Mobile solution for concrete delivery20 May 2011
The Telebelt mobile belt conveyor from Putzmeister is delivering masses of concrete at the Xiluodu hydroelectric project – the second largest hydroelectric project in China
The Xiluodu hydroelectric plant is currently being built on the Jinsha River – a tributary of the Yangtze. Its main purpose is to generate electricity but it also fulfils other tasks: flood protection, deposition of sediment, and improvement of shipping conditions, etc. It is expected to produce from 57 to 64bkWh of electrical energy each year.
As part of the US$7.36B project, a double-curved arch dam will create a storage lake of 12.67Bm3. The absolute elevation of the dam crest is 610m, the maximum height of the dam is 278m and the overall length is 700m. The total excavated material for this project amounts to 39.81Mm3, of which 25.61Mm3 is above-ground excavation and 14.20Mm3 is from the construction of tunnels.
In total, 16.72Mm3 of concrete is required for this project and 6.60Mm3 of this is required just for the body of the wall. The concreting work commenced in 2008. It is expected that the first generator sets can be installed in June 2012. From June 2013, the first electrical energy should be generated and the entire project should be completed by 2015.
The devices in the Xiluodu Dam that are planned for flood water flow include seven overflow drainage openings at a size of 12.5m x 13.5m, below them eight outlets at a size of 6m x 6.7m and four exceptionally large overflow tunnels (with a diameter of up to 15m) – two tunnels on the right embankment and two more on the left. The overflow capacity of the project amounts to 49,923m3/sec. The power generated by the overflows is almost 100MkW and is therefore the highest in the world. The four overflow tunnels are the largest of their kind in the world and have a discharge rate of 16,000m3/sec, which is about a third of the entire outlet capacity of the plant.
High demands on the concrete
The flow rate of the river is amongst the fastest in the world (up to 50m/sec). Since these four overflow tunnels were designed to cope with exceptionally large quantities of water at an extremely high flow rate, the concrete that is used here must be of outstanding quality. The difference between this concrete and a pumpable concrete mix lies mainly in the proportions of the individual concrete raw materials that are used. Pumpable concrete requires a relatively high flowability so that it can flow through the delivery line. This means that concrete raw materials such as cement and fly ash are required in large quantities. However, cement creates a lot of hydration heat when setting the concrete, meaning that the temperature and crack formation are difficult to control. The dissipation of the hydration heat may pose a problem, particularly with structures such as a dam.
Telebelt plays major role
Telebelt is a mobile belt conveyor that can continuously convey any kind of bulk materials and concrete and is unrestricted by the pumpability of the concrete. Telebelt is therefore considered an excellent solution for pouring high-quality mass concrete as it not only means that fewer cracks are formed but it also reduces the costs for the concrete, says Putzmeister.
The first Telebelt TB 105 delivered by Putzmeister has been used in the Three Gorges Dam project since 2000. To date, the number of operating hours amounts to more than 20,000 hours and the device continues to work properly. Due to this experience, the company responsible for the Three Gorges project ordered two more Telebelts of the new type TB 110G for the team from SinoHydro Bureau 7. Since the machines are convenient to operate and the boom can be gently and smoothly telescoped, swung, lifted and lowered, the two TB 110G devices are very popular on the construction site. The machine has evoked a positive response among the workers from SinoHydro Bureau 7, making concrete pouring easier.
In use across the site
The Xiluodu hydroelectric plant is a huge construction site. Several projects are ongoing at the same time and these are co-ordinated centrally. The individual construction teams work closely together. It is often the case that immediately after one concreting task has finished, the belt conveyor travels to the next site of use on the construction site. Thanks to its high levels of flexibility and mobility, the Telebelt is often used “on the front line”. The TB 110G from Putzmeister was therefore not only used on the construction sites of SinoHydro Bureau 7 (in other words, to construct the overflow tunnels, the foundations of the cable crane structure and for above-ground concreting, etc.), but it also considerably helped the construction sites of Hydro Bureau 6 and Hydro Bureau 14 (among others) when constructing the surge tank, the underwater outlet, and the main transformer building etc. As a result, on one occasion, the Telebelt was used on five different construction sites within six days, during which time it continuously placed 4800m3 of concrete for the overflow tunnel, the cable crane platform and the underwater outlet. The high level of efficiency demonstrated by the belt conveyor is another performance feature that is recognised on the construction site. For example, the TB 110G generally requires only 2.5 minutes to drain a mixer of 6m3 for the work on the cable crane platform and, at a slightly higher speed, it requires only 1.8 minutes to drain the mixer. This extremely high machine output significantly contributes to completing the work within the scheduled time.
For more information on the Telebelt conveyor system please visit www.putzmeister.com