Water Power and Dam Construction

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WWW.WATERPOWERMAGAZINE.COM MAY 2009 11

DIARY

Let IWP&DC’s readers know about your forthcoming conferences and events.

For publication in a future issue, send your diary dates to: Carrieann Davies, IWP&DC, Progressive Media Markets Ltd, Progressive House,

2 Maidstone Road, Foots Cray, Sidcup, Kent, DA14 5HZ, UK. Alternatively, email: cdavies@wilmington.co.uk, or fax:+44 208 269 7804

DIARY OF EVENTS

October

3-8 October

Canadian Dam Association Annual

Conference

British Columbia, Canada

CONTACT: Cana dian Dam

Association, PO Box 4490, South

Edmo nton Postal Station,

Edmo nton, Alberta, Canada

T6E 4X7.

Tel: +1 780 432 7236.

http://www.cda.ca.

12-13 October

2nd In ternational Conference on

Long Term Behaviour of Dams

Graz, Austria

September

27 September – 1 October

August

10-14 August

Inte rnational Ass ociation of

Hydraulic Engineering & Research

3rd Biennial Congress

Vancouver, BC, Canada

CONTACT: Stacey Ann P.

Gardiner, CMP, Congress

Manager, ASCE World

Head quarters, 1801 Alexander

Bell Driv e, Reston, Virginia

20191-4400, US.

IAHRConferenceManager@asce.org

16-18 August

34th Conference on Our World in

Concrete and Structures

Singapore

CONTACT: Conf erence

Secr etariat, CI-Premier Pte Ltd,

150 Orchard Road, #07-14,

Orchard Plaza, Singapore 238841.

Email: cipremie@singnet.com.sg.

www.cipremier.com.

Canadian Dam Association Annual

Conference

British Columbia, Canada

CONTACT: Cana dian Da m

Association, PO Box 4490, South

Edmo nton Postal Station,

Edmonton, Alberta, Canada T6E

4X7.

Tel: +1 780 432 7236.

http://www.cda.ca.

CONTACT: LTBD09 Organizing

Committee, Technikerstraße 4/II

8010 Graz, Austria.

www.ltbd09.tugraz.at.

14-15 October

Brit ish Hydropower Asso ciation

Annual Conference 2009

Liverpool, UK

CONTACT: Ellan Parr y, British

Hydr opower Assoc iation. 12

Rive rside Park, Station Road,

Wimborne, BH21 1QU, UK.

Email: info@british-hydro.org

www.british-hydro.org.

23-25 October

4th International Confere nce on

Prot ection of Structures Against

Hazards

Beijing, China

CONTACT: Conf erence

ecretariat, CI-Premier Pte Ltd, 150

Orchard Road, #07-14, Orchard

Plaza, Singapore 238841.

Tel: +65 6733 2922.

12 MAY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

TUNNELLING

• b) Existing west Kiewa power station that has a generation capac-

ity of 62MW. Supplied via the existing headrace tunnel and

lower west Kiewa diversion.

• c) Clover power station that has a generation capacity of 29MW and

located downstream of Junction dam along the east Kiewa river.

• d) Lake Guy/Junction dam, head storage for Clover power station.

• e) Bogong Creek Raceline, existing tunnel.

• f) Location of Bogong power development project (2x70MW) cur-

rently under construction.

• g) Existing tunnel (pressure pipeline) feeding McKay Creek power

station.

• h) Mckay Creek power station generation capacity of 150MW

provided for by a Pelton turbine.

• i) Rocky valley reservoir, main reservoir.

The basic operating principle of the Kiewa hydro scheme is to divert

and harness the two branches that feed the east Kiewa river, namely

the Pretty Valley branch and Rocky Valley b ranch, as well as the

HE Bogong power development project is situated within

the Alpine National Park in the state of Victoria, Australia.

Bogong village is approximately 380km northeast of

Melbourne. The east Kiewa river flows adjacent to Bogong

village, and this is the location of the construction and eventual com-

mercial operation of the power development project.

The Bogong project is designed and positioned to be integrated

wi th the existing power generating faci lities forming the Kiewa

valley hydroelectric scheme.

The projec t will in esse nce be the ‘final link’ in the scheme.

Construction of the existing Kiewa hydro scheme began in the late

1930s and was completed in 1961, with World War II temporari-

ly affecting construction works.

