A recently delivered, purpose-ordered GIA 10HR-B electric Häggloader is meeting all expectations guaranteeing no CO2 emissions – requiring reduced underground ventilation, plus fast cycle times and loading requirements for Norwegian tunnelling specialist contractor Haerhe Entreprenør on its Holsbru Kraftverk hydropower project.
Located close to Øvre Årdal, some 300km north west of Oslo, Hosbru Kraftverk is a hydropower plant tunnel extension which will allow Norsk Hydro to utilize previously unused water resources, including small mountain lakes and rivers.
These will feed a total of seven intake chambers into two turbines at Tyin – previously closed in 2004 – to increase production by 84 GWh, with the total power from Tyin power station exceeding 1600 gwh.
The project features a 6000m long tunnel accessed by a 150m adit. Haehre Entreprenør ordered the Häggloader to operate on two faces removing rock following drill and blast operations.
Haehre Entreprenør started site mobilisation June 2010 with an 18 month tunnel excavation completion date and handover to Norsk Hydro by February 2012.
The tunnel features a cross sectional area of 20m², and is just 4m wide and 5m high, making it ideal for the Häggloader.
The wheel-borne Häggloader is a rubber-tyred electro-hydraulic driven trackless loader with a back-hoe digging system – it can also be supplied with dual digging arms.
Featuring a hydraulic system to power an electro-hydraulic drive to provide low installation and energy costs, the GIA 10HR-B also ensures good quality air with no CO2 emissions, says the company.
The back-hoe digging system loads the ‘blasted’ spoil onto the unit’s conveyor system which fills the haulage vehicle with a constant flow of ‘spoil’.
Tunnelling operations
Utilising an underground jumbo drill rig, Haehre are drilling 65 holes on each of the two faces to a depth of 4.6m and achieving a rock fall of 86 m³; with up to three blasts a day on each face.
Featuring a loading speed of 3-4m³/min has, according to Project Manager Ernst Ove Johansen, helped to ensure a fast cycle rate loading the contractor’s fleet of 9 m³ dump trucks to achieve advance rates of up to 12 m/day on both faces.
“We have also excavated niches every 200 – 250 m – they could have been been even further apart, up to 400 m – but we optimised on 250 m to achieve the best cycle performance due to number and size of dump trucks we use,” said Johansen.
This compares with the requirement of every 50m using conventional tunnelling techniques with LHD loaders.
Shotcreting
Throughout excavations, the contractor has experienced considerable difficulties with cracked and decomposed granite conditions constantly changing. This has required extensive shotcreting throughout the tunnel, generally 6 – 8 cm thickness at 1 m³/m of tunnel.
Construction has also involved the installation of 2.5 bolts/m but depending on the quality of rock can be up to 5 bolts per section.
When the Häggloader leaves the face – to park in a niche during further drill and blast activities – it can operate on diesel power reverting to electric inside the tunnel using a 500 m long cable reel at 400 V and a unit mounted 160 m electric cable.
Fan system
Two GIA Swedvent AVH90 fan systems are also being used by Haerhe to ensure reduced energy consumption; each delivering 20 m³/sec through the tunnel when run at full speed after blasting to clean the face quickly from explosive emissions and during ‘mucking’ procedures. During scaling, drilling, charging, the fan speed is reduced to run at 50% which reduces the fan energy consumption to 15% but still having a minimum return velocity of 0.5m/sec.
To optimise the energy consumption of the ventilation cycle GIA can provide a ventilation control system with sensors measuring CO2 NOx emissions, velocity and temperature.
Only recently introduced, the new generation of Swedvent fans offer improved silencer design providing noise reductions of at least 3 dBA for its full range of fan motors rated between 10 – 500 kW to meet 75 – 85 dBA at 7m.
For more information, visit www.gia.se
