Prabhat Kumar Mandal

Cuttability of coal seams with igneous intrusions

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 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 mass 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 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 detail, 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 properties of different samples collected from different zones of the affected coal mass surrounding the intrusion band.