The current scheme basically consists of:

• a) Main operational control centre, terminal substation and regu-

lating pond located in Mount Beauty, with intakes from both

the west and east Kiewa rivers.

Tunnelling at Bogong

Bogong power station in Australia

was always envisaged as part of

the Kiewa Valley hydroelectric

development in Victoria, but it was

never built. However project

owner AGL recognised that

completion of this scheme

addressed future peaking and

renewable energy requirements in

the state, without the need for a

new dam. Paul Thomas of

McConnell Dowell highlights the

tunnelling components of

Australia’s largest hydro power

project for 25 years

Excavation work on the high pressure headrace tunnel which

forms part of the Bogong power development project

Power station

excavation

The main headrace tunnel

was excavated by TBM

cept design stage, that Bogong needs to be capable of 40m³/sec. The

head contract further specified the range of water levels. These levels

are summarised in Table 1.

ATERWAY DIAMETERS

A preliminary head loss assessment for a range of tunnels and liners

was undertaken to determine optimum diameters. The head loss was

determined for a flow of 38m³/sec which would reflect normal max-

imum station flow. The waterway diameters determined during the

concept design were based on evaluations of construction require-

ments and proposed methods of excavation.

The diameter ranges considered are summarised below:

• Headpond dropshaft 4m~7m diameter.

• Main headrace tunnel 4m~6m diameter.

• Downstream dropshaft 4m~6m diameter.

ONTRACT AWARD

Tenders were called by AGL Sou thern Hydro in early 2006. The

contract was awarded to McConnell Dowell Constructors (Aust) in

September 2006. The conditions of the contract are based on using

elements of the FIDIC Conditions of Contract for Plant and Design

– Build, First E dition 1999. The a warded contract sum was for

A$158,710,001.69. The scope of the contract works covered:

• The design and construction and lining of a tun nel co nnect ing

the McKay Creek power stati on with the proposed Bogong

power station.

• The design and construction of all permanent and temporary civil

works associated with power station infrastructure, including

roads, site facilities and revegetation.

McConnell Dowell Constructors subsequently appointed Halcrow

Pacific as the designer for the works. The contractual timeframe for

the works is 21 September 2006 to 20 December 2009.

Having eng a g e d Halcrow Pacific in Oct o b er 2006, McConnell

Dowell and Halcrow commenced detailed construction design for

both the permanent and temporary works. The original design pro-

gramme provided by Halcrow showed the entire design scope being

completed by late September 2007. At the time of preparing this arti-

cle the design phase is still ongoing optimisation and refinement with

an estimated 97% of the design scope completed.

TUNNELLING

west Kiewa river. Approximately 310m

of the Kiewa river catch-

ment is utilised, in addition to 32km of water transfer infrastructure

(aqueducts) from adjacent catchments with the majority water

coming from snow melt during the winter season.

Rocky Valley reservoir is the main storage for the Kiewa scheme

which can hold 28,000M litres of water. The Pretty Valley reservoir,

at an altitude of 1600m, is the highest storage dam for hydroelectric

generation in Australia. The water flows from this reservoir via a diver-

sion dam into the Rocky Valley branch into Junction dam and through

a series of tunnels and surface pipelines to McKay Creek power sta-

tion. The subsequent flow of water through the stations at lower levels

allows water to be reused to generate electricity prior to final discharge

into the Kiewa river from the regulating pond located at Mount Beauty.

ESIGN FEATURES

The viability of the Bogong project was first investigated by AGL

Southern Hydro in 2000. AGL subsequently engaged GHD and

SKM to develop a concept design. The main elements of the project

are summarised below and detailed in Figures 1 and 2 (Note: Actual

depths and gradients are indic ative a nd do not ref lect th e final

scheme). The main structural elements of the project are:

• Power station.

• High pressure headrace tunnel.

• Downstream dropshaft.

• Headrace access tunnel.

• Main headrace tunnel.

• Headpond dropshaft.

• Headpond.

YDRAULIC DATA

The proposed Bogong power station flow capacity was required to

match the discharge from McKay Creek station. This basically

equated to the minimum flow at Rocky Valley reservoir to produce

150MW a t McKay Creek of 37 m

/sec at Full Supply Level (FSL)

and 39m

/sec at Minimum Operating Level (MOL).

