Tower power beats dam building problems

The obstacles just kept piling up when the Mumbai, India-based Hindustan Construction Company Ltd (HCC) was contracted to help build the Tala Dam located in Chukha Dzongkhag in western Bhutan, a small kingdom in the Himalayas. The huge concrete structure had to be built in a confined space, in difficult terrain, and in water. However, HCC was not fazed by the challenge, and brought in a trio of tower cranes to combat the potential lifting problems.

The dam is 86m high and 95m wide, and this further added to HCC’s problems, as one crane alone could not span the entire width. The lifting team therefore decided to deploy two stationary cranes (a Potain K40/27C, and a K5/50C), and one travelling crane (also a K40/27C).

The K40/27C has a maximum jib radius of 70m, and a maximum load moment of 264tm (a maximum load of 16t at 15.4m radius), and the K5/50C has a maximum jib radius of 70m and a maximum load moment of 448tm (a maximum load of 20t at 22.4m radius).

Because of the topography at the dam site, it was decided that the cranes would work only at freestanding heights. A 26m high concrete pedestal was therefore constructed for the K40/27C, and another 14m tall for the K5/50C. However, because of their difficult location, getting a mobile crane in position to erect these cranes would have proved expensive and time consuming.

A 75t P&H crawler crane therefore assembled a Russian BK300 luffing type tower crane (which can lift 25t at 12m and 8t at 30m), and the BK300 assembled the K40/27C and K5/50C.

However, these two cranes stood on pedestals, and were still not big enough to cover the entire area of the dam, particularly the downstream portion. This called for mobilisation of yet another tower crane – the K40/27C – this time a travelling type.

HCC was then faced with the problem of how to make a crane travelling with a freestanding height and, at the same time, handle the job beyond the freestanding height. The solution that company came up with was a steel structure, 25m high by 36m wide, which carried rails. The K40/27C was placed on these rails.

The three cranes, working in combination, were now able to cover the required radii, but concrete for the dam was produced far away from their reach, and this led to yet another question – how could the concrete be transferred?

The answer was two 25t gantry cranes, with a trolley mechanism and two-way pick up track to facilitate movement of concrete wagons. A bucket carrying 3t of concrete was brought on the transport vehicle, shifted by a gantry, placed on the wagon waiting on the pick up track, moved to a location accessible by the tower cranes, and lifted by the cranes for final placement.

Although this project was one of the most challenging, HCC has, over the years, built more than 24 dams in most all parts of India. Of these, six dams were built for irrigation projects, and 18 were built for hydroelectric power projects. More than 12 million cu m of concrete and 5.5 million cu m of earthwork quantities have been placed in these structures.

The 1,020MW Tala hydroelectric project is the biggest joint project between India and Bhutan so far, and will generate 4865 million kWh/yr.

The run-of-the-river project, being managed by Tala Hydroelectric Project Authority, is located on the Wangchu River and, at 860m, is the region's largest high-head project.