Research On Mechanical Behavior And Constitutive Model Of Infected Organic Sand

Taking the infected organic sand of a project in Hainan Wenchang as the subject,some routine soil tests were performed to study the basic physical properties.The element,mineral composition and microstructure were analyzed by EDS,SEM and XRD.After summarizing several typical stress paths in project,three kinds of stress paths controlled triaxial tests were carried out under different confining pressures and drainage conditions by using the automatic triaxial tester produced by Geocomp Co.of USA.Then,the paper mainly analyzed the influence of confining pressure,drainage condition and stress path on soil stress-strain relationship,dilatancy law and shear strength parameters.Based on the results of consolidation drained shear tests and Duncan-Chang constitutive model,the constitutive relation of infected organic sand was researched.The main results of this study are as follows:(1)The material used in the tests is fine sand and particle size distributes in a narrow range.It is badly graded sand in engineering.Compared with ordinary sand,the sample has smooth surface and high psephicity.The soil particle has small pore space with some directivity.The content of organic matter in the sample sand is high,and it is adsorbed on the surface of soil particle.The low strength of soil cement mixing pile in this kind of sand is relevant to the organic matter.(2)According to the results of stress path triaxial tests,confining pressure,drainage condition and stress path all have a significant influence on the strength and deformation characteristics of the infected organic sand.? With the same stress path and drainage condition,the stress-strain curves of different confining pressures are similar in shape.And the greater the confining pressure,the higher the shear strength is,and more obvious the dilatancy is.? With the same confining pressure and drainage condition,the law of shear strength are as follows:the highest is increasing p path,followed by constant p path,the weakest is reducing p path;the law of dilatancy are as follows:the strongest is reducing p path,followed by constant p path,the weakest is increasing p path.? With the same confining pressure and stress path,the shear strength of CU is higher than CD test.The stress-strain curves of CU tests are strain hardening and the stress paths turn to the upper right.With the yield surfaces expanding,the yield stress increase.While the stress-strain curves of CD tests are strain softening and the stress paths turn to the lower left.The samples go into plastic flow phase after peak stress.? When the drainage condition and the stress path are different,the effective cohesive strength show evident differences while the effective internal friction angle are relatively close.? The stress and strain relationships of different confining pressures and stress paths were normalized based on p.The normalized results of CU and CD tests are good.The determination coefficients are 0.9931 and 0.9922;both of them are very close to 1.(3)Duncan-Chang model can accurately describe the relationship of stress and strain,but can't be used to simulate dilation of the sand.By modifying the tangent poison ratio,an improved Duncan-Chang model was proposed and the constitutive model parameters were obtained.