| With the construction of underground engineering becomes deeper and harder, Freezing technology will be the effective method in deep alluvium, containing water layer in the construction. The essence of the artificial freezing method is to enhance the stability of soil, reduce the deformation of the soil layer and block the flow of groundwater. Therefore, the frozen heave and thaw phenomenon arising in the freezing method construction will have an adverse impact on the urban land and buildings. However, numerical simulation of the temperature field and.displacement field of frozen soil curtain in subway tunnel can control the freezing time and soil freezing and thawing etc.In this paper, combined with a subway tunnel project instance, the model of horizontal freezing construction of tunnel is established by using finite element ANSYS software, numerical simulation was carried out on the temperature field of frozen wall after active freezing and the tunnel excavation under freezing condition, the temperature field of tunnel after active freezing tunnel and frost heave stress distribution during the freezing process was analyzed. The vertical surface displacement caused by the frost and the change regulation of displacement of soil layer with time was analyzed. The stress redistribution after tunnel excavation and displacement field distribution caused by excavation was analyzed.Through the numerical analysis of the soid temperature field after the active freezing, the thickness and the average temperature of the frozen curtain in different locations can be obtained. The calculated results are compared with the measured values, and the adjustment parameters are re calculated,and the freezing time of the tunnel is predicted to be 60-80 days, the average temperature of the frozen soil curtain is not higher than-10, and the thickness of frozen soil curtain will reach 2m. Through the coupling analysis of the temperature field and the stress field of the freezing curtain, it is known that, in addition to the freezing curtain, the closer to the bottom of the model, the greater the vertical stress. The horizontal stress direction of the upper surface is opposite to that of the negative temperature region, and there is a minimum stress value in the ground position, and then the stress increases with the increase of depth. The initial stress field and the displacement field are both horizontal and uniform distribution, the stress value of the soil layer is gradually increased, and the displacement value is gradually reduced. The maximum stress is 0.96MPa, the maximum displacement is 16.7mm.Through analysis of maintenance freezing tunnel excavation process, indicating that the first principal stress maximum value appeared in the vicinity of the tunnel bottom feet, about 0.3MPa,the third principal stress maximum value appeared at the bottom of the tunnel lining and temporary support, the maximum value is about 0.5MPa. After the tunnel is excavated,The stress on the center line of the tunnel is symmetrically distributed. The maximum shear stress appears near the bottom of both sides of the tunnel, the maximum value of about 0.15 MPa, due to the small curvature radius on both sides of the tunnel leads to stress concentration.The maximum bending moment is located at the junction of the lining and temporary support, which is about 152 KN ·m. Through the analysis of the stress field, displacement field and force of supporting structure during the tunnel is excavated, the correctness and safety of the design parameters of the freezing curtain is verified. The results can provides reference to similar construction methods. |
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