Static and Pseudo-Static Support and Strengthening Systems

It might be remarkable to find that, although stone and cable bolts have been used in underground mining and construction for decades (if not more than 100 years in the case of stone bolts), bolt elements and bolting systems continue to evolve and increase. Paper presented for the advancement of this symposium progress made in a fully packed resin and bolt cement grouting (Mikula 2004, Mold et al. 2004, Neindorf 2004), one mechanical swelling pass (Mikula 2004, Neindorf 2004) and bulbed cable (Yumlu & Bawden 2004) ), as an example.

Developments in supporting practices in the field that have accompanied greater productivity, greater excavation and larger equipment are specifically illustrated well by Neindorf (2004) which describes the evolution of land support practices at the Mount Isa mine for 30 years last.

In a detailed and valuable review paper, Windsor (2004) concludes that "the quality and performance of cable bolts used to stabilize transient, non-incoming production excavations has increased over the last 20 years to the point where they are now an important part. modern mining practices. Bolt cables have provided the industry with increased production, increased security and increased flexibility in the extraction process.

However, with the development of wider haulage and greater opening of mines, cable bolts are now also used to secure longer life, extracting infrastructure. "Windsor (2004) recommends" that greater care and attention to detail will be invested during the selection and installation of cable bolts for extracting mine infrastructure than those provided for mining production excavations ". He identified, in particular, the importance of geometric control, material quality, installation and testing of tunings and measuring devices used as cable handles.

It is also important to know that the use and effectiveness of stone and cable bolts in Australian underground coal mines has grown significantly in the past. Hebblewhite et al. (2004) show that significant trends over the past decade have included:

• Longer use of bolts;

• partial and mostly full encapsulation, polyester resin perforated bolts;

• use of threaded bolt mounting systems;

• adoption of pre-tensioning bolts in increasing number of applications;

• adoption of different steel grades to achieve more rigid and strong bolts; and

• variations to form deformation patterns and locking systems to improve transport and load loading performance.

A long-standing problem, but often seen as excessive, is corrosion resistance and longevity of rock and cable bolts. The initial Snowy Mountains installation which is generally considered to have pioneered the systematic use of rock binding in Australia (eg Brown 1999b) is now more than 50 years old. Therefore, it is inevitable that this problem will assume the importance given by the papers presented at this symposium (eg Bertuzzi 2004, Hassell et al. 2004, Hebblewhite et al 2004, Satola & Aromaa 2004, Windsor 2004). As noted by Hassell et al. (2004) and Potvin & Nedin (2004), the long-term corrosion resistance of popular friction rock stabilizers, remains a problem. Corrosion protection is one of the advantages offered by bolts and cables that are fully encapsulated.

However, there are suggestions that cement grouting alone does not provide long-term corrosion protection (eg 100 years) (Bertuzzi 2004). For long-term protection, two independent corrosion barriers are usually needed. Depending on the atmosphere and mineralogical conditions and groundwater in rock mass, corrosion can also affect surface equipment such as plates and nuts and bolts and the cable itself. Of course, galvanization provides protection to the steel underneath but does not have to be for a long time (Hassell et al. 2004, Windsor 2004).

Interestingly, in a detailed examination of 50 km of tunnels aged 35-40 years in the Snowy Mountains Scheme, Rosin & Sundaram (2003) found hollow steel bolts, hollow hollow steel cores very smooth to be in excellent condition, showing little evidence of corrosion. The grout protector of about 5 mm asphalt applied to bolt and face plates seems to work very well. Carefully controlled installation and grouting are prerequisites necessary for achieving that performance (Windsor 2004).

With the increasing knowledge, experience and availability of various analytical and numerical tools, installation of rock bolts and cables is now being designed to increasingly demand operational conditions in both civil engineering and underground mining. However, the installation ismost successful are usually those whose performance is monitored by a well-designed instrumentation system as part of a systematic observational approach (eg Moosavi et al. 2004, Thibodeau 2004, Thin et al. 2004, Tyler & Werner 2004, Yumlu & Bawden, 2004).

Shotcrete
Over the past decade, increased use of shotcrete for land support and control in infrastructure development, development and production in underground mines in Australia and elsewhere. Clements (2003) reports that nearly 100,000 m3 of shotcrete is applied annually in around 20 underground mines in Australia. Progress has been made in mixed design, testing, spraying technology and mixing that are combined to improve the effectiveness of shotcrete. Wet fiber reinforced shotcrete concrete is now an industry standard.

Of course, shotcrete has long been an important part of the support and strengthening system in underground civil construction where its use is well established even for soils that are softer than those commonly encountered in underground mining (Kovari 2001). In underground mining, shotcrete is now used for good effects not only for infrastructure excavation, in weak soils (eg Yumlu & Bawden, 2004), for rehabilitation, and in severe static or pseudo-static loading conditions (eg Tyler & Werner 2004 ), but as a support component and reinforcement system for dynamic or rockburst conditions (eg Li et al. 2003, 2004).

The toughness or absorption capacity of fiber reinforced shotcrete energy is very important in this application. The new toughness standard, the Determinate Panel Round test, has been developed in Australia and adopted in several other countries (Bernard 2000, 2003). The performance of fiber reinforced shotcrete measured in this test can vary significantly with type (usually steel or structural synthetic polypropylene fibers) and the dose of fiber used.

Mesh and liners sprayed
Another important change in support and strengthening training in underground mining in recent years is the increasing emphasis on mesh and liner spraying of several types as the main ground control mechanism. Although, because of the large amounts used and their importance as a support technique, shotcrete has been treated here as a special category of support, often included with other techniques in the spray-on liner class (eg Spearing & Den Haag 2003). The overall subject of mesh and sprayed liners has become so significant that it now has a series of specialist international meetings.

In some mining districts such as Western Australia and Ontario, Canada, mining regulations and codes of practice now require that some form of surface support, usually mesh, be used in all personnel entry excavations. In Western Australia, the Code applies to all posts higher than 3.5 m and requires that surface support be installed at least 3.5 m from the floor (Mines Occupational Safety and Health Advisory Board 1999). These provisions are part of the steps taken to understand and alleviate the danger of landslides in Western Australia and Australia's undersea Australian mines (Lang & Stubley 2004, Potvin & Nedin 2004).