Research On Three-dimensional Thawing Settlement Deformation Of Stratum During The Construction Of Subway Tunnel Using Horizontal Freezing Technique

As a special reinforcement technology of water-rich soft stratum,artificial ground freezing method has been widely used in subway tunnel construction in China.The thawing settlement of stratum can produce serious influence on the surrounding environment that lengtheneding the construction period of the subway and threatening the safety of structures due to the thawing of frozen wall.In view of this,this thesis studied the three-dimensional thawing temperature field and thawing settlement deformation law of the stratum during the construction of metro tunnel using artificial horizontal freezing method by the research methods of theoretical analysis,centrifugal model test,numerical simulation and field measurement.The main research contents and results are as follows:(1)Considering the soil temperature gradient in the frozen-thawed zone,the moving phase transition boundary equation is deduced based on the flat-panel thawing theory,and the analytical solution of the transient thawing temperature field is obtained;The thawing settlement coefficient term and compaction coefficient term of the thawed soil stability settlement calculation formula are used to reflect the thawing process of frozen soil and the consolidation process of thawed soil,and the analytical solutions of thawing shrinkage zone and consolidation zone radiuses are deduced.Then,the duration prediction model of ground surface thawing settlement during the thawing period of horizontal frozen wall of subway tunnel is established by using stochastic medium theory.The results of engineering case analysis show that the theoretical prediction value of ground surface thawing settlement deformation is closer to the field measured value after considering the thawing process of frozen soil and the consolidation process of thawed soil;At the initial stage of thawing,the ground surface settlement rate is large.After 30 days of thawing,the ground surface settlement tends to be stable.(2)A set of centrifugal model test system which can simulate the horizontal freezing construction process of subway tunnel is established.Using Butterfield dimensional analysis method,the similarity criterion of ground thawing sedimentation centrifugal test is deduced.Based on the local horizontal freezing project of a tunnel in Fuba line of Beijing subway,the centrifugal model test of three-dimensional thawing settlement of the stratum during the horizontal freezing construction of the subway tunnel is carried out.The evolution laws of the formation pressure,thawing temperature field and thawing settlement displacement field during the thawing period of the subway tunnel are studied.The results show that under the centrifugal acceleration of 30 g,the natural thawing time of horizontal frozen wall with the thickness of 40 mm is 170 min,which is about 2.13 times of the active freezing time;When thawing for 108.8min(equal to 68 days of prototype),the maximum thawing settlement displacement of the model surface is 1.023 mm,which is equivalent to30.69 mm of prototype,close to the field measured value.It verifies the reliability of the three-dimensional thawing settlement centrifugal model test.(3)Considering the phase change latent heat of frozen-thawed soil,the mathematical model of three-dimensional frozen-thawed transient temperature field of subway tunnel is established;Based on the orthotropic deformation characteristics of frozen-thawed soil,the instantaneous frozen-thawed strain component generated when the soil temperature reaches the frozen-thawed temperature is derived.Relying on the secondary development platform of ABAQUS finite element software,the user subroutine of three-dimensional deformation of frozen-thawed soil is compiled,and then the numerical simulation method of ground thawing settlement during horizontal freezing construction of subway tunnel is established by using the temperature displacement sequence coupling method.Similarly,based on the local horizontal freezing project of a tunnel on Fuba line of Beijing Metro,the three-dimensional thawing temperature field and thawing settlement deformation law of the tunnel during thawing period are studied.Compared with the centrifugal model test and field measured results,the accuracy of the three-dimensional thawing settlement numerical simulation method is verified,and it is necessary to consider the orthotropic deformation characteristics of frozen-thawed soil in the analysis of ground thawing settlement.(4)The established three-dimensional numerical simulation method of ground thawing settlement is applied to the freezing project of a plane oblique connecting channel of Fuzhou Metro Line No.5.The three-dimensional thawing temperature field and thawing settlement deformation law of the inner layer during the natural thawing period of the connecting channel are studied.The results show that after 68 days of thawing,the frozen wall basically thaws,and the thawing time of the frozen wall is about 1.51 times of the active freezing time;The maximum ground surface thawing settlement displacement is 24.1mm,a little error with the field measured value,which further shows that the three-dimensional numerical simulation method of stratum has high prediction accuracy.The research results of this thesis provide prediction methods for ground thawing settlement during the horizontal freezing construction of subway tunnel,and can provide a reference basis for the design and construction of horizontal freezing engineering of subway tunnel.Figure 124 Table 27 Reference 170...