The uncertainties surrounding the above values concluded, at con-

WWW.WATERPOWERMAGAZINE.COM MAY 2009 13

Table 1 – Range of watertables¹

Item Water levels (m AHD)

Headpond

Normal operating level (turbine rated output) 1067.2

Spillway crest level 1068

Maximum headpond level 1069

Tailwater

Minimum operating level (Lake Guy) 638.4

Minimum level at draft tube

(controlled by a weir in the Bogong Power Station) 641.5

Mean operating level 645.5

Maximum nor mal operating level 649.68

Maximum flood level (Lake Guy) 653

1 Bogong Power Development Tunnel and Civil Works Contract, Volume 1, Formal

Instrument of Agreement, Schedule 10B – Technical Particulars, AGL September 2006

High Pressure

eadrace

unnel Portal

658 m AHD

ownstream Dropshaft

(

~ 96 m drop)

eadpond

ropshaft

(

~ 80 m drop)

eadpond

1066 m AHD

McKay Creek

Power Station

ntersection between

BM and Dropshaft

750 m AHD

TBM Entrance

section – 1 km

@ 0.20% slope

~1 km @

0.20%

slope

ownstream D+B section

1.3 km @ 0.20% slope

~4.5 km @ 3.00% slope

Notes: All dimensions are indicative only and subject to confirmation

Height to width ratio is exaggerated

Headrace Access

Tunnel Portal

(TBM launch site)

~ 741 m AHD

Bogong Power

Station Site

Above, top: Figure 1 – Longitudinal section; Bottom: Figure 2 – Plan section

14 MAY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

TUNNELLING

McConnell Dowell was required under the head contract to guar-

antee the required rated discharge scheme of 38m³/sec (19m³/sec to

each unit) and to confirm the guaranteed minimum head loss which

was determined to be 18.689m, with a total estimated head loss of

15.985m. In order to derive the head loss, certain assumptions were

made during tender on construction methods, such as excavation

and liner types that would account for frictional losses. These are

summarised in Table 2.

OWER STATION STRUCTURE

The power station structure will eventually house two vertical shaft

Francis turbine g enerating sets . Under a deve loped gross head of

426m, each set will have a nominal rated output of 70MW. The

power station output will be connected to an existing 220kV trans-

mission line located adjacent to the power station at Bogong village.

This connection is facilitated through unitised indoor generator step-

up transformers, indoor gas-insulated switchgear and a single cir-

cuit 220kV underground XLPE cable connection. The existing

transmission line conveys the output of McKay Creek power station

through to the Mount Beauty terminal sub-station.

From a functional perspective, the power station will provide a

secure and water tight structure to accommodate all the hydroelec-

tric plant in addition to ventilation and visitors galleries. The final

power station structure will be almost entirely buried to ensure min-

imal visual impact to the environment.

IGH PRESSURE HEADRACE TUNNEL

The concept design developed a complete steel liner of 3.4m dia ID

for the entire 1200m of the high pressure headrace tunnel. The steel

liner wall thickness ranged from 34mm~40mm. The nece ssity to

provide the steel liner was to prevent hydraulic jacking or fractur-

ing of the adjacent rock whenever the internal wate r press ure

exceeds the minimum principal stress in the rock.

The head contract required the contractor to undertake a series of

hydrojacking tests with the design objectives of: (i) Minimising the

length of the steel liner; (ii) Positioning the downstream dropshaft to

minimise the length of the steel liner; (iii) Determine the permanent

lining requirements in the main headrace tunnel at the location where

the ratio of available cover to required cover is a minimum.

Through value engineering McConnell Dowell was able to reduce

the ID of the steel liner from 3.4m dia to 3.0m dia without com-

promising the hydraulic requirements. This resulted in significant

cost savings for AGL. Further optimisation of the steel liner length

was achieved following in-situ over coring and hydro-jacking tests.

AIN HEADRACE TUNNEL

As the Bogong Power Development is being constructed within the

Alpine National Park and to ensure no surface impact within the

park during construction, the concept design dictated that the main

headrace tunnel be excavated using a TBM. Therefore a tunnel of

5m dia was determined. The permanent support regime and lining

was envisaged to be unlined rock, rockbolts and shotcrete with pos-

sible steel sets in places. The determination of the permanent sup-

port and lining i s based on the rock mass classification (Barton

Q-System). Indeed this method of determination is used throughout

all the shaft and tunnel excavations. Based upon the derived Q-value

a support regime for the main headrace tunnel can be determined.

