AES Corporation has been carrying out work to extend the operating life of the 1000MW Chivor Hydropower Project which provides 6% of Colombia’s power demands. Chivor entered into service in 1977 with an initial life expectancy of 50 years and the company hopes this new work will extend operations for a further 50 years or more.
In a paper published in Water, David del Rio and his co-authors discuss this one-of-a-kind renovation project which will use a modern lining to address the buckling of a headrace tunnel, all while the plant remains in operation.
The problems can be traced back to the construction phase when two separate events occurred that directly affected the installed lining at one of Chivor’s two headrace tunnels. According to project records, the buckling occurred due to injection pressure during construction in the first case, and later due to the action of overpressure coming from a leak in the tunnels.
Corrected in 1981, the first buckling section of the tunnel was addressed with the installation of a steel pipe with conical transitions at its ends. In December 2019 dewatering was scheduled to remove weak material around the second buckling area and to install a new pipe. AES has been assessing the state of the pipelines since 2000, and its condition assessment led to investigations to select one of four different design alternatives to renovate this important part of the plant’s infrastructure.
The selected alternative considers a self-supporting lining capable of providing the appropriate structural resistance for different load conditions: material handling, internal pressure loads, temperature variation, and external pressure loads exerted by the water table over the empty tunnel.
As the authors explain, the detailed design allowed for obtaining the minimum wall thickness for handling, and the dimensions of straight pipe sections, transitions, and external stiffening rings. The material selected to build the new lining incorporates high-resistance technology and facilitates welding processes that must be carried out during the construction phase. Several issues also need to be addressed in a comprehensive investigation for the next stage, including but not limited to welding times, construction costs, construction schedule, logistic processes, and risk analysis.
Fire experiments
In their study published in the Journal of Safety Science and Resilience, Liu et al have carried out full-scale fire experiments at a hydropower station to investigate smoke propagation during tunnel construction.
In general, full-scale experiments model real smoke propagation scenarios and actual smoke development parameters, largely supporting the optimisation of smoke exhaust and emergency response. However, because the underground space of a hydropower station is composed of different types of caverns, the authors claim that current full-scale experiments in areas such as the main power houses and conjunction areas have not yet adequately presented complete fire scenarios and fire propagation processes in hydropower stations. Focusing on this gap, they built full-scale fire scenarios in an access tunnel, which is representative of traffic, construction, and tailrace tunnels, as well as corridors that occupy most of the underground space of a hydropower station.
The distributed temperature in the tunnel was measured for real-time recording of the smoke propagation process, combined with on-site observations. The flame height of the diesel pool fire, smoke temperature evolution and distribution, and smoke stratification and descent were analysed, and these results could provide on-site fire scenarios and data support for smoke control design and fire emergency response plans in hydropower stations.
Indian TBM
In other news, TERRATEC has announced that its Ø9.86m Hard Rock Double Shield TBM has made significant progress at the Vishnugad-Pipalkoti Hydropower Project in India, successfully excavating 431m in January 2024.
The TBM is the largest double shield machine in the Indian Himalayan Region and is currently working for Hindustan Construction Co, the primary contractor for this project. Specifically designed for the construction of a crucial low-pressure13km long head race tunnel, the TBM’s cutterhead boasts 19” disc cutters and twelve large bucket openings, facilitating excavation through expected hard rock with its 4200kW electric main drive delivering a torque exceeding 22,000kNm. As the TBM advances, universal reinforced concrete lining rings, 1500mm wide and 350mm thick, are installed, each comprising five segments plus a key.
TERRATEC is also providing its Continuously Advancing Tunnel Conveyor for the project which is capable of handling the various materials extracted by the TBM, expected to vary from sandy gravel to boulders.
Situated in Uttarakhand state, this 444MW run-of-river scheme incorporates the construction of a 65m high diversion dam across the Alaknanda River and a 3.63Mm3 reservoir. A diversion/spill tunnel, intake tunnels, underground sedimentation chambers, a headrace tunnel, a surge shaft, pressure shafts, and penstocks, along with two separate underground caverns for turbine and transformer installations, constitute the water conductor system.
Multipurpose tunnels
Research undertaken by the Tunnelling Institute of Pakistan and the University of Huston in the US, has proposed the innovative use of an existing road tunnel for water conveyance and power generation. Several road tunnels have recently been built in Pakistan’s northern region, near mountain peaks and bodies of water, and discussion focused on the feasibility of using an existing road tunnel on a high-speed, controlled excess motorway for multipurpose use by taking advantage of natural terrain features. The hybrid tunnel will result in significant cost savings compared to constructing a tunnel for a hydroelectric facility and in addition, the outflowing water can be used for irrigation of agricultural fields. The proposed site used in the study was the 1.3km long Tunnel No. 1 on the Swat Motorway, located close to the Swat River in Pakistan. The authors say that such measures will help the country which has been facing energy shortages for the past two decades and currently has a shortfall of over 5000MW.
This article first appeared in International Water Power Magazine.
