Study On The Poisson's Ratio Of Quartz Sand

Tri-axial test is one of the most common soil tests,which determines the soil constitute model parameters through the measurement of stress-strain relationship.The application of digital image processing technique for local deformation measurement in tri-axial test leads to much advantages comparing to traditional measuring method.It improves the accuracy of deformation measurement,and provides a new,more reasonable and effective method in specimen deformation measurement.By taking the advantage of digital image processing technique,the stress-strain characteristics and Poisson's ratio of Quartz sand are studied.The Quartz sand is studied through the tri-axial compression tests.Laboratory tri-axial tests are carried out in order to understand the stress-strain relationship in the small strain condition.The laboratory test results show that:(1) the stress-strain relationship of Quartz sand in the a little strain condition is measured as elastoplastic model.The linear part is very small and the axial strain is about 0.3%;(2) the shear modulus of the Quartz sand is very large in the small strain and the shear modulus is getting smaller with the increase of the strain;(3) the axial strain-volume strain relationship of Quartz sand is measured shrinked and the relationship is measured as elastic variation.The Quartz sand is studied through the tri-axial cyclic loading experiment.We get the relation of the axial,radial and volume strain-time.The test results show that:(1)In the first cyclic loading part,the variation is the elastic,the axial and radial variation is rather small and the volume will shrink in unloading.After 5 times cycle,the Quartz sand arrives the balance condition.(2) In the second cyclic loading part,the stress-strain relationship arrives the non-linear part,which is due to the slippage,rotation and crushing.the axial and radial variation is much smaller with the cycle experiment.that is because the variation of the Quartz sand arrives at the stable state.(3) In the third cyclic loading part,the slippage, rotation and crushing is vigorous,the plastic variation is increasing,the time of the stable state will be longer.(4) In the second cyclic loading part without the first part and the third cyclic loading part without the previous two parts experiments,we get the nearly same the variety law though they are different from the loading history.The Poisson's ratio is studied through the tri-axial compression tests and tri-axial cyclic loading experiment.The test results show that:(1) The relationship of the axial-radial strain is curve at the loading beginning and is the linear variation after some time.And the variety law is the same in the different cell pressure.(2)The Poisson's ratio is between 0.3 to 0.5 at the loading beginning.The axial strain is small when the Poisson's ratio arrives at 0.5.(3) For studying the Poisson's ratio,we divide the cyclic loading experiment into 3 periods.The Poisson's ratio is between 0.2 to 0.3 at the loading beginning,as the same as the tri-axial compression test.When the Poisson's ratio arrives at 0.5,the axial strain is very small.The Poisson's ratio of every cycle period keeps stable and the Poisson's ratio value is nearly the same as the value when the stress arrives at the every stress peak.Besides the Poisson's ratio number increase a little in the unloading parts and decrease a little in the loading part.