Mechanized Excavation for Hydropower Projects Werner Burger Herrenknecht AG, Schwanau, Germany ABSTRACT With the ever increasing demand for energy worldwide, hydroelectric power as a clean source has gained focus in recent years. Construction of new power plants as well as capacity increase and renovation of existing schemes are under consideration. For both options the use of underground space is an essential element of design creating a strong need for innovative mechanized excavation solutions. Long distance horizontal, inclined or declined tunnels as well as shaft and complex cavern excavations are often part of these schemes. Contrary to typical traffic tunnel projects the majority of hydropower projects are located in remote or environmentally sensitive areas thus creating additional challenges with regards to access and logistics. This paper highlights recent projects using technologies available today and provides an outlook into future developments. RÉSUMÉ Avec l´accroissement permanent de demande en énergie dans le monde, l´hydroélectricité, en tant que source d´énergie propre a vécu un regain d´intérêt ces dernières années. La construction de nouvelles centrales ainsi que l´augmentation de leur capacité et la rénovation des procédés existants sont en considération. Dans les deux cas, l´utilisation de l´espace sous-terrain est un critère d´étude essentiel générant un besoin fort pour des solutions innovatrices d´excavation mécanisée. Les grandes distances horizontales, les tunnels inclinés à pente montante ou descendante, ainsi que l´ excavation de puits et de cavernes complexes font souvent partie de ces procédés. Au contraire des tunnels types pour le circulation, la majorité des projets de centrales hydro-électriques est située dans des zones reculées ou très sensibles d´un point de vue environnemental, et de fait crée un défi supplémentaire en ce qui concerne les accès et les moyens logistiques. Le document met en évidence des projets récents utilisant les technologies disponibles à ce jour et fournit une perspective pour les développements futurs. 1 EXCAVATION METHODES AND TECHNOLOGIES The majority of underground hydropower schemes can incorporate nearly all of today’s available mechanized underground rock excavation technologies. The need for soft ground excavation technologies is less common. Depending on the ground conditions some are required for long distance transfer or access tunnels.

Due to the fact that hydropower is typically based on gravity or difference of height, inclined tunnel alignments or vertical shafts are an essential element of the systems. 1.1 Tunnels For horizontal or slightly inclined or declined alignments up to a 5% grade standard or close to standard gripper or shielded TBM systems can be used.

Between 5% and 15% grade handling and TBM supply system have to be adapted. This includes material handling systems and cranes on the TBM and especially the mucking and materials supply systems in the tunnel. Also special requirements for dewatering have to be considered for declines.

The additional needs for inclinations between 15% and 25% are determined based on the individual project and TBM design. Not only handling and tunnel supply systems are affected but also basic TBM excavation and primary mucking functions have to be reconsidered as well as all walkways, access and work stations. Also secondary activities such as maintenance works or cutter

handling have to be redesigned and adapted. A whole set of purely technical TBM machinery aspects such as hydraulics, lube systems, bearing loads etc. have to be looked at and designed for in detail (Brockway 1983).

Whereas according to EN16191 the need for an independent gripping system for inclinations between 15% and 25% shall be determined by the tunnel project risk assessment, such systems are a mandatory requirement for inclinations of 25% and more as well as increased factors of safety for the backup tow connections. 1.2 Shafts The typical depth of shafts for hydropower schemes can be several hundred meters. Conventional drill and blast shaft sinking method or raise boring methods are used, depending on the project conditions or construction sequence. Also a combination of a pilot shaft construction by raise boring followed by a drill and blast shaft extension is used.

The present development for larger and more powerful raise boring machines as well as recent developments in mechanized blind shaft excavation may as well open additional options in the near future.

In many cases shafts are not excavated from a surface access but connect different underground levels with the associated limitations on installation space and supply logistics.

2 CASE HISTORIES 2.1 Limmern Inclined Tunnels The “AXPO” power station “Linth-Limmern” (KLL) build in 1957 - 1968 is located in the Swiss alps at “Glarus” south of “Zürich”. The existing plant (approx. 300 MW) is

currently modified and extended to a pump storage plant with an additional capacity of approx. 1000 MW additional peak power.

The new underground power houses are positioned close to the existing dam reservoir at approx. 1850 m above sea level and will connect to the natural, but now extended lake “Muttsee” at approx. 2450 m above sea level. Part of the connection are two new, 1 km long inclined pressure shafts of 5.2 m excavated diameter at a gradient of 84 % (Fig. 1).

All logistics for organization, assembly and transports are done out of the main valley base camp at 800 m sea level.

Figure 1. Arial view (inclined tunnel in red)

There is no access road connecting the valley base

camp at 800m sea level to the site areas at 1850 m and 2450 m elevation. Access to the main work sites as power houses, caverns and pressure shafts is provided only by a large aerial cableway of 40 ton transport capacity and a 3000 m long access tunnel. All transport units had to be designed to be split into single modules that could easily be put into transport containers or attached to the universal load spreader of the cableway (Fig. 2).

