Tunnel visions16 November 2001
Tunnelling can be one of the most complex parts of hydro power projects. IWP&DC takes a look at some of the latest industry developments
Aquatic Sciences of Ontario, Canada has successfully completed an inspection of the 9.8km tailrace tunnel for Meridian Energy at the Manapouri power station in New Zealand. Using an underwater remotely operated vehicle (ROV), ASI surveyed the entire flooded length of tunnel in less than 24 hours using the ASI Mantaro, .
Meridian Energy of Christchurch, New Zealand, operates the Manapouri station, located at the west end of Lake Manapouri, in the south island. The hydroelectric facility draws water from the lake through seven penstocks to underground turbines. The water then discharges through a 9.8km long tunnel into Deep Cove, Doubtful Sound and eventually into the Tasman Sea. This tunnel is known as the first Manapouri tailrace tunnel, or 1MTT.
The plant was constructed to take advantage of the potential 178m difference in elevation between Lake Manapouri and Deep Cove. However, due to higher than anticipated friction in the tailrace system, the full potential has never been realised - the station has never been able to safely produce more than 585MW of a potential 700MW of power. A number of attempts to detect and/or significantly reduce this head loss have been unsuccessful. Due to the ever increasing demand for power and additional generating sources, a second tunnel (2MTT) is now under construction by using a tunnel boring machine (TBM) that runs parallel but approximately 75m to the south of the existing tunnel.
The remote inspection protocol included the ASI Mantaro, a long tunnel inspection ROV, tethered by a sophisticated umbilical that transmits sonar and video data real-time to the surface via fibre optic telemetry.
ASI has completed continuous surveys of 10km from a single access point using this robotic system, including inspections of a 120km water supply tunnel in Finland and an 8km headrace tunnel in Chile.
THE AIR THAT YOU BREATHE
In the tunnelling industry, health risks from air-borne particles and significant reduced life expectancy for underground workers is of great concern. Contractors' obligations to maintain a high air quality have to be met but at an acceptable energy cost. To help alleviate this problem, Norway-based Protan has developed a remotely controlled underground environment monitoring system that can monitor, moment-to-moment variations in tunnel atmosphere and automatically adjust the airflow.
The Intelligent Tunnel Ventilation (ITV) system monitors a full range of sensors collecting data for blasting fumes, diesel exhaust, methane, dust, extensometers, water pumps and computerised drilling rigs and tunnel boring machines. Built-in alarms indicate when air pollution rises to pre-programmed levels. ITV also collects input from other sensors measuring fan RPM, air output, and energy consumption. To protect against leaks, vent line pressures can be collected from pre-set points.
The result is a continuous, detailed picture of the tunnel atmosphere and the ventilation system. Computer feedback to pre-programmed sensors adjusts fans speeds to deliver, at any given moment, the right amount of air and maintain the optimum working environment. Program parameters can be changed to optimise the ventilation system while the system is running. Everything can be controlled from the site office using programs customised to the individual site requirements and all data is documented and saved.
Although Protan's ITV can be cabled, there is also a radio-based system which can support a range of add-ons. These include an integrated, on-site mobile phone system, personnel 'tagging' for security and safety and pre-set hot-key connection to suppliers and the emergency services.
A specialist catalogue from UK-based Woods Air Movement has been developed as a comprehensive guide to using the company's extensive range of Jetfoil and large JM Aerofoil fans for tunnel ventilation. The 52-page directory inspects a range of applications and gives advice on how Woods' equipment can provide solutions to tunnel ventilation problems. In addition to application advice, the catalogue includes a section on various methods of tunnel ventilation, product specifications and a step-by-step guide to calculating precise fan thrust requirements. There is also a section which demonstrates the correct way to install products for optimum performance.
'We designed the catalogue as an on-going communication tool, using a loose-leaf format which can be regularly updated with new information as it becomes available,' says Peter Hunnaball, industrial and commercial marine manager at Woods Air Movement. 'We wanted to change the concept of the catalogue to provide an invaluable handbook that would maintain a continual flow of information and allow us to develop strong relationships with our customers.'
WIRE BRUSH TAILSEALS
In segmental tunnelling, the gap between the inside of the tailskin and the outside of the segment can often be efficiently sealed by fitting rows of wire brush tailseals. Used in conjunction with specially formulated fibrous lubricants, these types of seals provide a low friction and airtight emulsion between the TBM and the tunnel lining.
Lanesfield Engineering Seals of the UK supplies wire brushes for both machine builders and contractors. Seals available from the company are specially designed to withstand the harsh conditions of the tunnelling environment. For less demanding applications, Lanesfield also offers spring plate seals available individually or as pre-welded sets, and fitted in one, two, three or four ring systems.
According to the company its wire brush tailseals, in conjunction with the correct lubricant, can withstand water pressures up to 9 bar.
At Underground Construction 2001, held in the London Docklands, UK from 18-20 September, a variety of companies involved in the tunnelling and construction industry were exhibiting. Here's a brief roundup of the big issues and those who were on show.
•Hunter Personnel Contracts (HPC) is a UK-established consultancy focused on providing human resources for companies associated with the tunnelling and construction industries. It provides dedicated on-site training teams to assist in the development of personnel at the time of new operation start up. This training is custom designed to suit each client and focuses on the development of the practical skills needed by personnel within the field engineering environment..
See www.hunterpersonnel.com for more details.
•A 3.8km tunnel transporting water from the US$150M Mananga dam to the Tisa treatment plant is being planned by Cenu Water Authorities in the Philippines.
•Picture perfect: QA Photos specialises in publicity photography of construction projects, specifically underground schemes. QA says it aims to produce cost-effective, memorable photographs which safeguard their clients' interests by supplying positive and safety conscious images for advertising and display purposes. URL: www.qaphotos.com.
Laura Donaldson is a freelance artist specialising in tunnel and construction projects. Working in oils, acrylics and watercolours, her works are commissioned for publicity or for adorning clients' office walls. Email:[email protected]
•The Philipp Holzmann Group has worked on many construction projects, including the Ertan hydro power plant in China where three large caverns had to be excavated in rock for the turbines, generators, transformers and surge chambers.