| Dynamic modulus and damping ratio are the two most important parameters of soil dynamic characteristics which play an important role in site seismic analysis and are also indispensable parameters in engineering design.At present,there were still some shortcomings in the laboratory test methods of dynamic modulus and damping ratio,such as the difference between undisturbed samples had a great influence on the test results,the remolded samples could not fully reflect the characteristics of undisturbed samples,and the influence of various factors on dynamic modulus and damping ratio were not completely clear,as well as the influence on seismic response of soil sites needed to be further studied.Based on the aboves,dynamic triaxial test,theoretical analysis and numerical simulation were used to systematically study the test methods of dynamic modulus and damping ratio of clay and their characteristics,as well as the influence of dynamic modulus and damping ratio on site seismic response.The main work and achievements were as follows:(1)A new testing method was proposed to overcome the shortcomings of existing testing methods,and the experimental results of the new method were compared with those of the conventional method.The results showed that the dynamic modulus and damping ratio under different confining pressures or consolidation ratios can be obtained by gradually increasing the confining pressure or consolidation ratio on a sample,meanwhile,it was necessary to ensure that the maximum principal stress in advance was less than the initial principal stress in later consolidation;the dynamic modulus and damping ratio under different vibration frequencies can be obtained by gradually reducing the vibration frequency on a sample.(2)The effects of confining pressure,consolidation ratio and vibration frequency on dynamic modulus and damping ratio of clay were studied by dynamic triaxial apparatus.The results showed that when confining pressure was in the range of 4001200 kPa,the dynamic modulus increases with the increase of confining pressure while the damping ratio decreased,and the effect on the dynamic modulus decreased gradually;when the consolidation ratio was in the range of 1.02.0,the dynamic modulus increased with the increase of consolidation ratio while the variation of damping ratio was not obvious;when the vibration frequency was in the range of 0.14.0Hz,the dynamic modulus increased with the increase of vibration frequency while the damping ratio decreased with the increase of vibration frequency,the influence of vibration frequency on dynamic modulus was less than confining pressure and consolidation ratio.The hyperbolic model was used to obtain the maximum dynamic modulus and damping ratio of clay,and the power function relationship between the maximum dynamic modulus and confining pressure,consolidation ratio and vibration frequency were established.(3)The normalized parameters of dynamic modulus/maximum dynamic modulus and damping ratio/maximum damping ratio were used to studied the normalized characteristics of dynamic modulus and damping ratio under different confining pressure,consolidation ratio and vibration frequency.The results showed that the dynamic modulus ratio and damping ratio of clay had good normalization properties;the normalized curves obtained by the conventional method and the new method had little difference,the normalized curves of the remolded samples were better than that of the undisturbed samples as a whole,and normalization treatment can effectively realize the comparative analysis of test results under different test conditions.The normalized curves ofEd/Edmax?d and?d/?dma x?d under different test methods,sample types,test conditions were obtained.The results showed that the value of Ed/Edmax+?d/?dm axranges from 1.00 to 1.05 when the dynamic strain in the range of 10-61.Among them,the undisturbed sample tested by new method has the lowest test value,the remolded sample tested by conventional method has the highest test value,and the remolded sample tested by new method in this paper has the middle test value,but the difference between the three is very small,which were all in good agreement with Hardin's empirical formula Ed/Edmax+?d/?dmax=1.(4)The Equivalent-linear Earthquake site Response Analyses(EERA)was used to studied the influence of dynamic modulus ratio and damping ratio on seismic response of single-layer homogeneous clay site.The results showed that the larger the dynamic modulus ratio and damping ratio were,the smaller the characteristic period of response spectrumgT would be,and the degree of reduction would increase with the increase of seismic wave amplitude.When the seismic wave amplitude was 0.1g,the influence of dynamic modulus ratio and damping ratio on peak acceleration of surfaceAmax was small.When the amplitude of seismic wave was 0.2g,the dynamic modulus ratio has greater influence onAmax,the larger the dynamic modulus ratio the smaller the surface peak accelerationAmax was,the damping ratio had less influence onAmax;when the amplitude of seismic wave was 0.3g,the dynamic modulus ratio and damping ratio have greater influence,the larger the dynamic modulus ratio and the damping ratio,the smaller the surface peak accelerationAmax was.The research results have reference value on the soil dynamic test method and certain fatual engineering value. |
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