Study On The Shear Strength And Disintegration Characteristics Of Loess Improved By Different Materials

Loess is widely distributed in northwestern my country,and its water sensitivity has brought many hidden dangers to slope engineering using loess as a building material.In recent years,Yan’an City has carried out large-scale geotechnical engineering projects,which greatly increased the probability of geological disasters and created many unpredictable engineering problems.Therefore,it is very necessary to mix various stabilizers into loess to eliminate some of the poor engineering properties of loess to meet engineering needs.Based on previous research results,this paper selects quicklime in traditional modified loess materials,polypropylene fibers in new carbon fiber materials,nano-silica in nano-scale particles,and guar gum extracted from the endosperm of legumes.Four types of improved materials are used to improve loess.The mixing ratio of different materials is characterized by mass fraction: lime 3%,6%,9%,12%;polypropylene fiber 0.2%,0.4%,0.6%,0.8%;nano-silica 0.6%,1%,2%,3%;Guar gum 0.25%,0.5%,0.75%,1%.The above one and two materials were added to loess to carry out experimental research on shear strength and disintegration characteristics.At the same time,with the help of water drop infiltration test and scanning electron microscope test,the microscopic mechanism of different materials to improve loess was discussed from a microscopic point of view.The main test results obtained in this paper are as follows:(1)A representative loess sample was taken at the site of a ditch construction site in Ansai District,Yan’an City,and the physical and mechanical properties of the soil for the test were determined through routine indoor geotechnical tests(particle analysis test,specific gravity test,critical moisture test,and compaction test).And provide data reference for the determination of the follow-up test plan.It is found that the plasticity index of loess is reduced after adding lime and nano-silica respectively.The liquid plastic limit of loess increases with the increase of nano-silica incorporation ratio,and first increases and then decreases with the increase of lime incorporation ratio.It shows that both lime and nano-silica can reduce the plasticity of loess and improve the engineering properties of loess,but the effect of lime on reducing the plasticity of loess is not as significant as that of nano-silica.(2)Direct shear tests were carried out on loess after adding different single improved materials,and the influence of moisture content,mixing ratio,pressure,number of dry,curing age and wet cycles on the shear strength index and stress-strain curve of loess was studied for different materials.The test results show that different materials can improve the shear strength of loess,and according to the test results,the best mixing ratio when different materials are mixed into loess alone is obtained.(3)Using cohesive force and internal friction angle as evaluation indicators,orthogonal tests were performed on lime-polypropylene fiber,nano-silica-polypropylene fiber composite modified loess,to determine the best mix ratio,and analyze different materials and moisture content Influence on the shear strength index of improved loess.Considering multiple factors,the best mix ratios of lime-polypropylene fiber and nano-silica-polypropylene fiber composite modified loess are: moisture content 13%,lime 9%,polypropylene fiber 0.6%;moisture content 13 %,nano silica 2%,polypropylene fiber 0.6%.(4)The disintegration test was carried out on loess after adding different single improved materials.The test results showed that the addition of lime and nano-silica alone prolongs the initial disintegration stage,but the final disintegration is 100%.Separate addition of polypropylene fibers and different mixing ratios after guar gum,the average disintegration rate and final disintegration rate of loess decreased significantly,and the disintegration resistance was significantly enhanced.The disintegration test of lime-polypropylene fiber,nano-silica-polypropylene fiber composite improved loess was carried out.The test results showed that the effect of composite improved loess with multiple materials was better than that of single material.Multiple materials composite improved When the loess is disintegrating,there is the best blending ratio of polypropylene fiber,which is 0.6%.(5)The water droplet infiltration test was carried out on guar gum modified loess after different drying and wet cycles.The results showed that guar gum can significantly improve the water repellency of loess,reducing the number of large and medium pores,increasing cohesion,and the structure tends to It is dense,and it is difficult for surface water to penetrate.The SEM image reveals the reinforcement mechanism of loess improved by different materials,and analyzes the deep-seated reasons why the shear strength and disintegration resistance of loess improved by a variety of materials are better than that of a single material.(6)Considering the engineering cost,the impact on the brittleness of loess and the impact on the shear strength and disintegration resistance of the loess,it is believed that the respective mixing ratios of lime-polypropylene fiber and nano-silica-polypropylene fiber should be used to improve the loess: Lime 9%,polypropylene fiber 0.6%;nano-silica 2%,polypropylene fiber 0.6%.