基坑开挖对抗拔桩极限承载力影响的模型试验研究

Model tests on ultimate uplift capacity of piles under excavation

采用模型试验的方法研究了砂土地基中基坑开挖对抗拔桩极限承载力的影响,试验过程中考虑了基坑开挖直径、开挖深度及坑底以下有效桩长不同的情况,共进行19组试验。试验结果表明:开挖深度相同时,基坑开挖直径越大,抗拔桩极限承载力下降越多,开挖直径为30 cm(10d)时,抗拔桩极限承载力较开挖前有明显下降,随着开挖直径的继续增加,极限承载力继续下降,但下降幅度逐渐减小,并趋于一个稳定值;开挖深度相同时,坑底以下有效桩长越短,开挖后抗拔桩极限承载力损失比例越大;开挖卸荷后坑内土体处于超固结状态,抗拔桩极限承载力大于土体为正常固结状态时,开挖深度相同时,坑底以下抗拔桩长度越短,开挖后桩周土体超固结比越大,抗拔桩极限承载力与土体正常固结状态相比增加比例越大;坑底以下有效桩长相同时,开挖深度越大,开挖后桩周土体超固结比越大,抗拔桩极限承载力也越大。

In order to realize the ultimate uplift capacity of model piles under excavation in sand,19 groups of model tests are conducted on different excavation diameters,depths,and different pile lengths under the bottom of pit.The results are obtained as follows： under the same excavation depth,the larger the excavation diameter is,the lower the ultimate uplift capacity of piles is.When the excavation diameter is 30 cm（10d）,the ultimate uplift capacity of piles decreases sharply.When the excavation diameter continues to increase,the decrease of the ultimate uplift capacity of pile is small,then the ultimate uplift capacity of pile tends to have a stable value.Under the same excavation depth,the shorter the pile under the bottom of pit is,the larger the loss of the ultimate uplift capacity is.The soil is overconsolidated after excavation,and the ultimate uplift capacity of piles is larger than that of the piles in the normal consolidation soil.Under the same excavation depth,the shorter the pile under the bottom of pit is,the larger the increased proportion of the ultimate uplift capacity of pile to that of the pile in the normal consolidation soil is.When the length of the pile under the bottom of the pit is the same,the deeper the excavation is,the larger the ultimate uplift capacity of pile is.