251 THE FEASIBILITY OF HORIZONTAL aND INCLINED SLICING OF A THICK COAL SEAMS IN CONJUNCTION WITH HYDRAULIC FILLIN G T N Singh, B.Sc., B.Sc. (Mining. Jihgg.) V isiting Lecturer, Department o f Mining lihgineering, U niversity o f Newcastle Upon Tyne, U.K. R D Singh, M.Sc.(Mining), A.I.S.M ., C.Ihg. Professor and Head o f the Department o f Mining Engineering, Indian School o f Mines Dhanbad, India S y n o p s is Mining of 20 metre thick coal seam of Sudamdih and Chasnala block of Jharia coal fie ld of India has become extremely d iffic u lt due to seam thickness, presence of surface features, old water logged workings and large water bodies. Die property is highly disturbed with gradient from 25° to 50°• Proneness of coal to spontaneous' heating has further aggravated the problem, leaving no alternative other than slicing in conjunction with hydraulic fillin g . The extraction of the fu ll thickness by horizontal slicin g was trie d in Sudamdih and Chasnala mines in ix /x seam and x ii/x iii/x iv combined seams respectivelyc The faces were system atically monitored for convergence, deformation and sliding due to mining, and were simultaneously subjected to Equivalent M aterial Model investigations for different strata control variants. The model study furnished the firs t conclusive information that the horizontal slicing after 4-5 slices was likely to fa il due to large scale movement of the roof coal mass, development o f cracks normal to bedding plane and likelihood of heating problems• The inclined slicing was subsequently tried, in Sudamdih along with the model investigation in the laboratory. The model investigations revealed that the inclined slicing in ascending order in conjunction with stowing was like ly to induce parting/separation along the loose top coal section after 4 slice workings. As an alternative, the seam was subdivided into two sections of 10 m each. The top 10 m coal was worked in ascending order with hydraulic fillin g which caused minor parting/separation along the roof. The extraction of the lower subjection after 3 slices became again d iffic u lt due to frequent failure of the partings• The panel size in the mine vras reduced to 60 m x 110 m, due to the presence of a railway line and workings in the upper horizons.Slicing of such a narrow panel up to 2 slice has been successfully completed,while the th ird one was in 253 progress without remarkable deterioration of roof and gate road conditions. Thick stable coal bed in between the compact stowed goaf and the loose roof coal was like ly to control the parting up to the next 2-3 slices due to narrow panel size but wide panel mining beyond k slices in the presence of loose coal might create heating and strata control problems with thinning of the p a r t i n g . The blocks under reference constitute major coking coal reserve of the country. As such concerted efforts are in progress for better exploitation of these seams. Cross inclined slicing with overcutting in conjunction with stowing has been suggested as an alternative method, for such seam workings. The efficacy of this method has been established in model studies. Introduction The g ift of nature in the foim of a number of thick coal seams under shallow depth covers in Jharia C oalfield of India, though has added considerably to coal resources of India, presents innumerable problems in exploitation due to teclinological inadequacies. Below the Jharia town, each square metre of the t'Own area contains nearly 85 tons of coal (including 35 tons of coking coal) and is threatened by creeping fires from the neighbouring areas-. At the southern outskirt oh" the; Jharia coal fie ld in the vicin ity of the great boundary fault Cvri.th a throw of over T500 m) the problem is equally d iffic u lt.. This area contains a huge reserve of prime coking co.al in some o f the thickest seams of the country «.• viz., ix /x seam of Suuamdih (.over 20 m thick),, x ii/x iii/x iv seams of Chasnala co llie ry (nearly 22 m thick}.. In this, belt the existence- of surface fires through quarries and inclines and the old workings flooded with water as a precaution against fire have given newer- dimensions to the problems. The seams arc dipping steeply in this area (25°-4-5°) and are traversed by a number o f sympathetic . -faults and dykes. Moreover, River bamodar, Adra-Gomoh Railway lin e and a number of other surface features, make surface subsidence control measures essential before planning any exploitation system. Experiments are underway to evolve suitable mining techniques to extract some of these thick, seams w ith minimum exploitation loss. Presented in this paper are the observations of the strata movement associated with different alterna­ tives of mining methods as studied by Equivalent M aterial Mine Models as well as those monitored in situ . 