| The liquefaction of sand is one of the main causes of loss of life and property in earthquake.The earthquake loss can be effectively reduced by treating the sand foundation well in advance in the area where liquefaction is easy to occur.However,the traditional soil reinforcement technology often has some defects in practical application.Among them,the compactness method interferes greatly with the surrounding environment,the permeability of cement grouting method is poor,the chemical modification method pollutes the environment,and the microbial community activity is easily affected by the environmental climate.Therefore,it is necessary to develop a new foundation treatment method that can solve the above problems.Colloidal Silica has very low viscosity and excellent material properties,can quickly penetrate the soil,and form the strength of continuous development of the gel foundation reinforcement.This method has the advantages of less disturbance to soil,no pollution and strong engineering adaptability.Based on this,this paper used Colloidal Silica to solidify and modify the fine sand widely distributed in the middle and lower reaches of Liaohe River Basin.Through undrained dynamic triaxial tests,the liquefaction characteristics of pure sand samples and improved sand samples were compared,and the improvement effect of Colloidal Silica on anti-liquefaction property of soil was evaluated.The main conclusions are as follows:(1)Using dynamic pore pressure u_d and dynamic strain?_d as the discriminant criteria of sand liquefaction,the number of cycles required for liquefaction is roughly the same.By comparing the N_f of each sample,it is found that the pure sand samples with D_r=30%and 40%show the characteristics of easy liquefaction when their CSR=about 0.3,while the pure sand samples with D_r=60%show the characteristics of easy liquefaction when their CSR=about 0.4.Based on the survey results of the soil taking point,as long as the CSR is greater than 0.4,the tested sand strata will show the characteristics of easy liquefaction.(2)The relative density D_r and dynamic stress amplitude CSR are the main controlling factors affecting the degree of sand liquefaction,and the relative density plays a decisive role in the development of sand liquefaction.With the continuous development of the relative density D_r of the sample,the dynamic stress intensity CSR required for liquefaction increases gradually with the equivalent dynamic loading times of the same Richter scale.When D_r exceeds a certain threshold,the sand is sufficiently dense and liquefaction is difficult to occur.(3)Colloidal Silica can well limit the pore pressure and strain development of sand.Compared with the pure sand sample,the maximum dynamic pore pressure,total strain and strain amplitude of the improved sand sample with 4%Colloidal Silica concentration are reduced by 96.67%,98.89%and 98.33%respectively after three weeks of curing.(4)The liquefaction resistance,strength and stiffness of the modified sand samples increase with the increase of Colloidal Silica concentration and solidification time.However,when the concentration of Colloidal Silica is high or the curing time is long enough,the growth of various properties of the sample will slow down gradually.After comprehensive analysis,it is considered that three weeks is the best solidification time of Colloidal Silica improved sand,and 4%Colloidal Silica concentration is the best grouting concentration of test fine sand.(5)Under cyclic loading,the stress-strain curve of the pure sand samples develops slowly to both sides in the form of"willow leaf"before and during the middle period of loading,and quickly deviates and deforms in the later period of loading.The stress-strain curve of the sand sample becomes more stable after the improvement of Colloidal Silica.The dynamic response is characterized by the slow translation of the curve in the early loading period and the constant and overlapping of the curve in the middle and late loading period. |
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