| The artificial ground freezing method is widely used in the construction of tunnels in water-rich and soft soil,but the frost heave in the freezing processes harms the safety of the upper structure.With the increasing number of projects which frozen tunnels underpass the upper-structure year by year,the phenomenon of the upper structure foundation deformation caused by frost heave has attracted great attentions.However,the deformation calculation method and its interaction mechanism of the upper structure during the freezing process is not clear.This paper aims at the essence of frost heave is caused by moisture migration as the starting point.Based on the Segregation Potential model and Darcy's law,a threedimensional mathematical model is established,which is utilized for calculating the moisture field in frozen soil.A model of the frost heave evolution caused by moisture migration is analyzed.The water migration velocity of frozen samples is measured by a water migration test,and the volume increase of the froze soil during the freezing process is calculated.The relationship of water migration under different moisture content,overlying load and freezing temperature is revealed.At the same time,based on numerical calculation and practical engineering,the law of frost heave mound size in the overlying layer during freezing underpass is proposed.The inverse peck formula for calculating the deformation of overlying soil is got.Based on the limit tensile strain method and thin plate deformation theory,the structural deformation of different forms and stiffness of upper-structures are converted.The proposed formula is verified by the methods of engineering measurement,similar simulation experiments,and numerical simulation.The main research results in this paper are as follows.1)Based on Darcy's law,the law of conservation of mass and the migration potential model,the moisture migration equation of unsaturated positively frozen soil is derived,and the freezing moisture migration experiment under supplementary water conditions is carried out.The influence of three factors on the water migration is quantitatively obtained,which are overburden load,moisture content and freezing temperature.2)The calculation method of water migration under the open system is derived,and the volume increase amount during the freezing process is obtained.The water volume increase amount under the open system condition can be calculated to reach110% of volume of frozen soil?3)Through summarizing literature data,similar simulation experiments data and numerical calculations data,it is proved that the ground surface deformation caused by artificial freezing method conforms to the Gaussian distribution law,and the influence range of the ground surface deformation is about 8i-10 i.4)It is concluded that the deformation law of the subsurface stratum conforms to the Gaussian distribution under the effect of frost heave.The modified Mair formula for frost heave is derived to calculate the size of the frost heave mound of the subsurface stratum.5)The freezing uplift formula for calculating the deformation of the overlying stratum during the freezing process is derived to solve the deformation of the stratum where the upper-structure is located.6)Based on the ultimate tensile strain method and the thin rectangular plate deflection formula,a structural deformation calculation method for different overlying structural forms and different stiffnesses is got.The soil deformation obtained by solving the freezing uplift formula is converted into structural deformation.The uplift of different upper structures under frost heaving can be calculated.7)The freezing project monitoring data is used to verify the accuracy of stratum volume increase amount,the Frost heave Peck formula and the calculation method of structural deformation.The measured value is close to the calculated value,which can meet the needs of safety evaluation and analysis in the freezing construction process.In the future,the engineering applications of freezing underpass and upperstructure will be more and more with the large-scale construction of urban subway tunnels in a water-rich soft soil layer.The results can provide the calculation method of the deformation of the upper-structure for the high-risk freezing engineering and can provide an effective reference for the freezing design and construction.The structural pre reinforcement or frost heave control measures can be taken in advance to avoid the major risks of the damage of the upper-structure in the process of freezing underpass.The research results provide a theoretical basis and calculation reference for the technical research and application of artificial freezing method in the field of high-risk underground engineering. |
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