北京砂卵石地层渗流条件下多排管局部冻结水平板成形规律研究

Formation rules of horizontal frozen plate with multiple rows in Beijing sandy gravel stratum under seepage condition

地铁暗挖车站盆形冻结由盆壁和盆底两部分组成闭合的止水空间,其中盆底可采用多排管局部冻结(板梳冻结)的方式。基于物理模型试验建立了板梳冻结的数值模型,所建模型能够有效反映物理模型试验的结果并再现冻结形态发展,二者共同揭示了渗流条件下板梳冻结的成形和温度场时空发展规律。研究发现:(1)渗流条件下,板梳冻结成型经历3个阶段,初始阶段冻土柱沿顺水流方向发展;第2阶段背水面最后一排冻结管冻土柱在垂直水流方向交圈;最后阶段冻结区域由背水面向迎水面逆向发展形成水平冻结板。渗流条件下的迎水面绕流造成前两排冻结管端部出现冻结凹槽,使得冻结板有效厚度有所损失。(2)在达到冻结稳定状态时,主体冻结区域的温度场在顺水流竖向剖面上的表现为水滴形态,低温部分以中部冻结管为中心呈对称分布;垂直水流竖向剖面上以中间行冻结管为中心对称分布,温度自核心低温区域向四周逐步升高;在冻结板厚度方向上中部温度比端部温度低。

Basin-shaped freezing technology is a water-proofing technology applied to underground excavation subway station in sandy gravel stratum,with the basin wall and basin bottom acting together to form a closed sealing space,the basin bottom uses comb freezing method to form a horizontal frozen plate.In this paper,based on the physical model test,numerical simulation is used to analyze freezing rules and the temperature field development of comb freezing method under seepage condition.The numerical model can effectively reflect the freezing shaping evolution of comb freezing,and the simulation results are in good agreement with the physical model test.Research finds that:(1)In the process of comb freezing under seepage condition,firstly,the frozen area develops along the flow direction,then the last row of freezing pipes on the back-water surface intersect in the direction of vertical flow and finally,the frozen area develops from the back-water surface to front-water surface and forms a closed horizontal frozen plate.Meanwhile,the effective thickness of the horizontal frozen plate is lost to some extent due to the flow around front-water surface.(2)The temperature field in the main frozen area shows a droplet shape along the direction of the flow,and the low temperature part is basically symmetrical distribution centered on the third row of freezing pipes,the temperature field in the vertical flow direction is symmetrical distribution centered on the middle row freezing pipes,and the temperature gradually increases from the core low temperature area to the surrounding areas,and the temperature at the middle of the freezing tube is lower than that at the end.