Study On Change Of Strength And Fissures Of Wet Expansive Soil Improved By Silt Soil Under Wet And Dry Cycles

Expansive soil contains a lot of hydrophilic minerals,and has obvious soil properties of hygroscopic expansion and dehydration shrinkage.Therefore,engineering disasters often occur every year in the world due to its poor engineering properties.Because the atmospheric environment changes from time to time,the sensitive expansion and contraction of expansive soils will cause dry shrinkage and swelling due to changes in the surrounding environment.This repeated dry shrinkage and swelling will cause the strength of the expansive soil to change and accompany cracks.produce.The engineering properties of expansive soil are studied and improved to reduce its harmfulness and improve engineering stability.In this paper,the expansive soil is treated with silty sand in the yellow pan area,and the expansive soil with 30% silty sand content is taken as the experimental object.Through laboratory tests,the strength change under the action of dry and wet cycles is studied.The characteristics of fissure development during the wet cycle were studied and analyzed.The experimental results show:(1)Control the moisture content with 11%,13%,15% and 17% as control points respectively,the samples of the modified expansive soil that reached the point of control moisture content during the dry-wet cycle were taken for a direct shear test to obtain the The shear strength has a linear relationship with the number of cycles,and it continues to decrease with the increase of the number of cycles;the cohesive force decreases rapidly with the increase of the number of cycles,then decreases slowly and stabilizes,and decreases during the first three cycles.The rate is very fast.As the number of cycles continues to increase,the decline rate becomes slow and stabilizes when going through the fourth and fifth cycles;the internal friction angle floats within the range of 10 ° ? 30 ° as the number of cycles increases.Affected by the wet and dry cycle is less obvious.(2)By studying the development of apparent fissures,it can be seen that during the first cycle,a slight fissure appeared at the edge of the soil sample.During the second and third cycles,the fissure began to gradually develop to the middle and gradually A fissure network was formed.During the four or five cycles,the fissure network gradually formed and there were no obvious new fissures,indicating that the development of the fissures had basically stabilized at this time;the quantitative analysis of the apparent fissures was performed using Matlab and Photoshop software.It is found that the fracture rate and fractal dimension of the apparent fractures show that the values of the fracture rate and fractal dimension also increase with the increase of the number of wet and dry cycles,but the fracture rate begins to increase slowly after the third cycle,and the After four cycles,the fracture rate only increased by about 0.75%,indicating that the fracture development at this time began to stabilize,and the fractal dimension also grew slowly after the second cycle,and the third cycle was only slower than the second cycle.Later increased by about 0.1,indicating that the main fissures at this time were formed,and then began to develop around.(3)Using environmental electron scanning technology to take photos of the internal microstructure of the modified expansive soil undergoing the effects of dry and wet cycles,and to study the characteristics of its microcracks,it was found that microcracks had slight cracks after the first cycle,and two or three cycles were performed.At that time,the micro-cracks began to develop gradually,and the cohesive bodies around the cracks began to loosen,accompanied by the scattering of clay particles,and the internal structure was damaged.After four or five cycles,the cracks began to develop and form,and no obvious cracks occurred.,Basically stable.