilling 40/20 rock bolts were used, in a mesh size of 1.00 m. x 1.00 m. All these rock bolts were drilled through the micropile umbrellas installed during the top heading excavation, as shown in Figure 10.

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Figure 10. Reinforcing rock bolts through micropile umbrellas

In addition, the top heading section was reinforced by means of a set of micropiles drilled next to the joints of the supporting system, assembled in a continuous reinforced concrete beam connected to the steel ribs. In Figure 11 the micropile heads and the beam reinforcement before cast can be observed.

Figure 11. Micropile heads and beam reinforcement for underpinning the section

Once the top heading section is reinforced, the bench excavation can take place. With this treatment, the settlement movements on surface were stabilised. The reinforcing was completed with the installation during the bench excavation of φ32 9-metre-long corrugated steel bars anchors, with an active force of 20 tons. The perforation of these anchors is shown in Figure 12. The perfect regularity of the top heading support and the reinforced concrete beam can also be observed. All these works had to be combined with the bench excavation, its supporting and the casting of the definitive tunnel invert, which meant great logistic complexity for coordinating different tasks, installations and work teams.

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Figure 12. Drilling of 20-ton anchors at side walls

2.4 Monitoring during and after construction

During the tunnel construction a global geotechnical monitoring of the excavation and supporting works were put into practice: monitoring of lithologies, structural network, rock mass classification, selection of supporting sections, reinforcements and special ground treatments. Besides, an exhaustive geometric controlling was carried out, both in the tunnel and in the upper surface. A total of 52 subsidence markers, 14 transverse subsidence sections 15 deep hole extensometers, 11 inclinometers, 10 open piezometers and 55 monitoring points on buildings were installed.

This monitoring system was complemented by the use of InSAR (Interferometric synthetic aperture radar) techniques. With this technology, it is possible to measure millimetre-scale changes in deformation of surfaces by comparing radar images, as shown in Figure 13.

As surface displacement information is obtained each time the satellite passes over the study area, this technique allows the collection of a historical record before the beginning of the works [7]. Besides, it can be used for confirming the extension of movements obtained by classic monitoring and also for collecting long term measurements, even when the works are completed.

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Figure 13. Use of radar images with InSAR techniques for monitoring subsidence 3. SPECIAL INSTALLATIONS AND OPERATIONAL SECURITY

The urban and critical character of the designed tunnels and underground infrastructures has made it mandatory the investment in some tunnel installations that provide security levels unique in the world.

These tunnels have an architecture of communications and control which guarantees a total physical and logical redundancy, on which several systems are based, such as the public address digital system or the fire extinguishing system using water mist, as shown in Figure 14. The objective of this system is confining the source of the fire, avoiding its spreading to other vehicles inside the tunnel and facilitating the work of the emergency teams. The effectiveness of this system is based on the high pressure the water is blasted so thousands of little drops with a lot of specific surface can induce a heat exchange with the fire, rapidly lowering the temperature in its vicinity. In this case, the system is designed for fire powers up to 30 MW, which is equivalent to the ignition of a heavy vehicle. In the buried section corresponding to the A8 highway, the system was sectioned in 21 sectors measuring 24 metres each. Once the fire is located by the detection system, the programmed algorithm activates the water mist system. The water is sprayed at 70 bar pressure in a set of three sections, the one in which the fire is located, the previous one and the following one. To obtain this pressure a set of 36 water pumps is used, fed from a 300 m3 storage tank which is located under the Control Building. The system was finally tested with a clean hot smoke test [8], in compliance with the legislation at regional level concerning technical instructions about safety and operation of tunnels (Decreto Foral de la Diputación de Bizkaia 91/2012).

Technical requirements for maintenance and operation of these tunnels have imposed the integration in this regard of three different levels of Public Administration, as well as the updating of the current procedure of maintenance and operation.

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Figure 14. Water mist extinguishing system during fire drill

4. CONCLUSION

The strategy of designing the new infrastructure prioritizing underground solutions, despite the existence of extreme geotechnical difficulties, has favoured the permeability between neighbourhoods, removing barriers and putting them back in Bilbao’s urban context. All the stakeholders have worked together in order to obtain an homogeneous and continuous landscape treatment, with the main objective of sewing the territory, increasing the connectivity among different population poles, not only through road networks, but also through pedestrian and visual systems, as shown in Figure 15 and Figure 16.

Figure 15. Before the works [9]

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Figure 16. After the works [9]

The urban transformation enabled by this operation has meant a successful full-scale trial that will guide the next strategic projects in Bilbao, currently at design stage: Metro Bilbao Line 3 extension between Casco Viejo and the airport; the Access towards the Abando Station of the high-speed railway connection of the Basque Country and the new underground freight rail bypass between Bilbao Port and the French border. In all these projects, to be undertaken over the next decade, tunnels will also play a preponderant role.

6. CITATIONS AND REFERENCES

[1] Otaola, P. (2017, June). La transformación de Bilbao. Revista de Obras Públicas, 3588, 10-19

[2] EP (2017, November 8). The Urbanism Awards 2018 reconocen a Bilbao como la Mejor Ciudad Europea. Deia, Retrieved from http://www.deia.com

[3] Rivas, P. (2013, December). Proyecto de urbanización de los barrios de Santa Ana, Bentazarra y Lezeaga en Bilbao. Transformación de los accesos a Bilbao por San Mamés. Equipamiento y Servicios Municipales,4-2013, 50-53

[4] Rivas, P. (2016, November). Túnel de Acceso a Bilbao por San Mamés. Paper presented at the “Jornada Técnica Túneles en el País Vasco”, Bilbao, Spain.

[5] Lunardi, P. (2008). Design and construction of tunnels. Analysis of controlled deformation in rocks and soils. Berlin: Springer-Verlag

[6] Rivas, P. (2011, November). Túnel en mina de los nuevos accesos a Bilbao por San Mamés. Ingeopres, 209, 22-41

[7] Raventós, J. (2017, September). Las aportaciones de la tecnología satelital en el control del movimiento del terreno en obras subterráneas. Revista de Obras Públicas, 3590, 86-97

[8] Quintana, J. (2005, February). Ensayo de Humo Caliente Limpio. El ensayo de incendio para la verificación de la seguridad de los túneles. Revista de Obras Públicas, 3452, 23-32

[9] Rivas, P. (2015, March). Proyecto de Accesos a San Mamés. Paper presented at the “VI Simposio de túneles de carretera”, Zaragoza, Spain.

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