Stability Analysis of Overburden Dump Slope—A Case Study of Marki Mangli-I Coal Mine

Open cast mining produces huge amount of overburden dump material and it is stored in the form of external overburden dump in pit dumping. Present investigation deals with stability analysis of overburden dump slope at Marki Mangli-I open cast coal mine. The stripping ratio of the Marki Mangli-I coal mine is 6.75 which is very large. Existing overburden dump of the mine consists of three benches of overall height of 30 m and bench width of 20 m. Geomechanical properties and shear strength parameters of the dump material are investigated in the laboratory. Stability analysis of existing and proposed vertically extended dump slope is assessed by limit equilibrium method (LEM) and probability analysis of critical sections at chainage 450 m and 550 m, respectively. Factor of safety calculated by simplified Bishop’s and Spencer-Wright method of LEM is same. FOS of critical section at chainage 450 m of existing and extended dump slope is found out to be 1.77 and 1.37, respectively. Factor of safety of critical section at chainage 550 m of existing and extended dump slope is found out to be 1.60 and 1.45, respectively. Probability of factor of safety less than 1.01, 1.50, and 2.0 is 0.2%, 2.1%, and 21.1%, respectively, for existing dump at chainage 450 m. Probability of FOS less than 1.62 is 1% extended dump at chainage 550 m. Probability of FOS less than 1.34 and 1.50 is 0.1% and 82.6%, respectively, for extended dump at chainage 450 m. Probability of FOS less than 1.53 and 1.7 is 0.1% and 47%, respectively, for extended dump at chainage 550 m. From the investigation, existing dump is stable with factor of safety more than 1.50 and proposed vertical extension of existing dump is not permitted as the factor of safety is less than 1.5 at critical sections.