真空负压作用下非饱和粉细砂层渗透注浆增注机制研究

Silty fine sand stratum which is common in underground engineering is a kind of typical weak strata. The vacuum permeation grouting is an effective method to treat the silty fine sand stratum. However, the lack of adequate research on the grout diffusion mechanism under the effect of vacuum negative pressure has led to the absence of scientific basis for the design of vacuum permeation grouting, which has seriously restricted its practical application. In order to solve the problems, the effect of vacuum negative pressure on the physical parameters of liquid bridges in unsaturated silty fine sand is firstly studied. Combined with “particle-liquid bridge-particle” model experiment, the rupture determination conditions of liquid bridge will be established. Then the rupture mechanism of the liquid bridge under the effect of vacuum nagetive pressure and the mechanism of improving grout injection ability caused by liquid bridge rupture will be revealed. Secondly, the influence of the vacuum negative pressure on the mechanical properties of the interface between grout, water film and particles will be studied. Combined with “grout-water film-particle” model experiment, the mechanism of improving grout injection ability caused by the interface mechanics under vacuum negative pressure condition will be revealed. Finally, based on the incremental injection mechanism, the grout diffusion boundary conditions under vacuum negative pressure will be established. The grout diffusion model of vacuum permeation grouting will be derived based on Maag’s model and cylindrical diffusion model, which will be verified and corrected through three-dimensional grouting experiment. This research will provide scientific basis for the perfection of vacuum permeation grouting theory and engineering practice.

粉细砂地层是地下工程建设中常见的不利地层，真空渗透注浆是治理粉细砂地层的有效方法。但目前对真空负压作用下的浆液渗透扩散机制缺乏充分研究，导致真空渗透注浆设计缺乏科学依据，严重制约其实际应用。针对以上问题，项目首先研究非饱和粉细砂土中真空负压对液桥物理参数的作用规律，结合“颗粒-液桥-颗粒”模型实验，建立液桥断裂条件，阐释真空负压作用下的液桥断裂机制，揭示液桥的断裂对提高浆液注入能力的作用机制。研究液桥断裂后真空负压对浆液、水膜、颗粒之间界面力学特性的影响规律，结合“浆液-水膜-颗粒”模型实验，揭示真空负压条件下的浆-水-颗粒界面力学特性对提高浆液注入能力的作用机制。最后，基于增注机制研究成果，建立真空负压条件下的浆液扩散边界条件，进而基于Maag及柱形扩散模型，建立真空渗透注浆浆液扩散模型，并开展三维注浆实验进行验证和校正。研究成果将对真空渗透注浆理论的完善及工程实践提供科学依据。

本项目通过理论和实验研究，探究真空负压促进浆液在非饱和粉细砂中的增注机理，为实际工程应用奠定理论基础。建立了非饱和粉细砂孔隙水液桥模型，推导了平衡状态下和施加负压状态下的液桥平衡方程，研究了不同负压情况下液桥形态变化及液桥断裂条件的影响。开展了真空负压渗透注浆实验，探究非饱和粉细砂的渗透和持水特性以及注浆扩散规律，得到如下研究成果：.（1）真空负压会破坏液桥与颗粒间原有的平衡状态，当弯液面液膜所承受的表面张力大于水的表面张力时，液桥发生断裂。液桥在负压状态下的含水量与基质吸力的关系在宏观尺度上仍然满足土-水特征曲线的变化规律，随着负压的施加，液桥体积变小，含水量降低，基质吸力变大。.（2）当土体基质吸力小于施加的负压时，土体内水分运移加强，土体渗透能力增加，加速土体内水分的流失，导致土体含水量降低，渗透系数降低。当土颗粒间的基质吸力大于施加的负压值时，则外加负压不能克服土颗粒间的基质吸力，土体内部逐渐形成新的平衡。.（3）液桥力是导致渗透系数降低的重要因素，土体真空度趋于稳定后，液桥重新形成新的平衡，并逐渐扩展与其他颗粒之间形成液桥，液桥的连接使得粘性作用加强，土颗粒连接更加紧密，造成负压加载后土体渗透系数降低。.（4）真空负压注浆过程中浆液扩散距离与非饱和土体中土颗粒间的液桥密切相关，当施加的负压值不能破坏土颗粒与液桥间的基质吸力时，浆液扩散距离波动较小，当施加的负压大于土颗粒与液桥间的基质吸力时，将导致土颗粒间的液桥断裂，使得土颗粒间孔隙通道增加，浆液扩散距离增大。.（5）真空负压注浆过程与土样初始含水量之间存在最优值，当土样初始含水量较低时，液桥相对稳定，随着土样初始含水量的增加浆液扩散距离变小，当施加的负压和土样初始含水量达到最优值时，土颗粒间的基质吸力与施加的负压相差较小，液桥的平衡最容易被打破，浆液能够在短时间内扩散更远的距离，注浆效果最佳。