Experimental Study On The Critical State Of Sand Considering The Influence Of Particle Characteristics

Flow liquefaction is one of the most catastrophic failure in geotechnical engineering and a classical soil mechanics subject.This paper eliminates the influence of particle shape on test results using crushed glass beads as an analogue sand,and studies particle characteristics,such as particle size,particle size distribution and fines content,and effective confining pressure on mechanical properties of sand,such as stress-strain relationship,susceptibility and degree of flow liquefaction and critical state,through a series of static undrained consolidation triaxial tests.This paper also analyzes the relationship between the state and the mechanical behaviors of sand.The main content and conclusions are as follows:① The uniformly graded clean sand all show nonflow behavior with strain hardening,and the trend of strain hardening gradually weakens as the increase of effective confining pressure σ’3 and decrease of dso.Furthermore,as the increase of dso,the critical state friction angle φ’CS in stress space increases linearly while intercept of critical state line in compression space decreases with the constant slope λ_c.In addition,flow potential index uf and initial state parameter Ψ₀ are introduced to quantify and predict respectively mechanical behavior of clean sand,that is,uf increases with the increase of σ’3 and the decrease of d₅₀.And the larger Ψ₀ is,the weaker strain hardening of clean sand would be.② The well-graded samples exhibited flow behavior or limited flow behavior,and the trend of strain softening increased significantly with the decrease of σ’3 and the increase of Cu.What’s more,instability state stress ratio η_IL and collapsibility index I_c are introduced to quantify susceptibility and degree of flow liquefaction respectively,and instability state parameter ΨIL is used to predict the "reverse behavior" of wellgraded sample.It is pointed out that the larger ΨIL is,the more susceptible to flow liquefaction the sample would be and the more serious flow liquefaction would be.In addition,φ’CS in stress space is not affected by Cu,while the relationship between λ_c and Cu in compression space indicates that the influence of Cu on flow liquefaction could be related to the compressibility.③ Specimens with fines content FC=10% show the same stress-strain response as clean sand because fines are almost filled in void within the grains.However,other sandfines mixtures show "reverse behavior",and their flow liquefaction will increase as the increase of FC.Besides,with the increase of FC,φ’CS in stress space increases gradually and critical state lines in compression space undergoes a obviously downward shift.Therefore,in compression space,equivalent skeleton void ratio e*quantifying fraction of fines in transferring force is introduced to obtain the unified critical state line which is only depended on properties of the host sand.Furthermore,η_IL and I_c are introduced and instability equivalent skeleton state parameter Ψ_IL*is put forward.It is pointed out that the lager Ψ_IL*is,the more serious flow liquefaction would be and the more susceptible to flow liquefaction specimens would be.