Study On The Phase Transition And Deformation Properties Of The Fluid-Plastic Slurry Without Initial Structure

Natural soft sediments(i.e.clayey soil)possess strong structure characteristics for long loading history,which leads to certain strength and stiffness at the macro level.The slurry differs from the natural ground in the formation processes.The dredged mud forms the slurry ground by drainage consolidation after being transported to the workyard through hydraulic reclamation and undergoing consolidation for a short time.The water content of untreated slurry is higher than liquid limit and needs to be improved by lessening the free pore water and form a stable EDL structure The structure development of the slurry is shown by the macroscopic phase transition from the viscoelastic Bingham mud with apparent fluid properties to the elastic-plastic soil with strong solid properties.However,there are still less researches on the phase transition of slurry being reported in soil mechanism,and the effective theoretical method is still under investigation to analyze the deformation of slurry with respect to the phase transition.Therefore,this thesis carries out experiments,theoretical analyses and case studies to insight into the phase transition,deformation and mechanical properties and deformation calculation theories for the fluid-plastic slurry without initial structure.The main investigations consist of the following parts:1.EDL theory is adopted to clarify the structural change and mechanism of phase transition of fluid-plastic slurry during consolidation accompanied by the decrease of water content.SEM and fractal theory are used to support and explain the above analysis in terms of microstructure change.A method to identify the boundary from the state of Bingham fluid into the elastic-plastic soil based on rheological tests.The research results provide a basis for the later studies on the behaviors of deformation and settlement analysis of slurry foundation.2.A rheological constitutive model is formed for the slurry in Bingham fluid state.Taking into account the characteristics of the Bingham slurry,physical factor method is put forward to calculate the deformation for the slurry.The method is used in cases with varied loading conditions including the self-weight consolidation,vacuum preloading and surcharge loading,which validates the reasonability and effectiveness of the method.The research results provide theoretical support to the later study on the deformation prediction for the slurry in Bingham fluid state.3.The initial water content apparently affects the compression consolidation paths of the slurry in v/v₀-p?-q space(or e-p?-q space),which is of great importance in correctly calculating the deformation of slurry.Triaxial tests are therefore performed to form the expression of Modified Cambridge Clay(MCC)elastic-plastic matrix considering the effect of initial water content.Moreover,the MCC model is adopted in the Finite Element Method(FEM)analysis to investigate the effect of initial water content on the ground settlement.The results provide theoretical support to the later study on the deformation analysis for the elastic-plastic slurry.4.Indoor model test on the direct vacuum preloading of slurry is carried out to investigate the deformation properties and the improvement effects.Analysis on the deformation of the slurry in the model test is performed on the basis of the previous researches,which validates the reasonability and effectiveness of research results.5.The deformation process is divided into two stages based on the Bingham fluid and the elastic-plastic solid states in the phase transition.An integrated piecewise method is proposed to analyze the settlement of the slurry foundation.The method is adopted to predict the settlement in a case study with a vacuum preloading engineering practice located in Tianjin.Reasonable settlement prediction can be obtained by the integrated piecewise method according to the calculation result.