Study On Mechanical Properties And Structural Characteristics Of Nano-SiO₂ Stabilized Loess

Loess widely distributed in many parts of the world.China owns the largest loess deposit.Due to its special properties and structures during loading and wetting,here has encountered many geotechnical problems,geohazards,and environmental problems,such as landslide,erosion,and settlement in loess.These have caused serious injuries and significant economic losses.In addition,there are a lot of development projects to create land by filling valleys with soils cut from hilltops in the Chinese Loess Plateau.This may aggravate to modify the properties and behaviors of loess,which will lead to more unpredictable geohazards and engineering problems.So,loess is not only common hazard material but also typically problematic soil.Hence,there is a great need to improve loess performance using eco-friendly stabilized methods,then to analyze the changes of stabilized loess properties and its mechanism.It is important to socio-economic value to security and life cycle in loess engineering.It is also curial afford new solution to soil erosion and geohazards in the loess plateau.In this study,the samples were taken from Malan loess in Lanzhou city,Gansu province,and Nano-SiO2 is selected as the stabilized agent.First,the dry nano-SiO2 was added to the dry loess with a weight ratio of 0.0%,0.2%,0.4%,0.8%,1.0%,1.5% and 2.0%.The cylindrical samples were prepared according to the designed water content and dry density.Then the samples with different nano-SiO2 contents were cured for 7,14,28 and 60 days,respectively.First,the unconfined compressive strength test was used to evaluate the sample quality during preparation.Then,the physical properties,unconfined compressive strength compressive and tensile strength of all samples were tested after curing.After that,the samples were tested and analyzed through XRD,SEM,BET,particle size distribution,and disintegration tests.Finally,the improved mechanism of mechanical properties of loess stabilized by nano-SiO2 was analyzed to assess the physical states,mechanical properties,structural stabilities and environmental effects of stabilized loess.This study evaluated their quality to sample similarity,sample uniformity,sample preparation of different researchers.The results found that the unconfined compressive strength test is a rapid and convenient method for sample preparation.The pressing direction of sample preparation and the direction of during loading can influence the consistency of the test results,and the samples prepared by different researchers can change the stress-strain curves.The results from physical and mechanical tests found that nano-SiO2 stabilized loess has lower water content and density with increasing curing days.The void ratio shows a very slight increase,which results in a looser packing.And the physical index shows a small change with the increase of the nano-SiO2 content;The unconfined uniaxial compressive strength,secant modulus,elastic modulus,tensile splitting strength increased with increasing nano-SiO2 content and curing days.However,the loess stabilized by 0.2% of nano-SiO2 content has also obvious improvement in mechanical performance.There is a good correlation between mechanical properties.Nevertheless,there has a low relationship between mechanical properties and physical index.These results show that the physical and mechanical properties of the stabilized loess are more dependent on curing days.The results from structure characteristics showed that there not only has no chemical reaction in the stabilized loess with different nano-SiO2 contents and curing days,but also no new mineral components.The microscopic results showed that the intra-aggregate pore will be filled by nano-SiO2,forming tighter contact and greater aggregate.Consequentially,there has greater inter-aggregate pore.The disintegration tests not only reveal the changes in the macroscopic properties,but also the adjustment of the aggregates and its microstructures.The physical and mechanical properties of stabilized loess can be confirmed by micro-,meso-and macro-structure characteristics.The results from mechanical analysis and performance assessment found that the mechanics includes the loss of water during curing,structure aggregation,and dispersion homogenization.It is key to the modification of physical properties and the improvement of mechanical properties.Compared the traditional water-additive ratio with the ratio of post-curing water content and nano-SiO2 content,the newly parameters: both the ratio of water content after curing and average particle size and the ratio of water content after curing and cumulative pore volume ratio have a better relationship with the mechanical properties of cured loess,indicating a close relationship between the properties and structure of cured loess.The results of performance evaluation show that the mechanical properties and structural stability of cured loess are improved obviously,and there is no noticeable change in the chemical environment effect.Hence,the performance improvement loess treated by nano-SiO2 have the characteristic of physical homogenization and chemical stability in the stabilized mechanism.From the results above,it can be concluded that the mechanical properties and structural characteristics of loess stabilized by nano-SiO2 are mainly the processes of physical modification.There is a close relationship between the macroscopic properties and microstructures,and the mechanical properties and structural stability are significantly improved without chemical activity.Therefore,nano-SiO2 can be used as a potential eco-friendly new material to stabilize loess.