不同刺入深度下桩端受力模型试验及数值模拟

Model Test and Numerical Simulation of Pile Tip Resistance Under Different Penetration Depths

通过自行设计的可视化模型试验,采用高清相机、显微数码及图像分析等技术,对纯砂中桩端埋入持力层不同深度的桩端刺入试验进行宏、细观研究.对随桩端刺入深度不同而产生相应的桩端刺入的受力、砂土的位移场和应变场及其细观机理进行分析研究.通过开发三维非圆颗粒,重点对纯砂中桩端刺入的室内试验进行PFC软件三轴数值模拟,将土体细观参数变化与宏观力学响应相联系,揭示桩刺入过程中桩端砂土的宏、细观演化机理.指出端阻力的发挥在细观上主要表现为桩端附近颗粒接触力的变化:桩端下部颗粒的压密范围、桩脚附近土体孔隙率和接触数变化趋势是端阻随埋深而变化的主要因素;达到极限端阻后,承载力的略微增加在细观上主要表现为持力层中桩侧颗粒孔隙率减小、接触力增大.

Macro and micro researches on pile tip penetration burried in different depths of bearing layer in pure sand were carried out by self-designed visual model test with the high-resolution digital imaging devices,the digital microscope visualization and image analysis procedures.The 3D non-circle particle PFC3D numerical simulation method was developed to mainly research the process of pile tip penetration in laboratary model tests in pure sand.The macro and micro variation of soil parameters were related with the macro mechanical response to reveal the mechanism of soil variation aroud pile tip in penetration.Results show that pile tip resistance is closely related to the particle contact force around pile tip in micro side： the compacted area of particles at the bottom of the pile tip,the changing tendency of porosity and coordination number nearby the pile foot mainly decide the possibility of pile tip resistance＇s change corresponding to the buried depths;when the ultimate pile tip resistance is reached,the slightly increase of capacity is caused by reinforcing effect induced by pile tip resistance to frictional resistance of pile surface side,which presents as the decreasing of porosity and increasing of contact force of particles around pile surface side in bearing layer in micro level.