Shear Strength Characteristic Of Baise Expansive Soil Under The Conditions Of Drying-wetting Cycle And Lower Stress

Shallow failure in expansive soil slope is an inevitable geological disasters under the influence of atmospheric drying-wetting cycle.Probing formation mechanism of shallow failure and trying to obtain the real strength of expansive soils in this boundary conditions had became the research hotspot recently in the engineering.Therefore,the direct shear and triaxial compression test in this paper to study the shear strength characteristic of Baise expansive soil under the conditions of drying-wetting cycle and lower stress were conducted.Firstly,the basic experiment of Baise expansive soil properties has been completed.The technical route was determined by assimilating recent research results.The experimental design considered the influence of drying-weting cycle and lower stress was carried out at the same time.The preparation method of triaxial sample was improved,the self-made saturation tool of triaxial sample was prepared,and it was convenient to conduct triaxial compression test in the Geotechnical Digital Systems.The four groups of consolidated-drained direct shear test were completed,and the shear strength envelope was fitted by the method of specification,double straight line and the generalized power function respectively.Compared with the fitted and measured values,the large difference of the fitted values by the specification and measured values in the low stress was obtained,and the four values in the high stress had no difference.The similar research conclusions was verified,and the comparison basis of analyzing triaxial compression test results was also provided.To delve into expansive soil strength characteristics when the shallow failure occur,the 4 groups of GDS saturated consolidated-drained triaxial test were carried out carefully.The experimental data was analyzed,and it was found that all the stress-strain curves was showed strain hardening model under setting confining pressure.The influence of rubber membrane on strength of expansive soil was corrected.The values of shear strength fitted by the method of the generalized power function and double straight line was also smaller than the values fitted by the method of specification under the low confining pressure and the values of shear strength fitted by the method of specification,double straight line and the generalized power function respectively had small difference under the high confining pressure when the difference between three kinds of values fitted by the method of specification,double straight line and the generalized power function respectively were contrasted,and the test results of GDS saturated consolidated-drained triaxial test was consistent with the consolidated-drained direct shear test.Thus,it was concluded that the expansive soil shear strength envelope under the conditions of drying-wetting cycle and lower stress is generally nonlinear characteristics.Finally,the influence of drying-wetting cycle on the swell-shrink characteristic and cranny property of expansive soil was analyzed,and the relationship between the swell-shrink characteristic,cranny property and shear strength of expansive soil were also discussed.The shear strength parameters of the direct shear and triaxial compression test were compared and analyzed.The strength attenuation characteristics of expansive soil were obtained: the swell-shrink characteristic of expansive soil decreased,the cranny of expansive soil increased and c value of expansive soil significantly decreased,and the shallow failure in expansive soil slope was been taken place with the number of drying-wetting cycle increased.Therefore,to conform to the actual results,the values of shear strength parameters should be obtained in the strength envelope included lower stress fitted by the generalized power function or double line when the shallow stability in expansive soil slope is analyzing.