Global experience leads to first-of-its-kind solutions

The Tehri Dam is a rock and earth-fill embankment dam on the Bhagirathi River near Tehri in Uttarakhand, India. At a depth of around 800 ft, it is the highest dam in India, distributing 270 million gallons of drinking water per day, irrigating thousands of acres of farmland and generating electricity to Uttar Pradesh, Delhi and other areas.

Project

Tehri Pumped Storage Project

Year

2013-ongoing

Location

Uttarakhand, India

Client

HCC Ltd, THDC Ltd

 

1000
project with all components underground
830
upstream reservoir level
615
downstream reservoir level

The 1,000MW Tehri Pumped Storage Plant (PSP) is part of the 2,400MW Tehri Hydro Power Complex and is being developed by THDC India, a joint venture of the Indian Government and the State Government of Uttar Pradesh. Made up of four reversible pump turbine units of 250MW each on the left bank of the Bhagirathi River, its operation is based on the concept of recycling water discharged between upper and lower reservoirs 

SMEC has been working on the project since 2013, addressing design issues encountered by another consultant and proposing alternate and ultimately successful first-of-their-kind designs. 

 “Rather than adapt during construction, our use of 3D modelling enables us to anticipate issues and devise solutions in response… The project had faced challenges with safety issues previously, so our ability to foresee problems and prevent potential incidents has been highly valued.”

– Neeta Arora, Director Design Centre

Geological challenges lead to a first-of-its-kind design
All the components of the Tehri Pumped Storage project are located underground, essentially inside one hill within the vicinity of the existing 1000 MW Tehri Hydro Power Project. 

The upstream and downstream surge shaft chambers were proposed to be 20-25m wide. As can happen with such projects, as geological information became available, it was apparent that the geological environment was too poor to construct chambers this wide 

Through extensive 3D analysis, including modelling rock bolting to replicate actual underground conditions, we re-planned the chambers and a width of 15m was determined as the best solution. However, the hydraulic conditions made it impossible to reduce the surge shaft diameter 

With a team of global experts in hydropower, tunnelling, and dams on the project, we designed a surge shaft chamber with the surge shaft slanting inward, in inverted form. This is the first time such a solution has been adopted in India, and potentially worldwide,” says Prashant Agrawal, General Manager, Hydropower and Dams “It was made a reality through the vast experience of the global specialist team.  

Optimising solutions through technical expertise
A previous consultant had planned for the tail race tunnel (TRT) outfall structure to be utilized as the inlet/outlet structure for the Tehri Pump Storage Project. However, this proposed arrangement had failed in physical model studies.  

Through a variation order, SMEC took up the challenge of proposing an alternate solution. Using detailed numerical modelling studies, we proposed converting the two larger outlet structures into four smaller ones. This modified TRT configuration was confirmed through physical model studies, bringing critical parameters including exit velocities, submergence and equitable distribution of flows under control. 

Safety as a priority
While the design solutions will help the project meet its deadlines and technical expectations, our digitally-enabled approach also enhanced safety on the project. In particular, the complex 3D analysis done on the underground caverns ensured the safety of all involved during excavation and operation. Rock bolting was modelled for each round of excavation, replicating the actual underground conditions. As a result, and despite poor geological conditions, two caverns have already been excavated while third is under construction and more than 50% complete 

 “Rather than adapt during construction, our use of 3D modelling enables us to anticipate issues and devise solutions in response,” says Neeta Arora, Director – Design Centre “The project had faced challenges with safety issues previously, so our ability to foresee problems and prevent potential incidents has been highly valued. 

While of immense value to the project, this will not only optimise solutions for our client but also shape changes in the geotechnical industry locally and internationally.” 

Collaborating with the surrounding communities on the project has led to many new job opportunities and associated development for the cities around the project location. Once complete, the Tehri Pumped Storage Project will further support the development of neighbouring areas, providing more reliable power supply that will boost employment and revenue.  

Download Technical Paper
Download the paper “3D Analysis and Design of Surge Shaft Chambers for Tehri HEP in India”, presented at the Underground Design and Construction Conference 2015. 

 

Project

Tehri Pumped Storage Project

Year

2013-ongoing

Location

Uttarakhand, India

Client

HCC Ltd, THDC Ltd

1000
project with all components underground
830
upstream reservoir level
615
downstream reservoir level

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