Study On Macro And Micro Creep Test And Nonlinear Model Of Zhuhai Soft Soil

With the issuance of the " The development plan for Guangdong-Hong Kong-Macao Greater Bay Area ",it can be foreseen that the future construction and development of the Guangdong-Hong Kong-Macao area will still be in the long-term and large-scale,but because of the large amount of soft soil widely distributed in the Guangdong-Hong Kong-Macao area,most of the projects had to be built on these soft soil sites with poor soil quality,which could easily lead to major engineering accidents such as foundation settlement and instability in the construction of the project.Exploring the creep of soft soil has always been a research hotspot,but few scholars have explored the mechanical behavior mechanism and regular of creep deformation characteristics about soft soil from the perspective of macro-micro coupling.At the same time,in the context of the construction of the Guangdong-Hong Kong-Macao Greater Bay Area,Zhuhai,the only coastal city connecting Hong Kong and Macao by land,has become an innovative highland and central core for the construction of the Guangdong-Hong Kong-Macao Greater Bay Area due to its geographical advantages.Therefore,in this paper,Zhuhai Hengqin soft soil is taken as the research object,and a series of macro tests(1-D compression creep tests,triaxial shear creep test)and micro tests(Scanning electron microscope observation,Image J software processing)systematically analyze the quantitative relationship between the corresponding macro and micro parameters of the soil and its creep deformation characteristics,study the internal relationship between the macro performance of the creep characteristics and the micro creep mechanism,and establish a suitable nonlinear creep constitutive model to guide engineering design and practice.The main research contents and conclusions of this paper are as follows:(1)Through 1-D compression creep tests,triaxial consolidated and undrained shear creep test of Zhuhai Hengqin soft soil under separate loading,the quantitative relationship between the corresponding macro parameters of the soil and its creep deformation characteristics is analyzed.By the test data,it is found that Zhuhai soft soil should belong to highlycompressible soil,and the creep is related to the loading duration.As the consolidation pressure increases,the amount of compressible deformation of the soil sample gradually increases,and the slope of curve about the decay creep stage increases with time,and the constant rate creep phenomenon is more obvious.At the same time,compared with the1-D compression creep test,it’s found that deformation in 1-D compression creep was significantly easier to stabilize than the triaxial shear creep deformation.(2)Through SEM(Scanning electron microscope)observation of the soil samples before and after the creep test,and using Image J software to process the SEM image,extract structural quantitative parameters that can describe the microscopic characteristics of soft soil to analyze the quantitative relationship of corresponding microscopic parameters about soil and its creep deformation characteristics.The study found that the micro structure of Zhuhai undisturbed soil is mainly laminated structure,flocculated structure and there is also aggregate structure.As the creep begins,the soil becomes denser and the connection strength becomes greater.As a whole the proportion of small-diameter particles and pores in the soil increases significantly,and the abundance of particles and pores continues to be concentrated in the range of 0.2 to 0.6(the development is toward the oblate direction),while the complexity is reduced(the edge is developing toward a more "smooth" direction).(3)According to the results of the extracted structural quantitative parameters describing the microscopic characteristics of soft soil,the quantitative relationship in the load-structural elements-soil micro structure is analyzed,and it is found that the interaction of pore deformation,particle deformation and structural connection deformation under the action of external load,constantly adjusts the microstructure.and the changes are mainly manifested in the changes of the size and shape in particles and pores.What’s more,the pore changes are the most obvious.(4)Based on the results of laboratory tests and numerical simulation,the creep deformation is divided into three parts(linear viscoelastic strain,linear viscoplastic strain and nonlinear viscoplastic strain)to establish equations respectively.Based on the semi-theoretical and semi-empirical modeling method,the volume strain is introduced into the Merchant model and the five-element Kelvin model,combined with the creep function that reflects the stress-strain relationship with the power function and the strain-time relationship with the hyperbolic relationship,which is suitable for nonlinear creep constitutive model of Zhuhai soft soil to guide engineering design and practice.