HAMM Vibratory Compactors 3412 HT compact an embankment dam at the foot of the Andes

They have been in operation for months now, in the valley of the Río Blanco: day in, day out, two untiring HAMM Vibratory Compactors 3412 have been moving up and down in their lanes, lending an impressive structure the stability it needs. The structure in question is the southern boundary of the 5 km² reservoir in Ovejería, near to the town Til-Til. Here, the Chilean company Minería y Montajes Con-Pax S.A. is constructing a gigantic dam, almost 3 km long, and made almost entirely out of sand.

72,000 tonnes of ore per day

The slag which is produced in the extraction of copper is collected in the reservoir. The shiny red metal is being mined on a large scale here, Chile having by far the largest deposits of copper in the world. The state-owned company Codelco produces the metal from this ore in a complex mechanical/chemical process. The slag produced as a waste product of this process is collected in the reservoir for subsequent treatment.

The scale on which one must think and work in this project is vast: each day some 72,000 tonnes of ore are mined. 95% of it ends up in the reservoir in the form of slag. This reservoir is bordered by mountains on three sides. On the south side, the new dam closes off the artificial lake. A large proportion of the construction material also derives from the copper mining process, for the sand used is extracted from the slag.

The valley near Ovejería has been filled with slag for as many as nine years now. The „lake“ which this process has created is now 42 m deep. The construction of the dam will considerably increase the capacity of the natural reservoir: once the dam has been completed, the volume of the reservoir will be large enough to accommodate the slag for the next 50 years.

The challenge: compacting a dam made of sand

The dam is currently growing, day by day – or rather night by night. For each night, sand with a moisture content of 16 - 20% is heaped onto the crest of the dam and then distributed by a bulldozer the next day, before being compacted in layers 20 cm thick. This work will continue until the dam has reached the planned height and width.

When the 32-m-high dam has been completed, its ramp will extend from the crest to a distance of up to 130 m into the next valley. This will create a slope between 22 % and 30 %. At first, the Chileans attempted to compact the sand with the traditional method, using a bulldozer which was towing a trailer-type roller. The downside of this method is that when the bulldozer is reversing over the compacted surface, its chain digs into the sand and loosens the material again. This is why the engineers at Con-Pax were on the look-out for a roller which could compact the non-cohesive sand effectively enough but offer full traction on a 30° slope. Their search for a solution inevitably led them to the HAMM vibratory compactors of the 3000 series with Hammtronic.

The solution: Vibratory Compactor 3412 with Hammtronic

It would not be inaccurate to dub these vibratory compactors „the mountain goats“ among modern compaction machines. The Hammtronic, a microprocessor-controlled operating and control system, monitors all engine and travel functions. It controls the starting, braking and speed. What‘s more, the load-limiting control effectively protects the engine from overloading. One particularly important aspect for the application in Chile is the fact that the intelligent Hammtronic system also attends to automatic slip control, constantly monitors the wheels and drums and continually adapts the available torque of the drive engines. This ensures that traction is optimum at all times and wheelspin is effectively prevented regardless of the nature, profile and slope of the surface being compacted.

Initial tests in autumn 2004 convinced the engineers immediately. Delighted with the high performance of the vibratory compactors, they opted to buy two of the machines with an operating weight of 12 t. Since then, they have been compacting some 7,400 m3 of sand each and every day. Six passes are planned in the rolling pattern, with one of these passes including an approach and a departure.

Quality doubled, emissions halved

The construction engineer and project manager Eduardo Araos is thrilled with the compaction quality. With the bulldozer, the compaction was very irregular, particularly in steeper areas. HAMM technology has provided a perfect solution. Samples and tests have repeatedly shown that the dam has the required compaction and stability in all areas.

The people responsible at Con-Pax are extremely satisfied, not only with the quality, but also because the rollers from Germany are exceptionally environmentally friendly and have cut their operating costs, too: with their extremely low fuel consumption, each one of the Hammtronic vibratory compactors can replace two „fuel-guzzling“ machines. And, in contrast to the bulldozer with a trailer-type roller, the vibratory compactors can also compact during reverse travel. As a result, the number of passes required has also been reduced. All in all, these benefits have halved CO2 emissions at one fell swoop.

Maximum availability

The vibratory compactors have now been working continually on this project for three years. With an annual total of 5,000 operating hours per machine, they are achieving a sensational availability. Three points have been crucial here: firstly, the robust and precise workmanship of HAMM rollers. Secondly, regular maintenance and inspection by the operator Con-Pax. And thirdly, excellent support comprising expertise and spare parts from Alejandro Saballa, service manager at Salinas y Fabres, HAMM‘s Chilean dealer, based in Santiago de Chile.

New application in dam construction identified

Con-Pax recognised the potential of HAMM‘s extremely gradeable rollers and will be counting on its high performance for other projects in future. The gradeability of HAMM vibratory compactors opens up new design engineering solutions to construction engineers. Current designs for new dams corroborate this: they have much higher slopes than was usual hitherto, due to the greater gradeability of the rollers. HAMM technology makes this possible.