Disaster Advances Vol. 6 (S6) December 2013

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1 Attempts to measure cuttability in selected colliery Stanisław Pruseka, Aleksander Wrana * Główny Instytut Górnictwa, Plac Gwarków 1, Katowice , Poland *awrana@gig.katowice.pl Abstrat The article presents an instrument for determining cuttability of coal and rock in underground conditions designed at the Glowny Instytut Gornictwa (GIG). The methods of measuring cuttability of coal and rock, which have been used in Poland and abroad so far, were reviewed. Then the main elements of the measuring instrument and the procedure of tests in underground conditions were described. Underground measurements of cuttability conducted in one of collieries in Poland were described. Key words: Mining, cuttability of coal seams, underground measurements Introduction Cuttability, which is defined as the force necessary to separate a specified amount of gangue or minerals, Has an important influence on the selection and durability of winning machines. The parameter determines power and dimensions of a winning machine, which is reflected in e.g. cost of fabricating and maintaining them. Negative consequences of selecting too big dimensions of cutting machines are particularly important in mining, especially in thin coal seams. That is why, within the framework of an international project realized by the Glowny Instytut Gornictwa (GIG) (Katowice - Poland) and the National Mining University (Dnepropetrovsk - Ukraine) titled: Technical and technological feasibility and economic validity of thin coal seams mining, the concept was devised and a prototype of the device for measuring cuttability of coal seams and surrounding them rock in underground conditions was fabricated. The article presents a review of methods of measuring cuttability of rocks and coal applied in different countries. The design of a new instrument for measuring cuttability of coal and rock in underground conditions was presented, and the full measurement cycle was characterized. Procedure and results of underground measurements conducted in one of collieries in Poland were presented as well. Selected methods of assessing cuttability of coal and rocks The sheer number of methods devised to measure cuttability of rock or coal seams shows, indirectly, how important the issue and the parameter really are. Measurements of cuttability were made for underground mining and tunnelling. Among the methods of assessing cuttability of coal and rock we can distinguish 1 : laboratory methods which assess index cuttability indirectly, recording drilling parameters, measurements of grindability, measurements of forces of machining with one or a set of cutting bits. In case of the first of the methods, Protodiakonow s index f is determined and tests on uniaxial compression strength (Rc) are conducted. asing on the values and various dependences the index of cuttability is calculated. Recording parameters of drilling in a seam, which was used in Russia, is based mainly on the analysis of the value of torque of a rod while drilling a hole in the face of a working. Measurements of grindability, as point of reference to assess cuttability, assume a share of grain classes in coal samples which is estimated after a fall from a certain height. The described methods are often subjected to a considerable error resulting from, most of all, not considering operational characteristics of cutting machines. Methods based on measurements of cutting forces on a cutting (193)

2 bit or a set of cutting bits are supposed to be much more accurate. oth laboratory methods, and measurements conducted in underground conditions can be distinguished here. Measurements of cuttability in laboratory conditions were made e.g. at AGH University of Science and Technology in Cracow 2, at CERCHAR in France 1, in the USA with the use of IN-SEAM TESTER 3, in Czech Republic at VVUU, a.s., Ostrava 4, and also at the Istanbul Technical University 5. It is worth pointing out that the research conducted at the Istanbul Technical University has a recommendation of the International Society for Rock Mechanics to be a standard for laboratory measurement of cuttability. Cuttability, in case of the research, is characterized with index SE calculated as a ratio of the force acting on a cutting bit and the volume of separated rock along a cut 6. FN SE Q MJ [ 3 m ] (1) - average force acting on a cutting bit [kn]; - volume of separated rock along a cut [m3/km]. To improve accuracy of assessing cuttability of coal and rock, a real shape of the groove is evaluated, basing on side break angle and cutting lines. In such a case the equation for calculating index cuttability (WU) is as follows: WU b 2g Pśr kn [ ] 2 1 tg ) cm (3) Pśr - average force of cutting [kn]; g - depth of cut [cm]; b width of a cutting bit [cm]; ψ side break angle [ ]. In respect to the value of index WU coal was divided into the following categories: easily cuttable WU < 0.10 kn/cm, averagely cuttable 0.11 kn/cm < WU < 0.65 kn/cm, hardly cuttable WU > 0.65 kn/cm. A separate category are measurement methods using specialist equipment to assess cuttability of coal in underground conditions. Underground tests have an advantage over laboratory ones, because they are conducted directly in a coal seam under true stresses, which reflect given geological-mining conditions. The tests also consider occurrence of cleavage planes in a seam. For the needs of Polish underground mining the cuttability tests were conducted with POS-1 and POU- M/1 devices 7 designed by ITG KOMAG and with a device used by the AGH University of Science and Technology in Cracow 8. In the devices the cutting force is determined basing on the pressure in the circuit. Additionally, the depth of cut is measured, and then index cuttability A is calculated with the following equation: P A g śr kn [ ] cm Pśr - average force of cutting [kn]; g - depth of cut [cm]. (2) Cuttability tests in underground conditions were also conducted in Czech Republic with ZP-1 device) and in Germany with a device designed by DMT GmbH & Co. KG 9. The DMT device is widely used for determining operating characteristics of coal planers (e.g. engine power) in given geological-mining conditions. The concept of the measurement is to record the cutting force for a standard cutting bit mounted in a measuring head while making a cut of depth of 2 cm. To classify coal seams, average force (Fs) acting on a cutting bit was used, assuming depth of the groove as a constant. Tests conducted according to the methodology enabled preparing a classification which divides coal seams as follows: well cuttable Fs < 1.5 kn, normally cuttable 1.5 kn < Fs < 2.0 kn, hardly cuttable 2.0 kn < Fs < 2.5 kn, very hardly cuttable 2.5 kn < Fs. Instrument for measuring cuttability of coal seams and surrounding rock designed at GIG (194)

