ABSTRACT

Due to the construction excavation and heavily raining, resulted in serious creep deformation on the Mayanpo slope. Through the analysis of the deformation monitoring material, together with the in situ detail geological survey results, this paper present the deformation characters of the slope rock mass. As an effective numerical method used in analysis the discontinue surface of geotechnical material such as fault, bedding plane and joints, DEM (Discrete Element Method) was used in this paper. With the two-dimension DEM software UDEC, this paper analysis the deformation characters and mechanism in detail. Three cases were used in the numerical modeling. First, an initial static loading is applied in this model to simulate the prevailing rock mass conditions at the site. Second, excavation cutting of the slope was simulated. Third, heavily raining was simulated by saturated the joint condition. In doing so, the model simulates the effect of degradation of discontinuities in the rock mass. This study has provided some insight into the deformation mechanism of the Mayanpo slope. The simulation results indicate that the deformation of Mayanpo slope rock mass was mainly controlled by weak interlayer, while the construction cutting and raining are the external inducing factors. The results of this paper can provide some reference to the similar engineering.

1. INTRODUCTION

The Mayanpo slope lies near a hydropower station under construction in southwest of China, it's the right place to provide materials to the hydropower station under construction according to the designed layout. In June 2006, parts of the Mayanpo slope excavation were carried out, including road cutting and basement excavation for engineering structure, which cause some parts of the rock mass near toe of the slope were removed. In July 2006, cracks appeared at the top of the slope and some blocks have the trend to slide. From August 2006, due to several heavily raining, the sliding velocity of blocks speed-up, and the gap of the joint become wider and wider, staggered joint appeared at parts of the surface of the slope, road, enclosing wall and building. The volume of the creep deformation rock mass at Mayanpo slope is estimated to be 5,600,000m3.

Discrete element method (DEM, Cundall, 1987) is an effective numerical method to analysis rock mechanical problems with discontinuities. Several authors have used this method to analysis slope stability problems. For example, Marc-Andre Brideau et al. (1999) used the above method to investigate the failure mechanism of the East Gate Landslide happened in 1997 in Canada; Rajinder Bhasin, et al. (2003) studied a 700-m high rock slope in western Norway using both static and dynamic methods by the numerical method of DEM, the results indicate that, the entire slope does not become unstable and that down-slope sliding and rotation of blocks occur mainly on the top layers of the slope. Zhang Chuhan, et al. (1997) used discrete element method to study the dynamic behaviors of three gorges shiplock slope in China, the numerical results agrees well with field measurements.

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