Experimental Study On Dynamic Modulus And Damping Ratio Of Gravel Under Uniaxial And Biaxial Cyclic Loading

Gravel material is widely distributed in Xinjiang,and it has good compaction,strong water permeability,not easy to liquefy and other excellent engineering characteristics,low mining cost,so it is widely used in the construction of earth rock dam.In the design of earth rock dam,the influence of earthquake and other dynamic loads on the dam body is usually considered,and the dynamic modulus and damping ratio of materials are important parameters to evaluate the seismic performance of the dam body.At present,the research on the static characteristics of sand and gravel has made a lot of achievements,but the research on the dynamic characteristics of sand and gravel under earthquake and other dynamic loads is not perfect,especially the research on the dynamic characteristics of sand and gravel under bidirectional cyclic load is less,and the accurate selection of dynamic parameters is still lack of basic data in the establishment of constitutive model and dynamic response analysis.Therefore,in order to prevent the instability of earth rock dam with gravel material as the main dam material under the action of ground motion load,it is necessary to carry out the experimental research on the dynamic modulus and damping ratio of gravel material.In this paper,through large-scale dynamic triaxial test,the dynamic modulus and damping ratio of gravel under different confining pressure and consolidation ratio are studied,and the differences of dynamic parameters between rockfill and gravel are compared and analyzed.On this basis,the influence of loading ratio（the ratio of dynamic stress amplitude of the later stage to that of the previous stage）on the dynamic modulus and damping ratio of gravel is further studied The influence of bidirectional cyclic load on dynamic modulus and damping ratio of gravel material is studied:（1）Under the same confining pressure and consolidation ratio,the maximum dynamic shear modulus of gravel material is higher than that of rockfill,and the maximum dynamic shear modulus of gravel material under low confining pressure is 13.4%～26.8%higher than that of rockfill.Under the same consolidation ratio,the maximum damping ratio of gravel material is 10%～13%lower than that of rockfill.The test results provide a theoretical basis for the optimal design of the“Silver Wrapped In Gold”structure of Niya reservoir.（2）With the increase of loading ratio,the dynamic strain of gravel material increases obviously under the same dynamic stress,and the maximum damping ratio increases continuously.According to the equivalent linear model,the piecewise fitting method is used to fit the test data ofε_d<0.01%andε_d>0.01%.The fitting degree of the straight line and the test point is greater than 0.96,and the fitting degree is higher.It is more reasonable to use the equivalent linear model to fit the constitutive relationship of gravel material under different test conditions.This method can provide a reference for dynamic triaxial data processing of gravel.（3）When the loading ratio is 1.0,the increase of dynamic stress amplitude is small,the compaction effect is significant,and the dynamic strain produced by lower dynamic stress is greatly affected.When the loading ratio is greater than 1.5,the maximum dynamic shear modulus G_dmaxtends to be stable under high and low confining pressures.When the loading ratio is 2.5,the pore pressure increases with the increase of dynamic strain,which has a great influence on the test results.It is suggested that the loading ratio of dynamic modulus and damping ratio test should be 1.5～2.0.（4）Under the action of bidirectional cyclic dynamic stress,the radial cyclic dynamic stress has a significant effect on the relationship between G_d-g_dand G_d-Vibration times N.The existence of radial cyclic dynamic stress under different confining pressures makes the dynamic shear modulus decrease obviously under the same dynamic shear strain level.With the increase of radial cyclic dynamic stress,the dynamic shear modulus decreases under the same dynamic shear strain.Under the same axial dynamic stress cycle vibration times,the increase of radial dynamic stress amplitude significantly reduces the dynamic shear modulus and shear stiffness of gravel material.（5）The dynamic stress-strain relationship of gravel material under biaxial cyclic loading can still be described by equivalent linear model.With the increase of radial dynamic stress amplitude,the maximum dynamic shear modulus G_dmaxdecreases and the shear stiffness decreases.The damping ratio of gravel material under bidirectional cyclic load is higher than that under unidirectional dynamic load,and the dynamic strain energy consumed by soil increases.