The instrument for measuring cuttability of coal seams and surrounding rock, designed at GIG, consists of the following main elements: Measuring Module, flame-proof computer OKG-1, Oil Power Unit

The Module can also smooth the surface of sidewalls, make a measuring cut recording the force on the cutting bit, and scan the groove after the cut. Fig.

with detachable heads shown in Fig. 2. The measuring head (cutting head) consists of a cutting bit and a strain gauge force sensor (Fig. 2a).

3 The instrument for measuring cuttability of coal seams and surrounding rock, designed at GIG, consists of the following main elements: Measuring Module, flame-proof computer OKG-1, Oil Power Unit ZZO-1. The design of the Measuring Module is presented in Fig. 1. Its main element is an instrument for measuring cuttability. The Module can also smooth the surface of sidewalls, make a measuring cut recording the force on the cutting bit, and scan the groove after the cut. Fig. 1 Elements of Measuring Module schematics (1 feed-in mechanism; 2- measuring head; 3 milling head; 4 scanning head; 5 hydraulic engine) The above mentioned functions of Measuring Module are realized with detachable heads shown in Fig. 2. The measuring head (cutting head) consists of a cutting bit and a strain gauge force sensor (Fig. 2a). The scanning head consists of two elements: a laser scanning the cut and a recorder (Fig. 2b). The head is used to measure geometry of the groove made with a measuring cut. The milling head is equipped with a hydraulic engine. The engine powers the milling head when it prepares the examined sidewall for the measurement (Fig. 2c). Fig. 2 Heads of Measuring Module - a) measuring head with a cutting bit; b) scanning head; c) milling head, smoothing the sidewall before a measuring cut. Movement of the heads along a coal sidewall is made with a transmission chain connected with a planetary gearbox and a hydraulic engine. Feed-in of the measuring head is done with a manually operated mechanism with two worm shafts (Fig. 1). The scanning head and the measuring head are equipped with sensors connected with flame-proof computer OKG-1. The computer records the measurement data and enables checking them on-site. The whole measuring unit is powered with Oil Power Unit ZZO-1 (Fig. 3). Its task is to produce flow of oil of appropriate pressure to power the hydraulic engines installed in the measuring unit and the milling head. The pumps suck oil from a tank, being an integral part of the device, which enables making measurements independently on availability of oil-water emulsion on-site and providing steady parameters of work of the device. Fig. 3 Heads of Measuring Module - a) measuring head with a cutting bit; b) scanning head; c) milling head, smoothing the sidewall before a measuring cut. (195)

The main advantages of the measuring instrument designed at GIG are: high accuracy of measurements made, due to smoothing the surface of a sidewall prior to a

Figure 4 shows the elements of a full cycle of measuring cuttability with the instrument designed at GIG 10, 11 Smoothing the surface of a sidewall Scanning the

In the immediate roof strata there was clay shale of thickness of 1.45 m 6.40 m.

In the floor of seam 308 there was clay shale. Compression strength of the roof rocks, basing on penetrometer tests, was approx. 16.6 MPa.

