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Limmern pumped hydro storage facility: TBM tunneling of an access gallery of 8 m diameter and with a gradient of 24%

Kirchhofer, Peter; Dipl.-Ing. ETH/SIA, Deputy Project Manager IG EB-KLL (Gruner AG, Emch + Berger AG Bern, Slongo Röthlin Partner AG), Head of Department, Gruner AG, Basel/CH Müller, Philippe; Dipl.-Ing. ETH, Overall Project Manager for Access Gallery I, Axpo AG, Baden/CH Voerckel, Manfred; Dipl.-Ing., Aker Wirth GmbH, Erkelenz/D

Limmern Pump Storage Plant – Access Tunnel with 8 m Diameter and 24 % Gradient

Peak energy from storage energy stations plays a key role for future power supply. In order to be able to cope with these changed demands for ensuring power availability in future, the Linth-Limmern AG utility is undertaking the expansion of the existing facilities by building the Linthal 2010 project in the Canton of Glarus. The Limmern cavern station between the Muttsee and the Limmernsee at 1,700 m asl forms the core of the new facility. The 4 pump turbines each generate 250 MW output. An access tunnel is being produced for transporting the big and heavy machine components and for carrying per- sonnel from Tierfehd (800 m asl) directly to the machine cavern and equipped with a cable car. The 3,764 m long inclined tunnel with 24 % gradient is to be driven for safety reasons using a gripper TBM with double fall-back secu- rity system. A cableway integrated in the back-up keeps the drive supplied.

1 Overview Linthal 2015

The demand for peak energy in the European grid, of which Switzerland is also a part, is growing steadily. The open market means that consumers can buy electricity anywhere. In keeping with this situation, the power grids must be regulated to ensure secure supplies. Furthermore, production peaks/shortfalls (from solar or wind power, for example) must be balanced out at short notice.

In general terms, consumption patterns and forms of production have changed considerably in recent years. New requirements in respect of security of supply have arisen. Peak-power storage facilities are playing a key role.

For that reason the Kraftwerke Linth Limmern AG (KLL) has inaugurated the project Linthal 2015 with a view to expanding existing facilities in the Canton of Glarus, Switzerland (Figure 1). The new construction of the Limmern pumped hydro storage plant will increase the total plant capacity from 1000 MW to1650 MW without the need to increase the size of the catchment area of 140 km2. KLL is a partner organization of the Canton of Glarus and Axpo AG. The Canton of Glarus holds 15% of the share capital and Axpo AG the remaining 85%.

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Figure 1 Overview of the Limmern pumped hydro storage facility

Work commenced on various preliminary items even before the official go-ahead for construction was given. For instance, the new construction cableways (Figure 3) and an additional gallery for accessing the project area were constructed. Final approval for the plant construction was granted in September 2009, and construction began in October 2009.

1.1 Limmern pumped hydro storage facility

The heart of the new plant is the Limmern central cavern, which is located 1,700 m above sea level and comprises an underground turbine cavern and a transformer cavern (Figure 2). The operations centre is situated between the Muttsee (new capacity level 2,474 m above sea level) and the Limmernboden Reservoir (capacity level 1,857 m above sea level). The two lakes will be connected via two headrace tunnels. In the turbine cavern, the water flows through four pump turbines, each with a capacity of 250 MW. For the purpose of storing energy, water can be pumped from Limmernboden Reservoir up to the Muttsee.

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Figure 2 Gallery system for construction and operation of the cavern system.

1.2 Muttsee extension

The Muttsee has a natural dam level at 2,446 m above sea level. It is to be dammed additionally by means of a new retaining wall which will be around 1,000 m long and 35 m high. The new capacity level at 2,774 m above sea level means that the usable capacity of the lake will increase from the present 9 million m3 to 25 million m3.

1.3 Access gallery I

The preparation of the construction site and ensuring permanent access to it during operation already presented special challenges when the existing power plants were built on the Limmernboden in the 1960s. The project area is so mountainous that it cannot be accessed by road. As was done in the 1960s, the first phase of the present site preparation is being carried out with the aid of two temporary construction

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cableways capable of carrying payloads of up to 25 tonnes (with exceptional capacities of 40 tonnes and 30 tonnes respectively).

Figure 3 Transport dumper with construction cableway 1

Access gallery I is being constructed to allow transportation of the large and heavy machine components during the construction phase as well as for transporting personnel during construction and operation directly from Tierfehd to the turbine cavern of the new operations centre. To meet the various transport requirements, the inclined gallery will contain a funicular railway with an eccentric Abt turnout carrying two reciprocating vehicles on a single track. Depending on the mode of operation, payloads of 40 tonnes (normal transports), 120 tonnes (heavy transports) and 215 tonnes (special transport for transformers) are possible. The various modes of operation for the funicular railway are summarized in Table 1. The difference in altitude of around 1,000 m between Tierfehd and the turbine cavern and the distance of nearly 4 km are negotiated with a gradient of about 24%.

