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为研究裂隙膨胀土的细观结构特征,对重塑膨胀土进行了干湿循环、三轴浸水和各向等压加载试验。利用CT(computerized tomography)机对试验过程中进行无损实时动态扫描,从细观上分析膨胀土裂隙的产生以及裂隙在水和外力作用下的闭合全过程。将细观扫描数据与宏观物理参数相联系,研究裂隙对膨胀土变形特征的影响。结果表明:无约束情况下对膨胀土进行干湿循环,试样边缘以及孔洞聚集区易形成裂隙;干湿循环造成膨胀土体积收缩存在一个稳定渐近线,体缩会趋于1个稳定值。裂隙膨胀土在浸水初期产生膨胀力并出现湿胀变形;随着浸水量的增加,软化效应产生且膨胀力逐渐减小,在围压和偏应力压缩作用下继而出现体缩现象;浸水后期,在偏应力作用下试样产生剪胀破坏,再次出现轻微剪胀变形。在水和荷载作用下,不规则裂隙和孔洞逐渐演化为较规则的圆形孔洞,且圆形孔洞趋于闭合;仅在外力作用时,裂隙较难完全闭合;水和外力的共同作用使得膨胀土裂隙的闭合效果要优于单纯施加荷载时的闭合效果。裂隙膨胀土在各向等压加载过程中存在明显屈服现象,以屈服点为分界,扫描数据和孔隙比随荷载的增大分为快速体缩段和缓慢体缩段,前者与裂隙在荷载作用下闭合并演化成孔洞有关;后者与加载后期孔洞较难闭合且形成的新结构具备抵御外部荷载的能力有关。研究成果可为进一步认识裂隙对膨胀土力学特性的影响提供参考。
In order to study the mesostructural features of fissured expansive soils, the remolded expansive soils were subjected to wet-dry cycles, three-axis soaking and isostatic load tests. The CT (computerized tomography) machine was used to perform non-destructive real-time dynamic scanning during the test. The fissures of the expansive soil and the closing process of the fissures under the action of water and external force were analyzed from the microscopic point of view. The mesoscopic scan data is linked with macroscopic physical parameters to study the influence of cracks on the deformation characteristics of expansive soil. The results show that under the condition of no constraint, the expansive soil is subjected to the wet-dry cycle, and the fissure is easily formed at the sample edge and the hole gathering area. The volume shrinkage of the expansive soil caused by the wetting-drying cycle has a steady asymptotic curve, . In the early stage of soaking, the swelling expansive soil produces swelling force and swell deformation. With the increase of immersion amount, the softening effect is generated and the expansive force is gradually reduced, and shrinkage occurs under confining pressure and deviatoric stress. Under the action of deviatoric stress, the specimen will have dilatancy and damage, and then slight dilatancy will occur again. Under the action of water and load, the irregular cracks and holes gradually evolve into more regular circular holes, and the circular holes tend to close. Only when the external force is applied, the fractures are more difficult to be completely closed; the joint action of water and external force makes the expansion The closing effect of soil fissures is better than the closing effect of simply applying loads. The fractured expansive soil has obvious yielding phenomenon under the isotropic pressure loading process. The yield point is the boundary. The scanning data and void ratio are divided into rapid constriction and slow constriction as the load increases. The former and the fracture under load Closing and evolving into holes; the latter is related to the ability to resist external loads by the new structures formed by later holes that are more difficult to close during loading. The research results can provide reference for further understanding of the effect of cracks on the mechanical properties of expansive soil.