Stochastic Analysis Of Geotechnical Parameters And Study On Stable Reliability Of Slope

Stability evaluation of slope has been an important research subject in geotechnical engineering. Until now, there are Safety Factor Methods and Reliability Methods for it. However, these methods have such defects as the following: Safety Factor Methods cann't consider the significant uncertainty existing in geotechnical parameters, pore-water pressure and other influencing factors of slope stability, which may lead to quite different risk levels associated with a same safety factor in different slopes; the existing Reliability Methods take the randomness into account, however, they are still imperfect in the accumulation of statistical data, statistical methods for geotechnical parameters and the reliability methods for calculating slope stability so that many shortcomings were brought about in calculation load, convergence, accuracy and practical values. In view of the above problems, the statistical methods of geotechnical parameters were studied further and the probabilistic distribution rules of typical rock and soil parameters were analyzed statistically based on extensively accumulating statistical data related to the randomness of geotechnical parameters and complement experiments. Some key problems in slope reliability analysis with one-mode failure were studied, followed by corresponding solutions. According to multi-failure mode slopes, the matrix-based system reliability method (MSR method) was improved and the difficulties in system reliability calculation of complex rock slopes were overcame by the proposed method and a computer program was developed to realize the above functions. The main work and conclusions are summarized as follows:1,The quantitative methods of rock and soil parameters uncertainties were studied and stochastic characteristics of partly typical soil parameters were statistically analyzed; more than 1500 groups of test data of strength parameters and statistical material extracted from 23 rock slopes were classified and reprocessed and some supplemental tests associated with mechanical parameters of rocks were carried out for quantifying the uncertainties, and the distribution rules of strength parameters were gained for partly typical rock mass. All of the above provide basic data for the reliability analysis of slopes . 2,Due to the hypothesis test can't be applied to the extreme cases that there is few or too many data for statistical analysis, new methods were proposed to solve the difficulties:(1) The case of large sample: an information entropy inference method and the least square approximation were studied; considering that the result by the former is sensitive to the borders of parameters and the result by the latter is unstable when the order of polynomial is high, orthogonal polynomial fitting methods were proposed and the calculation formula of Chebyshev polynomials and Legendre polynomials were deduced by utilizing the information of statistical moments of sample. The validity and advantages were proved by a simulation example and a project case.(2) The case of small sample: Bootstrap method was introduced into the distributions inference of geotechnical parameters for the first time in order to solve parameter distribution inferring by means of computer simulation on condition that statistical data are rather few; Bayes theory and its extension were adopted to utilize prior information fully so as to modify and improve the probabilistic model of geotechnical parameters continuously; in order to utilize multi-source information, "K-L information distance" was introduced into parameter distribution inferring firstly and K-L information fusion method was suggested. As a result, the objectivity and credibility of results by the multi-source information fusion method were improved greatly. It was shown by a simulation and a project case that these methods are good measures to infer the parameter distributions in the case of few data.3,Aim at some key problems to be solved concerned with reliability calculation for the slopes with one-failure mode (the establishment of limit equilibrium equations of slope, simulation technique and search tools for critical probabilistic slip surface and solving for the least reliability index), the corresponding solutions were proposed: based on limit equilibrium theory, the limit equilibrium equations of slopes were deduced with the safety factor Fs not being contained; suitable control parameters were chosen for circular surfaces to avoid generating invalid surfaces or leaving out key ones; the generation of non-circular surfaces was controlled by angles of interior vertices and by increasing the number of vertices gradually so as to improve simulation efficiency; the standard genetic algorithm for searching for the lowest reliability index was improved so as to enhance the efficiency and quality of the algorithm. It is shown by a test example and a case history that the results were in agreement with the actual situation; being different from the existing reliability methods, this method goes without the solving process of the safety factor so the calculation load was decreased remarkably and the convergence was improved.4,The slope stable reliability with multi-failure mode was studied from the viewpoint of system, a construction formula of event vector c in MSR method was suggested and the difficulty in calculating complex slope system reliability was overcame by adopting the modified MSR method combining with linear programming and multi-scale method. The results of the project application indicate that the method simplifies the identification of event vectors of components greatly and makes it easy to carry out the computer automatic recognition; combining with the linear programming and multi-scale method, the MSR method can be applied to calculate the complex system reliability for slopes and the optimization process can be implemented conveniently with good precision.