The support classes generally comprise 2400mm long CT bolts,

which are fully grouted and considered permanent. Steel fibre rein-

forced shotcrete (SFRS) is then applied to the immediate area of the

rockbolt tail to provide durability and comply with the 100yr design

life.

The Main Headrace Tunnel was completed in April. The appor-

tionment of the support classes is summarised in Table 3.

EOTECHNICAL INFORMATION

The contract contains a geotechnical baseline report (GBR) and a geo-

logical interpretative data report (GIDR). The main purpose of the

GBR was to document a baseline for ‘foreseeable physical conditions’

and determine baselines for conditions that could be anticipated during

construction. The GBR could not be used for design purposes.

Table 3 – Summary of support

class installed

Details MHT 4 MHT 3B MHT3A MHT2B MHT2A MHT 1

Q-Value Q≤0.4 0.4<Q≤2 0.4<Q≤2 2<Q≤10 2<Q≤10 Q>10

Tunnel 146 354 620 995 790 2787

length (m)

% of tunnel 2.55% 6.19% 10.83% 17.77% 14.0% 48.7%

length

Table 2 – Assumptions of

construction and liner details for

waterway

Waterway section Construction Permanent & support

method lining class

Headpond Concrete

Headpond dropshaft Concrete

eadpond dropshaft Drill and blast Unlined rock

Main headrace tunnel TBM Unlined rock

ain headrace tunnel TBM Shotcrete

Downstream dropshaft Drill and blast Concrete

High pressure headrace tunnel Drill and blast Concrete

igh pressure headrace tunnel Drill and blast Steel

Penstock & PS Steel

Tailrace Cut and cover Concrete

Power station construction

WWW.WATERPOWERMAGAZINE.COM MAY 2009 15

TUNNELLING

The main purpose of the GIDR was to present factual results of

the geotechnical investigations undertaken and hence be used in the

subsequent designs and locations/alignments of the key structural

elements. The investigations would also gather and assess existing

data available from the previous construction schemes.

The general geo logical features with in the project area com-

prise of rock of a Silurian age, migmatit ie unit which is typical of

a hi gh metamorph ic grade gneissic rock. It was however expect-

ed that the mai n waterway for the Bogong project would be con -

structed largely within the East Kiewa Granodiorte. Granodiorite

is a plutonic i gneo us rock, formed by an intrusion of quartz-rich

magma, which cools in batholiths or stocks below the earth’s sur-

face. It is usually only exposed at the surface aft er erosion and

plift have occurred.

The Bogong power station works commenced in March 2007

with th e construction of a 1:2000yr AEP flo od protection bank

between the site and the adjacent Lake Guy. A 4m deep layer of silt

then had to be removed from across the site.

The design of the power station was such that it was to be found-

ed on fresh rock, some 15m below the surface of the site and around

20m below the level the lake. A secant pile wall, surrounding the

power station footprint was constructed to support the sides of the

power station excavation and to minimise ground water ingress into

the area. CFA piling techniques were adopted with the piles augured

through colluvium and residual granodiorite down to fresh rock.

The material within the secant pile wall was then excavated down

to foundation level in five stages, with anchors and waler beams

being progressively installed to tie the walls back.

During exca va t i o n of the po w e r station site, it was determined

that there were significant benefits to the project in accelerating the

construction of the power station, mainly to provide early access to

the mechanical and electrical contractors responsible for assembling

and commissioning the turbines.

Consequently, the 16 month construction timeline was reduced to

13 months and the 1.5m thick base slab of the station was commenced

in October 2007. Overall dimensions of the Bogong power station

are 45m long, 25m wide and 34m high. In all, 10,000m

of concrete

and 1700T of reinforcing steel were required in its construction.

The primary equipment used for the power station construction

works consisted of:

• Favco STD1500 tower crane.

• RMD formwork systems.

• Putzmeister MX-28 placing boom and BSA-1409D pump.

