Experimental Study On Crushing Mechanical Properties Of Calcareous Sand Particles And Optimization Of K-G Constitutive Model

With the proposal of the Belt and Road Initiatives and the demands for national defense in the new era,the construction of the South China Sea has become an important task in China in the next few decades.Calcareous sand,as an important foundation soil in construction in this place,is different from terrestrial sand in that its grains demonstrate highly angular and irregular in shapes and contain intra-pores and is fragile,so it's no longer applicable to develop this place based on the engineering construction experience of terrestrial sand.For this reason,in this paper,a series of isotropic compression test and conventional triaxial consolidation drainage shear test and test under cyclic unloading-reloading conditions are performed for the mechanical properties and crushability of calcareous sand.Based on the results of conventional triaxial tests,an optimized K-G model considering fragility is proposed.The main conclusions are as follows:(1)The results of conventional triaxial consolidation drainage shear tests show that within a certain confining pressure range(100KPa~1100KPa),the stress-strain curve of calcareous sand is similar to that of conventional terrestrial sand,but slight softening will occur under high confining pressure,which is related to particle fragmentation.The greater the confining pressure,the heavier the particles are broken,which causes that volume strain will less likely reach a stable value.(2)Triaxial test results under cyclic unloading-reloading conditions show that this stress path makes the softening characteristics of calcareous sand more pronounced.And the size of the hysteresis loop,the shear modulus,and the volumecontraction under unloading are all related to the level of bias stress when unloading.The size of the hysteresis loop and the volume-contraction under unloading both increase at first and then decrease as the number of unloading times increases,which is because the level of bias stress during unloading increases first and then decreases.(3)From the view of crushability,the degree of fragmentation caused by the isotropic compression test is very limited,which is less than another two kinds of tests.It is mainly that particles with a size of 0.6 to 4.75 mm are broken.,and particles smaller than 0.3 mm are not easily broken.At the same time,the larger the amount of crushing,the greater the change in the grading curve.And this behavior always develops in the direction of particle mass-size self-similar fractal distribution.(4)In the e_c-lnp' semi-logarithmic coordinate system,the critical state lines of calcareous sand with different initial densities caused by fragmentation are three parallel straight lines.A critical state line and dilatancy equation considering fragility are established by assuming a reference critical state line and using the fracture parameter B_g.Finally,the optimized K-G model considering crushability is effective in describing the relationship between stress and strain of calcareous sand.