The determination of information point distribution and classfication of confidence level estimation of geotechnic solid rock kriging estimation parameter based on variogram analysis

Cohesion (c) and angle of internal friction(ϕ) are one of the inseparable geotechnical parameters in the stability analysis of mining slopes. The estimation process is needed in knowing the distribution or zoning of geotechnical parameters. In this study, the estimation process uses a geostatistical method where the data used collected from PT Bukit Asam Tbk. in the form of geotechnical drill data, laboratory analysis results of rock mechanics (c, ϕ) and drill logs. The data is processed into one database which includes the coordinates of information points (easting and northing), lithology and geotechnical parameters of intact rock (c, ϕ). Then form a variogram using a range of distance, nugget effect and sill that is tried to get the suitability of the data, seen from cross validation so that the estimated results are expected to be accurate and reliable. The accuracy and classification of the level of confidence of the kriging estimation results are grouped based on the distance between the information points obtained through variogram analysis by dividing the sill into three parts namely 1/3, 2/3 and 3/3 sill. In this study, the data is considered accurate and has a high level of confidence if it has a distance between information points 100-200 m, has a medium level of confidence if the information point is 200-400 m distance and has a low level of confidence if the distance between information points 400-700 m.