Eskihisar, Orhaneli, and Ilgin are important lignite open-pit mining regions in Turkey, which in the last 10 years have experienced problems with slope stability, according to long-term, in situ measurements. In this study, a mathematical model based on results of these in situ measurements was developed after statistical analysis, during which high statistical regression R2 values were obtained by using SPSS v16.0. The velocity and acceleration behaviors were then derived by the model developed. The critical moments during unstable periods versus deformation curves were detected by the derived velocity and acceleration curves.

1. Introduction

In open-pit mining, slope design and stability are important to the safety of the plant and its economy, for slope instability can cause loss of lives and property. Slope stability in open-pits depends on a few parameters, such as general slope angle, amount of rain, ground water, rock mass properties, drilling-blasting and excavation activities, and earthquakes.

Terzaghi (1950) indicated that for engineering and slope stability, minor non-systematic discontinuities are as important as major ones. The location of discontinuities, continuity, aperture, decomposition, and filling structures are important engineering parameters that effect slope stability. Morphology, kind of sliding material, grain size, shape of the movement, velocity, and age are also important parameters that should be taken into account.

Wieczorek (1984) emphasized that rock mass type, topographical conditions, climate and vegetation, and surface and/or ground water are prepared media for slope instability, while earthquakes and rain effect are trigger parameters. Keefer (1984) specified that the effect of earthquakes on slope instability was not yet fully understood. Though that study occurred 30 years ago, knowledge on the topic is still incomplete.

According toVarnes's (1978) commonly used classification, slope stability can be falling, tipping, circular or translational sliding, lateral spreading, or complex sliding. Özgenoğlu (1986) also investigated slope failure either containing a slide plane or not.

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