| Loess is mostly distributed in the northwest of China,in the northwest arid and semi-arid formation and the influence of the environment,northwest loess has a unique mineral composition and structural characteristics,there are mostly loose texture,large pore vertical structure development,collapsible and other special physical properties.In the construction of high-speed railway projects in the northwest,it is difficult to ensure the stability of the project when the loess is used directly as roadbed fill,and it needs to be improved.Traditional inorganic cementing materials have limited reinforcement effect,high energy consumption,high pollution and other shortcomings,double carbon strategy development will restrict the traditional curing agent solidified loess large area application and promotion.With the rapid development of materials science and organic chemistry,new soil reinforcement materials have been developed that are energy-saving,environmentally friendly,economical and efficient,and easy to construct.This paper discusses the feasibility of F1 new organic ionic curing agent reinforced natural loess(NL)and Bentonite solidified loess(BSL),through a series of physical and mechanical properties of indoor tests,analysis of the physical and mechanical properties of the soil and microscopic pore structure changes before and after reinforcement by F1,determine the best amount of F1 curing agent solidified loess,to provide technical support for the application and promotion of ionic curing agent in improving loess,the main research results are as follows:(1)By means of the bounded moisture content test and compaction test,the law of changes in the basic physical parameters of NL and BSL before and after reinforcement by F1 was studied,and the results showed that:F1 can significantly improve the water holding and compaction characteristics of NL and BSL.With the increase of F1,the plasticity index of solidified NL increases,the maximum dry density increases and then decreases,and the optimum water content decreases and then increases,while the plasticity index of solidified BSL decreases,the maximum dry density increases and then decreases,and the optimum water content decreases and then tends to level off.The dry density of the improved soil reaches its maximum at an F1 dose of 0.3 L/m~3 and the compactness of the soil increases significantly.(2)The compressive strength and CBR bearing strength of NL and BSL before and after the F1 reinforcement were systematically investigated by means of unconfined compressive strength tests and CBR tests,and their variation laws with the amount of F1 admixture.The results show that:The compressive strength and load bearing capacity of NL and BSL can be significantly improved by F1,and the optimum dose is 0.3 L/m~3.with the increase of F1 dose and age,the compressive strength of solidified NL and BSL increases first and then decreases,and the compressive strength of F1 solidified NL and BSL with the optimum dose of 0.3 L/m~3is significantly higher than the other dose and age of cured soil at 14 d and 7 d respectively;Compared with the unsolidified loess,the CBR of solidified NL and BSL increased by 125.12%and 550.42%respectively for 98 times of compaction and 0.3 L/m~3 F1 solidified NL and BSL non-submerged,and 74.34%and 374.61%respectively for submerged.(3)The effect of F1 on the stress-strain characteristics and shear strength of NL and BSL was analysed by triaxial tests,and the results showed that:The shear strength index of NL and BSL increased significantly after F1 reinforcement,and the shear strength was significantly enhanced.With the increase of the surrounding pressure,the shear strength of solidified NL and BSL increased continuously,and the stress-strain curve transformed from soft type to hardened type;compared with the unsolidified loess,the cohesion of 0.3 L/m~3 F1 solidified NL and BSL increased by 1.37 times and 1.55 times respectively,while the angle of internal friction increased by 1.17 times and 1.16 times respectively;the shear strength of F1 solidified NL and BSL reached the maximum at 400 k Pa perimeter pressure and 0.3 L/m~3 F1 admixture,which increased by 1.57 times and 1.36 times respectively compared with the unsolidified loess.(4)The effect of repeated freeze-thaw cycles on the freeze-thaw resistance of F1-solidified NL was analysed by freeze-thaw cycle tests.The results show that F1 can significantly improve the freeze-thaw resistance of NL and improve the mechanical properties and microscopic pore structure of NL under freeze-thaw action.The cohesion and angle of internal friction of NL solidified with F1 at 0.3 L/m~3 are increased to the greatest extent,and the cohesion and angle of internal friction of NL solidified with 15 times of freeze-thawing F1 can still be increased by16.64%and 4.47%respectively compared with that of unfrozen-thawed loess;At 15 freeze-thaw cycles,compared to the loess the small pores of the 0.3 L/m~3 F1 solidified NL were reduced by 17.84%and the pore area ratio and mean fractal dimension were reduced by 20.44%and 0.67%respectively.(5)Based on modern testing methods,the microscopic pore structure and mineral composition of NL and BSL before and after F1 reinforcement were systematically analysed.The results show that F1 effectively reduces the surfaceζ-potential of NL and BSL particles,decreases the thickness of the bound water film,changes the hydrophilic characteristics of the particles to hydrophobic ones,increases the inter-particle attraction,and promotes the coagulation and contact of soil particles through the effects of ion adsorption and exchange,thinning double electric layer,and modification of sulphonated oil,thus forming a more stable laminated structure of F1-solidified NL and F1-solidified BSL.The number of pores and pore area are greatly reduced,the porosity and fractal dimension are significantly reduced,and the particle skeleton and soil compactness are enhanced.Compared with the unsolidified loess,the number of pores of NL and BSL solidified by F1 with 0.3 L/m~3 decreased by 23.70%and 14.29%respectively,and the pore area decreased by 40.11%and 21.91%respectively;the mineral composition of NL remained the same after solidified by F1,but the content ratio changed significantly,the crystalline surface spacing decreased significantly,the intergranular spacing decreased,and the contact was closer. |
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