Experimental Study On Dynamic Response Of Remolded Saturated Coral Reef Sand

There are all kinds of coral reef sand and reef limestone in the Nansha Islands,which are very valuable material resources in the tropical ocean.In recent years,China has accelerated the construction of the Nansha Islands Foundation project and using the local coral debris is the only feasible way in construction of the island.Although the South China Sea area is geologically stable and the engineering seismic fortification requirements are relatively low,the dynamic response characteristics of coral reef particles,especially the dynamic characteristics of coarse granular materials,still have a wide range of application background.At the same time,due to less research at home and abroad,it has important guiding significance and academic value to do research on the stability of the foundation under dynamic action.In this paper,the dynamic response of coral reef sands from South China Sea was studied by using the dynamic hollow cylinder apparatus?HCA?and the large-scale dynamic/static triaxial test apparatus,including dynamic strength test,dynamic elastic?or shear?modulus and damping ratio test.the test results showed that:?1?Under cyclic torsional shear stress,the generalized shear strain?_g and circumferential shear strain?_z?of saturated coral sand specimen are strain cumulative effect and cyclic effect respectively.The liquefaction failure behavior has the characteristics of flow failure.With the initial angel of principal stress increasing,the cyclic effect of pore pressure and the cumulative effect of generalized shear strain are both accelerated and the dynamic strength of coral sand decreases obviously.?2?The dynamic stress-dynamic strain relationship of saturated coral sand specimen is suitable for Hardin-Drnevich model,and the dynamic shear modulus decreases with the increase of dynamic shear strain amplitude.The maximum initial dynamic shear modulus is 62.5MPa,and the damping ratio of coral sand increases with the increase of dynamic shear strain amplitude,and its value is distributed between 2%²0%.?3?When the specimen of G3 material is under the action of axial dynamic stress,the axial strain cumulative effect is obvious,the pore pressure is mainly cyclic effect and is obviously lower than the effective confining pressure,which indicates that the coral sand containing coarse grains is not easy to produce liquefaction.The influence of coarse grains on dynamic strength is not obvious,but there is a slight difference in the dynamic strength characteristic curve.?4?The backbone curve of the G3 material accords with the hyperbolic model approximately,the dynamic elastic modulus of the G3-45 skeleton dense structure material is higher than that of the G3-75 suspended dense structure material in the same dynamic stress level,about 30%⁵0%higher.The damping ratio of the two materials tends to be stable to the value of 20%²5%with the increase of dynamic stress amplitude.?5?The two methods proposed in this paper have little influence on the backbone curve and dynamic elastic modulus,but the method with ellipse fitting is relatively better.The original data method is more effective in calculating the damping ratio.