The contractor ARGE KWL, a joint venture of Marti AG and Toneatti AG, worked in great detail with the machine manufacturer Herrenknecht AG on machine design to address the challenges of machine transportation and site assembly. As the consequence of such joint efforts and the close collaboration TBM was ready to go on site after only 7 weeks of site assembly.

The TBM was assembled in horizontal position and moved to the launch position onto a ramp of approx. 25% inclination (Fig.3). The final shaft inclination (40° / 84 %) was then met by a TBM-bored vertical curve of r = 150 m. This launch procedure allowed the contractor to reduce the conventional drill and blast operations for the launch chamber and starter tunnel to a minimum and keep it within gradients that could be handled by standard equipment.

Figure 2. Transport of TBM components to the installation site

Figure 3. Assembly and starting configuration of the TBM

The TBM and gantry design was focused on safe and

ergonomic access ways and working positions for the miners and a straight internal material supply logistics. These high priority design targets for horizontal TBMs become even more important for such a steep inclined operation. In addition the full scope of safety elements had to be included to keep the 650 to total installation at all times in a safe and stable condition during the complete operational cycle.

The excavated muck is directed into a covered steel channel positioned in the invert. Adding water into the muck flow channel assures a smooth and continuous flow of the muck. The muck channel is extended in individual sections within the gantry area as the TBM makes moves forward.

All materials supply or transport of personnel up to the TBM - installation is done by a rail guided cable car driven by a fixed winch located at the bottom of the shaft. The rail extension takes place at same working position as the invert muck channel and the other services extension.

The winch concept allows emergency rescue of personnel from the heading even in case of total power outage.

Figure 4. TBM monorail system

The transport and supply of rock support materials,

consumables or spare parts along the gantry to the front end is realized by an overhead monorail transport system with redundant drive and brake installations (Fig. 4).

To keep the entire TBM and gantry installation in a safe and defined position during all operational cases as well as in exceptional or emergency conditions included are failsafe and redundant gripping systems. To meet this requirement, a set of total three gripper devices (including TBM) hold the installation safely in its position (Fig. 5). This set up offers full redundancy means at least 2 of the 3 devices are powerfully locked to the rock even while the installation is advancing or regripping. In case of emergency and/or power loss the double mechanical self-gripping device behind the TBM prevents it from sliding back. An adjustable “gripping diameter” allows compensation of non-regular geometrical conditions along the drive due to weak rock or overbreaks.

Figure 5. Additional gripping systems behind the TBM

The first drive of 1000 m was successfully completed

in autumn 2011 with a best production of 140 m/week. Along the drive the TBM had to pass through fault zones with weak and heavily fractured rock, also natural caverns in-filled with mud and water were hit and successfully

passed. These events drastically slowed down TBM progress due to the installation of heavy rock support. However in such cases the big effort from both, TBM manufacturer and contractor, done during design of the machines for well thought through workplaces and material handling systems paid off to successfully overcome the difficult conditions.

Figure 6. Breakthrough after first drive

After breakthrough (Fig. 6) the cutter head of the TBM

was removed and the TBM and gantry walked back through the tunnel down to the launch chamber where it was relocated for the second parallel drive. By the time of this paper in summer 2012 the works in the second inclined tunnel are well underway, including the passage of the fault zone again. Completion of the second drive is scheduled for the third quarter of 2012. 2.2 Nant de Drance Power Station The new Nant de Drance pump storage plant close to Martigny in Switzerland connects the two already existing dams Vieux Emosson (2225 m above sea level) and the Emosson dam (1930 m above sea level). The peak capacity of the new pump storage unit will be 900MW and the majority of the installations and structures will be located underground. The contactor is ARGE GMI, a joint venture of Swiss civil engineering companies Marti and Implenia. The complex underground tunnel, shaft and cavern structures will be constructed using the drill and blast method for caverns and short tunnels, raise boring and drill jumbos for shaft extension for the shafts using Herrenknecht RBR 600 Raise Bore Rig and a Herrenknecht drill jumbo for the conventional shaft extension. A major element of the total system is a 5600 m long rock tunnel with an excavation diameter of 9,45 m to provide access to the underground facilities from the valley level at Le Châtelard during construction and later operation.

Figure 7. Overview Nant de Drance underground structures (access tunnel in red)

The 9,45m access tunnel is 5600m long at an inclination of 12% (Fig. 7). The tunnel is excavated with a Herrenknecht Gripper TBM that was originally used for the excavation of the Lötschberg Tunnel (Fig. 8). The core machine was refurbished with the assistance of original manufacturer Herrenknecht AG. Whereas the basic machine functions and operational principles could remain unchanged major adaptations had to be done in other areas to address the 12% incline operation.

The work places in the L1 rock support area just behind the cutterhead shield had to be modified in combination with the adaptation of the rock support methods required by the specific project conditions. The majority of the material handling systems along the gantry had to be redesigned and adapted together with a redesign for the rubber tire based material supply through the tunnel.

Figure 8. TBM installation at the tunnel portal

For the Nant de Drance access tunnel with an

inclination of 12% it was possible to use a basic TBM system originally designed for horizontal drives and achieving an optimal and safe configuration for the inclined alignment by applying only moderate modifications.

