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泥膜的良好闭气性是保证泥水盾构带压开舱安全顺利实施的关键之一,要想提高泥膜的闭气性,首先应了解泥膜在带压开舱过程中的孔隙结构及渗透性变化。以南京纬三路过江通道在江底砂卵石地层中进行带压开舱为背景,在自制的试验装置中进行泥浆成膜和泥膜闭气试验,然后观测泥膜的孔隙结构和孔径变化,最后分析泥膜渗透系数的变化。研究结果表明:试验泥浆在0.2 MPa气压作用下6 h,在试验地层表面形成的泥膜厚度约为5.0 mm、孔隙率约为67%,在闭气过程中泥膜会发生压缩,且第一次单位压力引起的压缩量最大;随着闭气压力的增大,大孔隙组被优先压缩;泥膜基本单元体为骨架状结构,孔隙主要是粒间孔隙与架空孔隙,孔隙分布不连续、连通性差;孔径分布范围较广,其中在0.1~3.0μm的孔隙组占有绝对优势;本次试验中压缩后泥膜的渗透系数在10-9 cm/s量级。研究结果有助于明确泥膜在闭气过程中的变化,对后续提高泥膜闭气性的研究有重要的参考意义。
The good gas-tightness of the mud membrane is one of the keys to ensure the safe and smooth implementation of the mud shield with pressured open chamber. To improve the gas-tightness of the mud membrane, we should first understand the pore structure and permeability of the mud membrane in the process of pressure- Variety. Taking Nanjing Weisanjiangjiang River channel as the background, we carried out pressured-open chamber in the sand-pebble stratum of the riverbed, tested mud formation and mudflaps in a self-made test device, and then observed the pore structure and pore size change of the mud membrane. Finally, Analysis of mud membrane permeability coefficient changes. The results show that the mud thickness of the test mud formed on the surface of the test formation is about 5.0 mm and the porosity is about 67% under the pressure of 0.2 MPa for 6 h. During the process of gas closing, the mud membrane will compress, and the first time Unit pressure causes the largest amount of compression. With the increase of the closing gas pressure, the macro-pore group is preferentially compressed. The basic unit of mud membrane is a skeleton-shaped structure. The pores are mainly intergranular and overhead pores with discontinuous pore distribution and poor connectivity ; Pore size distribution of a wide range, of which pores in the 0.1 ~ 3.0μm group holds an absolute advantage; in this test the compressive permeability of the mud membrane in the order of 10-9 cm / s. The results of the study can help to clarify the changes of the mud membrane during the process of airtight closure and have important reference significance for the subsequent research on improving the gas barrier of the mud membrane.