Study On Influence Of Coarse Grain Content On Dynamic Characteristics Of Mixed Sand Soil

Since the 1960s,a series of studies on the dynamic shear modulus and damping ratio of sandy soil have reached a common conclusion,but most of these studies are focused on a single pure sand.However,natural sandy soil is not a single medium,and natural sandy soil contains many coarse grains,which are widely distributed and abundant.Coarse sand is a kind of good engineering material,widely used in engineering construction,in subgrade engineering as the foundation bed filler to deal with weak foundation.In this paper,Marine sandy soil from zhoushan sea area was selected as the mother sand,different coarse grain contents were added as the test object,and three sets of different effective confining pressures were applied by wille resonance column to conduct dynamic test.The following is the research work of this paper:1.The effects of different effective confining pressures and coarse grain contents on the dynamic shear modulus and damping ratio of mixed sand were studied by resonance column test.The relationship between dynamic shear modulus,damping ratio and dynamic shear strain under different influencing factors was obtained,and the influencing mechanism was analyzed.The results show that under the same confining pressure,the dynamic shear modulus of the sample decreases with the increase of shear strain,and the rule of damping ratio is contrary to it.Under the same coarse grain content,the dynamic shear modulus and the maximum dynamic shear modulus of the sample increase with the increase of confining pressure,and the rule of the damping ratio and the maximum damping ratio is opposite.Under the same confining pressure,the dynamic shear modulus and the maximum dynamic shear modulus of the sample increased first and then decreased with the increase of coarse grain content,and reached the peak when the coarse grain content was 70%.The damping ratio and the maximum damping ratio of the sample decreased first and then increased with the increase of the coarse grain content,and reached the minimum value when the coarse grain content was 70%.2.Using Hardin-Drnevich hyperbolic model for this article under the different content of coarse grain effective confining pressure of 21 groups of experimental data fitting analysis,prediction of mixed sand under different content of coarse grain shear modulus and shear strain relation,draw the conclusion:under the same ratio of mixed sand sample,the fitting parameters a,b and reduce with the increase of effective confining pressure;Under the same confining pressure,the fitting parameters a and b first decreased and then increased with the increase of coarse grain content,and the threshold value was 70%.3.The maitin-davidenkov equation,Stokoe equation and hardin-drnevich equation were used to predict the maximum dynamic shear modulus of mixed sand samples with different coarse grain contents and different effective confining pressures,and the results were compared with the maximum dynamic shear modulus of mixed sand samples.It was found that the maitin-davidenkv equation was most suitable for predicting the dynamic parameter model of sand samples in this paper.4.Using maitin-davidenkov model,Stokoe model and hardin-drnevich model to fit and analyze the sample data of normalized dynamic shear modulus and shear strain in this paper,the attenuation law of normalized dynamic shear modulus with shear strain under different boundary conditions is analyzed,and the parameters of fitting test data under different models are obtained.5.The empirical formula of damping ratio proposed by Chen guoxing is used to fit the experimental data of different coarse grain contents and different effective confining pressures in this paper,and the relationship between the damping ratio and the normalized dynamic shear modulus is analyzed.