Study on the factors affecting cracking of earthen soil under dry shrinkage and freeze–thaw conditions

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(Imax) are greater than the cohesion of the soil sample, the soil sample will germinate cracks.