TBM Carboniferous Rock Pajares

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SINGLE SHIELD TBM PERFORMANCE IN CARBONIFEROUS ROCK

THE CASE STUDY OF PAJARES-SOTIELLO

PERFORMANCE DES TUNNELIERS A BOUCLIER SIMPLE EN ROCHES

CARBONIFERES

ETUDE DU CAS DE PAJARES-SOTIELLO

Thomas CAMUS, NFM Technologies, France, [email protected]

Gilbert FONTANILLE, NFM Technologies, France, [email protected]

Jean-Luc CHAMPEAUX, NFM Technologies, France, [email protected]

Juan MARGARETO, FCC, Spain, [email protected]

Fernando FAJARDO, Acciona, Spain, [email protected]

1. THE PROJECT

Spain has launched a huge high-speed railway programme over the last 20 years. This network will soon be – when all the track sections under con-struction will be operational – Europe’s largest high-speed train network with more than 3,500 km. The programme required building a number of civil en-gineering structures among which the Pajares tun-nels discussed hereafter. This project is located along the Leon-Asturias line in the Northwest of Spain between the cities of León and Oviedo. It is a new by-pass that allows passing under the Cantabrian mountain range separating Asturias from Leon-Castile, with peaks over 2,500 m (see figure 1).

Figure 1 – Geographical location of the Pajares project

The project includes: • The main tunnel (Pajares base tunnel), 25 km in length;

• An additional section (Sotiello-Pajares tunnel) of 6.1 km;

• An access tunnel for safety and ventilation.

Both the Pajares and Sotiello tunnels are built as twin tubes of 8.5 m internal diameter, with connect-ing galleries every 400 m.

The project was split in 5 contracts that the end user ADIF (the Administrator of Railway Infrastruc-tures) awarded to 4 consortiums as follows: Contract 1: Pajares base tunnel, South side, East

tube (9.9 km) and West tube (15 km): UTE FCC - ACCIONA

Contract 2: Access gallery and a 4.2 km section of the Pajares base tunnel (South side, East tube): UTE Dragados - Obras Subterráneas

Contract 3: 10.3 km of the Pajares base tunnel, North side, East tube: UTE Ferrovial Agroman – Sacyr - Cavosa

Contract 4: 9.5 km section of the Pajares base tunnel, North side, West tube: UTE Copcisa - Constructora Hispánica -Brues and Fernández Construcciones - Azvi

Contract 5: Sotiello-Pajares tunnel, both tubes (5.9 km each): UTE FCC - ACCIONA

Four TBMs were used to bore the two base tunnel tubes from both ends, while a fifth machine built the access and ventilation gallery (see figure 2).

2. THE GEOLOGY

The overall tunnel length (30.3 km) is bored in a complex geology with the following 3 main forma-tions: • Shales and argillaceous shales: high plastic de-formations are anticipated when tunnelling in these sections, even more so because of their thickness. UCS ≤ 60 MPa

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• Sandstone and quartzite: rock in these sections is micro-fractured and therefore exhibits a low resis-tance and allows for water ingress. UCS ≤ 80 MPa

• Carbonatite: these are dolomitic calcareous rocks from which water ingress and karts can be ex-pected. UCS ≤ 60 MPa

• The remaining other sections are conglomerates and volcanic rock.

Figure 2 – Layout of the Pajares tunnels

All the rock formations follow an arrangement of alternating vertical layers of approximately 400 m in thick-ness oriented in the tunnel direction (see figure 3).

Figure 3 – Simplified geological profile of the Pajares tunnel

3. TBM SELECTION

Initially the project was planned to be built using conventional tunnelling methods that would be spe-cifically adapted to the local context and chal-lenges. In order to reduce the construction time, this solu-tion was finally rejected and a TBM approach was initiated. Spain had gained significant experience with TBMs used in similar geological contexts. Worth mention-ing are (also for the high speed railway) the Abdala-jis tunnel (twin tubes, 7 km long on the Cordoba-Malaga line) and the Perthus tunnel (twin tubes, 8.4 km long on the cross-border Figueres-Perpignan line). These projects had shown how crucial it was that the TBM be adapted to the local geological conditions and how the machines should implement mitigation approaches for the identified risks, even if their occurrence was considered as very small.

