Experimental And Numerical Research On Evaluation Of Strength Of Shallow Very Soft Clay By Spherical Penetrometer

The full flow penetrometer has been widely used to test the strength of soft soils since it was proposed.However,when testing the strength of shallow soils,the soil is not fully flowing around the probe,which reduces the accuracy of the resistance factor and affects the test results.Based on this,this paper proposes a spherical full flow penetrometer that can measure the soil pressure at different positions of the probe.By installing miniature soil pressure sensors at different positions of the spherical probe,laboratory model tests under different soil strengths are carried out to explore the relationship between soil pressure and penetration depth,resistance factor N and soil strength at different positions of the probe.ANSYS CFX15.0software which based on computational fluid dynamics method is used to simulate the penetration process of the spherical probe in the soil.The following conclusions are obtained:(1)The fitting relationship between the penetration resistance of the spherical probe in different soils and different soil strengths by the vane shear test is established.It is found that when the soil strength of kaolin is low,the linear relationship between the two is better,and when the strength is higher,the correlation is more discrete;while the linear relationship between the two in ball clay is always good.And the smaller diameter spherical probe can better reflect the change of soil strength with depth;(2)Through the analysis of the resistance factor calculated based on the strength of the vane shear test,it is found that the resistance factor can basically meet the normal distribution,and the resistance factor decreases first and then becomes stable with the increase of the soil strength,and the relationship between the resistance factor and the strength of the soil is established;(3)The soil pressure sensors at different positions of the probe were used to obtain the change law of soil pressure with soil strength and penetration depth during the penetration process,and the relationship between the growth rate of soil pressure at the equator and soil strength was established.The equation can be used to obtain soil strength quickly in field tests.The relationship between the critical depth at which the full flow mechanism occurs and the normalized strength is obtained by using the soil pressure sensor at 60° off the equator.The relationship between the soil pressure and the resistance factor and penetration depth are established,and the above equation is verified.Which can provide a reference for the value of the resistance factor during the in-situ test.(4)ANSYS CFX15.0 software is used to simulate the penetration process of the spherical probe in the soil.The thin-layer element method is used to simulate the friction effect between the soil and the probe surface.And the sub-domain dynamic grid technology can better prevent grid distortion problems,it can be applied to simulate large deformation problems.(5)The penetration process of the probe with different penetration rates is simulated,and it is found that the penetration resistance increases with the increase of the penetration rate,and compared with the literature,the effect of the rate effect on penetration resistance is quantified.In addition,the influence of the presence of water on the soil surface on the flow of the soil is explored,and it is found that the soil around the probe is easier to flow around the probe when the upper water exists than the upper air.