Atlas Copco Geotechnical Engineering Products

Roofex rock bolts

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3With Roofex, peace of mind comes as standardWhen rock moves, its comforting to know that youve chosen the markets only predictable rock bolt system.

Roofex is unique. It is a new and highly advanced rock bolt designed to dissipate and control high amounts of energy liberated from the rock mass deformation process. Roofex provides a predictability to the system behaviour and allows you to accurately adjust the support needed to keep the excavation from caving in.

4Roofex rock bolts

Safety in extreme conditionsRoofex is a unique rock bolt that can absorb energy from rock mass move-ment. It is designed to dissipate large amounts of energy liberated from the rock mass deformation process. This process can be a static phenomenon, as in the case of large convergence in yielding ground, or extremely sudden and violent as in a rock burst event. Roofex is designed to accommodate the whole spectrum of rock mass behaviour as well as being a solution for extreme conditions potentially occurring at depth.

Once convergence forces exceeds 80kN, this ingenious frictional sys-tem starts to extend along the rock deformation, dissipating the energy of the rock. The bolts sliding function allows the rock to move a predefined sliding length, up to 600 mm, before

absorbing element, creating friction which absorbs the energy released from rock movement. The energy absorber is also designed to provide enhanced mixing of the bonding agent. The mixing /stop element facilitates bolt installation by shredding and mix-ing the resin cartridges. This feature also ensures that the inner steel bar, sliding through the energy absorber, stops at the end of the sliding length, and allows for the reserve load capaci-ty to cope with residual loads. The two insulating steel sleeves act as decou-pling agents and corrosion protection.

Easily adapted to your operationRoofex uses common rock bolting equipment for installation. Once the hole has been drilled and resin car-tridges have been installed, the Roofex bolt is inserted while rotating. This action punctures the cartridges and

Tunnelling or drilling mining shafts in deep unstable rock conditions has always been a challenge for the geomechanical designers. With rock movements being difficult to predict, controlling them can be a head-ache. Whatever the type of support system, the deformation must be controlled and the tunnel or shaft kept from collapsing. Thats where Atlas Copco comes in! With years of experience in rock reinforcement, we have developed a new rock support system Roofex.

stopping. Once sliding length has been consumed, Roofex acts as a stiff rock bolt, with an ultimate load capacity of 100 kN. By allowing a certain amount of rock movement, Roofex releases the energy of the rock mass in a controlled manner.

An ingenious designThe Roofex rock bolt mechanism con-sists of a frictional steel to steel sliding system built up by a high strength steel bar, an energy absorber, a mixing /stop element, two insulating steel sleeves, a calibrated lock-nut and a steel face plate.

The unique energy absorber is the heart of the system that allows the inner steel bar to move towards the excavation at a stable and precise load. Once the rock starts to move, the inner steel bar is pulled through the energy

5theres a risk of a collapse. Predictable time and time againRoofex is a powerful tool in the hands of the geomechanical designers. Thanks to rigorous testing in several places around the world, as well as in lab tests, we have shown that the extension and final load characteristics are consistent. The energy released by the rock deformation process is absorbed by the steel to steel interac-tion of the energy absorber and the inner steel bar. Being preset at the manufacturing stage, this means that these bolts are insensitive to the exter-nal conditions.

With Roofex, the designers can predict the bolts behaviour and use it in their mathematical models. This optimises the rock reinforcement design of deep mines or tunnels and can also facilitate higher levels of safety and productiv-ity.

evenly distributes the resin around the rock bolt. The energy absorber is now fixed to the rock while the inner steel bar is free to slide inside the steel sleeves and the core of the energy absorber. This also minimizes the chances of the bar being pinned down by a rock burst. Installed at an early stage, Roofex still allows for extended rock movement. This means the life span of the support system is extended, the total cost of operation are reduced and the gallery can be opened for a longer period of time.

