Study On Mechanical Properties Of Nano MgO Modified Lime Solidified Loess Roadbed

As a special type of soil,loess has low strength,significant pore characteristics,and is prone to settlement when exposed to water,usually requiring reinforcement to meet the needs of engineering construction.The technique of reinforcing loess with inorganic binding materials such as lime and cement is already quite mature.However,these inorganic binding materials have problems such as high usage,high pollution,and high emissions during production.With the development of engineering construction in the northwest region,how to economically,efficiently,and environmentally reinforce loess has become a new research direction.Nanomaterials,due to their high surface energy and small size,are gradually being applied to the solidification of soil.This article focuses on the research of loess in Lanzhou area,aiming to use nano MgO as an additive to further improve the strength of the soil and reduce the use of inorganic cementitious materials by taking advantage of the characteristics of nanomaterials.The heavy compaction test,unconfined compression strength(UCS)test,California Bearing Ratio(CBR)test and rebound modulus test were used to study the influence of different nano MgO dosages and curing ages on the mechanical properties of lime-stabilized loess modified by nano MgO,and compared it with the mechanical properties of 8% lime-stabilized loess recommended in the 《Highway Subgrade Design and Construction Technical Regulations in Loess Area》(JTG/T D31-05-2017).In addition,the mechanism for strengthening the solidified loess was further analyzed through micro-experiments.The main research content is as follows:(1)According to the results of unconfined compressive strength test,the unconfined compressive strength of different curing proportions of solidified loess gradually increases with age.When the amount of nano MgO is between 0.3% and 0.6%,the unconfined compressive strength of lime-solidified loess modified by nano MgO increases accordingly.Within this range,the growth rate of unconfined compressive strength of the modified solidified loess is rapid,and after exceeding this range,the unconfined compressive strength of solidified loess gradually tends to be stable.Considering economic factors,it is recommended that the optimal range of nano MgO dosage in solidified loess is 0.3% to 0.6%.A prediction model of the unconfined compressive strength of nano MgO solidified loess and the age of maintenance was established through the logarithm function,providing reference for engineering practice.(2)According to the California Bearing Ratio test,the CBR of nano-MgO modified lime stabilized loess gradually increases with the age of the sample.Compared with 8% lime stabilized loess,the enhancement effect of nano-MgO modification on the CBR of stabilized loess is mainly in the early and middle stages,and the CBR gradually stabilizes in the later stage.The CBR of nano-MgO stabilized loess increases first and then decreases with the increase of nano-MgO content(0.3%～1.5%),and the maximum CBR of stabilized loess is achieved when the nano-MgO content reaches 0.4%.After the nano-MgO content reaches 0.8%,the strength development of CBR tends to be stable.The relationship between the CBR and the age of loess stabilized by different ratios can be fitted by Bradley function.By establishing the prediction formula,it provides a reference for the quality inspection of nano-MgO stabilized loess applied in road engineering.(3)From the rebound modulus test,it is shown that the rebound modulus of nano-MgO modified lime stabilized soil with different ratios tends to stabilize when the load level reaches level four.The rebound modulus increases with age,and the increase of rebound modulus of stabilized soil with nano-MgO added in the range of 0.3%-0.6% is more prominent than that in the range of 0.8%-1.5%.Compared with lime stabilized soil with 8% at the same age,the rebound modulus of nano-MgO modified lime stabilized soil can reach the later stage level of lime stabilized soil with 8% in the initial stage.By standardizing and regressing the mechanical index data of CBR and rebound modulus,the relationship between CBR and rebound modulus is established.(4)From scanning electron microscopy(SEM)and energy dispersive X-ray spectroscopy(EDS),it was found that in the early stage of curing of solidified loess,the generated fine flocculent substances are relatively small,the bonding degree between soil particles is low,and there are large pores.With the prolongation of the curing time,in the later stage of curing,the overall structure becomes denser,the pores are significantly reduced,and a large number of needle-shaped and granular structures appear.These generated substances work together to fill the internal pores of the soil and make the soil structure more compact and cohesive.