Work Progress on the PSP scheme ‘Nant de Drance’
(January 2009)

The company Aare-Tessin A.G. for Electricity (Atel) together with the Swiss National Railway (SBB) are planning the development of the Pumped Storage scheme ‘Nant de Drance’, which is located between the existing reservoirs Emosson and Vieux Emosson in the Canton of Valais, Switzerland. The Emosson Reservoir, with an approximate capacity of 225 million m³, acts at present as the primary storage for the existing hydro-power stations of the Electricité d’Emosson S.A. and the SBB and will serve in the future pumped storage scheme as the lower reservoir. The Vieux Emosson Reservoir lies at an elevation 300 m above the Emosson reservoir and has an approximate capacity of 12 million m³. The new pumped storage station 'Nant de Drance', with an installed capacity of 600 MW, will require the construction of a 5.6 km long main access tunnel, a machine cavern, a transformer cavern and two parallel waterway systems, each comprising an intake and an out take, headrace and tail race tunnels, with vertical pressure shafts, which will be in part armoured with steel liners.

Approach cutting to the drainage tunnel and location of the stilling chamber (Click for larger image) Excavation for the approach tunnel between site and the cantonal road Excavation for the drainage pipeline and part of the site installation

Since the beginning of construction in October 2008 various preparation works have been carried out in advance of the main construction phase. Included in the preparation works are; the forestry clearance in the area of the planned accommodation site and the portal areas of the tunnel drives, removal (after forestry clearance) of top soil and transport to temporary depots, installation of the relevant utilities such as electricity, water and sewage, preparation of access roads, with widening, where appropriate, dismantling of existing buildings, which obstruct the construction infrastructure (i.e. old military bunker) and in addition, extensive slope stabilization works in the portal areas areas are in progress. Due to the present meteorological conditions these works have been paused until weather conditions allow safe execution. Since November 2008, the Contractor of the preliminary construction lots Dénériaz S.A., has begun to mobilize on-site for the construction of the connection tunnel to the installation site and the de-watering gallery.

The construction of access roads to the portal areas have been carried out in parallel. The replacement of the pipeline from the de-watering works to the neighbouring hydro-electric power station (SBB) has been started. Excavation to a depth of up to 14 m will be required.

After test blasting, in which resulting vibration to neighbouring power stations was evaluated, the tunnel drive was started on 18. December 2008. The tunnel drive began for the above mentioned tunnel drives in double shifts. The break out of the 210 m dewatering gallery is expected towards the middle of February. The main construction work has been given to the consortium Marti/Implenia, and will start officially in January 2009 with the excavation and primary support of the portal area for the 5.6 km long main access tunnel. The tunnel has to be driven in the portal area only 3 meters under the existing railway line of the TMR in challenging geology, comprising unconsolidated colluvium and landslide material. Contemporaneously, the construction of the site village with accommodation and canteen facilities for up to 400 employees will be carried out.

Patrick Furrer - Wasserkraftanlagen

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Nam Ngum 2 – A Lender’s Engineering Assignment
(January 2009)

Nam Ngum 2 is a 615 MW hydroelectric project being implemented in Lao PDR for energy export to Thailand. The project includes a 181 m high concrete faced rockfill dam, with a total volume of about 9.5 million m³; open chute spillway on the right abutment, fully underground power waterways in the left abutment; outdoor powerhouse equipped with three Francis units of 205 MW each under a design head of 154.5 m. The river diversion during construction is achieved through two concrete lined diversion tunnels of 11.7 m diameter and 1,150 m average length. With an average river runoff of about 200 m³/s, the project generates 2,218 GWh/y, all intended for export to Thailand.
The construction of the project started in late 2005 and is presently at a well advanced stage, being foreseen to close the diversion tunnels and start the reservoir filling toward March-April 2010, to begin commissioning toward October 2010 and to have the plant fully in operation at the beginning of 2011.

Aerial View: Construction Progress at End November 2008 (Click images to enlarge)		Main Dam: Upstream Face at about 60% of Final Height - Preparation for the Starter Slabs Construction on the Right Abutment
Powerhouse Under Construction: General View		Powerhouse: Draft Tube Liner Under Erection

The project company is owned by private and semi-private Thai companies, with an important participation from the Lao Government. The main shareholder is a Thai construction company, which is also the EPC Contractor for the construction of the project. Financing is provided by a group of Thai banks.
AF-Colenco has been acting as the Lenders’ Engineer since 2005: after the initial project appraisal in view of the financial close, AF-Colenco is presently monitoring the construction from technical, time schedule and financial point of view. At the end of the construction, we shall witness the commissioning procedures and certify to the Lenders that the project is ready for commercial operation.
The Lenders’ Engineer figure was born with development of hydroelectric project by Independent Power Producers. The assignment is very interesting, as it requires a sound analysis of technical aspects, as well as understanding and when necessary mediating between the requirements of the Lenders, of the Developer and of the EPC Contractor.

Giuseppe Stevanella - Hydropower Plants

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AF-Colenco Ltd Awarded 1st Prize for a Geoscientific Computational Benchmark
(December 2008)

A team from AF-Colenco’s Department for Groundwater Protection and Waste Disposal participated in Couplex-Gaz, an international competition for the numerical modelling of two-phase (gas-water) flow and transport in porous media. ANDRA, the French National Agency for Radioactive Waste Management presented the nine participating teams with two test cases involving complex physical processes, extremely heterogeneous materials and different scales. Each team submitted its contribution in parts over a period of 2 years. The Scientific Committee evaluated the teams based on the solution approaches as well as computational efficiency, stability and accuracy.
In November 2008, the AF-Colenco team was awarded the €10’000 prize for the top team. This benchmark award is a great honour and demonstrates our excellence in geoscientific computing.

Jean Croisé - Groundwater Protection and Waste Disposal

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AF-Colenco Info November 2008
Selected topics presented in the AF-Colenco Info give an insight into some of our latest projects.