渗流作用下粗粒土冻结壁交圈规律及预测模型探索

Closure law and prediction model exploration of freezing wall forcoarse grained soil under seepage action

由于渗流作用下的冻结壁发育规律不明等原因,部分冻结法施工工程依靠人工经验,缺乏科学的预测模型,与精准化设计和控制还有很长的距离。为探索渗流作用下冻结法施工中粗粒土层冻结壁的演化规律,本文首先建立冻结法施工数值模型,并通过室内模型试验反演验证所建立模型的有效性和适用性。之后,考虑渗流速度、冻结管间距、环境温度、含水率和导热系数等五个因素,开展冻结壁形成正交数值试验,确定冻结壁交圈时间和厚度的主控因素。最后,通过数值模拟研究主控因素作用下冻结壁的发育和演化规律。基于结果建立临界流速、冻结壁厚度、冻结壁交圈时间的预测模型,给出冻结法施工参数的选择方案。结果表明,建立的冻土水热相变耦合模型可有效模拟渗流条件下土体冻结过程,能够满足冻结壁发育过程计算分析的需要。基于正交数值试验结果发现,渗流速度对冻结壁厚度和交圈时间的贡献百分比分别为78%和52%,是影响冻结壁能否交圈和最终厚度的主控因素。当渗流速度超过一定阈值时,冻结壁无法交圈。本文将这一阈值定义为冻结法施工中的临界流速。当冻结壁能够交圈,其最终形成的冻结壁厚度也主要由渗流速度决定,二者呈负指数函数关系。冻结管间距对冻结壁最终厚度影响不大,但是对冻结壁交圈时间影响较大,它们之间存在负指数函数关系。本文给出了0~6 m·d^(-1)条件下的临界流速、冻结壁厚度、冻结壁交圈时间计算模型,它们可为粗粒土地层的冻结法施工参数选择和施工工艺设计提供理论指导。

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.