| Artificial freezing technology is a construction method of pre-reinforcing loose and weak water-bearing strata by means of artificial refrigeration,which plays a temporary supporting role such as sealing water,retaining wall and resisting confining pressure.In order to evaluate the freezing effect and ensure the safety of construction,this paper takes the freezing process of saturated sand layer as the research object,and makes an in-depth study on the distribution of temperature field and development law of frozen wall in the freezing process of seepage and saline soil layer.Firstly,a control group model test was carried out.Based on Bakholdin's analytical solution of the freezing temperature field of a single tube,the reliability of the model test results was verified,and the conditions of different hole spacing,salt content,and seepage velocity were studied.The distribution law of freezing temperature field in the lower saturated sand layer is proposed.The calculation method of frozen wall thickness under different salt content and formation seepage conditions is proposed.Secondly,the coupling of seepage field and temperature field was achieved by using COMSOL finite element software,and the Heaviside step function was introduced to modify the physical parameters of the model,and the same numerical calculation model as the laboratory test conditions was established to realize the freezing process of saturated sand layer.Study on the distribution of medium temperature field and the development of frozen walls.Finally,through the comparative analysis of model test and numerical simulation results,the accuracy of the numerical calculation results is verified.The main results are as follows:(1)When freezing under the condition of no seepage,the temperature field after the intersection of the frozen wall is in good agreement with the Bakholdin's calculation model of the freezing temperature field of single row of pipes,which verifies the reliability of the model test;When freezing under seepage,the intersection time of the frozen wall becomes longer,theintersection position is inclined to the downstream,and the difference between the upstream and downstream temperature fields is obvious.(2)Under the condition of groundwater seepage,when the seepage velocity is small,the intersection time of frozen wall is almost unaffected,and the intersection position is approximately linearly related to the seepage velocity;when the seepage velocity is close to the limit velocity,the intersection time and position of frozen wall show an exponential growth trend.When the spacing of freezing pipes is 0.5 m,0.7 m and 0.9 m in the project,the limit seepage velocity that does not affect the frozen wall circle is 6 m/d,4 m/d and2.3 m/d respectively.(3)When the freezing temperature field tends to be stable,the erosion effect of water flow on the frozen wall gradually dominates,and with the increase of seepage velocity,the greater the erosion intensity is,the faster the heat exchange between the frozen pipe and water flow is in unit time,and the thickness of the downstream frozen wall first increases and then decreases.When the freezing time is fixed,the thickness of the upstream and downstream frozen wall decreases with the increase of the spacing between the holes.(4)With the increase of salt content,the relationship between the position of freezing wall and seepage velocity gradually transits from approximate parabola to linear correlation,and gradually approaches to the axial plane.Compared with the static water freezing of salt free sand layer,the thickness ratio of upstream and downstream frozen wall decreases exponentially with the increase of salt content.(5)Based on the analysis of the influence of seepage on the thickness of the frozen wall upstream and downstream of the pipe string,the function curve of the ratio of the thickness of the frozen wall changing with time under the condition of dynamic and static water is obtained.Secondly,according to the function of the temperature difference of the temperature measuring hole changing with time under the condition of dynamic and static water,the analytic formula of the temperature field of Bakholdin is modified according to the relationship between the salt content of the saturated sand layer and the frozen temperature,The function formula of the thickness of the frozen wall changing with time,velocity and freezing temperature is obtained in the process of freezing and after it tends to be stable,and the calculation result of the formula is basically consistentwith the measured value of the model.The research results have reference significance for the evaluation of frozen effect of seepage formation. |
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