There were also laboratory tests of compression strength of coal samples taken from the location where cuttability was measured.

Figure 5 shows the exact location of the underground tests of cuttability. Rescanning the surface Making the measurement cut Fig.

The cycle presented in Figure 4 is tightly linked with the methodology of determining resistance to milling devised at the Glowny Instytut Gornictwa.

The idea of the method is to compare the recorded shapes of the surface of the solid, before and after making the cut and then calculate the volume of separated

4 The main advantages of the measuring instrument designed at GIG are: high accuracy of measurements made, due to smoothing the surface of a sidewall prior to a measuring cut; and laser scanning which enables projecting, in detail, geometric parameters of the groove after a measuring cut. Figure 4 shows the elements of a full cycle of measuring cuttability with the instrument designed at GIG 10, 11 Smoothing the surface of a sidewall Scanning the surface underground measurements a roadway in seam 308 was selected. The roadway was driven in a seam of thickness of 1.65 m 1.80 m at the depth of 370 m. In the immediate roof strata there was clay shale of thickness of 1.45 m 6.40 m. The basic roof was formed of various grained sandstone with intercalations of clay shale of thickness of approx. between 11.9 m and m. In the floor of seam 308 there was clay shale. Compression strength of the roof rocks, basing on penetrometer tests, was approx MPa. Floor rock strength was 23.4 MPa. There were also laboratory tests of compression strength of coal samples taken from the location where cuttability was measured. As a result of the tests, the average compression strength for coal was determined to be 25.5 MPa. Figure 5 shows the exact location of the underground tests of cuttability. Rescanning the surface Making the measurement cut Fig. 4 Cycle of measurement of cuttability of coal seams and surrounding rock with the instrument designed at GIG. The cycle presented in Figure 4 is tightly linked with the methodology of determining resistance to milling devised at the Glowny Instytut Gornictwa. According to the methodology cuttability is characterised by a ratio of the force acting on a cutting bit and the volume of separated coal or rock. The idea of the method is to compare the recorded shapes of the surface of the solid, before and after making the cut and then calculate the volume of separated coal or rock. The next step is calculating the index of cuttability with the following dependence (Prusek et al. 2011b): A F V kn [ 3 cm ] (4) Fig. 5 Location of underground measurement in seam 308. The tests were conducted according to the procedure presented in Figure 4. The instrument designed at GIG for assessing cuttability installed at the face of the roadway is shown in Figure 6. F - average value of force measured on a cutting bit during the cut, V - volume of separated coal or rock. Underground measurements During underground tests the instrument was used in one of Polish collieries to assess cuttability of coal. For (196)

Fig. 6 The instrument for measuring cuttability installed at the face of the roadway According to the assumed measuring cycle, the first task was to smooth the surface

Figure 9 presents results of the measurements in form of a graph of the force acting on the cutting bit.

7 Heads of the measuring module a) smoothing the surface of the sidewall; b) scanning the sidewall surface prior to a measuring cut.

The next stage of the measurement was scanning the smoothed surface with the laser scanner. The process of scanning is presented in Figure 7b.

5 Fig. 6 The instrument for measuring cuttability installed at the face of the roadway According to the assumed measuring cycle, the first task was to smooth the surface of the sidewall with the milling head (Fig. 7a). Fig. 8 The measuring head with a cutting bit. Figure 9 presents results of the measurements in form of a graph of the force acting on the cutting bit. 16 Force [kn] 14 Force acting on a cutting bit [kn] Fig. 7 Heads of the measuring module a) smoothing the surface of the sidewall; b) scanning the sidewall surface prior to a measuring cut Position of measurment head [mm] Fig. 9 Values of the force acting on the cutting bit during tests of coal in seam 308. The next stage of the measurement was scanning the smoothed surface with the laser scanner. The process of scanning is presented in Figure 7b. Then the measuring cut was made and, simultaneously, the force acting on a cutting bit was measured and recorded. Figure 8 shows the measuring head with a cutting bit. As it can be seen in the graph in Figure 9 the maximum force acting on the cutting bit reached the value of approx. 14 kn. Average value of the force was 5.60 kn. The last stage of the test was scanning the groove after making a measuring cut to compare the results with the image of the smoothed surface (Fig. 10). (197)

