Construction work has been underway on two large-scale hydroelectric plants in Bhutan - the Punatsangchhu-1 project since 2009 and Punatsangchhu-2 since 2013. Both facilities are located on the Puna Tsang Chhu River, approximately 80 km and 94 km from the capital Thimphu.

Bauer Spezialtiefbau GmbH was previously involved in the construction of these two power plants. In 2011, the company constructed diaphragm walls up to 80 m deep for the upstream cofferdam and executed injection work on Punatsangchhu-1. Bauer returned to the site a few years later to carry out slope stabilisation after a massive landslide on the right bank of the river.

In 2014, Bauer was tasked to execute injection work to seal the Punatsangchhu-2 upstream cofferdam, a project that was successfully completed in 2015. “The Punatsangchhu-2 project involves the construction of a 90-m-high dam, an 8.5-km-long pressure tunnel and several caverns in the power plant complex,” said Frank Berner, operations manager at Bauer Spezialtiefbau.

Recently, Bauer was contracted again to perform specialist foundation engineering work on the project after an underground cavern collapsed at Punatsangchhu-2. The company was commissioned by main contractor Jaiprakash Associates Limited to carry out 18,000 m of soil injection for subsoil stabilisation as well as to install 19,000 m of tieback anchors.

Along with various equipment for the injection work, up to five drilling rigs are being used at the same time, including KR 806 and KR 909 rigs from Klemm Bohrtechnik GmbH. “The main challenge of this project is the cramped working environment. With a width of approximately 18 m and a height of 8 m, the work area is extremely small, creating an extremely challenging environment for equipment and personnel,” explained Mr Berner. “Also, we're in the Himalayas, which presents unique challenges for logistics.”

Bauer's work on the Punatsangchhu-2 project is expected to take around 15 months.

All images: Bauer Group