Experimental Study On Cracks Evolution And Mechanical Properties Of Pore-damaged Expansive Soil Subjected To Drying-wetting Cycles

Expansive soil is an unique geological material which is extremely sensitive to humidity condition. The soil volume will swell or shrink significantly along with the process of absorption and desorption. It has three representative characteristics, significant swelling or shrinkage, fissures and over consolidation. In the complex atmospheric environment, the drying and wetting cycles lead to a series of problems, such as uneven settlement of roadbed, cracking, landslide of slopes, fissures in buildings, which brings great harm to engineering construction and production. To find out its mechanism, the fissures effect on strength and stability of expansive soil should be focused on. The damaged condition, the regularity of fissures generating, development, evolution associated with existed damage and its impact on soil strength and stability are an important research topic.To study the effects of virgin holes-damaged, wetting-drying cycle, and the combined two on soil fissures evolution, mechanical, deformation and stability. The expansive soil taken from Anhui Hefei are remoulded at different initial damaged state. Wetting-drying cycls tests and triaxial shear experiments are conducted. From four aspects, initial damaged state(hole diameter is 0 mm、2.5 mm、5 mm respectively), cycles of wetting-drying, combined effect of initial hole-damaged and wetting-drying cycles and net confining pressure, its influences on crack, strength and deformation are discussed, and its regularity are revealed.The main research conclusions are as follows:(1) The shearing strength of the specimen increases at a large scale when the net confining pressure gets larger. When net confining pressure increases from 100 kPa to 200 kPa, the shear strength of the samples increases about 21.94%; When the net confining pressure increases to 400 kPa, the shear strength increases by about 42.90%, it suggests that confining pressure has an important influence on the strength of the expansive soil.(2) The shearing strength of the samples decreases with increasing of drying-wetting cycles, after 3 times, it attenuates to 70% ~ 80% with respect to the original ones. Furthermore, the effect amplitudes would be decreases when net confining pressure enhances. This is, because under a higher net confining pressure, part of the cracks can be repaired. Fissure is a significant factors affecting the strength of expansive soil. However, deep soil crack extension are inhibited for a higher net confining pressure. That’s why most of the expansive soil landslide shows shallow property.(3) According to different drying-wetting cycles of 0 mm, 2.5 mm, 5 mm holedamaged samples’ triaxial shear tests, it is found that the strength of soil samples are mainly affected by drying-wetting cycles, shear strength is not obviously influenced by the aperture size of the soil. This suggests that the climate of drying and wetting alternation is a major factors that affects the stability of expansive soil. By contrast, the influence of the original holes in the soil is weak.(4) In the process of shearing, samples shows shearing shrinkage. As the result of the existence of fractures produced by drying-wetting cycles, especially the holes, the samples show a strong shear shrinkage trend, the volumetric strain is two times larger in compare with the original ones. It is also shown that when the soil water content reaches a certain value, the fissures or holes in the soil will be repaired at a certain extent.