Primary or secondary support systemRoofex is mainly used as a primary bolting support. However, a situation when Roofex can be used as a second-ary suport, is where a tunnel has been reinforced with rock bolts, such as Swellex, with wire mesh and sealed with shotcrete. Roofex can then be installed as a secondary precaution. It is not only ideal for new tunnelling or mine shaft work, Roofex can also be used in existing installations where

Sliding length,pre-calculatedmaximumdeformation

Sliding length,pre-calculatedmaximumdeformation

Energy absorber(anchoring point)

Roofex rock bolt at installation

Rock mass movement - energy absorbing phase

Roofex rock bolt at max load and max deformation

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Mixing/stop element travelling inside steel sheathing

Combined mixing / stop element

Steel sheathing

Steel sheathing

High quality steel bar(partly threaded)

Face plate

Nut (hemispherical, with lock/nut effect)

Resin or cement

Energy absorber(with inserted steel pins)

6Roofex rock bolt static or dynamic applications

Roofex monitor bolts

Roofex rock bolts are universally applicable to a large variety of ground condi-tions and load applications.

The Roofex rock bolts are designed either for static or dynamic applications. The energy absorber consists of a hollow steel cylinder with inserted metallic pins deforming the inner steel bar sliding through it in a cold rolling process. For static applications of the Roofex rock bolts, ordinary steel pins are inserted into the energy absorber, whilst for the dynamic applications, because of heat genera-tion during the rapid movement along the steel bar, hard metal pins made from carbide have to be used. The system also includes face plates that are matched to each application - either static, as in yielding ground or for violent dynamic events.

Yielding ground conditions are characterised by relatively weak or broken ground with high stresses. With Roofex rock bolts designed for static applications, the sliding process is initiated by the rock mass expansion and the bolt slowly stretch-es under the prevailing rock mass pressure along the pre-defined sliding length until equilibrium is reached again.

Dynamic events such as rock bursts typically occur in massive hard rock with high stress. The Roofex rock bolt designed for dynamic applications is able to dissipate the sudden energy release and transfer it directly into movement along the pre-defined sliding path, without receiving major damages.

The Roofex concept also offers two types of monitor bolts that directly monitor rock mass movements and therefore provide predictability to the rock reinforce-ment system.

Once Roofex bolts are installed, the actual rock mass deformation at the roof and sidewalls of the excavation can only be determined by monitoring with surveyors. This will not always be an indication that the bolts work properly or that they are well bonded to the rock mass. By using Roofex monitor bolts, the effective move-ment of the inner steel bar through the energy absorber can be clearly monitored. In fact, using Roofex rock bolts together with Roofex monitor bolts is the reliable way to verify that the bolts function correctly in a given rock mass environment.

Range of products

Roofex rock bolts Rx8S and Rx8D

Roofex monitor bolts Rx8M and Rx8M+

7Roofex monitor bolt with added features (Rx8M+)

Roofex monitor bolt (Rx8M)

The rigid external version of the monitor bolt, with the green-yellow-red coded bar is very simple in terms of monitoring. The colours on the bar will be con-sumed by the sliding process, and the magnitude of the rock mass deformation can be easily observed.

Deformation

Roofex monitor boltRx8M at installation

Rock mass movement

Rock mass movement close to bolt capacity

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Anchoring point

Roofex Rx8M

As a consequence from customers feedback and additional enquiries from our customers center we have also developed a monitoring bolt that has a flexible telltale for safety and offers plate tensionability. The flexible telltale can also be replaced once it gets damaged or lost. This model of the monitor bolt has also a thread to mount the anchor plate directly on the excavated rock mass. As an added value it is furthermore possible to perform a pulltest of the monitor bolt. Once the predefined deformation is consumed, the monitor bolt will still work as an ordinary rock bolt.

Roofex monitor bolt Rx8M+ at installation

Anchoring point Deformation

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Rock massmovement2

Rock mass movementclose to bolt capacity3

Roofex Rx8M+

8At the Atlas Copco in-house laboratory in Feistritz, Austria, static pull testing on fully assembled Roofex rock bolts was performed. Various pre-set sliding lengths from 150 to 600 mm pulling length were used. The test successfully confirmed a constant load capacity of 80 kN over the full sliding length of the bolt.

In order to secure quality of Roofex rock bolts, pull test are still performed for quality control issues. A reasonable ratio of bolts is tested before bolts are available for delivery.

In the course of the development of the Roofex rock bolts, Atlas Copco has conducted an extensive laboratory and field testing program, to commit to our high quality standards.

