Influence Of Gravel Content On Maximum Shear Modulus Of Coarse-grained Soils

Soil dynamic characteristics are very important in the design of building foundation,earth rock dam and railway subgrade.Among the parameters representing the dynamic characteristics of soils,the maximum shear modulus plays a significant role in forecasting the deformation and liquefaction of soils.For many years,scholars pay more attention to the study of the maximum shear modulus of fine sand,but for the coarse-grained soils with larger particles,the research is less due to the limitation of test instruments.In this paper,the maximum shear modulus of coarse-grained soil materials from two different earth rockfill dams is studied by using the triaxial loading system and wave velocity testing system of the Institute of Earthquake Engineering of Dalian University of Technology.The specific research content is listed below.(1)In this paper,there are two kinds of materials used in the test,namely gravel soils KLBL and blasted materials RM.The two materials are taken from different areas of the project site,which are representative.The two kinds of materials were screened respectively,and the specific gravity,lithology and particle shape of soil materialof soil materials were analyzed and counted according to the specification.According to the specification,the demarcation particle size of coarse and fine parts was determined,and the gradation and working conditions used in the test were determined,so as to prepare for the subsequent tests.(2)In the process of determining the maximum shear modulus of soils,the accuracy of shear wave velocity test is very important.Firstly,the principles of the three most widely used methods for determining the propagation time of shear wave(first arrival method,peak-peak method and cross-correlation method)are clarified.Then,the wave velocity is obtained by using the three methods to process the test data of Fujian sand.After comparative analysis,it is concluded that the peak value has clear waveform and stable test results under each stage of confining pressure.Compared with the initial point,the peak point is easy to identify,which can reduce the error caused by subjective identification.Compared with the results of other scholars,the accuracy of the peak method is proved.The experimental study on two kinds of test materials was carried out under 8 different gravel contents and 7 different effective confining pressures.The results show that the threshold of gravel content is 80%.Before the threshold,the change of normalized maximum shear modulus is very small.After reaching the threshold,the shear modulus increases rapidly with the increase of gravel content.By analyzing the constants A and n in Hardin’s formula,it is found that when the gravel content is greater than the threshold,there is an exponential relationship between constant a and gravel content,and there is a linear relationship between constant n and gravel content.After introducing the gravel content in the corresponding form,the prediction effect of the maximum shear modulus is significantly improved.