Study On Dynamic Mechanical Properties Of Three Typical Geotechnical Material

Driven by the research of earthquake disasters,explosion in the soil,protective engineering,ground-penetrating weapon damage to the ground,and meteorites impacting pit formation on the surface,the research on the dynamic characteristics of geotechnical media under strong dynamic loading conditions is getting deeper and more precise.It has become one of the international research hotspots of geotechnical dynamics to obtain accurate dynamic constitutive relationship of geotechnical media by studying the dynamic characteristics of geotechnical media under strong dynamic load.In this paper,three kinds of typical geotechnical media,such as cohesive loess,non-cohesive sandstone,and granite,are used as research objects.The split Hopkinson pressure bar（SHPB）is used as the main experimental equipment.A series of experimental studies on its dynamic characteristics are carried out.It works as follows:Firstly,in view of the different properties of three typical rock and soil media,the fabrication process of the samples was explored and studied,and a method for making the samples with good internal density and water content uniformity was obtained.The consistency among the samples was good,which ensured the repeatability and consistency of the experimental data.The quasi-static mechanical properties of three samples were tested by the conventional soil mechanics method,and the basic quasi-static mechanical properties of the samples were determined.Secondly,the SHPB device was used to carry out experimental research on the kinetic properties of three media.The incident wave shaping technique was studied by many blow experiments,and the thin rubber sheet was selected as the incident wave shaper to effectively improve the stress uniformity in the sample.The deformation and failure process of loess samples were monitored in real time by using 2D-DIC test technology,and the real-time strain field characteristics of the samples were obtained,which verified the feasibility of the technology in SHPB experiment.Based on MATLAB,an efficient and accurate SHPB data processing software is prepared to provide the dynamic stress-strain relationship of the sample in real time,which can provide a reference for the determination of subsequent test plans and shorten the single experiment period.Based on the measured waveform,the dynamic constitutive relationship of samples under impact load is calculated.The experimental results show that the yield strength of loess under the strain rate of 161～1087s^-1 has no obvious correlation with the strain rate,while the yield strength and strain rate of granite and sandstone under the strain rate of 10～232s^-1 and 29～355s^-1 respectively have obvious effects.Under the corresponding experimental conditions,the energy dissipation per unit volume of loess,granite and sandstone increases nonlinearly with the increase of strain rate.Under the condition of the same strain rate,granite consumes the most energy per unit volume,sandstone takes the second place,and loess the smallest.The relationship between energy dissipation rate and strain rate of three kinds of geotechnical media is quite different.Finally,the dynamic loading process of granite samples is simulated by ANSYS/LS-DYNA software combined with the quasi-static and dynamic mechanical test results,and the model parameters of the combination of JH-2 model and tensile fracture softening model of granite under the test conditions are obtained.At the same time,the research method of the dynamic characteristics of geotechnical media explored in this paper can provide a reference for the subsequent research on the dynamic characteristics of geotechnical media.