Roofex testing program

Static pull test Dynamic drop test Mixing test

At the CANMET-MMSL laboratories in Ottawa, Canada, the dynamic capa-bility of Roofex rock bolts were tested. The tested bolts were installed in simu-lated bore holes, with variations of the loading parameters, drop mass and the fall height, to achieve variations of the impact energy. The dynamic load was simulated by dropping a mass over a selected distance onto the bolts.The tests showed that the peak load of the bolts is easily predictable and show little variations. The performance can be used to predefine the bolts sliding length adequately for a given dynamic event.

At the Atlas Copco laboratory in Feistritz, mixing tests were also per-formed in order to confirm proper shredding of the resin cartridges, subsequent mixing effect of the resin or mortar and distribution of the resin in front of the energy absorber to provide bonding inside the drill hole. The tests were performed by inserting the Roofex rock bolts under rotation into resin cartridge filled steel and plexiglass tubes, and was followed by pull out tests. The tests successfully proofed even mixing and consistent anchorage performance.

9An extensive field testing program with several test installations has been conducted throughout the development phase of Roofex.

Static field testingAfter an agreement with the mine management of Iberpotash, a test installation was performed in Vilafruns mine in Spain. Important convergences had been noticed in the roadways of this salt and potash mine, making it very suitable for testing Roofex rock bolts for static applications. Around 300 pieces of Roofex rock bolts and Roofex monitor bolts were installed. While performing these tests, Atlas Copco also got the opportunity to be a part of a study at the School of Mines UPM in Madrid.

Dynamic field testingWithin Altas Copcos extensive field testing program for Roofex rock bolts, also real time dynamic testing, using simulated rock bursts through blasting have been conducted. The test proce-dure was carried out in an abandoned drift at IAMGOLD Mine Doyon, Rouyn-Noranda, Quebec in Canada. The aim of this simulated testing was proving the Roofex bolt capacity under dynamic impact conditions.

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Technical specifications

Quick reference

Model Description

Rx8S Roofex rock bolt / 80 kN sliding load / Static application

Rx8D Roofex rock bolt / 80 kN sliding load / Dynamic application

Rx8M Roofex monitor bolt / 80 kN sliding load / Static application*

Rx8M+ Roofex monitor bolt with added features/ 80 kN sliding load / Static application*

Rx8 Plate Roofex plate suitable for 80 kN sliding load / Static and Dynamic applications

Rx8 Mesh washer Roofex mesh washer

Technical data

Ultimate load of failure 100 kN

Sliding load 80 kN 10 %**

Static energy absorption ~800 J/cm sliding length

Dynamic energy absorption ~290 J/cm sliding length (for first event)

General data

Steel bar 12.5 mm

Lock nut 28 mm (square)***

Steel bar thread left hand thread (right hand optional)

Energy absorber outer 30 - 34 mm

Recommended drill bit 33 - 36 mm

Anchoring method resin /cement

Recommended resin cartridge 28 mm

Recommended Resin column support 500 mm****

Overall length 1500-6000 mm (300 mm staggering)*****

Pre-set sliding length 150-600 mm (150 mm staggering)

CombinedMixing / stop element

Steelsheathing

Steelsheathing

High quality steel bar(partly threaded)

Face plate

Nut(hemispherical, with lock/nut effect)

Energy absorber(with inserted steel pins)

** Sliding loads might be adjusted to customer needs*** Other dimensions on demand****Adjustments might be possible due to installation conditions*****For Rx8M refer to Length index on page 11

*Dynamic on demand

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Dynamic performance for 15kJ impact (example)

Sliding length

Overall length

Sliding length

Overall length

Length index

Model Overall length (mm) Sliding length (mm)

Rx8S + Rx8D 2400/300 2400 300

Rx8M 2400/300 2700 300

Rx8M+ 2400/300 2700 300

Other model lengths accordingly

Load performance

Roofex Rx8S and Rx8D

Roofex Rx8M

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Displacement (mm)

Load

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Load - Displacement Diagram 15 kJ Impact

020406080

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Load

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Displacement (mm)

Static load performance (example)

Roofex Rx8M+

Sliding length

Overall length

Flexible/removeable telltale

Atlas Copco Geotechnical Drilling and Exploration www.atlascopco.com

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