Experimental Study And Numerical Simulation Of Deformation Characteristics Of Shear Bands Of Soil

Progressive failure of soil mass has always been a hot topic in geotechnical engineering.Strain localization is an important form of progressive failure,its main characteristic is that the initial continuous uniform deformation gradually evolves into a rapidly changing,discontinuous,non-uniform deformation with obvious displacement gradient,and this kind of discontinuity often starts from a certain area of the sample.The violent deformation is limited to a nearly parallel narrow belt with a certain width,and finally develops into a strip-shaped region with special properties,which is what we call shear band.In this paper,the consolidation undrained test of over-consolidated clay and unconsolidated drained compression test of sand are carried out respectively by means of plane strain apparatus with digital image measurement system.The digital image measurement technology can obtain the real-time strain field of the sample's surface and the strain information of each corner point which can accurate track the evolution process of the shear band.After analyzing the stress-strain curve of clay and sand,it is found that both soils have softening phenomenon in some degree,the softening effect of clay is mainly affected by pre-consolidation pressure,the softening effect of sand with high relative compactness is more obvious,and sand with different relative compactness has the same residual strength.Clay and sand have similar local deformation characteristics,the deformation at each point of the initial stage is basically coincident.As the axial displacement increases,the strain at each point begins to bifurcate,while the overall strain of the sample is maintained at a low Level,but localization has begun to happen;When the deformation continues to increase,the internal point and the external point show different deformation trends,the strain of the points in the shear band continues to increase,while the deformation of the points outside the shear band remains basically unchanged.In addition,the deformation rate at the inner point of the shear band is always greater than the overall deformation rateAfter analyzing the formation process of the clay's shear band,it is found that the clay's shear bands are all “X” type shear bands.The strain discrimination method for the initial and complete formation time of shear band is proposed.The dilatancy of soil is a unique deformation characteristic of soil.By analyzing the volumetric deformation characteristics in the localized zone,the dilatancy angle inside the soil is constantly changing,as the axial displacement increases,the dilatancy angle gradually increases and finally approaches a fixed value.The dilatancy angle in the shear band is much larger than the overall dilatancy angle.After considering the local dilatancy characteristics of soil,it is found that The Roscoe's Theory can predict the dilatancy angle well.It is believed that the formation of shear band is closely related to the movement of pore water.By analogy with clay,the deformation characteristics of the shear band of sand are analyzed.The shear band of sand is mainly of single type and "X" type.The overall volume deformation under different relative compactness and average particle size is dilatancy.The Arthur's Theory can accurately predict the inclination angle of the shear band with an error of less than 10%.The Cosserat continuum theory is used to simulate the plane strain test.It is found that the value of the dilatancy angle directly affects the deformation mode and equivalent strain field of the model.Using the local dilatancy angle proposed in Chapter 4,the simulated plane strain test can obtain deformation modes and equivalent strain field maps similar to the experimental results.Therefore,the use of local dilatancy angle can improve the accuracy of numerical simulation in localization research.