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Pakistan signs Dasu hydro tunnels contract 06 Apr 2017

Patrick Reynolds for TunnelTalk

A contract for the underground works in the first stage of the Dasu hydropower project in Pakistan has been signed with a major Chinese contractor. The Pakistan Water and Power Development Authority (WAPDA) signed the PKR64.4 billion (US$615 million) contract with China Gezhouba Group Company (CGGC) for the project’s first tunnelling package.

The contract for package MW-02 includes the first relatively short headrace, and the long tailrace tunnels, the upstream pressure shafts and downstream surge shafts, and work on the large powerhouse cavern complex that will eventually hold 12 generating units (Fig 1).

Contracts signed for Dasu hydro project
Contracts signed for Dasu hydro project

The 4,320MW Dasu project is on the Indus River, in north Pakistan, upstream of Dasu in Kohistan District and is being developed in two stages. Staged development of the Dasu project is designed to bring six of the proposed 12 x 360MW turbines online in Stage 1 to supply much-needed power as soon as possible and use the revenues earned to help fund Stage 2 first.

Another factor for two-stage development of Dasu is that the upstream Daimer Basha project on the Indus River, must be completed before Dasu can be built out to full capacity in the Stage 2 works.

Building the dam, first headrace and tailrace tunnels and installation of the first six turbines will commission the project’s 2,160MW Stage 1 by 2023.

Fig 1. Tunnel layout for the Dasu project
Fig 1. Tunnel layout for the Dasu project

Once fully developed, the project will include:

  • four 500m long concrete-lined headrace tunnels of 12m diameter;
  • four 131m deep pressure shafts with penstocks to three turbines each;
  • the main machine hall and a smaller transformer hall in the underground powerhouse; and
  • four concrete-lined tailrace tunnels of average 2,200m long and of 10m wide x 12.5m high, Each tailrace drains three turbines with the flows come together at a dedicate 37m wide x 45m high surge chamber on each.

The project includes further tunnels in PKR115 billion (US$1.1 billion) MW-01 contract awarded to CGGC to build the dam and hydraulic steel structures. The tunnels are:

  • two shotcrete-lined river diversion tunnels of 17m wide x 20m high and,1,260m and 1,100m long and
  • two 9.5m diameter sediment flushing tunnels of 820m and 680m long.

CGGC won both contracts on a lowest bid basis and the awards were signed in March. CGGC is involved in several other hydro projects in Pakistan, most with major tunnel excavations.

Geological expecations

The geology in the project area includes both igneous and sedimentary rocks. Upstream tunnels are to be excavated in granulite while the caverns are in coarsely crystalline dioritic granulite. The granulite rocks are characterised as generally massive to blocky, slightly foliated and strong to very strong. The tailrace tunnels are in amphibolite.

China contractor CGGC to build Dasu in stages
China contractor CGGC to build Dasu in stages

The project is located near the boundary of the Asian and Indian tectonic plates,and design development of the underground layout of the tunnels and caverns had to accommodate a fault zone passing through the site. The caverns were placed upstream of the fault zone, resulting in the relatively short headrace and longer tailrace tunnels.

Funding and procurement

Development of the project has major funding support of approximately US$1 billion from the World Bank. This is more than one-fifth of the estimated US$4.2 billion budget of Stage 1. The Bank has also been closely involved in the procurement process.

In the lengthy procurement process, bids for the two main lots on Stage 1 were received last year and opened in July 2016. WAPDA said three out of the four pre-qualified contractors submitted bids for the MW-02 lot for underground works. For the MW-01 for the dam, six out of seven pre-qualified firms tendered. Following an bid evaluation process, that included assessment by the World Bank, the client issued letters of acceptance to the lowest bidder on each lot at the end of 2016.

At the end of March 2017, WAPDA announced it had achieved another major milestone for Stage 1 by securing the country’s largest ever locally syndicated loans for an infrastructure project. Guaranteed by the Government, the total of PKR 144 billion (US$1.35 billion) is being provided by a group of banks led by Habib Bank. WAPDA has announced that an added series of international loans of up to US$350 million are expected to be signed soon.

Preparatory works for Dasu have started on site and main works are due to begin by mid-2017. Supervision on the project is by Dasu Hydropower Consultant, which is a joint venture of Nippon Koei, Dolsar and local firms Development Management Consultants (DMC), National Development Consultants (NDC) and Pakistan Engineering Services (PES).

References

           

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