Abstract: There are many studies on the spatial variability of mechanical parameters of jointed rock masses and the reliability of slopes with potential slip surface, but the research on the spatial variability of mechanical parameters of rock slopes and the uncertainty analysis of excavation unloading response (deformation and plastic zone) is limited. A probabilistic evaluation method for excavation unloading response of rock slopes considering the uncertainty of mechanical parameters is proposed. Based on laboratory rock mechanical tests and geological survey mapping data, the probabilistic statistical models of rock mass mechanical parameters of slopes are constructed by using Hoek-Brown empirical criterion and Monte Carlo analysis method, in which the uniaxial compressive strength (UCS) of rocks, the geological strength index (GSI) and the parameters of rock mass joints are input, and these probabilistic models are checked by the chi-square test. Based on the point estimation principle, the combination scheme of rock mass mechanical parameters is constructed, and the simulation analysis of slope excavation process is carried out by the numerical method to obtain the probability distributions of the slope safety factor as well as the displacement and plastic zone of rock masses after excavation. This method is used to analyze the rock mass mechanical parameters and excavation unloading response of a cutting slope along the Beijing-Qinhuangdao expressway under construction. The values and uncertainty distributions of rock strength, elastic modulus, cohesion and internal friction angle are obtained. By using the point estimation and FLAC^3D simulation method, the distributions of the slope safety factor as well as the displacement and plastic zone distributions of typical observation points are obtained. The comparison between the simulation results and the measured values shows the applicability of the proposed method. This study provides an effective way for the mechanical parameter estimation and stability evaluation of the rock cutting slope, and can provide a valuable reference for the decision-making process in practical engineering construction.

Key words: rock slope, mechanical parameter, unloading response, Hoek-Brown criterion, Monte Carlo simulation, probability analysis