Rock slopes stability attracts growing research interest over the past several decades as one of the fundamental issues in rock mechanics and rock engineering. The modelling strategy representing the actual behavior of structure plane is of importance to analyze and predict the stability of rock slope. In hard and semi-hard formations, the removable blocks exert critical effect on the stability of slope, which are induced by the intersection between structural planes and excavation surface. The determination of key blocks can provide the basis for selection of strengthening schemes. In this paper, non-contact measurement has been applied to get the information of deterministic structural planes, and the stochastic structural planes are generated based on the statistic methodology. Then block theory and limit equilibrium are utilized to analyze the stability of removable blocks. Lastly the volume ratio of key blocks and removable blocks is proposed to assess the stability of slope excavation surface. The authors have attempted to demonstrate the effectiveness of the proposed numerical method with reference to a slope project in China.

1 Introduction

In hard and semi-hard formations, the rocks were cut into blocks with different kind of shapes by pre-existing discontinuities, which exert detrimental effect on the rock mass strength. And the excavation surface often leads to destabilization of rock mass. Thus, in case where the progressive failure induced by the blocky rocks (i.e. the failure of intact rock is not involved) near the excavation surface, it will make the results somewhat radical utilizing the limit equilibrium method or strength reduction method to analyze the whole slope rock mass. However, the block theory (Goodman et al. 1985 and Warburton 1981) is powerful in terms of fast analyzing rock blocks around openings created by the intersection of the slope excavation surface and joints in the rock mass.

So far, so much great improvement has been made regarding block theory (such as probabilistic analysis (Song & Lee 2001) and rotational modes (Mauldon & Goodman 1996) and its application on engineering (such as in-situ stress (Mauldon et al. 1997), progressive failure analysis (Windsor 1997), stability analysis and support design (Windsor 1997, Wibowo 1997 and Fu et al. 2014). In this paper, we mainly focus on the stability analysis of blocky rock slope excavation surface based on key block theory. With the traditional key block method, the stability conditions of blocks on the exposed surfaces are assessed by applying a certain safety factor (Goodman et al. 1985 and Windsor 1997). However, the volume of key block and the overall stability of the excavation surface is often ignored. On the other hand, it is necessary mimicking the characteristics of pre-existing discontinuities to apply the block theory. In this paper, the spatial fracture network model is generated based on the site non-contact measurement and GeoSMA-3D (Wang et al. 2009, Wang et al. 2010, Wang et al. 2012, Wang et al. 2013, Wang et al. 2014), which also can accomplish the key block theory. Then with the safety factor, which is computed by limit equilibrium method, and volume of each removable block, the new discriminant parameters for the stability of block and excavation surface are proposed. Lastly, a case study will be simulated and the slope excavation surface stability will be analyzed by the new discriminant parameters.

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