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BISTRO-ANKER PROJECT - INTRODUCTION OF ROCK BOLTING TO KRASNOARMEYSKAYA-ZAPADNAYA NO.1 MINE
The rock bolting technology as a support method for coal mine workings has been recently stated to be one of the key factors in the process of modernisation and mechanisation of the Ukrainian coal industry. This support system has revolutionised the world coal industry having enabled to increase rates of reserve development and longwall retreat through the improved gateroad conditions. Rockbolting is considered as an instrument for production intensification, labour productivity improvement, reduction of mine costs, substantial improvement of mine safety and so - advance of the high cost and subsidised coal industry on its way towards economic viability.
The British coal industry is the world recognised leader in the use of rock bolting technologies at deep coal mines of severe geological conditions. The Advanced Technology (AT) rock bolting developed by RMT (Rock Mechanics Technology Ltd.), a British company, enabled the British coal industry to reduce coal extraction costs and made the industry profitable and attractive for privatisation. Despite the difficulties of overcoming the stereotypes settled, the new technology of roadway support was successfully and systematically introduced to coal mines replacing steel arch support which was usual and clear to most miners.
Several years ago Russia - the largest coal producer among the CIS countries - commenced the introduction of rock bolting technology to the mines of Kuzbass and Rostov regions where seam mining conditions are similar to the Ukrainian. The latest statistics has revealed successful results of rock bolts being used as a means of mine working support. At some mines of Rosugol SHC and particularly privatised coal mining enterprises up to 95% of total drivage are rock bolted developments. Rock bolting centres - the specialised structures established in Russia adopt a comprehensive approach to the introduction of the new technology rock bolting to the industry as well as to supplying required materials to mines.
The coal mining conditions in Ukraine are similar to those in the UK: - it is a deep mining in weak rib strata which is additionally complicated by geological faults, serious water inflows and gas evolving. Besides, the Ukrainian mines have very long workings and highly dispersed mining activities. Development work is of huge metal consumption for support and labour intensive consequently resulting to high costs. Therefore the necessity to introduce rock bolting in Ukraine has already become fully recognised. This will create the necessary prerequisites for the improvement of technical and financial performance of the mines.
The Ukrainian Ministry of Coal (MCI) developed the sectoral Anker programme aimed at the introduction of rock bolting as primary method of support on gateroad development. Within the framework of this programme in conjunction with Carbo Tech, a German company, the Carbospetspolymerkrep enterprise was conceived which is equipped with modern rock bolt and resin manufacturing lines. Since August 1999 the plant has made several thousand sets of these components.
The Geotechnical Mechanics Institute of the Ukrainian National Academy of Science in Dniepropetrovsk in conjunction with MCI established the Rockbolting Technology Centre (RTC) which, consulted by Donetsk Coal Consulting Centre (established under the Tacis programme), has developed the regulative documents and guidance on the use of rock bolting at local mines. In cooperation with Tacis Coal Consulting Centre the RTC has developed a training programme on the technology of rock bolting and system of strata conditions monitoring.
The Ukrainian mining consultants of the Coal Consulting Centre with the assistance of the EC experts who are the consultants of IMCL (International Mining Consultants Limited) and RMT (Rock Mechanics Technology) have undergone the specialist theoretical training at CCC followed by on-the-job practice in Great Britain at Tower (South Wales) and Longannet (Scotland) collieries. The experience gained has enabled to promote the advanced technology rock bolting among the specialists of Ukrainian coal mines as an instrument for reduction of a number of general mine costs and production intensification.
In August 1999 drilling and bolting trials commenced at Pavlogradskaya mine of Pavlogradugol SHC. The executive equipment was hydraulic drilling machines by Schmidt , Kranz & CO. GmbH (Germany). Because of technical and organisational reasons those trials did not demonstrate the estimated result. Firstly, the parameters of the drilling instruments had been selected improperly.
As further activities on the sectoral Anker programme progressed other problems with the introduction of rock bolting technologies occurred.
The Ministry of Coal Industry requested Tacis Coal Consulting Centre to provide assistance to the implementation of the Anker programme. Tacis CCC found an opportunity to invite the RMT specialists for the consultancy assistance.
