The Stress-strain Relationship And Strain Softening Characteristic Of Guiyang Red Clay

As a special soil,the Red clay widely distributed in the Yunnan-Guizhou Plateau and the middle west of Guangxi.It has poor physical properties and excellent mechanical property.As a main soil in Guizhou construction,the Red clay is often applied in foundation?water conservancy and slope.Although,there are some achievements on the study of the Red clay,compared with other clay,the achievement in strength and deformation is poor,especially in the strain-softening properties and mechanical properties.In the paper,the Red clay is took from the deep foundation pit of Guiyang Hengfeng centre.The test takes undisturbed clay and remolded clay in different moisture content as research objects.The test methods are unconsolidated-undrained?UU?? consdidated undrained?CU?and consolidation drained?CD?.The deformation and shearing strength characteristics of original Red clay are analyzed by UU?CU?CD tests.Analysis the moisture content effect on the strength and the deformation of Red clay.Then the stress-strain curve?strength and strain characteristics are analysised of undisturbed clay and remolded clay.The stress-strain curve of the original red clay is fitted and the softening characteristics is explored,which is based on consdidated undrained test data and the nonlinear model of Naning Hydraulic Research Institute.At last,perform numerical tests in FLAC3 D,the result can provide a calculation model in the project.The main contents include:1?The physical experiments and indoor triaxial compression test of red clay were carried out,the test include 59%,41%,35.2%,31.5% moisture content of UU,CU,CD test of the undisturbed soil and CU test of remolded soil.According to the experimental results,the stress-strain relationship and the strength-deformation characteristics of the original red clay under three kinds of test conditions were analyzed.The influence of water content on stress-strain relationship,strength index and failure morphology of red clay was analyzed.2?According to the experimental data of consolidated undrained test of the undisturbed and remolded red clay under 41% moisture content,we know that the stress-strain curves,shear strength,stress path,failure morphology,pore water pressure and consolidation displacement are different in the two states.The undisturbed soil has a strain softening characteristic,while the remolded soil has strain hardening characteristics.Besides,the shear strength of the undisturbed soil is greater than that of the remolded soil.The original soil is shear damage,however the remodeling soil is drum-like damage.It is tentatively speculated that the structural differences caused by the stress history and the irreversibility of the dry clay cementation are the causes of the differences in strength and deformation of the two soils.3?The model parameters and the mathematical expression of the stress-strain relation of the original red clay were calculated,which was based on the Consolidated Undrained Test data of the original red clay with 41% moisture content and the nonlinear model of Nanjing Hydraulic Research Institute.According to the mathematical expression,the stress-strain curve of the softening model is plotted.And the model calculation curve has a high consistency with the test curve via comparing and analyzing,which indicates that the model can express the stress-strain curve of Guiyang original red clay characteristic well.4?The FLAC^3D numerical simulation model of the standard cylindrical soil sample was established.The numerical simulation of the three-axis compression of the original red clay was carried out by adding the cohesion and internal friction angle calculated by the nonlinear model of Nanjing Hydraulic Research Institute into the FLAC^3D softening model.And the experiment results show that the stress-strain curve has a high consistency with the experimental curve,which indicates that the nonlinear model of Nanjing Hydraulic Research Institute can accurately reflect the softening characteristics of Guiyang original red clay.