Experimental Study On Effect Of Particle Shape And Non-uniformity Coefficient On The Mechanical Properties Of Sand

Soil strength and deformation are the two most studied aspects in the field of civil engineering.They are widely used and the focus of domestic and foreign scholars.In geotechnical engineering,the macro-mechanical properties(mainly strength and deformation)of natural sands are affected by many factors.Such as confining pressure,stress path,loading mode,saturation and drainage conditions.The influence of sands itself includes strength,particle size,particle size distribution,particle shape and density,etc.In this paper,triaxial consolidation drainage test is used to study the effects of particle shape and gradation(different non-uniformity coefficient)on the mechanical properties of sandy soil.The strength,deformation and dilatancy characteristics of sandy soil are mainly studied.The contents are as follows:(1)In order to study the effect of particle shape on the mechanical properties of sand,angular and rounded glass beads with the same material,particle size and different particle shape were mixed to form five kinds of specimens with different proportions(rounded glass beads content 0%,25%,50%,75%,100%).The particle shape of these mixtures is expressed by the overall regularity(_RO),which varies from 0.844 to 0.971.The experimental results show that under given confining pressure,peak-state deviatoric stress,peak-state axial strain and peak-state friction angle all decrease with the increase of the overall regularity(_RO),and the slope of fitting equation(Bolton's dilatancy equation)between peak-state friction angle and maximum dilation angle(dilatancy coefficient)is not affected by particle shape,while is 0.6.The intercept(critical-state friction angle)is affected by particle shape,that is,the critical-state friction angle decreases with the overall regularity(_RO).(2)The rounded glass beads were replaced with natural sand(Fujian sands)to carry out the test.There were also five different ratios(silicon sands content 0%,25%,50%,75%,100%).The variation of the overall regularity(_RO)between 0.844 and 0.939indicates that the overall regularity of natural sand particles are close to those of rounded glass beads.The results show that under given confining pressure,with the increase of Fujian sands content,peak-state deviatoric stress,peak-state axial strain and peak-state friction angle all decrease;the dilatancy coefficient is not affected by Fujian sands content,which is 0.6.The intercept(critical-state friction angle)is affected by Fujian sands content,that is,the critical-state friction angle decreases with silicon sands.(3)In order to study the effect of coefficient of uniformity on the mechanical properties of sandy soil,four different coefficient of uniformity(2.0,4.9,9.8,20.6)were tested with angular glass beads.The experimental results show that under given confining pressure,the increase of coefficient of uniformity(_uC)will lead to the increase of friction angle at peak state,while the decrease of excess friction angle(the difference between pick-state friction angular and critical-state friction angular)and maximum dilation angle;the dilatancy coefficient is not affected by coefficient of uniformity,while its intercept(critical-state friction angle)is affected by coefficient of uniformity.The critical-state friction angle increases with the coefficient of uniformity.