China remains an important market for shotcreting equipment and technology manufactured by Sika Tunneling and Mining (STM) of Switzerland. STM has had a presence in China since the introduction of China’s current ‘open door’ policy in the early 1990s, supplying initially the Aliva dry-mix rotor type machines, shotcrete booms and dosing unit components for assembly in China onto domestic mobile carriers.
STM’s latest export to China is an order from the client organisation of a spectacular project set in the historic Wutai County, the Xilongchi hydropower project in Shanxi Province. Designed by the Beijing Guodian Water Resources & Electric Power Engineering Co for the joint owners the Shanxi Electric Power Company and the Shanxi Local Electric Power Company, the project will take advantage of the highest hydraulic head of energy potential in China to drive four 300MW turbines in an underground powerhouse complex. Release of water from the upper 4.3Mm3 reservoir into two high pressure shafts and through 640m hydraulic head will allow 1805GWh of electricity to be generated each year. The turbines will then use off peak power to pump the water back to the upper reservoir, repeating the generating cycle.
Construction of the US$533M project started in June 2002 and is programmed over six years. The first turbine is scheduled to be on-line by April 2008 with the last commissioned by August 2009. To realise the project, more than 3.3Mm3 of earth and rock excavation and 8.7Mm3 of rock fill will shape the two man-made reservoirs.
The underground works, including the main 149.2m long x 23.55m wide x 49m high powerhouse cavern and the two 730m long x 3.5m-5.2m diameter high-pressure shafts and four 434m long tailrace tunnels, comprise more than 612,000m3 of excavation; and more than 439,000m3 of concrete and 1,586t of steel will be used to build the project.
Support of the underground powerstation excavations in the area’s competent medium-strength limestone comprises systematic rockbolting and 200mm thick application of wet-mix steel fibre reinforced shotcrete. Given the ready availability of construction labour in China and the country’s responsibility to provide employment to often unskilled workers, drilling charge holes for drill and blast excavation of the underground works is by hand using hand-held jack-legs.
For high-volume application of the shotcrete support, the project engineers realised the need to import shotcreting units from abroad and ordered two Sika-PM500 PC shotcrete mobiles from STM.
The Sika-PM500 machines are manufactured under the strategic alliance with Putzmeister of Germany. Each machine comprises popular BSA 1005 Putzmeister concrete piston pump, with a SA13.9 nozzle boom, an Aliva nozzle manipulator with its nine-movement pattern, and an Aliva-403 plc-controlled accelerator dosing unit mounted on a diesel-driven Lorenzana carrier. To avoid a stationary compressor the Sika-PM500 are equipped with an 11.5m3/hr compressor.
“There are wet mix shotcreting machines manufactured in China,” said Mr Arvin Yu, director of Harvest Industries and agent for STM in China, “but these are not of sufficient power, particularly when steel fibre is added.” Mr Yu explained that the theoretical maximum capacity of the Sika-PM500 PC shotcrete machines is 30m3/hr without fibre and up to 15m3/hr for 45kg/m3 fibre shotcrete. “Local wet-mix machines have a theoretical capacity of 11-12m3/hr, certainly no more than 15m3/hr maximum and a practical limitation of about 7-8m3/hr. With fibre added the output in practice drops dramatically to no more than about 3-4m3/hr – depending on the skill of the operator,” said Yu. “This limitation is influenced significantly by the less robust booms manufactured in China, which also have reach limitations. Locally produced booms are few in number,” he explained, “and these have a reach of about 11m from the ground to the rock face. The Sika-PM500 PC units with the SA13.9 booms, provide a reach of 15.5m from the ground to the nozzle and a maximum of 16.7m with the 1.2m spraying distance added.”
The two imported machines arrived at the Xilongchi site in March 2004 and the workers were advancing through the learning curve to reach optimum output. Together with learning the operation of the machines, this relies on so many additional factors. Yu listed among these the design and workability of the concrete mix; the logistics of concrete delivery from the batching plant; the compatibility of the accelerator to the different types of cement used in all different parts of China; and the skill and experience of the operators.
“There is also a need to break some bad habits that creep into the shotcreting process,” said Yu. “For example, full bags of fibre are often loaded into the batching plant mixer in one go rather than adding fibre slowly or by using a fibre-dosing hopper to the plant. Aggregate is also often not screened and big stones need to be picked out by a worker posted beside the hopper of the shotcrete machine.” The screen size on the concrete pump hopper is also often increased to increase feed of concrete and hopefully increase production. If the aggregate hasn’t been screened initially, this allows big stones to pass into the system and cause time consuming and damaging blockages.
“So delivery of a new machine always requires more than explaining the operation and maintenance,” said Yu. “It involves training operators to apply shotcrete skillfully as well as giving advice in the batching plant; sending cement and concrete samples to laboratories to help prepare a suitable mix and a compatible set of additives, including accelerator; and helping to solve logistical problems such as efficient delivery of concrete from batching plant to shotcrete machine.”
Within China’s tremendous push towards rapid expansion of its power, transportation and water management infrastructure, there are business opportunities for international suppliers who are conscious of the particular nuances of doing business in China, of working around the language barrier, and of respecting the astute business acumen of the Chinese customer.
STM maintains a good reputation in China and the new Sika-PM500 PC units on the Xilongchi project are the only project imports for its realisation. All other construction equipment is supplied within China. During a visit to the site, Mr Yu explained that “slowly, slowly, all things are changing and improving in China.” In tunnelling this includes a greater appreciation for high production, efficient logistics and improved quality of construction – aspects that STM with its presence, transfer of technology, and supply of modern equipment is making a contribution.
