Study On Size Effect Of Coral Gravel Triaxial Test

Coral gravel is a special geotechnical material formed by the remains of marine organisms through long-term physical,biological,and chemical actions.It is mainly distributed in tropical and subtropical sea areas.At present,the research on the shear characteristics of coral gravel has achieved phased results,but the test samples are mostly well-graded coral sand,and the impact of coral gravel size effect is often ignored in the research.The uneven particle gradation and irregular shape happen to be the distinguishing characteristics of coral sand gravel from territorial sand.Therefore,the study of the size effect of coral sand gravel has more scientific significance and practical value for the cognition of its shear strength and deformation characteristics.This paper takes coral grit with different particle sizes as the research object,and carries out indoor triaxial compression tests to systematically reveal the particle size effect of coral grit,sample size effect and its influence on mechanical properties.The main content and results of this article are as follows:(1)The basic physical parameters of coral gravel were tested and analyzed,and the results showed that the optimal vibrating time should be controlled within 15-20 minutes when testing coral gravel gradation by particle sieving method;the true density meter based on the principle of gas displacement can be accurate and reliable The specific gravity of high-porosity coral sand gravel is obtained;the minimum dry density of coral gravel decreases with the increase of the particle size,and the maximum dry density appears at a valley value when the particle size is 0.5-2.0 mm,and develops both small and large diameters.Shows an increasing trend.(2)The triaxial consolidation undrained compression test of coral gravel with different relative densities in the four particle size groups of fine sand,medium sand,coarse sand and fine gravel was carried out,and it was found that coral gravel has obvious particle size effect.The fine sand has obvious strain softening phenomenon.As the particle size gradually increases,the stress-strain relationship curve gradually develops from a strain-soft type to a strain-hardened type;the response of pore pressure shows that the dilatancy of coral gravel increases as the particle size increases.The development of the effective stress path curve of coral gravel in the four particle size groups is basically the same.As the particle size increases,the critical state line principal stress ratio M gradually increases,indicating that the position of the critical state line of coral gravel is affected by the particle size effect.Impact.(3)Aiming at the same relative density,a triaxial consolidation undrained compression test of coral gravel with different sample sizes was carried out,revealing the effect and law of coral gravel sample size.The research results show that the stress-strain curve relationship of coral grit specimens of different sizes is similar,and the strain hardening and softening trends do not change with the change of specimen size;the cohesive force of coral grit increases with the increase of specimen size.Gradually decrease,the change range of the internal friction angle is very small;with the increase of the sample diameter,the slope M of the critical state line gradually decreases.(4)Based on the particle size effect and sample size effect of coral grit,this paper gives the cohesion-like force and internal friction angle of coral grit under different relative densities,different particle size scales,and different sample sizes.The value range and effectiveness have been verified by the existing results,which provide an important reference for the rapid study of the basic strength parameters of coral grit with different properties on the project site.