无砟轨道基床翻浆形成条件模型试验与判别分析

Model Test and Discriminant Analysis on Formation Conditions of Subgrade Bed Frost Boiling of Ballastless Track

采用单元模型试验,开展了级配碎石细粒含量、持水状态、与底座接触条件等因素诱发的无砟轨道基床翻浆模拟;定义翻浆区域底座裂隙渗水流量与翻浆面积之比为等效降雨强度(I e),借助路基面积水临界雨强(I c),导出了以I e>I c为条件的路基面离缝积水持时(t d)表达式,提出了判别无砟轨道基床翻浆的“雨强-积水法”,分析了1年一遇降雨下沪宁城际铁路离缝积水特征。研究表明:离缝产生并积水、列车荷载作用是基床翻浆的必要条件,翻浆严重程度与离缝高度、填料细粒含量呈正相关;积水持时主要受雨强、裂隙尺寸和填料渗透性影响,积水持时内承受的荷载次数是翻浆产生的基本要素;对于沪宁城际铁路,其由填料渗透系数决定的临界雨强小于大气降雨控制的等效降雨强度,故易翻浆。

Through element filler model,a series of ballastless track subgrade bed frost boiling simulation tests were performed,which varied in fines content and water retention state of graded crushed stone,or its contact relationship with foundation plate.According to the ratio of seepage discharge with regard to the foundation plate fractures in frost boiling zone to frost boiling area,a parameter called“equivalent rainfall intensity(I e)”was introduced.With the help of critical rainfall intensity(I c)for ponding on formation surface,the expression to calculate successive ponding time(t d)that happened in formation surface gap can be established,if taking I e>I c as ponding condition.Furthermore,a new criterion called“rain intensity-ponding method”was proposed for assessing the frost boiling of existing subgrade bed of ballastless track.Finally,the gap ponding characteristics of Shanghai-Nanjing intercity high-speed railway were analyzed under the condition of unprecedented rainfall in a year.The results indicate that gap formation and ponding along with train load action are the necessary conditions for subgrade bed frost boiling of ballastless track.The damage degree of frost boiling shows positive correlation with graded crushed stone fines content and gap height.t d is comprehensively influenced by the rainfall intensity in line location,fracture size and filler permeability.The number of train load actions which the gap sustains is the basic factor of frost boiling occurring during the period of t d.For Shanghai-Nanjing intercity high-speed railway,the I c controlled by filler hydraulic conductivity is far less than the I e controlled by atmospheric rainfall intensity,which would easily trigger subgrade bed frost boiling.