The TBM specifications were set up in a collabora-tive effort from the end-user ADIF and the Spanish contractors. This task took more than a year after which the TBM manufacturers were also invited in order to fine-tune the specifications. The Pajares project encompasses many different geological problems:

• High risks of rapidly converging ground under a high overburden. Calculations made on the rock behaviour predicted a convergence of up to 100 mm over more than 25% of the TBM drive;

• A most varying rock strength, high in the sand-stone sections and low in the carboniferous shales;

• Significant water ingress estimated to reach 500 litres per second under a 800 m overburden;

• Risks of hitting methane pockets in the carbonif-erous shale sections;

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• A high abrasiveness reaching up to 5.75 (Cerchar Index) resulting in risks of intense wear and re-lated frequent maintenance operations. Single shield machines were chosen for multiple reasons: • The shield should be as short as possible in order to avoid being trapped in the quickly squeezing rock: single shield machines are shorter than double shields.

• Single shields can be sealed, therefore precluding water inflows inside the machine and in the tun-nel; water can be pumped out until all groundwa-ter is drained. This situation was made even worse for the South tunnel (contract 1) as both these tubes were bored with a downward slope, increasing the potential risk of flooding the tunnel.

• The productivity edge of double shields over sin-gle shield TBMs is effective in competent ground only. In incompetent ground the gripper thrust mode of double shields is not operative and single shields attain similar levels of performance. In the present case, the sections in incompetent rock were quite long, cancelling the theoretical advan-tage of double shields.

Figure 4 – NFM machine on site NFM supplied two machines for this project as part of contracts 1 and 3 (East tubes). The machines were designed and built in compliance with the above requirements and had the following distinc-tive characteristics:

• The cutter head featured translational motion by 600 mm longitudinally and an adjustable vertical offset of 100 mm. This allows extending the di-ameter by 200 mm thereby preventing jamming the shield in the highly squeezing ground condi-tions. Wedging the gage cutters and installing two additional disc cutters was the only manual opera-tion needed to change the excavation diameter from 9.9 to 10.1 m.

• The TBMs were equipped with an exceptional level of thrust of 232 tons per m

2, which exceeded

the standards for this type of machine. Together with a shield dimensioned for ground pressures up to 4 bar this allowed sustaining high advance rated in highly converging ground.

• A powerful dewatering system was implemented including a 200 m

3 buffer tank on the backup and

four 450 m3/h pumps meeting the predicted large

flow rates.

• Because the Abdalajis project had suffered from a methane explosion in May 2004, ADIF set particu-larly high standards in terms of gas hazards. The machines were equipped with an over-dimensioned ventilation system offering an air flow of 52 m

3/s with a 2-inlet extraction from the

excavation chamber (2 x 25 m3/s), and a swirling

air diffuser in the shield ensuring a gas mix below the ignition point. The extracted air was blown be-hind the backup. Several gas detectors installed throughout the machine monitored the methane concentration continuously. Part of the electrical distribution hardware was contained in an ATEX cabinet completing the safety approach and equipment.

• It was foreseen that ground treatment would be required so a drill was made ready for use at all times. The drill was attached to a specific annular support positioned forward of the ring erector, al-lowing for storage of the folded back drill at the crown. This arrangement provided a capability of drilling umbrella arches at a 10° angle with 17 and 5 injection points in the upper and lower parts re-spectively.

