The Influence Of Sample-preparing Methods On Experiment Results Of Saturated Silt In Different Stress Paths Shear Test

Because theoretical study always needs to be verified and improved by experiment, so laboratory soil test plays an important and irreplaceable role in geotechnical engineering research. Before a test beginning, sample-preparing may affects the result of test greatly. So, the influence of human and any other factors should be controlled. In laboratory static tri-axial test, many kinds of sample-preparing methods are used. Because of the influence of sample-preparing methods, practical operations and three-phase feature of soil, these methods may affect the result of experiment. In daily tests, the influence is always neglected by test personnel.In the test of this paper, some stress-controlled tests of CTC, TC and RTC were carried out on the saturated natural silt sand by using stress-controlled static tri-axial shear apparatus. In order to compare differences form stress path and confining pressure, consolidate Un-drained shear and consolidate drained shear tests were carried out under different confining pressure of 100kPa,200kPa and 300kPa. Before tests begin, sample soil from nature silty sand was prepared to cylinder specimen of height 80mm and diameter 39.1mm. The samples of 50% relative denseness were prepared by using dry-tamping method and wet-tamping method. Then the experiment results of stress-strain relationship, pore water pressure-axial strain relationship, volume strain-axial strain relationship, shear resistance indexes and effective shear resistance indexes were obtained while the influence of sample-preparing methods on experiment results was studied.In the consolidate drained shear tests, the results show that, in three different stress path, the samples of dry-tamping method presentstrainhardeningphenomenon while samples of wet-tamping method present strain softeningphenomenon. The peak values of principal stress difference from dry-tamping method are all higher than wet-tamping method, and the difference between peak values of two methods under CTC is higher than others. The dilatancy of samples under CTC is most obvious, RTC is least and TC is between them. All of internal friction angle calculated from dry-tamping method are bigger than wet-tamping method. The influence of stress path on internal friction angle is much less than sample-preparing methods. In the Un-consolidate drained shear tests, in three different stress path, the samples of dry-tamping method presentstrainand wet-tamping method presentstrain softening-phenomenon while these samples under CTC and TC present flow slidephenomenon and samples under RTC still have some remanent strength. The peak values of principal stress difference under the same confining pressure from dry-tamping method are all higher than wet-tamping method, and the difference between peak values of two methods under CTC is higher than others. Most of pore water pressure from wet-tamping method samples are positive, while because of stronger dilatancy, pore water pressure from dry-tamping method samples increase at first then decreases to negative value. All of effective internal friction angles calculated from dry-tamping method is higherthan wet-tamping method obviously. At the same time, effective internal friction angles from the same sample-preparing method in every stress path are almost same. The influence of sample-preparing methods on experiment results of consolidation Un-drained shear test is not negligible.Furthermore, some other influences were discovered in these tests. In order to improve the saturated degree, back pressure system was used in the tests of this paper. Although back pressure system was failed to use in the tests, the results of tests show that, in TC stress path, back pressure system unproved the saturated degree effectively, which increased from 95% to 98%. The peak values of principal stress difference under the same confining pressure from the samples applied back pressure are all higher than the samples non-applied back pressure. All of samples present weak strain softening. Because of stronger dilatancy, most of pore water pressure from samples increase at first then decreases to negative value until keep stable finally. All of effective internal friction angles calculated from samples under the same confining pressure is almost same. It shows that, there is little influence whether applied back pressure to effective internal friction angles on experiment results of consolidation Un-drained shear test.