反压条件下泥水盾构开挖面泥膜致密性评价试验

Evaluating Test on Compactness of Filter Cakes of Excavation Face in Slurry Shield Under Reverse Water Pressure

为了准确评价泥水盾构存在反向水压条件下开挖面形成泥膜的致密程度,利用自制的可施加反压的泥浆渗透装置,开展6组不同压力条件下的泥浆渗透试验,通过测试试验过程中的滤水量和地层孔压的变化,以及形成泥膜的厚度和含水量,计算泥膜渗透系数、干密度及有效泥浆压力转化率等指标,分析有、无反压条件下泥膜的致密程度差异及其形成机理。研究结果表明,反压的存在降低了有效泥浆压力转化率,使得形成的泥膜孔隙比和渗透系数更大,干密度更小,即泥膜结构更为疏松;采用滤水量与泥膜体积的比值较单独采用滤水量可以更准确地评价泥膜的致密程度,其比值越大表示单位体积的泥膜内含有的土颗粒越多,泥膜结构越致密。研究结果对实际工程中泥膜质量的评价及开挖面稳定性分析有重要意义。

In order to accurately evaluate the compactness of filter cakes formed on excavation face in slurry shield under reverse water pressure,a slurry infiltration apparatus available to apply reverse water pressure was used to carry out six groups of slurry infiltration tests under different pressure conditions.According to measuring changes of discharged water yield and pore water pressure in the stratum and recording the thickness and water content of filter cakes,a series of indexes including the coefficient of slurry infiltration,dry density of filter cakes and the effective conversion rate of slurry pressure were calculated.The differences of the compactness of filter cakes under different pressure conditions and formation mechanism were analyzed.The results indicate that the conversion rate of effective slurry pressure decreases,resulting from the existing of reverse water pressure.Hence,the void ratio and permeability coefficient of filter cakes become larger but the dry density is smaller.It indicates that the structure of filter cakes islooser.The compactness of filter cakes could be evaluated more accurately by using the ratio of the discharged water yield as well as the volume of filter cake.The larger the ratio is,the more soil particles are contained in the unit volume of filter cake and the more compact the structure of filter cake is.The results will be significant for evaluating the quality of filter cakes and the stability analysis of excavation face in slurry shield.