Experimental Study On The Maximum Shear Modulus Of Rockfill And Gravel

Rockfill material and gravel material are important filling materials in the construction of large-scale infrastructure such as earth rock dam.The maximum shear modulus of dam material is a very important parameter in the seismic response analysis and seismic safety evaluation of these projects.However,due to the strict requirements of the test equipment and the lack of the engineering data of the actual earth rock dam,the research data about the small strain dynamic characteristics of the dam building materials are rare at present.In this paper,the measured data of six earth rock dams in China are collected,and the test of the maximum shear modulus of rockfill and gravel materials is carried out by using the self-developed medium-sized triaxial shear wave velocity test device.The influencing factors of the maximum shear modulus are analyzed,which is intended to provide reference for the seismic performance discrimination of earth rock dams and the dynamic response analysis of dam materials test basis.The specific research contents are as follows:(1)Six earth rock dam materials in southwest and Northwest China are selected as test materials,which are commonly used rockfill and gravel materials for dam construction in Western China.In this paper,the measured data of the project are collected,the basic characteristics of these dam materials,such as lithology,specific gravity,particle shape,etc.,are statistically sorted out,and their basic characteristics are analyzed,which will provide reference for the research work of dam materials in the future.(2)Using the newly developed medium-sized triaxial shear wave velocity testing device,the shear wave velocity test of rockfill with different excitation frequency is carried out to explore the influence of excitation frequency on the test results of shear wave velocity.The results show that the shear wave velocity of rockfill increases slightly with the increase of excitation frequency,which can be ignored basically.Three methods to determine the propagation time of shear wave(i.e.initial arrival wave method,peak point method and crosscorrelation method)are compared.The results show that the results obtained by the three methods have little difference and the relative error is less than 3%.(3)Using the medium triaxial shear wave velocity testing device,the maximum shear modulus of dam material with different initial void ratio was tested,and the change rule of the maximum shear modulus of rockfill and gravel material was summarized to explore the influencing factors of the maximum shear modulus.The results show that the two most important factors affecting the maximum shear modulus of dam materials are the confining pressure and the void ratio,which increase obviously with the increase of confining pressure and the decrease of void ratio.In addition,the maximum shear modulus is positively related to the average particle size,Fourier shape parameters(profile,edge angle,texture)and the particle proportion,and negatively related to the particle nonuniformity coefficient.(4)Analyze and sort out the test data,extract the maximum shear modulus test results of the dam materials in the literature,and give the maximum shear modulus upper,lower envelope and average value curve of the dam materials based on this test and the data in the literature,so as to provide reference or reference for the dam materials when the test data has not been obtained in the project site.