At the first stage the RMT specialists together with the CCC staff carried out a careful on-site study at 11 mines. The study confirmed the perspective of the mines for introduction of rock bolting technologies. However, poor finance and the lack of special equipment in Ukraine did not allow to take and test core samples of the in-mine strata. It is impossible to have optimal rockbolting support rules designed without this investigation. Furthermore, monitoring of strata behaviour gets complicated and reliability and safety of the whole system will be questioned.
In addition, the measurement devices were missing which are required for roof strata behaviour control, electronic and mechanic displacement gauges for different heights acceptable in terms of accuracy and cheapness as well as light-weight mobile drilling machines and instruments and computer software. Thus feasibility of the use of hi-tech rock bolting was only based on simple on-site investigations of particular geological conditions, review of geological information submitted by the mines and experience of RMT on the use of the technology in the UK and other countries. Nevertheless it should be noted out that at that time a fundamentally new answer regarding the possibility and feasibility of the introduction of rock bolting in Ukraine was obtained.
In August 1999 the CCC initiated and developed the Terms of Reference for the BISTRO-Anker project. The project objective is to practically prove the possibility for the modern and universally recognised rock bolting technology to be introduced in Ukraine. The project consisted of two phases:
- Phase 1 included training and practical seminars carried out in the UK for a group of Ukrainian engineers;
- Phase 2 - continued training and practical application of rock bolting technologies at Krasnoarmeyskaya-Zapadnaya No.1 with the assistance of the British specialists.
The project was approved by the EC Delegation and the EC finance was allocated. RMT was appointed as the contractor for the project, CCC - as the Ukrainian partner, whilst the Rockbolting Technology Centre at GMI (of National Academy of Science of Ukraine) was determined as the beneficiary of the project.
Phase 1 of the project officially commenced on 5 December 1999 with a group of six Ukrainian specialists arriving to city of Bretby in England where RMT offices are based.
The company offers consultancy services in the area of mining geotechnical mechanics, manufactures and supplies specially designed control and measurement equipment for measurement of stress and strata movement. The unique specialisation in the area of strata behaviour investigation, design of systems and technologies of reinforcement, computer software and data processing, measurement and testing techniques introduced to production, developments in the field of structural materials and consumables enable the company staff to successfully address geotechnical problems that mines of many coal mining countries face. RMT provides virtually full supply of services to the British coal industry. Besides, the company participated in the export of the advanced technology rockbolting to Germany, USA, South Africa, Russia and other countries. Based at RMT there are continuous theoretical and practical courses on the technology of strata reinforcement to be given to mining staff, mine managers and inspectorate.
The training group was compiled by scientific staff of the RTC of GMI UNAS, specialists of Tacis CCC, Carbospetspolymerkrep JSC and Krasnoarmeyskaya-Zapadnaya No.1 mine. It therefore was attempted to combine scientific, training and manufacturing bases at the initial stage. During the first week the RMT staff presented a number of lectures and carried out laboratory works together with the Ukrainian specialists. The subjects were as follows:
- Methods of mine roadway support.
- Geology of coal deposits.
- Physical and mechanical properties of mine strata.
- Rockbolting for mine workings – feasibility theory.
- Rockbolting materials and requirements applied.
- Rockbolting drilling equipment and its operation.
- Pull tests.
- Rockbolting monitoring, materials and instrumentation for control of support.
- Designing of support rules.
- Organisation of rockbolting works in mine roadways.
- Safety and health on rockbolting.
- Rockbolting economics.
- Organisation of training for working staff.
The second week was concentrated on practical sessions, which were held on at Longannet colliery in Scotland. The mine is one of the newest in the United Kingdom and was put into operation in 1974. The mine supplies coal to the only consumer - regional thermal power plant, which supplies energy to Edinburgh, other cities and industrial consumers. The mine and the power plant were privatised 5 years ago by Scottish Coal and now operate on a fully commercial basis.
The enterprise mines one coal seam with thickness of 2.0-2.2 m at the current working depth of 500-700 m. The mine is rated to Category 3 on gas and is a subject to coal dust explosions. Full time staff is 432 men. In addition there are some 200 people currently employed on a contract/agreement basis representing different contractors. The mine is now at the stage of reconstruction of the transition to a new block. The length of mine workings in this block will amount to 18 km. The old mined block will be closed after salvage of coal clearance equipment. Mine output is 8000 t/day by one powered production face but simultaneous operation of two longwalls would be possible during the transition to another face. Longwall length is normally up to 250 m whilst runs of retreated longwalls are 0.5-2.5 km.