The station was completed within the accelerated timeline and was

handed over to the mechanical and electrical contractors to com-

mence their turbine installation works in November 2008. These

works are currently in progress with turbine #1 to be completed by

late June 2009 and #2 by late August 2009.

Running concurre ntly with the power station works, the high

pressure headr ace tunnel (HPHT) was also being constru cted.

The portal for this tu nnel is locat ed 15m to the southwest of th e

power station and immediately adjacent to the e dge of the secant

pile wall.

The HPHT is 1100m long and was excavated with an arched pro-

file of nominal dimensions 4.2 x 4.2m. The inbye 400m was lined

with unreinforced concrete with an internal diameter of 3.6m. The

outbye 700m was lined with a 3m internal diameter steel liner, the

annulus between the liner and the excavate d rock filled with a

20MPa concrete.

The p ortal and first 70m of excavation was through mainly

extremely weathered Granodiorite. This was cut using a Mitsui S200

roadheader with steel sets and shotcrete being employed as ground

support through this area. The transition to fresh granodiorite rock

was relatively sudden and drill and blast excavation was commenced

using rail-borne equipment. Temporary ground support consisted

of resin encapsulated rockbolts and mine mesh.

The primary equipment used for the drill and blast works con-

sisted of:

• Atlas Copco Raildrill 252.

• Hagglunds 8HR2 loader.

• 5 x Hagglunds 115-C muck cars.

• 15T Plymouth Locomotive.

• Charging deck / ANFO kettles.

nce excavation of the HPHT was completed, the permanent lining

was installed. The concrete lining was undertaken using a 9m long,

3.6m dia steel form. Concrete was delivered into the tunnel using

conventional agitator trucks and pumped through injection ports into

the form. A minimum concrete strength of 2MPa was required prior

to striking the form and through significant trialling prior to these

works commencing, a mix was developed that would achieve this in

eight hours. This relatively quick development of strength was essen-

tial in achieving the required 24 hour turnaround on the form.

The steel lining for the HPHT consisted of 58, 12m long by 3m

diameter steel modules ranging in thickness between 28–24mm and

each weighing 25–32T. These were transported into the HPHT on

rails using a purpose-built carrier supplied by Muhlhauser, Germany.

Once in the tunnel, each module was positioned and welded inter-

nally on a single-vee preparation to the previous module using semi-

automated FCAW equipment.

A production rate of four mod ules installed, welded and co n-

creted in each week was necessary to main tain the programme.

This was achieved through operating continuous shifts 24hrs/day,

five days/week.

Welding the headrace

tunnel steel liners with

semi-automated equipment

Steel liner being transported by

the Muhlhauser pipe carrier

16 MAY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

Welding times varied depending on the thickness of the pipe but

typically, each joint took 20-24 hrs to complete with two welding

machines ope rating concurrently. 100% NDT of all welds was

required and the work was completed without the requirement for

any re pairs. Filli ng of the annulus between the steel liner and the

excavated rock was undertaken once per week. A 20MPa self com-

pacting con crete mix was developed wh ich was ca pable of being

pumped long distances.

Concrete was delivered to the portal and pumped up to 700m into

the tunnel through a 125mm dia. high pressure delivery line using

a Schwing BP-5000 pump. Typically 400m

of concrete over a 10hr

period was required for each cyc le. The final connection of the

waterway between the HPHT and the turbines is currently under-

way. This consists of a 45T bifurcation that splits the waterway into

2 x 2m dia manifold branches connected to the main inlet valves

directly upstream of the turbines.

The bifurcation and manifold branches will then be encased in a

1000m

reinforced concrete anchor block and backfilled with anoth-

er 10m of fill material.

All material originally excavated from the power station site and

the high pressure headrace tunnel have been stockpiled adjacent to

Lake Guy. This material will then be recovered and used to bury the

power station, once all construction works have been completed. The

entire area will then be revegetated, effectively reducing the visual

impact of the project on the surrounding Alpine National Park.

OWNSTREAM DROPSHAFT

The downst r e a m dropshaft basically connects the ma i n headrace

tunnel to the high pressure headrace tunnel. The excavated sha ft

diameter was 4500mm and after lining with concrete it formed an

internal finished diameter of 4000mm. The required shaft depth was

96m. The me thod of excavating the sh aft was by Raiseboring

method using a Robbins LM97 Raiseborer with a 4.5m diameter

reaming head.

