Large structures: Working against the clock
By Helen Wright14 November 2012
Large structures such as dams, waterways, bridges and large buildings require vast quantities of materials to build, as well as labour, machines and, of course, money. A tailor-made approach to the equipment used in construction, as well as the logistics of getting everything onto often remote sites at the right time, is crucial to ensure these projects run smoothly.
One of the largest projects currently underway in the world is the expansion of the Panama Canal in Central America. Work on the US$ 5.25 billion mega project started in 2007 and is likely to be completed by the end of 2014, but while dredging work is well advanced, construction of the new locks is said to be seven months behind schedule due to design changes.
Nevertheless, placing of structural concrete is now underway on these elements of the scheme – a huge challenge thanks to the sheer scale of the project. According to Putzmeister, whose concrete pumping and placing equipment is being used on site by contractor consortium Grupo Unidos por el Canal (GUC) to help construct the third set of locks for the project, a massive 4.5 million m3 of concrete will be required for this phase. GUC comprises four companies – Sacyr Vallehermoso, Impregilo, Jan De Nul and Constructora Urbana.
The third set of locks – consisting of two 427 m long by 55 m wide by 18 m deep structures, one on the Atlantic Side and one on the Pacific side of the Canal – will create a new third lane of traffic, doubling its capacity and allowing longer, wider ships to pass through.
GUC brought in 12 Putzmeister Telebelt TB 130 telescopic belt conveyers to help construct the bottom portion of the new locks, while a new Telebelt TB200 is set to join the other machines before the end of the year. With a reach of 61 m, belt width of 610 mm and high capacity output of up to 4 m3/min, the TB 200 is the company’s newest, most advanced Telebelt. It will be beneficial for reaching the tallest portion of the lock walls, and will allow for even quicker placement of material.
Lucio Donadi, service manager for Agreconsa – one of the contractors in the GUC consortium – said, “The Telebelts are true multi-taskers and have been crucial in laying the foundation for this project. With their help, we are quickly finishing the bottom portion of the new locks.”
Working in conjunction with the Telebelts, six Putzmeister Jumbo Troughs are also serving as surge hoppers for consistent concrete placement. Four Thom-Katt TK 40 shotcrete machines are also on site, being used to stabilise excavation work on both the Atlantic and Pacific sides of the canal, while three Putzmeister 58 m and one 52 m truck-mounted concrete boom pumps were brought in to help build the lock walls. Two boom pumps are working on each side of the project.
Bob Weiglein, Telebelt division manager for Putzmeister America said, “On either side of the canal, we are dealing with two very different types of land. While we’ve encountered landslides and unstable soil on the Atlantic side, the Pacific side is rock, which has caused a host of other problems.”
The sheer size of the Panama expansion project has added unique difficulty to the placement of the massive amount of concrete, and resulted in a demanding pour schedule, Mr Donadi explained.
“The target monthly average of concrete to be pumped is approximately 100,000 m3 at each side of the project. We are placing concrete somewhere on site 24-hours-a-day. We’re pleased that the Putzmeister equipment has stood up to the challenging schedule. The ease of set up of the boom pumps has been beneficial, as well. With so many moving parts on site, having equipment that is easy to manoeuver is a huge time-saver,” he said.
Elsewhere in the world, the construction of dams for hydroelectricity generation continues – large-scale projects that are proving popular in both developed and developing countries alike.
But construction remains a significant challenge given the often remote areas that dams are located and the sheer volume and strength of concrete and other materials required to hold back the water.
A development in northern India to build a dam spanning a remote section of the Alknanda River in Uttarakhand illustrates these challenges. Potain, which supplied two MC 475 special application cranes for the project, said access to the job was a huge challenge because steep valley walls and mountains surround the site and required careful planning when transporting the tower cranes.
Apurba Kumar Mandal, territory service manager for Manitowoc Crane Care in India, was part of the team that moved and assembled the cranes. He said checking the roads and planning the route was the most difficult part.
“The roads leading to the jobsite are not designed for transporting heavy equipment, so our engineers checked that they were in good condition before shipping the cranes,” he said.
“Monitoring ground conditions and planning the transport schedule was a large part of this job. But once on site, the cranes were easy to assemble. The connections are smooth and the modular design makes the assembly process logical and straightforward, even for such large cranes.”
The 25 tonne capacity cranes are lifting general construction materials for contractor Larsen & Toubro to build the US$ 730 million dam, which will measure 285 m across and 92 m tall. The four-year project will create a 330 MW hydroelectric power station.
The ability to tailor equipment to specific projects is crucial in the field of large structures. On another hydroelectric project, for instance, Alisina provided climbing and shoring equipment to help with the construction of the Barrage Martil Dam in Tetouan, Morocco – said to be the most technically complex dam currently under construction in the country.
