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孔隙作为软土的重要组成单元,在软土性质发生改变时其变化最直接、最明显。研究软土固结过程中孔隙演化特征,对于认识软土排水固结机制具有重要理论意义。本文对大亚湾饱和细粒土在梯度压力下的孔隙结构进行微纳米尺度定量分析:将圆柱形土样进行真空冷冻升华干燥,利用同步辐射显微CT获取分辨率1.625μm的二维切片,应用Avizo软件的灰度阈值截断法将二维切片重建三维结构,采用形态学算法对三维孔隙结构进行量化和表征。研究表明:自沉状态下超过90%孔隙的等效直径为4~10μm,只有少数孔隙的等效直径大于40μm;土样在100k Pa压力作用后,大孔隙数量迅速减小,小孔隙数量迅速增加,表明初始状态下孔隙对压力最为敏感;大中孔隙容易被压缩消灭或被分裂为小微孔隙;随压力增加孔径变化趋于平缓,小孔隙和微孔隙占优势,孔隙的抗压能力与大小成反比。经梯度压力作用后土体从絮凝结构逐渐变成片叠结构,颗粒之间平行排斥,孔隙丰度逐渐减小,形状变得细长,方向趋于水平。本研究利用同步辐射显微CT技术结合三维可视化软件Avizo,建立具有真实孔隙结构特征的软土三维模型,从微纳米尺度分析了饱和细粒土的固结蠕变机理。
Pore as an important component of soft soil, the soft soil changes in the nature of the most direct changes, the most obvious. Studying the characteristics of pore evolution during consolidation of soft soil has important theoretical significance for understanding the mechanism of drainage and consolidation of soft soil. In this paper, the pore structure of Daya Bay saturated grained grained soil under gradient pressure was quantitatively analyzed by micro-nano scale. The cylindrical soil samples were vacuum frozen and sublimated. The two-dimensional slices with the resolution of 1.625μm were obtained by synchrotron radiation micro-CT. Avizo The grayscale threshold truncation method of software reconstructs the three-dimensional structure of the two-dimensional slice, and uses the morphological algorithm to quantify and characterize the three-dimensional pore structure. The results show that the equivalent diameter of more than 90% of the pores is 4 ~ 10μm under self-sinking condition, and the equivalent diameter of only a few pores is larger than 40μm. After the pressure of 100kPa, the number of macropores decreases rapidly and the number of small pores increases rapidly , Indicating that the initial state of the pore pressure is the most sensitive to; large and medium-sized pores can easily be destroyed by compression or split into small micropores; pore diameter changes with pressure tends to be flat, small pores and micropores dominate the pore compression capacity and size Inversely. After gradient pressure, the soil gradually changed from flocculation structure to lamellar structure, the particles were repelled in parallel, the pore abundance gradually decreased, the shape became slender and the direction tended to be horizontal. In this study, synchrotron radiation microscopy (CT) combined with three-dimensional visualization software Avizo was used to establish a three-dimensional soft soil model with true pore structure. The mechanism of the consolidation creep of saturated fine grained soil was analyzed from the micro-nano scale.