Experimental Research On Deformation Characteristics Of Dilative Sand Under Flow Stress Path

Flow failure in dilative sand slopes or structures with static driving stress were found in past earthquakes and model tests. This flow failure of dilative sand slops or structures is associated water swelling due to seepage of pore water after earthquake.Existing methods of evaluation based on the undrained behavior cannot always provide a realistic prediction to post-liquefaction deformation and strength behavior of saturated sands in practical natural drained conditions. Although this point of view was widely accepted and become a new hot spot in anti-seismic of geotechnical research, there is no important advances was made in the area until now.Elaborate and high quality triaxial compression tests were conducted firstly in this paper to reproduce the mechanical response of saturated sand in constant deviator stress or cyclic loading two kinds of flow stress path. To reveal stress-strain behavior and variation regularity of intensity of saturated sand in two kinds of flow stress path. Conclusions can be summarized as follows:(1)In the static triaxial test under the flow stress path:the stress path of water absorption with shear strain development is deeply affected by the initial density of the material,there is a peak deviator stress in this process. The larger the relative density of the sample, the greater the peak stress value is.(2)In the static triaxial test and dynamic triaxial test:The volume change of water swelling of sample during flow deformation is strongly affected by the dilatancy and initial density of the material. Denser sand should swell more water during flow deformation; the shear strain-volumetric strain relationships of the sample were hardly affected by the initial stress conditions if the initial density of the sample was the same.(3)The shear strain-volumetric strain relationships in the flow deformation of the sample has nothing to do with the two kinds of flow stress path. One is the constant deviator stress but changing of back stress by hand, the other one is cyclic loading.Next, this paper analyses the reason of slopes or structures composed of saturated dilative sand by seepage of water in sand element and dissipation of excess pore water. According to the constitutive mode for description of deformation characteristics of saturated dilative sand, the whole process of the dilative sand slopes or structures flow failure was reproduced by the method of numerical calculation:A period of time after the earthquake, Pore pressure tansfer to the upper part of the slope due to the different permeability.The pore water discharged from the bottom of the slpoe begins to accumulate in thin relative impermeable layer. Lateral displacement increases rapidly.Then flow failure occurred in a one-dimensional layered sand slope overlying with cohesive soil.