Yue Jianwei, Huang Xuanjia, Zhao Limin, Wang Zifa
School of Civil Engineering and Architecture, Henan University, Kaifeng, 475004, China.
Institute of Safety Evaluation and Restoration of Immovable Cultural Relics, Henan University, Kaifeng, 475004, China.
Sci Rep. 2022 Feb 2;12(1):1816. doi: 10.1038/s41598-022-05946-w.
Earthen sites are easily eroded by the natural environment, resulting in many micro-cracks on the surface. To explore the effects of environmental effects such as drying shrinkage and freeze-thaw on surface cracking, orthogonal tests that imposed these effects on the Zhouqiao site were conducted. Using range analysis, image processing technology, surface strength measurement and microstructure characteristic analysis, this paper explores the effects of soil thickness, water content, dry shrinkage, freeze-thaw cycles and other factors on the morphological characteristics of the site's surface cracks. The results show that under the action of dry shrinkage, the thickness of soil layer is the primary factor affecting the cracking of earthen soil. The thinner the thickness of soil layer, the lower the moisture content, and the more serious the cracking. The initial moisture content is the most disadvantageous factor affecting the reduction of the surface strength of the earthen soil. The strength around the soil sample is lower than that inside, and there are more cracks. Under the action of freezing and thawing, the main factors affecting the cracking and surface strength reduction of earthen soil are the initial water content and soil layer thickness, and the thicker the soil layer, the smaller the crack development and the lower the surface strength. Scanning electron microscope results show that under dry shrinkage and freeze-thaw conditions, the internal cracks of the soil samples exhibit different shape characteristics. Intergranular cracks appear most often under dry shrinkage conditions, and isolated cracks appear most often in the soil samples from the freeze-thaw cycle test. The cracks caused by these two types of external environment factors damage the earthen soil. According to the tension failure model and the definition of the first frost heaving theory, it can be determined that when the micro pore force F and the maximum frost heaving pressure P are greater than the cohesion of the soil sample, the soil sample will germinate cracks.
土遗址易受自然环境侵蚀，导致表面出现许多微裂纹。为探究干燥收缩和冻融等环境作用对表面开裂的影响，对周桥遗址施加这些作用进行了正交试验。本文通过极差分析、图像处理技术、表面强度测量和微观结构特征分析，探讨了土层厚度、含水量、干燥收缩、冻融循环等因素对遗址表面裂纹形态特征的影响。结果表明，在干燥收缩作用下，土层厚度是影响土坯开裂的主要因素。土层厚度越薄，含水量越低，开裂越严重。初始含水量是影响土坯表面强度降低的最不利因素。土样周边强度低于内部，裂纹更多。在冻融作用下，影响土坯开裂和表面强度降低的主要因素是初始含水量和土层厚度，土层越厚，裂纹发展越小，表面强度越低。扫描电子显微镜结果表明，在干燥收缩和冻融条件下，土样内部裂纹呈现不同的形状特征。干燥收缩条件下最常出现晶间裂纹，冻融循环试验的土样中最常出现孤立裂纹。这两种外部环境因素引起的裂纹会破坏土坯。根据拉伸破坏模型和第一冻胀理论的定义，可以确定当微孔力F和最大冻胀压力P大于土样的内聚力时，土样将会萌生裂纹。
