Laboratory Test And Numerical Simulation Of Pile Sinking Effect Of Jacked Pile Based On Airbag Loading

Jacked pile have the advantages of low environmental pollution and fitting the direction of green geotechnical development,and are widely used in pile foundation projects.The penetration resistance of jacked pile is an important element in the study of the sinking characteristics of jacked pile.This paper adopts the test method of realizing the self-weight of the overlying soil by loading the airbag on the surface of the model box soil.Fiber Bragg Grating(FBG)sensors were installed on the surface of the pile body and full-section pressure sensors were installed at end of the pile.Indoor static pile sinking tests in cohesive soils were conducted to systematically study the force characteristics of pile compression force,pile end resistance,pile stress and pile lateral friction resistance and the radial variation of pore water pressure and earth pressure in the soil around the pile during the penetration of the static pile.Combined with the theories such as pile side frictional resistance degradation effect,the pile side frictional resistance and pile compression force were corrected by fitting the degradation factors,and finally superimposed coupling obtained the static pile sinking characteristics for a pile diameter of 0.1 m and a pile length of 5.1 m.Based on the numerical simulation of the indoor test by CEL method of ABAQUS,the distribution law of pile compression force with penetration depth was compared and analyzed,and the change law of stress field and strain field of soil around the pile was analyzed.The main work and research results of this paper are as follows:(1)The 3-section static pile sinking test shows that: with the increase of penetration depth,the piling force,pile end resistance and pile side friction resistance all gradually increase,and the pile end resistance accounts for 54.78%～57.85% at the end of pile sinking,and the total pile side friction resistance accounts for 42.15～45.22%,and the pile end resistance accounts for the main part of pile sinking resistance;with the increase of depth,the pile shaft force gradually decreases,and the unit pile With the increase of depth,the pile axial force gradually decreases and the unit pile lateral friction resistance gradually increases;at the same depth,with the increase of penetration depth,the pile axial force gradually increases,while the unit lateral friction resistance appears to be a degradation effect.(2)When the pile penetration depth is small,the soil pressure and pore water pressure basically remain unchanged;with the increase of penetration depth,the soil pressure and pore water pressure gradually increase;when the pile end passes the depth of the sensor position,the soil pressure and pore water pressure here reach the maximum;as the penetration depth of the pile continues to increase,the soil pressure and pore water pressure gradually decrease.In the horizontal direction,the variation of soil pressure and pore water pressure shows a decreasing trend with the increase of horizontal distance from the sunken pile position,and the variation curve conforms to the power function curve.(3)Based on the theory of friction fatigue,the degradation coefficients were obtained as 0.736,0.623 and 0.44,respectively;considering that the degradation coefficient k of lateral friction resistance is not only affected by the shear depth(h/D),but also by the depth H of the soil layer at the investigation point,so the relationship equation between the degradation coefficient and the depth of the soil layer was established.the pile lateral friction resistance and pile pressure force obtained by the modified calculation of pile lateral friction resistance degradation coefficient are more reasonable,and it can also be seen that the degradation effect of pile lateral friction resistance is more significant;the pile pressure force during penetration process shows a fluctuating growth trend with the increase of penetration depth,and no obvious critical effect of pile lateral friction resistance is found.(4)The numerical analysis method of coupled Euler-Lagrange(CEL)in ABAQUS software was used to simulate the whole process of jacked pile penetration.The results show that the simulated compressive pile force basically matches the curve trend obtained by considering the degradation effect,and there is an obvious stress concentration in the soil at the pile end during the penetration process,and the radial influence range of the extrusion stress is about 6 times the pile diameter and the vertical influence range is about4 times the pile diameter.The deformation of the soil around the pile is larger and produces obvious shear zone,and the radial strain of the soil around the pile is about 2times the pile diameter,while the radial strain of the soil at the pile end is about 6 times the pile diameter.