ROM coal is of high ash content (up to 35%) due to a great number of geological faults, easily failured false roof of the seam and also because of mixed rock mass from development and extraction activities. All rock mass is then washed at a preparation plant where ash content is reduced to 8%. Developments are driven with a roadheader and the scope of drivage is about 1 km/month. This is achieved by three rockbolted development headings. Rockbolting is used as primary method of gateroad support. Main and access workings are supported with stiff steel arch support with corrugated steel lagging.
Rockbolting was introduced at the mine 8 years ago and enabled the enterprise to survive in difficult coal market conditions as the technology enabled to produce cheap competitive product. At the same time the rest of mines in Scotland (some 6 collieries) did not manage to survive under severe market conditions and did not become profitable and so - were closed down.
There are 6 men in a development face: roadheader operator, electrical mechanic and four development workers. The cross-section of the driven roadway is 15.5 m3 on development. Calculated length to be driven is 1.2-1.5 km. Transportation of rock mass from the face, delivery of consumables, delivery and return of staff is done by a belt conveyor with the belt width of 1 m.
Development drivage, installation of support and delivery of consumables are organised in the following way:
- Cut into 2.75 m with Anderson RH45 roadheader – 50 min.
- Advance to the face hand-held pneumatic bolting machines (two Turbo Bolters), pneumatic drills for rib bolting (two machines); connect drilling equipment to the roadheader board, bring consumables, hang on mesh panels with w-straps, temporary support – 25 min.
- Drill boreholes, install rockbolts in the roadway – 60 min.
- Remove the equipment – 10 min.
The development cycle duration is 145 min or 2.42 hours. Normally during a shift there are 2-3 cycles carried out providing the rates of roadway advance at up to 20 m/day.
The rockbolting consumables at Longannet colliery are of the following parameters:
- 24 mm Celtite AT capsules which contain a filled resin compound and a catalyst in two separate compartments. Capsules of various set speeds ranging from 0.5 min to 3 min are used. The capsule length is 350-800 mm. Capsules are packed by lots in cardboard boxes, marked with different colours and equipped with special plastic caps to secure placement in a borehole prior to rockbolt installation. The minimal strength of set resin is 80 MPa.
- Steel rockbolts are 21.7 mm in the core diameter. The diameter with raised ribbing is 23 mm. The threaded end of a rockbolt has M24 rolled thread. The length of thread is 150 mm. The non-threaded end of a rock bolt is cropped to an angle of 45* to ease breaking of capsules on rockbolt installation. The yield strength of steel is 25 t, the shear strength is 32 t. The nominal length of a rockbolt is 2.4 m. Rockbolts with the lengths 1.5 m, 1.8 m, 2.1 m can be used. The rod is installed in 27 mm borehole for roof support and rib support on the pillar side. On the longwall side glass reinforced rockbolts are installed. Steel rockbolts are used in association with domed washer plate, conical seat, anti-friction plastic washer and nut with a torque pin. All rockbolts are installed with the same preliminary tension through tightening the nut after initial hardening of the resin followed by the break-off of the torque pin. Longannet mine uses Polish rockbolts, which conform to British Standards and are significantly cheaper.
- Installation domed washer plates are made of 8 mm or 10 mm steel flat bar and have 35 mm central hole. The plates are either 100x100 mm or 150x150 mm.
- Steel W-straps are of several purposes. First of all the use of a strap is to hold up a metal mesh panel and to prevent roof failure in spaces between rows of rockbolts. The straps have 30 mm holes placed at the interval of 300 mm which enables to use a strap as a template for rockbolt installation. The roof straps are made of 2 mm steel of W-profile whilst rib straps are made of 0.7 mm tin-plate. These components should not be stiff and if required, they must reflect all irregularities of roof.
- Mesh panels for tightening of ribs and roof of a roadway are made of 3-5 mm steel wire by means of welding at 70 mm squares.
