Study On Vibration Liquefaction Characteristics Of Gravel Sand And Rubber Sand

Seismic sand liquefaction can cause serious secondary disasters such as surface subsidence,surface subsidence and foundation bearing capacity decline.Sandy gravel soil has better liquefaction resistance than pure sand because of its coarse gravel in grain gradation.The mixed soil composed of waste rubber particles and sand particles has the advantages of low dynamic elastic modulus and strong elastic deformation ability,which can play a role of shock absorption and energy dissipation.The dynamic response of gravel soil and rubber-sand mixed soil under earthquake,traffic and other dynamic loads is systematically studied and theoretically analyzed.The effects of various factors on the liquefaction resistance of the two sand soils are discussed.It can not only promote the environmental protection and sustainable treatment of waste rubber,but also seek ways to improve the dynamic characteristics of sand.In this paper,the dynamic characteristics of two kinds of sands under seismic loads are studied by using dynamic triaxial test system,and the numerical simulation of indoor liquefaction test is carried out by using particle flow software.The main conclusions are as follows:(1)The study of liquefaction characteristics of saturated gravel soil based on indoor dynamic triaxial test shows that the amount of gravel has a significant effect on the liquefaction characteristics of gravel soil.The liquefaction resistance of gravel soil increases nonlinearly with the increase of gravel content.The incorporation of fine gravel improves the drainage conditions of the soil,promotes the dissipation of excess pore water pressure,and improves the dynamic strength of the gravel soil.The dynamic shear stress level and the initial stress state of the soil are the key factors determining the dynamic characteristics of the gravel soil.For the gravel soil sample with the same gravel level,the larger the dynamic shear stress value,the faster the dynamic pore pressure rises and dynamic strain develops is.The faster it is.The lower the vibration frequency is the faster the dynamic pore pressure builds up and the smaller the vibrational liquefaction occurs.The two-way cyclic loading test with the same dynamic shear stress ratio of 180 degrees out of phase is compared with the results of the one-way cyclic vibration test.It is found that the gravel soil is more difficult to liquefy under the condition of bidirectional cyclic loading.The dynamic strength of the two-way cyclic test of gravel soil increased by 30% compared with that of the one-way cycle test.However,as the number of failure vibrations increases,the difference of dynamic strength between single and two-way cyclic loading tests decreases.(2)The cyclic shear test under the undrained condition of simulated seismic stress of rubbersand mixed soil by GDS dynamic triaxial apparatus shows that the rubber particle content has significant influence on the liquefaction characteristics of mixed sand,and the liquefaction resistance of mixed soil as the rubber content increases,it continues to decrease.When the rubber particle content is the same,the higher the dynamic shear stress level,the faster the development of the dynamic pore pressure,and the greater the axial strain generated by the mixed soil sample.The incorporation of rubber particles reduces the liquefaction resistance of the sand and reduces the shear stiffness of the mixed sand,but also improves the elastic deformation ability of the soil.The hysteresis curves of the rubber-sand mixed soil under different rubber particle contents are more regular and the double axial strain development is basically symmetrical.The rubber particle size and the ratio of the rubber particles to the particle size of the framework sand have a significant effect on the dynamic properties of the mixed sand.For the same framework sand,the smaller the particle size of the rubber particles,the greater the reduction of the liquefaction resistance of the mixed sand.When the ratio of the particle size of the skeleton sand to the rubber particles is 1,the larger the particle size of the rubber particles,the higher the liquefaction resistance of the mixed sand.Under the same dynamic shear stress ratio,the pore pressure and strain development under single and bidirectional cyclic loading are obviously different,which cannot be regarded as equivalent.(3)The macroscopic and microscopic numerical simulations of the indoor cyclic loading test of gravel and rubber-sand mixed soil were carried out by using the particle flow software.The macroscopic mechanical properties of the numerical test are consistent with the indoor test results.The greater the amount of gravel,the higher the liquefaction resistance of the gravel soil;the rubber particles effectively improve the elastic deformation performance of the sand.with the rubber content is increasing,the peak value of the dynamic bias stress of the mixed sand under the cyclic loading of the equal strain amplitude is decreases.By monitoring the mesoscopic structural changes inside the sample,it is found that the cyclic shear strain gradually destroys the stable sand skeleton structure,triggering the displacement of the sand particles,and the coordination number and porosity of the sample are sheared.The alternating action with dilatancy has a cyclical agitation change,the contact between the particles gradually detaches,and the pore water begins to bear the stress transfer,so that the average coordination number is continuously reduced,and after the sample is liquefied,the bottom value of the coordination number is reduced to zero.The porosity of the samples increases first and then decreases.The porosity increases after initial liquefaction,and the porosity decreases and becomes stable after initial liquefaction.The degree of pore inhomogeneity of the sample increases before the initial liquefaction,and stabilizes at a higher value after the liquefaction is stabilized.The dilatancy and rearrangement of the strong chain in each part of the sample caused by dilatancy and shearing of the sand under undrained cyclic shearing generally reduce the contact force between the particles with the increase of the cyclic vibration.