微观尺度下州桥遗址土干缩劣化机理分析

土遗址作为一种特殊的研究对象，探明土样结构的 干缩裂隙的演化规律，对合理保护土遗址具有重要意义。为研究州桥遗址土的干缩变形特性，开展了室内干缩试验；为能更深入地揭示土样干缩开裂与表面张力变化的内在机制，引入了表面张力梯度参数；基于SEM图片在ABAQUS软件中建立州桥遗址土在微观模型并进行了裂隙演化模拟。结果表明：土样裂隙演化过程可归纳为：拉应力场、单根主裂隙、二级水平、三级纵深裂隙、裂隙网络的形成。拉应力场与单根主裂隙持续时间长，而二级水平、三级纵深裂隙持续时间短；裂隙类型产生的机制归纳为：局部剪切、局部拉伸及局部混合拉伸-剪切三种形式，随着裂纹的发展，逐渐由拉伸作用力向混合拉伸-剪切作用力发展，主裂缝垂直于受力面向外延伸开裂；因水分子迁移路径长度不同，上层土样较更深处的土样更易产生较大的收缩变形，并引起纵深裂隙的发展，随着水分迁移路径趋于稳定，水平裂隙成为土样裂隙发展的主要因素；分析裂隙率玫瑰图发现，上半部分的土样裂隙率普遍比下半部分低，并且裂隙多集中与90°与270°方向上，表明微毛细孔隙及土样内部收缩过大是产生裂隙的原因；归一化结果表明该模型能较好地反映州桥遗址土微观损伤的产生和演化发展情况。研究结果对州桥遗址土裂隙修复与保护具有参考意义。

Micro-scale Analysis of Dry-shrinkage Deterioration Mechanism of Zhouqiao Earthen Soil

As a special research object, it is of great significance to explore the evolution law of shrinkage cracks in soil sample structure for the rational protection of earthen ruins. In order to study the dry shrinkage deformation characteristics of Zhouqiao earthen soil, an indoor dry shrinkage test was carried out; In order to further reveal the internal mechanism of soil shrinkage cracking and surface tension change, the surface tension gradient parameter is introduced; Based on SEM images, the microscopic model of Zhouqiao earthen soil was established in ABAQUS software, and the fracture evolution was simulated. The results show that the fracture evolution process of soil sample can be summarized as: tensile stress field, single main fracture, secondary horizontal and tertiary deep fractures, and the formation of fracture network. The duration of tensile stress field and single main fracture is long, while the duration of secondary horizontal and tertiary deep fractures is short; The mechanism of crack types can be summarized as follows: local shear, local tension and local mixed tension shear. With the development of crack, it gradually develops from tensile force to mixed tensile shear force, and the main crack extends outward perpendicular to the stress surface; Due to the different length of water molecule migration path, the upper soil sample is more likely to produce large shrinkage deformation than the deeper soil sample, and cause the development of deep cracks. With the stability of water migration path, horizontal cracks become the main factor for the development of soil cracks; By analyzing the rose chart of fracture rate, it is found that the fracture rate of the soil sample in the upper part is generally lower than that in the lower part, and the fractures are mostly concentrated in the direction of 90 ° and 270 °, indicating that the micro capillary pores and excessive internal shrinkage of the soil sample are the reasons for the cracks; The normalization results show that the model can better reflect the generation, evolution and development of soil micro damage in Zhouqiao site. The research results have reference significance for the repair and protection of soil fissures in Zhouqiao site.