考虑挤土效应的筒型基础沉放阻力数值分析及试验验证

Numerical analysis and test verification of penetration resistance for bucket foundation installation considering effect of soil squeezing

鉴于传统的筒型基础沉放阻力计算公式或数值分析方法均没有考虑筒壁内外侧挤土效应的差异,对于窄深型或是带分舱板的宽浅型筒型基础,由于筒壁或者分舱板的约束作用,基础内侧挤土效应有时远大于外侧,用传统方式计算沉放阻力可能存在较大误差。为揭示筒壁内外侧挤土效应的差异情况,采用显式的任意拉格朗日-欧拉(ALE)方法,针对土体大变形和接触非线性等问题,建立了能够实现筒型基础动态、连续沉放过程的有限元模型,模拟出了筒壁内外侧挤土效应。数值分析结果表明,当入土深度与筒径比达1.6时,筒壁内侧压力可达外侧的10倍左右。通过分析下沉过程中筒壁内外侧土体位移及应力分布,阐述了筒壁内外侧挤土效应差异的机制。最后,提出了考虑挤土效应的筒型基础沉放阻力计算公式,计算与试验结果吻合良好,大大提高了筒型基础沉放阻力的计算可靠性。

In view of the fact that the conventional formula or numerical method of penetration resistance for bucket foundation do not take the soil squeezing effect into account, large errors may occur for some bucket foundations with small diameter or large diameter with bulkheads in it as the restriction effect from the cylinder wall or bulkheads induced higher soil squeezing effect inside the cylinder than outside. In order to reveal the difference of soil squeezing effect between interior and exterior, an arbitrary Lagrangian- Eulerian method is used to simulate the dynamic continuous sinking process for real simulation of the soil squeezing effect during sinking by overcoming the problems which involve large deformation and nonlinear contact. The numerical analysis results show that the earth pressure of the internal cylinder wall is almost 10 times higher than that of the external wall when the ratio of the embedded depth to the diameter is about 1.6. The mechanism of the soil squeezing effect is elucidated by analyzing the soil squeezing displacement and stress distribution. At last, a penetration resistance formula for bucket foundation considering the effect of soil squeezing is proposed which obviously improves the stability of penetration resistance calculation since the calculation results are in good agreement with the test results.