Large Direct Shear Test Of Granular Materials Based On Acoustic Emission Technology

In the field of civil engineering,sandy soil,gravel and other granular materials are widely used in engineering because of their wide distribution and easy collection.Therefore,the research on granular materials is of great practical significance.At present,the research on granular materials is more about its macro mechanical properties,and less about the interior of materials.For a granular structure,from the macro point of view,it is a whole,but from the micro point of view,its internal particles are independent of each other.Only with a deeper understanding of its internal micro structure,can we better understand the essence of granular materials.Based on the conventional measurement methods of large direct shear test,the monitoring means of acoustic emission technology is added in this paper;Using fractal dimension as the description index of granular fabric characteristics,a series of large direct shear acoustic emission tests of granular materials with different fractal dimensions are carried out.The mechanical properties of granular materials with different fractal dimensions,acoustic emission characteristics in the process of shear failure and SOC behavior in granular materials are studied.The main conclusions are as follows::1)The reliability of the large direct shear equipment is verified by analyzing the mechanical properties of the sample by taking the fractal dimension as the characteristics of particle fabric and measuring the conventional mechanical parameters of the sample;The analysis of stress-strain curve shows that the shear strength increases with the increase of vertical load under the same fractal dimension,and the mechanical indexes with fractal dimension D = 2.52 are the best under the same vertical load;The critical point C at which the stress-strain curve reaches the residual strength is determined with the volume strain of 0.2)Combined with the stress-strain curve,the acoustic emission activity will decrease significantly when the stress-strain curve reaches the critical point C,and this phenomenon appears before the critical point;Taking 100 k Hz as the standard to distinguish the types of energy release between particles,the energy release of non-uniform sand in the shear process mainly comes from the crushing between particles,while the sliding release energy between particles is mainly concentrated in the early stage of shear,and the energy release of uniform sand in the shear process almost comes from the sliding between particles;This shows that compared with traditional mechanical methods,acoustic emission test can monitor the emergence of critical point C,and the particle state inside the sample can be analyzed by acoustic emission means,which reflects the advantages of acoustic emission monitoring means compared with conventional mechanical means.3)SOC studies based on sand pile model mostly determine the amount of sand Self-organization critical characteristics,the characteristics of the SOC inside the sand heap model is studied by acoustic emission means,which increases the physical test means of scatterbody SOC research.The analysis of this test shows that the power law characteristics and long-range correlation of the heterogeneous sand system are strong,showing strong selforganization critical characteristics,but the uniform sand system has no power law characteristics,and from the perspective of time persistence,it is closer to the disordered white noise sequence,indicating that the uniform sand does not present this characteristic.