The Size Effect Of Desiccation Cracking Behaviour Of Expansive Soil And The Evolution Characteristics Under Drying-Wetting Cycles

Under the influence of environment,engineering geology and hydrogeological conditions,the distribution range and thickness of expansive soil in nature exist obvious difference in the scale can affect the engineering properties of expansive soil,especially the dry shrinkage cracking of expansive soil,however,the problem in this aspect is often ignored by people.For the size effect of desiccation cracking behaviour of expansive soil and the evolution characteristics under drying-wetting cycles have been carried out the system research.Through the indoor preparation of different size conditions of the expansive soil samples by a large number of dry test,the influence of the dimension parameters such as one-dimensional condition,two-dimensional condition,height and width ratio of the expansion soil moisture evaporation,shrinkage and fracture development of expansive soil are analyzed,the evolution law of dry shrinkage cracking of expansive soil in dry wet dry circulation conditions was discussed.In addition,we analyzed the expansive open fracture closure and the relativity of solution process from the soil disintegration test.Get the following results:1.Evaporation:The evaporation process of one-dimensional expansive soil sample is almost the same as the two-dimensional sample;The evaporation process of expansive soil is divided into three stages:constant rate stage,rate stage and residual stage;With the increase of the initial thickness,the evaporation duration of expansive soil is prolonged,and the duration of the constant rate stage is also prolonged,constant rate stage has y=ax+b linear relationship;The evaporation process of expansive soil will be accelerated by wet-dry cycle,with the increase of dry-wet cycles,the evaporation duration of expansive soil decreases.2.Shrinkage:The thickness shrinkage law of one dimensional expansive soil sample is the same as the two-dimensional sample;The shrinkage of expansive soil can be divided into three stages:normal shrinkage,shrinkage of shrinkage and zero contraction the normal shrinkage stage has y=ax+b linear relationship,the slope indicates the contraction coefficient ?s;With the increase of the initial thickness of the expansive soil sample,the shrinkage time of the thickness of the soil sample is gradually prolonged,the moisture content is an important factor affecting the shrinkage of expansive soil.;the thickness of the wet-dry cycles makes the irreversible strain variable,the shrinkage deformation decreases with the increase of the dry-wet cycles.3.Cracking development:Under different size effect,the crack growth pattern and crack growth law of expansive soil have significant difference,the crack of a one-dimensional specimen is parallel to the straight crack,and the crack development tends to be simplified as the initial thickness increases;the crack of the two dimensional specimen increases gradually from the network type to the linear type of the crack,the quantity of the fracture is reduced,and the degree of fracture development is weakened.According to the different height to width than fracture rules that exist a certain size height to width than the critical value affected the expansion soil fracture morphology;cyclic wetting and drying process of expansive soil fissure could promote the development and slit number,the segmentation clods number was increased.4.The volume shrinkage process and crack growth process of expansive soil has a significant corresponding relationship,which common link is the change of the moisture content;During the dry-wet cycle,the expansive soil crack closure can be considered as the result of the disintegration and swelling.