The 6th Victor de Mello Goa Lecture: Development of large direct shear facility for geotechnical characterization and stability assessment of opencast mines dumps

As opencast coal production increases, a crucial challenge is safeguarding the stability and management of overburden dumps while prioritizing both safety and cost-efficiency. Determining the optimal stable dump slope dimensions during and after mining remains a key challenge for mining operations worldwide. Assessing the stability of overburden (OB) dumps is necessary to maintain them at the steepest possible angle without compromising stability. Understanding the shear strength, including cohesion and angle of internal friction, of the heterogeneous dump mass is crucial for this assessment. To evaluate the shear strength behaviour of OB materials, a large direct shear machine (LDSM) was designed and developed at Central Mine Planning and Design Institute, Ranchi. The LDSM features a shear box with dimensions of 1000 mm × 1000 mm × 1000 mm to facilitate testing materials with larger particle sizes. It can test large specimens with a thickness up to 500 mm and a maximum particle size (Dmax) of 80mm in accordance with ASTM D3080-98. Seven different OB materials from Magadh Coalfields, India were collected and tested for their shear strength. Using the obtained shear strength parameters, various slope profiles are assessed for stability using 2D limit equilibrium software such as Slide2 and GALENA. Probabilistic modelling is employed to generate a statistically distributed factor of safety (FoS) instead of a deterministic value, accounting for uncertainties related to input parameters. This paper aims to forecast the maximum safe height for OB dumps based on the determined shear strength parameters.