中文摘要：

通过模型试验及颗粒流程序数值模拟，较为系统地从桩端周围土体位移场、应力场、孔隙率变化场等角度，对砂土中桩端阻力随位移发挥的内在机理进行了研究。结果表明：不同密实度砂土扩张影响范围的不同是相同位移下桩端阻力存在差异的原因。在桩端阻力发挥的起始阶段，土体位移以竖向变形及斜向下挤出扩张为主。当桩端阻力呈现极限阻力态势时，土体位移以水平及斜向上扩张滑移为主。通过桩端周围土体位移场、应力场、孔隙变化场的相互印证，揭示了随端阻力的发挥，桩端周围土体的球孔状压密-扩张过程。采用颗粒流程序进行数值模拟研究，模拟结果与模型试验具有良好的一致性。

英文摘要：

Using model tests and numerical simulation by PFC%2D, the mobilization mechanism of toe resistance of piles in sand was studied. The variations of soil displacement, soil stress and void ratio around pile toe with the increase of toe resistance were observed in the model tests. At the same local displacement, compared with that in loose sand, larger toe resistance would be mobilized in dense sand because the influenced soil zones around the pile toe were larger. At the starting of the mobilization of toe resistance, the displacements of the soils around pile toe were vertical and inclined expansion downward. However, the displacements of the soils around pile toe turned to be horizontal and inclined expansion upward in the limit state of toe resistance. R was shown by the soil displacement, the stress field, and the variations of void ratios in the soils around the pile toe that the mobilization of toe resistance was accompanied with the sphere shape expansion of the soils around the pile toe. In the numerical simulation using PFC^2D, the pile and sands were simulated by walls and particles, respectively. The results of numerical simulation were well consistent with those of the model tests.