IWP&DC presents details on the latest equipment available on the market for tunnelling work at hydro power projects
Tunnelling can be one of the most complex parts of hydro power projects. Making sure you have the right equipment can be essential for the successful, and safe, development of a scheme. Here, we take a look at some of the equipment available on the market and investigate how they have been used at current development projects.
Developing Dakmi 4
Drilling contractor Song Da on Vietnam’s Dakmi 4 hydro power plant has taken delivery of two purpose-ordered Sandvik DT820 jumbo drill rigs; which despite encountering severe rock conditions are proving the key to keeping the tunnelling contract on schedule. Both units were ordered by Open Asia Heavy Equipment.
The proposed 172MW hydro power plant is located some two and a half hours drive west of Vietnam’s third city, Da Nang and close to the Cambodian border and will include a 420m long x 87m high concrete dam to hold back the Dakmi river; creating a 1450ha reservoir.
But it is rock conditions in the 3.37km long tailrace tunnel which is creating major problems for main contractor, Ho Chi Minh City-based IDICO and Song Da. Poor rock comprising sediment and badly fragmented and decomposed granite complying with Vietnamese standards of Class II, 1B, 1A2, 1A1 and edQ + eQ are being encountered.
At the power house portal conditions were particularly severe. With drilling starting at the beginning of May, advance rates were very slow and arduous. Up to 40 x 4.5m long rock bolts in two rows were installed at an angle of 15º together with steel mesh and shotcreteing plus erecting steel girders around the portal entrance.
The poor rock conditions continued to cause problems for Song Da 10m into the tunnel. As a result the contractors opted to halt proceedings and open a new temporary adit 195.7 m long to allow access into the proposed main tunnel.
By the end of May the adit had been completed allowing Song Da to open two new faces – one towards the inlet portal and the second back to the power house and outlet portal. Achieving advance rates of 4.5m/day in the adit, Song Da are hoping to meet a similar schedule in the main tunnel. Whilst rock conditions have improved in the new workings, some rock bolting is still required although the contractor is confident they can make-up lost time with the new Sandvik rigs.
Featuring two booms and a basket boom, the Sandvik D820’s are fitted with Sandvik 4.9m shank adapters and couplings. Throughout drilling at the 43.2m2 tunnel faces at the outlet end, Song Da are drilling 115 holes including the three x 102mm dia opening holes. For these, Sandvik R32 reaming bits are being used.
At the inlet end with a larger diameter 49.34m2 tunnel cross section, drilling with the second Sandvik D820 has been halted following a tunnel collapse, having advanced 145m. Following the clean up of an earlier collapse, a second ‘cave in’ has resulted in a 40m high hole to the surface with a 5m diameter.
Currently 40 concrete segments 35cm and 20cm thick and meeting 250 MAC standards are being installed around the perimeter of the tunnel wall; advancing in 40cm increments. (www.sandvik.com)
The Niagara project
The Niagara Tunnel Project is an ambitious project to tunnel 10.4km from the Sir Adam Beck Generating Complex to above Niagara Falls. The new tunnel will increase the power supply for owner Ontario Power Generation (OPG) by 150MW and will help to bolster the current power system, which is close to exceeding its capacity during peak months. OPG awarded the construction contract to Austria-based strabag AG, who chose a 14.4m (47.5 ft) diameter Robbins Main Beam TBM to bore the tunnel – named Big Becky. The setup also includes a 105m long back-up system, which will transport 1.7Mm3 of muck over three years via conveyor belt.
The tunnel is located predominantly in Queenston shale with some limestone, dolostone, sandstone and mudstone up to 200 MPa (29 ksi) UCS. The rock along the tunnel bore path is known to have high in-situ stress and there is potential for squeezing ground. An initial rock support lining of wire mesh, steel ribs, rock bolts, and shotcrete will be installed as the TBM advances. After tunnel excavation is completed, an in-situ placed concrete lining will be installed, and the final lining will include a waterproofing membrane system to ensure that water does not seep from the tunnel into the rock and cause swelling.
The Main Beam TBM, the largest hard rock TBM in the world, was assembled onsite in under 12 months – ahead of a tight delivery schedule. The onsite assembly is considered unprecedented for such a large TBM. The TBM began boring in September 2006.
The Main Beam TBM is the also first ever to utilize back-loading 20-inch cutters, which increase cutter life and reduce cutter changes in hard rock. Both 19-inch and 20-inch cutters can be installed in the cutterhead. The machine has a cutterhead thrust of 18,462 kN (4,150,422 lb) and a maximum torque of 18,670,000 N-m (13,770,285 lb-ft).
Following the completion of a planned outage on the TBM and conveyor, and the delays caused by the fall of Queenston shale and a small portion of the tunnel liner on 11 September, the TBM resumed operation on 8 December. Since restarting, the TBM has advanced 39m (at the time of going to press) and is now at the 5457m point, more than half way through the 10.2km journey.
Outage maintenance included TBM cutterhead repairs, modifications to the dust filters and ventilation ducts, repair of the excavated material conveyors and general maintenance on the other tunnelling equipment.
