Experimental Study On The Strength And Particle Breakage And Shape Change Of Calcareous Sand

The calcareous sand is widely distributed in the tropical and subtropical islands and reefs and the near-shore seabed.With the development and construction of the South China Sea,it has been used in large quantities in the construction of the South China Sea reef in recent years.During this period,it encountered many problems in engineering construction.The research on the mechanical properties of calcareous sand is extremely urgent.The calcareous sand has characteristics such as fragility,irregular shape,and development of internal pores,and its physical and mechanical characteristics are significantly different from those of terrestrial sand.Particle crushing alters the particle composition and particle shape of the sand and is one of the important factors affecting the mechanical properties of the calcareous sand.Therefore,in this paper,the strength,particle breakage and particle shape of calcareous sand were studied through a series of tests.The single particle tester was used to measure the strength of single particle,Weibull statistics was used to analyze the crushing strength of the particles,and the relationship between the broken shape of the particles and the type of particles breakage was studied.The results showed that different shapes of particles had different crushing forms.In this test,there are three main forms of broken particles.The larger the flatness and roundness are,the smaller the broken particles are;the different Weibull modulus of different particle sizes are different,and the characteristic stress is also different.The particles with an average particle size of1.79 mm,3.63 mm and 8.15 mm correspond to the characteristic stresses ? are 11.23 MPa,7.31 MPa and 4.62 MPa,respectively,indicating that the larger the particle size,the lower the crushing strength and the obvious scale effect.The triaxial tests of calcareous sands with different relative densities and confining pressures were used to study the changes of stress-strain curves and strength compositions of the calcareous sands.The results show that the sliding between the particles marks the stress reaching the limit state,and the particle breakage will hinder to reach the stress.To reach the limit state,under the conditions of this experiment,the relative motion of the particles under low confining pressure is slip,the shear band is formed,and the stress-strain curve is the softening type;the particle crushing under high confining pressure always occurs during the shearing process,making the stress can not reach the limit state,the stress-strain curve is strain-hardening type;thestrength of calcareous sand is mainly affected by the joint action of dilatancy,slip-orientation of particles,and particle breakage.Through particle sieving,Hardin's relative fragmentation rate was introduced to study the influence factors of particle breakage,the relationship between particle breakage and plasticity work,and the influence of particle breakage on strength.The results show that the impact of relative density on particle breakage is less than that of confining pressure.With the increase of confining pressure,the increment of particle crushing gradually decreases until the crushing reaches an upper limit value.At this time,the confining pressure and relative density have little effect on the particle crushing;the relative crushing rate increases nonlinearly with the plastic work and gradually increases;Under low confining pressure,the strength of calcareous sand is mainly provided by dilatancy and bite,and under high confining pressure,the particles are broken severely,so that the body deformation gradually develops from dilatancy to shear shrinkage,and the severer the fracture is,the more serious the shear is,dilatancy disappears and the bite decreases,so that the peak friction angle decreases and the shear strength decreases.The outline images of calcareous sand particles were obtained by optical microscopy.The shape parameters and fractal dimension of the particles were extracted with image processing software.The changes in particle shape before and after the calcareous sand test were analyzed.The results showed that the shape parameters of the particles decrease with the diameter decreases;the fragmentation of the particles has a fractal dimension.