World’s biggest raiseboring project

For the past 10 years, Sweden?s Kiruna Mine ? the world?s largest underground iron ore operation ? has been worked from a depth of 1 045 m, supplying high grade pellets to the world?s steel mills.

Now a new chapter in the mine?s rich history has just begun with a project to build a completely new haulage level 320 m lower down. This will extend the life of the mine by another 20 years beyond 2030.

Construction of the new 1 365 m level is a complex task exploiting all of the modern mining techniques you would expect on such a major development. But above all, it will showcase the technology required for developing shafts and ore passes by hosting the biggest raiseboring project of all time.

The new infrastructure requires the construction of a minimum of 55 000 m of shafts and ore passes ? 40 000 m at Kiruna Mine and a further 15 000 at the nearby Malmberget Mine ? all by 2014.

Bergteamet, which is one of Sweden?s leading providers of mining and underground services, is in charge of this part of the development work and is using Robbins raiseboring machines from Atlas Copco.

Uniquely powerful
As M&C went to press, two Atlas Copco raiseboring machines were on site, Robbins 73RM-DC and the larger 91RH C, while three more Robbins 91RH C machines were on order. All of the units are tasked with boring raises ranging from 90?360 m long and up to 5 m in diameter.

Weighing in at 33 tonnes, the Robbins 91RH C is an enormously powerful machine. It has a pulling power of 6 800 kN and a continuous torque of 450 kNm.

The rock consists of several different formations including granite with a compressive strength of 220?350 MPa as well as quartz porphyry with a strength of up to 350 MPa.

During upward reaming, the machine is also assisted in these hard rock conditions by the superior cutting capability of the Secoroc Magnum V cutters that are mounted in the cutterhead. Designed and manufactured by Atlas Copco Secoroc in Texas, USA, they are designed for maximum cutting effificiency in collaboration with these raiseboring rigs? massive rotation and feed forces.

Groups of four
Although the Robbins 91RHC is capable of boring raises up to 1 000 m long, they are being used here to bore a large numberof short ore passes in groups of four. These will be installed between the different levels, ultimately linking up the new level at 1 365 m.

Net penetration when boring pilot holes is 0.95 m per hour and each machine is averaging 10 m per day, depending on the rock formation and shaft length. Each raise will take several months to complete.

Bergteamet?s Project Manager at the Kiruna site is Håkan Johansson, one of the raiseboring specialists who last year assisted in the dramatic rescue of the trapped Chilean miners and where raiseboring was one of the methods used to reach them.

Johansson explains: ?The technology of crushing rock with the aid of a big reamer is well proven and we are using it here on a huge scale in co-operation with Atlas Copco. It represents the biggest raiseboring project in the world, and so far the results are very encouraging.

?One of the main reasons we think the Atlas Copco Robbins machines are ideal for this job is the power and control they give us, particularly when it comes to the hydraulic drive system on the Robbins 91.

?It has 585 kW of effective output which enables the very high torque to be fully maintained at a high rotation speed. During pilot hole drilling this prevents the drillstring from getting jammed, avoiding delays and possible damage to essential components.?

In addition to this, Bergteamet sees the RCS rig control system on the Robbins 91RH C as a major advantage enabling further automation to be used if required.

Continuous operation
Bergteamet has 57 operators and six mechanics at the site as well as a team of 12 at the nearby Malmberget Mine.

At the Kiruna mine, boring is carried out continuously, seven days a week, all year round. It takes a team of four to keep the big Robbins 91 RH C rigs working day and night while the smaller Robbins 73R machines require a team of only three.

The shift schedule, which is based on 10 hours per shift, allows for a certain overlap, but in practice only one operator per shift is needed.

During drilling of the pilot hole, the operator controls the process from the operators? control panel and also prepares each new extension pipe to be used, greasing the threaded joints and positioning the next pipe so that it can be easily lifted into place by the machine?s rod handling arm.

In addition, the operator keeps an eye on the effificiency of the flflushing procedure and also checks the type of rock being encountered so that there will be no surprises when it is time to start the reaming process, pulling the reamers upwards.

During reaming, the operator supervises the process using the control system?s wide variety of monitoring functions. These include anti-jamming protection which automatically stops the machine if jamming occurs and prevents the machine?s motor and other essential parts from damage.

Emma?s muscle
Operator Johan Garp was impressed by just how fast ?his? machine ? which he has named ?Emma? ? can drill a pilot hole.

?We are drilling at a rate of just under one meter per hour,? he says. ?The rock is very hard so the resistance is pretty tough. But tough or not, it makes no difference. Emma has plenty of muscle to put behind the bit.?

In Bergteamet?s service workshop at the 500 m level, all of the 1.5 m long drill pipes are quality checked for possible cracks before use. These are no ordinary drill pipes. They are machined in one piece to exactly the right shape and are made of high tensile steel in an exclusive process, enabling them to withstand extraordinary loads. Therefore the pipes have to be handled with the greatest of care.

During M&C?s visit, a new raise had recently been completed and its perfectly smooth and straight walls clearly showed how far raiseboring technology has come in recent years.

All miners will no doubt be keeping a watchful eye on Kiruna Mine as the expansion project progresses. But it is by no means the only Swedish mine to launch a major expansion as the current strong demand for minerals and metals continues to increase. The Garpenberg mine in central Sweden, is also undergoing a similar transition, and here too, Bergteamet is installing shafts and ore passes using Atlas Copco?s Robbins 91RH C raiseboring rigs.