Experimental Study On Dynamic Penetration Of Cylindrical Into Granular Materials

In this paper,through the combination of transparent soil and particle image velocimetry(PIV),the internal displacement of the transparent soil and penetration depth of the cylindrical object penetrating into the transparent soil were studied by using the self-designed cylindrical specimen penetration device.Transparent soil is a special kind of soil which is similar to natural soil and uses its internal transparent and visible characteristics to obtain the internal displacement of soil under certain conditions.The transparent soil model used in this paper is composed of a mixture of n-dodecane and 90 # white oil as pore fluid and a certain gradation of fused quartz as skeleton material.Laser line is transformed into laser sector by cylindrical mirror,and speckles are generated in transparent soil by laser sector,which can reflect displacement information of soil particles.The particle image velocimetry(PIV)technique is used to process the high frame rate images captured by high-speed cameras to obtain the displacement nephogram of the interior soil,which can be used to analyze the influence of the diameter,mass,shape of penetration end and velocity of the cylindrical specimen on the displacement in transparent soil.The particle image velocimetry(PIV)is used to process the high frame rate image captured by the highspeed camera to obtain the displacement inside the soil,which can be used to analyze the influence of the diameter,mass,shape of penetration nose and velocity of the cylindrical penetration on the displacement in transparent soil.The research focuses on the moment when the maximum displacement occurs during the penetration process and the soil displacement is stable.It is found that the shape of the nose affects the maximum displacement value and the height of the displacement cross section in the soil.The diameter of specimens has an effect on the maximum displacement of soil.The weight of the penetration affects the area of the cross section of the internal displacement of the soil.The speed of penetration affects the maximum displacement within the soil and the displacement cross-sectional area.When the mass difference is not too large,the influence of various factors on penetration depth is as follows:diameter> shape of penetration nose>mass;When the mass of penetration is doubled,the influence of each factor on penetration depth is as follows: mass> diameter>shape of penetration nose.Soil compactness plays a decisive role in penetration depth,penetration velocity and acceleration at any time during penetration.It is found that a denser core appears in front of the penetration end during the penetration process,and the size of the densifying core is related to the shape of the penetration end.The size of the densifying core is proportional to the resistance of the penetration,and then the densifying core will affect the acceleration,velocity and displacement of the penetration specimen,and finally the penetration depth of the penetration specimen.On the basis of the above research,the dynamic spherical cavity expansion theory of sand material is used to derive the predicted value.It is found that there is little difference between the predicted value and the experimental value,and the error is about 10%.There is a certain relationship between the prediction error and the quality.Under the same diameter and the penetration end,the larger the mass,the smaller the error between the test value and the prediction value.