泥水盾构加纤泥浆侵入复合地层成膜机理

Maintaining the stability of excavation face of large underwater shield tunnel is difficult in the uneven complex strata with different permeability. During tunneling, the key scientific problem is the formation of safe and effective slurry membrane by using bridging to clog slurry fine particles. The evolution law of slurry seepage flow in complex strata is complicated, and the slurry membrane is not uniform. The mechanism of slurry membrane formation and breakdown failure under high pressure is systematically studied in this project, by means of theoretical analysis, model test and numerical calculations. The research includes the following three points: ①The mechanics effect among particles, fiber and fluid evolves in the process of fiber membrane formation, growth and breakdown. The evolution mechanism of the mechanics effect can be revealed by analyzing the evolution law of water and earth pressure, soil deformation and membrane breakdown strength. ②The fiber bridging and particles clogging in the inner of strata are coupled with particles packing and consolidation on the excavation surface. The coupling mechanism can be studied by real-time tracking fiber slurry transfer and clogging outline, combined with measuring membrane microstructure. ③In the complex strata, the mechanism of slurry membrane formation can be revealed by analyzing the influence of the fiber shape and ratio on bridging and membrane formation efficiency. Then a new method of adding fiber in slurry, which is suitable for the formation of effective slurry membrane and reducing the risk of breakdown failure in the complex strata, will be put forward. It can be expected that the research project will obtain some theoretical basis for adding fiber in slurry, and maintaining the stability of excavation face for slurry shield in complex strata.

在透水性差异大、软硬不均复合地层中修建大型水下盾构隧道，利用架桥作用堵塞泥浆细粒及时形成安全有效的泥膜是解决开挖面稳定控制的关键科学问题。针对复合地层中泥浆渗透模式复杂、泥膜形成不均的特点，采用理论分析、模型试验和离散元仿真相结合的方法，系统研究了复合地层中加纤泥浆侵入成膜和泥膜加压击穿失效机理：①通过分析水土压力、土体变形、泥膜抗击穿强度等演变规律，揭示加纤泥膜结构形成、增长和击穿破坏过程中颗粒-纤维-流体间力学作用的演变机制；②通过对加纤泥浆在地层中迁移堵塞空间展布实时追踪和泥膜微观结构测定，探明地层内部纤维架桥及颗粒迁移堵塞效应与开挖面上颗粒堆积固结效应的耦合作用机制；③基于纤维外形和配比对架桥作用与成膜效能的影响分析，揭示复合地层中加纤泥膜形成机理。提出适合在复合地层中形成有效泥膜和降低击穿风险的新型泥浆加纤方法。项目成果为泥水盾构泥浆加纤技术和复合地层开挖面稳定控制提供理论依据。

在透水性差异大、软硬不均复合地层中修建大型水下盾构隧道，利用粗粒材料的架桥作用及时形成安全有效的泥膜是解决开挖面稳定控制的关键科学问题。围绕加砂泥浆侵入地层成膜特征的研究，从加砂泥浆粗粒材料的选取、泥浆侵入对砂性地层强度的影响、地层孔隙特征对成膜特征的影响、恒压加载的影响及加砂泥膜闭气性能几个方面开展研究。主要成果如下：.（1）为合理选取泥浆加砂材料，通过自制试验仪器开展泥浆悬浮砂粒能力分层测定，分析了沉降时间和砂粒粒径对砂粒在泥浆中沉降的影响规律，给出了泥浆悬浮砂粒能力的判别方法。.（2）对以轻质砂作为粗粒材料的泥浆性质进行性质测定，确定轻质砂及化学添加剂对泥浆性质的影响规律。.（3）在孔隙特征有良好连续性的不同砂性地层中开展泥浆侵入地层成膜试验研究，基于成膜特征指标与地层孔隙特征量化关系的构建，分析了地层孔隙特征对泥膜形成时间、不同阶段滤失量等泥膜特征的影响。根据孔隙体积大小对泥膜状态进行量化划分，确定临界孔隙体积。.（4）开展了恒压和恒速两种加载条件下加砂泥浆侵入砂性地层模型试验，通过滤失量曲线变化规律确定不同的泥膜状态，通过泥浆压力测定确定泥浆侵入地层的成膜历史。.（5）采用自制的泥膜闭气性试验装置，对添加有不同含量粗粒的泥浆进行泥浆渗透成膜闭气性试验，确定泥浆中粗粒材料添加量对泥膜闭气时间的影响规律，揭示了粗粒材料添加改变泥膜结构从而影响泥膜闭气时间的作用机理。