The stability of slopes can be assessed by a factor of safety, which is usually determined by a limit equilibrium method. In order to evaluate the factor of safety, we need such strength parameters as cohesion and the internal friction angle. In the monitoring of slope stability, displacements are commonly measured. Therefore, the strength parameters should be evaluated from the measured displacements. Sakurai and Nakayama (1999) developed a back analysis procedure for determining the strength parameters from the measured displacements. The back analysis procedure was successfully developed by introducing both an "anisotropic parameter" and "critical shear strain". Recently, on the basis of this back analysis procedure, a computer code called the "Universal Back Analysis Program for Slope Stability" (UBAPSS) has been completed. In this paper, UBAPSS is briefly described, and a case study is shown to demonstrate its applicability for assessing the slope stability at an open pit coal mine. The surface displacements were measured in the mine by GPS and the data were collected until failure occurred. The strength parameters were determined using the data obtained just one day before the failure occurred. The results of the back analysis indicate that the factor of safety becomes approximately 1.0. This means that the computer code UBAPSS is well applicable to the assessment of the stability of slopes.
The stability of slopes can be assessed by a factor of safety, which is usually determined by a limit equilibrium method. In order to evaluate the factor of safety, we need such strength parameters as cohesion and the internal friction angle. However, determining the strength parameters is not an easy task, because soil and rock have numerous geological and geotechnical uncertainties. However, the question of how to evaluate the strength parameters from the measured displacements is raised. To answer this question, Sakurai (1992) developed a back analysis procedure which can determine
the mechanism of the slope deformation, whether it is sliding or toppling,
the location of sliding planes, and
the strength parameters, such as cohesion and the internal friction angle, from the measured displacements, even only from the surface displacements.
The back analysis procedure was successfully developed by introducing both an "anisotropic parameter" and "critical shear strain". Recently, on the basis of this back analysis procedure, a computer code called the "Universal Back Analysis Program for Slope Stability (UBAPSS) has been completed. In this paper, UBAPSS is briefly described, and a case study is shown to demonstrate the applicability of the proposed back analysis procedure for assessing the slope stability at an open pit coal mine, where the surface displacements were measured by GPS and the data were collected until failure occurred. The strength parameters were determined using the data obtained just one day before the failure occurred. The results of the back analysis indicate that the factor of safety becomes approximately 1.0. This proves that the computer code UBAPSS is well applicable to the assessment of the stability of slopes.
