Experimental Study On Dynamic Shear Modulus And Damping Ratio Of Calcareous Sand In South China Sea

The South China Sea is located at the southernmost point of our territory and is rich in oil,gas and biological resources.At present,the construction of"Belt and Road"in China is in full swing,resource development and island reef construction in the South China Sea urgently,which is also of great strategic significance to the maintenance of Chinese marine territorial integrity.China has built a series of islands and reefs in the South China Sea,and has built military and civil infrastructure,among which calcareous sand is the main filling material for the construction of South China Sea.The dynamic properties of calcareous sand in the South China Sea were studied in depth as an important foundation filling material for various structures on the South China Sea filling islands and reefs has important engineering practical significance.The dynamic shear modulus and damping ratio are the two most important and basic parameters in the study of soil dynamic characteristics,the accuracy and rationality of its value are directly related to the reliability of the ground motion analysis results.In this paper,the influence of confining pressure,relative density,non-uniformity coefficient and average particle size on dynamic shear modulus and damping ratio of calcareous sand were investigated.The empirical formula for the maximum dynamic shear modulus G_max of calcareous sand in South China Sea is established by data analysis and calculation.Finally,the applicability of different viscoelastic dynamic constitutive models to calcareous sand in the South China Sea is analyzed and compared.The recommended values of dynamic shear modulus ratio and damping ratio of calcareous sand in the South China Sea under typical strain values and their upper and lower envelope curves are given.And compare the change range of dynamic shear modulus ratio and damping ratio of different soils.The main conclusions and results are as follows:?1?The dynamic shear modulus G of calcareous sand in the South China Sea increases with the increase of confining pressure,relative density,non-uniformity coefficient and average particle size;as the confining pressure increases,the dynamic shear modulus ratio G/G_max of the sample increases,but the relative density increasing,the dynamic shear modulus ratio G/G_max of the sample instead decreases,and the non-uniformity coefficient and average particle size have nothing to do with the dynamic shear modulus ratio G/G_maxof the sample;the confining pressure increases,the damping ratiolof the sample decreases,while the relative density increases,the damping ratiolof the sample increases,the non-uniformity coefficient and average particle size are independent of the damping ratiolof the sample.?2?No matter under any experimental conditions,the dynamic shear modulus G and the dynamic shear modulus ratio G/G_max of the calcareous sand samples both decrease with the increase of shear strain;the damping ratiolof the specimen increases with the increase of shear strain,but the damping ratio increases faster in the early stage and slower in the later stage,the damping ratio shear strain change critical value is about 5E-5.?3?The maximum dynamic shear modulus of South China Sea calcareous sand G_maxincreases with the increase of confining pressure,non-uniformity coefficient and average particle size increase,decrease as the porosity ratio increases?as the relative density increases?,in which the confining pressure increases to the maximum dynamic shear the modulus G_max has the greatest influence.?4?Using confining pressure,porosity ratio,non-uniformity coefficient and average particle size as variables,the maximum dynamic shear die of calcareous sand in South China Sea was established quantitative G_max empirical formula:???By analyzing the data,the formula has good predictivity for the maximum dynamic shear modulus G_max of calcareous sand in South China Sea,the prediction of the G_max value of other different types of calcareous sand is also universal,and the prediction error is basically not more than 20%,which is within the practical acceptance range of the project.?5?Using the modified H-D dynamic constitutive model to fit the experimental data of the South China Sea calcareous sand resonance column to obtain the recommended values of the dynamic shear modulus ratio and damping ratio of the calcareous sand in the South China Sea under typical strain values and the upper and lower envelope curve ranges.By comparing the variation range of dynamic shear modulus ratio and damping ratio of sand in South China Sea with other different soils,it is found that the dynamic shear modulus of sand in South China Sea G/G_max is slower than gravel,Toyoura sand and other terrestrial sand,the growth rate of calcareous sand damping ratio is lower than gravel,Toyoura sand and other terrestrial sand.