The project, which is expected to be completed by the end of 2012, also includes the construction of drinking water structures to convey and treat the additional quantities of water from the dam.
Alisina delivered a T1C one-sided climbing system with Multiform wall system and an interior climbing system to help construct the spillway for the dam. In addition to this standard equipment, Alsina also developed a bespoke solution using a 50TN support bracket and the Multiform system to be used where the construction was more complex. The manufacturer said concrete pouring for the project had so far been a success.
Falsework and formwork manufacturers are also in high demand to support the construction of large structures, and must tailor their equipment to each individual project. Peri focussed on reducing construction time by providing pre-assembled shoring equipment for the complex Holtwood hydroelectric power station expansion on the Susquehanna River in Pennsylvania, US, a project designed to increase the plant’s generating capacity by 125 MW.
The expansion includes a new intake structure as well as a powerhouse. Most of the new facilities’ structural components are characterised by their large dimensions, resulting in high loads being imposed on the formwork and shoring systems.
Contractor Walsh Construction used Peri’s Variokit heavy duty shoring towers to transfer the loads from the slabs for the new intake structure. Slab thickness ranged from 4.6 m to 13.2 m, and three separate six and four-legged Variokit towers were aligned in a single row in each of the bays, each capable of transferring maximum leg loads of 660 kN into the ground.
Peri delivered the shoring tower modules to the jobsite preassembled so site-work was kept to an absolute minimum.
Similarly, on another project to expand the high-speed rail network through Mulhouse in France, formwork manufacturer Meva worked with contractor Maïa Sonnier to support construction of new tunnels and bridges and ensure the project was completed on time.
The rail line passes over the Rhine-Rhone canal on a 20 m frame bridge, the construction of which was the biggest formwork challenge of the entire project, according to Meva. No bridge piers could be erected in the canal bed because they would have impeded shipping traffic, so the only solution was constructing the bridge in the form of a wide and long rectangle covering the entire width of the canal and resting on a row of columns on either bank.
Formed using Mammut 350, the columns are 1.6 m by 1.3 m wide and 1.3 m by 1.3 m long, with a centre-to-centre distance of 3 m. Mammut 350 was also used to form the 1.5 m high and 2.1 m wide concrete beams that rest on the columns and carry the concrete parts that make up the bridge superstructure.
These concrete parts – each weighing 40 tonnes – were poured on site, then placed with a crane onto the bridge beams and supported by MEP HD (heavy duty) props.
New airport terminals are also springing up around the world – another example of large structures that require tailored construction approaches, particularly when it comes to lifting ready-made components into place.
Two Terex CC 2800-1 lattice boom crawler cranes worked in tandem to help erect the steel frame for the maintenance hangar at the Berlin-Brandenburg International (BBI) airport in Germany.
Sub-contractor MAXIkraft Kran- und Schwerlastlogistik lifted both the 613 tonne door truss and the 240 tonne roof truss central section, on behalf of Industriemontagen Leipzig, using the Terex machines.
The door truss was first lifted and stabilised by the two CC 2800-1 units (working as the operation’s primary crane tandem team) with the help of another two 500 tonne telescopic cranes, after which it was moved 15 m to its final horizontal position. Once there, the truss was brought to an installation height of
30 m between the outer walls, where it was anchored.
However, while large structures like airport terminals and dams are usually built some way from urban areas, this is not true of some other projects. Thirteen Liebherr tower cranes are planned to cram into a crowded urban construction site to build a new hospital in Stockholm, Sweden, for example – a project that requires high precision anti-collision systems to be in place.
Six new towers ranging in height from six to fifteen storeys are under construction, and nine Liebherr tower cranes are currently on the 320,000 m2 Karolinska Solna University Hospital site. A further four will be delivered for contractor Skanksa over the next 12 months.
Richard Eriksson, Skanska’s crane & hoists operations manager said, “We are extremely aware of the importance of safety with this high density of cranes. With some of the jibs just 2.5 m apart, it is essential that there is no overlap at any time on this very crowded site.”
French anti-collision specialist’s technology Ascorell Systems has been fitted to every crane, together with Liebherr’s ABB system identifying dead zones.
As a further concern for the crane operators, the site is below the flight path to the old hospital’s heliport with helicopters flying just 20 m above the 100 m high Liebherr cranes, ensuring that crane heights cannot be increased under any circumstances.
At the peak of construction, Skanska said it expected that at least 30 mobile cranes would be employed on the site – with the majority being Liebherr mobile cranes.
They will be in constant demand unloading the nonstop supply of the pre-cast elements from the delivery trucks – with deliveries to site every 40 seconds and trucks adhering to strict ‘spot’ delivery times.
It is incredible to think that the logistics of such large projects can be planned down to the second, and a testament to the progress being made in management when it comes to building large structures.