Field monitoring of stability of dump – a case study

Abstract

This paper presents results of the, field investigations and laboratory studies carried out at Jindal Power Open Cast Coal Mine. Based on the various Physico-mechanical properties and the field studies, empirical models and numerical modeling studies were conducted for the stability of dump slope.

It was proposed earlier to have internal overburden dumps of maximum height of 30 m in each individual deck with four decks up to 120 m overall dump height. Presently overburden dump height is about 72 m with a maximum deck height up to 25 m in this mine. These dumps and slopes are observed to be stable at present. Stability analyses for the proposed dumps were undertaken using various techniques for the maximum dump height of 120 m, which is the ultimate depth of the mine. Initially a row of overburden was dumped forming an embankment with a width of greater than 15 m and height up to 5 m all around the proposed area for fly ash dump. A number of such areas were formed in a layer wherein the fly ash was dumped so that each dump of fly ash was separated by another overburden dump of 15 m wide in order to control the airborne quality of the fly ash. Fly ash was dumped within this area surrounded by overburden in alternate layers of height not exceeding 5 m in each layer and dozed. Therefore, each layer of overburden was followed by a layer of mixture of fly ash and overburden (fly ash 25%) and so on up to the height of 30 m. Stability of Dump slopes was monitored with total station and monitoring stations fixed at an interval of 20 to 30 m on the dumps at a distance of about 5 m from the crest of the dump slope. 47 monitoring stations were installed with 1.0 m long pipes and masonry pillars; 23 stations in the Pit 1 and 24 stations in Pit 2 and total station was used for measuring RL of the stations

Displacement pattern of the monitoring stations during November 2012 to the end of March 2013 indicated no significant displacement in the Overburden dumps with fly ash ensuring stability of the dump near majority of the stations. The dump is in the process of continuous settlement near 1/3rd of the stations. Therefore, further monitoring of reduced levels of the stations may be continued till all the stations show complete settlement.