Deformation Characteristics Of Artificially Structural Soil Considering Influence Of Time-Dependent And Stress Path

Since the 21st century,with the development of society and the rapid growth of the national economy,the process of urbanization in China has intensified.Along with the development of urbanization,large-scale projects such as super high-rise buildings,subways,and cross-river tunnels have emerged in large numbers,and the large-scale project construction can not be separated from underground excavation,so the foundation pit project has always been the focus of research.Most of the studies focused on remolded soils by triaxial undrained compression tests,However the structure of the soil and the actual stress path experienced by the excavation process are not taken into account,and it will bring great harm to the project.In addition,as a typical elasto-viscoplastic material,soil exhibits obvious rate-dependent and creep properties.But the present research on the mechanical properties of structure soil is mainly carried out under the condition of a single strain rate.If the time-effect characteristics of the structural soil are not taken into account during the engineering calculation,it will lead to problems such as instability in the construction phase and significant post-construction settlement effects.Based on the above reasons,a series of experiments were conducted to study the time-dependent deformation characteristics of artificially structured soils and their mechanical properties under different stress paths.(1)The method of artificially preparing structured soils were further improved and optimized.For the first time,urea is used as a soluble material to simulate the pore structure between particles,and the feasibility of the method was verified by the comparison of the macroscopic triaxial mechanical test between artificial soil and natural Zhanjiang soil and the change of micromorphology of the artificial soil before and after the experiment.(2)One-dimensional consolidation and compression tests of the structural soils with different cement contents(4%,6%,8%and 10%)were performed,and we study the effects of structural and structural strengths on the parameters of compression parameters before and after yielding.In order to study the actual stress state of subsoil more accurately,the triaxial undrained compression test of the structural soil was performed.The deformation characteristics of structural soil were studied more deeply by changing the cementation strength and pore number(e=1.3,e=1.5 and e=1.7)of the structural soil.(3)In order to study the time-dependent deformation characteristics of structural soils,one-dimensional consolidation creep tests and consolidated undrained triaxial sensitivity tests(0.01mm/min,0.1mm/min and1mm/min)of the structural soils with different cement contents(4%,6%,8%and 10%)were carried out,and the effect of cementation strength on secondary consolidation coefficient and rate-dependent of soil was analyzed.(4)In order to study the actual stress state and deformation characteristics of soil in excavation engineering,the undrained triaxial tests of the artificially prepared structured soils under different consolidation pressures(100kPa,200kPa and 300kPa)via different stress paths were performed.And the strength characteristics,failure characteristics and deformation characteristics of structural soils under different stress paths were studied in depth.(5)In this paper,an elasto-viscoplastic constitutive model that take into account the structural and rate-sensitivity of soils is established based on the surface-load yield criterion function of upper and lower loads and the basic idea of relative stress.The feasibility of elastic-plastic viscoplastic constitutive model was confirmed by the sensitivity test of structure soil.The result showed that elasto-viscoplastic constitutive model can better characterize the structure and rate sensitivity of soil.Based on the structural soil elastic-plastic viscoplastic constitutive model,the foundation pit of Panyu Hotel in Guangzhou City was numerically analysised with the aid of ABAQUS.Combined with the results of field observation,the deformation and displacement of the pile-foundation and soil ground surface are effectively predicted,which verifies the correctness of constitutive model.