Damping Characteristics Of Sandstone And Granite Under Triaxial Graded Cyclic Loading

Damping pparameter is an important index seismic design of engineering.Its accuracy isrelated to the rationality of seismic design,and has important significance for safe construction and operation of engineering in this paper,the damping characteristics of sandstone and granite under Triaxial Cyclic loading are stuidied,The main resulte are as follows:(1)Based on the viscous damping thery and the plastic deformation characteristies of rocks,aformal for caleulating the darmping parameters considering the plastic strain energy of rocks isestablished.(2)Development of variable amplitude grded cyclic teiaxial test and constant amplitude graded cyclic triaxial test,amalyzed the energy charaeteristics of dissipated energy.Ud,elastic energy Ud and plastic energy UP of sandstone and granite.The energy dissipation mechanism of sandstone and granite is stydied,and the wariation of three kinds of energy with strain fation,stress ratio.confthing pressure and cycle murnber is revealed.Theresults show that thedissipated energy.clastic and plastic properties of sandstone and granite increase with the inerense of strain ration.stress ration and confining pressure?In the sane,dissipated energy decrease first and then stabilized with the inerease of cycle number,and elastic energy isbasically stable in a certain range,The dissipated energy.elastic and plastic properties inerease with the number of cycles.(3)Damping characteristics of sandstone and granite under different stress ration,strain ration and contining prwssure are studied.The ewolution law of damping ration,damping coeffcient and dynamic elastic modulus with cycle number if revealed,The results show that the damping ration of sandstone and granite decreases first,them stab(?)zed,and theninereases with the(1)increase of stress ratio,strain ratio and cycle number,and increases with the increase of confining pressure.Damping coefficient and dynamic elastic modulus increase with the increase of stress ratio,strain ratio,confining pressure and cycle number.(2)The damping mechanism of sandstone and granite is revealed.Sandstone is cemented by sandy particles and its damping source is friction deformation between particles under cyclic loading.But the granite is formed by the complex physical and chemical interaction of grains.Extrusion deformation between grains and breakage of chemical bonds are the main sources of damping.The difference between the two kinds of rocks leads to the difference of damping characteristics between sandstone and granite.(3)Based on the law of entropy conservation and energy conservation,the evolution models of dissipated energy,elastic energy,plastic energy and damping ratio are established.The results show that the model can well describe the damping behavior and energy characteristics of sandstone and granite under Triaxial Cyclic loading.