A double-girder overhead travelling crane at the lower end of the railway (underground) can move loads of up to 40 tonnes onto the vehicle. Depending on the size of the parts and specific requirements, the loads are transported on a horizontal platform or on an inclined platform with the same inclination as the gallery. At both ends of the railway it is possible to drive road vehicles onto the rail vehicles and then transport them if required. For loading special loads, i.e. loads of over 40 tonnes, it is possible to detach the rail vehicle and move it from the end of the railway into the open. It is then possible to use special lifting gear to move payloads without any height restrictions.

Access gallery I is also used to transmit the power from the operations centre. The required 380 kV cables run along the shoulders. Approximately every 550 m a connector niche is needed for this.

1.4 Geological and geotechnical situation

Through the upheaval of crystalline rocks in the Limmern area during the formation of the Alps the sedimentary rocks lying on the basement buckled, folded and were pushed northward in stratified packages one above the other. The overlay surfaces of the individual strati rise from the south out of the Quinten formation northwards into the Cretaceous and tertiary layers. Most of the galleries and caverns of

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the Linthal 2015 project as well as the whole of access gallery I are located in the Quinten limestone formation (Figure 4).

The Quinten limestone formation is largely metamorphic and therefore prone to cleavage. In addition there is the sedimentary stratification, which in most cases exhibits a minor angular unconformity to the cleavage. The rock is cleft by one main fracture system and three secondary systems. Furthermore, access gallery I traverses the Mörtalbruch. This consists of tectonically sheared rock formations which are separated some decimeters from each other by sandy to clayey kakirite zones. It is not expected to encounter kakiritic formations across the entire fault zone, but rather tectonically stressed limestone with reduced stability.

Figure 4 Geological longitudinal profile of access gallery I

1.5 Hydrology

Quinten limestone is prone to karst processes. Water conducting fissures are expanded to karst conduits by chemical erosion, and karst water circulation may develop.

The entire mountain region is drained by a karst. It is assumed that the mountain water table is only a little higher than the receiving water table of the valley area around Tierfehd and the Limmerntobel. On this basis, it may be expected that most of the gallery sections will be above the mountain water table. The permeability of the rock is contingent on the opened fissures (Figure 5).

It is expected that only dripping water and runnels from fine crevices will be encountered over long stretches of the gallery. In comparison with other mountain regions, the karst is considered to be less problematical, because the catchment area is glacier-free and the main drainage flows in a northerly direction towards Tierfehd via a known cave system. Nevertheless, the possibility of karst water ingress above 100 l/s during the tunneling cannot be ruled out.

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Figure 5 Karst

2 Planning of access gallery I with funicular railway

For transport between Tierfehd and the turbine cavern, a funicular railway with a constant gradient proved to be the most economical solution. The turbine cavern represents the mountain terminus and therefore the end of access gallery I. Various different possibilities were investigated for the valley terminus. Both a solution with the valley terminus in a cavern and a short access way to it as well as constructing an open-air valley terminus were considered. In view of the unfavorable terrain leading to the funicular gradient and the resulting need to level the ground, it was decided to construct the valley terminus in a cavern with a length of 35 m and an access area of approx. 260 m2 to 360 m2. The access way is 220 m long.

This means that under normal operating conditions the procedure for transporting goods from Tierfehd to the turbine cavern is as follows: the loads are transported by road vehicle through the entrance to the valley terminus cavern. There they are loaded onto the funicular railway with the aid of a double-girder overhead travelling crane. The railway transports them to the mountain terminus in the turbine cavern, where they are offloaded using a hall crane.

At the same time as the best location for the valley terminus was determined, different construction techniques for dealing with the various gallery sections were investigated. The prevailing geological conditions allow for the use of both explosives and a TBM.

Following an exhaustive risk assessment the decision was taken in favor of an open hard rock TBM for the 3,764 m long, 24% steep gallery section. Safety requirements were the decisive factor in the selection of the tunneling method. The risk of tunneling into a karst and causing ingress of water during the work means that work on the floor in the vicinity of the tunneling face is restricted. Using the tunnel boring machine with its associated trailing equipment means that much work can be carried out without contact with the floor. The crew only has to be on the floor for isolated work items. In addition, the cutter head provides a degree of protection if a karst empties into the gallery. The safety margin is increased further by means of thorough preliminary tests using the TBM cutter head’s percussion drilling capacity (up to 100 m) and seismic tests.