6 Fig. 10 Image of a groove after a measuring cut in seam 308. Results of the underground tests enabled assessing cuttability of coal in the measurement location. The index WU was assumed as the index characterising cuttability, additionally, for comparison, the index A was determined. Values of the index WU, calculated with the results of the tests, are presented in Fig. 11. Values of index WU [kn/cm] 1,8 WU [kn/cm] 1,6 1,4 1,2 1 0,8 0,6 0,4 0, Position of measurement head [mm] Fig. 11 Values of the index WU, for coal in seam 308. According to the graph presented in Figure 11 the maximum values of the index WU are as high as 1.53 kn/cm, which, according to the classification described in point 2 allows to classify coal of seam 308 as hardly cuttable one. Average value of instantaneous indexes is 0.61 kn/cm which classifies the coal of the seam between averagely and hardly cuttable ones. Figure 12 shows the distribution of calculated, instantaneous values of the index A along the measuring groove. Value of index A for coal [kn/cm] 14 A [kn/cm3] Similarly to the index WU, there is a significant difference between the maximum instantaneous value of 12.4 kn/cm3, and the average value of 3.41 kn/cm3 of the index A. Summary At the Glowny Instytut Gornictwa there were conducted works aimed at designing a new instrument for measuring cuttability of coal seams and surrounding rock in underground conditions. They consisted of several stages, starting from devising a concept, through designing, fabricating a prototype, obtaining the certificate of compliance with ATEX Directive, specifying methodology of research, and finally, testing in underground conditions. Tests of cuttability in geological-mining conditions of seam 308 confirmed that it is possible to measure both the force acting on a cutting bit, and scan the shape of the groove with a laser. Values of the force acting on the cutting bit in a roadway in seam 308, together with particular geometric parameters of the groove, allowed to calculate the indexes characterising cuttability of a coal seam. Their values allow to classify coal of seam 308 as hardly cuttable one. It may be concluded that, for the current research needs, it is possible to use classification of cuttability of coal seams which applies the index WU. In the future it is planned to continue both underground and laboratory tests to create a classification of cuttability of coal seams basing on the index A. References 1. iały W. Analiza metod badania urabialności węgla. Przegląd Górniczy nr 4. (2002). 2. Krauze K. Urabianie skał kombajnami ścianowymi. Wydawnictwo Śląsk, Katowice. (2010) Position of measurement head [mm] Fig. 12 Values of the index A, for coal in seam Sundae L. Measurement of Coal-cutting Forces Underground With the In-seam Tester. NIOSH Report of Investigations. (1986). (198)

7 4. Sikora W., Fels M., Sołtysek K. Strugalność węgla. Prace GIG Komunikat nr 687. (1978). 8. Andrusiewicz W. Możliwość zmiany sposobu urabiania soli kamiennej w KS Kłodawa. Gospodarka Surowcami Mineralnymi Zeszyt 2. (2008). 5. alci C., ilgin N. Correlative study of linear small and fullscale rock cutting tests to select mechanized excavation machines. International Journal of Rock Mechanics & Mining Sciences nr 44. (2007). 6. Eskikaya S., ilgin N., Ozdemir L. Development of rapid excavation technologies for the Turkish mining and tunneling industries. NATO TU Excavation SfS Program project report. Mining Engineering Department; Istanbul Technical University.(2000). 7. iały W., Mizgała J. Koncepcja przyrządu do wyznaczania oporów urabiania. Mechanizacja i Automatyzacja Górnictwa nr 2. (2006). 9. Myszkowski M., Paschedag U. Longwall mining in seams of medium thickness - comparison between shearer and plow. 21st World Mining Congress. Kraków. (2008). 10. Prusek St., Rajwa S., Walentek A., Wrana A. Wykorzystanie nowoczesnych technik pomiarowych do oceny parametru skrawalności węgla i skał w warunkach in situ. Prace Naukowe GIG. Kwartalnik Górnictwo i Środowisko Nr 1/1/2011. Katowice. (2011). 11. Prusek S., Rajwa S., Wrana A., Walentek A. Determination of Cuttability of Coal Seams and the Surrounding Rocks in Underground Conditions by Means of a Device Designed at GIG. New Techniques and Technologies in Thin Coal Seam Exploitation, International Mining Forum, wyd. Taylor and Francis, LW ogdanka. (2011) (199)

Multislice Longwalling for Thick Seam Extraction - Properties of Goaf in the Roof and Gate Roads Behaviour

Multislice Longwalling for Thick Seam Extraction - Properties of Goaf in the Roof and Gate Roads Behaviour Presenter: Stanisław Prusek Authors: Prusek S.,¹ Lubosik Z¹., Płonka M 1., and Syrek B² ¹ Główny