Closure law and prediction model exploration of freezing wall for coarse grained soil under seepage action
Due to the unclear development rule of freezing wall under seepage action and other reasons,the par-tial freezing method construction project relies on manual experience and lacks scientific prediction models,and is still far away from precise design and control.In order to explore the evolution law of freezing wall in coarse-grained soil layers during the freezing method construction under seepage,this article first establishes a numeri-cal model for the freezing method construction,and verifies the effectiveness and applicability of the established model through indoor model experiments.Afterwards,considering five factors such as seepage velocity,freez-ing tube spacing,environmental temperature,moisture content,and thermal conductivity,an orthogonal numer-ical experiment was conducted to determine the main control factors for the formation of freezing walls,includ-ing time and thickness of freezing wall intersection.Finally,the development and evolution of freezing wall un-der influence of the main control factors were studied through numerical simulation.Based on the results,a pre-diction model is established for critical flow velocity,freezing wall thickness,and freezing wall intersection time,and provide a selection plan for the construction parameters of the freezing method.The research results in-dicate that:(1)A coupled soil freezing-thawing model established can effectively simulate the frozen soil pro-cess under seepage conditions,which can meet the needs of computation and analysis of freezing wall develop-ment process.(2)Based on the results of orthogonal numerical experiments,it was found that the contribution percentages of seepage velocity to the thickness of freezing wall and the intersection time are 78%and 52%,re-spectively,which is the dominant factor controlling whether a freezing wall can close and the final thickness.(3)When the seepage velocity exceeds a certain threshold,the freezing wall cannot be closed.This threshold is defined as the critical flow rate in freezing wall construction.When the freezing walls can be closed,thickness of the resulting freezing wall is mainly determined by flow velocity,and the two have an inverse exponential re-lationship.(4)The spacing between freezing pipes has little effect on the final thickness of freezing wall,but it has a great impact on freezing wall closure time.Furthermore,an inverse exponential relationship exists be-tween them.(5)Given formulas of freezing pipe spacing,freezing wall thickness and closure time of freezing wall under conditions of 0～6 m·d-1 is provided,which can provide theoretical guidance for parameter selection and construction technology design of freezing method for coarse granular soil layer.
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