不同平衡堆载条件下桩基承载特性的原位试验研究

沿海吹填围垦地区土质较差，淤泥软弱土层较厚，在后期填土作用下土体会产生很大的固结沉降。后期不同堆载填土方式对桥梁基础影响较大，可降低基桩承载力，同时平衡堆载主要增加基桩的沉降，而不平衡堆载则对基桩水平位移影响较大。结合台州湾大桥工程建设，选取3根基桩进行了平衡堆载（围载）试验，另外，选取了3根基桩进行了不平衡堆载试验，研究不同堆载条件下对桩基承载特性的影响。现场试验结果表明，平衡堆载条件下主要引起桩侧产生负摩阻力，堆载高度达到4 m，堆载面积为24 m×16 m时，负摩阻力总和达到2 687 kN左右，中性点深度约为29.5 m，约为0.36倍桩长，且负摩阻力的发展是随时间而变化的；不平衡堆载条件下主要产生土拱效应，使桩基产生较大的水平位移，试验中不平衡堆载对吹填区的影响主要在距离地面20 m范围之内，土中最大水平位移出现在距离地面4～5 m左右位置，而桩身最大水平位移出现在桩顶。

In situ experimental study of bearing characteristics of pile foundation under different balanced surcharges

The soil in the coastal reclamation area is generally very poor, embedded with thick soft oozy soil layers. The soil can produce great consolidation settlement under the effect of late filling. Different types of surcharges have an important effect on the bridge pile foundation, and reduce the bearing capacity of pile. Balanced surcharge and unbalanced surcharge mainly affect the settlement and the horizontal displacement of pile, respectively. Combined with the Taizhou Bay bridge project construction, three piles are selected to conduct balanced surcharge loading test, and another three piles are designed to conduct unbalanced surcharge loading test to study the bearing characteristics of pile foundation under different balance surcharges. The field test results show that the negative friction of pile side is caused mainly by balanced surcharge. When the surcharge load is up to 4 m and area is 24 m×16 m, the total negative frictional resistance is up to around 2 687 kN, and the depth of neutral point is about 29.5 m, nearly being 0.36 times the pile length. The development of negative frictional resistance changes with time. The unbalanced surcharge load mainly affects the pile foundation to produce soil arching effect, and gives rises to a large horizontal displacement of pile. In the unbalanced surcharge loading test, the surcharge mainly affects the area in the range of 20 m from the ground, the maximum horizontal displacement in soil appears around 4 to 5 m off the ground, and the maximum horizontal displacement of pile appears at the top of the pile.