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ROOFEX A NEW ROCK BOLTING CONCEPT FOR UNDERGROUND EXCAVATION UNDER HIGH STRESS CONDITIONS

Erich Neugebauer ATLAS COPCO

Rock Reinforcement from Atlas Copco

A new way to tackle safety in underground operations

Roofex - a new rock bolting concept for underground operations under high stress conditions

Erich Neugebauer, Atlas Copco Geotechnical, Drilling and Exploration

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BackgroundThe world markets persistent demand on raw materials and the continuous need for infrastructure expansion forces the mining and construction industry to develop underground structures in more sensitive and violent environments and at the same time the demand on safety is increasing.

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BackgroundThere is a need to actively control the energy liberated from the rock mass deformation process in high stress environments. Large convergences in weak, yielding grounds, where deformation is a slow and an almost static phenomenon. Dynamic events, commonly in hard rock where energy is released in a rapid and violent manner as in the case rock burst or earthquakes.

The ability of the support elements to yield under dynamic loading, through a predefined controlled displacement is critical in damping the dynamic load and minimizing rock ejection. Existing rock bolts designed to cope with the mentioned problems strongly depend on installation conditions, the interaction of the steel with the rock or on the bonding agent, and this may lead to sources of concern regarding their controlled performance. It is now time for a new innovation in rock reinforcement!

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Roofex rock bolt

Roofex Rx8 rock bolt, is a new, highly advanced rock bolt designed to dissipate and control high amounts of energy liberated from the rock mass deformation process. Through its steel to steel interface, Roofex provides a predictability to the system behaviour and allows you to accurately adjust the support needed to keep the excavation from caving in. Designed either for static or dynamic applications.

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Components

The key components of the Roofex rock bolt are:Inner steel bar Energy absorber Mixing / stop element

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Roofex an ingenious design

The bar isolation concept assures a free linear movement to maintain the constant sliding-load level along the entire pre-set sliding length. The sliding function creates friction between the fixed energy absorbing element and the inner steel bar which in turn absorbs the energy released from rock movement.8

Rock mass behaviour Support performancepi

Rock mass behaviour Characteristic lines after Fenner-Pacherprogressive rock mass relaxation, development of ground loosening pressure

Support resistance

elastic rock mass

rock mass at elastic limit

Radial deformation R

pi

Support resistance

characteristic line - stiff support characteristic line - flexible, ductile support characteristic line - soft support ROOFEX

System behaviour Characteristic lines with different support characteristics

Radial deformation R

Roofex load performance

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Installation procedureRoofex rock bolt, is easily installed using a bonding agent that is either a cartridge contained type (e. g. 2 component resin) or a premixed, pumped type (e. g. cement mortar)Cartridge type Pumped type

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Roofex monitor bolts complete the concept Provide easy monitoring of rock movement, verification of the performance of the Roofex rock bolts at the same time they provide rock support. There are two versions of the monitor bolt; the external version and the internal version. Both designed either for static or dynamic applications.

Components

Working stages

Installation

External monitor Internal monitor

External monitor - cartridge External monitor - pumped

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Why Roofex?Safety in extreme environments Designed to accommodate the whole spectrum of rock mass behaviour. By allowing a certain amount of rock movement, Roofex releases the energy of the rock in a fully controlled manner. After large rock deformations or rock bursts, where the sliding length has been consumed, Roofex bolts are still able to cope with prevailing residual loads, providing a reserve load capacity to the system.

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Why Roofex?Easily adapted to your operation The bolt is installed using conventional bolting equipment. The life span of the support system is extended. Gallery can be kept open for a longer period of time lower total cost of operation.

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Why Roofex?Provides predictability and control The steel to steel energy absorbing interface facilitates a stable load bearing capacity which is insensitive to external conditions

reliable, predictable performance preset at the manufacturing stage. The bolts behaviour can be accurately specified in numerical models, allowing the designer to pre-design the support system to the structures expected loading conditions and deformation span optimised rock reinforcement design. greater levels of safety and productivity.

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A problem solverRoofex is and will remain a specialty bolt, intended for special conditions (unstable ground, rock bursts, etc.) The investment in Roofex bolts gives positive benefits to the customer in a higher safety level through predictability of the bolts behaviour. The price of the bolt will be higher than a bolt for standard applications, however the cost is justified and easily returned by avoiding support failures, rehabilitation and interruption of production. The introduction of Roofex targets mine and tunnel designers, consultants and mining houses who can maximize the benefits that the product offers.

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Testing, Application and FutureIn the course of the development of the Roofex rock bolts, Atlas Copco has conducted an extensive laboratory and field testing program, to commit to its high quality standards.Selected installation and testing sites for Roofex rock and monitor bolts are: CANMET MMSL dynamic drop fall testing, Ottawa, Canada IAMGOLD Mine Doyon, dynamic field testing, Rouyn-Noranda, Canada Iberpotash, Vilafruns mine, Spain X-Strata Copper at Kidd Creek mine, Timmins, Ontario, Canada. Agnico Eagle at Laronde mine near Val DOr, Quebec, Canada. Brunswick Mining at Bathurst, New Brunswick, Canada. Somincor, Portugal. Cayeli and Koza mines, Turkey. Colorado School of Mines, Edgar Research Mine, Idaho Springs, CO, USA ZG Polkowice-Sieroszowice, KGHM Polska Miedz S.A., Polkowice, Poland. Chwalowice, Kompania Weglowa S.A., Rybnik, Poland. West Elk mine, Somerset, CO, USA Elk Creek mine, Somerset, CO, USA

A second generation of Roofex, the Rx20, offering a load range of ca. 200 kN sliding load and 240 kN ultimate load, has successfully passed the first field tests.

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We are committed to yoursuperior productivity through interaction and innovation.

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