Type of tunnelling Single Shield TBM

Excavation diameter 9.9 m

Extended diameter up to 10.1 m

Overall length (including back-up)

290 m with california switch

Number of 17” disc cutters

69 (+ 2)

Total power 8 000 kVA

Drive unit power 5 000 kW

Nominal thrust 130 000 kN

Unlocking thrust 180 000 kN

Nominal torque 25 000 kN.m

Unlocking torque 30 000 kN.m

Variable speed 0 to 5 rpm

Weight of shield 1 150 tonnes

Total weight 1 850 tonnes

Table 1 – Main characteristics of the NFM TBMs

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Figure 5 – Contract 3 jobsite and tunnel portals. The NFM machine is on the left.

4. TUNNELLING WORKS

As shown in figure 5, installing tunnelling job sites in a mountainous area is bound to be problematic. Special care was given reduce to the environmental impact as much as possible, resulting in the follow-ing approach for contract 3: • Space was only available for a one-day storage of segments at the job site. The precast concrete segment plant was located in the plain 10 km away from the tunnel portal, with a temporary storage 1.5 km away.

• Access to the jobsite was made through a narrow mountain road on which traffic was kept as low as possible. The extraction of the excavated materi-als was done with a belt conveyor extending from the tunnel entrance to a controlled dump site 2 km away.

• Assembling the TBMs was a challenge in itself because of the tight space available at the portal. Careful logistics planning was developed includ-ing temporary storage of equipment and parts or-ganised in the plain.

• All waste water was treated in a large capacity plant built as several small units deployed on the mountain slope. Figure 6 shows the contract 1 jobsite to which the access was much easier, resulting in fewer and more usual constraints.

Figure 6 – Contract 1 jobsite. The NFM machine is

on the right. The key events of the tunnel construction were in accordance with the planned geological accidents. The TBM team had to handle high inflows of groundwater, crown collapses due to the poor co-hesion of rock, steering problems due to the low tunnel face strength requiring very low thrust, unlocking the TBM trapped in squeezing rock dur-ing maintenance stops, and intense wear of disc cutters in the sandstone sections. However the machines progressed well and faster than planned. Breakthroughs occurred respectively 9 months (contract 1) and 7 months ahead of time (contract 3). Average and record advance rates are listed in Table 1.

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Contract Start date Breakthrough Total Average Best boring performance

(meters per)

Days Metres m/days Day Week Month

1 NFM 20/09/2005 21/05/2007 608 9856 16.2 51 238.5 860

3 NFM 08/04/2006 30/08/2008 875 10236 11.7 48 234 800

5 NFM 09/10/2008 24/09/2009 350 5862 16.7 46.5 276 1142

Table 1 – NFM machines performance summary

4.1 Contract 1

As shown in figure 7 the machine availability was high, with 50% of the time spent in production ac-tivities (excavation and ring erection). Stoppages were caused by cutter head maintenance (4% of time), geological problems (5.7% of time i.e. 30 days), and only 30 minutes because of a haz-ardous gas presence.

26%

24%20%

7%

7%

16%

Excavation time

Ring erection time

Stops for TBM or backup

maintenance

Stops due to muck conveyor,

service trains and cabling/ducting

Stops due to ground conditions

Misc. stops

Contract 1 NFM

Figure 7 – Production data for contract 1 NFM TBM The geological accidents were as follows: • Water inflow during several hours at a flow rate of 500 l/s (as predicted)

• Trapping of TBM after a maintenance stop: the shield remained jammed even when using the maximum thrust, so additional hydraulic jacks were installed in the rear shield. Thanks to this supplementary thrust the team succeeded in re-leasing the TBM within a few hours.

• Highly converging ground in the fault areas: a special organisation was set up before crossing such areas. This included checking and preparing the TBM in order to run without needing any main-tenance, and reinforcing the logistics team so as to avoid any disruption in the deliveries. At the end of its drive, the TBM was dismantled in a cavern built from the facing tunnel (contract 2). It was then refurbished and slightly modified, and then moved to the Sotiello portal (contract 5).

4.2 Contract 3

The machine performance was also high along this drive, although it suffered from more geological accidents than for Contract 1.

Tunnelling started in a highly weathered shale area, where a small collapse was observed (see fig-ure 8), which considerably slowed down the TBM progress: 30 weeks were needed to bore through the first 150 metres.

