Abstract

It is well know that the toppling failure of slopes often occurs in jointed rocks. It is obvious that the failure mechanism of toppling is not sliding, but may be the collapse of jointed rock masses associated with rotation of block movements. Therefore, a conventional approach for assessing the sliding of slopes cannot be applied because no particular sliding plane exists in toppling failures. To overcome this difficulty, the author proposes a back analysis method for determining the factor of safety for the toppling failures of slopes during/after their constructions by using measured displacements. Aiming at an easy application of the back analysis method to engineering practice, the author proposes a continuum model for simulating the mechanical behaviour of jointed rocks. The applicability of the method is demonstrated by physical model tests carried out in laboratory on jointed materials consisting of piling up of hundreds of aluminium bars. According to the proposed back analysis method, it is not necessary to assume the failure modes, either sliding or toppling, but it can identify whether sliding or toppling from measured displacements. In the proposed back analysis method both the critical shear strain and the anisotropic parameter play a major role. The critical shear strain can be determined by conventional laboratory experiments on an intact rock specimen with no worry about its scale effect, because the critical shear strain of large-scale rock masses is always greater than that of intact rocks, while the anisotropic parameters can be back-calculated from displacements measured on the ground surface by GPS so as to obtain a good agreement between the measured and calculated displacements. In this paper the proposed back analysis method is described together with the results of laboratory experiments.

1.
Introduction

In jointed rock masses, a toppling failure often occurs. It is obvious that the failure mechanism of toppling is not sliding, but may be the collapse of jointed rock masses associated with rotation of block movements. In order to assess the stability for toppling failure of jointed rocks, a discrete model such as Distinct Element Method (DEM) proposed by Cundall (1977) may be applicable, provided that all the joint systems of rock masses are known. However, it is almost impossible to explore all the joint systems of rock masses by field surveying, because of the complexity of joint systems. To overcome this difficulty, the author proposes a continuum model for simulating the toppling of jointed rocks, resulting that the factor of safety for toppling failure can be easily back-calculated from measured displacements. The applicability of the method is demonstrated by the laboratory experiments carried out on a jointed material consisting of piling up of hundreds of aluminium bars. According to the proposed back analysis method, it is not necessary to assume the failure modes, either sliding or toppling, but it can identify whether sliding or toppling from measured displacements.

This content is only available via PDF.
You can access this article if you purchase or spend a download.