- Specially designed equipment for installation of rockbolts with chemical capsules. These are pneumatic drilling machines with forced borehole water wash. The machines are designed for boreholes up to 50 mm in diameter and up to 15 m long. Drill rods have hexagonal profile and are 19 mm or 22 mm in diameter. Drilling machine is mounted on a pneumatic prop and is operated with lever switchboard, which will fully eliminate transmission of vibration to an operator. The pneumatic leg is two/three stage telescopic leg made of high-strength fiberglass pipes. The mine employs Vombat bolting machines (Australia) and British Turbo Bolters with pneumatic drive. This equipment is particularly simple in service and very reliable. Weight of equipped bolting machine is some 40 kg. Operating compressed air pressure is up to 6 kg/cm2. Air consumption is up to 3.5 m3/min, water consumption for borehole wash is 15-20 l/min.
Quality control and audit of support conditions in a rockbolted roadway is done visually during the entire life cycle. Particular role is allocated to control by instrumentation as without it rockbolting can not exist.
1. Rod pull out ram is used to determine load bearing capacity of a rockbolt and reliability of its confinement in borehole.
2. Specially equipped monitoring stations are used for measurement of roadway convergence on roof, floor and sides.
3. Sliding scale reference gauges (safety indicators) are installed into special control boreholes in every 15-20 m as a roadway is driven. These Tell-Tale systems enable not only to identify roof separation and subsidence, but also to measure subsidence with scales and indicate the depth of separation. Readings above the action levels foresee further reinforcement of roof support with additional rockbolts or conventional support.
4. Control boreholes are up to 7.5 m deep. The boreholes are equipped with a number of magnesonic gauges for strata displacement control. Readings are periodically taken by a special read-out equipped with a flexible probe and are then processed on a computer.
5. Strain gauge rockbolts are used to determine value, location and direction of load which is taken by the measurement rockbolt along its length.
Permanent information gathering and processing enable to develop a database for diagnostics of mining and geological conditions and computer modelling of potential processes that occur on mine roadway development and also to consider their interaction in the process of mine field extraction.
Practical training in underground conditions of Longannet mine enabled to strengthen the knowledge about rock bolting of mine workings. Also experiments as pull tests using a pull out ram, roof strata coring for the evaluation of physical and mechanical properties were carried out. The participants of the project obtained practical skills in operating a bolting machine and installation of rockbolts. Visits to development headings on working shifts discovered numerous interesting aspects of organisation of work in teams.
Particular attention should be focused on the achievement of high safety and health profile.
First of all it is unconditional observance of technological requirements in the course of bolting and monitoring of rockbolted sites throughout the entire lifecycle of roadway. Regular shift engineers who are responsible for mining inspect the roadways. It is very important that some simple monitoring devices, such as sliding scale safety indicators (Tell-Tales), allow any trained person entering a roadway to get visual appraisal of qualitative conditions of strata and bolting itself by looking at a location of the scales.
British mine has the only specialist authorised to organise and manage rock bolting of roadways – rockbolting engineer who is subordinated directly to the mine manager. This is the mostly important personage in rock bolting. Mining engineer with a minimum 3 years of practical experience in drivage and support of mine workings and who also was trained on special two week courses at RMT is appointed to this position. The rockbolting engineer is authorised to make all the decisions concerning rockbolting, evaluation of possibility to bolt a particular roadway, design of support rules and issue of a work permits, permits to stop working if necessary and also to arrange for training of mine staff in new technologies. In addition a bolting engineer co-ordinates all relations with the owners of intellectual property and advanced technology, suppliers of materials, equipment and personal safety items.
Provision of individual safety items for miners involved in rockbolting of roadways is not different to regular equipping. These are helmets, protective eyewear, headphones and gloves. Wearing individual safety is mandatory for everyone when underground.
Upon the completion of training in Great Britain according to the programme of two week training course for rockbolting engineers all the Ukrainian participants were issued the certificates that authorise them to carry out work using the British technology rockbolting.
In January-February 2000 Tacis CCC continued to prepare the implementation of Phase 2 of the project. Theoretical training of technical engineers and workers was organised directly at Krasnoarmeyskaya-Zapadnaya No.1 mine.
