Study On The Dynamic And Strain-softening Behaviors Of Kaolin Clays

In recent years,with the increasing demand for offshore oil and gas production,more andmore attention has been paid to the marine geotechnical engineering and its related research.In the present indoor model test research,except for a few items using field sampling soil,most of them use kaolin to simulate submarine soft clay.It has been studied that the clay samples can be obtained by using kaolin powder watering,vacuum stirring,static placing,ballast or centrifugal consolidation and so on.By controlling the ballast weight or centrifugal acceleration,the clay samples with different shear strength distribution can be obtained.The specimen obtained can be used to analyze the interaction between different types of foundation and clay,and the stability of submarine slope.In the literature,many experiences have been accumulated in kaolin consolidation and soil properties in laboratory,however there are still some issues to be improved: a)most studies have focused on the static strength of kaolin samples,but little has been known about the dynamic characteristics(especially the modulus damping and strength softening characteristics of kaolin samples under high frequency loads such as earthquakes);b)the strength and strain softening characteristics of kaolin sample are mostly measured by Cone and T-bar penetration test,little information has been published to compare with traditional test methods such as triaxial compression tests or direct shear tests;c)the testing method of strain softening characteristics of kaolin samples needs to be further improved.Therefore,the following studies have been carried out in this study:(1)Consolidation tests and shear strength tests of kaolin are carried out in this paper.Through the combination of consolidation tests and shear strength tests,the relationship between consolidation pressure and undrained shear strength Su of kaolin clay is summarized.Through the comparison between T-bar and Ball-bar static penetration tests and the unconsolidated undrained triaxial compression tests(UU tests),the correlation between different tests methods is summarized.The consolidated undrained triaxial compression tests(CU tests)of kaolin are also carried out.In the CU tests,the strain softening characteristics of kaolin are analyzed.(2)Experimental tests are carried out to study the dynamic characteristics of kaolin under different confining pressures.The dynamic shear modulus and damping ratio of kaolin clay vs.dynamic shear strain in the range of 10-4~100 are obtained by dynamic triaxial test.Besides,deformation behaviors of kaolin under dynamic load are found.What's more,the dynamic shear modulus and damping ratio of kaolin clay in small shear strain range(10-6~10-4)are obtained by means of the resonance column test.Some data of dynamic shear modulus and damping ratio of soft clay in the literature are summarized.(3)By using the CEL method in the large finite element software ABAQUS,the penetration processes of the spherical sounding instrument(Ball-bar)are numerically simulated.The effect of friction coefficients on the bearing capacity coefficient of Ball-bar isinvestigated.Then,the strain softening model is embedded into ABAQUS by the VUSDFLD in ABAQUS,thus the bearing capacity coefficients of Ball-bar corresponding to different strain softening parameters ?rem,?95 are calculated.Besides,the influence mechanism of strain softening parameters on the bearing capacity coefficient of Ball-bar is analyzed.