Study On Dynamic Response Of Saturated Sand Based On Energy Dissipation Caused By Particle Entropy Increasing

In order to cope with the growing population size,no matter what underground structures or high-rise buildings,it is inevitable to study the mechanical properties of liquefaction.The liquefaction triggered by strong earthquakes will cause the soil mechanical properties to be greatly weakened,which is shown by the reduced modulus and enhanced flow characteristics.Therefore,liquefaction must be studied.Most of the existing mainstream research methods reveal the liquefaction through the description of the phenomenon combined with other characteristics.The purpose of this paper is to analyze the liquefaction process from energy change based on the thermodynamic theory framework.The PFC particle flow software is introduced to simulate the details of particles in the meso level,and the theoretical framework of particle entropy based on statistical mechanics is proposed.The change characteristics of particle entropy and dissipative energy during liquefaction of saturated sand are analyzed.The main contents are as follow:(1)Based on the thermodynamics,the sand is regarded as a decoupled material.Combined with the differential expression of Helmholtz free energy under isothermal condition,the relationship between locked energy and dissipated energy in liquefaction process are divided by transfer curve.Based on the free field shaking table test of saturated sand,the characteristics of liquefaction of saturated sand and the development characteristics of dissipation energy have been studied.The energy dissipation characteristics and the pore pressure ratio have been analyzed,and the influences of the main shock,aftershock stage,different vibration amplitude and different buried depth(0.45 m and 0.65m)on the test results have been investigated.It is believed that the cumulative dissipated energy is increased by pore pressure ratio.When it comes to aftershock condition,pore pressure ratio is correlated with dissipated energy increment.(2)Based on the dynamic triaxial test,the cumulative dissipation energy development of undrained condition has been further studied.The relationship between dissipation energy and liquefaction characteristics have been studied by accurately controlling confining pressure and cyclic stress ratio.It is believed that compared with the confining pressure condition,the cyclic stress ratio has little effect on the final value of cumulative dissipation energy,but only on the process of the cumulative dissipation energy.When the confining pressure is constant,the final value of cumulative dissipation energy under different conditions tends to be the same.The concept of cumulative energy dissipation ratio has been put forward,and the relationship between the final value of cumulative energy dissipation and pore pressure ratio has been quantitatively described after normalization.(3)A three-dimensional loading program of cyclic liquefaction of saturated sand has been established by PFC software.The macroscopic liquefaction characteristics such as pore pressure ratio,stress and strain,and the development characteristics of dissipation energy have been studied.The relationship between the cumulative dissipation energy and the pore pressure ratio of saturated sand has been studied from thermodynamics.It is considered that cumulative dissipation energy is related to the pore pressure ratio,and both the strain amplitude or the confining pressure condition has an effect on the cumulative dissipation energy in PFC particle flow software,while the confining pressure is the dominant factor.(4)Based on the theory of statistical mechanics and PFC software,the mathematical expression of particle entropy has been defined based on the change of force chain in liquefaction.The force chain and liquefaction process from the microscopic point of view has been studied,and the cumulative dissipated energy modified by the particle entropy has been compared with the cumulative dissipated energy obtained from the linear transfer curve.It is considered that the theory of particle entropy considers the condition of solid-liquid phase change during liquefaction,which can reflect the cumulative dissipation energy of the real situation in a certain extent.