INTRODUCTION

Protectien of surface features and structures against ground movements due to extraction of coal seams underground as well as safety of men and material underground against water inrush from overlying water bodies has been, attracting attention of practising mining engineers in India since a long time. To obtain necessary information regarding various ground movement parameters under different working conditions investigations were initiated by the Central Mining Research Station (CMRS), Dhanbad, Bihar in 1964. The investigations conducted to far have enabled the authors to arrive at norms and relationships between ground movement parameters, which are being used to decide feasibility of extraction of coal seams under surface features and structures including water bodies. One such experiment, for the first time in India, was conducted at Sudamdih Project of Bharat Coking Coal Limited in Jharia coalfield, where two seams of 7.5 m and 22 m thickness were extracted by longwall ascending slicing with hydraulic sand stowing sand stowing underneath and in the vicinity of a main railway line and water- legged, old and unknown workings of three seams.

The extraction in 7.5-m thick XI/XII seam was done between 1971 and 1978, when about 656,000 tonne of coal was extracted. In 22-m thick IX/X seam extraction commenced by the end of 1975 and so far about 350,000 tonne of coal has been extracted. The railway line has since been made to subside by 385 mm, without affecting its normal operation. The underground workings have remained unaffected by overlying water-logged old workings. These investigations have been described briefly in this paper.

SUDAMDIH PROJECT

Sudamdih Project of Bharat Coking Coal Limited is situated in Jharia coal field about 20 km from Dhanbad railway station (Fig. 1). The Project was designed to produce 7,000 tonne of coal per day from VIII, VIIIA, special, IX/X, XI/XII, XIV and XV seams by longwall ascending slicing and chamber methods with hydraulic sand stowing. Most of the area of Sudamdih is covered with Barakar formation and almost all the seams in Jharia coalfield outcrop in this area. Strike of the formation in this area is almost East-West and dip due South.

Due to geological disturbances the dip of different seams was found to vary from 300 to 550º. The area is also affected by igneous intrusions, converting coal into jhama and peculier low-angle faults. Due to geology of the area, multiplicity of seams of coking coal dipping at 300 to 55º and presence of important surface features and structures like Damodar river, a main railway line, buildings, etc. the coal seams were to be worked with hydraulic sand stowing with horizon pattern of mining. For this purpose two 7. 5-m finished diameter and fully concrete lined shafts were sunk and horizon connections with coal seams were established at 200 m, 300 m and 400 m depths. The two shafts were sunk to work coal seams between, 200 m and 400 m depth.

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