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The inclined gallery has a diameter of at least 8.00 m (Figure 6). The gallery is clad with a single layer of shotcrete. The floor is covered with a base tubbing. The normal profile is defined by the space required for transporting the transformers. In the longitudinal direction, the 3,764 m of the inclined gallery include one bend about 80 m in length and another in the opposing sense of about 21 m. Each bend has a radius of 600 m.

Figure 6 Normal profile of access gallery I (inclined gallery)

It was planned to assemble the TBM in the valley terminus cavern, insert it into the starting tube and then assemble the trailing equipment during reduced tunneling operations.

The tender documents did not explicitly rule out the use of explosives to create the inclined gallery, so that companies could tender alternative solutions. On the other hand, the use of tired vehicles in the inclined gallery was ruled out for the tunneling work on safety grounds.

Creating the gallery from the entrance to the valley terminus cavern, with a length of approx. 220 m and a bore of about 50 m2, was planned as a full-section drill and blast tunneling operation. The horseshoe-shaped gallery has a gradient of 1%, and almost all of it is curved, with a radius of 300 m. To excavate the valley terminus cavern with a bore area of 260 m2 or 360 m2, a steep access gallery to the cavern ridges was planned from the access to the valley terminus. The further tunneling work was planned in six drill and blast stages.

The excavation of the turnout in the inclined gallery is initiated using the tunnel boring machine in a first phase. In the part of the bore later to be widened the reinforcement is reduced. After the TBM tunneling is completed, the circular profile will be widened and extended to a maximum bore area of 94 m2 over a length of approx. 220 m using blasting (Figure 7).

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Figure 7 Normal profile of the turnout

The access gallery I, with a single-layer shotcrete cladding and floor tubbing, is equipped with a funicular railway. The railway runs on a track consisting of prefabricated concrete elements which need to be laid with a high degree of precision. Each element has the base dimensions of 4.4 m length x 2.4 m width and is constructed together with the roller box. The access gallery I contains 7 different types of element. Between every two elements there is a loop abutment (50 cm long) aligned in the in situ concrete. The track is anchored to the floor tubbing using two shear connectors in the area of the loop abutments. The prefabricated elements are bedded in self-compacting concrete. The prefabrication of the elements includes the inserts for the subsequent rail attachment.

In the operating phase, the access gallery I will be drained using a separation system. The water emerging from the mountain is collected via drainage elements and conducted to the lateral drainage conduits at the foot of the vault. Inspection shafts are installed approx. 100 m apart to allow maintenance during the operational phase. As no connection duct is planned, the drainage ducts are dimensioned accordingly.

The collected tunnel water flows into the tunnel water pipe which lies next to the vault drainage. This is conducted (enclosed) through the inspection shafts of the vault drainage conduit and the drainage duct (enclosed) through the tunnel water duct inspection shaft. The tunnel water duct inspection shafts are equipped with siphons to ensure that fire cannot spread through them. The tunnel water is collected via the roller boxes. The corresponding discharge flows under the prefabricated elements, and in the vicinity of the loop abutments it is conducted in the direction of the tunnel water inspection shaft.

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3 Tunnel boring machine

3.1 Requirements

Tunneling an inclined gallery with a drilling diameter of 8.03 m and an inclination of 24% has never been attempted before. The most important criterion in selecting the tunneling method was maintaining the safety of the personnel and material.

The possibility of karst formations necessitates a bracing system which can react to a reduction in forces exerted or the partial absence of a tunnel wall. The tender required a TBM with a double bracing system.

Depending on the tunneling class, reinforcement is added using shotcrete, nets, anchors and arch constructions. Consolidation by means of a multi-section steel arch (TH section) as close as possible to the cutter head, which is planned as a contingency, may not be affected or damaged by the bracing.

When the TBM is shifted in preparation for the next tunneling stretch, the bracing is released. During this phase, an additional support system must secure the total weight of the TBM and trailing equipment, about 1,500 tonnes, against slipping. The same safety requirements apply to power failures, operator errors and failure of the TBM's hydraulic system.

3.2 Solutions

3.2.1 Machine concept

The TBM has an X-bracing that is divided into two levels. The bracing forces are distributed over a total of 16 bracing plates (grippers). The two bracing levels can be positioned and moved independently. This makes it possible to brace using varying displacements when steel rings are put in place, and weak points of the tunnel wall can be avoided. Each bracing plate can be moved individually. This allows for bracing in such a way as to avoid putting too much stress on the rock or the construction.

