Experimental Study On Dynamic Behaviour Of Calcareous Sand

Calcareous sand is a special geotechnical medium which composes much carbonate or other insoluble carbonates.It is generated in the marine environment and widely distributed in the South China Sea.Due to the special causes,calcareous sand has obvious different mechanical properties from the general terrestrial sand,and calcareous sand in the marine environment is inevitably affected by wind,waves,currents,earthquakes and other dynamic loads.Therefore,it is necessary to study the dynamic behaviour of calcareous sand in the South China Sea.It has important practical and theoretical value for further improving the mechanical properties of calcareous sand and guiding the actual engineering design and construction of calcareous sea.In this paper,the GCTS dynamic cyclic triaxial shear device and GCTS resonant column device are used to simulate the stress state of marine soil.Static simple shear test,cyclic simple shear test,and resonant column test are carried out on calcareous sand in the South China Sea.The dynamic behaviour of calcareous sand is systematically studied,and the correlation between static and dynamic shear properties of calcareous sand is discussed.The main work and research findings are as follows:1.The dynamic strength of calcareous sand is studied by cyclic simple shear tests under symmetric and asymmetric loading.The effects of relative compactness,initial consolidation pressure,initial shear stress and cyclic shear stress on the dynamic strength of calcareous sand is discussed and give the dynamic strength envelope of calcareous sand in the South China Sea.Meanwhile,the initial shear stress correction coefficient K?is used to measure the influence of the initial shear stress on the dynamic strength of calcareous sand,and compared with the existing K?research results of calcareous sand and quartz sand.2.Static simple shear test results are compared with the cyclic simple shear test results to study the correlation of static and dynamic shear properties of calcareous sand.By comparison,it is found that the variation trend of peak shear stress ratio?/??_v with shear strain in each cycle of cyclic simple shear test is close to that of shear stress ratio?/??_v with shear strain in static simple shear test,all conform to a good hardened quasi-hyperbolic relationship.Moreover,the cyclic stress ratio under different test conditions is on the same curve after being normalized by?_PT/?'_vc,and is not affected by the relative compactness and initial consolidation pressure.3.In order to evaluate the dynamic characteristics of calcareous sand in the offshore sites,resonant column tests are performed on the calcareous sand by GCTS resonant column apparatus.Meanwhile,the effects of consolidation pressure and relative compaction on the dynamic shear modulus and damping ratio are investigated and compared with quartz sand.It is found that calcareous sand showed higher maximum dynamic shear modulus,higher damping ratio,and faster stiffness degradation than its quartz sand under similar states of consolidation pressure and relative compaction.Generally speaking,calcareous sand showed higher G_max than its quartz sand when the shear strain is less than 10^-1%.Finally,a mathematical model of dynamic shear modulus ratio and damping ratio of calcareous sand is established according to the test results in this study.Combining with the existing research results of dynamic shear modulus ratio and damping ratio of calcareous sand,the variation range of dynamic shear modulus ratio and damping ratio of calcareous sand is given,which provides the basis for dynamic stability analysis of buildings in the construction of calcareous sand sites.