However, before the raiseboring activity could begin the follow-

ing had to be completed:

• Excavation of the high pressure tunnel.

• Excavation of main headrace tunnel beyond TBM Ch:812.50.

• Drill and blast a cuddy to accommodate the raiseboring unit.

Raiseboring activities commenced April 2008 and were completed

in May 2008. The raiseboring activities continued 24/7 and average

advancement rate of approximately 1.5m/shift. Spoil risings from

the reaming of the shaft were collected from the base in the High

Pressure Headrace tunnel and transported out to the spoil disposal

bin by rail mounted spoil cars. The raisebore method resulted in a

smooth line bore. Support of the shaft was provided by spot rock-

bolting and mining mesh as required.

The concrete lining of the shaft was constructed from the bottom

up. A working platform was suspended above the shaft. A simple

steel form panel shutter was used as the form. Concrete was poured

in 4m lifts with one pour being completed each day.

The main headrace tunnel is a 5m dia, 5700m long tunnel, plus a

100m for the tunnel stub. The tunnel alignment traverses under the

mountains of the National Park where tunnel depths exceed 200m

and up to 400m. The majority of the vertical alignment of the tunnel

is at 4% grade, this decreasing to 0.20% at the 600m radius

approach to the downstream dropshaft.

The main headrace tunnel is on the critical path. Until the main

headrace tunnel was completed the headpo nd drop shaft, con-

structed by raiseboring, could not commence. The main headrace

tunnel was always envisaged to be excavated using a TBM.

The GBR was used to determine the appropriate TBM. The GBR

predicted competent rock of 145MPa average strength and a Q value

of 10, which effectively suited a hard rock TBM over the distance

of about 6500m. McConnell Dowell procured a 5m diameter, refur-

bished Robbins TBM.

The TBM was refurbished by Herrenknecht i n Germany. The

TBM had completed two previous projects in Europe, the last one

being a water tunnel in Lugano, Switzerland. The TBM arrived on

Site in June 2007.

The TB M is a single gripper, main-beam hard roc k machine,

which basically involves the TBM gripping against the side walls of

the excavated tunnel and propelling itself forward by way of four

hydraulic propulsion cylinders connected to the main beam. The

combined force of the propulsion cylinders is approximately 1000t.

The rotating cutter head is connected to the main beam and series

of six frequency controlled electric motors producing 1800kw. The

TUNNELLING

Key design requirements

• Comply with required design life of 100 years.

• Operational dewatering requirements and associated timelines.

• Waterway support system and lining to satisfy operational variances for

starting pressures, transient pressures, and fault or rejection condition.

• Guaranteed minimum head loss to be provided at design flowrates.

• Seismic load resistance to Level 3, with exceedance probability of 1 in 2500.

• Safety and stability during the excavation process.

Construction work

A wide array of construction techniques, plant, and equipment were used and

continue to be used in the construction phase. These include:

• Tunnel boring machine (TBM).

• Raiseboring of deep shafts.

• Contiguous flight auger (CFA) RC piles.

• Roadheader excavation.

• Drill and blast.

• Ground anchor support.

• Hagglunds mining equipment.

Above, left to right: Bifurcation delivery; raisbore reaming head being installed at base of the downstream dropshaft; raisbore equipment

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TUNNELLING

TBM cutterhead is equipped with a total of 33 x 19” cutters. The

maximum cutterhead thrust is 10,395kN and maximum head rota-

tion is 10.9rpm. The gripping capacity of each gripper is 15,779kN,

with a combined gripping lateral force of 31,558kN (approx 3000t).

One stroke of the TBM is 1800mm and in anticipated conditions

would take approximately 40 minutes.

The TBM is also equipped with a probe drill with a range of 360°

and two roof bolting hydraulic rock drills for installation of rock bolts.

The photographs below capture the TBM being assembled. The

TBM was named by local school children ‘Aurora Australis’.

(Southern polar lights), representing the fact that the new tunnel and

power station will bring light to homes.

TBM excava tion began in earnest in August 2007. A launch

tunnel of 134m was constructe d in advance to accommodate the

assembly of the TBM and the back up which was 140m long. The

GBR predicted intact rock strengths for SW-Fr granodiorite would

have a mean UCS of 145MPa with an upper bound of 235MPa.

