Shakedown Analysis Of Slopes Subjected To Variable Pore-Water Pressure

Besides dead loads such as gravity load, slopes are usually subjected to othervariable loads. Among all of these variable loads, groundwater is an un-neglectablefactor. Since rainfall and other reasons, groundwater level may fluctuate within aprescribed range. This makes upper part of the slope body, which is above the basicwater level, subjected to the cyclic underground water variation. In the long-term,slopes operating at large-scale underground water fluctuation will eventually fail. Soit poses a disadvantage to slopes. Commonly accepted limit-equilibrium and limitanalysis methods can only be applied to linear static loading conditions. When theyare used in alternating load conditions, these methods not only lack of stricttheoretical basis, but also may overestimate slopes' stability. Typical example is theexpansive soft rock slope. Expansive soft rock slopes designed safely by limittheorem but eventually failed events are not rare in practical engineering. On theother hand, weather conditions such as rainfall in one region is a random event,accordingly, ground water locomotion also represent some randomicity. So peoplecan only obtain the range of the ground water level. Non-linear time-steppingmethod was developed to analyze the incremental deterioration of slopes. Althoughtheoretically it seems feasible, in practical analysis some difficulties may beencountered not only on how to describe constitutive model but also on loadconditions uncertainty. In this thesis, shakedown theorem in the Theory of Plasticitywas adopted to analyze the long-term stability for slopes subjected to alternatewetting and drying conditions. Research work includes:1. An upper bound shakedown analysis based on strong version of Koiter'stheorem is employed to analyze slope stability which subjected to alternate porewater pressure. Presently, there was no other related literature focusing on takingpore water pressure as the variable load to study the slope's shakedown character. Inthis study, in order to overcome the difficulties from time integrals, strong version ofKoiter's theorem was employed and a computer program was developed. Thisnumerically simple method greatly reduces the difficulties shakedown analysisbrought. It is also a promising attempt in geothechnical engineering.2. Element Integration Method (EIM) was proposed to analyze slope stability.From the compatibility conditions, adopting element meshing mode and employingupper bound theorem in the Theory of Plasticity, EIM constructed a kinematicallyadmissible velocity fields through a multi-wedge failure mechanism in the form of asmall number of discrete blocks with inclined surface and linear or curved bases.Based on the energy-work balance equation, the factor of safety can be calculated.The problem of finding optimum upper-bound safety factor can be set up as anonlinear programming problem by optimizing the slicing mode of each associatedvelocity field. EIM combines the advantages of Finite Element Method and theMethod of Slices. It provides a relatively powerful and general tool for employingupper bound limit theorem in slope stability analysis.3. Analyzing and comparing every factors influence on slope shakedown.Through a lot of numerical examples, results obtained from shakedown analysis ofslopes with different geometric features, ground-water patterns, strength parameters,sliding modes are compared with those obtained from the limit-equilibrium and limitanalysis method. A series of limit and shakedown safety factor curves were given inthe thesis. These figures provide some theoretical and designing basis for slopestability evaluation.4. Adopting shakedown theorem to quantificationally evaluate the long-termstability of expansive soft rock slopes. Employing shakedown theorem, long-termstability analysis of expansive soft rock slopes, which subjected to alternate porewater pressure, was performed. Results obtained using the present method are totallydifferent from those obtained using other commonly used methods. Theoretically,this gives an answer to the problem why expansive soft rock slopes with small slopeangles can not maintain their long-term stability.