The guidance of the cutter head is forced by the double bracing during drilling. It is not necessary to guide the cutter head constantly using the cutter head plate, which would cause extra wear on the drilling tools. The infinitely variable electric drive allows for smooth, low-vibration progress.

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Figure 8 Schematic diagram of the hard rock Gripper TBM

3.2.2 Safety in the inclined shaft

Automatic locking/monitoring ensures that a given minimum bracing force is maintained and that the TBM does not slip backwards. If the bracing force goes down, the anti-slip system is automatically activated at a pre-defined point before the critical minimum bracing force is reached. A nitrogen-based pressure system engages the bracing plates of the anti-slip system with the tunnel wall. If the downhill component of the acting forces increases, self-impeding levers augment the staying forces of the anti-slip system, further preventing the possibility of slippage.

The anti-slip system is also implemented when the TBM is shifted and the bracing is released according to plan. The staying force generated is a defined multiple of the downhill force, resulting from the total weight of the plant and the reactive forces.

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Beginn Bohrhub:

• TBM verspannt (rot) und Rückfallsicherung verspannt (rot)

• Vorschubzylinder eingefahren

• TBM-Abstützungen eingefahren (grün)

Ende Bohrhub:

• TBM verspannt (rot) und Rückfallsicherung verspannt (rot)

• Vorschubzylinder TBM ausgefahren

• Schleppzylinder ausgefahren

Umsetzen der Rückfallsicherung:

• TBM verspannt (rot), Spannschilder der Rückfallsicherung

einfahren (grün)

• Rückfallsicherung mit Nachläufer nachziehen (Schleppzylinder

einfahren)

Umsetzen der Maschine:

• TBM-Abstützungen ausgefahren, Rückfallsicherung verspannt

(rot), Verspannung einfahren (grün), Außenkellys vorschieben

(Vorschubzylinder einfahren)

• Ausrichtung: Laserausrichtung mithilfe der Abstützungen

Figure 9 Anti-slip system — operating sequence

3.2.3 Securing work

Immediately behind the cutter head plate there is a hydraulically driven anchor-drill device on each side of the TBM. As it can be swiveled and longitudinally displaced, the device can drill anchor positions in the respective upper tunnel quadrant at the same time as the tunneling progresses.

Also, shoring equipment can pre-assemble multi-part steel arches, place them in the tunnel and as required brace them against the rock.

Two mechanized spray jets placed to the left and right behind the TBM's cutter head shield on circular travelling rails can be used to apply an initial layer of shotcrete between the cutter head and the forward bracing in the ridge area if required.

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These three systems serve to allow early installation of the ridge protection without the need to stop the TBM before the drilling stroke has been completed.

3.2.4 Advance exploration

Located behind the forward bracing level a circular travelling rail runs round the TBM. A mobile percussion drilling device travels along it. The travelling rail allows for exploratory drilling in the tunnel wall anywhere around the TBM. Individual elements of the travelling rail can be removed to free transport passages during TBM operation.

The advance exploration is carried out during scheduled maintenance work on the TBM.

3.2.5 Trailing equipment

The 135 m long back-up train includes all energy supply systems for the TBM, secondary ventilation equipment, dust extraction equipment, pressurized air supply, water supply and disposal equipment, personnel rooms and the workshop.

The final tunnel preparation — floor tubbing and reinforced shotcrete shell — is completed in the back-up train. It can also be used for the placement of additional anchors.

A combination of coarse sieve and crusher, placed between the machine conveyor and the first back-up train conveyor, crushes oversized lumps of rock which remain in the spoil flow despite the gates in the drill-spoil openings of the cutter head. This protects the personnel and all the equipment in the tunnel behind the TBM from oversized rock lumps that could fall from the conveyor and roll down the inclined tunnel out of control.

The spoil is conveyed safely into the open air via a cascading conveyor system which is extended in 275 m steps according to the progress of the tunneling.

The tunneling equipment is supplied by means of a cable winch. The winch is mounted on the back-up train, so that material and supply trains can be pulled up into it from the valley terminus. The supply trains, consisting of three flatcars (each 10 m long) and a range of mounting jigs for the various materials and transport needs, are pulled at a maximum speed of 4 m/sec. One train unit can support a payload of max. 48 tonnes.