Indeed the GBR further stated that for 70% of the granodiorite will

lie between 110MPa and 180MPa.

Based on the above anticipated rock condition advance rates were

expected to achieve 535m per month. However actual observed rock

strengths in the main headrace tunnel during tunnelling were on

average 18 0MPa, some 24% higher than anticipated. This has

resulted in an average advance of approximately 340m per month.

McConnell Dowell elected to provide a continuous conveyor

system to covey excavated rock material from the TBM to the stock-

pile area. The continuous conveyor system was procured from H&E

Logistik GMBH of Germany.

The conveyor system, as the name suggest s, is a continuously

extended belt conveyor originally developed for use in the mining

industry. The belt i tself is 650mm wide and is able to transport

275t/hr. The conveyor is connected in the tunnel crown by chains.

The forward end of the conveyor (tail end) is fixed to and towed by

the TBM back up. The belt structure and troughing rollers are insert-

ed at intervals of about 3m.

As the tunnel advances the conveyor is extended with 600m of

belt sections. Each new section is jointed by the vulcanising process.

The conveyor belt is equipped with two 90kW drive units. The belt

speed of the conveyor is 2.8m/sec. The spoil is transferred to the

stock pile by a transfer conveyor which crosses above the Bogong

High Plains Road. The excavated rock is re-used by local authori-

ties for road rehabilitation projects.

EY DATES

At the time of writing this paper the power station and downstream

dropshaft were substantially complete. The main headrace tunnel

was successfully completed on 23 April 2009. The TBM has been

dismantled and the remaining components left in the tunnel stub.

The headpond dropshaft is currently being raisebored.

The power station, high pressure headrace tunnel and downstream

dropshaft will be ready to receive water by the end of June 2009.

The main headrace tunnel and headpond dropshaft will be ready to

receive water by the end of August 2009.

The turbines were being installed in the power station with prepa-

ration works ongoing for wet commissioning, which is expected in

mid September 2009. The turbines are expected to be operational

by October/November 2009.

Paul Thomas is the project manager for the Bogong power

development project. Email:

Paul.Thomas@macdow.com.au

Thanks are given to Shaun Paul, Section Manager Power

Station & High Pressure Headrace Tunnel, for

contributing to the article

To view further diagrams and photographs of the

excavation work, please visit the features section of

IWP&DC’s website at wwww.waterpowermagazine.com

Above, left to right: Transfer conveyor & muck bin; Headrace access tunnel portal; Overlooking the transfer conveyor (P. Thomas)

IWP& DC

TBM being assembled. The photograph

below shows the TBM ready for launch

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20 MAY 2009 INTERNATIONAL WATER POWER & DAM CONSTRUCTION

TUNNELLING

Combined, the Sir Adam Beck – Niagara generating stations pro-

vide 30% of OPG’s hydroelectric capacity and 35% of OPG’s clean,

renewable hydroelectric energy.

In 1956, the Schoellkopf plant was destroyed by a catastrophic

failure of the rock cliff which caused part of the plant to be pushed

into the Niagara river. In the early 1960s, NYPA built the 2400MW

Robert Moses generating station, and its com panion 300MW

Lewiston pump generating station, on the lower Niagara river oppo-

site the SAB plants. This allowed the US to use a larger portion of

the available water and the less efficient Adams and S choellkopf

plants were removed from service.

Progressively, the TP, OP and CNP plants on the Canadian side

of the river were also closed as 25Hz demand dwindled. OPG’s

remaining hydroelectric facilities at the Sir Adam Beck complex did

not have enough diversion capacity to fully utilise Canada’s alloca-

tion of Niagara River flow under the terms of the 1950 Treaty.

The Niagara tunnel project, now under construction, will restore

Ontario’s c apability to e ffectively utilise the water allocated to

Canada. When the new Niagara tunnel is in operation, the water it

delivers will permit the existing Sir Adam Beck generating stations

to produce 14% more energy, increasing average annual output by

about 1.6BkWh, enough to supply 160, 000 Ontario homes w ith

clean, renewable hydroelectric power.

