Influence Of Sampling Method And Stress Path On The Shear Behavior Of Saturated Medium Density Fine Sand

Tri-axial test plays an important role in laboratory experiment, it’s a very valuable tool to measure the soil shear strength index and study the constitutive model of soil. But in tri-axial experiments, in the absence of other limiting factors, it was found that the experiment results varies in different stress loading paths and the experiment results was influenced by the sampling methods,these caused great inconvenience to the relevant research. So it’s essential to undertaken the specific study of the influence of sampling methods and stress path on the shear response of sand samples.Firstly, the consolidation drained and un-drained shear tests were conducted on saturated fine sand of 50% relative density prepared by dry-rapping method and wet tamping method under three stress paths of conventional tri-axial compression CTC, constant stress tri-axial compression TC, reduced tri-axial compression RTC. The test results shown that the sampling methods have a great influence on the shear response of sand, under the same stress path test, the peak deviator stress and effective shear strength index of specimens prepared by dry-rapping method are obviously higher than those prepared by moist-tamping method; Stress loading path have a great influence on the shear response of sand, for the samples prepared by the same method, the peak deviator stress in different stress path test is different, ranked as CTC＞TC＞RTC, and the degree of contractive behavior of specimens showed in different stress path test is different, ranked as RTC＞TC＞CTC. During the experiment, we recognized some kind of cross-relation exists between sampling method and stress loading path.Besides, the consolidation un-drained conventional tri-axial compression tests were conducted on medium sand、fine sand and silty sand, the specimens used in the study were prepared by dry-rapping method or moist-tamping method, with the relative density of 50%. The test results shown that sampling method have a significant influence on the shear response of the sands used in the tests, the peak deviator stress and effective shear resistant index of specimens prepared by dry-rapping method are higher than those prepared by moist-tamping method. but the influence of sampling method on the shear response of sands differ by the kind of sand, for medium sand and silty sand, the samples prepared by dry-rapping method behaved contractive shear response, samples prepared by moist-tamping method behaved dilative shear response, for fine sand, the specimens all behaved contractive shear response and the difference between samples prepared by different methods in peak deviator stress is smaller than other sands tested in this paper.In this study we also compared the results of CTC experiment controlled by strain and stress, the results showed that for the samples prepared by moist-tamping method, under strain control condition the specimens behaved strain-softening response but under stress control condition the specimens behaved strain-hardening response, that means in CTC experiment the control condition may have influence on the shear response of sand. During the experiment we also found that under strain controlled experiments the shear rates has almost no influence on the sample’s stress-strain behavior.The sampling method has a great influence on the shear response of sand, it’s necessary to find out the reasons. At the end of this paper, we summarized the previous research and offered some suggestions for finding the reasons.