3.3 Technical data

TBM Model TB 803 E

Type identification Gripper TBM

Nominal drilling diameter using new tools 8.03 m

Drilling diameter with worn tools 8.00 m

Drilling speed max. 6 m/h

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Number of cutting tools 6 x centre, 57 x face, 3 x caliber

Cutting roller type 17-inch single-ring disk roller, back-mounted

Drilling stroke 2.0 m

Number of tunneling jacks 8

Maximum total thrust 22,520 kN

Working torque 5,443 @ 6.0 und 5,730 @ 5.7 kNm@rpm

Drive design peripheral drive / electric / converter

Breakaway torque 7,450 kNm

Cutter head RPM 0 - 7.1 RPM

Conveyor width 1,000 mm

Conveyor speed 0 - 2.5 m/s

Production volume 560 m³/h

Weight (basic machine without trailing equipment) approx. 750 tonnes

Installed capacity of basic machine 12 x 300 + 485 = 4,085 kW

Installation of securing material

Shoring equipment 6-piece ring, TH29

Anchor drilling device 2 pieces

Carriage — usable length 4 m

Deployment angle 90 °

Power pack in total 90 KW

Probe drill device 1 piece

Carriage — usable length 1.850 mm

Drill diameter 100 mm

Deployment range +/-180 °

Power pack 90 KW

Spray equipment 2 pieces

Spray capacity 3.5 m³/h

Radial travel 180 ° each

Longitudinal travel 2 m

Trailing equipment

Length 135 m

Gauge of winch track 900 mm

System 1 bridge + 8 trailing skids

Weight 550 tonnes

Shotcrete robot L2 2

Anchor drilling device L2 2

Tunnel ventilation duct 1800 mm

Electrical system of complete plant

Primary voltage 16,000 V

Main drive voltage 690 V

Subsidiary system voltage 400 V

Lighting voltage 230 V

Transformers 3 pieces

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Capacity 1,650 kVA

Table 1 Technical data: TBM and trailing equipment

4 Initial findings during execution

In view of the cramped space in the valley terminus cavern, the complex lateral assembly procedures for the tunneling and logistics equipment and the fact that the TBM is mobile, the decision was taken to assemble the TBM and all trailing equipment (total length approx. 160 m) in front of the entrance (Figure 10). In order to render the introduction of the TBM possible, the bore area of the valley terminus access was widened from 50 m2 to 70 m2. The TBM, together with the coupled-on trailing equipment (total weight of 1,500 tonnes), covered the approx. 255 m through the access way to the valley terminus and the valley terminus cavern up to the prepared starting tunnel under its own power using a stride mechanism. From the starting tunnel onwards the grippers were deployed to brace the machine.

Figure 10 Fully assembled TBM and trailing equipment in front of the entrance

Despite the fact that the TBM was not assembled in it, the size of the valley terminus cavern remained unchanged. The control room and various plant rooms for the operational phase are housed in the cavern. By carrying out assembly in front of the entrance it was possible to tunnel the 100 m length of the starting tunnel at the same time. During the final assembly of the TBM in front of the entrance the excavation and installation of the construction site station in the base of the cavern were carried out (Figure 11). In a later stage of the construction, this must be converted to the final terminus station of the funicular railway. It was not possible to excavate the final pit for the valley terminus station immediately on account of conflicting demands for space.

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Figure 11 Construction site station in the valley terminus cavern

The TBM began tunneling at the end of October 2010. The amount of water and the karst systems encountered so far in access gallery I correspond very well with the geological and hydrological forecast. Penetration into the turbine cavern is expected in Spring 2012.

5 Concluding remarks

The scheduling requirements in planning access gallery I including the funicular railway are closely connected with the overall project scheduling. Even during the planning stage it was important to bear the interfaces with the various other planning teams in mind.

As early as the construction project stage the tunneling project was investigated in detail with a systematic risk assessment, and the basic framework for the execution laid down. The tunneling unit was selected as the best choice in view of the unusual conditions, with a gradient of 24% over 3,764 m and an excavation shaft diameter of at least 8.00 m in rock prone to karst formation.

References

[1] Börker, M.; Ammon, C.; Frey D. (2010): Zugangsstollen I für Kraftwerke Linth-Limmern, Tunnel 8/2010, 25-31

[2] Jenny, H.; Mayer, C.M. (2010): Kraftwerk-Projekt Linthal 2015. Tunnel 8/2010, 37-42

List of figures and tables

Figure 1 Overview of the Limmern pumped hydro storage facility

Figure 2 Gallery system for construction and operation of the cavern system.

Figure 3 Transport dumper with construction cableway 1

Figure 4 Geological longitudinal profile ZS 1

Figure 5 Karst

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Figure 6 Normal profile access gallery I (inclined gallery)

Figure 7 Normal profile turnout

Figure 8 Schematic illustration of the hard rock Gripper TBM

Figure 9 Anti-slip system — operating sequence

Figure 10 Fully assembled TBM and trailing equipment in front of the entrance

Figure 11 Construction site station in the valley terminus cavern

Table 1 Technical data: TBM and trailing equipment