ABSTRACT:

The first step in stability analysis for soil and rock structures is precise determination of geological and geotechnical parameters. A common way of obtaining this aim is back analysis. Using instrument is a usual method in back analysis for significant surface and underground structures but because of costliness, it does not use for other structures. In soil and rock slopes which are included a bench or a number of benches, previous failures in a similar zone are used for back analysis in stability assessment. In this paper, slope movement monitoring data have been used for slope stability model calibration. Although, there are many methods to monitor slope movements, surveying is a suitable and economic method for surface mining. In comparison with the most common applied method, the method which is used in this paper is more quantitative and accurate that makes analyzer?s inexperience and mistakes less effective in the final result accuracy. In the proposed method, the displacement variations in surveying stations caused by mining and increasing slope height are used. The case study in this paper was Miduk open pit mine which is located in the south of Iran. FLAC software as a numerical analysis tool was used for modeling and mine slope stability assessment. According to displacement variations and comparing them with data obtained from surveying, final values for slope parameters have been calculated. In this way, movement monitoring ability was proved for back analysis of slope stability programming.

1. INTRODUCTION

It has been recognized for a long time that geotechnical modeling problems are data limited. While it is common in civil engineering to devote several percent of the project budget to rock mass characterization, in mining situations this figure is normally several orders of magnitude smaller. This necessitates a very different modeling approach from that developed in, e.g., civil, electrical or aerospace engineering. Rock failure occurs when stresses exceed the rock mass strength. There is considerable natural variability in the in situ pre-mining stress and rock lithology, deformation properties and strength. This results in uncertainty in both the accuracy of stress predictions and the strength to which these are compared. In addition to this ambiguity, the numerical model used, whether elastic, inelastic or otherwise, always represents an approximation to the actual rock mass behavior. Even the most complex material models still require simplifying assumptions to be made about one or more parameters. As a consequence the accuracy of all failure predictions using numerical modeling will be limited. The objective of this paper is to provide a methodology for back analysis of slope stability modeling. The method which is used in this paper is more quantitative and accurate that makes analyzer?s inexperience and mistakes less effective in the final result accuracy to design problems. Numerical model must accord with actual slope conditions for an accurate slope stability analysis programming. Using prior failures in similar areas is a usual procedure in slope stability analysis projects. In this method, first a slope failure result must be modeled by a numerical model, then numerical model resultant data can be used for similar zones or continuing of mining activity.

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