Wet And Dry Damage Of Bentonite Modified Loess And Self-healing After Soaking In Water

Loess is widely distributed in northwestern China,with poor impermeability,strong collapsibility,and significant structural and vertical joint development.Therefore,it has an important impact on the stability of water conservancy projects and building foundations in northwestern China.In addition,the massive loss of soil and water in the loess area has caused serious ecological damage.Bentonite is a sheet structure silicate formed by thixotropy of volcanic glass.The majority of the mineral composition is montmorillonite.It is a natural nano-material with a very small particle size and has strong water-swelling properties.The bentonite is mixed into the loess,and the characteristics of the swelling of the bentonite by water absorption can be used to greatly improve the permeability of the loess,so the bentonite is used to modify the loess.There have been a lot of studies on the permeability,strength characteristics and compressibility of bentonite-modified loess,but for the performance of bentonite-modified loess under actual climatic and engineering conditions under dry and wet cycling conditions and self-healing under water immersion There are few researches on the performance under combined conditions.In this paper,we will design a single-factor test plan for the above problems to explore the compactness,the amount of bentonite,and the temperature of the bentonite-modified loess during the dry-wet cycle process and the self-healing process.The analysis of its action law has reference significance for the application of anti-seepage materials in the northwest region and the selection of anti-seepage lining for landfills.The results of the study indicate that:(1)During the dry-wet cycle,the surface area ratio of bentonite-modified loess samples increased with the increase of the degree of compaction,and the rate of increase gradually decreased.After the degree of compaction is greater than 0.88,the effect on the crack stability area ratio becomes smaller;the amount of bentonite content has a significant effect on the crack surface area ratio of the sample surface.The sample with bentonite added is more effective than the sample without bentonite The rate is much larger,and the crack area rate increases significantly with the increase of the bentonite content,and the growth rate gradually slows down;under the influence of ambient temperature conditions,the high temperature environment will make the bentonite modified loess sample surface appear more than the low temperature environment.More cracks have a greater impact on the wet and dry damage process of modified loess;(2)During the process of self-healing in water,the area ratio of residual cracks on the sample surface increases with the increase of the degree of compaction,and the two are positively related.The greater the degree of compaction,the worse the degree of self-healing of the cracks on the sample surface;The amount of bentonite has a significant effect on the residual crack area ratio of the sample surface.The sample with bentonite added is much smaller in residual crack area ratio than the sample without bentonite,and the greater the amount of bentonite,the faster the healing rate of cracks.The faster,the better the degree of healing,and the amount of bentonite is positively correlated with the degree of fracture healing;under ambient temperature conditions,the residual area ratio of cracks under high temperature environment is greater than that under low temperature conditions.The weaker the self-healing ability of the cracks is,the worse the degree of healing;(3)The fissures have obvious middle width,narrow sides,and several major cracks.These cracks have earlier cracking time and longer development time,and their widths and lengths are obviously larger than those of later cracks.Many of the remaining cracks are extended from these major large cracks,and continue to extend and develop,forming many small cracks.These large and small cracks continue to develop,the large ones continue to extend,and the small ones continue to grow,eventually forming a fissure network.The stable crack area ratio of the bentonite modified loess sample is maintained at about 6%-7%.After the self-healing process of water immersion,the residual crack area ratio of the sample surface tends to 0,but the crack can be seen from the sample surface Traces left after healing;(4)After the dry-wet cycle process,the permeability coefficient of the sample under the influence of various factors increased,and the growth rate was large,reaching 55 to 60 times the original permeability coefficient,which greatly reduced its permeability.The greater the degree of compaction,the smaller the increase of the permeability coefficient;the greater the amount of bentonite,the greater the increase of the permeability coefficient;the higher the temperature,the greater the increase of the permeability coefficient.After the self-healing process after immersion in water,the permeability coefficients of all the samples decreased significantly,but there were some differences from the initial permeability coefficients,all of which increased to a certain extent compared with the initial permeability coefficients,but the growth rates were small Not enough to have a significant effect on the permeability of the specimen.