Shear Band Failure Test And Deformation Analysis Of Clay And Sand

Many problems in geotechnical engineering can be simplified to plane strain problem,such as sliding failure of foundation,deformation and stability analysis of embankment and foundation pit.Under the condition of plane strain,their failure usually belongs to the progressive failure caused by strain localization.Plane strain test plays an important role in the study of strain localization.It provides a great convenience to study the developing process of strain localization,when digital image measurement is applied to plane strain instrument.Because non-contact measurement of specimen deformation can be realized,and strain field contour could be obtained at any time.In this paper,consolidated undrained strain compression test for clay and consolidated drained plane strain compression test for sand are carried out to analyze influencing factors of strain localization by using a new type of plane strain apparatus.The influence of over-consolidation ratio(the ratio of consolidation pressure and shear confining pressure)on the strain localization is studied for clay,while the effect of relative density and shear confining pressure on it is discussed in sand.Through the analysis of the experimental phenomena and experimental data,it is found that the stress-strain relationship of the specimen is closely related to the density of the specimen and the shear pressure of the test.The larger the two,the more likely the specimen is to show the strain softening phenomenon.The two rows of the upper and lower ends of the specimen are obviously affected by the end constraint,so the the data of four lines should be removed when data processed;Based on the curves of lateral strain and vertica strain,the starting point and fully formed of strain localization was determined in the development of strain localization.The stress-strain relationships for points in and out-of-band and specimen overall are consistent,but the strain in the shear band is obviously greater.The failure process of the specimen is progressive,specimen in the test experienced the process of the initial deformation,the initial of strain localization,the deviatoric stress peak,the strain formed localization,the residual stress.And the failure pattern for clay is mainly presented with the "X" cross-type and the clay sample is prone to cracking at the intesection of the two shear band.The shear band for sand is mainly presented with the single type.The angle and the width of the shear band are measured,and the measured angle is compared with the three theoretical predictions.The theoretical inclination of the shear band for clay is less than the measured value.The inclination of shear band for the grained sand is between the Roscoe and Mohr-Columb theoretical predictions.The inclination of the shear band for coarse grain sand is the closest to Roscoe's theory It is found that the width of the shear band is related to the confining pressure.The development of pore water pressure is related to the overconsolidation ratio.In the case of relatively large consolidation,the specimen is prone to dilatancy,and the change of pore water pressure has a great relationship with the formation of shear zone.This provides a useful reference for further study on the mechanism of strain localization and failure behavior of clay soil.In this paper,the strain localization of the soil is discussed superficially,and the shortcomings of the new type of strain apparatus are found need to be further improved.