FEATURE
The future of rock reinforcement : locally ancored self-drilling bolts
ahead , is that we offer variety with these bolts . We have two basic designs based on the material property , and we have several models made of these two basic models that differ in shape . We have the bolt made of seamless tube and a thread on the outer side that is rolled evenly on the left and the right of the tube . These bolts are commonly either 1.5m , 2m , 2.4m or 2.5m , and they can be extended with a coupling . By offering an extendable solution , we are able to substitute cable bolts if you need to drill much deeper into the rock .
Mines are increasingly digging deeper to access unexploited minerals , and deeper mines present a whole host of challenges , including rockbursts , large deformation , squeezing and creeping rocks . With this in mind , rock bolting and strata reinforcement is more important than ever , and it may not be easy to rely on traditional methods . Normet is an innovative company whose dynamic D-Bolt has not been matched , despite attempts from the competition to reverse engineer a similar product . However , it is Normet ’ s range of self-drilling dynamic bolts ( SDDB ) that really has the future in mind .
A challenge with using traditional bolts is that a hole must be drilled before the bolt and grout are inserted , and with rock that deep being under so much stress , there is the risk that these drilled holes will not stay open . Additionally , fractured ground allows for water ingress , which can dilute the cement grout or polyester resin being used . Normet ’ s SDDBs overcome this problem as they can be drilled directly into the rock , making them ideal for fractured ground or unstable strata .
According to Martin Petranek , director of products and production for rock reinforcement at Normet : “ Using a selfdrilling bolt does half of the installation for you , and then all you need to do is use a pumpable thixotropic grout or resin to bond the bolt . At Normet , we offer hydrophobic sodium silica-based resins , so it won ’ t be diluted or flushed by water ingress , and is also able to flow through cracks to consolidate the rock .”
The deformable resin is able to absorb some of the energy from the rock , further reducing the risk of bursts . As for the bolts themselves , the installation of these selfdrilling bolts can be fully mechanised , so workers can stay back at a safer distance . “ You can use bolting machines that are able to install these bolts , and the operator is protected in ROPS / FOPS certified cab . Major mining manufacturers are already looking at developing new equipment for installing self-drilling bolts , so it ’ s really what the future demands ,” Petranek says .
With other competitors entering selfdrilling bolts into the market , what is it about Normet ’ s portfolio that sets it apart ? Petranek explains : “ Where Normet is
“ We are not limited to any size , it ’ s very customisable . Bolts can be tailored to customer demand , for length , diameter , even the length of the threaded section . We can also customise what kind of drill bit they want to use , as bolts will need to be able to drill a hole that is bigger than a coupling if the customer is doing extended drilling , but still kept as small as possible to limit how much grout that you need .”
It is not just the customisable design that sets Normet ’ s locally ancored selfdrilling hollow rock bolts apart from the competition . Normet has paid close attention to using materials that are best suited for mining applications .
“ Conventional rock bolts are usually manufactured from ordinarily construction steels , which is not really ideal . It has certain load-bearing parameters , and is fine for applications such as concrete reinforcement where it is pretensioned , but for mining there are challenges with the impurities in the steel . The steel is rolled in just one direction when it is manufactured into a bar , and the resulting impurities can make it very weak because of the microscopic bubbles in the steel . The material that we use for dynamic bolts is homogenised , which requires a different treatment to get a uniform structure and is much stronger .”
36 www . fmdrc-Zambia . com