Static Characteristics And Particle Breaking Characteristics Of Red Sandstone Coarse-grained Soil

Coarse-grained soil is often used as roadbed filler.Under the effect of vehicle load and subgrade confining pressure,coarse-grained soil is prone to particle breakage.However,the particle crushing has an important impact on the strength and deformation characteristics of coarse-grained soil,which greatly affects the safety and stability of the roadbed and pavement.In this paper,the red sandstone coarse-grained soil in Xiangtan area of Hunan Province is taken as theresearch object,and a large static triaxial shear test is performed on it to study its static characteristics and degree of particle fragmentation under different conditions.Evaluation of long-term stability and disease control have important theoretical research and guiding significance.The main research contests and conclusions of this article are as follows:(1)The basic physical properties of coarse-grained red sandstone soil were studied.Carried out SEM,EDS,XRD test and compaction test.Then through energy spectrum analysis and other methods,it were analyzed that the microstructure and pore fissures,element content and mineral composition,water content and maximum dry density of red sandstone coarse-grained soil.The results show that the cracks of coarse-grained red sandstone soil are more developed,with more pores and most of the structural forms are flaky.Red sandstone coarse-grained soil contains seven major element such as O,Mg,Al,Si,K,Ca,and Fe.The main mineral components are quartz,feldapar,calcite,mica,kaolinite,chlorite,illite,etc.The red sandstone coarse-grained soil was dried and measured to have a moisture content of12.86%;the maximum dry density of the red sandstone coarse-grained soil was about2.0g/cm~3.The maximum dry density basically shows the law of increasing with the increasing with the increase of coarse particle content in the gradation.(2)The static characteristics of red sandstone coarse-grained soil were studied.It was conducted that 20 large-scale static triaxial shear tests,and obtained the stress-strain relationship curves of red sandstone coarse-grained soil under different gradations,confining pressures and compaction degrees,and analyzed the strength and deformation characteristics of the triaxial test.It is obtained that the stress-strain relationship curve shows obvious nonlinear relationship,and the shear strength increases with the increase of confining pressure.The gradation with less coarse particle content showed a tendency to transform from low confining pressure strain softening to high confining pressure strain hardening,and the gradation with more coarse particle content showed obvious strain hardening characteristics with increasing confining pressure.Under the low confining pressure,the coarse-grained soil showed a trend that the shear strength increases with the increase of coarse-grained content,while at high confining pressure,when the coarse-grain content is large,the increase of the coarse-grained soil affects the shear strength smaller.When the gradation and confining pressure are the same,as the compaction degree increase,the shear strength gradually increase.The increase of confining pressure and compaction degree strengthens the inlay and bite effect betwwen coarse particles,which increases the interaction force between particles,and the peak shear strength increases accordingly.The moire strength envelope of red sandstone coarse-grained soil is nonlinear,the particles are closely meshed with each other,showing a certain cohesive force.The function expression of the envelope is obtained by fitting,and the expression of the internal friction angle is obtained by derivation.The internal friction angle decreases as the confining pressure increases.Particle breakage is the main reason leading to the redution of internal friction angle.(3)Study on the particle breakage of red sandstone coarse-grained soil after triaxial test.Particle crushing mainly occurs on the surface of coarse particles.Through particle-to-point contact,particle crushing occurs under the action of friction to generate more fine particles.The content of coarse particles is reduced and the content of fine particle is increased.The fractal dimension D is used as a measure of particle fragmentation.The fractal dimension D decreases as the content of coarse particle increases.With the increase of confining pressure,the content of fine particles increase,the fractal dimension gradually increases,the particle fragmentation tends to increase,and the crushing effect becomes more severse.With the same gradation and confining pressure,the increase of compaction degree gradually increase the fractal dimension D,and particle fragmentation increases with the increase of compaction degree,but the impact of compaction degree on particle crushing is more small.By analyzing the particle breakage in the three processes of the shear test,it is found that the particle breakage during the sample preparation process cannot be ignored.The particle breakage during the shearing process is mainly caused by shear stress.(4)A constitutive of red sandstone coarse-grained soil considering the particle breaking characteristics was established.Based on the Duncan-Zhang constitutive model,the fractal dimension D,a measure of particle breakage,is introduced.The relationship between the dimension D and the confining pressure is a hyperbolic function.The functional formula is substituted into the Duncan-Zhang constitutive model,and a red sandstone coarse-grained soil constitutive model considering particle fragmentation is established,and the verification is based on the triaxial test results.The analysis shows that the colculated theoretical curve agrees well with the axperimental stress curve.Especially for small and medium confinig pressures.Verified the rationality of the correction model.