极限荷载下桩筏基础共同作用性状的室内模型试验研究

利用自制模型槽,通过设计系列单桩带台与群桩的桩筏基础模型试验,研究了极限荷载下桩–筏板–地基土的应力与变形性状。试验结果表明,常规桩距桩筏基础极限荷载下表现出实体深基础性状;而大桩距桩筏基础,基桩先于板下土体达到承载力极限状态,后续荷载基本由板下土体分担,验证了塑性支承桩理论。加载过程中,桩–土的荷载分担比不断变化,6d及以上桩距时,桩达到极限荷载后即趋于稳定。利用桩的极限承载力的桩筏基础设计,应考虑极限荷载与工作荷载下桩–土荷载分担比的不同性状差别。桩间距越大,桩对土体的侧向位移的"遮帘作用"逐渐弱化,板下土体的位移特征趋于天然地基的特征,桩端平面以下土体应力受板下土体分担荷载的影响越明显,6倍桩距可视为常规桩基与复合桩基的分界点。

Model test on pile-raft foundation interaction under ultimate load

The model tests on single pile foundation and group piles foundation were designed to investigate the interaction behavior of pile-raft-soil under the ultimate load.The test results indicated that the behavior of group piles with spacing of 4d was like that of the block deep foundation under the ultimate load.As for pile groups with large spacing,the ultimate state of the piles was earlier to reach than that of the soil under the raft,and the following load was taken by the soil under raft.Thus,the concept of plastically bearing piles were validated.The proportion of load carried by piles and rafts changed during the tests.As for group piles with 6d spacing,when the piles were in the ultimate state,the proportion became invariable.The difference of the percentage of load carried by the rafts at the ultimate load and the design load of piles would be considered by using the ultimate bearing capacity in pile-raft foundation design.The pile barrier effect on soil lateral deformation decreased with the increasing pile spacing.The deformation behavior of the rafts in group piles was similar to that of raft foundation,and the soil stress under the pile tip was affected by load carried by the rafts.Spacing of 6d was the dividing value between the normally piled raft foundation and the composite pile foundation.