| Thick clay layers are widely distributed in alluvial strata in the central and eastern regions of China.In the well drilling engineering by freezing method,deep clay undergoes freeze-thaw action under high ground geostress,which will significantly change its engineering properties and have an important impact on borehole wall stability.Therefore,it is of great significance to deeply understand the consolidation characteristics of deep freezing-thawing clay.For this purpose,this paper studys the characteristics of rheological consolidation on deep freezing and thawing clay,and specific research work is as follows:1)The one-dimensional rheological consolidation test of high pressure by step loading is carried out on deep unloaded and loaded freezing-thawing clay,to explore the freeze-thaw action,initial moisture content,consolidation pressure and pressure of freezing and thawing on the influence law of the rheological consolidation properties of deep clay;2)Based on laboratory experimental data,rheological element model suitable for deep freezing-thawing clay is selected for secondary development in ABAQUS.Model UMAT is compiled,model parameters are fitted by least square method,uniaxial creep numerical analysis is carried out in ABAQUS to determine the degree of coincidence between numerical calculation results and test results.The main conclusions are as follows:(1)The creep deformation of deep freeze-thaw soil under each stage of consolidation pressure can be divided into three stages: instantaneous deformation,attenuated creep and stable creep.With the increase of consolidation pressure,the instantaneous strain and creep strain of freeze-thaw clay increases continuously,and the time to reach stable creep increases.With the increase of initial moisture content,the ratio of creep deformation to total deformation increases,the duration of attenuation creep increases,and the creep effect of soil sample becomes more significant.(2)The instantaneous deformation of unloaded freezing-thawing soil is smaller than that of unfreezing-thawed soil,while the creep deformation and the overall deformation are larger than that of unfreezing-thawed soil,and the difference gradually decrease with the rise of the initial moisture content and the increase of consolidation pressure.Affected by the influence of high stress in freezing-thawing stage,the instantaneous strain and creep strain of loaded freezing-thawing soil are smaller than that of unloaded freezing-thawing soil,but the time required for soil samples to reach consolidation and stability increases.(3)The secondary consolidation coefficient of deep unloaded freezing-thawing clay first increases and then decreases with the increase of consolidation pressure,and the peak value of the secondary consolidation coefficient occurs near 4MPa.The coefficient of secondary consolidation of loaded freezing-thawing soil is larger than that of unloaded freezing-thawing soil,and the greater the freezing-thawing load is,the greater the coefficient of secondary consolidation is.The influence law of initial moisture content on the secondary consolidation coefficient of deep freezing-thawing clay is as follows: the higher the initial moisture content is,the higher the secondary consolidation coefficient of soil sample is.(4)The lateral pressure coefficient of deep freezing-thawing clay is larger at the initial stage of consolidation and then decreased gradually with the increase of consolidation time.For freezing-thawing soil without loading,the higher the consolidation pressure is,the higher the initial moisture content is,and the higher the lateral pressure coefficient is.For freezing-thawing soil with loading,freezing-thawing load weakens the effect of initial moisture content and consolidation pressure on the lateral pressure coefficient.The lateral pressure coefficient of deep freezing-thawing clay after stabilization under this test conditions range from 0.40 to 0.649.(5)Based on the test results,burgers creep model is used to describe the creep deformation of deep freezing-thawing clay.Creep model parameters E1,E2,and ?2,each has a linear relation with consolidation pressure;The UMAT subroutine of the compiled Burgers creep model is used for the numerical simulation of the uniaxial creep of deep freezing-thawing soil.It is found that the numerical results are in good agreement with the laboratory experimental data,which verified the correctness of the UMAT subroutine.There are 73 pictures,19 tables and 111 references in this paper. |
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