The participants of the project had a meeting with Mr. L. Baysarov, Krasnoarmeyskaya-Zapadnaya No.1 mine manager, where fundamental issues concerning rock bolting activities were adjusted. The Mine Technical Board Meeting was held on where organisational actions were outlined and roadways for the experiment were selected. The support rules were designed by the RTC of GMI NASU and agreed with Donugi.
During the period 17-26 April 2000 the full scope of activities on Phase 2 of the BISTRO-Anker project was carried out at Krasnoarmeyskaya-Zapadnaya No.1 mine.
The objective of Phase 2 of the BISTRO-Anker project was to carry out scientific and industrial trials and feasibility study regarding the introduction of the advanced technology rockbolting, currently used at the British mines, to a Ukrainian mine and train the Ukrainian specialists in this technology.
According to the project terms 30 m of conveyor gateroad No.2-south in the incline of Block No.5 were driven in 10 days with ÊÑÏ-32 (KSP-32) roadheader. To support the roof 2.4 m rockbolts were used. The driven roadway was of the following parameters: 5.2 m (width) x 4.6 m (height). The first meters of the roadway were driven in-seam cutting 1.5 m of roof (with the strength of 50 MPa) followed by purely in-rock drivage. As the face advanced its cross-section was fully replaced by sandstone with strength of 80-100 MPa so further roadheader drivage and drilling of boreholes for rockbolts was no longer possible. The team was forced to transit to drill and blast method and steel arch support.
The following activities were carried out:
- Roof core
- Pull tests
- Drilling of borehole for a sonic extensometer, data reading and computer processing
- Tell Tale installation
- Installation of Tell Tale and Exto data processing software
- Testing of British, German and Ukrainian rockbolting consumables and Turbo Bolter bolting machine by Exchem.
To do 3-axial non-uniform compression test of strata it was planned to take a 50 mm/5 m roof core.
The site for coring was at 9 m from the face mouth (the thickness of roof cut was 2.95 m). Using a diamond bit core barrel the team managed to drill and take 2.5 m core. The drilling procedure was then ceased because of thinning of solid sandstone and extreme height of the roadway when the third stage of pneumatic prop at the bolter was turned on.
This test included 8 rockbolts of different lengths that were installed in the roof of the roadway driven. The objective of the test was to determine loads required to pull the rockbolts off the boreholes at different horizons. Thus, testing provides for determination of bond strength between rockbolt and surrounding strata. The rockbolt lengths were from 0.6 m to 2.2 m. Loads of up to 18 t were applied through hand-operated 30 t jack and were measured with a micrometer.
Six rockbolts out of eight demonstrated excellent results of the strata/resin/rockbolt system. The shortest two were displaced within the allowed limits at the load of 7 t and more. The probability of some roof separation at the depth up to 1 m was then confirmed by extensometer and tell tale readings.
Borehole for magnesonic monitoring station is normally 7.5 m long. In this case 35 mm borehole was drilled to the depth of 6 m at 9 m from the face mouth. 15 magnesonic sensors were installed in the borehole with a certain interval. On a daily basis readings were taken by flexible probe. Computer data processing enables to evaluate convergence of the roadway in the roof and visually demonstrate depth and magnitude of separation. The monitoring station was installed on 21 April at 1 m from the face. The graph reflects strata movement read-out on a daily basis from the installation day through the last readings taken on 26 April at 19.6 m from the face. Effectively separation occurred within the first day and reached up 3 mm at the depth of 0.4 m. The strata was then stabilised at the separation magnitude of 4 mm.
Safety Tell Tales are reference gauges with two sliding scales that are moved by strings and spring anchors which are placed in a borehole at the depths of 2.5 m and 5 m. Three-colour scales (green, yellow, red) are calibrated in millimetres. Good quality of rockbolting is determined according to relative position of the scales and relative position to the plastic body of tell tale which is set firm in a borehole mouth. Lowering of roof results into the tell tale body moving along the top scale or mutual movement of the scales. Action levels serve as a signal for additional actions to be undertaken in order to enhance load bearing capacity of a rockbolting system (for instance to increase bolting density).
Each tell tale station has its own number for organisation of systematic observation.
The first visual indicator was installed at 9 m from the roadway mouth along the centre line. The observations demonstrated that the values of roof convergence did not exceed 9 mm during the first several days which is absolutely acceptable.