The invert concrete (bottom of the finished tunnel) is now being installed and has advanced over 3000m. It is ahead of the target schedule. Assembly of equipment that will be used to install the tunnel arch (roof) is ongoing. Work on the intake structure, located at the International Niagara Control Works, about 2km upstream from the Horseshoe Falls also continues as planned. (www.robbinstbm.com)
Inclined, horizontal or shaft boring
Germany-based Aker Wirth delivers boring machines that are used in the exploration, mining, construction and tunnelling industry as well as in the construction of hydro power plants.
Aker Wirth’s history traces back to 1895 and the company entered into international business early in the 19th century. At the end of the sixties, TBM’s were added to the product portfolio.
In construction of hydro power plants, Aker Wirth’s TBM’s are used for the excavation of tunnels which serve as penstock, headrace tunnels, tailrace tunnels or access tunnels.
Tunnel boring machines for inclined boring were amongst the first machines manufactured once the company started its TBM production. A so-called back-stop device is the most important equipment the machine needs to be furnished with. This device safely keeps the TBM in its inclined position. Aker Wirth designs these devices for its TBM in-house. Aker Wirth’s x-shaped gripper system provides support to the TBM during tunnel boring and has helped the machines to achieve excellent performance in many projects worldwide, says the company.
For horizontal boring, Aker Wirth designs open type TBMs for excavation in hard rock and shielded TBMs for closed mode excavation in unstable ground. The machines are furnished with all equipment for the installation of the tunnel lining concurrently with the boring.
For shaft boring, Aker Wirth’s full size shaft boring machines and the company’s raise boring machines are well-recognized products in the industry worldwide, says the company.
Aker Wirth’s TBMs have recently been used for boring in the Kops II pumped storage project (Austria), Limberg II pumped storage project (Austria) and in the Ermenek hydro power project (Turkey). At present, the company designs and produces an 8m diameter TBM for excavation of an inclined tunnel in the Linth-Limmern project (Switzerland). This TBM will be used for the largest diameter inclined bore to date. (www.akersolutions.com)
Flex and inject
When working on tunnelling projects, waterproofing is obviously a major issue. RASCOflex AY108 from rascor is a versatile, environmentally compatible, polyacrylate-based, modified 2-component injection grout. A standard material, it can be used in most waterproofing applications, whether for the remedial grouting of cracks and joints or, in conjunction with the Rascotec injection systems, for preventative waterproofing systems, says the company. Features of the system include: stabilized gel; non-corrosive; high frost resistance; no adhesion required to sides of joint/crack; very high reactive and reversible swelling action.
Also from Rascor is the RASCOflex AY808, which is especially suited for works in tunnelling or specialised underground engineering works, which require a large volume of material, for instance the filling the cavities, backing injections or ground injections. Features of this system include: reactive and reversible swelling action; suitable for use in humid and wet environment; suitable for every mineral basis; stabilized Polyscrylate suited for use in large volumes.
The company also offers the RASCOtec injection channel, which is fitted with a flexible foam insert that enables it to lie flat over any base. The system is suitable for waterproofing all types of construction joint in general building and civil engineering works.
Features include easy fixing, 25mm wide contact surface over joint, no obstruction to steelfixing or formwork erection, may be worked as wood, multi grouting possible, remains flexible in the cold, and offers weather independent installation. (www.rascor.com)
Construction kit
There are many who look back with happy memories at the time when one could playfully build a technical world with the toy
construction kit. This idea and the experience gained from many civil engineering projects have been sources of inspiration for Peri, which has developed Variokit – a versatile construction kit with rentable, standardized components for numerous requirements in civil engineering.
The bene?ts of the Variokit formwork carriage include: few anchors required in wall areas due to system walers up to U 200; simple modi?cations for different cross-sections; optionally available hydraulic support for shuttering and striking as well as lifting and lowering; self-propelling or mobile solutions for moving complete units.
All components can be optimally adapted says the company: the HD 200 heavy-duty prop allows continuous height adjustment and grid-free longitudinal arrangement; the RCS slab beam can be ?exibly adapted; and the Variokit diagonal strut is continuously usable from 4m to 9m.
The extremely high loads carried by a tunnel formwork carriage during mined operations present a special challenge for Peri Variokit. In order to effectively manage the forces and, at the same time, provide construction site traf?c an access portal, the Variokit with anchoring components combination is supplemented with the SB brace frame system.
For smaller tunnel lengths (< 40 cycles) with short section lengths (< 20m) and tight construction schedules (< 12 months), solutions using rentable parts are considerably more cost-effective than complete project solutions with special steel components.
For tunnels constructed using mining techniques, the formwork is designed whilst considering ancillary conditions which are, in part, not compatible: large loads resulting from the fresh concrete pressure and dead weight; low individual weights due to tight space conditions during assembly and operations; minimum of material costs from high proportion of rental parts and small quantities; few operating elements and optimally adapted to suit construction progress; and simple operation of large units.
The system has a wide range of components, and components which have a mutual function are put together in groups. For example, a group consisting of heavy duty rollers or elements for lifting, lowering or moving.
Fundamental details such as scaffold tube connector as side protection is taken into consideration just as much as technical working requirements (e.g. concreting stud).
Also optimal additional components like the drive mechanism, electrical or hydraulic components are part of the wide range of possibilities provided by the Variokit, says Peri. (www.perime.com)