螺旋桩竖向抗拔极限承载力理论计算分析

Theoretical calculation on ultimate bearing capacity of helical piles under tension

在浅埋工况下提出含待定参数N的考虑桩型和土性参数的破坏模型,通过对待定参数求导的方式确定具体破坏面形式,获得竖向抗拔极限承载力;在深埋工况下提出椭球面破坏模型,并基于极限平衡原理对抗拔极限承载力进行求解。同时,开展砂土地基中螺旋桩单桩竖向上拔模型试验。研究结果表明:双锚盘螺旋桩(锚盘间距与直径比s/D=1.36)上层锚盘上方土压力随荷载增大而增大;下层锚盘上方土压力随荷载增大而减小,并在土体达到塑性阶段时趋于平稳。通过与本文模型试验、已有文献试验结果以及已有文献理论计算方法之间的对比分析,验证了本文所建立的理论计算模型的准确性与可靠性。

A failure model with undetermined parameter N considering pile type and soil parameters was proposed under shallow buried condition. The specific failure surface form was determined by the derivative of the parameters to obtain the ultimate vertical uplift bearing capacity;the ellipsoidal failure model was proposed under the deep buried condition, and the ultimate uplift bearing capacity was solved based on the limit equilibrium principle. Besides, the vertical uplift model test of single screw pile in sandy soil foundation was carried out. The results show that the earth pressure above the upper anchor plate of double anchor screw pile(s/D=1.36) increases with the increase of load;the earth pressure above the lower anchor plate decreases with the increase of load, and tends to be stable when the soil reaches the plastic stage. The accuracy and reliability of the theoretical calculation model established in this paper are verified by comparing the test results of the existing literature and the theoretical calculation methods of the existing literature with the model test results of this paper.