The Experimental Research Of The Pleistocene Epoch In The Quaternary Period Undisturbed Loess On The Basis Of A Comprehensive Theory Of The Structure Potential

With the implementation of western development strategy, the loess engineering isoften encountered in the construction project of western region. After investigation andstatistics, the pleistocene epoch in the quaternary period undisturbed loess is alwaysinvolved in loess engineering, but this unsaturated loess is a kind of strong structuralincomplete consolidation and collapsibility soil which leaded to the particularity andcomplexity of building engineering. These problems can be solved only by thedevelopment of loess mechanics theory and engineering technology. Therefore, a seriesof triaxial shear tests and structure study of the pleistocene epoch in the quaternaryperiod undisturbed loess were conducted with special unsaturated soil triaxial apparatusin this paper on the basis of adequate literature research, previous studies in relatedfields, a comprehensive theory of the structure potential and mineral compositionanalysis. The main results are as follows:①it is concluded that the quaternary minerals of the pleistocene epoch in thequaternary period undisturbed loess are mainly composed of quartz and albite throughthe scan of X-ray Diffraction, XRD. a series of laboratory test which is includingphysical properties tests and triaxial shear tests of the pleistocene epoch in thequaternary period undisturbed loess were conducted in order to obtain the physicalproperties and mechanical properties.②The matrix suction changing rule of the pleistocene epoch in the quaternaryperiod undisturbed and remoulded loess with the change of moisture content andconfining pressure is obtained on the basis of triaxial shear tests.it is concluded that thematrix suction of remoulded loess is higher but close to the undisturbed loess on thewhole through the matrix suction comparison between the undisturbed loess andremoulded loess.③The deviator stress changing rule of the pleistocene epoch in the quaternaryperiod undisturbed and remoulded loess with the change of moisture content andconfining pressure is obtained on the basis of triaxial shear tests. The undisturbed loessspecimens experience four stages from loading to failure, namely pressure dense phase,compression stage, micro crack development stage and shear failure stage, and it is ofbrittle failure （weak soft） type under low moisture content and confining pressure.The remoulded loess specimens is of plastic failure （hardening） and has no peak point. The shear strength expression of the pleistocene epoch in the quaternary periodundisturbed and remoulded loess were setted up with the relative strength index （c ’，’， b）which were calculated by mohr-coulomb yielding criteria.④Structural parameterm is proposed on the basis of predecessors’ research resultsand the front testm can reflect the combination impact of spheric stress, deviator stressand matrix suction to soil structural. In addition, the change mechanism of thepleistocene epoch in the quaternary period undisturbed loess and the changing rule ofm are revealed and explained, respectively. On this basis, the relationship betweenstrength parameters and structural parameters of the pleistocene epoch in the quaternaryperiod undisturbed loess is studied by triaxial shear tests.⑤A new constitutive relation expression was resulted when the Stress ratiostructural parameter is introduced into the constitutive model of the pleistocene epochin the quaternary period undisturbed loess（K—G model）,the Stress ratio structuralparametercan reflect the combination impact of spheric stress, deviator stress and matrixsuction to soil structural, the parameters in the expression can reflect the impact ofdifferent test conditions to the pleistocene epoch in the quaternary period undisturbedloess. The new constitutive relation can also describe the stress ratio—Partial straincurves which is soften, and the test results was close to the calculation results under newconstitutive relation. The new constitutive relation is a reliable and simple method.