ECIDING TO BUILD THE TUNNEL

Preparation for the new Niagara tunnel commenced in 1982, when

Ontario Hydro (predecessor of OPG) began to study the possible

expansion of its hydroelectric facilities on the Niagara river. Detailed

engineering, environmental and socioeconomic studies were con-

ducted from 1988 through 1994 with an environmental assessment

(EA) submitted in 1991 for the then planned project (two 500m

/sec

water diversion tunnels, a 3x900MW underground generating sta-

tion and transmission improvements between Niagara Falls and

Hamilton, Ontario).

Among the commitments made through the EA process was the

utilization of a tunnel boring machine (TBM) to excavate the tun-

nels from the outlet end, under the buried St. Davids gorge and fol-

lowing the route of the existing SAB2 tunnels through the City of

Niagara Falls. Other commitments in cluded re-use of excavated

materials and an agreement to compensate the host municipalities,

Niagara Region, Niagara Falls and Niagara-on-the-Lake, for fore-

cast project impacts on tou rism and municipal services. The EA

received approval from Ontario’s Minister of the Environment in

1998, including provisions to begin with construction of one tunnel,

the Niagara tunnel project.

HERE is over a century of hydroelectric development expe-

rience on both sides of the Niagara river. The first plants

were built adjacent to the falls, us ed only the hydraulic

head in the vicinity of the falls and all generated at a fre-

quency of 25Hz. The Canadian Niagara Power Company (CNP),

the Toronto Power Company (TP) and the Ontario Power Company

(OP) stations were built on the Canadian side while the Adams and

Schoellkopf sta tions were on the US side . The plants on the

Canadian side were built by private companies between 1900-10.

The OP and TP facilities were purchased in about 192 0 b y t he

Hydro-Electric Power Commission of Ontario which, in 1974, was

renamed Ontario Hydro, the immediate predecessor o f Ontario

Power Generation (OPG).

Sir Adam Beck GS No.1 (SAB1), built in the early-1920s, is OPG’s

third largest hydroelectric stati on wi th te n units h aving a t otal

installed capacity of 498MW. It was the first of the Niagara river

hydroelectric facilities to capture the hydraulic head avail able

through the rapids upstream and downstream from the falls, facili-

tating capture of 95% of the drop between Lake Erie and Lake

Ontario. A 20km long open-cut canal was co nstructed between

Chippawa and Queenston to deliver about 600m

/sec of Niagara

river water for hydroelectric generation at SAB1. Originally, the

SAB1 units all generated 25Hz electricity, but since Ontario’s 60Hz

standardisation in the 1950s, eight generators have been converted

from 25Hz to 60Hz. Two SAB1 units continue to supply 25Hz elec-

tricity to a few customers.

Sir Adam Beck GS No.2 (SAB2) is OPG’s largest hydro station with

16 units having a total installed capacity of 1499MW. SAB2 is the

flagship of OPG’s hydro fleet. It was constructed in the early 1950s

and first operated in 1954. Two 13.7m diameter, 8km long diversion

tunnels joined into a 3km long open-cut canal to deliver about

1200m

/sec of Niagara river water for hydroelectric generation.

During a major overhaul and upgrade of SAB2 between 1996 and

2005, the turbines, generators and other primary equipment were

replaced, renewing the station’s reliability and increasing its capac-

ity by 194MW.

The Sir Adam Beck Pump Generating Station (PGS) and reservoir

were also built in the 1950s, first operating in 1958. The PGS has

six reversible units with a combined nominal capacity of 174MW.

The PGS reservoir is a manmade lake, contained by a rockfill dyke

that rises above the natural terrain. The PGS reservoir is operated

over a range of 8.2m and has a storage capacity of about 20Mm

Water is typically pumped into the PGS r eservoir from the S AB

canals during periods of low electricity demand (over night and on

weekends) an d released to gene rate electricity at the PGS and at

SAB1/SAB2 during periods of peak demand.

New tunnel to optimize hydro

potential at Niagara

Ontario Power Generation’s Niagara tunnel project includes the planning, design and

construction of a 10.2km long, 12.7m internal diameter tunnel and associated facilities to

divert an additional 500m

/sec of water from the Niagara river upstream from the

Horseshoe Falls to the existing Sir Adam Beck generating stations near Queenston. The

design/build contractor, Strabag, is using the world’s largest hardrock tunnel boring

machine to excavate the tunnel. By Richard A Everdell

Water Power and Dam Construction - Issue May 2009

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