Study On Effect Of Content Of Ferrihydrite On Mechanical Properties Of Kaolin

There is a large area of granite weathered soil distributed in the south of China,which is mainly composed of kaolinite and quartz,and contains a small amount of iron oxides.Among them,kaolinite has the highest content,and there are many forms of iron oxides,such as goethite and hematite.Although its content is low(generally 5-10%),it has strong colloidal activity,It has a significant impact on the engineering properties of soil,such as disintegration,mechanical strength,permeability,etc.In order to investigate the influence of iron oxide colloids on the properties of weathered soil,the influence of ferrihydrite content on the properties of kaolin and its interaction mechanism were studied by artificially preparing ferrihydrite and blending it into kaolin.By conducting standard consolidation tests,consolidated undrained(CU)triaxial shear tests,unconsolidated undrained(UU)triaxial shear tests,and permeability tests on kaolin with different ferrihydrite contents,the influence of ferrihydrite content on the physical and mechanical properties of kaolin is explored,and its microstructure is observed through scanning electron microscopy tests to analyze its interaction mechanism.The main conclusions drawn in this article are as follows:(1)The influence of ferrihydrite content on the consolidation characteristics of kaolin was studied through standard consolidation tests.The results show that under the consolidation pressure of 0-3200 k Pa,the total deformation,compression coefficient,and compression index of the sample height decrease compared to kaolin with 0% ferrihydrite content,while these three indicators reach their minimum values at 7% ferrihydrite content;The compression modulus and consolidation coefficient show an upward trend,reaching the maximum value at 7% ferrihydrite content;Under the consolidation pressure of 100-200 k Pa,the compression modulus can better evaluate the compressibility of the soil mass,and the kaolin with 5% and 7% ferrihydrite content reaches the level of medium compressibility soil.The 7% ferrihydrite content has the most significant impact on the consolidation characteristics of kaolin.(2)The influence of ferrihydrite content on the mechanical strength of kaolin was studied through triaxial shear tests.The results showed that under different conditions of undrained shear tests,the peak stress,cohesion,and internal friction angle of kaolin with other ferrihydrite content increased compared to kaolin with 0% ferrihydrite content,while kaolin with 7% ferrihydrite content showed maximum values;Comparing the results of undrained shear tests under different conditions,it was found that the cohesion under the 7%ferrihydrite content UU test condition was 1.68 times higher than that under the same content CU test condition;The difference in internal friction angle between the 7% ferrihydrite content CU test and the same content UU test conditions is 2.11 °,which is 1.18 times the internal friction angle of the UU test.(3)The microstructure of ferrihydrite and kaolin was studied through scanning electron microscopy experiments,and their interaction mechanism was analyzed.The results indicate that the influence of ferrihydrite on the mechanical properties of kaolin is mainly influenced by four factors: flocculent colloid cementation,bridging structure connection between clusters,mutual embedding between particles,and charge dissipation.However,the impact of too little ferrihydrite is relatively small,while too much ferrihydrite attracts and aggregates with each other,resulting in a decrease in the effective contact area of soil particles,manifested as a peak in the shear strength index of kaolin when 7% ferrihydrite content is present.(4)The influence of ferrihydrite content on the permeability characteristics of kaolin was studied through a flexible wall permeability test.The results show that the impermeability of the rest of the kaolin with ferrihydrite content is improved compared with that of the kaolin with 0% ferrihydrite content.Under the condition of controlling the osmotic pressure and confining pressure,the impermeability of the kaolin with 5% ferrihydrite content is improved most significantly,and the permeability coefficient of the kaolin with ferrihydrite content of corresponding content appears the minimum value most times.