Rock-mass classification for design of roof supports - a statistical evaluation of parameters

Bieniawski's RMR method of rock-mass classification was used as the basis for developing a new classification suitable for Indian coal-measures strata. Statistical analyses were carried out on geotechnical data obtained from 150 published case records and detailed field investigations in underground mines. First, a general frequency survey of all the causative factors was made to identify the factors exercising deleterious effects on roof stability. Then, multivariate statistical analyses were performed on the quantitative part of the data. Principal component analysis (PCA) and factor analysis were used to evaluate the different groups of interrelated factors, and discriminant analysis was used to determine the relative contribution of the individual variables in differentiating different types of roof conditions. Based on these analyses, five parameters were selected for the classification; namely, spacing of bedding planes, rock strength, weatherability, groundwater condition and structural disturbances. New system was satisfactorily applied to over 50 case studies in India.