Mineral Composition Based Experimental Study Of Dynamic Behaviors Of Quaternary Marine Fine-grained Soil In The Typical Estuary Deltas Of Guangdong

The quaternary marine fine-grained soil is the main sedimentary layer of Guangdong typical estuary delta(i.e.the Pearl River Delta and the Han River Delta).Traditional soil classification method is based on the weight percent of particle size,which can not reflect the engineering characteristics of fine-grained soil.The relative ratio of clay minerals and non-clay minerals in fine-grained soil is a determinant in Atterberg's limits of soil classification.Besides,fine-grained soil particles and microscopic characteristics of the sedimentary minerals affect the macroscopic mechanical behaviors of soil under both the static load conditions and dynamic loading conditions such as strength,deformation,pore water pressure and dynamic stability.According to the research background of formation process of quaternary marine fine-grained soil in Guangdong typical estuary deltas,mineral composition and dynamic behaviors of remolded sediments are analyzed and the results show significant influence of sedimentary mineral composition on the dynamic behaviors,which were lack of thorough research.Based on the sedimentary mineral quantification,reliable energy analysis method is used to discuss dynamic behaviors including dynamic strength,dynamic deformation,dynamic pore water pressure and viscosity property.Meanwhile,pore structure characteristic by mercury intrusion porosimetry and microscopic structure characteristic by environmental scanning electron microscope are combined for microscopic characteristic analysis.Finally,dynamic behaviors and microscopic characteristics are successfully related and bridged,a pioneering attempt of interdisciplinary study of engineering geology,soil dynamics and micromechanics.The main research contents and conclusions of the thesis are presented in the following.(1)With reference to the weight percentage of main sedimentary minerals in the marine fine-grained soil sediments,pure minerals such as quartz,albite,sodium montmorillonite and kaolinite are used to remold marine fine-grained soil sediments.The reliable microstructure morphology of reconstructed samples provides conditions for subsequent dynamic behavior and microscopic characteristic researches.(2)Energy dissipations are separated into viscous property energy dissipation,plastic strain energy dissipation and elastic strain energy dissipation by energy-based method and the calculation models of accumulated energy dissipation are proposed.The viscous energy dissipation ratio(VEDR)is established in analogy to viscoelastic equivalent damping ratio.In addition,to cope with the lag of pore water pressure,the hysteretic pore water pressure energy dissipation ratio(HPWPEDR)is given based on the relationship between relatively effective pore water pressure and cyclic stress.(3)According to the growth rate relationship between viscous property cumulative energy dissipation and plastic strain cumulative energy dissipation,dynamic modes of fine-grained tailing soil and sedimentary mineral soil are reclassified as four categories: stable type,stable damage type,damage type and collapse type with consideration of three dynamic phases,i.e.,cyclic compaction or looseness,cyclic shear,and cyclic damage.Energy-based method explains the transitional and mutational failure mode of intermediate soil.Combined with effective stress path based characteristic lines,critical values of shear strains are determined in accordance with relevant microscopic mechanism.Meanwhile,the existing energy-based pore water pressure models are further developed to predict the time-history curve of pore water pressure.(4)Because of high clay minerals content(more than 50%)in sedimentary mineral soil,alternative growth rates between viscous property cumulative energy dissipation and plastic strain cumulative energy dissipation are not obvious.Furthermore,the weakly bound water transfer into free water film under approximate cyclic stress ratio is limited in sedimentary mineral soil group.Thus,integral relative slippage provided by free water is restricted,and the influence of the limit free water on the intergranular stiffness decreases.When weight ratios of sedimentary minerals and related plastic index change,clay mineral relations group has more significant influences on accumulated energy dissipation,attenuation of dynamic secant shear modulus,viscous property energy dissipation and hysteretic pore water pressure energy dissipation than non-clay mineral and clay mineral relations group.(5)The influence of internal energy change mechanisms during cyclic loading on dynamic behaviors such as dynamic deformation,dynamic pore water pressure and viscosity property is analyzed for soils including fine-grained tailing soil and sedimentary mineral soil.VEDR mutation criterion is established to distinguish the dynamic strength.The critical strain amplitude of the VEDR mutation point,different from small threshold strain,is another important threshold of the transition from moderate strain to large strain.And the traditional one-to-one correlation of the plastic index influence on engineering and dynamic behavior is found to be not applicable to sedimentary mineral soil.(6)Two microscopic characteristic parameters that show the pore structure and microscopic structure are coordinated in three aspects of porosity and void ratio,pore size and distribution and pore stratification and connectivity.This coordination demonstrate the reliability of the combined micro test method.In the end,microscopic dynamic behavior analysis method is preliminary put forward based on three sets of dynamic behavior parameters and microscopic characteristic parameters—critical strain amplitude and pore direction probability entropy,Davidenkov model parameters and perimeter-area fractal dimension and pore size distribution fractal dimension,and HPWPEDR and sandbox-counting fractal dimension.