Study On Confined Compressive And Triaxial Shear Behaviors Of Calcareous Sand In Coral Reefs

The calcareous sandis a marine biogenesis medium,which is characterizedbythe high porosity,irregular shape and particle crushing.There are some remarkable differences in the engineering behaviors between calcareous sand and quartz sand.Research findingsshowed that particle crushing affects the engineering behaviors of calcareous sand.At present,studies on particle crushing of calcareous sand aremostly qualitative analysis and less quantitative analysis.Constitutive models with particle crushing are rare.In this thesis,investigations of one-dimensional compression and triaxial shearing behaviors have been conducted on the calcareous sand collected from the Nansha Islands through laboratory tests,and it was analyzed about evolution of particle crushing and its effect on the engineering behaviors of calcareous sands.The research results of this thesisaresummarized as follows:1.The differencesbetween the calcareous sand and quartz sand are compared in one-dimensionalcompression tests.The relationship between the compression index and relative breakage is put forward.Furthermore,the empirical formulation about the relationship between the compression index and the relative density or vertical pressure is also derived.2.The long-term deformation behavior of calcareous sand is studied through one-dimensional creep tests.Test results showed that the percentage of creep of calcareous sand in the total strainranges from 9% to 18%.The relationship betweenthe strain and time increep tests can be expressed by a logarithmic function.3.The shearing behavior is investigated in the drained and consolidated triaxial tests on the calcareous sand.Test results showed that:(1)particle crushing occursat lower confining pressure;(2)particle breakage is closely related to the confining pressure and initial density;(3)at the same time,particle breakagehas effect on the critical state line,and there is a good correlation between breakage index and critical state parameters.4.Based on research results in triaxial tests,a nonlinear elastic model considering particle breakage is developed,and the method for determining the parameters is presented.Model predictions are in agreement with test data.This shows that the model can characterize the trend of stress-strain and volume change of calcareous sand.