A New Method For Testing The Dynamic Shear Modulus Of Soil And Its Application

Dynamic shear modulus and damping ratio are two indispensable parameters for site seismic response analysis.At present,these two parameters are mainly obtained through indoor tests such as common(self)vibration column test and dynamic triaxial test.When testing a soil sample,it is necessary to excite a load with multiple loads from small to large to obtain these two parameters at multiple strain levels to obtain the nonlinear deformation characteristics of the soil.These are the two The traditional test method of the parameter ignores the influence of the previous excitation or stress history on the dynamic deformation characteristics of the soil.In order to reduce the influence of stress history on the soil dynamic characteristics,this paper based on the natural vibration attenuation curve obtained from the soil column self-vibration column test,analyzed the fluctuation characteristics and "non-frequency-guaranteed" characteristics of the curve in detail.Based on this,a new method for testing soil dynamic deformation characteristics was developed.1.Qualitative analysis of the fluctuation characteristics of the soil column natural vibration attenuation curve,and comparing with the ideal vibration attenuation curve,it is found that the fluctuation frequency of the soil column natural vibration attenuation curve does not remain unchanged,that is,"non-frequency guarantee";After quantitatively analyzing the quantitative relationship between the half-period value of the soil column natural vibration attenuation curve and the strain amplitude within the half-period,it is found that as the half-period strain amplitude decreases,the half-period value gradually decreases(or the half-period frequency gradually increases)).Therefore,it is considered that this is the unique "non-frequency-guaranteed" characteristic of soil as a strong nonlinear material.2.Based on the "non-frequency-guaranteed" characteristic,an analysis method of maximum shear modulus is proposed to refine the analysis of traditional test results,and it is found that the traditional test method has the most significant influence on the disturbance of clay,so the refinement of soil dynamic deformation characteristics parameters is established.Test new methods3.A new refined test method was used to test the soil dynamic deformation characteristics of sand,silt and cohesive soil.The test results are in line with the current basic understanding of the changing laws of soil dynamic deformation characteristics,further verifying the rationality of the method;The Boltzman formula with statistical significance is used to fit the change law of soil dynamic characteristic parameters with strain growth,and the rationality of the application of the formula to the description of soil dynamic deformation characteristics is illustrated from the macroscopic level.