Stability Evaluation Method And Application Of Highway Roadbed And Bridge Foundation In Karst Region

It is one of the important technique problems of expressway construction to analyze and evaluate the stability of roadbed and bridge foundations in karst region at home and abroad. In this paper, combined with the research project "Study on the design, construction and quality monitoring of foundations in karst and mined-out region along expressway" financed by the Department of Communication of Hunan Province, based on system theory, a deep analysis has been made by deterministic and non-deterministic methods. At last a series of analyzing and evaluation methods for roadbed and bridge foundation's stability are set up by feedback of engineering application.Firstly, based on known methods, eleven and nine factors of the karst cave's stability under roadbed and bridge foundation are respectively abstracted and the models of two stages fuzzy synthetic judgment are set up by using analytic hierarchy process (AHP). Then fuzzy function curves and tables are adopted to establish membership functions for continuous index factors and discrete index factors respectively. And the weight of each factor is established by grey correlation coefficient analysis, AHP and Delphi method respectively. Accordingly, the two stage fuzzy synthetic judgment evaluation methods of the cave stability under roadbed and bridge foundation are found.According to limit equilibrium analysis theory, considering parameters and appraises' fuzzy quality, the fuzzy limit-equilibrium-analysis models of roof stability of cave under roadbed and bridge foundation are developed. Calculation formulas of stability safety factor of karst roof are derived by using decompose theorem. Considering decision-makers' respective preference, conversion standard and evaluation methods from the value of subjection degree to probability evaluation are put forward. Accordingly the fuzzy limit-equilibrium-analysis methods of roof stability of cave under roadbed and bridge foundation are set up.A new fuzzy set taxis index is put forward by thoroughly researching known methods which not only contain order relation and order function but also consider the effect of fuzzy maximum set and minimum set at the same time. Based on others work, approximate calculation formulas of triangular fuzzy number are derived to improve calculation efficiency. Combined with fuzzy multiple attribute decisionmaking (FMADM) and analytic hierarchy process (AHP), the conception and method of fuzzy multiple hierarchy multiple attribute decision making (FMHMADM) is put forward and the FMHMADM models of roof stability of caves under roadbed are developed in this paper. Then fuzzy attribute sets, fuzzy weight sets, fuzzy decision technique and fuzzy sets taxis method are set up and the FMHMADM method of roof stability of cave under roadbed is advanced.Introduced numerical manifold method (NMM), the elastic-plastic NMM which based on triangular limit cover is established. Nets intelligentized formation, release loads calculation, loads displace method and physics cover digging for dig simulation are dealt with and the program for dig simulation by elastic-plastic NMM was worked out by using Visual C++ as well. Combined with strength reduction technique, stability evaluation of karst cave roof by strength reduction NMM is proposed. The safety thickness of cave roof under roadbed in karst region is found by large numbers of numerical analysis.It is difficulty to predigest model of stability analysis of cave under bridge foundation to a two dimensions model. So the stability evaluation of karst cave roof under roadbed and bridge foundation by strength reduction FEM are put forward by using commercial soft ware of FEM, reasonable models, effective failing rule and dichotomy idea respectively in this paper. And the safety thickness of cave roof under roadbed is found by large numbers of numerical analysis in karst region which accords with the result of NMM analysis.Lastly, the two deterministic methods (Strength Reduction NMM and Strength Reduction FEM) and three of non-deterministic methods (Fuzzy Synthetic Judgment, Fuzzy Limit-Equilibrium-Analysis and Fuzzy Multiple Hierarchy Multiple Attribute Decision Making) are used in the supported engineering and fed back by the results. Accordingly, a series of analyzing and evaluation methods for roadbed and bridge foundation's stability are set up and proved be feasible and effective by it's engineering application.