Experimental Study On The Effects Methods Of Preparing Samples On The Deformation And Shear Resistance Characters Of Saturated Nantong Silty Sand

The static triaxial test is an efficient means to obtain shear resistance index anddeformation characters of soil. It is widely used in engineering at present. All the experimentsin laboratory have a step of preparing samples. As for static triaxial test, there are two ways tocarry on the tests. One is using the undisturbed samples, the other is using the disturbedsamples. When using the disturbed samples, different methods of preparing samples couldlead to different internal fabric of soil in the sample, which will induce different mechanicsbehavior of samples.Based on the general test results in grain analysis test, specific gravity test, and relativedensity test of saturated Nantong silty sand, this paper focus on the different methods ofpreparing samples by carrying on the static triaxial tests. The effect of differentsample-preparing methods on the relation of stress and strain, stress path, shear resistanceindexes, steady state, steady state angle of internal friction, and parameters of Duncan-Zhangmodel of saturated Nantong silty sand are investigated in this text. In the mean time, directshear tests of different preparing samples methods are also carried on to compare with theresults of static triaxial test.The static triaxial tests in this text take two kinds of test means which are consolidationundrained triaxial shear tests and consolidation drained triaxial shear tests by using straincontrolling triaxial apparatus. In consolidation undrained triaxial shear tests, the initialconsolidation pressure are 100kPa, 200kPa, and 300kPa separately, while the initialconsolidation pressure is 100kPa in consolidation drained triaxial shear tests. The samplesinclude undisturbed samples and disturbed samples. The disturbed samples are distinguishedinto dry samples method and moist samples method, and dry samples are further distinguishedinto tamping method and vibration method. The initial relative density of disturbed samplesare 20%, 45%, and 70% respectively. The direct shear tests using disturbed samples use slowmodel, and the consolidation pressure are 100kPa, 200kPa, 300kPa, and 400kPa separately.The direct shear tests are distinguished into dry samples method and moist samples method,and the initial relative density are 45%, and 70% respectively. The test results show that there is an obviously influence in static triaxial test results anddirect shear tests of saturated Nantong silty sand resulted from different preparing samplesmethods. In consolidation undrained triaxial shear tests, the stress-strain relation and stresspath of samples prepared by dry samples method both display hardening-part dilative model,while the stress-strain relation and stress path of samples prepared by moist samples methodnot only are different from the results of samples prepared by dry samples method, but alsoeffected by confining pressure and initial relative density. The stress-strain relation and stresspath of samples prepared by moist samples method mostly display total softening-contractive.model. The total shear strength indicesψ_cu and the efficient shear strength indicesψ' obtainedfrom dry samples method both are obviously bigger than that obtained under moist samplesmethod by 10% to 40%. There is no steady state observed in the tests of samples prepared bydry samples method, but the maximum efficient angle of internal friction of the samplesprepared by dry samples method is basically the same to the steady state angle of internalfriction of the samples prepared by moist samples method. Based on the study above, theconcept of similar steady state is put forward in this paper. In consolidation drained triaxialshear tests, the stress-strain relation of samples prepared by dry samples method show thetrend of strain hardening followed by strain softening, while the stress-strain relation ofsamples prepared by moist samples method not only are different from the test results of drysamples method, but also effeted by initial relative density. In direct shear tests, the shearstrength indicesψ_s obtained under dry samples method are bigger than that obtained undermoist samples method by 13% to 15%.