Stability Analysis Of Fill Embankments On Rock Slope

Since Western Area Development policy was issued by the government, mountainous highways have expanded rapidly. Fill embankments on rock slope foundations are the common problems in the construction of mountainous highways. Up to the present, the system research of the stability of the fill embankments on rock slope foundation, the relevant engineering measures and design methods are not developed. Therefore, to study stability of fill embankments on rock slope foundation is of practical significance in engineering construction.Based on the project of the working character of embankments on rock slope foundation in the railway from Changde to Jishou, the dissertation is dominated by the work performance, deformation, failure mechanism, stability calculation method and construction application. The stability of fill embankment on rock slope foundation is studied by means of full scale of model experiments, numerical and theoretical analysis. The major research findings are as follows.The First, According to the practical experiences in the expressway construction on the mountain region, full scale model experiments are carried to analyze the embankments performance on rock slope. The test design and instrumentation were introduced. During the experiments, the vertical force distribution, displacements of slope, the shape and location of the slip surface in the embankments were also investigated. The failure location, shape, stress distribution, displacements and settlement regulations were found out when the fill embankment on slope foundation is under unstable condition.The Second, FLAC software is used to analyze the major failure models of fill embankment on rock slopes. There are surface failure (whole failure), curve failure (partial failure) and zigzagging curve failure (partial failure). Studies are focused on various kinds of failure models and grades of slope, proportion of embankment heights and width and physical mechanical properties of earth filling, specific shapes of sliding surface under various kinds of conditions. Meanwhile, works are carried to determine various inclination angles of the slopes, various heights of earth filling and different widths of embankment fillings. Impacts on ultimate carrying capacity are analyzed for the high fill embankment foundation at different angles of roadbed. Effects of excavation steps on stability of fill embankment on rock slope foundation are discussed preliminarily. Proper shape of excavation steps is proposed.The Third, based on numerical results and model experiments, using upper bound theorem of limit analysis, velocity fields are established for different failure models. Equaling external power rate to internal energy dissipation, ultimate beating capacity formula of fill embankment on rock slope foundation was obtained. The corresponding program is coded with Visual Basic. The upper bound solution is easy to obtain, and physical meaning is clear without redundant presumptions. The numerical results show that the upper bound solutions are slightly bigger than those using FLAC method. Therefore, the upper bound method of limit analysis is precise and reliable, and can be used in stability analysis for foundation on rock slopes.The Forth, limit equilibrium method is used in the dissertation. Based on experimental and numerical results, formulas of limit equilibrium of horizontal slice method are derived, and are programmed correspondingly by Visual Basic for different failure models of rock slope embankment. The results show that the solution of bearing capacity of embankment is reasonable with the limit equilibrium of horizontal slice method. Limit equilibrium of horizontal slice method is much closer to actual solution than vertical slice method, because it not only satisfies strength equilibrium but also moment equilibrium between slice filling of embankment. The solution with limit equilibrium method is lower than the actual solution. For practical engineering, the two methods are considered so that the solutions upper bound theorem of limit analysis and limit equilibrium slice analysis are determined. The safety coefficient or ultimate beating capacity usually can be restrained within a small range. Thus, proper solutions are likely to be obtained.Finally, according to construction experiences, generalized are technical principles of engineering design of high fill on rock slope foundation based on the experimental results, rock slope embankment failure mechanism analysis and stability calculation method. Consolidation design and construction applications of high fill on slope foundation under different construction conditions are introduced. These are of instructive significance for design and construction of high fill on slope foundation in mountainous area so as to ensure safe and expedite traffic.