Following the request of mine specialists the next three tell tales were installed after the next 6 m of drivage in one line across the roadway. One of them was installed in the middle and the other two - nearby the sides. These tell tales revealed roof displacement in the range of 3-6 mm.
Tell tale readings are observed on a shift basis. Readings are taken on a daily basis for further computer processing. Therefore it is always possible to get a true picture of rockbolting conditions along a roadway in the cover zone of monitoring stations.
Boreholes for rockbolts and monitoring stations were drilled with regular 27 mm drill bits (British) and 32 mm bits (German, Ukrainian). The time periods for full completion of a 2.4 m borehole were 2.5 min and 5 min correspondingly. However, transition to purely in-stone development ultimately required the use of diamond instruments.
To support 15 m of the roadway 22 mm British rockbolts were used. Stamped torque-pin nut is a particular feature of such rockbolt. Torque-pin is cut off by the torque of bolting machine as soon as the top end of a rockbolt has been fixed in a borehole with hardening fast set resin. Such design does not require additional manipulations with a drilling machine on changing of adapters for rockbolt installation and tightening of a nut. The w-straps are 2 mm thick and 2.5 m long. This length is determined by parameters of transportation container.
Further bolting was carried out using German rockbolts and consumables made by Carbospetspolymerkrep plant. The rockbolt diameter was 28 mm with the installation tail on the end. The shear strength of the rod is over 40 t. The straps were 5 mm thick with the length of 2.5 m.
Poor profile of the roof on drivage hampered the drill-in procedure resulting into upset of the bolting pattern.
The resin capsules by Exchem (Great Britain) and Carbospetspolymerkrep (Ukraine) demonstrated increased set speed which complicated the installation of rockbolts. As result, some 20% of rockbolts were installed with a lack of quality as they were not inserted into boreholes to full length of the rod.
According to the contract on the BISTRO project there was no original roof lagging materials to be supplied. Reinforced mesh was used as lagging which complicated its installation greatly.
All the activities on roof bolting and preparation of monitoring stations were carried out using Turbo Bolter, which is a drilling machine by Exchem, United Kingdom.
CONCLUSIONS
The demonstration of rockbolting as a method of roof support carried out in the conveyor roadway driven, as well as full-scale geotechnical investigation at Krasnoarmeyskaya-Zapadnaya No.1 mine proves the application of the advanced technology possible. Rockbolting would be mostly applicable as a means of support in mixed coal and stone faces in gateroad where later on during mining of highly productive longwalls problems of longwall t-junctions will be eliminated. Junction support can be fully mechanised with two sets of support of a larger size. For the first time it will be possible to predict and adjust roadway behaviour at all stages of its life cycle.
However, it is only systematic approach in the introduction that will provide reliable and safe operation of rockbolted workings. Stage by stage application of the rockbolting technologies in various workings, sections of the mine as well as in other mines will require a complex of measurements and observations to be carried out and improved work organisation.
The activities to improve the use of rockbolting at Krasnoarmeyskaya-Zapadnaya No.1 mine can be described as follows:
- Further adjustment of support rules:
- Orientation of rockbolts (all vertical);
- Bolting density;
- Side reinforcement.
- 2 or more operational bolting machines of appropriate size used in a face.
- 22 mm rockbolts are more feasible than 28 mm ones. Firstly because of substantially increased rates of borehole completion. Furthermore, rockbolt in assembly with torque-nut is technologically more effective and handy to install.
- Better profile of surrounding roof and ribs to be cut with a roadheader in a rectangular face.
- Straps and mesh panels assembly to be used across the entire width of roadway.
- Mesh panels to be equipped with hooks for ease of installation.
- Mechanisation issues to be addressed on:
- Horizontal boreholes drilled for reinforcement of roadway ribs;
- Installation of straps and mesh panels;
- Temporary support during the rockbolt installation procedure.
- Continued testing of safety indicators designed by the Rockbolting Technology Centre at GMI NASU;
Continued training of staff involved in rockbolting of roadways.
Rockbolting of the roadway is currently suspended. The face has been transited to drill and blast method of development. However, the mine plan for the third quarter includes drivage and rockbolting of a new longwall panel the incline of block 5. Hopefully, it is going to be one of successful stages of technical rearmament and improvement of mining facilities of the mine.