1.0 INTRODUCTION:

Mining at Kasnau - Matasukh lignite mine near Nagaur (Rajasthan) started in January 2003 at two pits viz Kasnau and Matasukh, which are approximately 2 km apart. The mine was initially developed on a benching pattern of 10 m (h) and 12 m (w), with a bench slope of 600 in both the pits. Before opening the mine no geo-technical investigations were carried out in the area. Both the pits were developed simultaneously and lignite seam was touched by the end of the year 2003. The pits have been developed to a depth of approximately 50 m from the surface. However, the working in both the pits had been plagued by the problems of slope failure and huge inrush of water in the pits, particularly from the confined aquifer below the lignite seam with hydrostatic head of 22 to 25 m., which ultimately lead to cessation of mining operations at both the pits. To ensure the stability of slopes; geo-technical investigations of soil formation comprising overburden, lignite seam, inter burden as well as formations underlying lignite seam were undertaken. Based on the above investigation, the design of optimum safe highwall slopes had been suggested in August 2004. Further, it was decided to restart work in Matasukh pit only. On the basis of the report for design of highwall slope and the rehabilitation plan submitted by CMPDI, DGMS granted the permission under Coal Mines Regulation 1957 to extract lignite from Matasukh pit with following stipulations:

  • Height of the bench in overburden and in lignite at Matasukh pit shall not be more than 3 m and the width thereof shall not be less than 6 m at any place.

  • Groundwater level shall be kept and maintained at least 2 m below the planned pit bottom at that point. Necessary instrumentation in this regard will be installed.

  • The width of the benches shall not be reduced to less than the prescribed width at any stage, so however that the overall pit slope shall not become steeper than 23.2 degrees from horizontal unless separate permission is obtained from this Directorate.

After obtaining permission to mine lignite, rehabilitation of Matasukh pit was started. In order to meet the condition (b) above, drilling started at 15 sites in April 2005 for installation of a battery of pumps. After undertaking rehabilitation of mine as per above stipulations, lignite was extracted for two cycles. While operating the mine, the following points have arisen before the management, slope designer and office of the DGMS:

  • The depressurisation of confined aquifer in mining area could not be achieved to a desired level of 2 m below the pit floor

  • The quantity of water handled was far in excess of the initial estimations

  • Since the quality of water pumped was very poor, its disposal had become a problem for the management.

Further, the cost of pumping water had raised a question mark on the economic viability of the mine.

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