Study On The Dynamic Characteristics Of Cohesive Soil And The Inherent Laws Of Its Original And Remodeling State

This paper takes the natural sedimentary soil in a new construction project in a Hebei Province as the research object,uses indoor geotechnical tests to determine the basic physical properties of the natural sedimentary soil,and divides the natural sedimentary soil in this area according to the plasticity index;Triaxial compression tests were performed on the original samples of clay and silt and their reshaped samples,and the Duncan-Chang constitutive model was used to obtain nonlinear static parameters;Vibration cycle triaxial tests are performed on natural sedimentary soil layers at different depths,and the relationship curves of dynamic shear modulus,damping ratio and shear strain of soil layers at different depths are obtained.The dynamic shear modulus is normalized,and the relationship curve of G/G_max～γis drawn.In order to explore the inherent laws of the dynamic characteristics of the original specimen and the reshaped specimen,the dynamic parameters of the two are obtained by controlling the same test conditions.Analyze the effect of consolidation method on dynamic parameters and fit the test data points to obtain the inherent law of the original and reshaped specimensThe main research content includes two aspects.On the one hand,the dynamic characteristics of the naturally deposited clay are studied in combination with actual engineering;On the other hand,statistical analysis is used to analyze,fit and determine the internal relationship between the original and reshaped specimens in terms of modulus,dynamic strength and other test data.In order to solve the problem of lack of original samples for testing in engineering practice and scientific research,the dynamic characteristics of reshaped samples are used to find the dynamic characteristics of original samples.The main research contents and conclusions of this paper are as follows:（1）The consolidation and drainage test of the sample found that the stress-strain curve of silt is strain-softening type,and the stress-strain curve of clay and silty clay is strain-hardening type.（2）On the basis of dividing the soil layers of the natural sedimentary soil on the actual engineering site,the dynamic characteristics of the soil layers of different depths are studied.The soil layers of different depths represent the application of different sizes of consolidation confining pressure to the sample.The results of the consolidated undrained test found that the initial dynamic shear modulus of silty clay increased with the increase of the consolidated confining pressure,and the shear modulus decreased with the increase of the dynamic shear strain.When the dynamic shear strain is 2×10^-4,the shear modulus begins to decay sharply;the damping ratio increases with the increase of the dynamic shear strain.When the specimen produces the same shear strain,the greater the consolidation confining pressure,the smaller the damping ratio.（3）In order to explore the inherent laws of the original and reshaped samples in terms of modulus and dynamic strength,this paper also selects samples with similar physical properties to perform dynamic triaxial tests.Different consolidation ratios and different confining pressures were applied to the original and reshaped samples,and the multi-stage cyclic load test and single-stage cyclic load test were performed to obtain the modulus and dynamic strength indexes of the original and reshaped samples.The test results found that the E_dmax and dynamic strength of the undisturbed sample were greater than that of the remolded sample,and the modulus and dynamic strength increased with the increase of consolidation ratio and confining pressure;During the vibration process,the dynamic pore water pressure is directly related to the dynamic strain,and the relationship between the dynamic strain of destruction and the vibration number can be expressed by two types of failure curves,linear and logarithmic.（4）Organize and analyze the dynamic characteristics of the original and remolded specimens,draw the fitting curve of the two,and obtain the fitting formula.It was found that the relationship between the original state and the reshaped specimen in terms of modulus and dynamic strength can be expressed by a linear function.（5）Establish the relationship between the dynamic parameter S_d and the sensitivity S_t,and analyze the influence of the structure on the dynamic strength of the original and reshaped specimens.The test results found that the increase of the consolidation ratio can weaken the influence of the structure on the dynamic strength of the original and reshaped specimens.This paper uses the parameter m to quantify this effect.When the parameter m is larger,the soil structure is stronger.