Study On Physical And Mechanical Properties And Creep Characteristics Of Loess Improved With Rice Husk Ash

Loess,as a wind-deposited sediment widely distributed in China,is the most common natural building foundation and fill material in the Midwest.The unique soil forming process and existence environment make loess with poor engineering characteristics,which leads to geological hazards and engineering problems such as slope slide,roadbed settlement and building foundation sinking.With the continuous promotion of Belt and Road strategy,the construction activities of road traffic,water conservancy and hydropower,bridges and tunnels in Northwest China are rapidly increasing,therefore,it is of practical engineering significance to take effective improvement measures to improve the engineering properties of loess for the prevention and control of geological hazards and engineering construction in loess areas.Due to the limitations of traditional soil stabilizers in terms of production costs and environmental disturbances,scholars have begun to explore other new,more low-carbon and eco-friendly curing agents.Rice husk ash is gradually applied in geotechnical engineering due to its good pozzolanic properties.In order to evaluate the feasibility and applicability of rice husk ash for improving the mechanical properties of loess,a series of indoor geotechnical tests and microscopic testing techniques were conducted to investigate the effects of rice husk ash on the basic physical and mechanical properties,microstructural characteristics and long-term creep properties of loess in detail.Then,within the framework of geotechnical breakage mechanics,the creep breakage mechanism of modified loess is discussed from a microscopic perspective,and a binary medium creep model of modified loess is established based on homogenization theory.Finally,the proposed model is fitted and validated according to the experimental results.The main research contents and conclusions in this paper are as follows:(1)The effects of rice husk ash content on the physical property index and static mechanical properties of modified loess were investigated in detail through indoor tests.The results indicated that the liquid limit,plastic limit,plasticity index,and optimum moisture content of the modified loess increased with increasing rice husk ash admixture.However,the maximum dry density of the modified loess decreased as the admixture increased.The stress-strain curves of the improved loess transformed from strainhardening to strain-softening with the increase of rice husk ash admixture.The mechanical properties of the modified loess were significantly improved,and the compressive strength,shear strength and deformation modulus of the specimens increased with the increase of rice husk ash admixture.(2)The mineral composition,microstructure and pore distribution of the modified loess were analyzed by microscopic testing techniques,and the curing mechanism was discussed based on the experimental results.The study showed that there is no new mineral component generated in the modified loess compared with the plain loess.Due to the cementation and filling effect of rice husk ash,the internal structure of the modified loess is denser and more stable,thus exhibiting superior mechanical properties.The filling effect of rice husk ash is further confirmed by the CT test results,and the average porosity of the modified loess decreases with the increase of rice husk ash admixture,with a minimum value obtained at 9% admixture.(3)The creep properties of the modified loess were analyzed in detail by performing triaxial creep tests.The study showed that the modified loess undergoes attenuation creep at low stress levels and non-attenuation creep at high stress levels.Compared with the plain soil,the higher the dosing of modified loess,the longer the development time of the isokinetic creep phase in the non-attenuation creep curve and the higher the creep rate in the accelerated creep phase.In addition,the effect of rice husk ash admixture on creep deformation was analyzed in focus,and it was found that the initial deformation modulus as well as the long-term strength of the specimens increased with the increase of rice husk ash admixture,showing a positive correlation,and the damage form of the specimens changed from plastic damage to brittle damage.(4)Based on the theory of geotechnical breakage,the creep breakage mechanism of rice husk ash modified loess is discussed,the evolution equation of breakage parameters considering rice husk ash admixture is proposed,the binary medium creep intrinsic structure model of modified loess is derived with the use of the homogenization theory,and the rationality of the model is verified based on the experimental data.The comparison results showed that the developed model can reflect the creep properties of modified loess well.In addition,parameter sensitivity analysis was conducted to discuss the influence law of structural parameters on the model prediction results.