Study Of Strength And HM Coupling For Hangzhou Clay Based On Microscopic Analysis

Strength is one of the significant properties of clay.The formation of clay strength is complicated,which is a combination of various factors.In fact,the macro property is controlled by the microstructure.Therefore,it will be helpful to study from the microscale.This thesis focuses on the issue of clay strength,and the main contents are:Exploring the quantification method of clay micro structure based on SEM;Building the strength theory based on the SEM experiment of Hangzhou clay and cemented-clay.And the validation has also been conducted;The proposed strength theory has been applied to the constitutive model of cemented-clay to consider the influence of microstructure;At last,the Hydro-Mechanical coupling has been studied to prepare for the new strength theroy that need to consider multiphysics.Conclusions are drawn as follows:(1)The improved quantitation method for characterization of clay microstructure is proposed,which has a higher reliability and higher efficiency for obtaining micro-parameters from the SEM images.The influences on strength from milling,drying,magnification and number of SEM images have been analized,as well as the threshold determination for image processing.This improved method is applied to the study of Hangzhou clay,and the suggested method is:SEM samples should be milled from the same direction,the Liquid nitrogen freeze drying method is better,and at least 5 SEM images should be obtained,with magnification of 1500.(2)Based on the theorical analysis,they are the interaction force of particles'contact,forces generated by the bonding water,the spacial arrangement and distribution of clay particles that control the clay strength.Therefore,four micro-parameters(Image porosity,Mean shape factor,Particle gradation entropy and Orientation probability entropy)are determined to represent the influence factors on clay strength.To reflect the combined influcence of these four micro-parameters,the comprehensive micro-parameter is proposed.According to the experiment results,there is an exponential function relationship between Hanzhou clay strength and comprehensive microparameter,which is also verified by the adhesive friction theory.(3)The improvement of clay strength is mainly due to the modification of microstructure.And the micro structure can be described by the porosity,particle shape,size and arrangement characteristics.And they can be quantified by the micro-parameters of Image porosity ns,Mean shape factor F,Particle gradation entropy Ge and Orientation probability entropy Hm,respectively.The influence of each micro-parameter on the strength is sorted from strong to weak:Ge>ns>F and Hm.Therefore,in the engineering practice of Foundation treatment,it is better to select a curing agent that can help to improve the Particle gradation entropy Ge.(4)Learning from the experiment results from Hangzhou cemented-clay and Taizhou cemented-clay,the relationship between cemented-clay strength and comprehensive micro-parameters is also an exponential function,which is similar to the relationship between Hangzhou clay strength and comprehensive micro-parameters.This effectively shows that the strength theory proposed in this paper is reasonable.(5)The Modified Structural Cam Clay model(MSCC model)is verified to be fit for the unconfined compression experiment of cemented-clay.The influence of microstructure on clay strength can be considered by substitute the relation ship between model parameter(the mean effective yield stress)and the strenth(unconfined compressive strength of cemented-clay).Then the New Modified Structural Cam Clay model(NMSCC model)is proposed.(6)In the aspect of Hydro-Mechanical coupling,the original HM model based on the Mixture Coupling Theory(HM-elastic model)only considers the elastic deformation,so it can't be used to describe materials that has plastic property,such as clay.To deal with this issue,the HM-plastic model based on the Mixture Coupling Theory is proposed,which is achieved by introducing the Modified Cam Clay model into the foundamental constitutive equations.This HM-plastic model is fit for the clay.This research is an important step to further study the multi-scale and multi-physics coupling for clay in the more complicated conditions.