Abrasivity of Indian Coals - an Assessment

The performance of any coal wining machine is influenced by a panoply of variables may it be controllable or uncontrollable in nature. The cutting performance of any tool in particular, is governed by various factors such as strength of rock, RQD, fracture spacing, inclination of the bedding planes, insitu state of stress, abrasivity and design parameters of tool namely, width, cutting angle, clearance angle, rake angle and composition of tool etc. This paper synthesizes the experience gained while studying the cutting performance of shearer into a workable classification known as RAR (Rock Abrasivity Rating), that can help select a feasible cutting system. Assessment of abrasivity and its effect on the performance of cutting tool are brought out. The results of abrasivity studies at the various longwall sites in India viz., VK7, JK5, GDK9 of Singareni Collieries, Dhemomain of ECL and Moonidiah of BCCL susidaries of Coal India Ltd. using an equipment designed and fabricated at Indian School of Mines, Dhanbad known as ISMAT Index are presented and a comparative study of various rock properties such as Rebound Number, Compressive Strenght and NCB Cone Indentor Index with ISMAT Index is also done with an aim to standardise it

Improving roadheader performance in Indian coal mines - a system development approach and field investigations

A systematic analysis of the operational and design requirements of mechanized roadway development system (RDS) employing roadheaders is presented in this paper. The operational and design relationships developed for mechanized roadway development system (MRDS) provide analytical, numerical and empirical tools for improved planning and performance. The mathematical expressions for roadway development rate (RDR), operating time of a roadheader, waiting time of conveyor extensions and roof bolting time were derived. The expressions derived for RDR are for two sets of conditions: (i) under equipment failure conditions (ii) under roof failure conditions. The objective of this paper is to present a strategy for enhancing the roadway development rate (RDR) employing roadheaders and its validation through Indian case studies. The RDR should match the production rate of roadheader with belt conveyor and roof bolting advance after a careful analysis of the delays encountered in these subsystems. The improved design methodology in a nutshell includes delineation of critical variables and their influence on RDR and development of a deterministic cum stochastic model to finally choose a right roadheader system configuration

Development of a drill energy utilization index for aiding selection of drill machines in surface mines

Drill machines used in surface mines, particularly in coal, is characterized by a very poor utilization (around 40%) and low availability (around 60%). The main purpose of this study is to develop a drill selection methodology and simultaneously a performance evaluation technique based on drill cuttings produced and drilling rate achieved. In all 28 blast drilled through were investigated. The drilling was accomplished by 5 different drill machines of Ingersoll-Rand and Revathi working in coal mines of Sonepur Bazari (SECL) and Block-II (BCCL). The drills are Rotary and Rotary Percussive type using tri-cone rock roller bits. Drill cuttings were collected and sieve analysis was done in the laboratory. Using Rosin Ramler Diagram, coarseness index (CI), mean chip size (d), specific-surface area (SSA) and characteristic particle size distribution curves for all the holes drilled were plotted. The predictor equation for drill penetration rate established through multiple regressions was found to have a very good correlation with an index of determination of 0.85. A comparative analysis of particle size distribution curves was used to evaluate the drill efficiency. The suggested approach utilises the area under the curve, after the point of trend reversal and brittleness ratio of the respective bench to arrive at drill energy utilization index (DEUI), for mapping of drill machine to bench. The developed DEUI can aid in selecting or mapping a right machine to right bench for achieving higher penetration rate and utilizations. Keywords: Drill cutting parameter, Coarseness index, Mean chip size, Specific surface area, Particle size distribution curves, Drill energy utilization inde

Blasting Problems in Underground Constructions through Deccan Trap Formation: Some Experiences at Koyna Hydro-Electric Project, Stage IV

The underground excavations of Koyna Hydro-electric Project, Stage IV were carried out by drilling and blasting through Deccan trap formations consisting mainly of basalts and volcanic braccia. Overbreak in the basaltic formation and underbeak in the volcanic braccia increased the cost and time of construction considerably. Modifications in the sequence and method of excavation and implementation of smooth blasting practice improved the produotivity substantially. The paper reports in details the rock mass condition ~ nd the blasting problems in the machine hall, the head race turnnelm and the surge shaft, the reasons behind such problems in retrospect Of rock mass-explosive interaction, the modifications made in the blasting practice and the improvements obtained thereby. The observations and the results reported herein can help set guidelines for the planning and execution of future construction work in the similar formations

Pot-hole Subsidence in Underground Coal Mining: Some Indian Experiences

Subsidence is a gradual or sudden depression of the ground on the surface due to extraction of minerals from underground. It occurs in two forms, namely, trough and pot-hole subsidence. Trough subsidence is a depression covering a large surface area, whereas pot-hole subsidence is a localized phenomenon which occurs due to sudden collapse of overburden into the underground voids. Pot hole is extremely hazardous as it does not give any prior indication before its occurrence. Several pot-holes have occurred in the recent past in the coal mines of South Eastern Coalfield Limited and therefore the study assumes great importance. This paper presents the mechanism, behaviour and critical influencing parameters concerning pot-holes. Field investigations and analysis carried out on pot-holes which occurred in some of the Indian coal mines are presented for highlighting the importance of the same

Mechanical wear of cutters in tunnel boring machines – a comprehensive review

Factors that determine the selection of method to excavate a tunnel depend upon the geology, economy and site conditions, but when it comes to the economics of tunnelling then it has to be chosen correctly as per the methodology. Cutters are an integral part of a tunnel boring machine and its performance depends largely on these. In order to ascertain various factors of cutters that influence the performance of the machine, a comprehensive study of literature was carried out. The method involved referencing the citations to a particular publication from which the importance of factors responsible for cutter wear in TBM were decided. In order to categorise the impact of different variables on cutter wear, the references were divided into wear, mechanical, geological and engineering categories based on citations reviewed and observed. Cutting conditions of disc cutters has been reviewed and evaluated based on findings of different authors