Study On The Development Mechanism Of Micro-cracks In Variegated Clay

The Tertiary variegated clay in the Qinshui Basin,Shanxi is a special mediumexpansive soil,and the Tertiary cohesive soil at the interface of the loess-tertiary clay layer is dewatered and cracked,providing an advantageous channel for rainwater infiltration and softened by water.Under the influence of excavation and unloading,landfill loading and hydrodynamic action,the slope stability of this stratum is poor,and multiple unsettled contact surfaces of loess and variegated clay have collapsed,which has caused great impact during the construction of high-speed railway.In the future,there will be potential risks to the safe operation of high-speed rail.Therefore,it is of great significance to study the cracking and development mechanism of this kind of variegated clay cracks to prevent and control landslide disasters.(1)Through the drywet cycle test and evaporation at different rates,the tertiary variegated clay completely reveals the relationship between the cracking of this type of variegated clay and the water content and evaporation.Among them,the yellow-green clay contains more montmorillonite Compared with illite,the volume loss of water is large,and it is most susceptible to cracking,followed by gray-green clay.The high organic content of grayblack clay basically does not generate cracks.(2)The cracks are extracted by image threshold segmentation processing,which intuitively shows the cracks.Morphological characteristics,quantitative calculation of crack width,length and area changes;CT scan of gray-green clay with different water content,and image processing techniques such as deep learning to obtain three-dimensional morphological characteristics of micro-cracks in the soil.The study found that although the original cracks are small,they control the follow-up The main factor of crack expansion is the formation of primary cracks in the process of water loss and shrinkage.The secondary cracks are generally small,and the width and length of the cracks are smaller than the primary cracks.They can be used as the "cracking core" for the next crack;(3)The uniaxial tensile strength of the soil with different water content was obtained by the uniaxial tensile test of the soil,and the cracking mechanism of the soil was discussed.The cracking process of the soil can be roughly divided into the stable-cracking stage,the rapid expansion stage and the re-stabilization At this stage,the water-sensitive minerals in the clay absorb water and expand,and the microstructure changes such as soil particles,pores and cement are caused by the shrinkage of the soil,which is the internal cause of the cracks in the clay.The tensile strength of the soil itself and the matrix suction are the control of the soil.Key mechanical indicators of body cracking;(4)It is proposed that in the engineering application,after the excavation of this water-sensitive clay slope,flexible slope protection or spraying mud should be used to protect it in a timely manner to slow down the loss of soil moisture.Drainage avoids large changes in the moisture content of the surface layer of the soil and thus avoids shrinkage cracks.