Experimental Study On Radial Deformation Characteristics Of Sand And Gravel Under Static And Dynamic Conditions

Sand gravel is the main building material of geotechnical structures such as earth-rock dams.When designing and calculating geotechnical buildings,accurate material parameters play an important role in evaluating the safety of geotechnical buildings.At present,these parameters are generally obtained through triaxial tests,but there are many problems in the traditional triaxial measurement methods(such as the volume change measured by the drainage method cannot exclude the influence of the water reservoir and the membrane penetration),so that the test results have a certain deviation from the actual.In this paper,the self-developed triaxial apparatus with a square cross section is tested,and the axial displacement and radial deformation of the sample are measured by local displacement meter(LDT)to achieve accurate measurement of axial and radial deformation.Base on the apparatus,this paper carried out isostatic consolidation test,monotonic loading test and cyclic loading test for a certain dam sand gravel material(the maximum confining pressure of the test is 800 kPa),which foci on the radial characteristics of sand and gravel under different loading conditions.What's more,the result of the local measurement is compared with the traditional measurement method's.(drainage method to measure the volume change,external displacement sensor to measure the axial strain).The main conclusions are as follows:(1)The results of isostatic consolidation test show that the sample exhibits obvious anisotropy during the isostatic consolidation process.According to the local measurement results,the radial strain of the sample is about 3 times as the axial strain when the confining pressure is less than 250 kPa..When the confining pressure is between 400 kPa and 800 kPa,the radial strain is approximately 1.5 times as the axial strain.As the confining pressure increases,the degree of anisotropy of the sample gradually decreases.Comparing the results of the two measurement methods,the traditional measurement overestimates the axial strain of the sample but underestimate the radial strain of the sample,which can not truly reflect the anisotropic properties of the sand and gravel under isostatic conditions.(2)The results of monotonic shear test show that when the axial strain is less than a certain strain(about 0.5%~1%),the deformation modulus obtained by the traditional method is less than the local measurement's result.When the axial strain is greater than the value,the two kind of deformation modulus obtained by the measurement method are basically the same.In addition,conventional measurements can over estimates the sample volume change and underestimate the radial deformation of the sample.The greater the axial strain is,the greater the difference in radial strain between the two measurements.The parameters K and Kb of the Duncan Zhang E-B model obtained by the local measurement method are 1.32 times and 1.46 times of the traditional measurement results respectively,and the modulus index n,m obtained by the local measurement method is larger than the traditional measurement results.(3)Cyclic loading test results show it's different from the assumed face that Poisson's ratio is constant.When the dynamic axial strain is less than a certain strain(about 0.17%~0.22%),with the dynamic axial strain increasing,the ratio of the dynamic Poisson increases from 0.1 to about 0.45,but when the dynamic axial strain is greater than 0.22% and less than 0.31%(test stop strain),the dynamic Poisson's ratio gradually decreases from the maximum value to about 90% of the dynamic axial strain increases.This is caused by a decrease in the magnitude of the volume change due to cyclic dilatancy.In addition,the dynamic Poisson's ratio obtained by the conventional measurement method is greater than the local measurement result.