Modelling of Creep Behavior of Claystone in Mae Moh Open-Pit Mine Using the Soft Soil Creep Model

Abstract

Mae Moh lignite mine is the largest open-pit mine in Thailand. The current mine operation is with over 250 m depth. The mine has been operated for over 50 years and would have a plan for the further operation of the next 20 years approximately. With a much deeper mine operation, this open-pit mine would be unavoidably to deal with more stress condition complexity of slope stability analysis, in particular for the long-term(time-dependent) stability. The long-term slope stability generally relates to the material “creep behavior” of which the time-dependent effect of a small deformation scale continually takes place under the constant stress condition. The main component of the Mae Moh open-cut slope is “claystone” which can be classified as the soft rock. It has properties in between soil and rock, causing difficulties in setting an appropriate test facility and determining a constitutive model to investigate its creep behavior. This study aimed to investigate the use of the soft soil creep (SSC) model to describe the creep behavior of the Mae Moh claystone based on a series of test results obtained creep tests from an own customized triaxial creep test facility designed to suit with the soft rock-like material. Plaxis 3D, the powerful commercial finite element program, was also used to simulate such creep behavior using the SSC model, one of its build-in constitutive material models. The Mohr-Coulomb (MC) model was also used as a benchmark in the finite element simulation. Results showed the SSC model could better simulate the time-dependent deformation of the Mae Moh claystone than using the MC model. It could be noticed that the SSC model would be an option to describe the creep behavior of the soft rock, using derived inputs based on the soft rock properties as it can be seen from a good agreement between test results and simulation of the slope of this study.KeywordsCreep behaviorTriaxial creep testSoft soil creep modelClaystone