Figure 8 – Collapse at the start of Contract 3 Beyond this point the machine performance was similar to that of the other drives, with an average of 15.2 metres per day. Figure 9 shows the overall production data, confirming the increase of time lost for poor ground conditions.

19%

15%

26%

7%

19%

15%

Excavation time

Ring erection time


maintenance




Misc. stops

Contract 3 NFM

Figure 9 – Overall production data for contract 3 NFM TBM

The machine was dismantled inside the tunnel by cutting off the shield, leaving the outer shell in the ground while other parts of the TBM were salvaged for reconditioning and future use.

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4.3 Contract 5

This drive was bored using the TBM from Con-tract 1. Very good performance was achieved thanks to a simpler geological context and a lower overburden, reaching a record of 1142 metres per month.

27%

23%17%

14%

1%17%

Excavation time

Ring erection time


maintenance




Misc. stops

Contract 5 NFM

Figure 10 – Production data for contract 5 NFM

TBM

The compared advances of all machines used on the project are shown in figure 11.

Figure 11 – Compared performance of the five TBMs used on the Pajares project

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5. LESSONS LEARNT – CONCLUSIONS

The Pajares tunnel project demonstrates that hard rock TBMs can bore tunnels in challenging geologi-cal contexts, pass through areas indicated as risky, and complete the drive in minimum time, below the predicted planning.

The average daily advance rate of the single shield machines was in the order of 16 m including all stops for maintenance and because of geological accidents. In similar geological conditions double shields performance is 22 to 23 m per day approx as can be observed in Pajares (Contract 2, in the tunnel section) or in Abdalajis ([3]). In gneisses and granite, such as found in Guadarrama (SCS up to 150 MPa), performance measured over an impres-sive total of 56 km (both tubes) is 16.5 m/day approx. This average figure includes the progress made while operating in single shield mode. In sec-tions where the double shield mode could be used continuously, the advance was stable at 22 m/day.

Single and double shields are a most reliable solu-tion for tunnelling in difficult conditions, offering a much higher protection to the personnel than with open (gripper) machines. Thanks to the progress made over the last years, this also applies to the large diameter tunnels such as required for the railway tunnels, whether for standard or high-speed lines.

The key lesson learnt from the Pajares project is that the geology must be fully known and under-stood in terms of potential impact on the TBM op-eration. Simultaneously, the TBM needs to be per-fectly adapted to the geological constraints. The Pajares experience increases our confidence in meeting the challenges of future high-speed railway tunnels to be bored in geologies of similar complex-ity. As an example, single or double shield TBMs can be used for the Lyon-Turin project tunnels that are planned in extremely changing geologies with very high overburden.

Implementing on-board ground prediction ahead of the tunnel face would be a significant plus for such large projects, allowing the operation team to pre-pare the machine for the potential risks.

6. REFERENCES

Source of photos: ADIF and NFM Technologies

[1] Raùl Miguez Ballo (2005), The Pajares Tunnel

[2] Mario Pelaez Gonzalez, Jose Carlos Arrayo Cedron, Noelia Alfonso Fernandez (2009), Ex-perience Acquired in the Excavation of Rail-way Tunnels in Spain Using Tunnel Boring Machines, Proceedings of the World Tunnel Congress, Budapest, Hungary

[3] Remo Grandori (2006), Abdalajis East Railway Tunnel (Spain) - Double Shield Universal TBMs Cope with Extremely Poor and Squeez-ing Formations, Proceedings of the World Tunnel Congress, Seoul, Korea

[4] Xavier Delaporte, Michel Ducrot, Jean-Luc Trottin (2009), Le Tunnel du Perthus, Tunnels et Ouvrages Souterrains, n°213

[5] Lucía Díez Cadavid, David Luengo Troitiño (2009), Tratamiento de Aguas en la Variante de Pajares, Jornadas Técnicas de la Variante de Pajares

Documents

TBM Carboniferous Rock Pajares