255 Geology of the area The area under reference forms the south eastern boundary of Jharia coalfield (Figure 1). The seams dip steeply in the area, are traversed by a number of minor faults and are burnt in some sections due to igneous intrusions. The sequence of seams and th e ir partings in Sudamdih and Chasnala areas are shown in the exploded views in the same figure. The seams x ii/x iii/x iv have joined in Chasnala outcrop side to form a 22 m thick seam and tend to part down below into two separate sections due to a sand dyke. The area contains a ll the seams up to xvi seam, most of which outcrop in the area. The formation in general is strong sandstone and shale. Fireclay is met in the area in the form of thin bands. High permeability of the formation noticed during shaft sinking and subsequent workings shows the degree of geological disturbance in th e a re a . The ix /x combined seam in oudumdih block is the main source of eking coal, the thickness of which varies from 18.5 m to 22.5' m. In the steeper section, the thickness tends to decrease. A number o f seams are burnt in the area including a section of ix/x seam which is b u r n t to 1 CJ-16 m thickness on the rise side. The intrusion has damaged the seam along the hanging wall side resulting in pulverisation and flowing tendency in the coal. Methods o f mining The combined x ii/x iii/x iv seam was extensively worked by b o rd and p i l l a r m e thod up to th e y e a r 194-9 i n C h a sn a la C olliery adopting a modified method o f horizon system while only development along the floor was done in the Sudamdih take. The workings were extended through inclines driven along apparent dip to over 60 m depth. The Chasnala workings were nearly 1 500 m along the strike , from horizon A to L, with overall recovery of The workings in both the blocks were abandoned due to unfavour­ able conditions and were subsequently flooded to prevent extension of fire . The workings were again resumed a fte r 1960 when the seams were approached through shafts. As a number o f steeply dipping seams occur in this area, horizon system of deve­ lopment was adopted. The lower workings were started after leaving barriers below known lim it of old workings. The seams were worked by horizontal slicing (or Kazimierze method of mining as the Polish engineers name it ). 257 Horizontal Slicing The horizons were developed, to approach d iffe re nt seams normally 100 m apart and were interconnected by raises at 100 m intervals to form blocks. Extraction w ithin the blocks was done in ascending order with level faces extending from footwall to hangingwall and advancing along the strike line in between two raises. The middle raise served as coal transport channel fo r two identical faces on its either side and carried the coal to the lower horizon through a shaker conveyor or chute. The goaf was fille d by sand up to the roof. Timber props and bars were used as face support (figure 2). Conventional cycle of d rillin g and blasting and loading o f coal on panzer conveyor- was adopted. The goaf was stowed after 2 to 3 cycles of advance. The essence o f the methods adopted at ^iidamdih mine is shown in. figure 3. The method was modified in Chasnala LCE-I panel to bord and p illa r development and depillaring in conjunction w ith stowing due to the presence of stone dyke in the middle of the seam. S cientific Investigation • EQUIVALENT i-uVr.iWA.LAL MODEL 11WHST1 CATIONS : The mothou of mining adopted a rb itra rily was subjected to eadivalent m aterial mine model investigations. The mouels were made on a geometrical scale o f 1 :100, using gypsum binder w ith sand and mica in a frame 200 cm x 1 5 cm x I 20/200 cm, which could be tilte d from 25°-50°. The model was basically aimed to anticipate any sliding tendency of the barrier in the presence of fireclay band in the flo o r along which excessive water'seepage was noticed* Instrum entation was also planned to measure movement along the hangingwall and deformation Of the roof coal m ass.