Reconstruction of the Gurtnellen hydropower plant: high-precision work under difficult conditions
A team from Josef Muff AG (JMAG) is involved in the renewal and extension of the hydropower plant at Gurtnellen, which is nearly 120 years old. In this interview, chief fitter Klaus Hertling provides some insights into the thrilling but challenging work on this project.
Marketing: Mr Hertling, can you describe a typical working day on the Gurtnellen construction site?
K. Hertling: Work starts as early as 5.30 am. Back down in the valley, our team starts by preparing one of the twelve-metre pipes that we need to extend the power plant. The pipe is then transported uphill to the construction site via the installation cableway that was set up specially for this project. The team themselves take the 'official' funicular and cover the remaining 1.1 kilometres to the site on foot.
On site, the pipe is lowered into the trench already prepared by the civil engineering construction contractor, where it is aligned and fitted by our people. It also has to be pre-heated so that it can be welded. After welding from outside is completed, a worker climbs into the pipe to face-grind it from inside. The inspector then checks the weld seam by performing magnetic powder, ultrasound and radiographic tests. Once everything is correct, the pipe is insulated.
Apart from the unusual location, what is special about this project from the technical viewpoint?
One unusual feature of pressure pipes like those used in the Gurtnellen hydropower plant is that the diameter of the pipes decreases constantly towards the valley. So the principle is: the lower the position, the smaller the pipe so that the water pressure stays constantly high. Up on the mountain, the 12-metre pipes that we install have a diameter of 900 millimetres; midway, the diameter is 800 millimetres and further down, in the valley, it is 700 or 600 millimetres. A 900 mm pipe weighs about 3.2 tonnes, so it's not exactly light. As already mentioned, certain preparations are needed so that it can be installed.
This is also true of the other pipe components. Preformed parts that require a lot of welding work are prefabricated in our workshop in Sarmenstorf. Examples of these include intake tubes, adapters, Y-branch pipes and the distributor pipe that consists of segments.
Can you tell us about the team that JMAG deploys on site?
Our on-site team consists of four individuals: the chief fitter, another fitter, a welder and an inspector. All members of the team take part in the daily work and each of them has their own task area. Apart from my coordinating role, I myself am responsible on site for measuring the angled cuts, so I prepare the work for the following day. I forward all the measurement results down to the valley, where the next pipe will be cut and welded together directly on the spot. This means that another twelve metres of pipe will be ready for us to process the next morning.
Your description makes it sound like the procedures are fairly well coordinated and smooth. So what are the challenges posed by this project?
The greatest challenge so far has been to set fixed point 4. Joining the pipes together at the manhole has also caused us some headaches. Fixed point 4 is where the steep section of our pipe begins, with a space gap that has to be precisely aligned. The surveyor had to draw the coordinates for the intersection on the foundation with great accuracy. There is very little space for the connection from the fixed point to the manhole; one section passes under the hiking path and continues back into the site next to the original pipe. The whole job was made more difficult because space is so confined.
Nevertheless, these challenges also make the work exciting. In fact, the entire project is an extremely exciting venture: we're certainly never bored here. You have to keep your mind on the job – apart from anything else, you can't go back quickly to fetch something you've forgotten. That's why I always write everything down.
Here at Gurtnellen, I'm able to make very good use of my previous professional experience – I worked in pipeline construction abroad for 16 years before I joined JMAG. The pressure pipeline that we're installing here at Gurtnellen is already my sixth in the eleven years that I've been working for JMAG. As a general rule, I find that this sort of work is straightforward.
A final question: do you expect you'll be able to keep to the schedule for the Gurtnellen reconstruction?
According to the schedule, two seams have to be welded each day – that means installing 24 metres of pipe – and we usually manage to achieve that. The original plan called for 1 to 1.5 seams per day, so as far as JMAG is concerned, we have everything under control. There tended to be more problems with the underground construction in the past because the rock into which the trench for the pipes is cut was much harder than expected. It couldn't be cut away as anticipated and had to be blasted away metre by metre.
Completion of the topmost section is scheduled for the end of September/October 2016. At present, a large part of the pipe has still not been buried, so that is delaying the follow-on work to some extent. Our goal is to complete the upper section from the catchment to the mountain station of the funicular before winter.
Also, all the technical equipment has to be 'brought into the warm' before winter. The connection of the central gallery pipe with fixed point 9 and the distributor pipe with the Y-branch pipe are planned as winter jobs. The construction contractor needs to have reconstructed the plant's brickwork by then.