The tunnel excavation was completed on August 22nd

2012, the system was able to overcome difficult ground conditions combined with heavy water inflow and proved to be the right concept for such an application. 2.3 Raise Boring For The Pump Storage Plant

Vianden

The pump storage plant (PSP) Vianden (Luxembourg) was put into operation in 1963/1964 with 9 sets of machines and in the mid-1970s it was extended to include a 10th machine unit. The PSP Vianden has a capacity of 1,100 MW with its 10 machine units. The operator, Société Électrique de l'Our (SEO), extends the capacity by 200 MW through the installation of an 11th machine unit, which uses the existing upper and lower basins, but has its own system of waterways and inlet and outlet paths (Fig. 9).

Figure 9. (1) upper reservoir, (2) inlet and outlet tower, (3) vertical pressure shaft, (4) machine cavern, (5) inlet and outlet tower lower reservoir

The construction of the facilities to accommodate the 11th machine was under the responsibility of the consortium PSW Vianden Los 1, consisting of the companies ZÜBLIN, STRABAG and JÄGER. The contract included, among others, the construction of an inlet and outlet tower in the upper reservoir, followed by a vertical pressure shaft.

The contract for the construction of the pressure shaft was awarded to Edilmac dei F.lli Maccabelli S.r.l. by the consortium Vianden. The pressure shaft extends to over 300 meters from the upper reservoir down to the powerhouse level.

According to the tender documents, the raise boring method was selected for the construction of the vertical pressure shaft. The final internal diameter of the pressure shaft is 4,50 meter, the excavation diameter is 5,46 meter.

After contract award in April 2010 Herrenknecht AG started manufacturing its newly developed raise boring rig RBR 550VF. After full workshop preassembly and extensive shop testing (Fig. 10) the machine was shipped to site and started operation on November 16

th, 2010. On

January 18th

, 2011 the drilling of the 282 meter deep shaft was completed (Fig. 11) (Künstle et al. 2011).

Figure 10. Shop testing of the RBR 550VF

The Herrenknecht RBR 550VF is one of the largest rigs of its kind ever used. It is distinguished by a compact, modular design and has a powerful and highly efficient center-free drive. Herrenknecht's proven variable frequency controlled drive concept allows for variable speed and torque control. The rig is designed for a shaft depth of up to 1,000 meters. Project key data:

Raise Boring Rig 550 VF

Pump storage plant Vianden, Luxembourg

Client: Société Électrique de l'Our S.A.

Customer / machine operator: Edilmac dei F.lli Maccabelli S.r.l. (Italy)

Shaft depth: 282 m

Shaft diameter: 5,460 mm

Pilot hole: 15" / 381mm

Drilling start: 11/16/2010

Breakthrough: 01/18/2011

Best reaming rate: 18.2 m at 01/12/2011

Rock strength up to 130 MPa

Figure 11. Breakthrough on January 18

th, 2011

3 FUTURE DEVELOPMENTS Based on the situation that many of the “green” sources of energy such as wind or solar power need in combination efficient as well as environmentally friendly ways to store and provide energy on short demand pump storage schemes offer an already well-established and proven solution. This can include entire new plants or even more upgrades of already existing facilities.

In both cases the use of underground space is an essential element of the planning. Besides the rapid technical development for underground excavation equipment for traffic and utility infrastructure the recent activities for mechanization in mine development (Lovejoy 2012) could present a valuable contribution for hydropower applications.

Herrenknecht as well as a number of other manufacturers of underground excavation equipment are engaged in the development of more flexible rock excavation technologies and equipment compared to today’s circular cross-section rock TBMs. These technologies will finally be able to provide a more mechanized alternative to the drill and blast methods applied today for some of the complex underground structures required for hydropower schemes.

Further development of the proven raise boring technology towards more powerful and stronger machines as the Herrenknecht RBR 900 can open up new fields for the raise boring method for shaft excavation as well as parallel developments for mechanized blind shaft sinking machinery. A higher level of mechanization in shaft construction finally could offer an alternative to steep inclined shafts. Also the new generation of Herrenknecht BBM boxhole boring machines as presented by Künstle et al. (2012) may offer new plant design options. 4. CONCLUSION The availability and use of mechanized excavation technologies and systems for underground structures has opened additional options also for hydropower projects.

Developments and new solutions from other applications such as underground mine development will find their way into the civil construction world as well as in reverse. The ability to place facilities underground opens the options for new power plants or extensions of existing ones with a minimized surface impact. Brockway, J. 1983. Incline / Decline Boring With Tunnel

Boring Machines, Rapid Excavation an And Tunneling Conference Proceedings 1983: 743-760

Künstle, B. and Frey, A. 2011. Vertical Shaft Construction

at the Pump Storage Plant Vianden/Luxembourg, Tunnel, 4/2011: 56-59.

Künstle, B. and Burger, W. 2012. Safe Slot Hole

Excavation With A New Boxhole Boring Machine, SME Annual Meeting 2012, Seattle, WA, USA

Lovejoy, C. (Editor) 2012. Fast Forward, Mining

Magazine, June 2012: 68-73.