The Effects Of Sample-preparing Methods On Tri-axial Test Results Of Saturated Medium Sands

Tri-axial test is one of the most important tests in soil tests, having played an important role in the development of soil mechanics. However, the tri-axial test results are affected by many factors; here in this paper, the influences of sample-preparing methods are focused to be studied.Take the saturated natural medium sand and Fujian standard sand for example; after taking the normal tests such as the particle distribution analysis, the specific gravity test and the relative density test, this thesis focuses on the study of influences of three different sample-preparing methods on the tri-axial test results. Influences here are mainly about the influences of stress-strain relationship, the stress path, the shear resistance indexes and Duncan-Zhang Model Parameters. The tri-axial test apparatus in this thesis is strain controlled apparatus, specimen diameter 39.1mm, specimen height 80mm. For natural medium sand, using the dry sampling method and moist sampling method with initial water content of 9%, consolidated un-drained and consolidated drained tests are studied; controlling the initial relative density 30,50, and 70%, the initial surrounding pressures 100,200, and 300kPa; meanwhile, initial water content of moist-sampling method 4,7, and 9% are also studied to find the influences of initial water content to moist-sampling samples'results. For Fujian standard sand, using the dry sampling method and water pluviation method, controlling the initial relative density 50%, the initial surrounding pressures 100,200, and 300kPa, consolidated drained tests are studied. The relative densities of these two sands after consolidating are also studied when initial surrounding pressure is 200kPa. The courses of the influences of different sample preparing method are also studied in the end.According to the study, different sample-preparing methods have apparent influences on the tri-axial test results. Consolidated un-drained and drained tests'study of the natural medium sand shows that, in the same axial strain, all of the dry-sampling samples present a higher stress-strain curve than the moist-sampling samples; correspondingly the pore water pressure curve and the volume change curve are lower than the moist-sampling curves. The failure line of dry sampling method and moist sampling method is the same; but different sampling methods have different failure modes, which need to be noticed. Test results of Fujian standard sand show:in the low surrounding pressure, different sample-preparing methods nearly have no influences to the test results, the test curves of dry-sampling samples and water pluviation samples are nearly coincide; in the high surrounding pressure, the influence is apparent:dry-sampling curve and water pluviation curve are nearly coincide before water pluviation curve reaches to the peach, after that the curve of dry-sampling are higher than the water pluviation curve; both low surrounding pressure and high surrounding pressure curve shapes are similar, that is to say, different sample preparing method does not affect to describe the stress-strain property or the shear shrinking or dilatancy property.The shear resistance strength indexes and Duncan-Zhang Model Parameters in different sample-preparing methods in consolidated drained tests are compared in the end and found: for middle dense sand, it is better to get indexes and parameters through moist-sampling method for saturated natural medium sand; it is better to get indexes and parameters through water pluviation method for saturated Fujian standard sand.