侧阻软化对摩擦桩承载特性的影响
Influence of lateral friction degradation on bearing capacity of friction pile

结合现场试验达到破坏的摩擦桩,分析侧阻产生软化的范围及其对侧阻力、桩端阻力和承载力的影响。试验结果表明:临近极限荷载时上部土层侧阻产生软化,极限荷载下硬塑、可塑粉质黏土的侧阻软化段长度分别为4和8 m;硬塑、可塑粉质黏土软化段的侧摩阻力值分别较极值平均小14.98%和22.23%,但侧阻软化段对该层土总的侧摩阻力值影响较小;试桩破坏时桩端阻力未充分发挥,圆砾土桩端阻力的试验值较勘查值和规范值(下限值)分别小10.80%和25.67%,硬塑粉质黏土桩端阻力的试验值较勘查值和规范值分别小22.11%和29.52%。对于侧阻易产生软化的摩擦桩,采用现行规范计算其承载力时桩端阻力应考虑一定的折减。
In combination of failed friction piles in field test, the extent of lateral friction degradation and its influence on lateral friction, pile tip resistance and bearing capacity were analyzed. The results showed the following findings: Lateral friction of upper soil degraded when close to ultimate load, length of lateral friction degradation zone under ultimate load is about 4m in hard plastic silty clay and 8m in plastic silty clay. Lateral friction of hard plastic and plastic silty clay is respectively 14.98% and 22.23% less than extreme value, but lateral friction degradation zone had little influence on the total value of lateral friction of this layer. Pile tip resistance didn’t fully played a role when test pile was broken, the test value of pile tip resistance in round gravel soil is respectively 10.80% and 25.67% less than exploration value and norm value (lower limit), the test value of pile tip resistance in hard plastic silty clay is respectively 22.11% and 29.52% less than exploration value and norm value. For friction piles apt to degrade in lateral friction, the value of pile tip resistance should be reduced when bearing capacity is calculated using existing norm