粗粒材料粒径及含量对高渗透性地层泥浆成膜效果的影响

泥水盾构工程遇到高渗透性地层时，会发生泥浆大量流失的情况，从而使泥膜形成困难，进而导致开挖面失稳，而粗粒材料的添加可有效改善泥膜难以形成的情况。为探究粗粒材料的添加对泥膜形成的影响，选用密度小的蛭石作为粗粒材料，通过改变其粒径和含量（体积分数），在自制的泥浆渗透试验设备中开展泥浆渗透成膜试验。以滤失量和成膜时间作为评价指标，分析粒径与含量对成膜效果的影响，并提出合理的粗粒材料粒径范围。结果表明： 1）地层平均孔径D0〖TX-〗对粗粒材料的添加具有参考意义，控制粗粒材料粒径在D0〖TX-〗/2～2D0〖TX-〗时有助于泥膜的形成，随着粗粒材料粒径的增大，成膜效果出现先增大后减小的现象； 2）当粗粒材料含量在20%～40%时，含量越大，成膜效果越好，但随着含量继续增大，这种效应会减弱； 3）当粗粒材料含量在20%～60%时，粗粒材料粒径的影响程度要大于含量，粒径的增大会削弱含量带来的增益效果； 4）实际工程中建议主要考虑粗粒材料粒径的选择。

Influence of Particle Size and Content of Coarse particle Materials on Film forming Effect of Slurry in High Permeability Formation

When slurry shield boring in high permeability stratum, a large amount of slurry will be lost, which would cause difficult formation of filter cake and even instability of excavation face. The addition of coarse particle materials can effectively improve the forming effect of filter cake. In order to explore the influence of the addition of coarse particle materials on the formation of filter cake, the vermiculite with small density is selected as coarse particle material to carry out slurry permeation and membrane formation test in self made slurry permeation experiment equipment by changing its particle size and content. The filtrate loss and filter cake forming time are taken as evaluation indices to analyze the influence of particle size and content on film forming effect, and a rational particle size range of coarse particle materials is proposed. The experimental results show that: (1) The average formation pore diameter D0〖TX-〗 has reference significance for the addition of coarse particle materials; the coarse particle materials with particle size of D0〖TX-〗/2~2D0〖TX-〗 is conducive to the formation of filter cake, and with the increase of the particle size of coarse particle materials, the film forming effect increases first and then decreases. (2) When the content of coarse particle materials is between 20% and 40%, the larger the content of coarse particle material, the better the film forming effect, but as the content continues to increase (larger than 40%), the effect weakens. (3) When the content of coarse particle materials is between 20% and 60%, the influence of the particle size of coarse particle materials is greater than that of the content, and the increase of particle size will weaken the gain effect brought by the content. (4) It is suggested that the selection of the particle size of coarse particle materials should be mainly considered in practical engineering.