Risk Analysis On Open-Pit Slope Based On Reliability Theory

ABSTRACT:In the excavation process of open-pit slope, the aim of engineering practice is to achieve an unity between security and economy. In order to solve this problem, the study on open-pit slope economic risk analysis based on reliability theory was conducted in this paper. In the face of objective fact that there are some uncertainty and randomness existed in open-pit slope project, based on the depth analysis of open pit slope characteristics, with reliability theory as the main line, the analysis steps and procedures of open-pit slope economic risk were constructed. Four key problems, including failure mode recognization of slope, slope target reliability determination, deduction of slope random variable probability distribution and selection of reliability calculation method, were studied pertinently. The main contents and conclusive results are as follows:(1) The identification of open-pit slope potential failure mode is one of the most basin works to study the unstability and failue of slope. Based on the theory of distance discriminant analysis and combined with the characteristics of open-pit slope instability, nine factors, including the uniaxial compressive strength of rock, structural plane angle, the position of structural plane slope plane, groundwater conditions, types of rock mass structure, cohesion, internal friction angle, slope height, slope angle, were selected to build a distance discriminant analysis model to identify the potential failure mode of open-pit slope. Linear discriminant fuctions were obtained through training of21sets information of typical open-pit slopes. The resubstitution method was used to varify the identification ability of this model. The research results show that, the misjudge rate of the model is0.05and the discriminant ability is higher. This model was applied to the instability mode discrimination of three open-pit slopes. This paper provided a new method to identify the potential failure mode for open pit slope.(2) According to the requirements of engineering reliability unified standard, and considering the current situation and development trend of China’s open pit mining technology, and combining with the slope engineering technical specifications of non-coal open-pit mine, the service life and three security levels of open-pit slope was determined. On this basis, the study of acceptance damage probability of open-pit slope at home and abroad were collected and analyzed, and the target reliability in five current reliability unified design standards, including building, hydraulic, highway, railway and port, were also referenced, the acceptance damage probability for the first failure model (with symptomatic before failure) of open-pit overall slope under I security level was determined as1×10-3and the corresponding index of target reliability is3.1. The basic standard and criterion of open pit mine slope reliability analysis was also given and was applied in the open-pit mine reliability design in second phase expansion project of Chengmenshan Copper Mine.(3) Based on normal information diffusion principle, a probability model deduction method of shear strength parameters with small sample size is presented in this paper. Considering the sample size of rock shear strength parameters is small in general, the testing data of rock uniaxial and triaxial compression were regarded as basic information, and information base of shear strength parameters with small size was constructed according to the permutation and combination theory. And the sample data of cohesive force c and internal friction angle φ were also obtained using robust regression estimation method. Finally, based on the normal information diffusion theory, the probability distribution functions of c and cp were deducted. K-S test method was used to compare the results of traditional fitting-test method and presented method. The results show that, the probability distribution of shear strength parameters based on normal information diffusion principle is more close to the actual probability distribution. Whether in terms of test value and the cumulative probability, the results of presented method are better than the traditional fitting-test method.(4) According to the different situation of open pit mine slope limit state equation has two continuous random variables:anti slide force and sliding force and multi-random variables, the computational formula of failure probability based on information diffusion principle was obtained. At the same time, the limit state equation is constructed based on the safety factor, information diffusion equations of random variable expectation and standard deviation were given. The calculation method of failure probability and reliability index of open-pit slope was also obtained.(5) The second phase expansion project of Chengmenshan Copper Mineas was considered as the engineering background, the economic risk analysis model of south open pit slope was constructed. The information base of shear strength parameters with small size was constructed by using the testing data of rock uniaxial and triaxial compression. The slope safety factor and the most dangerous sliding surface can be obtained by using the simplified Bishop method. With the increaseing of slope angle, the change rule of the reducing cost of stripping rock, failure probability and potential landslide volume were analyzed. At last, the best optimization solution of south open pit slope with the maximum economic risk benefit was obtained.