Experimental Study On Dilatancy Of Sandy Soil Under Dynamic And Static Loads

Sandy soil is one of the most common and representative granular media materials.Its mechanical,physical and engineering properties are more and more concerned by many experts and scholars in China.Investigating the change of shear strength and deformation characteristics of sand under different conditions,and applying the results to practical engineering,will have great significance for the future development of soil mechanics.At present,the problems of shear strength,deformation characteristics,shear dilatancy and energy dissipation in dynamic load tests of sand materials under dynamic and static loads have not been solved.In this paper,the GDS dynamic triaxial test system was used to carry out triaxial tests on sandy soil under different stress paths under dynamic and static loads.Through the comparative analysis of all the test results,the stress-strain;deformation characteristics,strength characteristics,shear expansion characteristics of sand materials under different stress paths,as well as the change law of hysteretic curve and energy dissipation under dynamic load are studied.The main research results are as follows:（1）In the static load test,the sample volume shrinks at first and then volume expands in the isobaric stress path test;in the bias deviatoric test,the strain hardening appears in the early stage of loading,but the softening phenomenon in the later stage is not obvious,which is slightly different from the strain hardening softening phenomenon in the isobaric consolidation test.The peak strength of different stress paths is different in bias consolidation test,which shows that different stress paths will affect the strength of sand.（2）When the initial stress state is the same,the dilatancy of the three stress paths;constant?₃ tests,equal p tests and constant?₁ tests are successively enhanced;the specimen of the conventional triaxial compression test is at the low stress level,while the constant?₃ tests,equal p tests and constant?₁ tests are at the medium stress level.In the strain hardening stage,the shear shrinkage decreases with the increase of confining pressure,while in the strain softening stage,the shear expansion decreases with the increase of confining pressure.In the equal p test,when the confining pressure is lower than 400kPa,the smaller the confining pressure is,the faster the dilatation occurs,the larger the confining pressure,the greater the dilatancy;when the confining pressure reaches 533.3kPa,the volume strain decreases compared with the that for 400kPa,and the dilatancy is smaller.（3）During the dynamic load test,the dynamic pore pressure increases rapidly in the early stage and tends to be stabilized in the later stage.The final dynamic pore pressure is equal to the effective consolidation confining pressure.Under the same confining pressure and dynamic stress condition,the time required for the consolidation test to reach the stable pore pressure state is longer than that of the constant pressure test.When the same dynamic stress is applied,the larger the effective confining pressure,the slower the strain increases,otherwise,the faster the strain increases.The equal pressure paths correspond to shear and expansion failures.The smaller the confining pressure is,the faster the shear expansion occurs,and the larger the confining pressure is,the slower the expansion occurs;When the confining pressure of the bias pressure path is small,shear induced dilatancy occurs,and when the confining pressure is large,shear induced dilatancy occurs first and then shear induced contraction and failure occur.（4）The larger the contour of the hysteresis curve,the greater the viscosity of the soil body,and conversely,the smaller the viscosity of the soil body.The larger the overall tilt angle of the hysteresis curve,the greater the stiffness of the material and the better the elasticity.Conversely,the smaller the stiffness of the material and the worse the elasticity.On the contrary,the smaller the rigidity of the material,the worse the elasticity will be.The more sparse the hysteretic curve,the greater the structural damage of the material,otherwise,the smaller the damage.The area of the hysteresis loop increases with the increase of the applied dynamic stress.On contrary to the change of energy in the shear expansion stage,the energy in the vibration process is continuously dissipated in the shear expansion stage,while the energy in the whole process is continuously increased with the increase of vibration times in the shear expansion stage.