导管法水下混凝土灌注厚度的颗粒流模拟

依托北京地铁8号线永定门外站深基坑工程,介绍了导管法水下混凝土灌注工艺在深基坑封底工程中的应用。基于颗粒流理论和细观力学理论,将土体微细观结构与宏观行为联系起来,采用PFC数值软件建立了水下混凝土灌注模型,实现了砂卵石地层单导管、多导管水下混凝土灌注过程的可视化,得到各时段的灌注情况及最终封底结果。对比同位置实测厚度曲线,得到最大误差0.3 m,验证了模型的合理性。分析了影响深基坑水下混凝土灌注厚度的敏感性因素(导管布置形式、地下水位高度)。结果表明:基于颗粒流理论的PFC数值仿真技术适用于模拟导管法水下混凝土灌注过程; 导管布置稀疏,颗粒无法相互作用,容易出现“堆积”和“凹陷”现象,平均灌注厚度不足3 m; 参考单导管水下混凝土3 m的扩散半径,适当加密导管,可保证封底厚度; 地下水位越高,厚度起伏越大,水位越低,灌注厚度越均匀; 工程允许范围内,适当加密导管可保证混凝土封底厚度; 采取降水措施降低地下水位,可保证封底平整度。

Particle Flow Simulation of Underwater Concrete Filling Thickness by Tremie Method

Based on the deep foundation pit project of Yongdingmenwai Station of Beijing Metro Line 8, the application of the underwater concrete filling process of the tremie method in the deep foundation pit sealing project was introduced. On the basis of particle flow theory and micromechanics, the micro-structure and macro-behavior of soil were connected. The underwater concrete filling model was established by PFC numerical software. The visualization of underwater concrete pouring process of single-tremie and multi-tremie in sandy pebble stratum was realized, and the pouring situation and final sealing results in each period were obtained. Comparing the measured thickness curves of the same position, the maximum error was 0.3 m, which verified the rationality of the model. The sensitivity factors affecting the thickness of underwater concrete in deep foundation pits(the form of tremie arrangement and the height of groundwater level)were proposed. The results show that the PFC numerical simulation technology based on particle flow theory is suitable for the underwater concrete filling process of simulated tremie method. When the tremie layout is sparse, the particles can not interact, the more likely to appear “stacking” and “sinking”, the average filling thickness is less than 3 m. Refer to the diffusion radius of 3 m of single-tremie underwater concrete, the tremie should be properly encrypted to ensure the thickness of the back cover. The higher the groundwater lever is, the greater the thickness fluctuation is. The lower the water level is, the more uniform the filling thickness is. Within the scope of the project, the appropriate encryption of the tremie can ensure the thickness of the concrete back cover. The use of precipitation measures to reduce the groundwater level can ensure the flatness of the back cover.