1、Cuttability of coal seams with igneous intrusions Rajendra Singh*, A.K. Singh, P.K. MandalAbstract On the basis of physical inspection of exposed area in a gallery, the coal mass near an igneous intrusion band is divided into four zones; called as (1) normal, (2) pulverized, (3) Jhama and (4) mixed
2、zone excluding the dyke/sill. Some simple field and laboratory studies were carried out to visualise the nature and extent of variation of strength and cuttability across these zones of igneous intrusion in a coal seam. Influence of intruded igneous materials over the in situ strength of the coal ma
3、ss was studied by Schmidt hammer, while the influence over cuttability of the seam was studied through monitoring of current drawn by roadheaders during mechanised gallery drivage in coal seams consisting of igneous intrusions. Both strength and cuttability across the band of igneous intrusion were
4、found to be highly dependent upon the proximity and extent of the intrusion. In fact, the requirement of current for gallery drivage across the coal mass with igneous intrusion was observed to be quite high in comparison to that required for the normal coal mass. To understand this phenomenon in det
5、ail, a number of samples were collected from the coal intrusion interface and were subjected to laboratory tests for physico-mechanical properties along with cuttability testing with a drag bit type coal plough rig. The laboratory study showed wide variation in physico-mechanical and cuttability pro
6、perties of different samples collected from different zones of the affected coal mass surrounding the intrusion band. D 2002 Elsevier Science B.V. All rights reserved.1. IntroductionCoal is a concentrated form of invaluable natural energy. Its proper exploitation is important not only foreconomical
7、development but also for environmental, ecological and conservation points of view. Mecha- nised extraction of coal provides better production, productivity and safety. However, mechanical cutting of coal is difficult because of higher strength coal seams in India (Singh, 1999). This situation becom
8、es even more difficult in a coalfield with large number of igneous intrusions in the coal seams. Jharia coalfield is becomes important if the drivage/working encounters traversed by a number of different igneous intrusions affecting workability of a considerable number of coal seams. Here, a number
9、of coal seams have been baked in absence of oxygen (Jhama formation) during the intrusion of the igneous materials. Depending upon various factors like temperature of the igneous mate- rial, duration of the igneous activity, size of the entry channels in the basin sediment, etc., the composition of
10、jhama varied within wide limits (Chandra, 1992). Currently, powerful coal cutting machines are available in the market to cut harder and harder rock, but a better understanding of progressive change on the behavior of a coal mass around the jhama/dyke contact plane becomes important if the drivage/w
11、orking encounters an igneous intrusive frequently in the coal mass。2. Literature review Although the first coal retrieval machine was developed and used in a British coal mine more than 130years ago (Walker, 1902), most of the studies on coal cutting were done only within the last five decades. The
12、effect of cutting tool and machine parameters, geo-mining conditions and physic mechanical properties of coal over cutting force was studied by a number of authors and, theoretical aspects of coal cutting were detailed in the late 1950s (Evans, 1958). The exper- imental results of extensive work con
13、ducted in this field by Pomeroy (1963, 1964) provided the effects of tool geometry and other operational factors on the cutting force. Initially, Merchants theory (Merchant, 1944) of basic mechanics of the metal cutting process was applied to give an analytical equation of the cutting force for coal
14、/rock cutting (Roxborough and Rispin, 1973). Further research thrust in this field led to construction of a full scale boom tunneling research rig in a laboratory (Speight and Fowell, 1987) to obtain accurate cutting data. On the have been developed to describe the process of chip formation. Experim
15、ental results of the tool rock interaction have been used for the improvement in cutting efficiency with the pick cutting machines (Hekimoglu, 1995; Bilgin et al., 1996). An empirical model of in situcuttability of hard coal seams was developed (Singh et al., 1995) to estimate the power of a coal-cu
16、tting machine considering the geo-mining domain of the field in totality. However, even with all these studies, the mechanism of the coal cutting is not well under- stood mainly due to the inherent complex processes. The exact stress analysis during the chip formation is yet to be developed. In the process of chip formation, crack propagation is the basic phenomenon for coal disintegration during cutting. This mechanism of fr
